CA1066872A - Method and apparatus for the fabrication of pure alumina from al2o3 and silica containing raw materials by leaching with hydrochloric acid - Google Patents
Method and apparatus for the fabrication of pure alumina from al2o3 and silica containing raw materials by leaching with hydrochloric acidInfo
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- CA1066872A CA1066872A CA248,468A CA248468A CA1066872A CA 1066872 A CA1066872 A CA 1066872A CA 248468 A CA248468 A CA 248468A CA 1066872 A CA1066872 A CA 1066872A
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Abstract
METHOD AND APPARATUS FOR THE FABRICATION OF
PURE ALUMINA FROM Al2O3 AND SILICA CONTAINING
RAW MATERIALS BY LEACHING WITH HYDROCHLORIC ACID
Abstract of the Disclosure A process for the production of pure alumina from alumina and silicate containing raw materials comprising feeding said raw material into the top of an acid resistant leaching tower; continuously feeding a leaching liquor containing hydrochloric acid into the bottom of said leaching tower, continuously flowing said leaching liquor upward through said raw material to leach out the alumina as a solution of aluminum chloride, withdrawing said solution enriched in aluminum chloride toward the top of said tower zone; withdrawing said raw material solid residue from the bottom of said tower zone to convey said solid residue from said leaching tower into a separation zone at a level higher than the level of said leaching tower; and separating said solid residue from said carrier liquid in said separation zone.
Apparatus for producing alumina according to this method includes the corresponding means.
PURE ALUMINA FROM Al2O3 AND SILICA CONTAINING
RAW MATERIALS BY LEACHING WITH HYDROCHLORIC ACID
Abstract of the Disclosure A process for the production of pure alumina from alumina and silicate containing raw materials comprising feeding said raw material into the top of an acid resistant leaching tower; continuously feeding a leaching liquor containing hydrochloric acid into the bottom of said leaching tower, continuously flowing said leaching liquor upward through said raw material to leach out the alumina as a solution of aluminum chloride, withdrawing said solution enriched in aluminum chloride toward the top of said tower zone; withdrawing said raw material solid residue from the bottom of said tower zone to convey said solid residue from said leaching tower into a separation zone at a level higher than the level of said leaching tower; and separating said solid residue from said carrier liquid in said separation zone.
Apparatus for producing alumina according to this method includes the corresponding means.
Description
~6q~
The Prior ~rt G~rman Patent No. ~14,128 (1921) propos~s the use of HCl solutions for the leaching oE ~1203 fr~m minerals, such as bauxite, clay or other sources, for the product.ion of pure alumina especially for the aluminum indust.ry. The need for such a process has become more important over the years, since the better grade and higher quali-ty bauxites, needed for the Bayer process have ~ecome rarer. U.S. Patent No. 2,24g,761 proposes leaching clay with hydrochloric acid on a continuous countercurrent basis, in which the separation of iron contained in the clay is by organic ` solvents and the aluminum chloride crystals are washed with a ; mother liquor. These prior proposed methods of a hydrochloric acid leaching have several disadvantagesO One difficulty is the ~ complications of.these proposed methods which make them prohibit-"! ively expensive and which, in combination with the corrosiveness ;}, of ~1, result in high equipment cost and expensive maintenance costs.
~ _bjects of The Invention i It is an object of the present invention to prov.ide ;~ 20 an economical process and apparatus for producing pure alumina from alumina and silicate containing raw materials comprising ~, conta tïng this raw material with a leaching liquor containing HCl.
-,- Another object is to provide process and apparatus ' :1 .
`~ for producing pure alumina from raw material containing alumina and silicate in which the decomposition of ALC13. 6 H~0 into Al(OH)3, HCl and water provides fresh aqueous solution of HCl ~ which is recycled baek to the leaching tower to be utilized as `~ leaching liquor.
. -, , .
'; A further object of the invention is to provide a ~olution rich in AlC13 which also contains an amount of FeC13 su~ficient to perm.it the crystalliza-tion and separatiQn o:E AlC13 i in sub~tantial quantities by merely lowering the temperature of . . i.
;~ the solution and recycle the HCl and H20 formed during A1C13O~
:, : - -.-~66~372 6 1120 decomposition.
These and other objects of the present invention will become apparent as the description thereof proceeds~
Description Of The Invention The above-mentioned disadvantages of the prior art processes can be overcome by the present invention in which the ~ raw material may first be treated, for example, by calcination .~ and disaggregation, in order to sufficiently increase its A1203 solubility and then extracted with HCl preferably by counter current leaching.
.~
As an embodiment of the invention there is provided a process for the recovery of alumina from A1203 and silicate containing raw materials which comprises continuous.ly extracting .~ . , .
said raw material by counter-current leaching in an essentially vertical tower, with a solution containing essentially HCl and -. FeC13, to extract AlC13 from said raw material, crystallizing ALC13.6H20 from said leach solution by the substantially continuous : .
:l washing with concentrated hydrochloric acid, moving said ~ : :
, ~ . . .
AlC13 . 6H20 crystals upwards through a closed essentially :~
,~
horizontal, slightly inclined crystallizer-washer thermal decomposer ..
~ with conveyor meansl washing said moving AlC13 ~ 6H20 crystals by a .~, counter-current flow of pure concentrated hydrochloric acid con~
densate in said crystallizer-washer thermal decomposer, heating said moving AlC13 . 6H20 crystals in said thermal decomposer to .~.
~: convert them into AltOH)3 and recovering the pure alumina.
_e Drawings My invention will be described by reerence to the accompanying drawings which illustrate preferred embodimeints of ~;~ the invQntiOn but ara not intended to limit the invention to the ~`30 em~odiments shown. .
Fig~ 1 shows the acid leaching and aluminum oxide recovery`system as a whole.
.
.~ Fig. 2 shows the liquid-solid-separator in greater ~ 2 -.~
'~06 detail.
Fig. 3 is a sectional view alony thc line 2-2 of Fig~ 2.
` Fig, ~ shows a modiEied leachinc~ tower and th~ heat ;~ exchang~r Eor pre~leating the motll~r li~uor ~rom the crystallizer.
Fig. 5 shows a modified form of raw material charging ; chute and leaching tower.
Fig. 6 shows a modified form of washing crystallizer.
Fig. 1 shows a vertical leaching tower 1 open to the atmosphere at its top lined with acidproof material such as - 10 bric]c or other acidproof material. Its horizontal cross ~ection is smaller at the top than near the bottom. A pre-pared (calcined) solid raw material, such as clay, is fed continuously or semi-continuously into the top of the tower 1 through the feeder 10. The leached solid residue goes to the bottom of tower 1 and is continuously or semi-continuously , removed.
An HCl containiny leaching liquor is introduced contin-uously through the screen-pipe 6 near the bottom of towér 1.
~j The leaching liquor flows upwards through the particles of the solid raw material in the tower 1 and is heated by the dissolution heat of A1203 in the acid, while the solid raw ~`
material moves slowly downward countercurrently. The solution leaves the tower 1 throùgh the overflow pipe 7 located at least 1.5 $o 2 meters below the raw material feeder 10, which open at its top and which is maintained full o~ solid raw ~ ~ ~aterial up to thP level 39. The overflow solution is a hot ,~ solution of AlC13; and, after passing through the balancing containPr 8 or surge *ank and the backwashable sand filter 9, îs introduced through pipe 36 into the AlC13 crystalli~er 19.
~ ,~
~, 30 The leaching tower 1 is operated at a very low upward flow -~ ~ velocity of the leaching liquor through the solid raw material.
;' The advantage of this low velocity i~ that the entire 601id !
b/ ~ 3 -.. . .
``l ~ ' , . .~
, - - -1~6~
material wi.~h all its leach~d out, ~i.n~ parti(~:Lcs move~ down toward the bottom o~ tower 1 at a regulatecl outlet speed controlled by one or more screw conveyor~ 2, preferably hori-zontal in position. By the use of low flow velocity, very ~ew fine, r~sidue particles are carried up and out of the top of tower 1 into the sand-filter 9 so that backwashing o~ filter need only be performed after long time intervals. The level indicators 37 and 38 continuously indicate the-pressure drop in filter to show if backwashing of the sand-filter 9 is needed.
An alternative way to provide a clear AlC13 solution is to maintain in the upper region of the leaching tower 1 such an excess amount o~ the solid raw material, that the rising :.
leach liquor solution will have already lost practically all of its free HCl content before it reaches the overflow level 7, The additional thick layer of unreacted new raw material, such as clay or bauxite, functions as a mechanical filter, which is not influenced by chemical disintegration of the raw material.
.~1 . . .
: In order to monitor the operating conditions in the upper part ~-; .::
~-~ of the leaching tower 1, one or more sampler tubes 76 and 77 ,. . .
lFig. 5~ may be provided at different levels for the removal o~ leach solution for analysis of its free ~Cl or AlC13 at ~-these levels. ~
! The raw material for the leaching step, should be thoroughly ~ -i ~dried,~before being fed into the feeder shaft 10 of the leaching "~ to~er 1, in order to avoid intxoducing an excess of water into the AlC13 ~olution and in order to provide a margin for the ~;
~3~ quan~it~ of wash water need~d for the solid residue ~as will be described later).
, ~ ~ . . --Sl Total calcination of all the raw material is unnecessary . ,~ . .
and some uncalcined material is desirable from the po:int of ~-view o~ A1203 dissolution due to the high concentration o~
~eC13 in the leaching li~uid and to preven~ing an extended ''~1 .
~ .... ..
~ cb/
;' ' ' .
~a~661~2 residence time in the leachincJ tow~r 1. In c~rtain cases a lesser amount o~ washincJ wclt~r ~or t:he sol.i.d residue ma~ b~
used as a conse~uence of re~idual w~ter of crystallization o~ the caolinite which dissolves in the ~lC~13 solution.
It is useful first to drive. off all free moisture from the raw material, for example, by utili~inq the hot combustion ~aste ~ases from the decomposer 23 for the AlC13. 6 H20 crys~als or from other heat sources o~ the process. There are at least two elements of apparatus in which water vapor is ~ormed.. ~he .~ ., .
first is in the AlC13 . 6 H2n decomposer 23, in whi~h in the ...
formation of Al(OH)3, three mols of water are liberated, and in the formation of A1203, 4.5 mols of water are liberated ...
~rom one mol of AlC13 . 6 H20. The second is in the dryer 26 .. .
for the evaporation of HCl and ~2 from the resulting fraction .~ -o~ mother liquor. About 4.7 mols of.water are formed per 1 :~ -i mol o$ A1203 produced, based upon a content of 11.7% FeC13 .~i in the mother liquor and a content of 2.6~ Fe203 and 34% A1203 ::
in.the raw material.
. ............. An additional st.ripper column ~1 ~Fig. 5) may be provided : ~
on column 1 to insure complete prevention of HCl solution or ..
i~ vapor escaping from the top of tower 1. ` . .
.i Hot HCl-H20 vapor mixture from furnace dryer 26 may be passed through the stripping layer 66, shown in Fig. 5, composed .l~ of dxy pieces of calcinated bauxite or cal~inated clay. The introduction of the hot H20-HCl vapors from dryer furnace 26 is made through conduit 72 into the ring space ~3. Condensation ".
o~ waker from these vapors happens only initially when a new charge of cold calcinaked bauxite or clay is fed in. Feeding hot calcinated material, condensation o~ water can be nearly fullx avoidedO
Absorption o~ HCl on the other hand is possible, because ~ chemically active A1203 reaction sites are available. The .. ~ , :`~ Cb~
,',' : - . ' ' i~ , .
6i~37;Z~
vapors rise upwards throu~h the layer 66, whiah is supplied at such a ra-te w:ith new cal~inatecl material as to never exhaust perfectly its reacting A1203 cont~llt. Irhus the llCl ~apors can reack with the A1203 contained therein, while the vapors are too hot to allow considerable amounts of water to condense.
The bulk of water vapor passes through the layer 6~ free of HCl and into the atmosphere, or through an exhaust stack.
It is preferable that the raw material in layer 66 not ` be completely exhausted of A1203 when it finally joins the layer :`; 10 71. The vertical dimension of layer 66 must be such to provide - a sufficient thickness of the raw material, which thickness ..
depends upon the ra-te of absorption of the ~Cl vapors. The ~ .
.:.-:
~ amount of HCl vapor in question is only about 2% of the total ~ ~Cl required for the A1203 dissolution reaction.
~ It is also preferable that the horizontal cross section - -,':~ ' .
r 0~ the stripper layer 66 is such that the speed of the HCl .:~.
'.! Yapors is kept low therethrough. Thus the volume of layer 66 ~ should provide a sufficient residence time for these vapors. .:
~i . .. : : :
~ Depending.upon size and shape of the equipment, the linear .. ~.
., 20 speed of the vapors should not exceed more than about 5cm/sec, ~ll corres~onding to a diameter of the stripper layer of about 2.8 .-- meters, and based upon a.production of 100 tons per day of .::
.:1 ~roduct.
' The most efficient method for the elimination of water ... -::
~ the raw material is by calcining the clay or bauxite, which ij . .
.l: not only eliminates the water of hydration in the caolinite, but also increases the reactivity of the A1~03 toward HClo ~ he stripper layer 66 has to absorb only about 2~ of the totally reacting HCl, and so it is useul to provide for the . :,~ . .
absorption of HCl the mentioned separate stripper layer 66 -.
~j~ : at a level above the ~eeder shafk 10. This separate layer 66 is se~arated from layer 71 b~ a sluice gate 67, which i~
.
,. . .
c~/ . . .- 6 -: i .
preerentially ~ed with calcinated r~w material. Il~t HCl-~l20-vapors are passcd throucJh tllis lclycr 66, while the fee~der shat 10 is fed with calcined or non calc:ined ra~ materia:l ~rom ~he top and HCl solution from the bottom of the leaching tower 1.
This has the advanta~es: thai-t if the raw material is to be substantially non-calcined,then only about 4-6~ of the total raw materia:l fed into feeder 10 has to be calcined. There is apartial hydration of only a~mall fraction of the stripper raw material by the water vapor to be elim:inated. There is no need for the hot HC1-H20-vapors from dryer 26 to heat up *he total amount of feed material; so the temperature rise of the small amount of stripper material is larger and its select-., .
ivity to the HCl-H20-mixture is better. The hot HC1-H2~-vapors coming from furnace 26 can be removed by partial vacuum ' on the upper end of the stripper 66, with only negligible inter- -'iJ ference with the raw material feeding.
Before the stripper capacity of column 66 is exhausted the sluice gates 67 are opened for a moment and the nearly exhausted stripper load enters the feed shaft 10 to become ~art of the total feed material.
The hot AlC13 solution from the top of tower 1 afte~
~, passing through the filter 9 flows with a temperature of about 120C through line 36 to a crystallizer thermal decomposer tube 19 - 23 in which the AlC13 solution is crystallized and therma1ly decomposed to Al~OH)3 by the following reactions 2AlC13 . 6 H2D ~ heat ) 2Al~O~)3 + 6 HCl . 6H2o The crys*allizer-thermal-decomposer tube, or "hot-cold tube~ composed o~ the hot zone 19 and cold zone 23 and is pre~erably made of densely impreg~ated graphite, titanium, 30; taDtalum or other HCl resistant materials with the exception of those component parts which cause the rotation of the "hot-cold tube". A olear solution of AlC13, at about 120C
~ 668'~2 leaves the sandfllter 9 by ~.ravlty flow, or by pump pressure, and flows throuc.lh pipe 36 into the relativcly colcl crystallizer zone 19 of the "hot-cold tube" opcrating at about 10C -to 60C, p.referably at 55C. There it mixes with the mother uor already present in ~he crystallizer, whi.cll remains . after the AlC13 . 6 H20 crystallization from prior solution of ~lC13 flowed throuyh crys~alliæer 19. ~he AlC13 present in the solution entering through pipe 36 is caused to crystallize out as AlC13 . 6 H20 by the combined actions of lower temper-ature and reaction with the HCl-H20 vapors coming from the relatively hot zone decomposer 23 of the "hot-cold tube", eliminating in this manner the maj.or portion of the AlC13 ` ..
content of the AlC13 solution introduced through pipe 36. These - :
`1 . . .
. AlC13 . 6 H20 crystals are moved forward in the crystallizer :.
1 . ,: . :
zone 19 towards and into the relatively hot zone decomposer 23 -by the action of the flights of screw conveyor 24 o the rotat-;~ ing cr~stallizer 19. These crystals pass through the prefer- . -`. . entially conical intermedia~e washing zone 25 between the rela~
. ~ .
3j tively cold portion 19 and the relatively hot portion 23 of . .
the rotating "hot-cold tube". The average temperature of ~: the relatively cold portion 1~ is about 55C, while the temper-' ature of the hot zone 23 is from 300C to 400C with the average being about 350C. The junction of the decomposer 23 and the ~a~hiny zone 25 is e~uipped with a heat insulating gasket 44.
.., ~
~ Tubes 19 and 23 are connected so as to rotate at the same speed. ..
... .
In the hot decomposer zone 23 the AlC13 crystals are converted into Al~OH)3 and moved by the flight 24 to the 3 collecting bin 43.
! The excess o~ cold mother liquor flows from the cool 3a cr~stallizer zone 19 into the U-tube 59 and the overflow pipe 42 and is pumped in~o the heat exchanger 35 and into the collec~ing tank 33 at about 50C. Pipe 59 ha~ the branch ., '.;' ~ :., .~, cb/ . - 8 - ::
.,~. , .
; ~ .,:
,.1 ,~ ,, . . . ' ~ . I ' ~ ' .
pipe 60 with the valve 61 and an enlar~ed pipe with the hydro~
meter or density indicator 49. The density indicator 49 per-mits the detection of changes ln the coMposikion of the effluent mother licluor, especially with re~ard ~o ~eC13 content. It i.s then possible to coxrespondingl~ d.ivert la.rger or smaller amounts of this mother liquor ~hro~gh valve ~9, flowmeter 30 and the pipe 31 in-to the rotating dryer furnace 26 which is at a temperature of between 250C to 350C pre~erably about 300C, in which HCl and water are then evaporated. The HCl ~.
and water are condensed and incorporated in-to the ~ain part of mother liquor flowing to the heat exchanger 35 while the residue remaining after evaporation, rich in Fe203 crystals . ia transported by screw conveyor 27 into container 28.
'J, The AlC13 . 6 H20 crystals move upwards through the : :
.. conical intermediate washing section 25 of the "hot-cold .
~; tube'' ~23 - l9); which is kept relatively cold by cooling ..
.
~ater ~or example sprayed onto its outside. During the ad-vance of these crystals t they are contacted by the HCl-H20 Yapors flowing countercurrently downward from the decomposer 23. The va~ors condense partially on the relatively coLd AlC13. .
6 ~2 crystals moving through the throat of the washing zone 25 and on the relatively cold walls of the conical intermediate ashing zone. These condensed vapors form a concentrated solution of hydrochloric acid, which acts on the crystals as a washing liquor wlth a ver~ high efficiency, as the condensed liyuors flow continuousl~ countercurrently downward into the relatively cold crystallizer zone 19 together with the mother .~ . : .
l~ : li.~uor containing ~eC13 originally present on the crystal ..
~ur~aces. In this manner a washing action takes place, which ~ 30~ i~ repeated man~ tLmes und~r c.ountercurrent flow conditions by :~ the extremel~ pure concentrated hydrochloric acid condensate :-., j, ~ , . . .
durlng the entire time tha crystal~ of AlC13 .`6 H~0 are ~^ . ~ - : .'. ' ~;~ Cb/ ~- 9 -transported through the intcirmediate cone 25. Wllen the crystals oE AlC13 6 1l20 fi~ lly arrive in khe decomposer 23 the~ are very pure ~nd produce a ver~ pure r iron free, Al(OH)3. These crystals are thermally decomposed in the crystalli7.er 23 according to the equation given above and discharged into the collecting bin ~3.
. The above-described steps in the comb:ined "hot-cold tube"
`` 23 - 19 are promoted by a slight upward incl.ination o pre~er- :
ably ahout 5 from the entrance of tube 36 to the outlet of decomposer 23.
As an alternative embodiment for us.e in very large pro- .
duction units it is preferable to utilize, instead of a rotat-ing hot-cold tube 19 - 23, a stationary hot-cold tube, which is e~uipped with one or more.rotating flight conveyor means . for advancing the solid material therethrough. In this hot-cold vessel the same chemical and physical process steps occur as in the rotating hot-cold tube embodiment. The stationary ` vessel has the advantage, that large bearing and hous~in~s are partially or completely eliminated.
Another alternative to the stationary hot-cold tube is a hot-cold tube of large diameter which rotates very slowly . and in addition contains internal conveyor means, to keep the solidmaterial movingO
Metals, such as titanium alloys, tantalum, etc., which ~; are not corroded by HCl may be u~ed instead o impregnated raphite in the hot-cold tubes 19 - 23 and in o*her parts o jjl~ the process.
;: Stationary vessels o titanium can bP protected against .
i corrosion by the preisence o chlorine gas in ~ low concentration. ~ .
! ~: 30 The~presence of chlorine gas also keeps the iron chloride i oxidized to ~eC13 . The chlorine gas should be of such low ~ ~ ~
aoncentration, that there is no reduction in the surface : :
b~ ~ - 10 - . :
. . . .
,. , . : .
66~'7~
condensAtion conc~itions for HCl and H~0 vapors.
A consiclerclble ~educt.ion of ~he heat recluiremen-~s for the thermal decolTlposit:ion i.n the clecomposer ~one 23 ma~ be ef~ected i~ washing of the crystals in the intermediate wash-ing æone 25 is not made directly by the condensing HCl-~120 vapors bu~ instead the washing is made by the spraying of hydro-chlor.ic acid,which forms, the HC1-H20 vapors, after having been compressed by a heat pump into the washing zone 25 These vapors transfer their heat of condensation to the AlC13 . 6 H20 cr~stals to be decomposed. This embodiment has the advantage that the consumption of cooling water for the crystallizer 1~ is substantially reduced. The most convenient type of heat pump, depending upon the cost relation of elec~ric energy to heat energy, may be a liquid ring pump or a steam injector .
pump.
In the case of liquid ring pumps, the HCl-H20 vapors produced in the decomposer 23 are drawn in, compressed and pumped into the heat exchange conduits of the crystal de-~;~ composer 23. These conduits act as condensers r in which --~
the heat of condensation is transferred through their walls, ~:' ~hich walls may be composed of titanium, a titanium alloy or ~, .
tantalum, to the decomposer. This heat is absorbed by the ~ AlC13 . 6 ~2 crystals, whose thermal decomposition is initiat-.~"!i ed at about 105C. The HCl~H20 vapors, newly generated, are i ; ~ ai~o drawn in bX the heat pump and during their compression, 1~ the~ are again usea for heating and decomposing new AlC13 . 6 H20 crxs~als. The condensate of HCl and H2Q is used for washing ~,Jj ~ ` new AlC13 . 6 H20 crystals, while they pass ~hrough the inter-mediate washing zone 25, wherein the condensate is sprayed under its own pressur~ onto the crystals. The excess of con-densate and the noncondensed HCl vapor i~ incorporated into ~-'l - .
the mother li~uor of cr~stallizex 19.
", . , . ' ~' ~b/
.. i - -.:
~i ` ~ ' .`... !
~6687~:
When steam injectors are used as heat pumps, a portion of the IICl-H20 condensate ~o:rm~icl in t}le conduits o~ t.he : condenser elements is pumped into a boiler, and t]lC ~IC 1 -~1120 vapor fo.rmed under pressure in ~he boiler is used in the steam injector heat pumps for the compression of new IICl-H20 vapors rom the decomposer 23 from atmospheric pressure up to thei.r condensation pressure in the heat exc:hanger conduits of the .. ~. -decom~oser 23. All the I~Cl H20 condensate is fully u-tilized with a portion being the washing liquid for the AlC13 . 6H20 crxstals in the intermediate washing zone 25, and with the remainder being directly incorporated into the mother liquor of the crystallizer zone 19.
The composition of the HCl-H20 vapor mixture from the decomposer 23 being about 66 weight % HCl and only 33 weight H20, part of the EICl vapor ~rom the decomposer 23, which cannot be absorbed in the concentrated acid, condenses under the pressure and temperature conditions of the heat pu~p.
There is (usually) a quantitative excess of ~Cl over H20 in ~i ~
. the decomposition vapors, which are compressed by the heat pump and which are then released by an automatic safety pressure ~ :
release valve into the head space of the crystallizer 19, ~ . -i.'l ~ where the~ are cooled and dissolved in the mother liquor at .
about 55C. This release of the undissolved fraction of com-ressed HCl gas means thermodynamically an energy loss. This ~i los~s is ~ept as low as possible by displacing the releasing . .:
of this HCl gas to a location do~n-stream from the coldest zone of the decomposer because there the insoluble HCl components are the least value at equal preissure. -If the heat exchanger surface area of the crystallizer .~:
: ! ` .
decomposer xone 23 is sufficient, it is possible to reduce the heat re~uirement.~or the cr~stallizer decompositi.on to one-third or less, a fact which is .important for the economy : ~: , 3 eb~ ~ 12 - ~
~6f~
of the process. Tlle washing efficiency of the sprayed HC1-II20 condcn~ate, instead o vapors condensing on the crystals, on the ~lC13 . 6 II20 crystals in -the washing ~one 25, is a~
least as e~ficient as of the condensing vapors.
. There is an advantage to releasing the HCl-H20 vapors into the decomposer zone 23 at a few points along its length, because in this manner a much smaller diamete.r decomposer tube 23 is sufficient for the flow of the vapors. Moreover it is possible to condense the vapors from the different sections of the decomposer length separately. The fi.rst vapors ~.
produced in the low decomposition temperature ran~e are rich in water and poor in ~ICl, such that this constitutes an I inexpensive method for eliminating water from the system with-.. out consumption of added heat for evaporation. This embodiment . ispreferably for a lengthy decomposer.
; In another alternative the mother liquor can be pre- :
concentrated using a heat pump with a boiler ~not shown), which .. : :
is positioned between the flowmeter 30 and the feed pipe 31 .. :~
of the dryer 26. The said pre-evaporation is terminated before . - .
I 20 the concentration of the FeC13 exceeds the maximum allowable : .
i; : lLmit of about ~5%; and consequently the viscosity of the solu-ti~ will h~ve no negative effect on the evaporation. ..
~,~ There is also the possibility of extracting the bulk of .i1 he FeC13 content of the diverted mother liquor or of the pre-concentrated diverted mother liquid by isopropyl-ether or another solvent, according to known procedures. : .
~nother advantage of the present invention is that the : thermal decomposition of the AlC13 . 6 H20 cr~stals does not roceed beyond the point which would produce an unsatisfactory solid end product.- Also it is possible to avoid h~ving larger :~ .
~ractions o~ water-produced by the decomposition of the AlC13.
' : 6 H2a join th~ mother liquor recycled into the crystallizer 19 ~ ~. i . .
-' cb~ ~ ~3 ~
;i 6~72 than is needed.
Th~ c:lear ~lC13 so:l.ut:ion at about 120C, which l~av~
the sandfilter 9, usually contains a major amount oE ~lC13 .
and a ver~ m.inor amoun~ of HCl from the raw material. In this case cooling alone cannot cause a suf~icient crystallization o~ AlC13 . 6 H20 because the solubility of AlC13 is very slightly dependent upon the temperature. The rate of crystalli~ation can be increased, however, by u~ilizing a concentrated solu-tion of hydrochloric acid, which is generated in the hot-cold 10 tube 23-19.
On the other hand, if the ore starting material in leach-; in~ tower 1 is rich in Fe203, then a leaching solution rich in .
FeC13 is produced. Thus the AlC13 . 6 H20 crystallization can then be carried out just by the cooling of the AlC13-FeC13 .
solution comin~ from filter zone 9. -. .
The solubility of AlC13 in pure water is as follows: ~ .
at - 4QC : 26.8% AlC13 :
!
. at + 25C : 31.6% " .
.. , .. ~ ' ..
~. at ~ 98C o 33.2%
-3' This shows that the crystallization of AlC13 . 6 Hz0 -from essentially pure aqueous solutions of AlC13 would be eConomically unfeasible, if lowering of the solution temperature .. :
~ere the only crystallization st~p performed. For this reason ~æ~: : a concentrated solution of hydrochloric acid is needed for ~' a ~atisfactory crystallization.
Z~ However if the AlC13 solution contains sufficient amounts o FeC13, cooling alone can cause sufficient crystallization : ::
:`t ~
to bring it closer to economical feasibility.
~; ~ substantial increase in the FeC13 content of the leaching .:~
~olu~ion, for example from 2~ up to 12%, gives the additional ~: advantage that for the elLmination of a certain amount of FeC13 i ~rom the circulating solution, only one-sixth o the amount of ~b~ .- 14 -water has to be evaporated. The exccss o:E FeC13 altcrnatively can be elimina~ed from thc le~chillcJ solu~ion by trea~ment w.i.th iso~rop~l ether.
The xesidue rom the rotating furnace 26, accumulated in tank 28, is primarily Fe203 And .c~n be used as refractory material in a high temperature ~urnace or for the produc~ion of ~i~ments.
Each of the three rotating chambers ~a) the "hot~cold tube" 23-19 for the crystallization of and for the decomposition o~ AlC13 . 6 H20, (b) the rotating tube 17 for the solld extraction residue, and tc) the rotating tube 26 for the evapora~ .
; tion o~ the diverted portion of mother liquor is necessarily provided at each end thereof with bearing housings. It is :~ :
~referable to maintain these three rotating tubes under a ~ .
slight vacuum of about 2 mm of water, in order to prevent the ~ :
escaping of HCl containing vapors even in very small amounts. . :
This small vacuum is applied, for example, to the collecting ,. . .
! t~nk 33 for furnaces 26 and 17 and con-tainer 14 by maintaining a continuous slight vacuum on the small washing tower 50. The l 20 very small amounts of air drawn in finally reach the washing tower 50 and therein are liberated f~om their HCl content by Water~washing or a calcium hydroxide solution and are then .~ discharged into the atmosphere wi~hout pollution. The vacuum , .: ' in $he system is checked by the readings of .the three air ~lowmeters Sl~ 52 and 53 and is controlled by ~he vacuum intensity ~ ~ on the washing tower 50 of tank 33.
-' The small amount of acid, eventually discharged from the ;~ stuffing boxes of the three pumps 20, 40 a~d 54, is collected to~ether with a little water and from time to time is recycled 30 back into the circulating liquid, in order to compensate for a de~iciency of water eventually resulting from the production ; o~ ~l(OH)3 instead of A1203.
., .
,' , ~/ 15 , ~66~372 Fig. 6 shows an altcrnative to the conical intermediate washin~ section 25 oE the hot-cold tub~ :l9-23 shown :Ln Fi~. 1. Fig. 6 shows the intermediate washillg secti.on 25a made o~ densely .impreynated graphite, equiE)ped with external metallic rein~orcing ribs 69, while E'iy. 1 shows a conical sec~ion, made for example, of tantalum or lli~Pcl.
The heating of the rotating tubes 17, 26 and 23 is from the outside by gas or oil fired burners respectively using the above discussed heat pump systems at least in the lower . ..
temperature zones. Tha cooling of the relatively cold rotating crxstallizer 19 is by spraying water from outside, possibly combined with the cooling effect of ~orced air, in the case ~ -:
that the water temperature is not low enough.
If the concentration of FeC13 is about 10% to 1~% by weight in the leaching liquor, then the AlC13 concentration in the solution leaving the leaching tower 1 can reach about `/ 27 weight % or more. This will result if the leaching liquor be~ore its entrance into the heat insulated leaching tower ~ 1~ is preheated under the pressure of auxiliary pump 54, so ;-1~ 20 high that the leaching li~uor, due to the dissolution heat ; o~ A1~03 in hydrochloric acid, reaches a temperature of about 118C or more. The temperature to which the leaching liquor has to be preheated for that purpose, depends upon the type and upon ~ -the pretreatment of the solid raw material. For leaching calcined ra~ material a ~ower preheating temperature is sufficient com-ared with the case of noncalcined raw material, because the i xeaction energy of calcined raw material is higher than that ~ o~ noncalcined material.
.~ The higher temperature in the leaching tower 1, which , .
~ becomes possible by a high FeC13 cvntent, as well as by o~er-pressure, results in the advanta~e of a higher rate o~ dissolu-tion and o~ a higher percentage yield of A1203 leached out ., .
cb/ - 16 - ~
~, . . . .
~ 66872 of the cla~, baux.ite, etc. B~ .inCreasincJ the FeC13 concentra~
tion of ~he soluti.ons lo abollt 10 to 12~ the rcsult is an increase in the boiling point of the soluti.on from about 106C
or solutions contailling small concentrations of FeC13, up to 118 to 120C for solutions containing 10 to 12% FeC13.
In order to achieve more reaclily the maximum temperature in the leaching tower 1, and to avoid boil.i.ng the AlC13 solution in the leaching tower, this soluti.on is kept under a superatmospheric pressure in the leaching tower 1 as well as in the sandfilter 9, preferably by a liquicl column in the feeder sha~t 10 up to level 4 created by automatic throttling of valve 47, as shown in the alternative of Fig. 4. Above this liquid column the open feeder shaft 10 contains the additional raw material layer reaching level 39, as shown in Fig. 5 so that i~ spite of the overpressure on the hot AlC13 solution leaving the leaching tower 1 the open feeder shaft'10 for raw material remains open ~o receive addi~ional raw material, :
j Be~ore the filter ~ becomes clogged, it is backwashed as ollo~s. The valves 47 and 45 of the filter 9 are closed, so that the passage of filtered AlC13-solution from valve 47 to the pipe 36 of the crystalli~er 19 is intexrupted, Valves 46 and 48 are then opened; and the pump ~0 and the stirrer 55 are put into operation, A high pressure stream of pure AlC13 ~;
;~ . -solution backwash liquid then flows from container 8 through pump 20, valve 48 and sandfilter 9 and pipe 21l so as to lift the , ~ cake from the filter bed. -The suspension created by the tirrer 55 flows through pipe 21 and screen pipe 22 into the lower part o~ tower lt close to the outlet scre~ conve~or 2 ~ or ~he solid residue. Thexe the fine particles stick to the t ~30 larger re~idue particles and are taken ~ff with them by the ~ outlet ~crew conveyor 2. After a few seconds o~ backwash ths ' .
above menkioned valves 47, 45, 46 and 48 are re~urned to their ~4 cb; ~ 17 ~
1; . ~' : ' 7~' original positions, pump 20 an~ stlrrer 55 are shut d~wn, so tha~ ~h~ normal leaching proccss c~n cont:inue.
The shor~ conveyor scrcws 2 push the leached solld residue from the bottom of tower 1 lnto the pipe 3, where a suf:Eiciently rapid 1Ow of circula~ing carrier liquid propells the residue up .into se~arator 5 whi.ch houses a cylindrical screen drum 11, ~igs 2 and 3, rotating about a substantially horizontal sligh-tly inclined axis. This screen drum 11 rests on graphi~e bearings 56 and 57. It has a multilayer screen wall 12 and on its inside conveyor flights 15. The carrier liquid filters through the screen wall 12 of the rotating screen drum 11. Small ~mounts of fines, which leave the screen drum 11 together with the carrier liquid are harmless. The filtered carrier liquid .. :
flows into the container 14 and out through discharge pipe 68 to the recirculation pump 40. The moist solid residue is discharged from the end of drum 11 and carried through pipe 18 ..
into ~he rotating furnace 17 at 250C to 350C, preferably at 300C, and made, for example, of densely impregnated graphite, titanium alloy, tantalum or other HCl resistant material. The HCl vapor and ~ater vapor formed in ~urnace 17 are condensed in the heat exchanger 35 and flow into collecting tank 33 at about 50C in the form of a concentrated solution of hydrQchloric acld. This concentrated solution is pumped by means of pump 64 ox auxiliary pump 54 through screen pipe 6 into the lower . pOrtion of leaching tower 1 as fresh leaching liquor.
~: ~he dry leached residue from furnace 17~ free of ~Cl and rich.in sio2, is transported by the screw flights of conveyor 58 into the container 41 and can be used, for example, for the ~abrication of cement.
3~ The screw conveyor flights 15 in the separator 5 are made o~ an acid resistant substance such as tantalum sheet, :~:
Ti-pd ~heet or pol~ester. Screen drum 11 has a li~uid per- ~
cbi ~ 18 - .
.
, .
~6~87~
meable multilay~r wall 12 preferably made of two layers o acid ~roof perfoxclt~ sh~ct, exp~ndecl she~tor mcsh o;E tc~ Alum, Ti~pd, h~rd poly~inyl chloride ~PVC) polyester or simiJar material ~etween which one or more la~ers of an acid proo~
filter cloth such as PVC, ~eflon ~ or the like is enclosed.
The pipe 63, located beneath the rotating tube 11, serves as an emergency over~low for the liquid from the pan 14, in order to prevent any major amounts of liquid from reaching the residue fallpipe 18 and the heated rotating tube 17.
The residue separator 5 is equipped with a second pipe 80 on the side opposite pipe 13 for the introduction of washing li~uid, installed in a coaxial manner in a hollow axle within the graphite bearing 57. Through this additional tube 80 is periodically fed a washing liquid, such as a limited amount of ~ater, which has to be added to the system to compensate for H20 losses, especially if calcined raw material is used. This limited ~uantity of water 1s sufficient for washing the solid residue, if it is dosed in a number of portionwise doses and , . . .
v i$ the r.p.m. speed of the screen drum 11 is increased temporarily.
~ 20 The additional ~eed pipe 80 is loca~ed in such a manner that ; ~ -'~J the ~ashing water is distributed over the entire amount of xesidue present at that time in the separator 5. The separation and ~ashing process is divided into three separate steps, and ~!: can be automatically controlled by programmed equipment..~ ~ These three steps are as follows:
J~ ~ ' The Separation Step A:
The carrier liquid containinq solid residue is fed through t~e 3 into the screen drum 11. The screen drum 11 rotates at ,: :
such a speed, that the centrifugal acceleration upon the solid residue is substantially higher than the force of ~ravity. The ~-i .
~ hi~h speed rota~ion is ~rom 100 to 250 r.p~m., preferably from .- 1~0 tv 150 x~p~m., in order to distribute the solid residue .i :
" . ~: .
ob~ - 19 - ;
. ~ .-:
., ;~ ~ . .. . . .
~:366~
unifoxmly over the cylindricAl periphery of filtex wall 12 o~ the screen drum 11 arld to holcl it in place. This avoids ~mbalancing and overloadin~ the bearin~s o~ the scxeen drwn 11, ~hich would o-therwise be unavoidable during the transition ~rom l~w to high angular speed.
Wash S~
Washing of the solid residue in the screen drum 11 occurs ~hile the screen drum 11 is main-tained at a rapid ro~ation.
The circulation pump 40 is stopped; and the valve 7~ releases wash water into the feed pipe 80, preferably in a number of ~ortionwise doses.
Separation Step C:
The valve 74 for wash water is closed. The screen drum 11 is returned to a slower rotation - in the range of 5 to 15 r.p.m.
such that the centrifugal acceleration on the solid residue is aonsiderably still than the force of gravity. The screw conveyor ~lights 15 within screen drum 11 can advance the residue through drum 11 and then discharge the same through outlet tube 18.
~ he washing steps are repeated as often as is necessary during the separation procedure.
The transition from high revolution speed to low revolution ~ -~
speed, or vice-versa, of screen drum 11 is made necessary, -~ecause the tube 11 with its screw conveyor bands 15 at low r . ~ Om . advances the residue through the length of drum 11 to the outlet 16. However when drum 11 is rotated at a high r.p.m., ;~
the solid residue is held in place without advancing. `~
In the case of very lar~e scale production units it is preferable to ins~all a number of residue separators in parallel~
operating with ~taggered separation and washing cycles. In .
~30 this manner oversized separators are avoided and the residue ; can leave ~he leaching tower 1 semi-continuously or continuously.
Fil~ex~ or centxifuges may be used in place of screen drum 11-12.
, : ,: .' .
~ - 20 - ~ ~
:, ' '' '~ -.
66~
The above-described resid~e washing m~thod is preferably carried'out wi~h a number of por~ionwise injec~:ions of wasllincJ
~ater, which permits almost total separa~ion of the resiclual s.olid from its content of IICl and AlC13 with a minimum of wash water. Thls permits disposal of the re~idue without dry-ing it, or to dr~ it by direct heating instead of the more co~tly indirect heatiny, until it is used, for installce, as an additive in cement production.
In the embodiment of Fig. 4 the solution pregnant with AlC13 leaves the sandfilter 9 through pipe 36a and flows through the heat exchanger 70 into the crystallizer tube 19. HCl containing mother liquor at about 50C is pumped through heat exchanger 70 by pump 54 which receives HCl solution from collecting ~ank 33. Crystallization of AlC13 and conversion to Al~OH)3 is performed in tubes 19 and 23 and mother liquor and wash liquor, HCl condensate, etc. flows through pipe 59 ~' and a part of it eventually into dryer furnace 26. "~
In the embodiment of Fig. 5 an extension feeder shaft 10 . '~-~or tower 1 through which calcined or uncalcined raw material '. .
maX be fed into tower 1 through which HCl is 10wed counter- ' current to the r'aw materi.al feed. :.
The following examples are illustrative o the invention .~' ' without being deemed limitative in any manner. . '~
: EXAMPLE 1 ' The mother liquor leaving the crystallizer 19 through ,~ conduit 59 had a temperature of about. 55C and has the follow-.
ing composition: about 3.5~ AlC13., about 11.7% FeC13, about ~ -22.9% HCl, and about 61.9% H20. :
It was used as leaching li~uor in tower 1 after ha~ing been ~:
: 30 preheated. The mother l~quor was pumped ~y the pump 54 through -~,:
'the.countercurrent .heat exchan~er 70. A solution of AlC13 at :
~ ; 'a temperature o~ at least 120C coming from the pressure resistant -' f ~
~:~ cb~ . - 21 - ' , - . . . .
sand~ilter 9 flows thro~!gh th~ pipc 36a of hea~ exchanger 70 (Fig. 4). This system oE~ered the advantage that ~IIC A:l.C13 solution arr.ivecl in a pre-cooled sta~e in the crys-tallizer 19, thus sav.ing cooling water, and that the leaching li~uor was ~reheated without further consumption of heat energ~. f Formation o~ crystals stic]cing -to -the ins.ide wall of the central pipe of heat exchanger 70 was not observed.
A leaching liquor with the above composition produced a solution o~ AlC13 leaving the leaching tower 1 at about 118C
or higher and with the following composi.tion: about 27 weigh-t % AlC13, about 10 weigh.t ~ FeC13, and about 63 weight % H20.
After heat exchange with the mother liquor, the AlC13 solution from sandfilter 9 entered the crystallizer 19 at a temperature of about 85C, where it was cooled to about 55C.
The bulk of the AlC13 content was crystallized to produce AlC13 .
6 H20; and washed with the equivalent quantity of HCl~H20 vapors from the thermal decomposition of previously crystallized AlC13 . :~
6 H20. In this manner the mother liqu~r was transformed into `~ a new leaching liquor with the above-stated composition and temperature. Contemporaneously the mother liquor, which had : entered the heat exchanger at its original temperature of 55C
had been preheated under pressure from pump 54 and by heat txansfer ~ith the AlC13 leach solution to about 60 to 90C.
.. This. preheated mother li~uor was introduced into the leaching :~ .
~ to~er 1 through screen pipe 6 to be utilized as the new leaching ., .
uor.
The pump pressure during heating the mother liquid is important, because at normal atmosphexic pressure the leaching :
'6 ~ uor containiny 22.9% ~Cl boils off HCl vapor at about 75C.
.~ 3~ A preferred pump pressure range is about 1 to 4 atmospheres over pressure.
It had been found, that 1000 parts by weight of a solution ", cb~ 22 -.
.. .. . .
~66l~372 rich in AlC13 with the following approxima-te composition:
27~ AlCl3, 10~ FeC13 and 63~ llz0 y:ield~ about 434 parts by weight o~ pure ~.LC13 . 6 H20, if cooled in the crystall:Lzer 19 ko about 55C. The equivalent quantity of HCl and ~12 vapors enters the crystallizer and are absorbed in the mother liquor.
The mother li~uor leaving the crystallizer 19 had the following composition: about 3.S% AlC13, 11.6~ FeC13, 22.9% HCl, and 62.1% H20, in spite of the fact that it had been cooled only to about 55C.
Cooling of the mother liquor to only 55C is important, because the heat transfer requirements of the cooling system for the crystallizer 19 are substantially reduced both a~ to the ~:~uantity of cooling water and as to the required initial tempera~
ture of the water.
This invention has the advantages of ~1) a relatively non-complicated method for leaching alumina from silicate containing ~ :
cla~vs, (2) substantially lower costs because of the continual -~
: recxclin~ of the mother li~uor from the crystallizer into the leaching tower as a concentrated solution of hydrochloric acid ;~to be used as fresh leaching liquor, and ~3) the presence in ~the leaching liquOr of an effective amount of FeC13 which permits ~:
the crystallization and separation of AlC13 in substantial : ` .
~uantities from a solution thereof, by onl~ lowering the tempera~
ture of the solution. Other advantages will also be apparent ; . -to persons skilled in this art. ~::
Although the present invention has been disclosed in .
connection with a ew preerred embodiments thereof, variations and~modifications may ~e resorted to and equivalent equipment :us d in place of that specifically described without departing .
~ xom the principles of the invention or the scope of the attached ~: : claimsO
cb/ - 23 - ~ .
!": . ' ~` ' ~: . ' , , !
The Prior ~rt G~rman Patent No. ~14,128 (1921) propos~s the use of HCl solutions for the leaching oE ~1203 fr~m minerals, such as bauxite, clay or other sources, for the product.ion of pure alumina especially for the aluminum indust.ry. The need for such a process has become more important over the years, since the better grade and higher quali-ty bauxites, needed for the Bayer process have ~ecome rarer. U.S. Patent No. 2,24g,761 proposes leaching clay with hydrochloric acid on a continuous countercurrent basis, in which the separation of iron contained in the clay is by organic ` solvents and the aluminum chloride crystals are washed with a ; mother liquor. These prior proposed methods of a hydrochloric acid leaching have several disadvantagesO One difficulty is the ~ complications of.these proposed methods which make them prohibit-"! ively expensive and which, in combination with the corrosiveness ;}, of ~1, result in high equipment cost and expensive maintenance costs.
~ _bjects of The Invention i It is an object of the present invention to prov.ide ;~ 20 an economical process and apparatus for producing pure alumina from alumina and silicate containing raw materials comprising ~, conta tïng this raw material with a leaching liquor containing HCl.
-,- Another object is to provide process and apparatus ' :1 .
`~ for producing pure alumina from raw material containing alumina and silicate in which the decomposition of ALC13. 6 H~0 into Al(OH)3, HCl and water provides fresh aqueous solution of HCl ~ which is recycled baek to the leaching tower to be utilized as `~ leaching liquor.
. -, , .
'; A further object of the invention is to provide a ~olution rich in AlC13 which also contains an amount of FeC13 su~ficient to perm.it the crystalliza-tion and separatiQn o:E AlC13 i in sub~tantial quantities by merely lowering the temperature of . . i.
;~ the solution and recycle the HCl and H20 formed during A1C13O~
:, : - -.-~66~372 6 1120 decomposition.
These and other objects of the present invention will become apparent as the description thereof proceeds~
Description Of The Invention The above-mentioned disadvantages of the prior art processes can be overcome by the present invention in which the ~ raw material may first be treated, for example, by calcination .~ and disaggregation, in order to sufficiently increase its A1203 solubility and then extracted with HCl preferably by counter current leaching.
.~
As an embodiment of the invention there is provided a process for the recovery of alumina from A1203 and silicate containing raw materials which comprises continuous.ly extracting .~ . , .
said raw material by counter-current leaching in an essentially vertical tower, with a solution containing essentially HCl and -. FeC13, to extract AlC13 from said raw material, crystallizing ALC13.6H20 from said leach solution by the substantially continuous : .
:l washing with concentrated hydrochloric acid, moving said ~ : :
, ~ . . .
AlC13 . 6H20 crystals upwards through a closed essentially :~
,~
horizontal, slightly inclined crystallizer-washer thermal decomposer ..
~ with conveyor meansl washing said moving AlC13 ~ 6H20 crystals by a .~, counter-current flow of pure concentrated hydrochloric acid con~
densate in said crystallizer-washer thermal decomposer, heating said moving AlC13 . 6H20 crystals in said thermal decomposer to .~.
~: convert them into AltOH)3 and recovering the pure alumina.
_e Drawings My invention will be described by reerence to the accompanying drawings which illustrate preferred embodimeints of ~;~ the invQntiOn but ara not intended to limit the invention to the ~`30 em~odiments shown. .
Fig~ 1 shows the acid leaching and aluminum oxide recovery`system as a whole.
.
.~ Fig. 2 shows the liquid-solid-separator in greater ~ 2 -.~
'~06 detail.
Fig. 3 is a sectional view alony thc line 2-2 of Fig~ 2.
` Fig, ~ shows a modiEied leachinc~ tower and th~ heat ;~ exchang~r Eor pre~leating the motll~r li~uor ~rom the crystallizer.
Fig. 5 shows a modified form of raw material charging ; chute and leaching tower.
Fig. 6 shows a modified form of washing crystallizer.
Fig. 1 shows a vertical leaching tower 1 open to the atmosphere at its top lined with acidproof material such as - 10 bric]c or other acidproof material. Its horizontal cross ~ection is smaller at the top than near the bottom. A pre-pared (calcined) solid raw material, such as clay, is fed continuously or semi-continuously into the top of the tower 1 through the feeder 10. The leached solid residue goes to the bottom of tower 1 and is continuously or semi-continuously , removed.
An HCl containiny leaching liquor is introduced contin-uously through the screen-pipe 6 near the bottom of towér 1.
~j The leaching liquor flows upwards through the particles of the solid raw material in the tower 1 and is heated by the dissolution heat of A1203 in the acid, while the solid raw ~`
material moves slowly downward countercurrently. The solution leaves the tower 1 throùgh the overflow pipe 7 located at least 1.5 $o 2 meters below the raw material feeder 10, which open at its top and which is maintained full o~ solid raw ~ ~ ~aterial up to thP level 39. The overflow solution is a hot ,~ solution of AlC13; and, after passing through the balancing containPr 8 or surge *ank and the backwashable sand filter 9, îs introduced through pipe 36 into the AlC13 crystalli~er 19.
~ ,~
~, 30 The leaching tower 1 is operated at a very low upward flow -~ ~ velocity of the leaching liquor through the solid raw material.
;' The advantage of this low velocity i~ that the entire 601id !
b/ ~ 3 -.. . .
``l ~ ' , . .~
, - - -1~6~
material wi.~h all its leach~d out, ~i.n~ parti(~:Lcs move~ down toward the bottom o~ tower 1 at a regulatecl outlet speed controlled by one or more screw conveyor~ 2, preferably hori-zontal in position. By the use of low flow velocity, very ~ew fine, r~sidue particles are carried up and out of the top of tower 1 into the sand-filter 9 so that backwashing o~ filter need only be performed after long time intervals. The level indicators 37 and 38 continuously indicate the-pressure drop in filter to show if backwashing of the sand-filter 9 is needed.
An alternative way to provide a clear AlC13 solution is to maintain in the upper region of the leaching tower 1 such an excess amount o~ the solid raw material, that the rising :.
leach liquor solution will have already lost practically all of its free HCl content before it reaches the overflow level 7, The additional thick layer of unreacted new raw material, such as clay or bauxite, functions as a mechanical filter, which is not influenced by chemical disintegration of the raw material.
.~1 . . .
: In order to monitor the operating conditions in the upper part ~-; .::
~-~ of the leaching tower 1, one or more sampler tubes 76 and 77 ,. . .
lFig. 5~ may be provided at different levels for the removal o~ leach solution for analysis of its free ~Cl or AlC13 at ~-these levels. ~
! The raw material for the leaching step, should be thoroughly ~ -i ~dried,~before being fed into the feeder shaft 10 of the leaching "~ to~er 1, in order to avoid intxoducing an excess of water into the AlC13 ~olution and in order to provide a margin for the ~;
~3~ quan~it~ of wash water need~d for the solid residue ~as will be described later).
, ~ ~ . . --Sl Total calcination of all the raw material is unnecessary . ,~ . .
and some uncalcined material is desirable from the po:int of ~-view o~ A1203 dissolution due to the high concentration o~
~eC13 in the leaching li~uid and to preven~ing an extended ''~1 .
~ .... ..
~ cb/
;' ' ' .
~a~661~2 residence time in the leachincJ tow~r 1. In c~rtain cases a lesser amount o~ washincJ wclt~r ~or t:he sol.i.d residue ma~ b~
used as a conse~uence of re~idual w~ter of crystallization o~ the caolinite which dissolves in the ~lC~13 solution.
It is useful first to drive. off all free moisture from the raw material, for example, by utili~inq the hot combustion ~aste ~ases from the decomposer 23 for the AlC13. 6 H20 crys~als or from other heat sources o~ the process. There are at least two elements of apparatus in which water vapor is ~ormed.. ~he .~ ., .
first is in the AlC13 . 6 H2n decomposer 23, in whi~h in the ...
formation of Al(OH)3, three mols of water are liberated, and in the formation of A1203, 4.5 mols of water are liberated ...
~rom one mol of AlC13 . 6 H20. The second is in the dryer 26 .. .
for the evaporation of HCl and ~2 from the resulting fraction .~ -o~ mother liquor. About 4.7 mols of.water are formed per 1 :~ -i mol o$ A1203 produced, based upon a content of 11.7% FeC13 .~i in the mother liquor and a content of 2.6~ Fe203 and 34% A1203 ::
in.the raw material.
. ............. An additional st.ripper column ~1 ~Fig. 5) may be provided : ~
on column 1 to insure complete prevention of HCl solution or ..
i~ vapor escaping from the top of tower 1. ` . .
.i Hot HCl-H20 vapor mixture from furnace dryer 26 may be passed through the stripping layer 66, shown in Fig. 5, composed .l~ of dxy pieces of calcinated bauxite or cal~inated clay. The introduction of the hot H20-HCl vapors from dryer furnace 26 is made through conduit 72 into the ring space ~3. Condensation ".
o~ waker from these vapors happens only initially when a new charge of cold calcinaked bauxite or clay is fed in. Feeding hot calcinated material, condensation o~ water can be nearly fullx avoidedO
Absorption o~ HCl on the other hand is possible, because ~ chemically active A1203 reaction sites are available. The .. ~ , :`~ Cb~
,',' : - . ' ' i~ , .
6i~37;Z~
vapors rise upwards throu~h the layer 66, whiah is supplied at such a ra-te w:ith new cal~inatecl material as to never exhaust perfectly its reacting A1203 cont~llt. Irhus the llCl ~apors can reack with the A1203 contained therein, while the vapors are too hot to allow considerable amounts of water to condense.
The bulk of water vapor passes through the layer 6~ free of HCl and into the atmosphere, or through an exhaust stack.
It is preferable that the raw material in layer 66 not ` be completely exhausted of A1203 when it finally joins the layer :`; 10 71. The vertical dimension of layer 66 must be such to provide - a sufficient thickness of the raw material, which thickness ..
depends upon the ra-te of absorption of the ~Cl vapors. The ~ .
.:.-:
~ amount of HCl vapor in question is only about 2% of the total ~ ~Cl required for the A1203 dissolution reaction.
~ It is also preferable that the horizontal cross section - -,':~ ' .
r 0~ the stripper layer 66 is such that the speed of the HCl .:~.
'.! Yapors is kept low therethrough. Thus the volume of layer 66 ~ should provide a sufficient residence time for these vapors. .:
~i . .. : : :
~ Depending.upon size and shape of the equipment, the linear .. ~.
., 20 speed of the vapors should not exceed more than about 5cm/sec, ~ll corres~onding to a diameter of the stripper layer of about 2.8 .-- meters, and based upon a.production of 100 tons per day of .::
.:1 ~roduct.
' The most efficient method for the elimination of water ... -::
~ the raw material is by calcining the clay or bauxite, which ij . .
.l: not only eliminates the water of hydration in the caolinite, but also increases the reactivity of the A1~03 toward HClo ~ he stripper layer 66 has to absorb only about 2~ of the totally reacting HCl, and so it is useul to provide for the . :,~ . .
absorption of HCl the mentioned separate stripper layer 66 -.
~j~ : at a level above the ~eeder shafk 10. This separate layer 66 is se~arated from layer 71 b~ a sluice gate 67, which i~
.
,. . .
c~/ . . .- 6 -: i .
preerentially ~ed with calcinated r~w material. Il~t HCl-~l20-vapors are passcd throucJh tllis lclycr 66, while the fee~der shat 10 is fed with calcined or non calc:ined ra~ materia:l ~rom ~he top and HCl solution from the bottom of the leaching tower 1.
This has the advanta~es: thai-t if the raw material is to be substantially non-calcined,then only about 4-6~ of the total raw materia:l fed into feeder 10 has to be calcined. There is apartial hydration of only a~mall fraction of the stripper raw material by the water vapor to be elim:inated. There is no need for the hot HC1-H20-vapors from dryer 26 to heat up *he total amount of feed material; so the temperature rise of the small amount of stripper material is larger and its select-., .
ivity to the HCl-H20-mixture is better. The hot HC1-H2~-vapors coming from furnace 26 can be removed by partial vacuum ' on the upper end of the stripper 66, with only negligible inter- -'iJ ference with the raw material feeding.
Before the stripper capacity of column 66 is exhausted the sluice gates 67 are opened for a moment and the nearly exhausted stripper load enters the feed shaft 10 to become ~art of the total feed material.
The hot AlC13 solution from the top of tower 1 afte~
~, passing through the filter 9 flows with a temperature of about 120C through line 36 to a crystallizer thermal decomposer tube 19 - 23 in which the AlC13 solution is crystallized and therma1ly decomposed to Al~OH)3 by the following reactions 2AlC13 . 6 H2D ~ heat ) 2Al~O~)3 + 6 HCl . 6H2o The crys*allizer-thermal-decomposer tube, or "hot-cold tube~ composed o~ the hot zone 19 and cold zone 23 and is pre~erably made of densely impreg~ated graphite, titanium, 30; taDtalum or other HCl resistant materials with the exception of those component parts which cause the rotation of the "hot-cold tube". A olear solution of AlC13, at about 120C
~ 668'~2 leaves the sandfllter 9 by ~.ravlty flow, or by pump pressure, and flows throuc.lh pipe 36 into the relativcly colcl crystallizer zone 19 of the "hot-cold tube" opcrating at about 10C -to 60C, p.referably at 55C. There it mixes with the mother uor already present in ~he crystallizer, whi.cll remains . after the AlC13 . 6 H20 crystallization from prior solution of ~lC13 flowed throuyh crys~alliæer 19. ~he AlC13 present in the solution entering through pipe 36 is caused to crystallize out as AlC13 . 6 H20 by the combined actions of lower temper-ature and reaction with the HCl-H20 vapors coming from the relatively hot zone decomposer 23 of the "hot-cold tube", eliminating in this manner the maj.or portion of the AlC13 ` ..
content of the AlC13 solution introduced through pipe 36. These - :
`1 . . .
. AlC13 . 6 H20 crystals are moved forward in the crystallizer :.
1 . ,: . :
zone 19 towards and into the relatively hot zone decomposer 23 -by the action of the flights of screw conveyor 24 o the rotat-;~ ing cr~stallizer 19. These crystals pass through the prefer- . -`. . entially conical intermedia~e washing zone 25 between the rela~
. ~ .
3j tively cold portion 19 and the relatively hot portion 23 of . .
the rotating "hot-cold tube". The average temperature of ~: the relatively cold portion 1~ is about 55C, while the temper-' ature of the hot zone 23 is from 300C to 400C with the average being about 350C. The junction of the decomposer 23 and the ~a~hiny zone 25 is e~uipped with a heat insulating gasket 44.
.., ~
~ Tubes 19 and 23 are connected so as to rotate at the same speed. ..
... .
In the hot decomposer zone 23 the AlC13 crystals are converted into Al~OH)3 and moved by the flight 24 to the 3 collecting bin 43.
! The excess o~ cold mother liquor flows from the cool 3a cr~stallizer zone 19 into the U-tube 59 and the overflow pipe 42 and is pumped in~o the heat exchanger 35 and into the collec~ing tank 33 at about 50C. Pipe 59 ha~ the branch ., '.;' ~ :., .~, cb/ . - 8 - ::
.,~. , .
; ~ .,:
,.1 ,~ ,, . . . ' ~ . I ' ~ ' .
pipe 60 with the valve 61 and an enlar~ed pipe with the hydro~
meter or density indicator 49. The density indicator 49 per-mits the detection of changes ln the coMposikion of the effluent mother licluor, especially with re~ard ~o ~eC13 content. It i.s then possible to coxrespondingl~ d.ivert la.rger or smaller amounts of this mother liquor ~hro~gh valve ~9, flowmeter 30 and the pipe 31 in-to the rotating dryer furnace 26 which is at a temperature of between 250C to 350C pre~erably about 300C, in which HCl and water are then evaporated. The HCl ~.
and water are condensed and incorporated in-to the ~ain part of mother liquor flowing to the heat exchanger 35 while the residue remaining after evaporation, rich in Fe203 crystals . ia transported by screw conveyor 27 into container 28.
'J, The AlC13 . 6 H20 crystals move upwards through the : :
.. conical intermediate washing section 25 of the "hot-cold .
~; tube'' ~23 - l9); which is kept relatively cold by cooling ..
.
~ater ~or example sprayed onto its outside. During the ad-vance of these crystals t they are contacted by the HCl-H20 Yapors flowing countercurrently downward from the decomposer 23. The va~ors condense partially on the relatively coLd AlC13. .
6 ~2 crystals moving through the throat of the washing zone 25 and on the relatively cold walls of the conical intermediate ashing zone. These condensed vapors form a concentrated solution of hydrochloric acid, which acts on the crystals as a washing liquor wlth a ver~ high efficiency, as the condensed liyuors flow continuousl~ countercurrently downward into the relatively cold crystallizer zone 19 together with the mother .~ . : .
l~ : li.~uor containing ~eC13 originally present on the crystal ..
~ur~aces. In this manner a washing action takes place, which ~ 30~ i~ repeated man~ tLmes und~r c.ountercurrent flow conditions by :~ the extremel~ pure concentrated hydrochloric acid condensate :-., j, ~ , . . .
durlng the entire time tha crystal~ of AlC13 .`6 H~0 are ~^ . ~ - : .'. ' ~;~ Cb/ ~- 9 -transported through the intcirmediate cone 25. Wllen the crystals oE AlC13 6 1l20 fi~ lly arrive in khe decomposer 23 the~ are very pure ~nd produce a ver~ pure r iron free, Al(OH)3. These crystals are thermally decomposed in the crystalli7.er 23 according to the equation given above and discharged into the collecting bin ~3.
. The above-described steps in the comb:ined "hot-cold tube"
`` 23 - 19 are promoted by a slight upward incl.ination o pre~er- :
ably ahout 5 from the entrance of tube 36 to the outlet of decomposer 23.
As an alternative embodiment for us.e in very large pro- .
duction units it is preferable to utilize, instead of a rotat-ing hot-cold tube 19 - 23, a stationary hot-cold tube, which is e~uipped with one or more.rotating flight conveyor means . for advancing the solid material therethrough. In this hot-cold vessel the same chemical and physical process steps occur as in the rotating hot-cold tube embodiment. The stationary ` vessel has the advantage, that large bearing and hous~in~s are partially or completely eliminated.
Another alternative to the stationary hot-cold tube is a hot-cold tube of large diameter which rotates very slowly . and in addition contains internal conveyor means, to keep the solidmaterial movingO
Metals, such as titanium alloys, tantalum, etc., which ~; are not corroded by HCl may be u~ed instead o impregnated raphite in the hot-cold tubes 19 - 23 and in o*her parts o jjl~ the process.
;: Stationary vessels o titanium can bP protected against .
i corrosion by the preisence o chlorine gas in ~ low concentration. ~ .
! ~: 30 The~presence of chlorine gas also keeps the iron chloride i oxidized to ~eC13 . The chlorine gas should be of such low ~ ~ ~
aoncentration, that there is no reduction in the surface : :
b~ ~ - 10 - . :
. . . .
,. , . : .
66~'7~
condensAtion conc~itions for HCl and H~0 vapors.
A consiclerclble ~educt.ion of ~he heat recluiremen-~s for the thermal decolTlposit:ion i.n the clecomposer ~one 23 ma~ be ef~ected i~ washing of the crystals in the intermediate wash-ing æone 25 is not made directly by the condensing HCl-~120 vapors bu~ instead the washing is made by the spraying of hydro-chlor.ic acid,which forms, the HC1-H20 vapors, after having been compressed by a heat pump into the washing zone 25 These vapors transfer their heat of condensation to the AlC13 . 6 H20 cr~stals to be decomposed. This embodiment has the advantage that the consumption of cooling water for the crystallizer 1~ is substantially reduced. The most convenient type of heat pump, depending upon the cost relation of elec~ric energy to heat energy, may be a liquid ring pump or a steam injector .
pump.
In the case of liquid ring pumps, the HCl-H20 vapors produced in the decomposer 23 are drawn in, compressed and pumped into the heat exchange conduits of the crystal de-~;~ composer 23. These conduits act as condensers r in which --~
the heat of condensation is transferred through their walls, ~:' ~hich walls may be composed of titanium, a titanium alloy or ~, .
tantalum, to the decomposer. This heat is absorbed by the ~ AlC13 . 6 ~2 crystals, whose thermal decomposition is initiat-.~"!i ed at about 105C. The HCl~H20 vapors, newly generated, are i ; ~ ai~o drawn in bX the heat pump and during their compression, 1~ the~ are again usea for heating and decomposing new AlC13 . 6 H20 crxs~als. The condensate of HCl and H2Q is used for washing ~,Jj ~ ` new AlC13 . 6 H20 crystals, while they pass ~hrough the inter-mediate washing zone 25, wherein the condensate is sprayed under its own pressur~ onto the crystals. The excess of con-densate and the noncondensed HCl vapor i~ incorporated into ~-'l - .
the mother li~uor of cr~stallizex 19.
", . , . ' ~' ~b/
.. i - -.:
~i ` ~ ' .`... !
~6687~:
When steam injectors are used as heat pumps, a portion of the IICl-H20 condensate ~o:rm~icl in t}le conduits o~ t.he : condenser elements is pumped into a boiler, and t]lC ~IC 1 -~1120 vapor fo.rmed under pressure in ~he boiler is used in the steam injector heat pumps for the compression of new IICl-H20 vapors rom the decomposer 23 from atmospheric pressure up to thei.r condensation pressure in the heat exc:hanger conduits of the .. ~. -decom~oser 23. All the I~Cl H20 condensate is fully u-tilized with a portion being the washing liquid for the AlC13 . 6H20 crxstals in the intermediate washing zone 25, and with the remainder being directly incorporated into the mother liquor of the crystallizer zone 19.
The composition of the HCl-H20 vapor mixture from the decomposer 23 being about 66 weight % HCl and only 33 weight H20, part of the EICl vapor ~rom the decomposer 23, which cannot be absorbed in the concentrated acid, condenses under the pressure and temperature conditions of the heat pu~p.
There is (usually) a quantitative excess of ~Cl over H20 in ~i ~
. the decomposition vapors, which are compressed by the heat pump and which are then released by an automatic safety pressure ~ :
release valve into the head space of the crystallizer 19, ~ . -i.'l ~ where the~ are cooled and dissolved in the mother liquor at .
about 55C. This release of the undissolved fraction of com-ressed HCl gas means thermodynamically an energy loss. This ~i los~s is ~ept as low as possible by displacing the releasing . .:
of this HCl gas to a location do~n-stream from the coldest zone of the decomposer because there the insoluble HCl components are the least value at equal preissure. -If the heat exchanger surface area of the crystallizer .~:
: ! ` .
decomposer xone 23 is sufficient, it is possible to reduce the heat re~uirement.~or the cr~stallizer decompositi.on to one-third or less, a fact which is .important for the economy : ~: , 3 eb~ ~ 12 - ~
~6f~
of the process. Tlle washing efficiency of the sprayed HC1-II20 condcn~ate, instead o vapors condensing on the crystals, on the ~lC13 . 6 II20 crystals in -the washing ~one 25, is a~
least as e~ficient as of the condensing vapors.
. There is an advantage to releasing the HCl-H20 vapors into the decomposer zone 23 at a few points along its length, because in this manner a much smaller diamete.r decomposer tube 23 is sufficient for the flow of the vapors. Moreover it is possible to condense the vapors from the different sections of the decomposer length separately. The fi.rst vapors ~.
produced in the low decomposition temperature ran~e are rich in water and poor in ~ICl, such that this constitutes an I inexpensive method for eliminating water from the system with-.. out consumption of added heat for evaporation. This embodiment . ispreferably for a lengthy decomposer.
; In another alternative the mother liquor can be pre- :
concentrated using a heat pump with a boiler ~not shown), which .. : :
is positioned between the flowmeter 30 and the feed pipe 31 .. :~
of the dryer 26. The said pre-evaporation is terminated before . - .
I 20 the concentration of the FeC13 exceeds the maximum allowable : .
i; : lLmit of about ~5%; and consequently the viscosity of the solu-ti~ will h~ve no negative effect on the evaporation. ..
~,~ There is also the possibility of extracting the bulk of .i1 he FeC13 content of the diverted mother liquor or of the pre-concentrated diverted mother liquid by isopropyl-ether or another solvent, according to known procedures. : .
~nother advantage of the present invention is that the : thermal decomposition of the AlC13 . 6 H20 cr~stals does not roceed beyond the point which would produce an unsatisfactory solid end product.- Also it is possible to avoid h~ving larger :~ .
~ractions o~ water-produced by the decomposition of the AlC13.
' : 6 H2a join th~ mother liquor recycled into the crystallizer 19 ~ ~. i . .
-' cb~ ~ ~3 ~
;i 6~72 than is needed.
Th~ c:lear ~lC13 so:l.ut:ion at about 120C, which l~av~
the sandfilter 9, usually contains a major amount oE ~lC13 .
and a ver~ m.inor amoun~ of HCl from the raw material. In this case cooling alone cannot cause a suf~icient crystallization o~ AlC13 . 6 H20 because the solubility of AlC13 is very slightly dependent upon the temperature. The rate of crystalli~ation can be increased, however, by u~ilizing a concentrated solu-tion of hydrochloric acid, which is generated in the hot-cold 10 tube 23-19.
On the other hand, if the ore starting material in leach-; in~ tower 1 is rich in Fe203, then a leaching solution rich in .
FeC13 is produced. Thus the AlC13 . 6 H20 crystallization can then be carried out just by the cooling of the AlC13-FeC13 .
solution comin~ from filter zone 9. -. .
The solubility of AlC13 in pure water is as follows: ~ .
at - 4QC : 26.8% AlC13 :
!
. at + 25C : 31.6% " .
.. , .. ~ ' ..
~. at ~ 98C o 33.2%
-3' This shows that the crystallization of AlC13 . 6 Hz0 -from essentially pure aqueous solutions of AlC13 would be eConomically unfeasible, if lowering of the solution temperature .. :
~ere the only crystallization st~p performed. For this reason ~æ~: : a concentrated solution of hydrochloric acid is needed for ~' a ~atisfactory crystallization.
Z~ However if the AlC13 solution contains sufficient amounts o FeC13, cooling alone can cause sufficient crystallization : ::
:`t ~
to bring it closer to economical feasibility.
~; ~ substantial increase in the FeC13 content of the leaching .:~
~olu~ion, for example from 2~ up to 12%, gives the additional ~: advantage that for the elLmination of a certain amount of FeC13 i ~rom the circulating solution, only one-sixth o the amount of ~b~ .- 14 -water has to be evaporated. The exccss o:E FeC13 altcrnatively can be elimina~ed from thc le~chillcJ solu~ion by trea~ment w.i.th iso~rop~l ether.
The xesidue rom the rotating furnace 26, accumulated in tank 28, is primarily Fe203 And .c~n be used as refractory material in a high temperature ~urnace or for the produc~ion of ~i~ments.
Each of the three rotating chambers ~a) the "hot~cold tube" 23-19 for the crystallization of and for the decomposition o~ AlC13 . 6 H20, (b) the rotating tube 17 for the solld extraction residue, and tc) the rotating tube 26 for the evapora~ .
; tion o~ the diverted portion of mother liquor is necessarily provided at each end thereof with bearing housings. It is :~ :
~referable to maintain these three rotating tubes under a ~ .
slight vacuum of about 2 mm of water, in order to prevent the ~ :
escaping of HCl containing vapors even in very small amounts. . :
This small vacuum is applied, for example, to the collecting ,. . .
! t~nk 33 for furnaces 26 and 17 and con-tainer 14 by maintaining a continuous slight vacuum on the small washing tower 50. The l 20 very small amounts of air drawn in finally reach the washing tower 50 and therein are liberated f~om their HCl content by Water~washing or a calcium hydroxide solution and are then .~ discharged into the atmosphere wi~hout pollution. The vacuum , .: ' in $he system is checked by the readings of .the three air ~lowmeters Sl~ 52 and 53 and is controlled by ~he vacuum intensity ~ ~ on the washing tower 50 of tank 33.
-' The small amount of acid, eventually discharged from the ;~ stuffing boxes of the three pumps 20, 40 a~d 54, is collected to~ether with a little water and from time to time is recycled 30 back into the circulating liquid, in order to compensate for a de~iciency of water eventually resulting from the production ; o~ ~l(OH)3 instead of A1203.
., .
,' , ~/ 15 , ~66~372 Fig. 6 shows an altcrnative to the conical intermediate washin~ section 25 oE the hot-cold tub~ :l9-23 shown :Ln Fi~. 1. Fig. 6 shows the intermediate washillg secti.on 25a made o~ densely .impreynated graphite, equiE)ped with external metallic rein~orcing ribs 69, while E'iy. 1 shows a conical sec~ion, made for example, of tantalum or lli~Pcl.
The heating of the rotating tubes 17, 26 and 23 is from the outside by gas or oil fired burners respectively using the above discussed heat pump systems at least in the lower . ..
temperature zones. Tha cooling of the relatively cold rotating crxstallizer 19 is by spraying water from outside, possibly combined with the cooling effect of ~orced air, in the case ~ -:
that the water temperature is not low enough.
If the concentration of FeC13 is about 10% to 1~% by weight in the leaching liquor, then the AlC13 concentration in the solution leaving the leaching tower 1 can reach about `/ 27 weight % or more. This will result if the leaching liquor be~ore its entrance into the heat insulated leaching tower ~ 1~ is preheated under the pressure of auxiliary pump 54, so ;-1~ 20 high that the leaching li~uor, due to the dissolution heat ; o~ A1~03 in hydrochloric acid, reaches a temperature of about 118C or more. The temperature to which the leaching liquor has to be preheated for that purpose, depends upon the type and upon ~ -the pretreatment of the solid raw material. For leaching calcined ra~ material a ~ower preheating temperature is sufficient com-ared with the case of noncalcined raw material, because the i xeaction energy of calcined raw material is higher than that ~ o~ noncalcined material.
.~ The higher temperature in the leaching tower 1, which , .
~ becomes possible by a high FeC13 cvntent, as well as by o~er-pressure, results in the advanta~e of a higher rate o~ dissolu-tion and o~ a higher percentage yield of A1203 leached out ., .
cb/ - 16 - ~
~, . . . .
~ 66872 of the cla~, baux.ite, etc. B~ .inCreasincJ the FeC13 concentra~
tion of ~he soluti.ons lo abollt 10 to 12~ the rcsult is an increase in the boiling point of the soluti.on from about 106C
or solutions contailling small concentrations of FeC13, up to 118 to 120C for solutions containing 10 to 12% FeC13.
In order to achieve more reaclily the maximum temperature in the leaching tower 1, and to avoid boil.i.ng the AlC13 solution in the leaching tower, this soluti.on is kept under a superatmospheric pressure in the leaching tower 1 as well as in the sandfilter 9, preferably by a liquicl column in the feeder sha~t 10 up to level 4 created by automatic throttling of valve 47, as shown in the alternative of Fig. 4. Above this liquid column the open feeder shaft 10 contains the additional raw material layer reaching level 39, as shown in Fig. 5 so that i~ spite of the overpressure on the hot AlC13 solution leaving the leaching tower 1 the open feeder shaft'10 for raw material remains open ~o receive addi~ional raw material, :
j Be~ore the filter ~ becomes clogged, it is backwashed as ollo~s. The valves 47 and 45 of the filter 9 are closed, so that the passage of filtered AlC13-solution from valve 47 to the pipe 36 of the crystalli~er 19 is intexrupted, Valves 46 and 48 are then opened; and the pump ~0 and the stirrer 55 are put into operation, A high pressure stream of pure AlC13 ~;
;~ . -solution backwash liquid then flows from container 8 through pump 20, valve 48 and sandfilter 9 and pipe 21l so as to lift the , ~ cake from the filter bed. -The suspension created by the tirrer 55 flows through pipe 21 and screen pipe 22 into the lower part o~ tower lt close to the outlet scre~ conve~or 2 ~ or ~he solid residue. Thexe the fine particles stick to the t ~30 larger re~idue particles and are taken ~ff with them by the ~ outlet ~crew conveyor 2. After a few seconds o~ backwash ths ' .
above menkioned valves 47, 45, 46 and 48 are re~urned to their ~4 cb; ~ 17 ~
1; . ~' : ' 7~' original positions, pump 20 an~ stlrrer 55 are shut d~wn, so tha~ ~h~ normal leaching proccss c~n cont:inue.
The shor~ conveyor scrcws 2 push the leached solld residue from the bottom of tower 1 lnto the pipe 3, where a suf:Eiciently rapid 1Ow of circula~ing carrier liquid propells the residue up .into se~arator 5 whi.ch houses a cylindrical screen drum 11, ~igs 2 and 3, rotating about a substantially horizontal sligh-tly inclined axis. This screen drum 11 rests on graphi~e bearings 56 and 57. It has a multilayer screen wall 12 and on its inside conveyor flights 15. The carrier liquid filters through the screen wall 12 of the rotating screen drum 11. Small ~mounts of fines, which leave the screen drum 11 together with the carrier liquid are harmless. The filtered carrier liquid .. :
flows into the container 14 and out through discharge pipe 68 to the recirculation pump 40. The moist solid residue is discharged from the end of drum 11 and carried through pipe 18 ..
into ~he rotating furnace 17 at 250C to 350C, preferably at 300C, and made, for example, of densely impregnated graphite, titanium alloy, tantalum or other HCl resistant material. The HCl vapor and ~ater vapor formed in ~urnace 17 are condensed in the heat exchanger 35 and flow into collecting tank 33 at about 50C in the form of a concentrated solution of hydrQchloric acld. This concentrated solution is pumped by means of pump 64 ox auxiliary pump 54 through screen pipe 6 into the lower . pOrtion of leaching tower 1 as fresh leaching liquor.
~: ~he dry leached residue from furnace 17~ free of ~Cl and rich.in sio2, is transported by the screw flights of conveyor 58 into the container 41 and can be used, for example, for the ~abrication of cement.
3~ The screw conveyor flights 15 in the separator 5 are made o~ an acid resistant substance such as tantalum sheet, :~:
Ti-pd ~heet or pol~ester. Screen drum 11 has a li~uid per- ~
cbi ~ 18 - .
.
, .
~6~87~
meable multilay~r wall 12 preferably made of two layers o acid ~roof perfoxclt~ sh~ct, exp~ndecl she~tor mcsh o;E tc~ Alum, Ti~pd, h~rd poly~inyl chloride ~PVC) polyester or simiJar material ~etween which one or more la~ers of an acid proo~
filter cloth such as PVC, ~eflon ~ or the like is enclosed.
The pipe 63, located beneath the rotating tube 11, serves as an emergency over~low for the liquid from the pan 14, in order to prevent any major amounts of liquid from reaching the residue fallpipe 18 and the heated rotating tube 17.
The residue separator 5 is equipped with a second pipe 80 on the side opposite pipe 13 for the introduction of washing li~uid, installed in a coaxial manner in a hollow axle within the graphite bearing 57. Through this additional tube 80 is periodically fed a washing liquid, such as a limited amount of ~ater, which has to be added to the system to compensate for H20 losses, especially if calcined raw material is used. This limited ~uantity of water 1s sufficient for washing the solid residue, if it is dosed in a number of portionwise doses and , . . .
v i$ the r.p.m. speed of the screen drum 11 is increased temporarily.
~ 20 The additional ~eed pipe 80 is loca~ed in such a manner that ; ~ -'~J the ~ashing water is distributed over the entire amount of xesidue present at that time in the separator 5. The separation and ~ashing process is divided into three separate steps, and ~!: can be automatically controlled by programmed equipment..~ ~ These three steps are as follows:
J~ ~ ' The Separation Step A:
The carrier liquid containinq solid residue is fed through t~e 3 into the screen drum 11. The screen drum 11 rotates at ,: :
such a speed, that the centrifugal acceleration upon the solid residue is substantially higher than the force of ~ravity. The ~-i .
~ hi~h speed rota~ion is ~rom 100 to 250 r.p~m., preferably from .- 1~0 tv 150 x~p~m., in order to distribute the solid residue .i :
" . ~: .
ob~ - 19 - ;
. ~ .-:
., ;~ ~ . .. . . .
~:366~
unifoxmly over the cylindricAl periphery of filtex wall 12 o~ the screen drum 11 arld to holcl it in place. This avoids ~mbalancing and overloadin~ the bearin~s o~ the scxeen drwn 11, ~hich would o-therwise be unavoidable during the transition ~rom l~w to high angular speed.
Wash S~
Washing of the solid residue in the screen drum 11 occurs ~hile the screen drum 11 is main-tained at a rapid ro~ation.
The circulation pump 40 is stopped; and the valve 7~ releases wash water into the feed pipe 80, preferably in a number of ~ortionwise doses.
Separation Step C:
The valve 74 for wash water is closed. The screen drum 11 is returned to a slower rotation - in the range of 5 to 15 r.p.m.
such that the centrifugal acceleration on the solid residue is aonsiderably still than the force of gravity. The screw conveyor ~lights 15 within screen drum 11 can advance the residue through drum 11 and then discharge the same through outlet tube 18.
~ he washing steps are repeated as often as is necessary during the separation procedure.
The transition from high revolution speed to low revolution ~ -~
speed, or vice-versa, of screen drum 11 is made necessary, -~ecause the tube 11 with its screw conveyor bands 15 at low r . ~ Om . advances the residue through the length of drum 11 to the outlet 16. However when drum 11 is rotated at a high r.p.m., ;~
the solid residue is held in place without advancing. `~
In the case of very lar~e scale production units it is preferable to ins~all a number of residue separators in parallel~
operating with ~taggered separation and washing cycles. In .
~30 this manner oversized separators are avoided and the residue ; can leave ~he leaching tower 1 semi-continuously or continuously.
Fil~ex~ or centxifuges may be used in place of screen drum 11-12.
, : ,: .' .
~ - 20 - ~ ~
:, ' '' '~ -.
66~
The above-described resid~e washing m~thod is preferably carried'out wi~h a number of por~ionwise injec~:ions of wasllincJ
~ater, which permits almost total separa~ion of the resiclual s.olid from its content of IICl and AlC13 with a minimum of wash water. Thls permits disposal of the re~idue without dry-ing it, or to dr~ it by direct heating instead of the more co~tly indirect heatiny, until it is used, for installce, as an additive in cement production.
In the embodiment of Fig. 4 the solution pregnant with AlC13 leaves the sandfilter 9 through pipe 36a and flows through the heat exchanger 70 into the crystallizer tube 19. HCl containing mother liquor at about 50C is pumped through heat exchanger 70 by pump 54 which receives HCl solution from collecting ~ank 33. Crystallization of AlC13 and conversion to Al~OH)3 is performed in tubes 19 and 23 and mother liquor and wash liquor, HCl condensate, etc. flows through pipe 59 ~' and a part of it eventually into dryer furnace 26. "~
In the embodiment of Fig. 5 an extension feeder shaft 10 . '~-~or tower 1 through which calcined or uncalcined raw material '. .
maX be fed into tower 1 through which HCl is 10wed counter- ' current to the r'aw materi.al feed. :.
The following examples are illustrative o the invention .~' ' without being deemed limitative in any manner. . '~
: EXAMPLE 1 ' The mother liquor leaving the crystallizer 19 through ,~ conduit 59 had a temperature of about. 55C and has the follow-.
ing composition: about 3.5~ AlC13., about 11.7% FeC13, about ~ -22.9% HCl, and about 61.9% H20. :
It was used as leaching li~uor in tower 1 after ha~ing been ~:
: 30 preheated. The mother l~quor was pumped ~y the pump 54 through -~,:
'the.countercurrent .heat exchan~er 70. A solution of AlC13 at :
~ ; 'a temperature o~ at least 120C coming from the pressure resistant -' f ~
~:~ cb~ . - 21 - ' , - . . . .
sand~ilter 9 flows thro~!gh th~ pipc 36a of hea~ exchanger 70 (Fig. 4). This system oE~ered the advantage that ~IIC A:l.C13 solution arr.ivecl in a pre-cooled sta~e in the crys-tallizer 19, thus sav.ing cooling water, and that the leaching li~uor was ~reheated without further consumption of heat energ~. f Formation o~ crystals stic]cing -to -the ins.ide wall of the central pipe of heat exchanger 70 was not observed.
A leaching liquor with the above composition produced a solution o~ AlC13 leaving the leaching tower 1 at about 118C
or higher and with the following composi.tion: about 27 weigh-t % AlC13, about 10 weigh.t ~ FeC13, and about 63 weight % H20.
After heat exchange with the mother liquor, the AlC13 solution from sandfilter 9 entered the crystallizer 19 at a temperature of about 85C, where it was cooled to about 55C.
The bulk of the AlC13 content was crystallized to produce AlC13 .
6 H20; and washed with the equivalent quantity of HCl~H20 vapors from the thermal decomposition of previously crystallized AlC13 . :~
6 H20. In this manner the mother liqu~r was transformed into `~ a new leaching liquor with the above-stated composition and temperature. Contemporaneously the mother liquor, which had : entered the heat exchanger at its original temperature of 55C
had been preheated under pressure from pump 54 and by heat txansfer ~ith the AlC13 leach solution to about 60 to 90C.
.. This. preheated mother li~uor was introduced into the leaching :~ .
~ to~er 1 through screen pipe 6 to be utilized as the new leaching ., .
uor.
The pump pressure during heating the mother liquid is important, because at normal atmosphexic pressure the leaching :
'6 ~ uor containiny 22.9% ~Cl boils off HCl vapor at about 75C.
.~ 3~ A preferred pump pressure range is about 1 to 4 atmospheres over pressure.
It had been found, that 1000 parts by weight of a solution ", cb~ 22 -.
.. .. . .
~66l~372 rich in AlC13 with the following approxima-te composition:
27~ AlCl3, 10~ FeC13 and 63~ llz0 y:ield~ about 434 parts by weight o~ pure ~.LC13 . 6 H20, if cooled in the crystall:Lzer 19 ko about 55C. The equivalent quantity of HCl and ~12 vapors enters the crystallizer and are absorbed in the mother liquor.
The mother li~uor leaving the crystallizer 19 had the following composition: about 3.S% AlC13, 11.6~ FeC13, 22.9% HCl, and 62.1% H20, in spite of the fact that it had been cooled only to about 55C.
Cooling of the mother liquor to only 55C is important, because the heat transfer requirements of the cooling system for the crystallizer 19 are substantially reduced both a~ to the ~:~uantity of cooling water and as to the required initial tempera~
ture of the water.
This invention has the advantages of ~1) a relatively non-complicated method for leaching alumina from silicate containing ~ :
cla~vs, (2) substantially lower costs because of the continual -~
: recxclin~ of the mother li~uor from the crystallizer into the leaching tower as a concentrated solution of hydrochloric acid ;~to be used as fresh leaching liquor, and ~3) the presence in ~the leaching liquOr of an effective amount of FeC13 which permits ~:
the crystallization and separation of AlC13 in substantial : ` .
~uantities from a solution thereof, by onl~ lowering the tempera~
ture of the solution. Other advantages will also be apparent ; . -to persons skilled in this art. ~::
Although the present invention has been disclosed in .
connection with a ew preerred embodiments thereof, variations and~modifications may ~e resorted to and equivalent equipment :us d in place of that specifically described without departing .
~ xom the principles of the invention or the scope of the attached ~: : claimsO
cb/ - 23 - ~ .
!": . ' ~` ' ~: . ' , , !
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for the recovery of alumina from Al2O3 and silicate containing raw materials which comprises continuously extracting said raw material by coutercurrent leaching in an essentially vertical tower, with a solution containing essentially HCl and FeCl3, to extract AlCl3 from said raw material, crystallizing AlCl3.6H2O from said leach solution by the substantially continuous washing with con-centrated hydrochloric acid, moving said AlCl3.6H2O crystals upwards through a closed essentially horizontal, slightly inclined crystallizer-washer thermal decomposer with con-veyor means, washing said moving AlCl3.6H2O crystals by a countercurrent flow of pure concentrated hydrochloric acid condensate in said crystallizer-washer thermal decomposer, heating said moving AlCl3.6H2O crystals in said thermal de-composer to convert them into Al(OH)3 and recovering the pure alumina.
2. The process of claim 1 in which said AlCl3.6H2O
crystallization is continuous, the AlCl3.6H2O crystals are continuously washed with cool HCl solution, the mother liquid of the crystallization step containing HCl and FeCl3 is recovered from said crystallization step, and reused as new leaching liquid, the AlCl3.6H2O crystals are continu-ously converted into Al(OH)3 and H2O and HCl vapors, and the H2O and HCl vapors are condensed and used as washing means for said AlCl3.6H2O crystals.
crystallization is continuous, the AlCl3.6H2O crystals are continuously washed with cool HCl solution, the mother liquid of the crystallization step containing HCl and FeCl3 is recovered from said crystallization step, and reused as new leaching liquid, the AlCl3.6H2O crystals are continu-ously converted into Al(OH)3 and H2O and HCl vapors, and the H2O and HCl vapors are condensed and used as washing means for said AlCl3.6H2O crystals.
3. A process for the production of pure alumina from alumina and silicate containing raw materials comprising feeding said raw material into an acid resistant leaching tower near the top thereof; continuously feeding a leaching liquor containing essentially hydrochloric acid and ferric chloride into the bottom of said leaching tower zone, so as to continuously flow upward countercurrently through said raw material to leach out the alumina as a solution enriched in aluminum chloride leaving a raw material solid residue, withdrawing said solution enriched in aluminum chloride from the top portion of said tower; withdrawing said raw material solid residue from the bottom portion of said tower zone providing a flowing carrier liquid containing hydrochloric acid conveying said solid residue away from said leaching tower separating said solid residue from said carrier liquid and recovering the carrier liquid, crystallizing and recover-ing aluminum hydroxide from the leach solution enriched in aluminum chloride.
4. The process of claim 3 further comprising conveying said solution enriched in aluminum chloride at about 120°C
from said leaching tower into a backwashable sandfilter zone;
providing a feeding shaft zone inside the upper end portion of said leaching tower zone; and adding amounts of new raw material into said feeding shaft zone up to a sufficient height to absorb rising HCl vapors and to prevent escape of said vapors into the atmosphere.
from said leaching tower into a backwashable sandfilter zone;
providing a feeding shaft zone inside the upper end portion of said leaching tower zone; and adding amounts of new raw material into said feeding shaft zone up to a sufficient height to absorb rising HCl vapors and to prevent escape of said vapors into the atmosphere.
5. The process of claim 4, further comprising back-washing said backwashable sandfilter zone by preventing said solution enriched in aluminum chloride from flowing into said backwashable filter zone; flowing said solution into the bottom portion of said backwashable filter to remove raw material residue trapped in said filter; and transport-ing said residue with said solution into the bottom portion of said leaching tower to become agglomerated with the raw material solid residue therein.
6. The process of claim 4, wherein said solution en-riched in aluminum chloride leaving said sandfilter zone at about at least 120°C and comprising, by weight about 27%
AlCl3, about 10% FeCl3 and about 63% H2O, passes through a heat exchange zone and into a crystallizer zone at about 50° to 55°C; cooling said solution enriched in aluminum chloride to about 80°C in said heat exchange zone and pre-heating a mother liquor from said crystallizer zone, flow-ing countercurrently to said solution, from about 50°C to 55°C to about 60°C to 90°C.
AlCl3, about 10% FeCl3 and about 63% H2O, passes through a heat exchange zone and into a crystallizer zone at about 50° to 55°C; cooling said solution enriched in aluminum chloride to about 80°C in said heat exchange zone and pre-heating a mother liquor from said crystallizer zone, flow-ing countercurrently to said solution, from about 50°C to 55°C to about 60°C to 90°C.
7. The process of claim 4, wherein said leaching liquor, after having reacted and lost substantially all its free HCl, passes through an additional layer of new raw material from which it cannot dissolve any more Al2O3.
8. The process of claim 4, further comprising convey-ing said solution enriched in aluminum chloride at about 120°C into the cold crystallizer zone portion as about 25°C
to 75°C of a crystallizer-thermal-decomposer zone containing a mother liquor, said aluminum chloride precipitating in said cold zone portion as AlCl3.6H2O crystals; transporting said crystals through an intermediate washing zone portion into the hot thermal decomposer zone portion at about 300°C
to 400°C to convert said AlCl3.6H2O crystals into Al(OH)3 and into vapors of HCl and water; removing the Al(OH)3;
conveying said vapors countercurrently to said crystals and from said hot zone portion through said intermediate washing zone portion into said cold zone portion, and partially condensing said vapors on the surfaces of said AlCl3.6H2O crystals and on the cold inside surfaces of said intermediate washing zone portion and of said cold zone portion; whereby concentrated hydrochloric acid is formed, which washes said AlCl3.6H2O crystals, free of the adhering FeCl3 containing mother liquor, transforming the mother liquor into a new leaching liquor; and recycling said new leaching liquor into said leaching zone.
to 75°C of a crystallizer-thermal-decomposer zone containing a mother liquor, said aluminum chloride precipitating in said cold zone portion as AlCl3.6H2O crystals; transporting said crystals through an intermediate washing zone portion into the hot thermal decomposer zone portion at about 300°C
to 400°C to convert said AlCl3.6H2O crystals into Al(OH)3 and into vapors of HCl and water; removing the Al(OH)3;
conveying said vapors countercurrently to said crystals and from said hot zone portion through said intermediate washing zone portion into said cold zone portion, and partially condensing said vapors on the surfaces of said AlCl3.6H2O crystals and on the cold inside surfaces of said intermediate washing zone portion and of said cold zone portion; whereby concentrated hydrochloric acid is formed, which washes said AlCl3.6H2O crystals, free of the adhering FeCl3 containing mother liquor, transforming the mother liquor into a new leaching liquor; and recycling said new leaching liquor into said leaching zone.
9. The process of claim 8, further comprising recy-cling the major portion of said mother liquor from said cold zone portion to the bottom portion of said leaching zone, diverting a minor portion of said recycled mother liquor into a heated rotating zone at about 250°C to 350°C to evaporate HCl and water leaving a residue primarily of Fe2O3; condensing said HCl and water into a condensate in a condenser zone, recycling said condensate to said leaching zone to be added to the leaching liquor; and removing said residue of Fe2O3; to limit the increase or the FeCl3 concen-tration in the leaching liquid.
10. The process of claim 9, further comprising elimi-nating excess water from said heated rotating zone as a hot vapor mixture of HCl and water vapor, charging a superimposed stripper layer of raw material containing Al2O3 into a zone space above said leaching zone, and recycling said hot vapor mixture through said stripper layer to remove said HCl.
11. The process of claim 8, comprising condensing vapors of HCl and water from said hot decomposer zone, spray-ing a portion of said condensed vapors onto the cooled inside walls of said intermediate washing zone, and spraying the remaining portion of said condensed vapors onto the moving crystals of AlCl3.6H2O.
12. The process of claim 8, further comprising period-ically withdrawing a portion of the mother liquor from said crystallizer zone, concentrating said portion, and recycling said concentrated portion back to said mother liquor in said crystallizer.
13. The process of claim 3, in which said leaching liquor further contains from 2% to 20% by weight of FeCl3.
14. The process of claim 3, wherein said separating of said solid residue from said carrier liquid comprises intro-ducing said carrier liquid conveying said solid residue into a rotating separation zone provided with a liquid permeable acid-proof wall; passing the major portion of said carrier liquid through said wall; recycling said carrier liquid to said leaching zone; transporting said solid residue to the end portion of said separation zone; collect-ing said solid residue at said end portion; and conveying said solid residue into a rotating dryer zone.
15. The process of claim 14, further comprising intermittently spraying washing water onto the solid residue from the leacjing zone in said separation zone; separating said washing water from said solid residue; and discharging said washed solid residue from separation zone substantially free of HCl and AlCl3; whereby said rotating drying zone can be eliminated.
16. The process of claim 3 further comprising pre-heating said leaching liquor containing HCl and an optimum concentration of FeCl3 to at least such a temperature that the heat of reaction with Al2O3 in the raw material in said leaching zone raises the temperature of said leaching liquor to at least about 120°C.
17. The process of claim 16, wherein said preheating of said leaching liquor is by heat exchange with a solution enriched in AlCl3 leaving said leaching zone at about at least 120°C.
18. The process of claim 10, wherein a leaching liquor comprising by weight, approximately 1.5 to 4% AlCl3, approximately 8 to 14% FeCl3, approximately 22 to 25% HCl and approximately 57 to 67% H2O is preheated to about 60°C
to 90°C.
to 90°C.
19. The process of claim 3, further comprising moni-toring the concentration of the AlCl3 solution at different levels in the leaching zone and adjusting the flow of solution through said leaching zone.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,468A CA1066872A (en) | 1976-03-22 | 1976-03-22 | Method and apparatus for the fabrication of pure alumina from al2o3 and silica containing raw materials by leaching with hydrochloric acid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA248,468A CA1066872A (en) | 1976-03-22 | 1976-03-22 | Method and apparatus for the fabrication of pure alumina from al2o3 and silica containing raw materials by leaching with hydrochloric acid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1066872A true CA1066872A (en) | 1979-11-27 |
Family
ID=4105522
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,468A Expired CA1066872A (en) | 1976-03-22 | 1976-03-22 | Method and apparatus for the fabrication of pure alumina from al2o3 and silica containing raw materials by leaching with hydrochloric acid |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1066872A (en) |
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| WO2013037054A1 (en) * | 2011-09-16 | 2013-03-21 | Orbite Aluminae Inc. | Processes for preparing alumina and various other products |
| US8597600B2 (en) | 2007-05-21 | 2013-12-03 | Orbite Aluminae Inc. | Processes for extracting aluminum from aluminous ores |
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- 1976-03-22 CA CA248,468A patent/CA1066872A/en not_active Expired
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