DE1417888C - Process for the production of sodium chromate from noritic chrome ores - Google Patents

Description

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The invention relates to a method for the manufacture explanation for the fact that the method does not

the development of sodium chromate from noritic ores with a guide to the technology. a relatively low ratio of Cr to Fe From Swiss patent 338 431 is

(1.3 to 2.3) and a Cr., O ₃ content of 40 until it is known to add chromite ores with anhydrous soda

55%. Such ores are processed in the Bushveld complex into 5 pellets and these then at around

Transvaal, the Great Dyke in Southern Rhodesia and to roast at 950 ° C. These pellets can be

won the Stillwater Complex in Montana. moderately small amounts of lime, according to the examples

Unless otherwise stated, Ann do not refer to more than 20% included. However, if pellets that

gave in parts and percentages by weight. contain no more than about 20% lime and are made of

The hitherto common practice of producing io noritic ores are to be roasted,

Sodium chromate composed of noritic chrome ores will only be about 65% of that obtained in the ore

The dried chromium was obtained by drying the ore.

Ore ground to a grain size below 0.074 mm. According to German patent specification 599 299 the powdered ore with finely divided sodium are made from mixtures of chrome ore, alkali carbonate, leached residue and lime and alkaline additives such as lime, briquettes mixed and pressed the powdery mixture in one, and these briquettes are roasted in a shaft mechanical oven, usually a rotary roasting oven at temperatures up to 1050 ° C, brought in where the roasting took place. This method, however, this method has proven to be unusable has a number of disadvantages, of which the more important ones should be mentioned for the processing of chromium which is difficult to roast: 3 ° ores, such as Transvaal ores, in which the ratio

1. Noritic chrome ores, especially Transvaal fr. Fe only about 1 6 (compared to about 2 9 in the ore, are difficult to oxidize, and there are ^[r _"t mainly processed ores ^ago) · Therefore, in this method, only amounts proportionate, ^proven Moreover, this must known excessively low conversions to chromate ER ^{Ve, r} (?:.. ^h { ". ^s'" _t ^{emem Sch} ^ htofen d h can open aims The technical yields were not in the * ^{5 Mch} J ^I in a Drejirostofcn performed range from 75 to 90% water-soluble chro- ™ ^ld ™> ^{wei1 dle} compressive strength of the briquettes to overall

mat, based on the chromium content of the ore. ß,. '. ",, ..., _n . . ,., "___, .-

ο η ■ α r? LfU j r> - *! .- υ ι λ According to British patent specification 755 112

2. When roasting is carried out, the <,. ... ^ _o . „„, „, R;„ u; „ut ο- α wi α α η ·· ♦ c " ^{en made of} chromium-containing ore, soda, lime and water trz light rings on the wall of the grate furnace τ ,,,,,. " _f . 5. ■ · τ *. _mn ο « , · _α , ~ n v \ AAT, - .. η * ·· 3o pellets formed and at a temperature of 900 as well as large lumps that interfere with the rusting process.. · _11n . 5 _or, - ■ ₄ ... f, "..

it ~ j »~ r * -UA a UA- π · - -c to 1200 C rusted. These pellets also have

3. To the mixture, the overall au · τ- »ι c * *> * * * _<n rj, · _4Λ through the grate furnace, j. ul U-UT-- yet a compressive strength of only about 10 kg and is conductive, desired mechanical prop- _t . _u α "· ο α r> ■ · ι a- u ■ " K " _ft 1 ·. AJ r · · also contain, according to the examples of these bonds, the ore became inert. ·," . * u ^ * α η ι u- η «. j _n A _ar u- _t ," L, ", - · λ- \" _t ■ , ..,,. heat-resistant materia, usually made of- * - u- <■ u »τ c ■ ο j

. """, R ...,. ^b,. * _ '. 35 stochiometric amount of anhydrous soda,

leached residue added. That does ie- ^.,, ·. ■. * ^,, ......

j. . ^& , · ,,,., ^& _T c u-J c \ particles with such a low compressive strength can

η hh ^ ^VOn u 'v ^g " ^ic ht ι" be roasted in a rotary kiln, and moreover

Oven load per gram of extracted batch _{; dJ Use a} " _{r such open Me}

Lich chromate required. _{r o} , _t . ™ · u

_Λ r » _T , .., ..., anhydrous soda uneconomical.

4. Drying the 1 and marrying the exhausted r,, -. , _n ^ u ■ uu τ, - , _ct „_ ■. _. τ, j · 40 It has now been found that chromium in a large amount of clog before it is admixed with the _{ore to be processed in Λ} , u ■ ■ u i- · UI ₁ · the furnaces is with considerable- ^A !? ^s _R ^booty ^ ^uch of nontischen ores verhaltn.slichen costs connected. ^{with a} low ratio of Cr: Fe

cr>"u a- e · T-iu α o -uj den can, if the pulverized ore together with

5. Through the fine particles of the mixture, the _{hydrated calcium} , water and the stoichiomem are introduced into the furnace, the atmosphere of _{soda ash is transformed into pellets} . Sphere contaminated, so that it becomes necessary _{for the p} «, _{first that is, heating to a}

• Take precautions to contain the dust- _{T ature by whom} i _2stens 480 ° C and hardened

to meet the salary of the plant. From the loading _d / _{b. ;} . _d roasting zone in a certain way

constituents of the mixture have both lime at _low temperature to be roasted, as well as soda irritant effect, and the residue _Ge J _{enstand of} the invention is a method for

can not leached chromate corresponds _Herst ^ _{n of Natriu} mchromat from noritischen

hold, of which are known to be harmful _{chromiumZ (} f _{n by roasting pe} "_{ets> the one Ge} .

for the respiratory system. ^ of _{the pulverized Er2es with about the stoichio} .

It is also already known to use the concentration of beach sand for the conversion of the rate contained in the ore, of which practically all of the silica required 55 chromium to sodium chromate

separated by mechanical ore pressing methods is the amount of anhydrous soda with or without water

and containing chromium, titanium and zirconium, which is characterized by being

to grind, with slaked lime, anhydrous a mixture consisting essentially of 100 parts

Soda and water mix, the mixture to ore, the anhydrous soda. 60 to 80 parts of hydrate spherical particles with an average diameter of ⁶ ° siert nondolomitic lime or 75 to

from 1.3 to 5 cm or more, these 115 parts on another hydrated dolomi-

spherical particles at a temperature of about table lime (or an equivalent amount of

290 ⁰ C to dry and the dried particles another hydrated lime) and 50 to

to be roasted at a temperature of 700 to 800 ° C. 70 parts of water to small pellets in which the Among other things, this proposal has the disadvantage that 65 components are evenly distributed, processed,

that only a relatively small conversion of these pellets by heating to a temperature

hardens to chromates and thus a relatively low degree of at least 48O ⁰ C and then roasts them,

Sodium chromate yield is achieved. This can be done by looking at them in a manner known per se

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an oxidizing atmosphere conducts, whose per se oxide, silicon dioxide and iron in the ore and The known roasting temperature of 535 to 815 ° C prevents the formation of soluble silicates Inlet end to 1090 to 1205 ° C at the outlet end and aluminates in the leaching liquids. He serves as a

the oxidation zone increases. Thinner, i.e. it sets the amount

The mean particle size of the material which is meltable as the starting material in the ovens is down, and he The powdery ore used is expediently reduces the loss of sodium, i. h ,, he leads

25 to 75 μ. to a decrease in the amount of insoluble

The pellets suitably have a mean largest sodium compound in the residue.

Dimension no more than about 1.27 cm and the amount of hydrated lime is critical

preferably an average size of 0.8 to 1.1 cm. io If more than the specified amounts are used

They can be spherical or of any other shape, for example, so the lime combines with the chrome

wise cylindrical, be. to insoluble complex calcium chromates. When

The shaping of the particles can be in any of the amounts of hydrated lime used in

usual pelletizing, such as the ranges given above, will be the

in a rotating pan, which with the powder formation of such insoluble complex calcium

hydrated ore, hydrated lime and sodium carbonates are reduced to a minimum. When a

bonat is charged with water spraying. hydrated lime is used, whose CaO-

By suitable adjustment of the inflow, the mate content can be considerably different from the above

If the food and the speed of rotation of the pan is too low, the amount of such must be hydrated

a steady outflow of particles of the desired calcium carbonate such that it supplies CaO in an amount

Achieved size above the pan beak. In which that of the in the 60 to 80 parts hydrated (not

In the mixture, the water serves as a means for agglomondolomitic) lime or in the 75 to 115 parts

rieren or binding of the solid components and rea- contained in hydrated dolomitic lime

Yaws also corresponds to the formation of the sodium carbonate.

of a hydrate. This will make tablets of such 25, if desired, leached waste mechanical strength obtained that they in the previous approach in the to be pelletized subsequent heating to retain their shape, the mixture is introduced to the mechanical however, unless heated, is not sufficient to improve the behavior of the particles in the furnace, the agitation required during roasting. Such leached waste becomes in addition to that to allow. Another 30 hydrated lime is added by heating. That in the hydrati-enhancement the mechanical strength of the divided dolomitic lime contained magnesium achieved mainly due to the formation of oxide represents an ideal diluent for that hard, crusty, anhydrous sodium carbonate ore mixture because it is inert. Hence in need of a is due. mixture to be pelleted, the hydrated dol-

The hydrated lime used is preferably 35 containing lime, no leached residue slaked or hydrated lime to be incorporated in finely divided. If other forms of shape, for example, a grain size below 0.2 mm. The term "hydrated lime" is intended to encompass all of these habitually such leached residue, but in forms of hydrated lime, including less than that previously used with hydrated dolomitic lime. Hydra- 40 Advantage can be introduced into the mixture. The hydrated non-dolomitic lime contains about 70% of the amount of leached residue need not be greater than CaO, while the hydrated dolomitic lime must be more than 60 parts per 100 parts of ore.
The particle size of sodium carbonate, and also of hydrated dolomitic lime, that of hydrated lime is not critical as long as about 45% of the available CaO and the remaining 45% of these particles are small enough to contain a sufficient amount of mainly MgO and Water of hydration to allow the good mixing with the ore and contains CaO; in the hydration of dolomitic lime particles to a uniform distribution of the ore particles, only the calcium oxide is converted into calcium hydroxide with regard to the particles of anhydrous soda, while the MgO does not lead to noticeably hydrated lime. Commercially available is tized. Surprisingly, when using 5 ° light anhydrous sodium carbonate and the hydration of hemihydrated dolomitic lime, the commercial lime has the highest conversion of chromium into the ovalent particle sizes. In general, the best ErForms are achieved. Results obtained when the components of the pelletized

The hydrated lime serves several purposes. Mixture a particle size of 20 to 125 μ

It is important to have used hydrated lime 55.

because when using non-hydrated although the ore is preferably dried, Lime particles of insufficient strength before being pulverized and kept pulverized what will probably be due to a hydra- dried ore with the rest of the constituents of the too tion of the lime is mixed within the particle back-pelletizing mixture, can also is to feed that to an expansion and thereby an ore that contains exactly the amount of water * leads to a disintegration of the particle. Hydrated by the amount of lime later added to the ore is plastic when moist and burnt-in lime, can be completely extinguished, supported when wet thereby the shaping of the particles. He is ground and the ground ore with the right one more reactive in the ovens than unslaked lime. Amount of quick lime to be mixed, whereby It accelerates the roasting, 65 in the mixture slaked lime (calcium hydroxide)

Hydrated lime performs all of the functions of not being formed. If the ore is too wet, it will be

hydrated lime and has all the advantages of dried lime ^:

this on, d. that is, it combines with aluminum, so that it is quenched with the lime

this reacts. The mixture of slaked lime and ore that is now dry because the lime is the water contained in the wet ore is then absorbed with sodium carbonate and others Water mixed and pelletized.

The binding in the freshly formed particles apparently depends mainly on the formation from sodium carbonate monohydrate. When the particles are applied in the method of the invention

whose deposited material is conveyed out of the chamber 21.

Hot gases from the particle inlet end 25 of a rotary roasting furnace 26 flow through the dust chamber 21 and heat the particles conveyed by conveyor 18 therethrough. The heated particles are brought out at 27 in the rotary roasting furnace 26, in countercurrent to hot oxygen-containing Gases flowing through the furnace. These are called

The high temperatures occurring are heated, io gases are preferably generated in that an even better bond is achieved, which is presumed to be a result of the burner 28 at the particle outlet mainly due to the formation of anhydrous
Sodium carbonate and the resulting formation

due to hard shells and crusts,

Appropriate fuel supplied to the end 29 of the roasting furnace burns. Secondary air for entertainment the combustion of the fuel and the delivery through which a solid particle is formed. The amount of oxygen desired in the furnace is on Entity of calcium hydroxide and the sodium outlet end 29 of the furnace as initiated by the carbonate particles cause the ore particles indicated by arrow at 30. The remaining arrows indicate the evenly in the other components in each direction of flow of the hot combustion products Particles are dispersed. Although the particles and oxygen through the roasting furnace 26 and the are sufficiently hard that they are ao chamber 21 in the rotary roasting furnace.

If air is used to form substantial amounts of dust, the oxygen is made up of the oxidizing atmosphere in the roasting furnace 26 still porous enough to be produced in the rotary roasting furnace, the next to the outlet end 29 exists oxidizing atmosphere present on the ore part of the furnace in contact with the roasted product can get inside the particles, so that the atmosphere mainly consists of air, because through practically all of the chromium present in sodium- the chimney creates a draft in the furnace, and the chromate is transferred. Secondary air for combustion occurs at the particle

The pellets are preferably fed to a temperature outlet end of the rotary roasting furnace. When the secunrature from 480 to 600 ° C and in particular about därluft with the fuel and the combustion 535 Heated to 540 ° C to harden it so that it mixes 30 products, the oxygen content drops when circulating at the roasting temperature, the gas mixture formed does not decompose. This will get over fall or dust. The heating can thereby take place for most of the length of the roasting oven of the sour, that a hot gas is passed over it, or that the material content in the furnace is kept sufficiently high, the temperature of the pellets can be increased gradually to create an oxidizing atmosphere. the for example at a rate of about 35 oxygen content of the gases under these conditions 140 ° C / min. are increased until they exit the value of the roasting oven is in the range

from 6 to 12 percent by volume.

As mentioned, air enriched with oxygen can be used to create the oxidizing atmosphere or oxygen-enriched roasting oven gas, from which the carbon dioxide has been removed, into the oven be directed. If you work under these conditions, the oxygen content of the between 6 and 60 vol-

12 percent by volume oxygen. When using 45 lumens percent. Such roasting furnace gases are enriched air, or if the recycled especially if it contains significant amounts of

Oxygen, for example more than about 20%> contained, is passed through the furnace again after Carbon dioxide is removed from it to reduce losses

keep. Avoid the residence time of the pellets in the roasting furnace 50 oxygen.

is preferably between about 2 and 4 hours. The hot particles enter from the furnace

one or more leach containers 31, each having a perforated or sieve bottom. This Containers can hold 22 to 601 roasted products each. A weak sodium chromate solution covered it the hot roasted product and percolates through it. Strong sodium chromate solution is drawn from the bottom of the container drawn off, and the level of the solution above the roasted particles is increased by adding water in the proportions given above, weak sodium chromate solution was added to the nissen is loaded. The particles thus formed retain 16 containers. The sodium chromate solution are continuously drawn into a hopper 17- is usually withdrawn from the container when brought by them to a conveyor, they preferably have a concentration of about 0.72 kg of sodium in the form of a conveyor belt has 19 chromate per liter, and the solution will be so long reach. This conveyor belt pulls the parts 65 from the bottom of the container, like their cones in a roasting furnace dust chamber 21 with a centration relatively high, for example above Chimney 23 and a screw conveyor 24 remain on their approximately 0.42 to 0.48 kg sodium chromate per liter, lower end for removing dust and an- If the concentration drops below this value,

Has reached the initial roasting temperature of 815 ° C. The pellets are preferably heated by they are passed through the outlet gases of the roasting oven at a temperature of 535 to 760 ° C.

The roasting takes place preferably in a rotary kiln, through which they are guided with constant circulation will. When air is used as the source of oxygen, the oxidizing atmosphere contains 6 bis

Roasting furnace gas is added after removal of the carbon dioxide, the oxidizing Atmosphere up to 60 percent by volume of oxygen

and especially about three hours.

The invention is illustrated by the drawing which is a flow sheet of the process.

The pelleting machine of the usual type 10 consists of a rotating pan driven by a motor 12 11, continuously from line 13 with a dry mixture and from line 14 with

Claims (8)

7 - 8 the liquid outflow from the container is interrupted in exchange with the hot outlet gases of the rotary roast, the particles are covered with water, oven conducts. and the container drain is directed to the supply of the hot hard particles into the rotary weak solution which is introduced for the next roasting furnace in which an oxidizing atmospheric batch of roasted product is used. If the rust prevails sphere 5 and the temperature is between 760 ° C product is completely leached substantially at Teilcheneinlaßende and 1205 ⁰ C at Teilchenläßt to expire the container and used, the outlet end varied. The residence time of the particles of the leached material, if desired as a dilution, is 3 hours,
means for pelletizing or discarding it. Each toasted particle contains 20.5 ⁰ Zo Cr ₂ O., The strong sodium produced in this way, 99.7% of which is oxidized and 97.3% water-soluble Chromate solution is concentrated or in others. The roasted particles contain 42.4% Way further processed according to usual methods. water soluble sodium chromate. In general, for 1001 particles, about 1 kg of chromate recovered is only 2.36 kg 70 9001 water and about 56 0001 weak reverse roasting oven product required,
guided solution used for leaching. 15 The particles are arranged as described above The following examples illustrate the leached. The chromium content of the leached recovery. Parts are by weight. Stand is on the order of 3 weight percent Cr ₂ O ₃ . Example! In the two examples above, the roasting takes place ao without difficulty, d. i.e. no rings are formed 100 parts Transvaal chrome ore concentrate with one or lump of ore agglomerates.
46.73% Cr ₂ O ₃ content, 76 parts hydrated So the present invention consists of one Lime with a content of 72.2% CaO, 65 parts of a process for the production of sodium chromate from anhydrous soda and 30 parts of leached back noritic chromium ores including Transvaal ore, was a previous approach with an as that is difficult to oxidize. The process results in a content of about 4.35% Cr ₂ O ₃ are in an unusually high yield of chromate, leads rotating pan pelletizer through feed- not to the formation of rings and large lumps would be pelleted from 60 parts of water. Those formed in the rotary kilns, which interfere with the roasting process, and the particles have a diameter of 0.8 to the amount of mixed feed, which per kilo-1.1 cm. They are slowly heated to 30 grams of recovered soluble chromate at 538 ° C. in about four and a half hours by passing them into direct heating - the furnace is extremely exchange with the hot gases of a rotary roasting furnace, little. In the method of the invention, one having a temperature of about 760 ° C is conductive. Loading of around and even less than 3 kg The hot hard particles formed in this way are introduced into the roasting oven product per kilogram of soluble soluble in the rotary roasting oven, in which an atmospheric chromate is required. This means a down sphere 6 to 12 volume percent oxygen prevails reduction by more than 2 kg per Röstofenbeschickung and its temperature at about Teilcheneinlaßende kilogram of recovered soluble chromate 76o C and about ⁰ is 1205 ⁰ C at the outlet. compared to the known roasting process, ie with the residence time of the particles in the rotary roasting oven only half of the total roasting oven charge is 3 hours. The particles passing through this furnace can produce the same yield of soluble chromate as they are obtained through the. oxidizing atmosphere pass through, steadily around- As hydrated for the process of the invention rolled. Lime is used and the mixing of the The roasted product is collected and components of the particles analyzed in the presence of water. Each particle contains about 19.6% Cr ,, O ₃ , by 45, there is also dust formation in which 97.3% are oxidized and 89.6% are water-soluble. Charging of the roasting furnace with the particles greatly. The content of water-soluble chromium in all parts is reduced. The atmospheric impurities, chen corresponds to a 92.1% extraction of the previously obtained when the ore was charged with the powdery-chromium content. The roasted product de-lime, the powdered anhydrous soda contains 37.4% water-soluble chromate as Na ₂ CrO ₄ . 50 etc. in the furnace do not occur.
Per kilogram of obtained chromate are in this
Example only 2.68 kg of roasted product processed. The means a reduction of about 50% of the patent claims: Amount of roasting furnace charge, the chromium obtained per kilogram in the previously known processes. 55 1. Process for the production of sodium mat is required. chromate from noritic chrome ores by roasting pellets, which are a mixture of the powdered Ore with about the stoichiometric for 100 parts of ore of the type used in Example 1, the implementation of that contained in the ore 90 parts dolomitic lime (containing 60 chromium to sodium chromate required amount about 47% CaO) and for the formation of the hemihydrate of anhydrous soda with or without water hydrated, 65 parts anhydrous soda, all ingredients, characterized in that parts in powdered form, are in a rotating one a mixture of essentially 100 parts ^ "_ ° ' ^anne pelleting machine with the addition of ore of anhydrous soda, 60 to 80 parts 61 parts of water pelleted. The particles have a 65 hydrated non-dolomitic lime or medium size of 1.1 cm. They are dried from 75 to 115 parts of hydrated dolomitic and hardened. by slowly putting them on lime (or an equivalent amount of a ^ S- C heated so that they are in direct heat from other hydrated lime) and 50 to 70 parts Water processed into small pellets in which the components are evenly distributed, these Hardens pellets by heating them to a temperature of at least 480 ° C and then roasting them, by passing them through an oxidizing atmosphere in a manner known per se known roasting temperature of 535 to 815 ° C at the inlet end to 1090 to 1205 ° C at the outlet end the oxidation zone increases. 2. The method according to claim 1, characterized in that the pelletizing particles are formed, the largest dimension of which is on average no more than 1.27 cm. 3. The method according to claim 1 or 2, characterized in that the particles in the grate zone be circulated and pass through this zone in a time of 2 to 4 hours. 4. The method according to any one of the preceding claims, characterized in that the Particles to solidify them are heated to 480 to 600 ° C. 5. The method according to any one of the preceding claims, characterized in that the Particles, in order to solidify them, are heated by having them in direct heat exchange conducts the roasting process with hot gases. 6. The method according to any one of the preceding claims, characterized in that the Particles are roasted in a rotary roasting oven. 7. The method according to any one of the preceding claims, characterized in that the Particles are roasted in an atmosphere that contains 6 to 60% oxygen on leaving the furnace contains. 8. The method according to any one of the preceding claims, characterized in that the hydrated lime is formed in situ by mixing wet ore with quick lime. 1 sheet of drawings