US2671725A

US2671725A - Production of zinc

Info

Publication number: US2671725A
Application number: US80916A
Authority: US
Inventors: Robson Stanley; Derham Leslie Jack
Original assignee: National Smelting Co Ltd
Current assignee: National Smelting Co Ltd
Priority date: 1949-03-11
Filing date: 1949-03-11
Publication date: 1954-03-09
Anticipated expiration: 1971-03-09

Description

March 9, 1954 s, RQBSON ETAL 2,671,725

PRODUCTION OF ZINC Filed March 11, 1949 7 Sheets-Sheet l i o 8 a u I t m u & y a I hive/170119 STANLEY ROBSON AND LESLIE JACK DERHAM March 9, 1954 Filed March 11, 1949 F/GZ.

s. ROBSON ETAL PRODUCTION OFZINC 7 Sheets-Sheet 2 v l/lvmfars STANLEY ROBSON AND LESLIE JACK DERHAM m gamma/{W (541mm March 9, 1954' Filed March 11, 1949 s. ROBSON ET AL 2,671,725

PRODUCTION OF ZINC 7 Sheets-She'et s 'r S TA NLEY ROBSON AND LESLIE JACKDERHAM S. ROBSON ET AL March 9, 1954 PRODUCTION OF ZINC 7 Sheets-Sheet 4.

Filed March i1, 1949 F/ G. 7. so 62 44 67 4s 66 46 l/ I! I I l/ I I 1 I I I l I s/ s3 7 2 40a 14 147 so 5: 52 48+;

1 If 1 III 4- I v 6 9 G49 60 39 K h 4 so il Il III ll v,

MVHMOSITQNLEY R BSON AND DERHAM March 9, 1954 s. ROBSON ETAL PRODUCTION OF ZINC 7 Sheets-Sheet 5 Filed March 11, 194 9 "I \BIE W f a m w ,4 ffa me ya March 9, 1954 s. ROBSON ETAL. 2,671,725

I PRODUCTION OF ZINC Filed March 11, 1949 7 Sheeis-Sheet e QTKNLEY ROBSON AND LESLIE JACK DERHAM March 9, 1954 s'. ROBSON E .TAL 2,671,725

PRODUCTION OF zmc Filed March 11, 1949 7 Sheets-Sheet 7 fifiiev ROBSON AND LESLIE JACK DERHAM mi fwmmm (WFBMMM Patented Mar. 9, 1954 UNITED STATES PATENT OFFICE PRODUCTION OF ZINC Application March 11, 1949, Serial No. 80,916

Claims.

1 This invention relates to the production of zinc and has for its object improvements in the I method of and apparatus for producing zinc.

The invention relates more particularly to the recovery of zinc from a body of molten lead that has been used as a condensing medium for zinc vapor obtained in zinc smelting operations.

Prior proposals to use molten lead as a condensing medium for zinc vapor obtained in smelting operations have not met with much favor. One of the main reasons, of course, is the cost of the large amount of lead that must be employed. Another, is the difficulty of recovering the small amount of zinc from the large amount of lead in a satisfactory manner. In view particularly of renewed efforts to find a way commercially to smelt zinc bearing materials in a blast furnace, attention is again directed to the possibility of using molten lead as a condensing medium for zinc vapor.

Gaseous mixtures containing zinc vapor, carbon monoxide, and a substantial amount of carbon dioxide are especially difiicult to treat in a zinc condensing operation because of the tendency of the carbon dioxide to react with the zinc to form an objectionable amount of the zinc oxide. The following composition is typical of the gaseous mixtures derived from blastfurnace smelting of zinc-bearing ores, residues or the like.

Zinc-bearing gaseous mixtures of similar type can also be derived from the electro-thermic smelting of zinc, but in this case the zinc content is usually rather higher and the CO2 content may be rather less.

A method of condensing and recovering the zinc values from a gaseous mixture of the type referred to is disclosed in our co-pending application Serial No. 535,290 filed May 12, 1944 (which has since issued into Patent 2,464,262 of March 15, 1945), of which the present application is a continuation-in-part. The method of condensing comprises bringing the gaseous mixture while still hot into intimate shockchilling contact with circulating molten lead in a condensing zone maintained at a temperature not greater than 550 C. to cause the gaseous mixture to cool to a temperature below that at which the carbon dioxide can react with the zinc to form objectionable zinc oxide, condensing the zinc vapor in the lead and accumulating a body of the solution.

The method of recovering the condensed zinc comprises cooling the lower portion of the body of lead-zinc solution to a temperature below 413 C., but not below the melting point of lead, to precipitate zinc therefrom while maintaining the upper portion of the body of the solution above 418 0., permitting the precipitated zinc to rise into the upper portion of the body of solution with the resultant remelting of the zinc and the formation of a supernatant layer of molten zinc, removing molten zinc from this supernatant layer and returning the molten lead from which the zinc was precipitated for re-use in the condensing step.

While this method of recovering condensed zinc from molten lead has given excellent results, we have found that when the lower portion of the lead-zinc solution is cooled to a temperature as low as 418 0., some of the precipitated zinc crystals tend to adhere to the sides of the vessel in which they are precipitated. Unless scraped from the sides of the vessel, the crystals tend to build up and thus to insulate the vessel. To this extent, at least, the method is a drawback and leaves something to be desired.

Investigation confirms our discovery that zinc may be recovered from molten lead used as a condensing medium for zinc vapor and that drawbacks of the type mentioned may be avoided, while at the same time gaining certain other operating advantages.

In accordance with the method of the invention for recovering zinc from a body of molten lead used in a condensing zone as a condensing medium for zinc vapor obtained in a smelting operation, the condensation of zinc vapor is continued until the zinc content of the molten lead builds up to a point corresponding to the saturation point of the lead for zinc at a temperature above the freezing point of the zinc but below the temperature of the lead in the condensing zone. The resulting lead-zinc solution is accumulated in a substantially quiescent body. The body of molten lead-zinc solution is cooled to a temperature above the freezing point of the zinc but at which dissolved zinc separates and rises to the top of the body of solution to form a supernatant layer of molten zinc and an underlying layer of molten lead. The supernatant layer of molten zinc is separated at least in part from the underlying layer of molten lead and solution containing the remaining molten lead is returned to the condensin zone for re-use in the condensing step.

Since the lead-zinc solution from the condensing zone is not cooled low enough to permit zinc crystals to precipitate, the molten zinc remains in solution in the molten lead. The temperature, drop, however, is sufficientv to cause moltenzinc in solution to separate, in effect, and rise as such to the top of the body of solution. Since zinc has a lower specific gravity than lead, the molten zinc rises to the top while the molten lead settles to the bottom. The molten-zinc at the top may be drawn oil" readily, and thus be recovered separately from thelead.

For a specific application of the method of the invention, reference may again be made to our prior method of recovering condensed zinc from molten lead, described above andas disclosed in our copending application. Instead of cooling the lead-zinc solution to such a low temperature as 418 C.,,the temperature is kept above 418? C., and precipitation of zinc crystals is avoided. In

'this connection, we found that if the body of molten lead coming from the condensing zone is saturated with. zinc at the temperature at which the condensation is effected, any subsequent cooling of it will cause molten zinc to separate, or rather a molten solution of zinc-richalloy whose lead content is very small and may be ignored, sincefurther treatment will in any case be necessary if a high purity zinc is ultimately required.

Therefore, in accordance with the present invention, the condensation of zinc vapor in the circulating molten lead is, continued until the zinc content of the molten lead exceeds. at least 1.7% by weight; the lead-zinc solution is then accumulated in a substantially quiescent body which is allowed to cool sufficiently to permit some of the zinc dissolvedtherein to separate and rise as such to the top of the body of solution to form a supernatant layer of molten zinc and anunderlying layer of molten lead, the supernatant layer of molten zinc being thenseparated,

at'least in part, from the underlying layerof -molten lead and the solution containing'the remaining molten lead being returned to the condensing zone for re-use inthe condensing step. Preferably the resultant lead-zinc solution is accumulated in a cooling zone removed from the condensingzone and the body of solution is cooled to a temperature below 506 C., but above tion of the supernatantlayer of molten zinc.

The necessity for recinsulatingthe leaduntil the dissolved zinc content exceeds. atleast 1.7% arises from the fact, which can. be verified from the phase diagram of the binary lead-zinc system, that at temperatures exceeding 413 C. the lead-rich component of the liquid phase contains 1 .'7 and upwards of zinc; hence,.unless the total zinc content exceeds 1.7%, the zinc-rich component from which alone the zinc values can be recovered, will not be present at all.

The circulation of molten lead in the condensing zone by means of which-the condensation of zinc from the gaseous mixture derived from the blast-furnace or other smelting apparatus] effected may be produced by means of a rotary paddle wheel or the like device operating in an enclosed condensing-chamber and dipping into a pool of.molten lead so as to producea shower of molten lead through which the gaseous mix ture derived from the smelting zone is compelled topass, the molten lead being continuously withdrawn from the pool for transfer to the recovery blast iurnace or other smelting apparatus so that the gaseous mixture issuing from the smelting zone reaches the condensing zone without any substantial. loss of temperature. This is -important. because the gases leave the smelting zone at a temperature not very much above the ;equilibrium.temperature of the reaction between zinc vapour, carbon dioxide, carbon monoxide and zinc oxide, having regard to the composition of the gases usually encountered. The reaction is At temperaturesbelow the equilibrium temperature thereaction proceeds from left te -right. {The to raise the equilibrium temperature toi a value not far short of that at. which the gases leave the smelting zone, so that a 'relativelysmall drop of temperature between :the smelting andpondensing zones will be suificient to .reverse the reaction above-mentioned and causethe formation of objectionable zinc oxide.

The recovery zone comprises essentially avessel into which the zinc-lead .solution is delivered fromv the condensing zone and which, is ..p rovided with means for withdrawing the supernatant layer of molten zinc,or ratherzinc-fich alloy from the top, and means for tapping, the partially de-zinced molten. leadfrom thesbottom for returnto the condensing. zone. Suitable means may beprovided formaintaining this Vessel at the correct temperature.

The invention further contemplates a, I Q ification of the condensation step of the process in which the condensation is carried ou t in two stages with counterflow of the molten lead and gaseous mixture, the condenser being modified by subdividing it---into I two compartments, each containing a paddle-wheeler like showering device. .Thegaseous mixtureis introducedinto the compartment next; the zinc-vapour producing component and transferred thence through an opening in ,the partition separating the-compartments to the. more remote-compartment from which it is finally exhausted;, andmolten leadis introduced into the compartmentremote fromthe zinc-vapour producer, and withdrawn from the other compartment into, which it-fiows via a connectingpassage.

We have found that when operatingwithtwostage condensation in this manner, theiormer upper limitationof 550 C. ,on thetempcrature of thecondensingzone canebe relaxed assign as Concerns the firststage of condensation -in-the compartmentnext ,the zinc-vapour. producer, in which the, temperature may r sato,;6Q0 :-C. -,or even 625.C., the second stage-(of;-condewation being conducted so that the riseof temperature of the lead therein is slight,'the..temperature of the lead leaving this stage being preferably below 500 C. and in any case no greater than 550 0.

Our experiments show that when two-stage condensation is employed in this manner the zinc-vapour-bearing gases are adequately shockchilled in the first stage of condensation, and furthermore that dross formation in the condenser is minimised by keeping the temperature of the first stage of condensation above 550 C. and preferably up to about 600 C.

An embodiment of an apparatus suitable for the performance of the method of the invention is diagrammatically illustrated in the accompanying drawings, of which Figure 1 is a view, somewhat schematic, in side elevation of a zinc smelting and recovery plant, comprising a blast furnace and twin condenser assemblies including zinc-recovery apparatus, partly sectioned on the line l-i of Figure 2;

Figure 2 is a plan view, also somewhat schematic of the plant partly sectioned on the line 2-2 of Figure 1;

Figure 3 is a somewhat schematic view in end elevation of the plant;

Figure 4 is a detail view in section on the line 44 of Figures 1 and 3;

Figure 5 is an enlarged detail view in section on the line 5-5 of Figure 2;

Figure 6 is an enlarged detail view in section on the line 66 of Figures 1 and 2;

Figure '7 is a central vertical section of the zinc-separating component on the line 'l-'! of Figure 9;

Figure 8 is a central vertical section of the zinc-separating component on the line 8-8 of Figure 9;

Figure 9 is a plan of the zinc-separating com ponent;

Figure 10 is a section on the line III-40 of Figures 7 and 8; and

Figures 11 and 12 are partial views, similar to Figures 1 and 2, respectively, illustrating a modified arrangement.

The zinc smelting plant illustrated in Figures 1 to 3, comprises a blast furnace II, twin condensers I2, zinc-separators i3, and zinc-collectors 14. The blast furnace gases containing nitrogen, carbon monoxide, carbon dioxide and zinc-vapour pass from the blast furnace into each condenser through an outlet l5 and a downwardly extending passage it and beneath a hanging wall ll. The interior of each condenser I2 is subdivided into two compartments l8 and 19 by means of a lower or foot wall 20 and an upper or hanging wall 20' between which is an opening 2|. In the compartment I8 is disposed a horizontal rotor 22, having buckets or pockets, formed in its circumference as shown in Figure 1. A similar rotor 23 is disposed in the compartment [9. Beneath the

rotors

22, 23 respectively are

sumps

24, 25. The rotors are revolved in the direction indicated by arrows in Figure 1 by mechanical means (not shown) situated outside the condenser.

The condenser l2 terminates at the end remote from the blast furnace II, in an outlet 26 communicating with an uptake 2'! from which extends a downwardly sloping pipe 28 (see Figure 3) communicating with a gas-cleaning apparatus (not shown). From the top of the uptake 2! extends a stack 29 which is normally shut off from the uptake by means of a damper 30 shown in Figure 4 in the closed position by full lines and in the open position by dotted lines.

The compartments l8, l9 are connected at the" bottom by a passage 3! (see also Figure 6). The base of the condenser is built up alongside lower or foot wall 20, inside the compartment l8 and in the built up part is provided a shallow transverse trough 32 (see also Figure 6), the walls of which are of unequal height, the wall forming the lower edge of the opening 2! being higher than the other. At the end remote from the passage 3| the floor of the trough 32 is sloped downwards to enable the trough to communicate through an opening 33 in the wall of the condenser with an external well 34, the upper edge of the opening 33 being below the floor of the horizontal part of the trough 32. From the upper part of the well 34 a trough 35 (see also Figure 5), communicating with the well through an opening 36 in its floor, leads to the zinc separator l 3. The well 34 and trough 35 are covered with a refractory roof, but for convenience of reading the drawings the roof is not shown. In the bottom of the wall of the compartment H) of the condenser is an opening 37 (Fig. 2) from which extends a pipe 38 communicating with the pipe 59 of the zinc-separator l3, hereinafter described.

The zinc-separator i3 (Figure 7) comprises a cylindrical shell 39 of sheet steel with closed bottom, the sides of which are lined with a silicon carbide refractory l0, and the bottom with firebrick ll. It is supported on a base 42 and has a drain &3 in the bottom, normally closed by a plug (not shown). The lining of the upper part is of silicon carbide refractory or firebrick and tapers internally to a neck 44, closed by a removable plug 5. The lining 40 is extended on one side to accommodate a trough t6 forming a continuation of trough 35 (Figures 2 and 5) and on the opposite side to accommodate a trough communicating with the zinc-collector H (see Figures 1 and 2), the latter being a rectangular pot made of any suitable refractory material, and having means (not shown) for tapping oif the contents.

The trough 46 is prolonged by an arcuate trough 4? (see Figure 9) from the ends of which two channels as extend downwardly in the mass of the lining 46 terminating in openings 29 (Figure 7) in the interior of the chamber enclosed by the lining til, 40.

The trough 5b is deepened at its inner end to form a well 59 and is extended beneath a hanging wall 55, whose lower edge is below the level' of the floor of the trough 50, to form a channel 52 in the lining 40 terminating at an internal opening 53 just below the neck 04.

In the vertical plane at right angles to the centre line of the troughs 36, 50 (Figures 8 and 10) the lining til, 40 is extended inwardly to form a vertical internal rib 54 supported on an angle section beam 55 and bracket 55 (Fig. 8, right hand side) and enclosing the upper part of a vertical steel pipe 56, which is bonded into the rib 54 by means of hooks 5'! and extends from above the top of the separator, where it is closed by a cover 58, to near the bottom of the separator, its lower end being open. A horizontal pipe 59 branches from pipe 56 at a slightly lower level than the floors of troughs 46, 5t and is connected to the pipe 38, hereinbefore mentioned (see Figures 2, 3).

The upper part of the shell 39 is surrounded by a sheet metal jacket 60 having an inlet GI and an outlet 62 whereby cooling air is circulated through the jacket. A similar sheet metal jacket 53 with inlet 64 and outlet 65 serves for circulatgxgg heated air round the lower part of the shell The blastfurnac'e gases containing zinc-vapour (Figures l and 2) pass from the furnace outlet I5 through passage it, without sensible loss of temperature, into the condenser compartment l-8- where they meet a shower of molten lead thrown up by the rotor 22 and are thereby shock-chilled so that a part of their zinc-vapour content is condensed and dissolved by the molten lead without serious oxidation or the formation of obnoxiousquantities of blue-powder. The gases, still containing some zinc-vapour, then pass through opening 2i into compartment 18 to meet a second shower of molten lead thrown up by rotor 23, whereby further condensation and solution of zinc is eltected. The gases, now substantially stripped ofzinc-vapour, finally leave the condenserby the-outlet 26, uptake 27 and downwardlyextending pipe 28- to enter the gas-cleaning apparatus.

Molten lead continuously enters the compartment- 19 through pipe 33 and leaves this compartment, after dissolving some zinc, by way of channel 34 to enter compartment it, in which it dissolves morezinc. Some of the lead thrown up by the-rotor 22 in this compartment falls into the elevated trough 32, whence it runs through opening 33, well 3d, opening 35 and trough 35 intothe' trough d6 of the zinc-separator K3, the openings 33 and-36 being drowned. Any overflow fromtrough 32 escapes over the lower of its walls back into compartment E8. The upper or hanging wall 2-0 above the opening 2i ensures that no-large amount of lead is splashed directly into trough 32 from compartment it, having regard to-the direction-of-rotation of rotor 23.

The zincy-lead received by trough 45' (Figure 9) flows into arcuate trough 5! and down through the channels 43 and openings 39 into the chamber of the separator, while molten lead from the bottom of the separator containing a smaller amount of dissolved zinc flows up pipe 5B- (Figure 8') and out through pipe 59 to enter compartment i9 of the condenser by pipe 38.

The upper part of the separator chamber (Figures 8-and is cooled-by the air flowing through jackets 69, causing some of the zinc to separate from the molten lead as a zinc-rich alloy containing a small amount only of'lead and to float on the top of the body of lead in the separator chamber, the level of the face of separation being indicated (Figure 8) by dotted line 63-, which is above the openings 49 of channels 48. Cooling of the zincy lead in the well 3& and trough 35, leading to premature separation of zinc, is minimised by roofing the well and trough as previously described.

The separated zinc flows out (Figure '7) by opening 53, channel 52, well 53 and trough 5%) into the'zinc-collector M (Figure 2), the hanging wall 5| (Figure '7) providing an air seal for the interior of the separator-chamber.

The levels of molten metal in the trough 4e, and neck 34 and in trough 55 are indicated by dbttedlines-tt, and i i, respectively (Figure '7), and-the level of molten lead in the pipe'59 by dotted line 58 (Figure 8). The trough 58 terminates ina spout delivering into the collector l4 and the level of the floor of trough 5%] determines the level {51 within narrow limits depend ing on the rate of flow in the trough 53, the width of the trough being great enough to enable a shallow streamer-molten metal to maintain-thelvel 51- due to variations of flow rate, being errpressible as fractions of the mean depth of the stream, are minimised. The vertical distance be tween levels 6''! and 68 determines the depth of the zinc layer from level 61 to the separation level 69 in accordance with elementary hydrostatic principles, having regard to the density ratio of the two liquids, viz. lead saturated with zinc and zinc saturated with lead, at the temperature of the upper part of the separator chamber.

The circulation is maintained by gravity owing to the head provided by the difference between the level 66 of the zincy-lead in the trough 46' (Fig. 7), which is determined by its level (Figure 1) in trough 32, and the level 88 (Fig. 8) of the lead in'pipe 59, there'being no'great diifer'en'ce of density between the" liquid filling channels 18 and" in' trough 41, it and that filling pipe" stand in pipe 59.

Ihe channels 68 are inclined so as'to' give the zincy-lea-d flowing down them a tangential entr into the separator-chamber, thus assisting even distribution of flow down the chamber.

The jacket 53 is thermostatically controlled to maintain a predetermined tem erature-say 450 C.--highe r than the melting point of zinc saturated' with lead, viz. 418 C., in' the lower part of the separator chamber. Zincylead enters the chamberthrough openings 49 at a higher temperature. Its excess heat is extracted by the cooling air circulated through jacket Eli thus maintaining the upper part of the chamber at substantially the same temperature as the lower part, any tendency for the upper part to be cooled below the temperature maintained in the lower part-being prevented by convection.

The percentage of Zinc separated from the leadin the separator represents the difference between the zinc concentration in the lead leaving the outlet 33 of the condenser compartment i8 and that in lead saturated with zinc at the'temperature of the separator E3; The lead leaving the condenser is not usually saturated withzinci- Lead enters the condenser compartment I9- from-the separator i3 at the separator temperaturesay 450 C. As it passes through the-con denser in counter-current to the furnace gases, condensing zinc-vapour as it goes, it receives'th'e heat of condensation and'talces up heat fromthe non-co'ndensable gases and its temperature therefore rises, the temperatures of the compart'-' ments l8, It beingregulated, e. g. by adjusting the amount of external lagging, which may be provided by removable refractory blocks (not' shown) so that the lead leaves the compartment- [9 by passage 35 at a temperature betweenAS Q C. and 580 C. and leaves compartment 58 by 'the' trough 32 and well 3 3 at a temperature between 550 C. and'6'20" C.

It will be evident that no zinc can be separated until the body of lead in the separator is saturated with zinc at the temperature at which the separator is maintained. The requisite zinc concentration in this body of lead is about 1.7 at 418 C. and about 2.2% at 450 C. If lead containing less than the requisite concentration'of zinc is initially introduced into the circuit, it'will have to be cireulated'through the condenser and separator; absorbing zinc from the furnace gases, butyielding no zinc in the separator, until it"b'ecomes saturated with zinc at the separatortehipera'ture'. Once't-his concentration has beenat requ'ireed flow-rate, whereby variationsof thetained any" further zin'c condensed'from the-fur 9 nace gases is separated substantially completely and recovered in the collector M.

The efficiency of extraction then equals the efficiency of condensation, and this depends on (a) the temperature at which the furnace gases leave the condenser, which, ideally is little above the temperature of the lead bath in the second condensing zone #9, and (b) the concentration of zinc-vapour in the gases entering the first condensing zone IS. the partial pressure of zinc-vapour in thegases leaving the second condensing zone and hence the zinc-vapour concentration in the spent gases. The condensation efficiency is measured by the difference between the initial and final ratios of zinc-vapour to inert gas divided by the initial ratio. If the temperature (a) is 450 C., the partial pressure of zinc-vapour over lead is approximately 0.36 mm. Hg, and the corresponding concentration in the spent gases is 0.047%; if the Efliciency (percent):

In practice, of course, it is bound to be somewhat lower, but by suitably matching the massflow-rates of the furnace gases and of the circulation of molten lead in a condenser and separator whose capacities are suitably matched to that of the furnace, a close approach to the ideal efficiency may be achieved.

In a plant as described above the rate at which lead is circulated is about 100 times the rate of zinc production, by Weight, e. g. for a zinc output of 10 tons per diem, the lead circulation would be about 1,000 tons per diem. The total weight of lead in the circuit is not critical, but in a plant having an output of 10 tons of zinc per diem about 70 tons would be a suitable figure for the total amount of lead in the circuit.

The process as above described may be modified and simplified by using single-stage condensation in which case the apparatus is similar, but modified as shown in Figures 11 and 12, the second condenser compartment !9 and rotor 23 of Figures 1 to 3 being omitted and the pipe 38, which is connected with the pipe 59 of the separator 53, communicating with an opening 31 in the bottom of compartment 18, while the gas outlet corresponding to outlet 26 of Figures 1 and 3 is located above the trough 32 in compartment 13 (see Figure 11).

With single-stage condensation the temperature of the compartment 98 is regulated so that the lead leaving it by trough 32 and well 34 has a temperature between 500 C. and 550 C., the process being otherwise as previously described.

We claim:

1. In the method of recovering zinc dissolved in a body of molten lead used cyclically in a zinc vapor condensing zone as a condensing medium for zinc vapor obtained in a zinc smelting operation, the resulting molten zinc-rich lead being treated in a zinc separating zone to recover zinc, the improvement which comprises condensing the zinc vapor in molten lead that is at least saturated with zinc at the temperature maintained in a substantially quiescent body of molten zinccontaining lead in the zinc separating zone, continuing said condensation of zinc vapor until the zinc content of the molten zinc-containing lead The first factor (a) determines 10 builds up to a point corresponding to the saturation point of the molten lead for zinc at a temperature below the temperature of the molten zinc-containing lead in the condensing zone but above the temperature at which the molten zinccontaining lead is maintained in said quiescent body, moving the resulting zinc-rich molten lead from the condensing zone to the zinc separating zone at a temperature substantially above the freezing point of the zinc, forming and maintaining the quiescent body of the molten zinc-containing lead in the separating zone at a temperature still substantially above the freezing point of the zinc but at which zinc separates and rises to the top of said quiescent body to form a supernatant overlying layer of molten zinc and an underlying layer of molten lead saturated with zinc at its prevailing temperature, removing molten zinc from the supernatant layer while still maintained at a temperature above its freezing point, separately collecting the molten zinc so removed, and withdrawing molten lead lean in zinc while still substantially above the melting point of the zinc in the lead-zinc mixture from the bottom portion of the underlying layer in the form of a continuous stream and returning it at such temperature to the condensing zone for re-use in condensing more zinc vapor.

2. Method according to claim 1, in which the molten lead-zinc leaves the quiescent body and enters the condensing zone at a temperature of about 450 C.

3. Method according to claim 1, in which the gaseous mixture from the smelting operation makes its first contact with the molten lead-zinc in the condensing zone while the molten lead-zinc is at a temperature above 550 C. but not higher than 620 C.

4. Method according to claim 1, in which the molten zinc-rich lead is moved from the condensing zone to the quiescent body of molten solution in the zinc separating zone without a substantial drop in temperature.

5. Method according to claim 1, in which the substantially quiescent body of molten zinc-containing lead in the separating zone is in the form of an elongated relatively large upright body, and the molten zinc-rich lea-d from the condensing zone is added to the quiescent body at a point well below the supernatant layer of molten zinc so as not to interfere with the formation thereof.

6. Method according to claim 1, in which the zinc vapor is present in a gaseous mixture obtained from a blast furnace smelting operation; the condensing step includes a first stage of condensation and at least one subsequent stage of condensation with the molten lead-zinc circulating countercurrently to the gaseous zinc vapor mixture, the gaseous mixture first contacting the molten lead-zinc in the first condensing stage and then contacting the same in a subsequent condensing stage; the molten lead-zinc from the quiescent body in the separating zone enters the subsequent condensing stage Where the gaseous mixture from the first condensing stage makes contact therewith; the resulting molten lead-zinc passes from the subsequent condensing stage to the first condensing stage at a temperature substantially below 550 C.; the gaseous mixture from the smelting operation makes its first contact with the molten lead-zinc in the first condensing zone while the molten lead-zinc is at a temperature above 550 C. but not higher than 620 C.; and the resulting molten zinc-rich lead 1 1 leaves the first eondensm sta e for the separati zone.

Method according to claim 1. in which the upper p rtion of molten nen aining le d in thequiescem be y is eooled and the lower portion heated to place and maintain .the body as .a whole at a substantially uniform temperature to .I-aeil-itate separation of the zinc and iormation of .the snpernatant layer of molten zinc.

8. Method according to elaim 1, in which the major portion of the temperature of the quiescent body is below 500 C. 110 facilitate separation of the zinc and iormation of the supernatant lay r of m lten zine...

9. Method according t elaim in whi h con- 141 1101 5 circulation of the molt n zine-containin lead :thmu h the ine s parating z n to t Jlfillfii g Zone is maintained by gravity.

10. Method according to claim 9, in which molten zinorcontaining lead in the condensin zone is raised from .a lower inlet level 120 a higher outlet level to provide .the required hydro-static head ,for maintaining the circulation of the molten zin -containing le d throug the Zinc sop Mating zone.

STANLEY .RQBSON.

JACK DERHAM.

References Cited in the I118 01 P ent Number Number UNITED STATES PATENTS Name Date Ziesing Aug. 14 1917 Johnson Mar. 16, 1920 Perkins Nov. 17, 19.36 Neve Apr. 15,, 1941 Handwerk et a1. Dec. 28, 1948 Handwerk et a1 Dec. 28, 1948 Robson Dec. 28, 1948 Robson et a1 Mar. 15, 1949 'G jGCkEbO Apr. 26, 1949 Robson June 14, 1919 FOREIGN PATENTS Country Date Great Britain Oct. 31, 1945 OTHER REFERENCES Metals Handbook, 1939 ed.,, pages 1748-1749.

Claims

1. IN THE METHOD OF RECOVERING ZINC DISSOLVED IN A BODY OF MOLTEN LEAD USED CYCLICALLY IN A ZINC VAPOR CONDENSING ZONE AS A CONDENSING MEDIUM FOR ZINC VAPOR OBTAINED IN A ZINC SMELTING OPERATION, THE RESULTING MOLTEN ZINC-RICH LEAD BEING TREATED IN A ZINC SEPARATING ZONE TO RECOVER ZINC, THE IMPROVEMENT WHICH COMPRISES CONDENSING THE ZINC VAPOR IN MOLTEN LEAD THAT IS AT LEAST SATURATED WITH ZINC AT THE TEMPERATURE MAINTAINED IN A SUBSTANTIALLY QUEISCENT BODY OF MOLTEN ZINCCONTAINING LEAD IN THE ZINC SEPARATING ZONE, CONTINUING SAID CONDENSATION OF ZINC VAPOR UNTIL THE ZINC CONTENT OF THE MOLTEN ZINC-CONTAINING LEAD BUILDS UP TO A POINT CORRESPONDING TO THE SATURATION POINT OF THE MOLTEN LEAD FOR ZINC AT A TEMPERATURE BELOW THE TEMPERATURE OF THE MOLTEN ZINE-CONTAINING LEAD IN THE CONDENSING ZONE BUT ABOVE THE TEMPERATURE AT WHICH THE MOLTEN ZINCCONTAINING LEAD IS MAINTAINED IN SAID QUIESCENT BODY, MOVING THE RESULTING ZINC-RICH MOLTEN LEAD FROM THE CONDENSING ZONE TO THE ZINC SEPARATING ZONE AT A TEMPERATURE SUBSTANTIALLY ABOVE THE FREEZING POINT OF THE ZINC, FORMING AND MAINTAINING THE QUIESCENT BODY OF THE MOLTEN ZINC-CONTAINING LEAD IN THE SEPARATING ZONE AT A TEMPERATURE STILL SUBSTANTIALLY ABOVE THE FREEZING POINT OF THE ZINC BUT AT WHICH ZINC SEPARATES AND RISES TO THE TOP OF SAID QUIESCENT BODY TO FORM A SUPERNATANT OVERLYING LAYER OF MOLTEN ZINC AND AN UNDERLYING LAYER OF MOLTEN LEAD SATURATED WITH ZINC AT ITS PREVAILING TEMPERATURE, REMOVING MOLTEN ZINC FROM THE SUPERNATANT LAYER WHILE STILL MAIN-, TAINED AT A TEMPERATURE ABOVE ITS FREEZING POINT, SEPARATELY COLLECTING THE MOLTEN ZINC SO REMOVED, AND WITHDRAWING MOLTEN LEAD LEAN IN ZINC WHILE STILL SUBSTANTIALLY ABOVE THE MELTING POINT OF THE ZINC IN THE LEAD-ZINC MIXTURE FROM THE BOTTOM PORTION OF THE UNDERLYING LAYER IN THE FORM OF A CONTINUOUS STREAM AND RETURNING IT AT SUCH TEMPERATURE TO THE CONDENSING ZONE FOR RE-USE IN CONDENSING MORE ZINC VAPOR.