US2668047A - Production of zinc - Google Patents

Description

s. ROBSON ErAL 7 PRODUCTION OF ZINC Feb. 2, 1954 7 Sheets-Sheet 1 Original Filed March 11, 1949 INVENTORS STANLEY ROBSON AND Y ml? 5mm B LESLIE JACK DERHAM ATTORNEYS Feb. 2, 1954 S. ROBSON EI'AL PRODUCTION OF ZINC 7 Sheets-Sheet 2 Original Filed March 11, 1949 INVENTORS STANLEY RQBSON Ann 3 8w Q Q 8 Q BY LESLIE JACKIDERHAM Emmi fclMfiMdA VTTW-rBaH/W moneys S. ROBSON El AL PRODUCTION OF ZINC Feb. 2, 1954 Original Filed March 11, 1949 7 Sheets-Sheet 3 Pi .3 i 29 mvsurons STANLEY ROBSON AND LESLIE JACKDERHAM ATTORNEYS 1954 s. ROBSON ETAL PRODUCTION OF zmc 7 Sheets-Sheet 5 Original Filed March 11, 1949 mvsm'ons STANLEY ROBSON AND L w w m LESLIE JACK DERHAM I BY Fawn ,lll FEM/wan ATTORNEYS Feb. 2, 1954 S. ROBSON EI'AL v PRODUCTION OF ZINC 7 spews-Sheet 6 Original Filed March 11, 1949 mvsurons STANLEY ROBSON Auo BY uzsus JACKDERHAM 'Fwmiz 5mm rTi'ammm ATTORNEYS Feb. 2, 1954 s. ROBSON ETAL 47 PRODUCTION OF zmc oii inai Filed March 11, 1949 7 Sheets-Sheet 7 Fly]! 26a iii-f" =3;

I I I WIZTZWJAJTW FEM/mm ATTORNEYS Patented Feb. 2, 1954 PRODUCTION OF ZI'NCII Stanley Itiflison', El'ifield, and Leslie Jack Derham,

Severn Beach,- England; assigno'rs-to The Nation'al smelting Company Limited, London, Englanixa Britishtcompany" 'rig'inal application. March 11,- 1949; sen-er No.

80;!)16'. Dividdand thisapplication'February" 4; 1950, Serial No. 148,065

8 Claims. (015266-)- Tfii's invention relates tothe productionof zinc and has for its obj'ect improvements in apparatus for producin'g zinc; The invention relates more particularly tothe recovery of 'zinc'from a-body of molten le'adthat has been used as a. condensing medium for zinc vapor obtained in zinc smelting operations;-

P'rior 'preposafs to use----moltenleadas a condensing-medium'for' zine vapor obtained insmelting operationshave not 'met-* with much favor. O'ne'cf themain reasons, of course; is the cost of the-large amount 'oflead that must be employed. Another; the difli'oulty of recovering the small amount of-"zinc from'the-large amount of lead in a -satisfaetory manner: In viewparticularly of renewed efiorts to find a waycommercially to smelt zinc-"bearing' 'materials in a blast furnace. attention-"is -again -direeted" to'the' possibility" of using molten' lead as a condensing medium for zincvaporz' Gaseous mixtures *containing "zinc" vapor; carbon monoxidep anda substantial amount of carbon dioxide are especiallydiflieult to treat ina zine-"condensing operation-because of 'thetenm ency of the carbon dioxide to-react with the zinc to form an objectionable amount of the zinc oxide. The following composition istypical of the-gaseous mixtures derived from blast-furnace smelting ofzinc-bearing ores, residues orthe like:

Per cent by volume Zincvapourv.. -7 5 COa Y.. r 5 COM 27 63 Zihe bar-ing "gaseous mixtures of similar type cam alsou-be derived from the "-el ectro-"thermic smelting-bf zine; but iri'this ease the zinc con-'- tentis-usuallyrather higher and the COrcontentmay be rather-less:

method of condensing and recovering the The method of? recovering the condensed zinc comprises cooling: the lower "portion' of the body oflead-zine-solution to 'atmperature below418 (3;, but :not' below the melting pointof lead; to precipitate :zi-ne therefrom while maintaining the upper portioni'bf 'the-ibo'dyi'of "the solution above 4m 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 ofta supernatant layer'ofmolten zinc, removingmolten-zinc from' this supernatant layer andireturningfthe: molten= lead from which the zinc was precipitated for= re=use 'in'th'e condensing step.

While-this methbdrof recovering condensed zine from mo'lten lead 'has been given-excellent results, we have found that whenthe lower portion of the lead-zinc: solution is cooled 'to I a temperature as low as '418'-Cf., some of the precipitatedzinc crystals tend-" to adhere-to'the sides ofthe "vessel in which they are precipitated;- Unless scraped from-thewsides of the-vessel; theery'stalsi tend to buildup: and thus' to" insulate the vessel. Tothis extent, atleast; the method" isra' drawback and leaves something to be desired:

Investigation confirms" "our discoverythat zinc may berecoveredfrom molten 'l'eadused as a condensing' medium for: zine vapor and that drawbacks of the typementioned may be avoided,

while at -'-the" same time-"gaining certain" other operating advantages:

In accordance" with' the" method of the invention for-recovering zihefrom-a body of molten lead used in axwcondensing zone as acondensin'g medium fon'zinc 'vapor obtained in a smelting operatiom the condensation: ofzinc vapor is continued: until the zinc content of the molten lead 'builds'upzto a point corresponding to the -saturation point of the lead for' zinc 'at a temperature abovethe freezing pointof the zinc but below the temperatIire of' the-lead in the condensing zone. The--resulting=.lead-"zinc solution is aocum'ulated. in asubstantially' quiescent body; The body of moltenlead-zinc solution is cooled'to a temperature :above the freezing point of the zine but at which dissolvedzinc separates and rises to the top of the body" of solution to form asupernatant layer at molten zin-c and an underlying layer of molten lead; The-supernatant layer of molten zinoisseparated at: least inpa'rt' from the underlying-,layerof molten: lead and solution containing the remaining. moltenllead is returned to the condensing 5 zone-"ion "re usein the condensing step.

Since the lead-zinc "sohitionirbm the-condensing zone is not cooled low enough to'perm'itzinc crystals to precipitate, the molten zinc remains in solution in the molten lead. The temperature drop, however, is sufficient to cause molten zinc 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 ofi readily, and thus be recovered separately from the lead. v

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 and as 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 efiected, any subsequent cooling of it will cause molten zinc to separate, or rather a molten solution of zinc-rich alloy whose lead content is very small and may be ignored, since further 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 sufliciently to permit some of the zinc dissolved therein to separate and rise as such 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 being then separated, at least in part, from the underlying layer of molten lead and the solution containing the remaining molten lead being returned to the condensing zone for re-use in the condensing step.

Preferably the resultant lead-zinc solution is accumulated in a cooling zone removed from the condensing zone and the body of solution is cooled to a temperature below 500 C., but above the freezing point of zinc to facilitate the formation of the supernatant layer of molten zinc.

The necessity for recirculating the lead until the dissolved zinc content exceeds at least 1.7% arises from the fact, which can be verified from the phase diagram of the binary lead-zinc system, that at temperatures exceeding 418 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 which a part at least of the zinc values have been extracted.

The rotary paddle wheel may be replaced by an oscillating paddle or by a helical type rotor rotating on a vertical axis or by any other convenient device for showering the molten lead.

The condensing chamber is preferably arranged as close as possible to the outlet of the blast-furnace 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 symbolized by Zn+COz2ZnO+CO At temperatures below the equilibrium temperature the reaction proceeds from left to right.

The equilibrium temperature of this reaction increases as the CO2 content of the gases is increased relatively to their other content; and the CO2 content of the gases from a blast-furnace in particular, or, in some instances, from an electrothermic furnace, is sufficiently high in relation to the content of zinc vapour and CO to raise the equilibrium temperature to a value not farshort of that at which the gases leave the smelting zone, so that a relatively small drop of temperature between the smelting and condensing zones will be sufiicient to reverse the reaction abovementioned and cause the formation of objectionable zinc oxide.

The recovery zone comprises essentially a vessel into which the zinc-lead solution is delivered from the condensing zone and which is provided with means for withdrawing the supernatant layer of molten zinc or rather zinc-rich alloy from the top, and means for tapping the partially de-zinced molten lead from the bottom for return to the condensing zone. Suitable means may be provided for maintaining this vessel at the correct temperature.

The invention further contemplates a modification of the condensation step of the process in which the condensation is carried out in two stages with counterfiow of the molten lead and gaseous mixture, the condenser being modified by subdividing it into two compartments, each containing a paddle-wheel or like showering device. The gaseous mixture is introduced into 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; and molten lead is introduced into the compartment remote from the zinc-vapour producer and withdrawn from the other compartment into which it flows via a connecting passage, 7

We have found that when operatinig with twostage condensation in this manner, the former upper limitation of 550 C. on the temperature of the condensing zone can be relaxed as far as concerns the first stage of condensation in the compartment next the zinc-vapour producer, in which the temperature may rise to 600 C. or even 620 C., the second stage of condensation being conducted so that the rise of 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 G.

Our experiments show that when the two-stage outlet ISthrcugh passage 16, without sensible loss of temperature, into the condenser compartment [8 where they meet a shower of molten lead thrown up by the rotor 22 and are thereby shockchilled so that a part of their zinc-vapour content is condensed and dissolved by the molten lead without serious oxidation or the formation of obnoxious quantities of blue-powder. The gases, still containing some zinc-vapour, then pass through opening 2l into compartment [9 to meet a second shower of molten lead thrown up by rotor 23, whereby further condensation and solution of zinc is effected. The gases, now substantially stripped of zinc-vapour, finally leave the condenser by the outlet 26, uptake 2'! and downwardly extending pipe 28to enter the gascleaning apparatus.

Molten leadcontinuously enters the compartment l9 through pipe 38 and leaves this compartment, after dissolving some zinc, by way of channel 3i to enter compartment 18, in which it dissolves more zinc. 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 34, opening 36 and trough 35 into the trough 46 of the zinc-separator l3, the openings 33 and 38 being drowned. Any overflow from trough 32. escapes over the lower of its walls back into compartment [8. The upper or hanging wall 23) above the opening 21 ensures that no large amount of lead is splashed directly into trough 32 from compartment [9, having regard to the direction oirotation of rotor 23.

The zincy-lead by trough 4B (Figure 9) flows into arcuate trough 41 and down through the channels 48 and openings 49 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 56 (Figure 8) and out through pipe 59 to enter compartment 19 of the condenser by pipe 38.

The upper part of the separator chamber (Figures 8 and 10) is cooled by the air flowing through jackets 60, 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 69, which is above the openings 49 of channels 48. Cooling of the zincy lead in the well 34 and trough 35, leading to premature separation of zinc, is minimized by roofing the well and trough as previously described. a

The separated zinc flows out (Figure 7) by opening 53, channel 52, well 58 and trough 50 into the zinc-collector [4 (Figure 2), the hanging wall 51 (Figure 7) providing an air seal for the interior of the separator-chamber.

The levels of molten metal in the trough 46, and neck 45 and in trough 50 are indicated by dotted lines 55, and 5?, respectively (Figure 7), and the level of molten lead in the pipe 59 by dotted line 68 (Figure 8). The trough 50 terminates in a spout delivering into the collector I4 and the level of the fioor of trough 50 determines the level 61 within narrow limits depending on the rate of flow in the trough 59, the width of the trough being great enough to enable a shallow stream of molten metal to maintain the required flow-rate, whereby variations of the level 61 due to variations of flow-rate, being expressible as fractions of the mean depth of the stream, are minimized. The Vertical distance between levels 51 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 68 (Fig. 8) of the lead in pipe 59, there being no great difference of density between the liquid filling channels 48 and in trough 41, 46 and that filling pipe 56 and in pipe 59.

The channels 48 are inclined so as to give the zincy-lead flowing down them a tangential entry into the separator-chamber, thus assisting even distribution of flow down the chamber.

The jacket 53 is thermostatically controlled to maintain a predetermined temperature-say 450 C.--higher than the melting point of zinc saturated with lead, viz. 4 8 0., in the lower part of the separator chamber. Zincy-lead enters the chamber through openings 49 at a higher temperature. Its excess heat is extracted by the cooling air circulated through jacket 60 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 lead in the separator represents the difference between the zinc concentration in the lead leaving the outlet 33 of the condenser compartment 18 and that in lead saturated with zinc at the temperature of the separator l3. The lead leaving the condenser is not usually saturated with zinc.

Lead enters the condenser compartment 19 from the separator 13 at the separator temperaturesay 450 C. As it passes through the condenser in counter-current to the furnace gases, condensing zinc-vapor as it goes, it receives the heat of condensation and takes up heat from the non-condensable gases and its temperature therefore rises, the temperatures of the compartments I8, 19 being regulated, 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 19 by passage 3| at a temperature between 450 C. and 500 C. and leaves compartment l8 by the trough 32 and well 34 at a temperature between 550 C. and 620 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 circulated through the condenser and separator, absorbing zinc from the furnace gases, but yielding no zinc in the separator, until it becomes saturated with zinc at the separator tem-' perature. Once this concentration has been attained any further zinc condensed from the furnace gases in separated substantially completely and recovered in the collector l4.

The efficiency of extraction then equals the emciency of condensation, and this depends on (a) the temperature at which the furnace gases leave densinglzone l9, and (b) the-.concentrationpt zinc-vapour in the gases entering-the firstcondensing zone iii? The first factor-(d) determines the .partial pressure of zinc-vapour in theagas'es laving the second 'con'clensingi zone and hence the zinc-vapour concentration in then spent gases. The condensation"e'fiiciency is measureclby 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 initial concentration in the furnac gases is the ideal condensation efficiency is just over 99%, being given by the equation:

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 tons per diem, the lead circulation would be about 1,600 tons per diem. The total weight of lead in the circuit is not critical, but in a plant Efiiciency (%)=100X =99.1l

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 H3 and rotor 23 of Figures 1 to 3 being omitted and the pipe 38, which is connected with the pipe 59 of the separator l3, communicating with an opening 3'! in the bottom of compartment 18, while the gas outlet 26 corresponding to outlet 26 of Figures 1 and 3 is located above the trough 32 in compartment [8 (see Figure 11).

With single-stage condensation the temperature of the compartment 18 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.

This application is a division of our copending application Serial No. 80,916, filed March 11, 1949.

We claim:

1. Smelting apparatus including, in combination with means for producing gases containing vapor of the smelted metal and a separator in which a quiescent body of a molten solution of the smelted metal in a second metal is accumulated, a condenser comprising a closed chamber having a gas-mixture inlet receiving the vaporbearing gases from the producing means, a spentgas outlet, an inlet receiving solution partially stripped of the solute metal from the separator, an internal trough elevated above the last-mentioned inlet, an outlet communicating with the trough and delivering solution enriched in the solute from the trough to the separator, and mechanical means for showering the solution inside the chamber, whereby the solution becomes enriched in the solut metal by condensation and solution from the vapor contained in the gases,

and for raising-someof theenrichedsolution thetroughr 2 Apparatus according" to -claim- 1, including an =eXternaltrough communicating wit-h the intrough," and delivering-to the separator.-

3. Apparatus according to"cla im--1,-in'which th'ej =condnse'rchamber is subdivid'ed-into a first and a second compartment by :apartitioncomprising a foot wall'andfa hanging wall defining between them an-opening for the-passage of the vaporbearing gases from the first to the second compartment, the gas-mixture inlet being in the first compartment and the spent-gas outlet and solution-inlet being in the second compartment, and the foot wall constituting one wall of the internal trough, which is situated in the first compartment and whose other wall is lower than the foot wall, the apparatus further including a passage below the level of the internal trough inter-connecting the compartments and enabling solution to flow from the second to the first compartment, and mechanical solution-showering means in each of the compartments.

4. Apparatus according to claim 3, in which each mechanical showering means comprises a horizontal rotor having surface indentations enabling it to pick-up molten solution from a pool thereof into which it dips, the direction of rotation of both rotors being such that their upper parts move against the general direction of flow of the vapor-bearing gases, whereby the lower part of the rotor in the first compartment moves towards the internal trough and splashes molten solution into it.

5. In apparatus for separating a mixture of lighter and heavier molten metals, the improvement comprising a normally closed chamber for receiving and separating the molten metals, an inlet channel at the top of the chamber for directing the molten metals thereto, an inlet duct connecting the inlet channel with the interior of the chamber, the discharge opening of the inlet duct being at a lower level than the inlet channel but well above the bottom of the chamber, an outlet channel communicating with the interior of the chamber near its top and well above the inlet duct discharge opening for the withdrawal of separated lighter molten metal, said outlet channel extending under a depending wall con stituting an air seal and terminating in an outlet trough, a second outlet channel communicating with the interior of the chamber near its top for the withdrawal of separated heavier molten metal, said second outlet channel being at a level below that of the inlet channel and the first outlet channel but well above said inlet duct discharge opening, and an outlet duct extending downwardly from the second outlet channel to the bottom portion of the interior of the chamber, the intake opening of the outlet duct being at a level well below that of the discharge opening of the inlet duct to facilitate withdrawal of the separated heavier molten metal from the chamber.

6. Apparatus according to claim 5, in which the lower portion of the chamber is provided with .means for heating the same to establish and maintain suitable temperature conditions in the body of molten metals in the interior of the chamber to facilitate their separation.

7. Apparatus according to claim 5, in which the upper portion of the chamber is provided with means for cooling the same to establish and 11'- maintain suitable temperature conditions in the body of molten metals in the interior of the chamber to facilitate their separation.

8. Apparatus according to claim 5, in which the lower portion of the chamber is provided with means for heating the same, and the upper portion of the chamber is provided with means for cooling the same to establish and maintain suitable temperature conditions in the body of molten metals in the interior of the chamber to facilitate their separation.

STANLEY ROBSON. LESLIE JACK DERHAM.

Referenoes Cited in the file of this patent UNITED STATES PATENTS Number Robson June 14, 1949

Claims (1)

1. SMELTING APPARATUS INCLUDING, IN COMBINATION WITH MEANS FOR PRODUCING GASES CONTAINING VAPOR OF THE SMELTED METAL AND A SEPARATOR IN WHICH A QUIESCENT BODY OF A MOLTEN SOLUTION OF THE SMELTED METAL IN A SECOND METAL IS ACCUMULATED, A CONDENSER COMPRISING A CLOSED CHAMBER HAVING A GAS-MIXTURE INLET RECEIVING THE VAPORBEARING GASES FROM THE PRODUCING MEANS, A SPENTGAS OUTLET, AN INLET RECEIVING SOLUTION PARTIALLY STRIPPED OF THE SOLUTE METAL FROM THE SEPARATOR, AN INTERNAL TROUGH ELEVATED ABOVE THE LAST-MENTIONED INLET, AN OUTLET COMMUNICATING WITH THE TROUGH AND DELIVERING SOLUTION ENRICHED IN THE SOLUTE FROM THE TROUGH TO THE SEPARATOR, AND MECHANICAL MEANS FOR SHOWERING THE SOLUTION INSIDE THE CHAMBER, WHEREBY THE SOLUTION BECOMES ENRICHED IN THE SOLUTE METAL BY CONDENSATION AND SOLUTION FROM THE VAPOR CONTAINED IN THE GASES AND FOR RAISING SOME OF THE ENRICHED SOLUTION INTO THE TROUGH.

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