CA1064708A

CA1064708A - Process for separation and recovery of metal values from sulfide ore concentrates

Info

Publication number: CA1064708A
Application number: CA230,782A
Authority: CA
Inventors: Enzo L. Coltrinari; James E. Reynolds
Original assignee: Cyprus Metallurgical Processes Corp
Current assignee: Cyprus Metallurgical Processes Corp
Priority date: 1974-10-21
Filing date: 1975-07-04
Publication date: 1979-10-23
Also published as: ES441060A1; JPS5164403A; GB1516127A; FR2288788B1; FR2288788A1; DE2542877A1; JPS5953335B2; IE41867B1; IE41867L

Abstract

ABSTRACT OF THE DISCLOSURE
An improvement in conventional processes for recovering metal values from sulfide ores containing lead, zinc and silver sulfides in which process the metal sulfides are converted to chlorides by chlorination followed by solubilization of the chlor-ides with a sodium chloride leach and subsequent recovery of the metals from their chlorides in accordance with a conventional flow sheet including crystallization, cementation, precipitation, fused salt electrolysis, etc., with chlorine being recovered for reuse by electrolysis of the sodium chloride leach solution substantially depleted of lead, silver and zinc, the improvement being a pollution-free process which comprises:
(1) recycling the sodium chloride solution depleted of a major percentage of lead and silver to the sodium chloride or brine leaching step; and (2) controlling the concentration of zinc and other impurities in the sodium chloride or brine leaching solution by bleeding a portion from the recycle stream of (1) above, removing lead, zinc and other metal impurities from the bleed stream, electrolyzing the bleed stream to produce chlorine, sodium hydroxide and a weak sodium chloride solution followed by recycle of the chlorine to the dry chlorination step and weak sodium chloride solution, after concentration, to the leach solution to control the concentration of zinc chloride and other impurities in the leach solution. A further improvement is the use of an alternate dry chlorination procedure for the sulfide ores and, particularly, ores such as the tetrahedrite-tennatite series which are more satisfactorily chloridized by dry chlorination than by wet chlorin-ation. Another improvement is use of a flow sheet by which no impurities are removed from the process in the form of chlorides so that no chlorine is lost from the system.

Description

1~i6470~
BACKGROUND OF THE_ NVENTION AND PRIOR ART
~ The invention comprises chlorinating sulfide ore ; concentrates to convert the metal sulfides therein to chlorides from which the metals are subsequently reco~ered in accordance with a flow sheet to be described. The invention resides prin-~ipally in the flow sheet irrespective of the chlorination pro-cedure, and the combination of the flow sheet with the chlorin-ation s~bp. Lead and silver are the principal metals which can be economically recovered from these ores.
Conversion of metallic sulfides into chlorides in metal recovery processes is not broadly new~ ~queous chlor-ination of metal sulfide concentrates, with erric chloride and chlorine gas in a sodium chloride or calcium chloride soIu-tion has been performed. Patent 1,736,659 to Mitchell discloses a process exemplifying this mode of recovery of metal values from sulfide ores using a wet chlorination process~ The process of this patent does not include recycle of leach solution or ..:
j sodium chloride solution, includes a roasting step with con-sequent air pollution, includes removal of chloride from the 2q system in the lead chloride, removal of iron from the system as th~ hydroxide rather than as carbonate, and differs in other aspects from the flow sheet of this invention.
Another publication of interestis the article entitled "The Dry Chlorination of Complex Ores" by Ionides in Mining and Scientific Press, Volume 112, May 27, 1916. This article discloses partially dry chlorinating concentrates of metal sulfides, including lead, zinc and silver sulfides, wlth chlor~
ine gas with final chlorination being accomplished in a roasting step in the presence of air in which the ferric chloride formed in the chlorination step is decomposed to produce chlorine which completes the chlorination of the metal sulfides. The ; process is directed chiefIy to the production and electrolysis of zinc chloride and is not a pollution-free process as sulfur

- 2 jrc:/J~r~, - 1~6~7~)~
dioxide is produced in the roasting step and released to the atmosphere. The procedure for recovering metals from the chlor-ides in this process lacks the features which the process of the Mitchell patent lacks as outlined above and differs in other respects from the flow sheet of the present invention.
It has been found that when the chlorination praduct of this invention is treated with sodium chloride to solubilize the metal chlorides, an undesirable build-up of impurities, particularly zinc chloride, in the brine leach solution occurs which adversely affect the ability of the solution after a period of time to solubilize silv~r and lead chlorides from the chlorinated ore product. The present process provides a means for overcoming this problem and obtaining high recoveries of silver and lead.
BRIEF STATEMENT OF THE INVENTION
The invention is an improvement in processes for treat-ing sulfide ore concentrates containing lead, silver and zinc sulfides to recover principally silver and lead, part of the improvement comprising conducting the recovery of the metals fr~m ~heir chlorides resulting from the chlorination step in a mann~r to prevent build-up of impurities, including zinc chlor-ide, in the sodium chloride leach solution used to solubilize the metal chlorides formed in the chlorination step. The pro-cess includes as an alternate to wet chlorination of the sul-fides a dry chlorination procedure using dry chlorine gas under heat conditions to convert the sulfides to chlorides and vol-atilize the chlorides of arsentic and antimony if these metals are present followed by solubilizing the chlorides with sodium ; chloride solution. The dry chlorination procedure is particu-larly effective on sulfides of the tetrahedrite-tennantite series alone or combined with some other mineral, such as galena~

jrc ~Jo ~64~8 After chlorination of the sulfi~es by whatever method the metal chlorides are separated from the resulting solution and ~he metals lead and silver, which are of principal interest, recovered from the separated aqueous chlorides. Lead chloride is ~rystallized out of the solution by cooling and lead recover-ed from the lead chloride by fused salt electrolysis with the chlorine produced being recycled to the chlorination step. The silver is removed from the lead chloride-depleted solution by cementation. The lead and silver depleted solution, from which a bleed stream is separated, is recycled to the sodium chloride brine leach. The bleed stream after final removal of lead and silver therefrom by iron cementation is neutralized with sodium carbona~e to remove zinc and other metal impurities therefrom as carbonates followed by electrolysis of the re-sulting solution to produce chlorine which is recycled to chlor-ination, with some of the weak sodium chloride electrolyte, after concentration~ being recyled to, the, sodium ch,loride br,ine leach ~` to prevent build-up of zine and othex impurities therein in the continuous process, and sodium hydroxide from the electro-20 - lysis being carbonated and recycled to the neutralization step.
It is an important feature of the process that the separation of a prescribed amount of bleed stream ~rom the ;' recycled sodium chloride leach solution, and the subsequent recycling thereof to the sodium chloride leach after removal of zinc and other metal impurities therefrom results in zinc chloride being removed from the brine leach solution substan-tially at the rate it is being added to thereby prevent its build-up in the brine leach solution with resultant inhibition of the solubilization of lead chloride. Another important feature of the invention is the conservation of chlorine feature in which no chlorine leaves the system as chloride in impurities or otherwise but any removal of chlorine ~s as chlorine gas jrc~ ~ 4 ~

- ~9G47~i rough electrolysis so that it can be recycled to the dry chlorination step without any substantial loss of any chlorine introduced into the system either for dry or wet chlorination.
A distinct advantage of the process is that it is pollution-free with no chlorine or lead vapors or compounds being released to the atmosphere and substantially all of the sulfide sulfur being converted to elemental sulfur rather than to sulfur dioxide as in the prior pyrometallurgical processes.
In one particular aspect the present invention provides a process for recovering metals from a sulfide ore concentrate containing lead, silver and zinc sulfides comprising the steps of: (a) chlorinating the concentrate to convert the metal sulfides to metal chlorides and convert the sulfide sulfur in the ore to e:Lemental sulfur; (b) leaching the residue of step (a) with aqueous sodium chloride to dissolve lead and silver chlorides and remove these chlorides ~rom the remaining solids; (c) cooling the sodium chloride leach solution to precipitate substantially all of the lead chloride followed by separating it from the leach solution, (d) recovering the silver from the lead chloride depleted leach solution remaining from step (c); (e) removing a bleed stream - from the solution remaining from step (d) and recycling the remainder of the solution to the leach solution of step (b); tf) removing substantially all o the zinc and other impurities from the bleed stream; (g) subjecting the bleed stream to electrolysis to produce chlorine gas; (h) recycling the purified bleed stream to leaching step (b); and (i) recycling the chlorine gas to the dry chlorination step (a).
In another particular aspect the present invention provides a process for treating a galena/tetrahedrite ore concen-trate including lead, silver, antimony and zinc sulfides comprisingthe steps of: (a) dry chlorinating the pulveriæed concentrate with chlorine gas to convert the sulfides to chlorides, volatilize the ~1/3~i', -5-70~3 :imony chloride, and convert the sulfide sulfur to elemental sulfur, said chlorination being carried out at a temperature of from about 50C to 150C; (b) leaching at a temperature of about 80~C to 100C, the residue from step (a) with an aqueous sodium chloride solution containing about 250 to 300 grams/liter of sodium chloride to dissolve lead chloride and silver chloride to extract these chlorides from the remaining solids; (c~ cooling the sodium chloride leach solution from step (b) to about 20C
to precipitate substan~ially all of the lead chloride and separating the lead chloride therefrom; (d) fusing the lead chloride from step (c) and electrolyzing the fused salt to produce chlorine gas and lead; (e) recycling the chlorine gas from step (d) to step (a);
(f) recovering the silver from the lead chloride depleted leach : solution remaining from step (c) by cementation with metallic iron;
(g) removing from about 5% to 15% by weight of the silver and lead depleted leach solution from step (f) as a bleed stream and recycling the remainder of the solution to the leach solution of - step (b); (h) removing any lead and silver remaining in the bleed stream by iron cementation; (i) precipitating zinc and other impurities from the bleed stream with sodium carbonate; t;) regen-erating chlorine gas from sodium chloride in the bleed solution by electrolysis; (k? recycling the chlorine gas from step (;) to the dry chlorination step of step (a); (1) carbonating the sodium hydroxide formed in step (j) to form sodium carbonate and recycling the sodium carbonate to precipitation step (i); and (m) recycling sodium chloride solution from step (j) to the leaching step tb).
In yet another particular aspect the present in~ention provides in the process for recovering metals from ores containing lead, silver, and zinc sulfides including chlorination of the sulfide ore to yield the chlorides of the metals and liberate elemental sulfur,and including the steps of leaching the chlorides with sodium chloride to separate lead and silver chlorides, ~ 5a-~l ~16~

separating lead chloride from silver chloride by cooling the leach solution, and recovering silver by cementation from the lead chloride depleted solution; the improvement which comprises preventing build-up of zinc and other impurities in the leach solution by reducing the concentration of zinc and other impurities in a portion of the lead and silver depleted leach solution and recycling it to the leaching step.
In a further particular aspect the present invention provides in the process for recovering metals from sulfide ores containing at least the sulfides of lead, silver, and zinc in which the sulfides are converted to chlorides by chlorination, the chlorides solubilized in sodium chloride, lead chloride removed from a leach solution by crystallization for recovery of lead, silver recovered from the leach solution by cementation, æinc removed from a bleed solution as zinc carbonate, and the purified leach solution of sodium chloride subjected to electrolysis to produce chlorine, the improvement comprising performing the chlorination step with dry chlorine gas to thereby convert the metal sulfides to chlorides and the sulfide sulfur to elemental sulfur.
In yet a further particular aspect the present lnvention provides the process fo recovering metal values from minerals of the polymorphic series of complex metal sulfides tetrahedrite-tennantite comprising: (a~ subjecting the minerals to dry chlorination with chlorine gas in the absence of oxygen at a temperature between about 50C and the melting point of sulfur to convert substantially all of the sulfide sulfur to elemental sulfur in solid form and to effect conversion of the metal compounds to metal chlorides, and recovering metal from the chlorides.
BRIEF DESCRIPTION OF THE DRAWINGS
The present process will now be described with refer~

ence to the annexed drawings wherein:

1~
~ 5b-~1 ~6~7~;)l!3 Figure 1 is a generalized flow sheet illustrating the process of the present invention performed as a continuous process.
Figure 2 is a diagrammatic illustration of a ~otary kiln for conducting the gas/solid chlorination step of the process of the invention countercurrently when dry chlorination is used.

DETAILED DESCRIPTION OF THE PROCESS AND SPECIFIC EXAMPLES

-The present invention will be illustrated with respect to a galena/tetrahedrite concentrate on which a dry chlorination procedure was used. It is to be understood that this process is applicable to other ores containing the sulfides of ; lead, silver and zinc and that chlorination is not restricted to dry chlorination as wet chlorination can be used. The general reactions occurring in the chlorination step are:

- (1) MS + Cl2 ~ MCl2; wherein M = Pb~ Zn, Cu, Fe, -~5 Ag, etc.
(2~ S2 + C12 -----~ S2 C12 ~'~ (3) MS + S2Cl2 ~ MCl2 ~ 3/2 S2 (4) Sb2S3 + 5 C12 --~ 2 Sb Cl5 + 3/2 S2 The concentrate used in the illustrative example had the following analysis:
Sllver0.30% _ 0.35%
~ead68% - 70%
Antimony0.80% - 1.4 %
Sulfur (Total) 14% ~ 17%
Zinc 4% - 6%
Iron 2% - 4%

~ j -5c-7~3 The ore concentrate was ground beore chlorination to -65 mesh.
The ground concentrate was dried as the dry chlorination pro-cedure was used and the dried concentrate subjected to dry chlorination.
In order to most efficiently utilize the chlorine, contact of the pulverized concentrate with chlorine gas was done in a countercurren~ system. As shown in Fig. 2, the con-centrate in finely divided form enters the upper end of a rotary kiln and dry chlorine gas is introduced at the discharge end of the tube so that the most highly concentrate chlorine gas composition contacts the more nearly completely chlorinated concentrateO A sweep gas which is inert, for example, nitrogen gas, is recirculated along with the chlorine to remove sulfur chlorides as explained later.
The length of the kiln is divided into two zones.
The zone approaching the discharge end operating at a temp-erature of approximately 115C and the upper end of the tube operating at a temperature o~ from 8t)-115C. Chlorination occurs primarily in Zone 1, and evolution of sulfur chloride gases occurs in Zone 2. The off gases containing volatilized antimony p~nta-chloride (Sb C15) are removed in a scrubber and antimony cam-pounds recovered therefrom. The same results will be obtained if the concentrate contains the sulfide of arsenic.
A definite amount of chlorine gas per tone of concentrate is metered into the kiln to substantially convert the lead and silver valuesto the chlorides in the continuous process. A kiln temperature range between 50-150C is satisfactory, a pre-ferable range being between 80-115C.
To avoid excessive stickiness during the reaction, the temperature within the kiln should be maintained below the melt~
ing point or sulfur, which is about 119C. Since the reaction between the lead sulfide (PbS) and chlorine is quite exothermic~
some cooling may have to be done in Zone 1, or alternatively~

jrc:~ - 6 -~36~7015 ~ddition of inert materialS such as sand, recycled productt or the like~ as a diluent for the concentrate can be used.
In ~one 2, heat may be applied in order to increase the vapor pressures of sulfur chlorides so that they can be swept forward by the sweep gas, nitrogen.
It is desired to have a minimum of sulfur chlorides in the chlorinated product to avoid objectionable hydrolysis in the subsequent sodium chloride leach. Such a reaction for g2cl2 is represented as follows:
S2C12 + 2H2O = 2HCl ~ H2S + SO2 ~or polythionic acids) The amount of chlorine gas required for chlorination depends upon the composition of the concentrates. For the galena/tetrahedrite concentrates, most of the chlorine is used to chlorinate the galena (PbS). These concentrates assay approx-imately 70~ lead, and the theoretical requirements of chlorine for the reaction PbS ~ C12 = PbC12 ~ S per ton of concentrate is ; 480 lbs. of chlorine. The remaining 100 - 140 lbs. of chlorine (the total chlorine addition being from 580 - 620 lbs. of chlorine per tone of concentrate), chlorinates the tetrahedrite and some of the sulfides of other metals such as, zinc, iron, copper and others. The following example illustrates the dry chlorination of lead sulfide concentrates and subsequent sol-ubili~ation of the resultant metal chlorides with sodium chloride in accordance with the flow sheet of the invention.
EXAMPLE I
Chlorination Conditions:
Apparatus 3 Compartment rotary kiln zone 1 Reaction: C12 Addition 580-600 lb/ton Pb9 ore Inert Gas Nitrogen N2:C12 = 1:1 Vol.Ratio Temperature 80C

Time 2 Hr.
Zone 2 Reaction: Inert Gas Nitrogen Temperature 110-115C
Time 1.5 Hr~

jrc:~' ~647~
~each Conditions: Pulp Density 50 g Chlorinated Product per liter Leach Solution Leach Solution 2 sn g~l NaCl, pH 1.5 Temperature 95C
Time 1.5 to 3 Hrs.

Results: Assay~ %
Pbs Chlorinated Leached Concentrates Product Residue 100 g ~21 g l~o 6 g . . ... .... . . .. _ . . . ..

10 Ag 0.34 0.28 ~012 Pb 70 58 .12 Sb 1.2 .41 .098 Zn 4~5 3.7 16 Fe 2.7 2.3 7~9 Cu .94 .80 ~18 Cl <~1 23 % Sb Volatilized During Chlorination = 59 Extracted Furing NaCl Leach - Ag = 99.3 Pb = 99-9 Sh = 96 Zn - 33 Fe = 47 Cu = 97 The results of the example show that more than 99 percent of the lead and silver content of the concentrate was converted to the chloride and extracted during the brine leach. In additioh a substantial amount of the antimony was recoverPd.
Substantially all of the sulfide sulfur was converted to elemen-tal sulfur in this dry ahlorination step.
It was found by using dry chlorination and the flow sheet of Fig. 1 that low temperature (80 - 115C), dry chlvrination with controlled ahlorine addition (580 ~ 620 lbs. of chlorine jrc:~O - 8 -per tone of concentrate) followed by a sodium chloride leach at 90 - 95C for an hour extracted 99~ of the silver, 99.9% of the lead, 33% of the zinc. 47% of the iron, 97% of the copper and 96% of the antimony. During chlorination, antimony was vol-atilized, probably as Sb C15, and recovered Erom the off gases of the chlorination stepO Arsenic if present can also be re-aovered in this manner. Substantially all of the sulfide sul-ur in the metal sulfides was converted to elemental sulfur.
This is an improvement over pyrometallurgical processes in whlch the sulfur is released as polluting sulfur dioxide.
The invention will now be further des~ribed with refer-ence to the flow sheet of Fig. 1.
The leaching referred to in the example is performed as follows. Irrespective of whether dry or wet chlorination is used the flow sheet of Fig. 1 is followed beyond the chlor-ination step. The chlorinated product is leached in the brine leach with sodium chloride solution to solubilize the lead and silver chlorides, and other metal chloride impurities. After start-up, the brine leach solution is supplemen~ed with recyled sod~um chloride in the continuous process as shown. The leach solution for the tetrahedrite/galena concentrate during oper-ation ordinarily contains from 260-280 grams per liter of sodium chloride, approximately 40 grams per liter of lead, about ~15 grams per liter of silver, 15 - 30 grams per liter of zinc, 15 - 30 grams per liter of ferrous iron, and lesser amounts of copper, antimony, calcium, magnesium, manganese, aluminum, etc.
The leaching step, irrespective of the concentrate being pro-cessed, is preferably performed at a temperature of from about 80 - 100 C. The leach slurry is filtered hot and the residue discarded or processed to recover the elemental sulfur if desired.
The next step as appears from the annexed flow sheet of Fig. 1 is the recovery of lead. The solu~lized lead jrc~

7~
.
chloride is crystallized from the ~odium r~loride leach sol-utio}l by cooling from 80 - 100C to approxlmately 15-20C .
The crystalline lead chl~ride is separated ~rom the solution by centrifuging, dried, and electrolyzed in a fused salt cell to produce product lead, and chlorine gas which is re-cycled to the chlorination step.
The next step is the recovery of silver. The silver is precipita~ed from the lead chloride~depleted soaium chloride leach solution- by ~ementation with metallic iron or lead to produce an impure silver sponge containing some copper, lead, iron and other trace impurities. This sponge must be refined to produce a pure silver product. The lead and silver-depleted leach solution minus a bleed stream is recycled to ~rine leach as shown.
About 5 15~ of the recycled leach solution is bled off from the main stream as a bleed stream. The ~ain pur-- pose of this is to treat this amount of the main stream as described below to remove impurities, especially zinc ~chloride, and recycle the impurity--depleted bleed stream to the brine leach, all for the purpose of controlllng the con~
centration of zinc chloride and other impurities in the leach solution. Zinc chloride is known to appreciably decrease the solubility of lead chloride in sodium chlori~e solutions.
Accordingly, in order to maintain maximum dissolution of lead chloride the zinc chloride and other impurities are removed through the bleed stream at substantially the same rate at which they axe introduced from the chlorination step.
Another purpose of the bleed stream and its treat-ment is to pexmit removal of the impurities in a form other than chlorides with consequent loss of chlorine from the system, and to recover chlorine as gas so that it can be re-cycled to the chlorination step wlthout any loss of chlorine from the system.

irc:.~ D - 10 -7~)8 As shown in the flow diagram~ lead remaining in the bleed stream is removed by cementation with metallic iron and the resultant spange lead recycled to the silver cementation step. Any silver cemented out will be recycled likewise. The lead in solution in the bleed stream is decreased from about 15 grams to .2 grams per liter.
The bleed stream is next neutralized with sodium car-bonate at a pH of abou~ 8.5 and at a temperature of about 50 - 80C to percipitate zinc~ iron and other metal impurities as carbonates in a readily filterable form. Sodium carbonate is used here because its reaction with zinc chloride produces sodium chloride which is subsequently submitted to electro~
lysis ~o that no chlorine is lost from the system in the removal of zinc and other impurities.
The bleed solution after solids removal is subjected to electrolysis to produce chlorine gas, sodium hydroxide, ana a weak sodium chloride solution. The prior removal of zinc , and other impurities from the solution greatly facilitates the electrolysis as the electrolysis is almost physically impos-sible with zinc and the other impurities present in the electrolyte. The sodium hydroxide is carbonated to produce sodium carbonate which is recycled to the neutralization step.
The chlorine gas is recycled to the chlorination step and the impuri~y depleted sodium chloride bleed solution after con~
centration is recycled to the leach step to prevent zinc build-up in the leach solution as explained above.
The process can, of course, be performed both con-tinuous or batch.
Based on the results obtained with the process using a dry chlorination procedure a material balance for a typical commercially available lead sulfide concentrate (galena/tetra-hedrite) is as follows:

jrc~

47(~8 ESTIMATED MATERI~L BALANCE FOR GALENA/TETR~HEDRITE
.
- Lb./Ton Concentrates . . , . , _ .
Ag Pb Sb Zn Fe Cu S -Input ' -PbS Concentrates 6.80 1400 24.0 30.0 54.0 18.8 320 Iron Powder 36 .- ~
' 6.80 1400 24.0 90.0 90.0 18.8 320 Products Lead 1385 Ag SpGnge 6.70 5 9 5 18 Sb Chloride 14 +10 Leach Residue 0~10 8 1 60 2~ ~8 ~10 Impurities Carbonates 2 30 56 6.80 1400 24 90 90 18.8 ~32 All the chlorine gas added is used internally~

The Material Balance Table shows that theoreticall~ all ~' of t~e lead and silver can be recovered by the process with . ..
the loss of no 'c~lorine from the system. After start-up virtually no chloride addition to the continuous process is needed subject to ordinary losses due to mechanical operations, such as, filtration, concentration, etc.
While the invention has been illustrated by its appli-cation to thé lead, silver and zinc containing tetrahedritefgalena ~' concentrate and the use of a dry chlorination procedure, it is by no means limited to this ore and technique. The invention i~cludes the use of dry or wet chlorination techni~ues on ores in general containing lead, zinc and silver, the flow sheet beyond the chlorination step being applicable irrespective of the method of chlorination. The flow sheet can be used to recover metals'from their chlorides produced by wet chlorination of their sulfides with results comparable to those produced in the example.

jrc 1~ - 12 -It is seen from the above description of the invention that a process has been provided for the recoYery of metals from their sulfide ores by chlorination of the sulfides to chlorides follo~ed by solubilization of the chlorides with sodium chloride and subsequent recovery of the metals from the chlorides, in which process substantially all of the sulfide sulfur in the ore ls converted to elemental sulfur, build-up of zinc chloride and other impurities in the sodium chloride leac~ solution is prevented, no chlorine is lost from the system ~y removal of any impurities aR chlorides, the chlorine ; of t~e metal chloriaes from which metals are recoYered being recovered as a gas for recycle to chlorination, and in which there is no appreciable loss of chloride from the s~stem. The invention includes the combination with the chlorination step of the recovery of all chlorine as a gas so that the recovered gas can be reused in the chlorination step. The process has the overall ad~antage that it is pul.lution-free with no chlorine gas escaping from the system and no lead compounds or vapors or sulfur dioxide being released.
' ' .

;.rc~ r~

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for recovering metals from a sulfide ore concentrate containing lead, silver and zinc sulfides comprising the steps of:
(a) chlorinating the concentrate to convert the metal sulfides to metal chlorides and convert the sulfide sulfur in the ore to elemental sulfur, (b) leaching the residue of step (a) with aqueous sodium chloride to dissolve lead and silver chlorides and remove these chlorides from the remaining solids;
(c) cooling the sodium chloride leach solution to precipitate substantially all of the lead chloride followed by separating it from the leach solution;
(d) recovering the silver from the lead chloride depleted leach solution remaining from step (c), (e) removing a bleed stream from the solution remaining from step (d) and recycling the remainder of the solution to the leach solution of step (b);
(f) removing substantially all of the zinc and other impurities from the bleed stream;
(g) subjecting the bleed stream to elactrolysis to produce chlorine gas;
(h) recycling the purified bleed stream to leaching step (b); and (i) recycling the chlorine gas to the dry chlorination step (a).

2. The process of claim 1 performed continuously.

3. The process of claim 1 in which any lead and silver remaining in the bleed stream of step (e) is removed by iron cementation before removal of zinc in step (f).

4. The process of claim 1 in which zinc is removed from the bleed stream in step (f) by neutralizing the bleed stream with sodium carbonate to form sodium chloride and zinc carbonate.

5. The process of claim 4 in which sodium hydroxide formed in the electrolysis of sodium chloride in step (g) is carbonated to form sodium carbonate which is recycled to the neutralization step.

6. The process of claim 1 in which the bleed stream of step (h) is concentrated before recycling to leaching step (b).

7. The process of claim 1 in which the concentrate is chlorinated in step (a) by dry chlorination with dry chlorine gas.

8. The process of claim 7 in which the dry chlorin-ation is carried out at a temperature below the melting point of elemental sulfur.

9. The process of claim 7 in which the temperature of dry chlorination is from about 50°C to 150°C.

10. The process of claim 7 in which the sodium chloride leach solution contains from about 250 to 300 grams per liter of solution of sodium chloride.

11. The process of claim 1 in which the leaching step (b) is carried out at about 80°C to 100°C.

12. The process of claim 1 in which the sodium chloride leach solution in step (c) is cooled to about 20°C
to precipitate lead chloride.

13. The process of claim 1 in which the silver is recovered in step (d) by cementation with metallic iron.

14. The process of claim 7 in which the concentrate is galena/tetrahedrite ore.

15. The process of claim 1 in which the concentrate is chlorinated in step (a) by a wet chlorination step.

16. A process for treating a galena/tetrahedrite ore concentrate including lead, silver, antimony and zinc sulfides comprising the steps of:
(a) dry chlorinating the pulverized concentrate with chlorine gas to convert the sulfides to chlorides, (claim 16 continued) volatilize the antimony chloride, and convert the sulfide sulfur to elemental sulfur, said chlorination being carried out at a temperature of from about 50°C to 150°C.
(b) leaching at a temperature of about 80°C
to 100°C, the residue from step (a) with an aqueous sodium chloride solution containing about 250 to 300 grams/liter of sodium chloride to dissolve lead chloride and silver chloride to extract these chlorides from the remaining solids;
(c) cooling the sodium chloride leach solution from step (b) to about 20°C to precipitate substantially all of the lead chloride and separating the lead chloride therefrom;
(d) fusing the lead chloride from step (c) and electrolyzing the fused salt to produce chlorine gas and lead;
(e) recycling the chlorine gas from step (d) to step (a);
(f) recovering the silver from the lead chloride depleted leach solution remaining from step (c) by cementation with metallic iron;
(g) removing from about 5% to 15% by weight of the silver and lead depleted leach solution from step (f) as a bleed stream and recycling the remainder of the solution to the leach solution of step (b);
(h) removing any lead and silver remaining is the bleed stream by iron cementation;
(i) precipitating zinc and other impurities from the bleed stream with sodium carbonate;
(j) regenerating chlorine gas from sodium chloride in the bleed solution by electrolysis;
(k) recycling the chlorine gas from step (j) to the dry chlorination set of step (a);
(1) carbonating the sodium hydroxide formed in step (j) to form sodium carbonate and recycling the sodium carbonate to precipitation Step (i); and (m) recycling sodium chloride solution from step (j) to the leaching step (b).

17. The process of claim 16 in which the concentrate includes arsenic sulfide and the arsenic is volatilized in dry chlorination step (a).

18. The process of recovering metal values from minerals of the polymorphic series of complex metal sulfides tetrahedrite-tennantite comprising:
(a) subjecting the minerals to dry chlorination with chlorine gas in the absence of oxygen at a temperature between about 50°C and the melting point of sulfur to convert substan-tially all of the sulfide sulfur to elemental sulfur in solid form and to effect conversion of the metal compounds to metal chlorides, and recovering metal from the chlorides.

19. The process of claim 18 in which chlorination is performed at a temperature between about 80°C and the melting point of sulfur.

20. The process of claim 18 in which the minerals contain silver.

21. The process of claim 20 in which the silver containing mineral is tetrahedrite.

22. The process of claim 18 in which sulfur chlorides formed during dry chlorination are reacted with the metal sulfides to form metal chlorides and elemental sulfur.

23. The process of claim 22 in which the process is performed by introducing the metal sulfides and dry chlorine gas countercurrently into the reaction zone and an inert sweep gas is introduced into the reaction zone to bring sulfur chlorides formed during the dry chlorination into contact with metal sulfides entering the reaction zone.