CA1156048A

CA1156048A - Process for the recovery of lead and silver from minerals and process residues

Info

Publication number: CA1156048A
Application number: CA000354083A
Authority: CA
Inventors: Robert S. Salter; Roy S. Boorman; Ross D. Gilders
Original assignee: Provincial Holdings Ltd
Current assignee: Provincial Holdings Ltd
Priority date: 1980-06-16
Filing date: 1980-06-16
Publication date: 1983-11-01
Also published as: FI71342C; JPS6352094B2; FI71342B; EP0042702A1; JPS5729541A; EP0042702B1; DE3166293D1; ZA813982B; PT73185A; PT73185B; AU549357B2; ES502948A0; AU7184681A; IE52179B1; FI811847L; IE811310L; ES8301284A1

Abstract

ABSTRACT OF THE DISCLOSURE
Residues containing lead as lead sulphate and silver in the form of native silver or silver chloride, sulfide or sulphate, as well as silver complexes with other metals, and resulting from the roasting and leaching of sulfide concentrates containing lead, zinc, copper, and silver are treated to produce a high grade lead and silver product containing lead predominantly as calcium plumbate in a process wherein the residue is leached with brine, the resultant leach solution treated with lime to precipitate lead as oxychlorides, and the resultant lime-oxychloride precipitate is calcined to produce a mixture of calcium orthoplumbate and lead oxide. Residual chloride can be washed easily from this product which may then be treated in a lead blast furnace to recover lead and associated silver in their elemental state.

Description

This invention relates to the extraction of metal compounds from metal bearing materials and more particularly to t~e extraction and recovery of lead values in a calcium plumbate and/or oxide product from minerals or lead bearing materials. Silver which may be present in association with the lead may be recovered as native silver, silver chloride, sulfide or sulphate, or a silver complex with other metals, or in some other form from which it can be recovered by conventional techniaues.
The recovery of a high grade lead product suitable for treatment for metal recovery from lead bearing minerals has usually been accomplished by flotation concentration of coarse grained lead sulphide deposits into a concentrate containing greater than 50~ lead and pyrometallurgical reduction of this concentrate in a blast ~urnace. The reserves of these coarse grained lead sulphide deposits are rapidly being depleted. The major new reserves of lead are being found in fine grained massive sulphide deposits containing ~' 1 15~0~
sulphides of zlnc, lead, copper, silver, and iron. ~ecoveries into high grade lead concenlrates are typically low from these deposits, necessitating significan~ reduction in grade to maintain economic recoveries. It will be necessary for some of these deposits to resort to the production of bulk zinc, lead, copper concentrates to insure high recoveries. Several new processes are available for treating these low grade and bulk type concentrates includlng ferric chloride leach processes, copper chloride leach processes, sulphuric acid-oxygen pressure leach processes and the sulphation roast process. The lead and silver in the latter two processes report in a low grade lead sulphate-hematite leach residue. In the ferric and cupric chloride leach processes, leach filtrates are produced which contain lead and silver as chlorides in a concentrated brine solution. The present process has application for lead and silver recovery from the leach residues and brine solutions generated in all of these processes.
Substantial reserves of lead and silver also exist in leach residues from electrolytic zinc plants. These residues typically assay 15-40~ lead as lead sulphate and for the most part are considered as unsuitable as feed for a conventional lead smelter except in small amounts. Ano~her source of low grade materials is 51ag ~rom lead smelters. Lead is prasently recovered from these sla~s by energy intensive ~umin~ processes. The present process can be employed directly to recov~r lsad and silver E~om zinc plant residue5 and a~ter either sulphuric acid leaching or sulphation roasting to ~ecover lead and silver ~rom slags.
It is known that lead ~ulphate and associated silv~r may be solubilized by means o~oncentrated brines as proposed in Canadian Pa~ent 1~,918, ~883); Canad~an Patent 228,518,(1919); and U.S. Bureau ~0 - 2 -1 ~ 5~0~8 of .~.ines sulletin 1~7,(1918). Whilst these methods solve th~ problem of separating the le~d and silver from the residues there has been som~ economic difficulty in the subsequent recovery of the lead and silver from the solution in a usable form.
West Ger~an Patent 2,500,453, (1976) descr.ibes a method of leaching lead sulphate containing material in sodium chloride solution and after residue separation, precipitating the Pb from solution with milk of lime~ The lead precipitates contain greater than 10~ chloride and 11~ sulphate and are not acceptable to conventional lead smelters except in small amount and at depressed prices due to the deleterious effects of chlorides on acid plant catalysts, baghouses, and refractories.
Canadian Patent 228,518,(1gl93;United States Patent 4,063,933, (197~; and processes currently being developed by the U.S. Bureau of Mines, Minemet Recherche,(France), and Cominco Limi.ted (Canada), advocate lead recovery hy the precipitation of lead chloride crystals from solution by evaporation and/ox cooling. The subsequent recovery of lead metal to be accomplished by electrolysis. Capital and operating costs are projected to be much higher for these processes than for conventional smelting.
Australian Patent 28,957,~1971)describes a method of precipitating lead chloride from brine solution by c041 Lng followed by reacting said lead chloride with water and calcium sulphate to produce a lead ~ulphate precipitate and calcium chloride solution. Although low chloride levels in the lead sulphate were obtainable with rigorous wa.~hing, the pxQduct ls a~ain ~uitable -to lead smelters in lim:Lted quantit.ies and mu~t be t.reated on a sin-ter machine to remove ~15~
sulphur before the blast. Capital and operating costs are projected to be high for the process since the brine solution must be heated for high lead solubLlity and then cooled for lead chloride precipitation.
Canadian Patent 228,518,(1919)describes a method of lead recovery from concentrated brine solution by direct precipitation as sulphide or sulphate. These precipitates are difficult to wash and contain significant amounts of entrapped chlorides.
Again conventional lead smelters will accept only small quantities.
Canadian Patent 1~918 describes a method of precipitating lead and silver from brine solution by cementation on metallic zinc. Recently other researchers have rediscovered the cementation techique and advocate either zinc or iron as cementation media.
High grade metallic lead and silver cementates are produced in these processes which are acceptable to lead smelters at premium prices at high tonnage. Considerable economic penalties are incurred to produce good quality cementates, however, since the cementation reagents are expensive and the zinc or iron in the lean brine re~ulting from cementation must be recovered in a form acceptable for sale or reuse. This can be accomplished only at considerable cost.
It is an objective of this invention to provide a process ~or the extraction and r covery of lead and silver into a product which will be acceptable t4 conYentional lead smelters in large ~onnages and at a premium price.
Furt~er objectiv~s are ~or the proce~s te consume minimum energy and the reagent~ us~d to be recovered and either reu~ed with high ef~tciency or credited in the sale o~ t:he laad product.

1 1~60~8 In accordance with a broad aspect of thi.s invention there is provided a process comprising the steps of (1) preparing a solution of lead chloride by dissolving lead sulphate contained in an ore or process residue in an acidic concentrated chloride brine; (2) separating the solution so formed from insoluble gangue or other residue; (3) forming a prec.ipitate of lead oxychloride by adding lime to said solution and separating said lead oxychloride precipitate from the residual lean brine solution; (4) reacting the said oxychloride precipitate with oxygen and lime in a reactor at an elevated temperature to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides; (5) washing said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (6) separating the resulting residue obtained from the resulting chloride brine;
and, (7) washing said residue containing calcium plumbates and/or lead oxides with fresh water to remove residual chlorides.
In another broad aspect there is provided a process for gaining lead and silver values eomprising the steps of (1) preparing a solution of lead chloride and silver compounds by dissolving lead sulphate and silver compounds contained ln an ore or process residue in an aeidie eoneentrated ehloride brine;

(2) separating the solution so ~ormed ~rom insolubl~ ~angue or o~her re~idue; t3) ~ormin~ a preeipita~e of lead oxychlo~ide and silver eomp~unds hy adding lime ~o said ~olution and separating said precipitate from the residual lean brine solution;

1 1560a,8 (4~ reacting the said oxychloride precipitate with oxygen and lime in a reactor at an elevated temperature to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides and most of the silver as silver or silver compounds; (5) washing said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (6) separating the resulting residue from the resulting chloride brine; and, ~7) washing said residue containing calcium plumbates and/or lead oxides, as well as silver and silver compounds, with ~resh water to remove residual chlorides.
In accordance with another aspect of this invention we provide an improvement in a process comprising the step of (1) preparing a solution of lead chloride by dissolving lead sulphate contained in ore or process residues in concentrated chloride brine, thereby also dissolving any silver associated with the lead; (2) separating the solution so formed from the insoluble gangue and other residues; (3) forming a precipitate of lead oxychloride (and any silver which may be present) by adding lime to the solution and separating the lead oxychloride and silver precipitate from the residual lean brine solution;
(4) recycling the lean brine, normally after concentration thereof such as by evaporation or by addition of further chloride and also normally after re-acidification by the addition of ~urther acid, ~or reuse in the ~urth~r extraction o~ lead sulphata a~ under s~eps (1) and ~2). ~h~ improvem~nt compr:isas ~5) xeac~in~ the said praaipita~e ~on~aining lead oxychlorida 1 ~ S~04~
with oxygen such as by air and with excess lime present in the precipitate, and if desired adding fresh lime, in a reactor at a temperature above 325C for longer than one half hour to produce a calcine containing most of the lead as calcium plumbates and lead oxides, and containing any silver present as native silver, silver chloride, sulfide or sulphate, and complexes of silver with other materials; (6) repulping said calcine in water and/or dilute chloride brine to remove soluble chlorides;(7) separating the residue obtained in step (6) from the resulting chloride brine; (8) recycling the brine resulting from step ~7), with the optional treatment rnentioned above, for further extraction of lead sulphate under the previous steps; (9) washing the said residue from step (7) with fresh water to remove residual chlorides; and (10) recycling the chloride brine obtained in step (9) to step (6) and/or recycling the said chloride brine, again with the optional treatment mentioned above for reuse in the further extraction of lead sulphate under the previous stép.

In one aspect the present invention provides, in a process comprising the step of forming a precipitate of lead oxy~
chloride by adding lime to a chloride brine solution cont:aining lead chloride, and separating said lead oxychloride precipitate from the residual lean brine solution; the improvement which comprlse~ reaqting the said oxychloride preaipitate Wi~h oxygen and lime in a reactor at a temperature above 325C. ~or longer than Q.S hour~ to produce a calcine containing most. of the lead as calai~n plumbates and/or lead oxides; repulpln~ said aalcine 1 1 5~)'18 in water and/or dilute chloride brine to dissolve sol~ble chlor-ides; separating the residue obtained from the resulting chloride brine; and wash.ing said residue containing calcium plumbates and/
or lead oxides with fresh water to remove residual chlorides.
In another aspect the invention provides a process for gaining lead and silver values comprising the steps of preparing a solution of lead chloride and silver compounds by dissolving lead sulphate and silver compounds contained in an ore or process residue in an acidic concentrated chloride brine; separat:ing the solution so formed from insoluble gangue or other resiclue; and forming a precipitate of lead oxychloride and silver compounds hy adding lime to said solution and separatiny said precipitate from the residual lean brine solution, characterised by the further steps of reacting the oxychloride precipitate with oxygen and lime in a reactor at an elevated temperature to produce a calcine con-taining most of the lead as calcium plumbates and/or lead oxides and most of the silver as silver or silver compounds; washing the calcine in water and/or dilute chloride brine to dissolve soluble chlorides; and separating the resulting residue containing calcium plumbates and/or lead oxides, as well as silver and silver compounds, from the resulting chloride brine.

~ 7a -~ 15~0~8 In the drawings which accompany this invention:
Figure 1 is a schematic flow sheet showing certain aspects of the present invention;
Figure 2 is a graph showing the relationship between calcium chloride addition and sulphate in solution;
Figure 3 is a schematic flow sheet showing a lead-silver recovery plant employing certain aspects of this invention.
The advantages of producing a calcium plumbate product are as follows:

.- 7b -1 ~ 560~8 i) calci~n plumbate is not water or cold brine soluble and will not react with chloride brines under neutral or basic conditions to reform lead oxychlorides.
ii) entrained chlorides in the plumbate calcine can be easily removed and reduced to very low levels by washing with water or unsaturated brine solution.
iii) plumbate repulp solutions Eilter rapidly, leaving a dry residue.
iv) plumbate products can be briquetted and fed directly into a lead smelter blast furnace without prior sintering, increasing smelter throughput for smelters in which the capacity is limited by the sinter machine.
v~ as reported by Denev, D.G. et al in Dokl. Bolg. Akad. Nauk, Vol. 26, 11, 1973, page 1485 calcium orthoplumbate is an oxidant for lead sulphide at high temperature resulting in the products PbO, CaO and SO2 and hence would make a good dilutant for galena concentrate on a sinter machine.
vi) CaO is a product ofthe rPduction of calcium plumbate and is also required as a slagging agent in lead blast furnaces, usually at high tonnages. Accordingly, since the use of some calcium plumbate as feed to a lead smelter would reduce the requirement for lime, some credit should be given ~or the lime in the plumbate product.
vii) the production of a calcium plumbate product allows for the use o~ lime ~or the precipitation of the lead ~rom the brine 1-3ach olutlon and al~o a~ a reaatant in the high temperature aonversion o~ oxychloxide to plumbate~ Llme i9 a relatively ln~xpensive, ea~y to handle, envi~or~entally acceptable, and readily available commodlty.

3~
~ :.3 ' _ ~ _ 1 1 560~

~;iii) the use of lime results in the formation of calcium chloride after the conversion of the metal chlorides (lead, zinc, copper, iron) to oxides. This calcium chloride is recycled in the brine to the lead sulphate leach and results in the precipitation of most of the sulphate as calcium sulphate into the leach residue.
Accordingly the plumbate product is low in sulphate.
Also, the low soluble sulphate in the leach enhances the solubility of lead and silver allowing for leach operation at lower temperatures, resulting in a lower energy consumption and less maintenance due to decreased corrosion. The effect of calcium chloride on sulphate solubility in sodium chloride brine solution is shown in Figure 2. The solubility of lead as lead sulphate in 269 gpl NaCl brine increases from about 13 gpl at 35C
to about 18 gpl lgrams per liter) at 35C when CaC12 is added to yield a brine containing 34 qpi C~C12. Lead solubility is directlv proportional to the brine saturation and the sulphate concentration in the brine.
Since calcium chloride is a more expensive commodity than sodium chloride a~d since there appears to be a lower limit to the soluble sulphate in the brine leach solution attainable with calcium chloride and since sodium chloride i5 easier to remove ~rQm leach re~idue by washing, it seems to be preferable but not n~c~ary to use a concentrated sodium chloride brine as the ba~e soluti~n u~ing the lime ad~i~ions ~n ~teps (3) and ~5) as the source Q~ calcium chloride ~or sulphate removal. Small amoun~s o~ ~res~
NaC1 and CaC12 will be required to make up ~or losses in ~e leach residue ~nd product.
~ 9 _ .. .. ~ . .. .

0 '1 ~

Lead and silver extractions into brine can be accelerated by increasing the acidity by addition of an acid such as hydro~
chloric or sulfuric acid which will ensure at least mildly acidic conditions. The optimum pH in ~he brine leach for high lead and silver extraction, efficient residue washing, and low lime consumption appears to be about 1.5.
Extractions of lead from lead sulphate material into brine are very high and may approach 99~ with the proper choice of reten~ion time, temperature, brine composition, and residue washing t0chniques as long as the solubility limit of the lead is not approached. ~ead extractions fall from 99% at 75~ of lead chloride saturation to 96% at 86~ of saturation to 91% at 94 of saturation for brine leaching }n 269 gpl NaCl - 33 gpl CaC12 - pH 1.5 brine at 35C and 1.5 hours leaching time.
The saturation limit of lead as lead chloride in this brine is 18.3 gpl.
Silver extraction by brine is very depe~dent on the nature ~
and prior history of the lead sulphate containing material. Some materials, usually those which have been very recently produced in a roaster or leach process exhibit silver extractions greater than 8Q%. Other materials, usually stockpiled, exhibit lower silver extractions of about 50%. Silver recoveries can be inareased from these materials by flotation recover~ of a silver c~nc~ntr~e and using ~he~present proaess on th~ flotation ~all~ngs whiah con~ain mQst of the lead and all the remaining silver. ~he silver ~lotatio~ conaentra~e and ~he plumbat~
prod~ct ~an then b~ combined ~or sale ~o aonventional l~a~ smeltexs.
Flotati~n proces~ei 8uch a~ desarib~ by M~rl~ama,E. and Yamamato,Y.
in AIME World Symposlum o~ Mining and M~allurgy o~ ~aad and Zinc, ,; 30 10 1 1S60~8 Vol. II, 1970, page 215 have been shown to yield silver concentrates wlth hlgh silver assays and recoveries from lead sulphate containing materials.
Another option in the present proces-s is the production of separate silver and lead products. Silver can be removed from the brine leach solution by cementation on a suitable metallic medium such as zinc, iron, or lead. With proper stoichiometric conditions, retention time, and pH nearly all the silver can be recovered in a high grade metallic product containing some little lead and copper as contaminants. Lead along with the solubilized cementation agent would then be recovered in ~e plumbate product as in steps (3) - (9).
When lead is precipitated from brine solution by the addition of a base as in step (3) of the process, the lead compbunds formed will depend on the pH or the mole ratio of base to lead chloride and the total chloride concentration. Table l shows the effect of these variables on the nature of the lead precipitate when lead is precipitated from a brine solution containing 15 gpl lead as lead chloride at 45C and a retention time of 1.5 hours. Shorter retention times can be employed but chloride levels in the precipitate will increase unless the temperature is increased above 45C. Silver is coprecipitated with lead. Most of the brine soluble impurities which are present in the lead sulphate containing starting material such as zinc, copper, iron, bismuth, and arsenic also copr~cipitate with l~ad. T~e ba~t process eaonomics are ob~ained with lime as the precipita~ion agent at an addition rate he~ween l.Q and 5.5 mole ratio of lime to lead chloride. The excess lime also acts as a 10cculating agent for oxychloxide precipita~e, l 1560~

Table 1 Effect of the Mole Ratio of Base to Lead Chl.oride and the Total Chloride Concentration on the Lead Precipitate NaCl CaC12 Concen- Concen- Mole Basetration tration Ratio Lead Precip.itate (gpl) CaO 269 15 0.75 PbOHCl Na2C3 269 15 1.0 PbOHCl NaOH 269 15 2.0 PbOHCl CaO 269 15 1.5 3PbO-PbC12-nH2O ~
minor 2PbO-PbCl2~nH2O
CaO 269 33 1.5 3PbO~PbCl2~nH2O +
minor 2PbO~PbC12~nH2O

2 3 269 33 1.5 3PbO~PbC12 nH2O +
minor 2PbO-PbC12-nH2O
NaO~ 269 33 3.0 3PbO-PbC12-nH2O +
minor 2PbO-PbC12-nH2O
CaO 269 33 10.0 3PbO-PbC12-nH2O
NaOH 269 33 20.0 6PbO-PbCl2-nH2O

~"

0 ~ ~
resulting in iml)~oved solid~liquid seEJaration.
~ lthoLIgh it is desirable to produce a precipita-te containing as little chloride as possible, very low chlorlde-oxychlorides canrlot be precipitated from concentrated brine unless uneconomic quantities of sodium hydroxide are used. Since they are very soluble, all excess sodium hvdroxide and/or sodium carbonate must be neutraliæed with hydrochloric acid before the lean brine resulting from precipitate separation can be recycled to the brine leach step (1). The use of sodium hydroxide precipitating agent also results in excessive reagent calcium chloride makeup requirements.
Ermilov, V.V. and Aitenov, S.A. in Trudy Institut Metallurgi Obogashcheniia, Vol. 30, 1969, page 47 proposed a method for producing a lead (iv) oxide precipitate from concentrated brine by adding equal molar quantities of calcium oxide and calcium hypochlorite to lead chloride. Although the reaction is irreversible and regenerates calcium chloride into solution, and the product can easily be washed to less than 0.5% chloride, the economics are unfavourable due to the value of hypochlorite in comparison to lead metal and lime.
If the lime addition in the precipitation step (3) was less than 2.5 mole ratio to lead, then after separation of the lead oxychloride precipitate from the lean brine solution, the precipitate is repulped with water or any reasonably unsaturated brine solution produced in the proces~. Lime is added to the pulp to bring the mole ratio ~f the total lime additlon in the process to bel;ween .S and 5.S. A~tar solid/li~uid separation the pulp is subjected to thermal tr~atmant. Alternatively the lead oxychloride precipitate l 15~0~
may be blended with lime to increase the total mole ratio to between 2.5 and 5.5, without repulpins and ~he blend subjected to thermal treatment.
If the lime addition in step (3) was greater than 2.5 mole ratio to lead, then repulping and/or further lime addition is not necessary before thermal treatment.
The lead oxychloride-lime blend is heated in a reactor in the presence of oxygen or air. The reactor can be a rotary kiln, furnace, roaster, autoclave or any devi~e commonly used for thermal treatment. The retention time in the reactor depends upon the desired degree of conversion of oxychloride to plumbate and oxide, the temperature in the reator, the lime to lead mole ratio, and the oxygen partial pressure. The effects of these variables on the nature of the calcine product are shown in Table 2. At reaction temperatuxes above 500C sintering of the product appears and volatilization of lead chloride begins. Preferred conditions appear to be a totai process lime addition to lead mole ratio of about 3, a reaction temperature of about 400C, a retention time of about l hour, and an excess of oxygen for lead oxidation.
Pressure above atmosphericis not required for the reaction to be complete within 2 hours, Sufficient air or oxygen can be supplied for the reaction by convection, free or forced, or by pressurizing the reactor.

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Pl ~ ~.5 -11560~8 It issurprisfng that calcium orthoplumbate (Ca2PbO4) is formed at high yields with such low temperatures and short retention times. Calcium orthoplumbate in a pure form (>90%) is a valuable commodity and is used in the manufacture of primers for steel and galvanized steel, of pigments and of binders for paints. It also has use in the plastics and resin industries. The common commercial production method is the reaction of PbO with lime and air or oxygen at temperatures above 700C. The reaction kinetics are reportedly slow below this temperature and the reaction will not go below 500C. It has baen reported by Denev, D.G et al in Dokl.Bolg.Akad.Nauk, Vol.26 11,1973, page 1485, however, that additions of small ~uantitles ;
of NaCl to the reaction mixture speed the kinetics. The present invention differs from the customary practice in that the reagent for calcination is lead oxychloride and not lead oxide. Also, ~ ;
the oxychloride i5 contaminated with significant quantities of NaCl and CaC12. Accordingly, the kinetics and energetics of plumbate ~ormation have been altered significantly from commercial experience.
: 20 Figure 3 is a schematic plant layout for a particulsr embodiment ~- of the invention relating to example 1.
. :
The following examples illustrate the practice of our invention :~ but should not be constxued as limiting.

S~mpl~s ~ ho~ sulp~uric acid leach ~es~due~ ~b~ained ~rom ~he , '~ s~lphatio~ roa~tln~ ~nd leachin~ o~ bulk zinc-lead-coppe~~5ilver , 5ulphide ~o~cantrates assayi~ 30-32~ æn, 3.5-10~ Pb, ~.7~ Cu, 4.4 -oz/~ ~t~o~ ounce per ~hort ton) ~ilv~x, and 14-23~ Lron were processad accordingly to the , ~ 15~0'1~

invention. A sample (example 10) of a hot acid leach residue from a dead roast zinc plant was also processed. The residues assayed as in Table 3.
The residues were leached in brines of composition given in Table 4. Residue was added at a ratio of 15 gm of contained lead per litre of hrine. The leaches were conducted at 35-40C for 1.5 hours. Leach residues were allowed to settle and the thickened residues filtered and washed with ~resh brine. Extractions of lead and silver are given in Table 5. All of the zinc, iron and copper as sulphates in the hot sulphuric acid leach residues leached along with the lead and silver. Copper and bismuth assays in the brine were 40 and 45 mgpl respectively.
One pregnant brine solution (example #6) was treated with zinc dust at an addition rate of 0.5 gpl producing a cementate containing 99% of the silver, 95% of the copper and 80~ of the bismuth in the pregnant brine.
The remaining pregnant brines and the solution resulting ~rom the zinc dust cementation test were then treated with lime at 1.5 mole ratio to lead in the brine solution. The temperature and retention time were 45C and 1.5 hours respectively.
Precipitates were allowed to settle and the thickened precipitat~s filtered.
~ he precipi~a~es in all tests wer~ ~hen hlend~d with lime, ~ xequir~d, to bring the total mole ratio of l.ime added to the proce~s to lead in the precipitate to 1~75~5.5. The blends were 1 ~S60~

Table 3 Assays (wt%) of Hot Acid Leach Residues (Dry Basis) Example ~

._ _ ZnFe2O4 1.5 1.5 5.0 (Zn,Fe)S 1.0 0.9 1.0 Fe23 52.8 63.2 10.0 PbSO~ 31.1 10.9 46.7 CaSO4 H2 6.8 6.2 6.0 SiO2 1.8 1.8 25.0 As 0.2 0.2 0.5 S 0.6 0.5 0.3 ZnSO4 1.1 4.0 0.5 CUSO4 0.1 0.3 0.1 Fe2(SO4)3 1.6 5.7 0.7 Ag (ppm) 639 310 250 Gangue 0.4 0.4 3.0 - ~ 18 ~

Table 4 Brine Compositions Example ~ MgC12 NaCl CaC12 pH
(gpl) (gpl) (gpl) 1 - 300 - 1.5 2 - 250 - 1~5 3 - 269 15 1.5

4 ~ 269 33 1.5 - 269 33 ~.5 6 - 269 33 1.5 7 280 - 33 1.5 8 50 220 33 1.5 9 - 269 33 1.5 - 269 33 1.5 3~

. . . -- , ~ 1 5~04~

Table 5 Extractions of Lead and Silver Example# P~ extraction (%) Ag extraction (%) :~ 9 97 71 ~: 10 96 69 1 1 5 ~
Table 6 Lime ~ddition and Plumbate Product ~Dry Basis) Assays ~wt.%) Total Example # Lime Ca Cl Fe Zn Ag (oz/ST) to lead 1 3.0 60 22 0.6 1.4 1.5 34 2 1.75 67 12 4.8 1.8 1.9 38 3 ~.0 51 29 0.3 1.2 1.2 27 4 3.0 ~0 22 0.4 1.2 1.1 41

5.5 42 36 0.2 1.0 1.0 17

6 3.0 57 21 0.4 1.3 3.3 <1

7 3.0 59 22 0.4 1.3 1.3 37

8 3.0 60 22 0.5 1.2 1.3 38

9 3.0 54 20 0.4 3.0 3.0 50 3.0 61 22 0.5 0.7 0.7 40 j~ ' ", 0 ~ 8 treatecl in an oven with ;~ slow purge o~ fresh air for 1.0 hours at 400C. The calcines were repulped to 50% pulp density for 15 minutes in rresh w~ter and filtered and displacement washed with a volum~ of water equal to the calcine repulp water. The assays (dry basis) of the resulting plumbate products are given in Table 6.

Example 11 A sample of the hot sulfuric acid leach residue used in example 5 was repulped in water at 10~ pulp density, American Cyanamid flot~tion reayents Aero 404 (trade mark~ promoter and Aerofroth 77A
(trade mark) (~rother) were added at 600 g. and 60 q. per metric ton of residue respectively. After 5 minu~es conditioning time, flotation was initiated and a stable froth was maintained for about 7.5 minutes.
The concentrate obtained assayed 18~ Pb, 24% Fe, 1.8% Zn, and 635 oz/ST silver. Silver recovery from the head material was 70%.
The tailings from the flotation were treated in the process exactly similar to example 4. Silver recovery from the tailings was 35%, result;ng in an overall silver recovery of 81~.

As will be apparent to those skilled in this art, the process of this invention may be applied to the recovery of metals from a variety of metallurgical products such as ores and concentrates, ~melter dusts, metal drosses, middling concentrates from ~lotation ~rocessing, slags and process residues, and other like sources oE
lead and silver,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process comprising the steps of (1) preparing a solution of lead chloride by dissolving lead sulphate contained in an ore or process residue in an acidic concentrated chloride brine; (2) separating the solution so formed from insoluble gangue or other residue; (3) forming a precipitate of lead oxychloride by adding lime to said solution and separating said lead oxychloride precipitate from the residual lean brine solution; (4) recycling said lean brine for reuse in the further extraction of lead sulphate as under steps (1) and (2); the improvement which comprises (5) reacting the said oxychloride precipitate with oxygen and lime in a reactor at a temperature above 325°C for longer than 0.5 hours to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides; (6) repulping said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (7) separating the residue obtained in step (6) from the resulting chloride brine; (8) recycling the brine resulting from (7) for reuse in the further extraction of lead sulphate as under steps (1) and (2);
(9) washing said residue containing calcium plumbates and/or lead oxides resulting from step (7) with fresh water to remove residual chlorides; and (10) recycling the chloride brine obtained in step (9) to step (6) and/or recycling the said chloride brine for reuse in the further extraction of lead sulphate as under steps (1) and (2).

2. In a process for gaining lead and silver values comprising the steps of (1) preparing a solution of lead chloride and silver compounds by dissolving lead sulphate and silver compounds contained in an ore or process residue in an acidic concentrated chloride brine; (2) separating the solution so formed from insoluble gangue or other residue; (3) forming a precipitate of lead oxychloride and silver compounds by adding lime to said solution and separating said precipitate from the residual lean brine solution for recycling said lean brine for reuse in the further extraction of lead sulphate as under steps (1) and (2); the improvement which comprises (5) reacting the said oxychloride precipitate with oxygen and lime in a reactor at a temperature above 325°C for longer than one half hour to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides and most of the silver as silver or silver compounds; (6) repulping said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (7) separating the residue obtained in step (6) from the resulting chloride brine; (8) recycling the brine resulting from (7) for reuse in the further extraction of lead sulphate as under steps (1) and (2); (9) washing said residue containing calcium plumbates and/or lead oxides, as well as silver and silver compounds resulting from step (7) with fresh water to remove residual chlorides; and (10) recycling the chloride brine obtained in step (9) to step (6) and/or recycling the said chloride brine for reuse in the further extraction of lead sulphate as under steps (1) and (2).

3. A process as in Claim 1 wherein the lime in step (5) is excess lime present in the precipitate from step (3).

4. A process as in Claim 3 wherein fresh lime is added to supplement the excess lime present in the precipitate.

5. A process as in Claim 2 wherein the lime in step (5) is excess lime present in the precipitate from step (3).

6. A process as in Claim 2 wherein the fresh lime is added to supplement the excess lime present in the precipitate.

7. A process according to Claim 1 wherein the concentrated chloride brine comprises a saturated or nearly saturated solution at room temperature of one or more inorganic chlorides in water.

8. A process according to Claim 1 or Claim 2 wherein one component of the chloride brine is calcium chloride.

9. A process according to Claim 1 or Claim 2 wherein the chloride brine comprises an aqueous solution of calcium chloride and one or both of sodium and magnesium chloride.

10. A process according to Claim 1 or Claim 2 wherein the chloride brine includes calcium chloride, and wherein the mole ratio of calcium chloride to lead sulphate is greater than 4.

11. A process according to Claim 1 wherein step (1) is performed at a temperature in the range 30°C to the boiling point of the chloride brine, at a pH between 1.5 and 4.5, and a retention time of 0.5 - 2.5 hours.

12. A process according to Claim 11 wherein the temperature is ambient.

13. A process according to Claim 11 wherein the pH is controlled at 1.5.

14. A process according to Claim 11 wherein the retention time is 1.5 hours.

15. A process according to Claim 1 wherein step (3) is performed by adding lime at a mole ratio of between 0.75 and 5.5 to dissolved lead.

16. A process according to Claim 15 wherein lime is added at a mole ratio of 1.5 to dissolved lead.

17. A process according to Claim 15 wherein the retention time is between 0.5 and 2.5 hours and the temperature in the range 30°C to the boiling point of the chloride brine.

18. A process according to Claim 17 wherein the retention time is 1.5 hours and the temperature is ambient.

19. A process according to Claim 1 wherein step (5) is performed by adding lime to the said oxychloride precipitate to increase the total of the lime additions in step (3) and step (5) to between 1.75 and 5.5 mole ratio to lead.

20. A process according to Claim 19 wherein the total lime addition is 3.0 mole ratio to lead.

21. A process according to Claim 1 wherein step (5) is performed at a temperature above 350°C for longer than 0.5 hours.

22. A process according to Claim 21 wherein the temperature is 400°C for 1.0 hour.

23. A process according to Claim 1 wherein step (5) is performed with a mole ratio of oxygen to lead in excess of 0.5

24. A process as in Claim 23 wherein the oxygen is in the form of air.

25. A process according to Claim 2 wherein lead and silver are recovered in the residue from calcine washing step (9).

26. A process according to Claim 1 wherein lead is recovered in the residue from calcine washing step (9).

27. A process according to Claim 2 wherein silver is recovered by cementation on one of metallic zinc, iron, or lead between step (2) and step (3).

28. A process according to Claim 2 wherein a portion of the silver is recovered from the lead sulphate containing material by flotation prior to step (1).

29. A process according to Claim 1,steps (3), (5), (6), (7), and (9) inclusive,wherein the solution from which lead oxychloride is precipitated , is any chloride brine solution containing lead chloride.

30. A process according to Claim 29 wherein the chloride brines lean in lead resulting from any or all of steps (3), (7), and (9) are recycled to dissolve fresh lead chloride.

31. A process as in Claim 1 or 2 wherein the brine is concentrated before recycling.

32. A process as in Claim 1 or 2 wherein the brine is concentrated by evaporating or by adding further chloride before recycling.

33. A process as in Claim 1 or 2 wherein the brine is re-acidified before recycling.

34. A process as in Claim 1 or 2 wherein the acidic concentrated chloride brine has a pH of about 1.5.

35. A process according to Claim 2 wherein step (1) is performed at a temperature in the range 30°C to the boiling point of the chloride brine, at a pH between 1.5 and 4.5, and a retention time of 0.5 - 2.5 hours.

36. A process according to Claim 35 wherein the temperature is ambient.

37. A process according to Claim 35 wherein the pH is controlled at 1.5.

38. A process according to Claim 35 wherein the retention time is 1.5 hours.

39. A process comprising the steps of (1) preparing a solution of lead chloride by dissolving lead sulphate contained in an ore or process residue in an acidic concentrated chloride brine; (2) separating the solution so formed from insoluble gangue or other residue; (3) forming a precipitate of lead oxychloride by adding lime to said solution and separating said lead oxychloride precipitate from the residual lean brine solution; (4) reacting the said oxychloride precipitate with oxygen and lime in a reactor in an elevated temperature to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides; (5) washing said calcine in water and/or dilute chloride brine to dissolve soluble chlorides;
(6) separating the resulting residue obtained from the resulting chloride brine; and, (7) washing said residue contain-ing calcium plumbates and/or lead oxides with fresh water to remove residual chlorides.

40. A process as in Claim 39 wherein the chloride brines resulting from the steps are recycled for reuse in the process.

41. A process for gaining lead and silver values comprising the steps of (1) preparing a solution of lead chloride and silver compounds by dissolving lead sulphate and silver compounds contained in an ore or process residue in an acidic concentrated chloride brine; (2) separating the solution so formed from insoluble gangue or other residue; (3) forming a precipitate of lead oxychloride and silver compounds by adding lime to said solution and separating said precipitate from the residual lean brine solution; (4) reacting the said oxychloride precipitate with oxygen and lime in a reactor at an elevated temperature to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides and most of the silver as silver or silver compounds; (5) washing said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (6) separating the resulting residue from the resulting chloride brine; and, (7) washing said residue containing calcium plumbates and/or lead oxides, as well as silver and silver compounds, with fresh water to remove residual chlorides.

42. A process as in Claim 41 wherein the chloride brines resulting from the steps are recycled for reuse in the process.

43. In a process comprising the step of (1) forming a precipitate of lead oxychloride by adding lime to a chloride brine solution containing lead chloride, and separating said lead oxychloride precipitate from the residual lean brine solution; the improvement which comprises (2) reacting the said oxychloride precipitate with oxygen and lime in a reactor at a temperature above 325°C for longer than 0.5 hours to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides; (3) repulping said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; (4) separating the residue obtained in step (3) from the resulting chloride brine;
and (5) washing said residue containing calcium plumbates and/or lead oxides resulting from step (4) with fresh water to remove residual chlorides.

44, A process according to claim 43 wherein the chloride brines lean in lead resulting from any of the steps (1), (4) or (5) are recycled to dissolve fresh lead chloride.

45. A process according to claim 44 wherein the brine is concentrated before recycling.

46. A process according to claim 45 wherein the brine is concentrated by evaporating or by adding further chloride before recycling.

47. A process according to claim 44 wherein the brine is re-acidified before recycling.

48. A process according to claim 47 wherein the acidic concentrated chloride brine has a pH of about 1.5.

49. A process for gaining lead and silver values comprising the steps of (a) preparing a solution of lead chloride and silver compounds by dissolving lead sulphate and silver compounds contained in an ore or process residue in an acidic concentrated chloride brine; (b) separating the solution 50 formed from insoluble gangue or other residue; and (c) forming a precipitate of lead oxychloride and silver compounds by adding lime to said solution and separating said precipitate from the residual lean brine solution characterized by the further steps of (1) reacting the said oxychloride precipitate with oxygen and lime in a reactor at an elevated temperature to produce a calcine containing most of the lead as calcium plumbates and/or lead oxides and most of the silver as silver or silver compounds; (2) washing said calcine in water and/or dilute chloride brine to dissolve soluble chlorides; and (3) separating the resulting residue containing calcium plumbates and/or lead oxides, as well as silver and silver compounds, from the resulting chloride brine.