DE2602827A1 - PROCESS FOR TREATMENT OF A PRECIOUS METAL CONCENTRATE - Google Patents

Description

UEXKÜLL a GTOLBERG PATENTANWÄLTE

2 HAMBURG 52

BESELEIRSTRASSE 4 DR. J.-D. FRHR. by UEXKÜLL

"y R Tx" ^ $ *} "7

4 £ OU> £ © £ / DR-ULRICHGRAFSTOLBERG

DIPL.-ING. JÜRGEN SUCHANTKE

National Institute (Prio. January 29, 1975

for Metallurgy _{ZA 75/0593} _ ₁₂₈₅₃₎

1 Yale Road, Milner Park

Johannesburg / South Africa Hamburg, January 26, 1976

Process for the treatment of a concentrate containing precious metals

The invention relates to a method for treating mixtures from metals of the platinum group, gold and silver and in particular the treatment of so-called platinum metal concentrates such as residues of sulphide brines and the like, and also of various solid intermediate products such as insoluble leaching residues, etc., which can arise in the processing of such materials.

All economical refining processes for metals of the Platinum groups are basically hydrometallurgical processes. The first and essential step in this procedure is hence the dissolution of the valuable components from the starting material.

However, the platinum metals are extremely difficult to dissolve and highly active media such as aqua regia are generally found use during extended leaching times. Self

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under extremely severe leaching conditions will generally a complete dissolution of the valuable accompanying metals is not achieved, and in particular the secondary platinum metals (Rhodium, ruthenium, iridium and osmium) are only attacked to a small extent. In addition, the degree of dissolution of the metals varies greatly from batch to batch and in the generally depends on the type of process steps which the starting material is used before the leaching of the platinum metals has been subjected.

Because of these difficulties, it is common practice to multi-stage processes with pyrometallurgical and hydrometallurgical To apply steps to achieve the dissolution of the platinum metals. A widely used application Finding series of steps is the following:

1) Performing an initial treatment on a concentrate of platinum metals, gold and silver with aqua regia

2) Melting the residue with black lead and a reducing agent to form an alloy of lead and platinum metals

3) Treating the resulting lead with nitric acid as a separating medium

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4) Treating the residue of step 3) with aqua regia.), .- which vden- largest · - ^ e il. -.from; .Platinum and ^ palladium ·; · however, only a little of the secondary platinum metals dissolves

.5) Melting the back, which is rich in secondary platinum metals. Standes with sodium peroxide and

6) Treating the melting cake with water and neutralizing with hydrochloric acid to obtain a solution of the chlorides secondary platinum metals.

Various circulatory streams occur when practicing this currently used procedure.

A large number of steps are required and a substantial proportion of the platinum metals are in the recycle streams bound. Many of the circulatory streams are at the beginning in the form of solutions; in order to isolate the precious metals contained in these currents, they must first be made insoluble will. Generally, reduction to metal using zinc as a reducing agent does, however this step is time consuming, expensive, and not completely effective.

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In addition, it is generally stated that many noble-'inetallhaltigeix. Raw materials. a gr.oßejc .. part: the .. in it., contained base metals are not effective before leaching which allows platinum metals to be separated using a milder leachant such as sulfuric acid. These Base metals therefore contaminate the. Precious metals, de- ... hold leachates and thus do both the refining steps and recycle considerably more difficult.

The invention is based on the above difficulties in refining platinum overcome by

1) a procedure is proposed by means of which a a large proportion of the base metal content in the starting material is effectively separated from the noble metals lets before the dissolution of the precious metals themselves takes place and / or

2) a method is proposed, with the help of which a large proportion of the contained in the starting material Precious metals in a single step under

• Use of chlorine as an oxidizing agent and hydrochloric acid as a solvent can be dissolved and / or

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3) a method is proposed, with the help of which the · noble! Metal-containing liquid cycle flows ■■ easily- '' · '* · can be worked up so that the noble metals contained therein are isolated without intermediate reduction with zinc can be done by taking the reduction during the

- · ·., ··. Separation of base metals. · ■

In the present context, “precious metals” are understood to mean mixtures of some or all of the platinum metals, which above may also contain gold and / or silver. "Base metals" include all metals except the previously mentioned "precious metals" Understood.

The invention accordingly provides a method of treatment a precious metal-containing concentrate, which is characterized in that an alloy of aluminum and Generated precious metals and at least the majority of the precious metals by means of a suitable leaching process in solution recovers.

According to a preferred embodiment of the invention the alloy is first subjected to a leaching step serving to separate the base metals, while the noble metals subsequently recovered in a second leaching step under strongly oxidizing conditions, the leaching the base metals is carried out in two steps, viz

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first under reducing conditions by means of a weak acid, - ^. during the. · second. · step-under - conditions · carried out --- · '·· - ■ ··. * ·> ^{: which} leads to the dissolution of Copper are suitable.

The alloy of aluminum and precious metals preferably has a. Aluminum! Precious metal? Ratio between about. 1O: -1- and 1: -1. · - ■ · on.

The formation of the aluminum alloy can be accomplished in a number of ways, but the following three approaches have proven to be useful proven to be particularly favorable, which can be used for concentrates of various quality and composition:

1) Concentrates with a high precious metal content (above about 50%) and essentially metallic character (for Example lead residues after the divorce) can be treated as follows:

a) The material can simply with an equal weight of aluminum at a temperature above TOOO C under "a protective atmosphere" to avoid " an oxidation of the aluminum are melted together.

b) The material can be mixed with a small proportion (5 to 25% by weight) of a suitable base metal oxide or sulfide, preferably iron (III) oxide or iron (II) sulfide, and

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a sufficient amount of aluminum powder, preferably-.weise ... the G.ewicht, of a _{.Kpnzentjrats:} appropriate amount are mixed. This mixture is then ignited in a suitable manner, so that the base metal oxide and the aluminum react and the aluminothermic reaction that sets in generates the heat required for the formation of the alloy.

2) Concentrates with a medium precious metal content (between about 30 and 50%) with a high base metal content but low silica concentrations (less than 5%), but which are preferably free of silica, can be treated similarly as described above, apart from of the fact that there is often a sufficient amount of base metal oxides or sulfides present so that the addition of further iron (III) oxide or iron (II) sulfide is unnecessary is. The addition of some flux such as calcium oxide (CaO) can be useful in cleaning up what is formed during the reaction To make alumina soluble in the solvent for the base metals. These types of concentrates include certain residues of sulphide brine and residues after an initial leaching.

3) · Materials with a medium or low precious metal content (Precious metal content of less than 30%) with a high content of base metals and a high silica content are preferably initially alloyed with iron,

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whereupon the iron / precious metal alloy thus obtained continues Mt ^>; Aluminum is' alloyed ',' ^:: "to 'obtain' an 'alloy' ^? '"'"V" · which contains about 30% Fe, 30% Al, 30% precious metals and 10% other base metals such as Ni, Pb , Cu, etc. This step is more conveniently carried out - although not necessarily in an electric arc furnace - as follows:

a) The concentrate is mixed with coal and lime, pelletized and possibly reduced at about 800 C existing precious metal oxides roasted to metal.

b) The roasted material is melted together with scrap iron in an electric arc furnace, so that a Alloy with a precious metal content of about 50% and a calcium-iron-silica slag is created, which has a low precious metal content.

c) The slag is poured off, after which aluminum scrap is added to the iron alloy in such an amount becomes that an alloy with an Al content of about 30% is formed.

This procedure is particularly suitable for concentrates with a high silica content and a low precious metal content, for An example of certain residues from sulphide ore leaching can of course also be used in other cases Find.

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In all of the above cases, the alloy formed in this way is "then - preferably - as". · Follows · ■ further treated ί

1) The aluminum and iron content of the alloy become common under strongly reducing conditions under

,. , ..,. application of a weak acid, depleted. All circular; . . currents, which are acidic and contain precious metals can be used in this step. It was a very effective precipitation of the precious metals is observed and the exhausted leaching liquid only shows has an extremely low precious metal content.

2) The residue from the first leaching is then subjected to a more intensive leaching at a potential which is sufficient to dissolve copper. Many known methods are available for this purpose And in particular the Falconbridge leaching system, which works with a precisely set potential (Journal of Metals, May 1975, pages 6-9 "The recovery of nickel copper and a precious metal concentrate form high grade precious metal mattes "L.R. Hougan, H. Zacharissen) using gaseous chlorine as Oxidizing agents can be used here.

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3) The residue of the second Auslaugschrittes will subsequently with · hydrochloric acid "commercial ^starch;" (such as "10 * 'n)' - ^'· treated using chlorine gas as the oxidizing agent This leaching has proven to be rapidly and completely, and if. a residue remains - if it remains, it consists of insoluble substances such as silicic acid and aluminum oxide with a low noble metal content of typically less than 5000 ppm noble metals in total.

Various experiments that have been carried out so far are described below are described in order to explain the implementation of the invention by means of individual examples.

example 1

The concentrate treated in this case had an intermediate platinum metal content and came from a copper-nickel sulfide ore leach plant. The concentrate contained about 30% precious metals (platinum metals + Au + Ag) and about 30% base metals, the remainder being oxygen, sulfur and silica. was standing. A sample of this material was first treated with 12 η hydrochloric acid using chlorine as the oxidizing agent, whereby the following parts of the precious metals dissolved:

Pt Pd Ph Ru Ir 80.8% 70.7% 32.7% 14.6% 64.8%,

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These results could be significantly improved by one: · .- ,. - Another ·· sample of the ^ material was subjected to a 'reductive " ^Y " roasting before the "leaching", but complete dissolution was still not achieved, as the following values for the proportion of dissolved platinum metals show:

Pt Pd Ph Ru Ir 98.4% 98.3% 81.9% 52.4% 96.9%

A third -probe of the material was then reduced by aluminothermic with an equal weight of aluminum powder, placing the two components are mixed together and the mixture was fired by heating at about 100O ⁰ C. The reacted material was first treated with 12 η hydrochloric acid to remove aluminum and base metals and then with 12 η hydrochloric acid and Cl ₂ as an oxidizing agent to dissolve the platinum metals. The results for the leaching of this reaction mass were as follows:

Pt Pd Rh Ru Ir 99.6% 99.4% 87.8% 96.9% 96.9%

The residue remaining after the leaching thus had a markedly lower platinum metal content and could in practice be returned to the ore smelting furnace.

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1602827

Example 2
,, ...-.- JDaS-, in ... this example -used- · concentrate ahholte ^ de ^ zmfor "■ '■' described, however, had a lower precious metal content (- 20%) and was of its whole kind The following results were obtained by treating this raw material with 12 η hydrochloric acid and chlorine:

Pt Pd Rh Ru Ir 63 _y 9% 53.7% "30.9% 16.4% 45.2%

In this case, reducing roasting of the material before leaching did not bring as much improvement as in Example 1, because only the following shares of precious metals were dissolved:

Pt Pd Rh _f Ru Ir

89.2% 94.2% 38.1% 3.4% 16.5%

After an aluminothermic reduction in the same manner as described in Example 1 were after the subsequent Resolution get very good results:

Pt Pd Rh Ru Ir ....

99.3% 99.4% 97.6% 95.6% 87.3%

This example also shows that the base metals can be separated practically completely by leaching with sulfuric acid _{prior to the HCl / Cl 2 treatment, if one under}

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oxidizing conditions works. The following resolution - .. -as-typicalr.

Cu Ni Fe Cr Al

91.2% 85.5% 87.7% 25.5% 95

The proportion of platinum metals dissolved together with the "base metals" was negligibly small.

Example 3

The concentrate treated was a concentrate of secondary platinum metals, which accrued during the divorce and aqua regia treatment of a lead obtained as described above; it contained about 60% platinum metals, 20% lead and 20% other base metals.

Both a direct treatment with HCl / Cl- and a corresponding one Leaching after previous reduction with hydrogen proved almost completely ineffective with this material, as the following values show:

Ru Rh ■ Ir without pretreatment 0% 18.5% 2.2%

with hydrogen reduction

as a pre-treatment. 5.7% 14.6% 6.7%

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A sample of this concentrate was then made by ·. -Mixing it with .an-equal-.weight quantity - aluminum powder · ¹ and ·· ■ -. '. Treated 20 wt.% FeS. This mixture was ignited by heating to 1000 ° C. and the reaction mass was first treated with 200 g / l sulfuric acid to remove the base metals and aluminum, and then subjected to a treatment with- · - ....- 12 η HCl / Clp . After leaching for two hours, the following dissolution values were achieved.

Ru Rh Ir

89.6% 92.9% 95.8%

This experiment was repeated on a larger scale and it was found that practically all of the added and the base metals originally present were dissolved by sulfuric acid. The subsequent HC 1./Cl ₂ treatment gave similar dissolution values after two hours, namely

Ru Rh Ir

90.8% 93.1% 90.3%

A third experiment was carried out with this concentrate, in which 5 kg of concentrate were treated in a similar manner as before. The alloy was first treated with 10 η HCl with the addition of 500 g Fe ₃ O ₃ until the noble metals just began to dissolve. It was filtered immediately afterwards and an analysis showed 45 ppm of noble

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metals, 7 g / l Fe, 3 g / l Pb and 120 ppm Cu. Then -., · ... · - .. with vI.Q • 'nvHCi / Clvj. leached / ■■ this-handling was extended to eight hours in contrast to the two-hour test duration. The increase in the leaching time increased the dissolution values considerably, as the following values show:

Ru _c Rh Ir

99.1% 99.5% 99.3%

The leaching liquid contained 54 g / l precious metals, 150 ppm Cu and 1.6 g / l other base metals, which simultaneously shows that most of the base metals had previously been separated.

The above leaching process was in contrast to the preferred three step process previously described in two Steps executed. The results of the three-step process are not yet available, but it is from the following Reasons preferred to dissolve the copper in a separate step. When dissolving iron, aluminum and similar base metals, strong, reducing conditions prevail, if with Hydrochloric acid or sulfuric acid solution is used. In this step there is practically no possibility that also solve precious metals. In the second step, which serves to dissolve the copper, more oxidizing conditions prevail, so that the possibility increases that noble

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dissolve metals. In addition, a much smaller .. ,, .. -, vessel., Is required,. · To -dissolve -the copper-then- ■ - · to be carried out so that even smaller volumes of solution have to be worked up on dissolved noble metals. The conditions in each of the first two solution steps can "be" optimized and a system can be made easier to achieve optimal efficiency to adjust.

Example '4

This example illustrates another method of practicing the invention. A concentrate similar to that of Example 3 was mixed with an equal amount by weight of aluminum powder and the mixture was melted together in a muffle furnace at 1000 ° C. for two hours. After the molten mass had cooled, it was _{treated with 200 g / l H 7} SO ₄ to remove the aluminum and the base metals, whereupon the residue was dissolved in 12 η HC1 / C1 ₂ . The degrees of resolution in% in this case were as follows:

Ru Rh Ir

. .95.6. %. . 91, -5% - 96.3%

. Example 5

· An approximately 20% precious metals, 16% silica and 14% iron oxides containing concentrate was at with charcoal for one hour

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8OO ° C heated. The added amount of coal depends on the content • of iron and platinum group metals · · y from which in the form "of -. ^ Oxides" ·· "■ · * ''·" · present. The duration of roasting depends on the kinetics of the reduction process and therefore varies with the temperature, composition, particle size and mineralogy of the material.

The reduced material was divided into two parts, each of which was further treated as follows.

The reduced material was melted together with lime (CaO) in an amount of about 1 part at 16000 ° C; Scrap iron was added and the melt was cooled. The metal was separated from the slag and proportioned with aluminum of 0.4: 1 alloyed from aluminum to precious metal alloy at 1600 C by first melting the metal and then solid aluminum to which metal has been added. After cooling, the aluminum alloy with 10 η HCl treated and the residue was dissolved in 10 η HCl and chlorine, no residue remaining. The recovery of the various platinum metals from the solutions results from the following table:

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Tabel

Precious metals in the initial sample in%

Precious metals in the slag in ppm

Noble metals in the HCl solution in ppm Pt Pd "Rh Ru 'Os Ir Au 1.11 6.40 2.99 6.51 1.43 0.44 670 ppm

2434 (920)

(4.3)

Precious metals in the

HCl / Cl solution in ppm 700 5063 2019 4438 850 3151600

(743) (5583) (2O19) (4775) (835) (330) (1714)

retained in the slag Precious metals in%

Precious metals recovered from the alloy in% by forming the difference

Precious metals recovered from the alloy (calculated from the values of the HCl / Cl ₂ solution). 3 (1.4)

97 (98.6)

109.3 (108.1)

The differences in the values for the recovery of the precious metals are obviously due to analytical errors. The numbers in brackets refer to the second Half of the original reduced material.

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Example 6

JSChIIeBiICh _- -WUrOe ^ cLLe, -use · of · a · precious metal · ■ · - - - - ■ - · - - - - - - - - - - - - - - - - - - - - - - - investigated the precipitation effect through the aluminum alloy.

..40. Liters of an artificially produced circulatory stream of about 2 η HCl and containing

Ru Rh Pd Pt Ir 6000 ppm 5031 ppm 735 ppm 3 ppm 1250 ppm

were with 1 kg of a crushed aluminum / precious metal alloy brought together. The alloy had a 100% particle size of less than 1.25 cm clear mesh size and the treatment was carried out for 6 hours at 60 ° C.

The solution was filtered off and had the following values:

Ru Rh Pd Pt Ir 1.5 ppm N.N. 0.4 ppm N.N. 6 ppm

(N.N. means not detectable)

The precipitation thus apparently took place with a high degree of efficiency instead of.

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■ - 20 ■ - ·

The experiments described above were carried out in order to. “... ·. ·. show, -'mxt .daß.ein -.erfindungsgemäßes process -in -the · ^{Practice; "} '*'■" good success is feasible. When using hydrochloric acid, a strength of either 10 η or 12 η was used. However, it should be clear that acid of any strength can be used, but more dilute acids require longer treatment times in order to achieve the same result. Any sulfuric acid concentration up to a maximum strength of about 500 g / liter can also be used.

The invention thus provides a method which has the following characteristics:

1) It enables the existing base metals to be separated prior to the dissolution of the platinum metals by leaching with dilute sulfuric acid or hydrochloric acid and

2) it increases the solubility of platinum metals in an oxidizing hydrochloric acid solution to a very large extent, so that practically complete dissolution is achieved.

The method can be applied to any platinum metal-containing material as it is in the various stages of

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conventional refining processes and in particular ■ is suitable: it. to work up the following materials:

1) Raw material for the refinery, which makes it unnecessary to subsequently treat the residue. In practice

. : - would this residue, if it occurs at all, be due to the high value of the platinum metals despite the low platinum metal content at an earlier stage of the process, for example to the sulphide melt,

2) the residue from the first leach and

3) the residue from the divorce and aqua regia leaching of the lead, with an application of the procedure takes the place of the potentially dangerous sodium peroxide melt.

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Claims (10)

Claims 1. Process for the treatment of a concentrate containing precious metals, characterized in that an alloy of aluminum and precious metals is produced and at least the .Main part, the. Precious metals, by means of .a, suitable .. ·. Recovered leaching process in solution. 2. The method according to claim 1, characterized in that the alloy is initially used for the separation of base metals under conditions which dissolve the Prevent precious metals from being leached with an acid, and that you can use the residue of the first leach to dissolve which leaches precious metals under strongly oxidizing conditions. 3. The method according to claim 1, characterized in that the alloy is first used to remove the main component of base metals leached with an acid under strongly reducing conditions so that the residue of this first leaching then leaching with an acid under conditions such that copper dissolves, and that the remaining residue is finally ■ Dissolution of precious metals under strongly oxidizing conditions leaches. 609832 / 0S49 COPY 4. The method according to claims 2 or 3, characterized in that • draws - that. .-one the, · first-leaching · for · removal · 't "■ · ■ · ■ · ■ of the main part of the base metals with hydrochloric acid or sulfuric acid. 5 ... Method according to claim A ₁ . characterized, in that a * is used as an acid recycle stream which contains small amounts of precious metals, which are precipitated during the discharge process. 6. The method according to claims 1 to 5, characterized in that that the noble metals are dissolved in hydrochloric acid using gaseous chlorine as an oxidizing agent. 7. The method according to claims 1 to 6, characterized in that that the alloy is finely divided by mixing the concentrate with a suitable amount Aluminum and heating the mixture to form a molten alloy. 8. The method according to claim 7, characterized in that · one of the mixture to achieve a strongly exothermic adding a sufficient amount of base metal oxides and / or sulfides to the aluminothermic reaction. 609832/0649 9. The method according to claims 1 to 6, characterized in that ^ that., one.the, aluminum.alloy.ng..thereby · .-, represents that one starts with an iron / precious metal alloy forms, separates the silica contained in the slag formed and adds the required amount of aluminum the iron alloy clogs. 10. The method according to claims 1 to 9, characterized in that that the aluminum alloy has a weight ratio of aluminum to noble metals of 10: 1 to 1: 1. coll 6O9832 / QS49 COPY