FI120315B - A process for treating a pyrite concentrate containing gold, copper and arsenic - Google Patents

Description

METHOD FOR THE TREATMENT OF PYRITIC, GOLD, COPPER AND ARSENIC

FIELD OF THE INVENTION

The invention relates to a process for the treatment of a pyrite copper sulphide concentrate which contains, in addition to copper, arsenic and fine or invisible gold bound to sulphide minerals. In the process, the concentrate is dissolved in a solution containing chloride. The leaching of the raw material is carried out under conditions in which the copper, iron and arsenic of the raw material dissolve, but the gold-containing material remains insoluble. The resulting chloride solution is passed to neutralization where it is doped with iron and arsenic. The purified copper solution is led to liquid-liquid extraction. In the leaching back extraction step, the copper is transferred to a sulfate solution which is led to copper electrolysis. Gold is recovered from the leaching residue in some known manner.

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BACKGROUND OF THE INVENTION

The problem with many gold-copper concentrates is that a significant proportion of gold is bound to pyrite as an invisible gold. This is the case, for example, in gold-copper ores containing arsenic, where up to 50% of the gold is in pyrite. The remainder of the gold is either metallic or bound to enargite (CU2ASS4), arsenopyrite (FeAsS), and other minerals. Such ores also contain copper, most often in the form of enargite or chalcopyrite (CuFeS2). Exploitation of these ores requires the preparation of a bulk concentrate containing copper, free gold and a maximum of 25 pyrites. The treatment of arsenic and the high content of pyrite sulfur place the main constraints on establishing a profitable overall process for such a concentrate.

WO patent application 2004/035840 describes a process for recovering metals, particularly copper, from a copper-containing raw material, wherein the material is dissolved in a chloride-containing solution. The leaching of the raw material is performed oxidatively at a pH of at least 1.5 and at a redox-2 potential of 480-500 mV vs. Ag / AgCl, whereby the copper in the leaching copper chloride solution is essentially bivalent. At the same time, the sulfur contained in the concentrate precipitates elementally, and iron also precipitates. The precious metals contained in the concentrate do not dissolve but go into the leaching residue.

5 The leaching residue is subjected to sulfur foaming to give a sulfur concentrate which also contains precious metals (gold + PGM). The major part of the sulfur is separated from the sulfur concentrate in known ways and thus a precious metal PGM concentrate is formed. The chloride solution formed during the leaching of the raw material, containing copper and other possible precious metals, is led to liquid-10 liquid extraction. In the extraction, the copper is first transferred to the organic phase by extraction and back-extracted to a sulphate solution which is led to copper electrolysis. There is no mention of how the arsenic in the raw material behaves, nor how the sacred gold-containing sanctum is recovered.

U.S. Patent No. 4,023,964 describes a process for making copper. In the process, the copper sulphide concentrate is dissolved in a copper (II) chloride-sodium chloride solution. The solution has a NaCl concentration of 100-300 g / l and a pH of not more than 1, at which time the iron dissolves. The resulting solution, in which copper is predominantly monovalent, is divided into two portions, one of which is subjected to iron deposition as goethite by introducing air into the solution. The cupric chloride solution formed during the goutite precipitation is recycled to concentrate leaching. The second portion of the solution is led into contact with the extraction solution. During the extraction, air is introduced into the solution to oxidize the monovalent copper 25 to the divalent copper. In the extraction, the copper binds to the organic phase and the copper depleted cupric chloride solution is recycled to concentrate leaching. In the back extraction, the organic phase and the copper bound thereto are contacted with aqueous sulfuric acid. The resulting copper sulfate solution is led to the elemental copper preparation and the organic phase 30 back to the extraction step.

The process described in U.S. Patent No. 4,023,964 is useful in that it dissolves the copper sulphide concentrate as chloride, which is passed to liquid-liquid extraction and the copper is recovered as a copper sulphate solution. Further treatment of the copper sulfate solution, for example by electrolysis, is well known in the art and produces pure copper. The process is complicated by the fact that the solution is divided into two branches, one of which precipitates the dissolved iron and only one of which is led to extraction. In the copper chloride solution from the leaching, the copper is mainly monovalent, whereby it must be separately oxidized during leaching. When oxidation occurs with extraction, there is a risk that the extractant will also oxidize and be unusable. The process preferably recommends extraction at a temperature of 60 ° C, which is practically too high and causes destruction of the extractant. The method does not address the treatment of arsenic-containing materials or the behavior of gold or, more generally, gold in pyrite.

PURPOSE OF THE INVENTION

A process has now been developed for the treatment of pyrite copper sulphide concentrates containing gold, copper and arsenic. Copper chromium, pyrite, enargite and 20 other bulk arsenic-containing minerals, such as arsenic chromium, are concentrated in aqueous chloride solution under conditions where copper, iron and arsenic are dissolved but the pyrite and gold remain in the leaching residue.

SUMMARY OF THE INVENTION

The invention relates to a process for the treatment of a pyrite copper sulphide concentrate containing gold and / or platinum metals (PGM) and arsenic, wherein the concentrate is dissolved in an aqueous solution of copper chloride and an alkali chloride. It is typical of the process that the redox potential of concentrate leaching is adjusted by supplying an oxidizing agent to a range of 400 to 600 mV with respect to the Ag / AgCl electrode and the pH is adjusted to a range of 0.2 to 1, arsenic is soluble and 4 gold and / or PGM bound to these minerals are released. Pyrite and its gold and / or PGM and liberated gold and / or PGM and sulfur remain in the leaching residue. The formed iron and arsenic-containing cupric chloride solution is neutralized to precipitate iron and arsenic, then the neutralized iron and arsenic-free cupric chloride solution is subjected to a liquid-liquid extraction step, from which copper is recovered to an aqueous sulfuric acid solution and electrolysed to recover the elemental copper. The raffinate formed in liquid-liquid extraction is recycled to concentrate leaching.

According to one embodiment of the invention, the leaching residue is subjected to sulfur flotation. The gold and / or PGM-containing sulfur concentrate or leaching residue obtained from flotation is preferably subjected to a pyrometallurgical treatment to recover the gold and / or PGM, whereby they are introduced into the smelter or roasted. The leaching residue may also be subjected to hydrometallurgical treatment by pressure leaching.

According to the invention, the iron and arsenic-containing cupric chloride solution formed by leaching the copper sulphide concentrate is neutralized to a pH of 2 to 2.5 to precipitate iron and arsenic from the solution. The neutralization is preferably carried out with 20 limestone, lime or lye. Iron and arsenic are mixed from the solution as ferric arsenate and as goethite or ferric hydroxide.

A small amount of gold, possibly dissolved in the leaching step, is doped back into the leaching residue by means of a reducing agent or adsorbent. A typical adsorbent is activated carbon.

LIST OF FIGURES

The method according to the invention is illustrated by the following figure 1, which shows a flow diagram of a preferred embodiment of the invention.

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DETAILED DESCRIPTION OF THE INVENTION

The pyrite bulk concentrate containing gold, copper and arsenic is passed to a leaching step where the leaching is carried out with a solution of hydrochloric acid containing copper chloride and alkali chloride. In practice, the dissolution is generally carried out in 5 multi-steps, but for simplicity is described in the diagram as a single step. Dissolution is performed by counter-current or co-current. The redox potential of the leach is adjusted to 400-600 mV vs. Ag / AgCl by means of oxygen or other oxidant. The acid content of the leaching step is adjusted to be in the range of 20-100 g / l, whereby the pH is below 1, but preferably at least 0.2. Under these conditions, iron and arsenic dissolve, but sulfur precipitates. The generic term used in the description of the invention refers to gold and / or platinum metals (PGM).

The amount of alkali chloride used in the solution is in the order of 100 g / l. Alkali is preferably sodium. The amount of alkali chloride is relatively low, since the copper is bivalent in the solution, which means that even the amount of alkali chloride required is low. The leaching conditions are adjusted so that the iron in the concentrate, except for pyrite, is soluble in the same way as the arsenic in the concentrate. Gold does not dissolve, but 20 is liberated upon decomposition of enargite and other arsenic minerals and goes into leaching waste.

Reactions in the leaching process of the invention are illustrated by the following reaction formulas: 2Cu3AsS4 + 12H + + 5½ O2 = 6Cu2 + + 2H3ASO4 + 8S + 3H2O (1)

CuFeS2 + 4H + + 02 = Cu2 + + Fe2 + + 2S + 2H20 (2) 30 FeAsS + 202 + 3H + = S + Fe2 + + H3ASO4 (3) 6

If a small amount of gold has dissolved in the concentrate leaching step, it is precipitated back to the leaching residue by use of a suitable reducing agent or adsorbent, for example activated carbon. This is followed by a solution / solids separation to separate the sulfur, sacred and 5 gold in the solids. The arsenic-free leaching residue thus obtained is treated in a suitable manner to recover the gold. The leaching residue includes, in addition to sulfur, the gold released by the decomposition of minerals, the sacrificial agent and the gold contained therein, but not iron and arsenic. As a result, the amount of leaching residue is relatively small and has many possibilities for further treatment.

The leaching residue can be subjected to sulfur flotation (not shown in detail) to give a blender and sulfur concentrate containing almost all of the gold in the concentrate used as starting material. Depending on the composition of the leaching residue 15 or the further process, the leaching residue may also be treated without a sulfur enrichment step. The gold content of the sulfur concentrate formed and / or the leaching residue is so high that it can be subjected to pyrometallurgical treatment. This can happen, for example, in a smelter, where the recovery of precious metals is high. Another possible further treatment method is roasting, in which the sacred is oxidized and sulfur is burned and gold is dissolved from the roast with cyanide. The leaching residue can also be hydrometallurgically treated by pressure leaching in an autoclave, whereupon the sacred decomposes and gold can be liberally dissolved in cyanide.

When the leaching is carried out at the high acid concentration described above, the solution obtained in the solid separation must be neutralized before being introduced into the extraction step. In the process of the invention, the iron and arsenic are also removed from the solution by precipitation as ferric arsenate (FeAs04 2H2O) in the process of neutralization. Since the amount of iron is generally higher than that of arsenic, the excess iron is precipitated in the same step as goethite (FeOOH) or ferric hydroxide (Fe (OH) 3). Precipitation is effected by neutralizing the solution to a pH of about 2 to 2.5. The neutralization 7 is carried out with a suitable neutralizing agent such as limestone, lime or lye (NaOH).

The divalent copper chloride solution 5, purified from impurities and solids, is subjected to extraction. Copper back extraction from the organic solution is carried out in aqueous sulfuric acid which is subjected to electrolysis to recover the elemental copper. Since known copper extraction agents are selective for mainly divalent copper, the cupric chloride solution can be subjected to direct extraction without oxidation steps.

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The extraction step is described in the diagram as only one step, but it includes the extraction and back extraction steps that are normally included in the extraction. In the extraction step, the aqueous cupric chloride solution is contacted with the organic extractant and the copper is subjected to the organic phase. The extraction step includes 15 normal mixing and settling portions, although they are not described in more detail in the diagram. Suitable extraction agents are any known copper extraction agent such as oximes diluted in a suitable solvent, for example kerosene.

The aqueous chloride aqueous solution of the extraction stage, raffinate depleted of copper and having an increased acid content, is recycled to concentrate leaching. The organic solution from the extraction steps is recycled through washing. In the back extraction, the organic solution containing the divalent copper ion is contacted with an aqueous sulfuric acid solution and the copper 25 enters the aqueous phase as sulfate, where it is recovered by electrolysis. When copper recovery is carried out by copper electrolysis, the electrolysis return acid can be used as back sulfuric acid in aqueous extraction.

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Claims (12)

A process for treating a pyritic copper sulphide-containing gold and / or platinum metals (PGM) and arsenic, the dissolution being dissolved 5. a saline aqueous solution of copper chloride and alkali chloride and sulfur remains in the precipitate formed in the solution, characterized in that the potential of dissolution is regulated by the addition of an oxidative substance to the range 400 - 600 mV in relation to an Ag / AgCl electrode and the pH is controlled to the range 0.2 -1, whereby the sulfur ίο copper and the copper, iron and arsenic which are present in the arsenic minerals dissolve and the gold and / or PGM bound to these minerals are released, the pyrite and the gold and / or PGM contained therein, and the gold and / or PGM released and the sulfur remaining in the solution residue; the formed iron and arsenic-containing copper chloride solution is neutralized to precipitate iron and arsenic, whereupon the neutralized iron and arsenic-free copper chloride solution is led to a liquid-liquid extraction step, from which the copper is recovered in an aqueous solution of sulfuric acid, which is removed to the and the refinate of the liquid-liquid extraction 20 is returned to the solution. Process according to Claim 1, characterized in that flotation of sulfur is carried out on the solution residue. 25 Method according to claim 1 or 2, characterized in that a pyrometallurgical treatment is carried out for the gold residue and / or PGM on the solution residue. 4. A method according to claim 3, characterized in that the solution residue is led to a smelter. 5. A process according to claim 3, characterized in that the solution residue is ruptured. 6. A process according to claim 1 or 2, characterized in that, for the recovery of the gold and / or PGM, a hydrometallurgical treatment in the form of a pressure solution is carried out on the solution. Process according to claim 1, characterized in that the ferrous and arsenic-containing copper chloride solution is neutralized to a pH of 2 to 2.5 for precipitation of iron and arsenic from the solution. 8. A process according to claim 7, characterized in that the neutralization is carried out with limestone, lime or lye. 15 9. A process according to claim 7, characterized in that iron and arsenic are precipitated from the solution in the form of ferric senate and ingot or in the form of ferric hydroxide. Method according to claim 1, characterized in that a small amount of gold dissolved in the dissolution step is precipitated into the solution residue by means of a reducing agent or an adsorbent. Method according to claim 10, characterized in that the adsorbent is active koi. A process according to claim 1, characterized in that the oxidative substance is oxygen or an oxygen-containing gas.