FI120406B - Process for hydrometallurgical treatment of a sulfidic material containing zinc and copper - Google Patents

Description

METHOD FOR HYDROMETALLURGICAL TREATMENT OF SULFID MATERIALS CONTAINING ZINC AND COPPER

FIELD OF THE INVENTION

The invention relates to a process for recovering precious metals from a sulphidic, at least copper and zinc-containing raw material, such as concentrate, by hydrometallurgical treatment. The raw material consists of copper sulphide and zinc sulphide, which are dissolved in an alkali-copper (II) chloride solution. From the resulting solution, divalent copper chloride is removed and the solution is subjected to zinc extraction to remove the zinc from the alkali chloride-copper (I) chloride solution. The solution from the zinc extraction and depleted of zinc is led to final solution purification and copper recovery. The reagents needed in the process are mainly obtained as products of the chlor-alkali electrolysis associated with the process.

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BACKGROUND OF THE INVENTION

U.S. Patent No. 6,007,600 describes a process developed by Outokumpu Oyj for hydrometallurgically producing copper from a copper-containing raw material, such as copper sulphide concentrate. According to method 20, the raw material is dissolved in countercurrent leaching with concentrated alkali chloride-copper (II) chloride solution in several steps to form a copper (II) chloride solution. Since both divalent copper and impurities formed from other metals are always present in the solution, the solution is subjected to divalent copper precipitation and solution purification. Pure copper (I) chloride solution is precipitated with alkali hydroxide to copper (I) oxide and the oxide is further reduced to elemental copper. The alkali chloride solution formed during the precipitation of copper (I) oxide is further processed in chlor-alkali electrolysis, which produces chlorine gas and / or chloride solution for leaching the raw material, alkali hydroxide generated by electrolysis for the precipitation of copper (I) oxide and hydrogen reduction. This method is called the HydroCopper ™ process. U.S. Patent No. 6,007,600 describes a copper recovery process 2 as a whole, but focuses primarily on pure copper sulfide concentrates.

U.S. Patent No. 5,487,819 describes a method for hydrometallurgically producing copper from a raw material containing copper and optionally other valuable materials, such as a sulphide concentrate. According to the method, the raw material is dissolved in countercurrent solution with sodium chloride-copper chloride solution in several steps. If the raw material contains sulphides other than copper sulphides, the method describes dissolving the other sulphides in the first stage of leaching, from which the solution is removed for further processing. The dissolution of the insoluble raw material is continued to form a copper (I) chloride solution and a precipitate containing iron and sulfur. Further treatment of the solution to be removed from the first leaching step is, after thickening and filtration, for example the removal of silver and mercury. In the second 15 steps iron, arsenic, bismuth, mercury, antimony, etc. are removed.

by known methods. When the solution comprises lead and zinc, the lead is first recovered by its own electrolysis, then the zinc is recovered from the solution by a second electrolysis. According to the publication, in both electrolysis, the metal is produced on a cathode which is wiped so that both lead and zinc are recovered in particulate form at the bottom of the cell.

The recovery of zinc and lead in electrolysis, which produces particulate metal, is unlikely to be industrially used. In any case, practical implementation seems difficult.

From WO patent application 2006/070052 there is known a method for recovering precious metals from a sulfide concentrate, wherein the concentrate is first dissolved in a sulphate milieu to dissolve a precious metal other than copper and the copper is leached from the remaining precipitate by chloride leaching. Thus, other valuable substances such as zinc or nickel are recovered in a pure sulphate environment.

From U.S. Patent No. 4,288,304, a process is known in which a zinc-containing sulfide concentrate, also containing other precious metals such as copper, is led to a chloride-based leaching to recover the precious metals. The leaching of precious metals from the concentrate takes place with divalent copper and possibly also contains alkali metal chloride to improve the solubility of monovalent copper. After leaching, the copper in the solution is mainly in monovalent form. The precious metal solution is first led to a liquid-liquid extraction of zinc, which is carried out with an organic phosphoric acid such as D2EHPA. In the zinc extraction, hydrogen ions are formed in the solution and the pH of the solution decreases, but the method prevents the pH from falling outside the range of 0.3 to 1.5 by supplying oxygen to the extraction step, whereupon the monovalent copper is oxidized and water is formed. If the amount of copper in the concentrate is low, it is recycled to leaching and part can be recovered by cementing. If the amount of copper is higher, the solution of 15 zinc extraction with divalent copper is led to the copper extraction.

It is typical of the process of US 4,288,304 that the conditions of the extraction step are controlled by supplying oxygen there. However, it has been found that when feeding oxygen, the organic extraction solution also oxidizes, which is an undesirable phenomenon and prevents an efficient extraction process. In the process, the copper is oxidized back to divalent during the zinc extraction, but the reduction of divalent copper to metal by electrolytic treatment requires more energy than the monovalent reduction. It has also been found in 25 practical experiments that the oxidation of copper during extraction using organic phosphoric acid causes difficult precipitate formation which complicates the extraction.

PURPOSE OF THE INVENTION

In the process of the invention, the purpose is to recover not only copper but also zinc from the sulphidic raw material containing copper and zinc. Zinc recovery takes place in 4 sub-processes that are coupled to the copper recovery process, whereby the solution from copper (II) chloride-alkali chloride leaching is led to the liquid-liquid extraction of the zinc. Zinc extraction maintains conditions under which the copper in the solution remains monovalent and oxidation of the extraction solution is avoided.

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SUMMARY OF THE INVENTION

What is essential for the process according to the invention is what is stated in the claims.

The invention relates to a process for recovering copper and zinc from a sulphidic raw material containing them by hydrometallurgical treatment. The raw material is dissolved in concentrated alkali chloride-copper (II) chloride solution and the resulting copper (I) chloride solution, which also contains dissolved zinc, is subjected to liquid-liquid extraction to recover the zinc from the solution. Hydrogen ions generated in the liquid-liquid extraction step 15 are neutralized with alkali hydroxide. By neutralization, the pH of the extraction is adjusted to a range of 2 to 4, thereby preventing the copper (II) chloride in solution from oxidizing to the copper (II) chloride. The zinc is recovered from the organic solution in a manner known per se in a sulfuric acid solution, and the metallic zinc is preferably formed by zinc electrolysis. Copper (I) oxide is precipitated from the zinc-depleted copper (I) chloride solution with alkali hydroxide and is suitably reduced to metallic copper.

According to a preferred embodiment of the invention, the sulphidic raw material is a sulphide concentrate.

According to another embodiment of the invention, the sulfide feedstock is a zinc-containing copper sulfide precipitate.

The process according to the invention is characterized in that the alkali chloride copper (II) chloride solution has an alkali chloride content of at least 200 g / L.

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It is typical of the process according to the invention that the alkali used is sodium.

In the process of the invention, liquid-liquid extraction includes extraction washing-5 and back extraction steps. The washing solution for the liquid-liquid extraction washing step is an aqueous solution of zinc salt, adjusted to a pH of 1 to 3. Preferably, the zinc content of the scrubbing solution is adjusted to be in the order of 10-30 g / L and the ratio of extraction solution to scrubbing solution flows is in the order of 5-40: 1.

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The process of the invention is characterized in that the copper recovery process involves chlor-alkali electrolysis.

For the process, it is preferable to use an alkali hydroxide formed by chlor-alkali electrolysis to neutralize the extraction step and precipitate the copper (I) oxide from the copper (I) chloride solution. The alkali chloride solution formed by the precipitation of copper (I) oxide is led to chlor-alkali electrolysis to dissolve the raw material, neutralize the extraction and recover the copper, alkali hydroxide and hydrogen required for copper recovery.

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LIST OF FIGURES

Fig. 1 shows a flow diagram of a process according to the invention for treating copper-zinc sulphide concentrate.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a process for the recovery of zinc from zinc and copper-containing sulfide materials by extraction prior to copper recovery. The copper and zinc containing material is dissolved in an alkali chloride-Cu (II) chloride solution to obtain the alkali chloride from the chlor-alkali electrolysis of process 30. Zinc and copper-containing material means mainly zinc and copper-containing sulphide concentrate or the product of any process step, sulphide precipitate containing metals.

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In the case of copper-zinc sulphide concentrate, the amount of copper is usually about twice, even three times, the amount of zinc. Such an concentrate has, for example, the following composition: Cu 14%, Zn 3.4%, Fe 5 35%, S 42%, Pb 0.5%, As 0.3% and Sb 0.1%. Leaching under atmospheric conditions is essentially as described in U.S. Patent No. 6,007,600. Atmospheric conditions refer to the temperature up to the boiling point of the solution, i.e. about 105 ° C, and the pressure generated when non-pressurized reactors are used. Figure 1 shows a diagram of the dissolution of a zinc-containing copper-zinc concentrate. The total concentrate, i.e. Cu-Zn concentrate 1, is passed to the leaching step 2, where the leaching is effected by countercurrent leaching with concentrated alkali chloride-copper (II) chloride solution 3. The amount of alkali chloride in the solution is at least 200 g / l. Alkaline chloride is usually sodium chloride. During leaching reactions, the compounds in the concentrate decompose and the resulting elemental sulfur, iron and arsenic compounds as well as gold and other precious metals (PGM) remain in the leaching residue. Where necessary, the leaching residue is treated as desired to recover, for example, gold and other precious metals. Oxidizing gas such as air or oxygen is fed to the leaching step 2. Zinc is soluble in ZnCl2 as zinc chloride and copper as a monovalent cupric chloride in CuCl.

The solution from the leaching step 2 is a zinc chloride-containing copper chloride-alkali chloride solution 4. The amount of copper in the solution is in the order of 50-100 g / L. Most of the copper chloride is CuCl as the monovalent cupric chloride, but some are also CuCl2 as the cupric chloride, whereby the solution is preferably subjected to precipitation 5 whereby the divalent copper is precipitated, for example, as basic copper (II) chloride with Cu2Cl (OH) 3 alkaline hydroxide such as NaOH. Copper (II) chloride precipitation from solution is described, for example, in EP-30 14434399. The basic copper chloride is either dissolved in its own leaching step and the copper (II) chloride formed is recycled to 7 concentrate leaching or directly back to concentrate leaching (dotted line).

Zinc can be selectively separated from 5 copper (1) chloride solutions obtained from HydroCopper leaching by 6 liquid-liquid extraction processes. Liquid-liquid extraction produces a pure zinc solution suitable for zinc electrolysis to produce zinc cathodes. However, if necessary, a conventional zinc sulphate solution purification process prior to zinc electrolysis may be incorporated into the process, but this is not further described in the flow chart.

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In the zinc extraction step 7, a commercial extractant such as D2EHPA (di- (2-ethylhexyl) -phosphoric acid) or organic phosphinic acid, known under the trade name Cyanex 272, for example, can be used. The concentration of the extractant in leach solution 8 is selected from % by volume. The extractants are diluted in a suitable hydrocarbon solvent, for example Shellsol D70. The zinc extraction is performed using one or more serially connected extraction steps. The extractors can be mixer-clarifier devices, which are connected upstream. The figure shows the extraction solution with a dashed line and 20 aqueous solutions with a solid line.

In the steps of the extraction step, the acidity of the aqueous phase is adjusted to pH 2-4 by neutralizing the hydrogen ions generated in the extraction reaction with sodium hydroxide, which is obtained by chlor-alkali electrolysis in the HydroCopper process. The use of sodium hydroxide or alkali in the process is advantageous because it is obtained as a product of the chlor-alkali electrolysis involved in the process. Although lye is more expensive than lime as a product, its use in neutralization is still more advantageous, since at the pH range used calcium is leached with zinc and causes problems later in the process. From the extraction process 30, the dewaxed raffinate solution 19 proceeds to the copper deposition steps.

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For example, when extracting zinc from a feed solution containing 25 g / L Zn, 45% v / v D2EHPA extraction solution can be used. Then the volume ratio of the organic extraction solution to the volume flow rate of the aqueous solution is n.

1.3 -1.5: 1 95-100% zinc yield can be achieved.

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The zinc-containing organic extraction solution LO (Loaded Organic) 9 contains impurities after extraction. Impurities are either chemically extracted or transported in the leach solution as a result of physically incomplete phase separation in water droplets. The impurity concentrations ίο are brought to a sufficiently low level by passing the extraction solution to a washing step 10 consisting of one or more serially connected washing steps.

The washing solution for the washing step is an aqueous solution 11 containing zinc salt and an acid which has been adjusted to have a pH of about 1-3. When the zinc concentration of the wash solution is high enough, e.g. 10-30 g / L is Zn, the zinc is not re-extracted to the acidic wash solution. The impurities are re-extracted into the acidic wash solution 12 and replaced by zinc, which is transferred to the organic solution. By adjusting the flow ratio of the leach solution to the wash solution, which may be from 5 to 40: 1, the leach solution phase can be sufficiently pure.

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If desired, an additional scrubbing step may be used after the scrubbing step, in which unexcluded water droplets containing impurities from the previous scrubbing step are removed from the extraction solution with clean water.

The solution used in this washing step can be used to prepare the solution for the previous washing step (not shown in detail).

From the impurity-purified organic extract solution CLO 13 (Clean Loaded Organic), the zinc is transferred to the aqueous solution in the back-extraction step 14.

When the extraction solution is in contact with the aqueous solution LE (Lean 30 Electrolyte) 15, which is not typically a sulfuric acid solution from zinc electrolysis, the zinc is liberated from the extraction solution to the acid solution as zinc sulphate in an inverse reaction. The back extraction j 9 can be carried out in one or more back extraction steps in which the zinc is virtually completely removed from the leach solution phase 8 which returns to the leach step 7. The re-leaching rich zinc electrolyte RE (Rich Electrolyte) 16 contains 50-150 g / l zinc zinc depending on the electrolysis process. In zinc electrolysis 17, zinc is recovered from solution and precipitated on cathodes.

When using D2EHPA extractor, the iron contained in the feed solution 6 is so strongly extracted in the extractant that it is not removed from the leach solution as much as in the washing and re-leaching steps. This causes the iron to accumulate in the leach solution, which reduces its transfer capacity. The iron can be removed by passing a small side stream of the extraction solution to a separate acidic iron removal step 19 using concentrated hydrochloric acid.

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The aqueous solution or raffinate 19 from the extraction step 7, from which the zinc has been removed, is led to the copper recovery. The raffinate solution also contains, in addition to copper, a small amount of other dissolved metals which are recovered from the solution in a known manner in solution purification step 20 prior to copper precipitation from the solution. One known method is described in EP-A-1497474, where the separation of impurities is accomplished by ion exchange.

In solution purification, lead dissolved with copper is precipitated from the solution by known methods. From the pure copper (I) chloride solution 21, copper (I) oxide is precipitated by alkali hydroxide in the precipitation step 22. The copper (I) alkali chloride solution formed is precipitated by chlor-alkali electrolysis 23 to produce the chlorine, alkali hydroxide and hydrogen needed to dissolve the raw material. The resulting copper (I) oxide 24 is suitably reduced in the reduction step 25 to metallic copper. If precious metals, especially gold, are present in the multi-component concentrate, it is also possible to recover them by, for example, the method described in WO 03/091463 related to the HydroCopper process.

Although the invention has been described herein as a process for recovering zinc and copper 5 from concentrate, the process is also suitable for further treatment of a sulphidic zinc and copper-containing precipitate.

EXAMPLES Example 1 A copper zinc sulphide concentrate containing 14% copper, 28.5% iron, 40.4% sulfur, 2.4% zinc and 1.6% arsenic is dissolved under atmospheric conditions where the concentrate is leached by counter-current with concentrated alkali chloride-copper (II) chloride. The solution from the leaching step is a zinc chloride-containing copper chloride-alkaline chloride solution. The solution is passed to a solution purification in which divalent copper is precipitated as the basic copper (II) chloride with Cu 2 Cl (OH) 3 alkaline hydroxide, sodium hydroxide NaOH and the copper (II) chloride formed is recycled to concentrate leaching. The zinc is then selectively separated from the copper (I) chloride solution obtained from the HydroCopper leach by a liquid-liquid extraction process. Liquid-20 fluid extraction produces a pure zinc solution which is suitable for zinc electrolysis to produce zinc cathodes. The aqueous solution or raffinate from the extraction step is led to the copper recovery. The raffinate solution contains not only copper but also a small amount of other dissolved metals which are recovered from the solution, for example by ion exchange.

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Example 2

An example is the HydroCopper plant located near the zinc plant. Copper-zinc sulphide concentrate, 14.5% copper, 34.1% iron, 40.3% sulfur, 5.3% zinc and 0.2% arsenic, is leached under atmospheric conditions where the leaching is effected by countercurrent leaching with concentrated alkali chloride-copper (II) chloride solution . Various copper and zinc-containing fines from the zinc plant can also be fed into the leaching process. The solution resulting from the leaching step 11 is a zinc chloride-containing copper chloride-alkaline chloride solution. The solution is passed to a solution purification where the divalent copper is precipitated as the basic copper (II) chloride with Cu 2 Cl (OH) 3 sodium hydroxide NaOH and the copper (II) chloride formed is recycled to concentrate leaching. The zinc is then selectively separated from the copper (I) chloride solution obtained from the HydroCopper leaching by a liquid-liquid extraction process. Liquid-liquid extraction produces a pure zinc solution which is fed to a zinc plant in the factory area. The aqueous solution or raffinate from the extraction step is led to the copper recovery. The raffinate solution 10 contains not only copper but also a small amount of other dissolved metals which are recovered from the solution, for example by ion exchange.

Claims (15)

Process for the recovery of copper and zinc from a sulphidic raw material containing zinc and copper, characterized in that the sulphide material is dissolved with an alkali chloride copper (II) chloride solution for the solution of copper and zinc, after which the zinc is recovered from the solution by liquid liquid extraction, wherein the pH of the extraction step is set within the range 2 - 4 by the addition of alkali hydroxide to prevent the oxidation of the copper (l) chloride; after extraction, the copper is precipitated from the zinc-low copper (l) chloride solution by means of alkali hydroxide as copper (l) oxide, which is reduced to metallic copper. Process according to claim 1, characterized in that the sulphidic ice raw material is sulphide-like. Process according to Claim 1, characterized in that the sulphidic raw material is a zinc-containing copper sulphide precipitate. 20 4. A process according to claim 1, characterized in that the alkali chloride copper (II) chloride solution's alkali chloride content is at least 200 g / L. 5. A process according to claim 1 or 4, characterized in that alkali is sodium. 25 6. A process according to claim 1, characterized in that the liquid-liquid extraction includes extraction, washing and ather extraction steps. Process according to claims 1 and 6, characterized in that as an aqueous solution in the washing step of the liquid-liquid extraction, an aqueous solution containing zinc salt and whose pH is set to be in a class of 1-3 is used. Method according to claim 7, characterized in that the zinc content of the washing solution in the washing step is in a class of 10 - 30 g / L. s 9. A process according to claim 6, characterized in that in the washing step, the ratio of the flows of the extraction solution to the washing solution is 5-40: 1. Process according to claim 6, characterized in that the aqueous solution in the ether extraction step of the liquid-liquid extraction is a sulfuric acid-containing solution. 11. A process according to claims 1 and 6, characterized in that the sulphidic raw material contains iron, wherein the iron which has been dissolved in the solution step and which has been bonded to the extraction solution in the extraction step is removed by passing part of the extraction solution to de-icing which takes place. using a strong hydrochloric acid. 20 12. A process according to claim 1, characterized in that the process for the recovery of copper involves chlor-alkali electrolysis. 13. A process according to claims 1 and 12, characterized in that for the neutralization in the extraction step and for the precipitation of the copper (1) oxide from the copper (1) chloride solution, such an alkali hydroxide which is included in the chlor-alkali electrolysis contained in the process of copper recycling. Process according to claims 1 and 12, characterized in that the alkali chloride solution formed in the precipitation of the copper (1) oxide is led to chloro-alkali electrolysis to produce the chlorine, alkali hydroxide and the hydrogen needed in the dissolution of the raw material. in the neutralization of the extraction and in the recovery of copper. Process according to claim 1 for the recovery of copper and zinc from a sulphidic framework material containing zinc, copper and iron, characterized in that the sulphide material is dissolved with a strong alkali chloride-copper (II) chloride solution for the solution of copper and zinc. a mainly iron and sulfur containing solution residue and a zinc-containing alkali chloride copper (l) chloride solution, or from which the zinc is recovered from the solution by liquid-liquid extraction, whereby the pH of the extraction step is set within the range 2-4 by adding the in ether extraction to a sulfuric acid aqueous solution and the metallic zinc is electrolytically recovered from the zinc sulfate solution; From the zinc-low copper (I) chloride solution formed in the extraction step, the copper is recovered by means of alkali hydroxide as copper (I) oxide, which is reduced to metallic copper.