MX2008010509A - Method for recovering copper from a copper sulphide ore - Google Patents

Abstract

The invention relates to a method whereby copper is recovered from a copper sulphide ore containing pyrite. According to the method the ore is ground and leached into a solution containing sulphuric acid in atmospheric conditions by means of trivalent copper. As the copper sulphide leaches out, the trivalent iron is reduced to divalent and is oxidised back to trivalent by means of oxygen during leaching. Leaching is carried out in a closed reactor, where the undissolved gas rising from the solution in the upper section of the reactor is circulated back into the suspension of solution, solids and gas. Leaching is performed in the presence of both divalent and trivalent iron and preferably with the dissolved copper acting as a catalyst to promote leaching. The conditions are adjusted to be such that the pyrite of the ore essentially does not dissolve.

Description

METHOD FOR THE RECOVERY OF COPPER FROM A COPPER SULFIDE MINERAL Field of the Invention The invention relates to a method with which copper is recovered from a copper sulfide mineral containing pyrite. According to the method, the ore is ground finely and leached in a solution containing sulfuric acid under atmospheric conditions by means of trivalent copper. As the copper sulfide exits by leaching, the trivalent iron is reduced to divalent and is oxidized back to trivalent by means of oxygen during leaching. The leaching is carried out in a closed reactor, where the undissolved gas rising from the solution in the upper section of the reactor is recirculated back to the suspension of the solution, solids and gas. The leaching is carried out in the presence of both divalent and trivalent iron and preferably with dissolved copper acting as a catalyst to promote leaching. The conditions are adjusted such that the pyrite essentially does not dissolve.

Background of the Invention A significant part of the minerals containing copper sulfide is the Chalcopyrite mineral CuFeS2, of which the most common processing method after enrichment is pyrometallurgical smelting - anodic deposition - electrolytic purification. Nowadays, however, there is also interest in the hydrometallurgical processing of copper sulphide minerals, wherein the first stage of treatment itself is also commonly the formation of a flotation concentrate, after which usually at least one stage of Leaching of the concentrate takes place under autoclave conditions. The other main occurrence of copper sulfide is the chalcocite, Cu2S, which is processed mainly in the same way as chalcopyrite. Chalcopyrite and chalcocite are usually in the same mineral and often the amount of chalcopyrite is predominant. The leaching of minerals containing chalcopyrite and / or chalcocite with the aid of trivalent iron in a solution containing sulfuric acid is described, for example, in WO 2005/042790 and 2005/005672. In both cases the oxidation of the divalent iron formed in trivalent leaching is carried out in autoclave conditions, although at least part of the leaching of the concentrate could be carried out under atmospheric conditions. The copper sulphate solution formed in the leaching is brought to the recovery of conventional copper. A method for the hydrometallurgical recovery of copper from chalcopyrite and other sulfides is described in the publication of the patent of the United States of America 4.1 15.201. In this method the sulfide mineral is ground to a fineness where the particle size has a maximum of one micrometer. The sulfurous solids are leached in an acidic solution, in which the amount of ferric ions is sufficient stoichiometrically to oxidize the copper contained in the copper sulfide material. Part of the iron is removed from the copper sulphate solution by precipitation of the ferrous sulfate from it, after which the solution is brought to the copper electrolysis. The solution coming out of the electrolysis, which is diluted in relation to the copper, is taken to a separate stage, in which the ferrous iron still in solution is oxidized to trivalent before bringing the solution back to the sulphide leaching. In the method, the leaching and formation of the trivalent iron used in the leaching takes place in different stages. Patent EP 815,270 describes a method for leaching sulphide minerals, where the ore also contains iron. According to the method, the ore is ground to a fine where the P80 is 20 microns or less. The leaching takes place by means of ferric iron and sulfuric acid in an open reactor and oxygen is fed into the reactor to oxidize the ferrous iron formed in sulfide leaching, back to ferric iron. All the examples in the publication describe the treatment of the flotation concentrate. The copper sulphate solution formed in the leaching is brought to conventional extraction and electro refining. The disadvantage of the last two atmospheric methods described above is considered as the fact that for leaching to be successful, the ore has to be ground very finely, which consumes energy and thus raises grinding costs. In addition, it can be said of the last method that oxidation in an open reactor has to be with the entry of an excess of oxygen, because not everything can be brought back into circulation.

Objectives of the Invention The purpose of the invention is to eliminate the disadvantages of the methods presented above. A copper sulfide mineral containing pyrite is fed to the leach in a considerably thicker form than that described above, thus saving milling costs. The leaching of the ore and the oxidation of the ferrous iron to ferric iron take place with the help of oxygen in the same stage in closed reactors under atmospheric conditions, so that the oxygen efficiency becomes greater than in an open reactor. An acidic solution containing iron is used for the leaching of the ore, which in addition to the ferrous and ferric iron also includes copper, which acts as a catalyst to promote leaching.

SUMMARY OF THE INVENTION The essential features of the invention will become apparent in the appended claims. The invention relates to a method for leaching copper from a copper sulfide mineral containing pyrite, wherein the finally milled ore is leached into a solution containing sulfuric acid and iron in a single step. The grain size of the ore is of the order of 95-100% below 150 μ. Oxygen is fed into the leach stage and leaching is carried out under atmospheric conditions with a solution having an iron concentration of about 20-50 g / l, of which the amount of ferric iron is therefore less than 10 g / 1 and the amount of copper at the beginning of the leaching is 8 - 12 g / 1.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a flow diagram of the method according to the invention.

Detailed Description of the Invention The method according to the invention is particularly suitable for the leaching of a copper pyrite-sulfide mineral of the chalcocite type, although of course it can also be adapted for the leaching of other sulphide minerals. The method is described below with reference to Figure 1. The purpose in the method is to leach a particular sulfide mineral without enrichment pretreatment. The conditions of stage 1 leaching are adjusted in such a way that as little as possible of the pyrite contained in the ore is dissolved. The ore is milled for leaching at a grain size of 95-100% below 150 microns and preferably at a size around 50-150μ. so that it contains as little as possible of the finest fractions. The ground ore is fed into the first leach reactor. The number of reactors in series in the leaching stage can vary according to the need, but both the leaching of the ore and the oxidation of ferrous iron to ferric iron take place during the same stage. The following reactions typically occur in the leaching of copper sulfide ore: Cu2S + 2 Fe2 (S04) 3 2 CuS04 + S + 4 FeS04 (1) CuS + Fe2 (S04) 3 CuS04 + S + 2 FeS04 (2) S + 3 Fe2 (S04) 3 + H20 6 FeS04 + 4 H2S04 ( 3) 2 FeS04 + H2S04 + ½ 02 Fe2 (S04) 3 + H20 (4) FeS2 + H20 + 3 ½ 02 FeS04 + H2S04 (5) A solution is used for the leaching of the copper sulfide ore with a sulfuric acid concentration of at least 20 g / 1, preferably 70-95 g / 1. The total iron in the solution is 20 - 70 g / 1, where the amount of trivalent iron is at least 10 g / 1, the Fe + 3 / Fe + 2 ratio is preferably adjusted in the 0.5 - 1.2 and the amount of dissolved copper of around 8 - 12 g / 1 at the beginning of leaching. Preferably the solution is refined from the extraction stage, from which most of the copper has been removed. When the solution used in leaching is of the kind described above, it has been found that reactions 1, 2 and 4 proceed almost one hundred percent, but reaction 3 was only about 5% and reaction 5 (solution of pyrite) of around 3%. As can be seen from the previous reactions, sulfuric acid is only generated in reactions 3 and 5 and all the rest of the sulfur is recovered as elemental sulfur. When copper is present in the solution used for the leaching of the ore, it helps in the regulation of the oxidation-reduction potential of the leaching. Obviously, the concentration of copper in the solution increases as the leaching proceeds, because the purpose is to leach the copper in the ore, but in general in the leaching according to the prior art the concentration of the refined copper it is low, in the range of less than 2 g / 1. The leaching potential is adjusted to be in the range of 450 - 550 mV vs. an Ag / AgCl electrode at the end of the leaching. The relatively high iron concentration in addition to the copper concentration facilitates adjustment of the potential level mentioned above. The adjustment of the potential also facilitates the limitation of the pyrite solution, which consumes a lot of oxygen and increases the need for neutralization. The leaching of copper sulfide ore takes place at a temperature of 85-95 ° C. The regulation of the temperature of the reactor is done indirectly. An indirect mechanism of temperature regulation is to use defiectors, in which case a medium, for example steam or cooling fluid, is circulated. Another method is to equip the reactor with heating / cooling coils. The advantage of indirect regulation is the fact that no excess water is introduced into the leaching stage. The leaching mother liquor, that is, the refining of the extraction, is preheated to a temperature of 70-80 ° C with the heat of reaction generated in the leaching. Typically, oxygen is fed into the reactors of the leaching stage to oxidize the ferrous iron to ferric iron, but the oxygen feed into each reactor is not absolutely essential. Oxygen can be fed as oxygen, as air enriched with oxygen, or as air. By controlling the temperature accurately, the pyrite solution can also be regulated and thus lower the cost of leaching. The reactors are equipped with effective mixers, which keep the solids, liquid and gas in suspension. The effective mixing maintained in the reactors allows the feeding of a fairly thick solid into the leach stage. The oxidizing gas is preferably fed below the mixing element, from where the mixer sucks it into the suspension. The mixing element is preferably composed of 2 blade mixers located on the same transmission shaft, which are shaped in a manner appropriate for the purpose. The peripheral speed of the mixer is adjusted to be less than 5 m / s so that the sheets of the mixer do not wear out fundamentally. The reactors are equipped with a cover so that the gas that accumulates on the suspension can be recirculated back to the suspension with the help of the top sheet mixer and only the amount equivalent to the amount of gases other than oxygen in the gas , be removed from the upper section of the reactor. However, the reactors are not autoclaves but act at atmospheric pressure. The suspension flows from one reactor to another as an overflow. The solution that forms in the leaching, which contains copper sulfate known as PLS (Pregnant Leach Solution), is brought to a solids separation and to a cooling. The separation of solids can be effected, for example, in two steps such as thickening and filtration, but in the figure it is illustrated as a single stage for the purpose of greater simplicity. The lower separation flow 2 consists of the ore gangue (silicates), undissolved mineral such as pyrite, sulfate, and a small amount of elemental sulfur that is generated in the reactions. The separation overflow 2 is a solution of copper sulphate, with a copper concentration of around 20 - 50 g / 1, and in which there is still iron present at around 20 - 70 g / 1, partially in ferrous and ferric form, so that the concentration of ferric iron It is at least 10 g / 1. The concentration of sulfuric acid in the solution is of the order of 18-22 g / 1. The copper sulfate solution is brought to cooling 3, where the solution is cooled, so that its temperature is suitable for extraction. The mineral in general, also always contains a small amount of calcium and arsenic, and now by means of cooling, sulfate and ferric arsenate are precipitated from the solution, so that they do not precipitate during extraction in the first extraction cell . The copper sulfate solution is brought to liquid-liquid extraction, which is carried out in two stages according to the invention. The fact that the concentration of copper in the raffinate that comes out of the first extraction stage can be left higher than normal, by means of which the copper contained in the raffinate acts as a catalyst for the leaching, can be considered as a Advantage of the extraction in two stages.

Another advantage is the fact that, in relation to the second extraction stage, the substances dissolved from the ore and / or harmful for the leaching and extraction can be removed from the refining without great copper losses. Any known copper extractant is suitable as an extractant, diluted in a suitable solvent such as kerosene. It is also beneficial for the method that the concentration of the extractant in the extraction solution be adjusted to be high, in the range of 35-45%. The step of the extraction solution is illustrated in the figure by a dotted line, so that the solution that goes into extraction, BO (with low organic content), is shown by a segmented line of points and dashes and the LO solution (charged in organic) that contains copper that comes out of the extraction is represented by a dotted line. In the first stage 4 of the extraction, 65-75% of the copper content of the PLS is extracted into the extraction solution, whereby the copper concentration of the aqueous solution to be removed from the extraction, ie, the refined, remains with an 8 - 12 g / 1. As the copper concentration of the raffinate decreases, its concentration of sulfuric acid rises according to the following reaction: CuSO4 + 2 HR? CuR2 + H2SO4 (6) In the reaction, R means the hydrocarbon part of the extractant, which forms a complex with the copper in the organic solution and the hydrogen ion part of the extractant forms sulfuric acid in the aqueous solution with the sulfate. Most, that is, over 90% of the refining is taken back to the leaching of ore 1, but a small part, in the region of 3 - 8%, is taken to the second extraction stage 5. This part is adjusted according to the requirements so that the iron concentration of the raffinate does not rise above 70 g / 1 or that its content of impurities such as its zinc content does not rise too high. The refining carried to the second extraction stage is neutralized in the neutralization stage 6 before the extraction step by means of a suitable neutralization agent such as limestone or limestone. Before neutralization the sulfuric acid concentration of the solution is around 60-70 g / 1 and is neutralized to a pH value of 1.6 - 1.8, so that the solution is suitable for extraction. In the second extraction stage, the copper is removed from the solution until the concentration is around 0.5 g / 1 or even lower. The refining solution II from the second extraction stage is removed from the circuit through the precipitation stage 7, whereby zinc and iron dissolved from the ore during leaching are precipitated from the solution, that is, mainly the Iron of pyrite, for example by means of lime. The neutralization tank 6, which is mainly sulphate, is also taken to the precipitation stage. The precipitate and the formed solution are removed and processed in an appropriate manner. The LO solutions of both extraction stages, which contain an abundance of copper, are combined and brought to the washing and desorption stages, which are illustrated together with the reference number 8. The aqueous solution leaving the desorption, which is the RE (rich electrolyte) that is carried to the electrolysis 9, contains about 45 - 50 g / 1 of copper. Electrolysis is a conventional electrolytic extraction. The LE (poor electrolyte) that leaves the electrolysis is recirculated as an aqueous solution for desorption.

Examples Example 1 In one test we leached copper sulfide ore containing pyrite that had been ground to a size of 95% below 150 microns. The leaching was carried out in five reactors arranged in series and the leaching was done at a temperature of 90 ° C. The leaching took place by means of the recirculated raffinate from the first extraction stage. The leaching time was 9 hours and during this time 91.8% of the copper was dissolved. The analysis of the mineral was the following: Table 1 The analysis of the raffinate used for leaching and the PLS formed in leaching are given in Table 2.

Table 2 The reactors in the leach stage were equipped with baffles, where steam was introduced into the baffles of the first reactor to heat the reactor space. The raffinate was heated before being fed into the leaching stage with heat recovered in the cooling of the PLS, but the control of the final temperature of the solution was effected by baffle steam. Since the reactions that take place in the leaching are exothermic, the subsequent reactors were cooled by means of cooling liquid that flows in the deflectors. The solution flowed from one reactor to another by gravity. The reactors were mixed with the aid of double sheet mixers and the oxygen required for the oxidation of the iron was fed below the mixer. The redox potential of the leaching stage was adjusted to be 400 - 550 mV vs. an Ag / AgCl electrode. The suspension of the solution and the solids upon being removed from the last leach reactor was brought to thickening. The composition of the lower thickener flow was as follows: Cu 0.55%, Fe 31.1% and Zn 0.1%. The overflow flow of the thickener was a copper-rich PLS, which was brought to cooling prior to extraction. The solution was cooled to a temperature below 38 ° C, to make it suitable for extraction. In relation to the cooling of the solution, the sulphate and the ferric arsenate were precipitated from it, and were removed from the solution by means of thickening and filtration. The extraction of the PLS was carried out in two stages, the first of which comprised two extraction cells in series. The copper concentration of the PLS was 40 g / 1. The concentration of the extractant used for the BO organic extraction solution was 40%. During the first extraction stage, about 70% of the copper in the PLS was extracted into the organic solution and the copper concentration of the resulting refining was around 12 g / 1. The refining of the extraction was almost all recirculated back to the leaching of the ore, but about 6% of it was taken to the preneutralization procedure that precedes the second extraction stage, with the help of the iron content control and zinc of the solution circulating in the leach and extraction circuit. In addition to refining, the wash water of the various precipitates was taken to a preneutralization so that the Cu concentration of the solution became 7.2 g / 1. The neutralization of the solution was carried out with lime from a concentration of H2SO4 of 80 g / 1 to a pH value of 1.6 - 1.8. The clear solution resulting from the separation of solids was taken to the second extraction stage, which comprised a single extraction cell. The extraction solution used was the same extraction solution as that of the first extraction stage. In the second stage, 93% of the copper contained in the aqueous solution was extracted, so that the Cu concentration of the solution to be removed from this stage was only 0.5 g / 1. The copper-rich organic solutions that come out of both extraction stages were combined and directed to the desorption and washing stage, which consisted of two desorption cells, a wash cell of the extraction solution and a solution tank. THE organic. During the washing step, the chlorides and ferric iron contained in the solution were removed from the organic solution by washing with water. In the desorption cells the copper was extracted from the organic solution in an aqueous solution, which was the lean electrolyte LE that comes out of the electro refining of copper. The aqueous solution that comes out of the desorption was a copper-rich electrolyte (RE), which was directed to electrolysis.

Example 2 In one test, copper sulfide ore containing pyrite that had been ground to a grain size with 95% below 150 microns was leached. The leaching was carried out in a reactor at a temperature of 90 ° C. The leach reactor was equipped with defiectors. The mixing element was equipped with both a lower mixer and a top mixer. The top mixer was a Type A mixer, and the bottom mixer was a GLS type mixer. The leaching time was 8 hours. A synthetic leaching solution corresponded to an extraction refining, in which the Fe + 3 / Fe + 2 ratio was adjusted to a value of 0.75: 1. The solution was preheated before being fed into the leach reactor. The solids content of the slurry in the reactor was adjusted to 400 g / 1. The amount of oxygen fed into the test was a constant value of 80 ml / min / 1 (slurry). The analysis of the ground ore and the leaching solution was as follows: Table 3 In this test, 93.9% of the copper dissolved. There were 41.5 g / 1 of copper, 49.4 g / 1 of iron and 21.1 g / 1 of sulfuric acid in the solution of the leaching product. Accordingly, the composition of the product solution cooled to < 38 ° C is an appropriate feeding solution as such for the next subprocess, that is, copper extraction. The analysis of solids separated from the slurry, the leaching residue, after leaching is presented in Table 4.

Table 4 Example 3 In one test, a copper-rich PLS obtained from the leach was fed to an extraction system, which consisted of two extraction cells, one LO tank loaded in organic, one wash cell and two desorption cells. The extraction system operates based on the countercurrent principle. The amount of extractant in the organic phase was 45 vol.%. The temperature of all the different solutions was 35 ° C. In the extraction 74% of the copper contained in the PLS was transferred to the organic phase. Water droplets were removed from the organic phase loaded in the LO tank. The ferric iron was removed by washing the organic phase charged with copper in the wash cell with acidic wash water. In the desorption copper was removed from the organic phase loaded with an electrolyte solution (LE), forming a copper-rich electrolyte solution (RE). Both solutions of the test product were suitable for further processing; refining as a mother liquor for leaching and RE for electrolysis. Table 5 shows the analysis of the solution of the leaching product or PLS, the solution fed from leaching or refining extraction, the desorption feed solution (LE) and the desorption product solution (RE).

Table 5

Claims (18)

1. Claims 1. A method for the leaching of copper from a copper sulfide mineral containing pyrite, by means of which the finely ground ore is brought to a solution containing sulfuric acid and iron, which is oxidized during leaching, characterized in that the copper sulfide ore is ground at a granularity of 95 -100% below 150 μ? and carried to a leaching stage, which is carried out under atmospheric conditions and in which the leaching is carried out with a solution, the iron concentration thereof is approximately 20-70 g / 1, of which the amount of ferric iron is at least 10 g / 1, the amount of copper at the beginning of the leaching is 8 -12 g / 1 and the concentration of H2S04 of a minimum of 20 g / 1.
2. 2. A method according to claim 1, characterized in that the temperature of the leaching stage is 85-95 ° C.
3. 3. A method according to claim 1 or 2, characterized in that the leaching stage is carried out in closed reactors.
4. 4. A method according to claim 1, characterized in that the oxygen is fed in the leaching step.
5. 5. A method according to claim 1, characterized in that the grain size of the ore is in the range of 50-150 μp ?.
6. 6. A method according to claim 1, characterized in that the Fe + 3 / Fe + 2 ratio of the solution entering leaching is adjusted in the range of 0.5 - 1.2.
7. 7. A method according to claim 1, characterized in that the oxidation-reduction potential at the end of the leaching stage is adjusted to be 450-550 mV vs. Ag / AgCl. A method according to claim 1, characterized in that the copper-rich aqueous solution (PLS) leaving the leaching step is brought to a two-stage liquid-liquid extraction, in which the refining of the first The stage is mostly recirculated back to the leaching of copper sulfide ore. 9. A method according to claim 8, characterized in that prior to liquid-liquid extraction the copper-rich aqueous solution is cooled. 10. A method according to claim 9, characterized in that ferric sulfate and arsenate are removed from the copper-rich aqueous solution in connection with cooling. 11. A method according to claim 9, characterized in that the thermal capacity of the aqueous solution rich in copper is used to heat the solution, that is, the raffinate that enters the leaching step. 12. A method according to claim 8, characterized in that more than 90% of the refining of the first extraction step is recirculated to the leaching of copper sulphide and the remaining is carried to the second extraction stage. 13. A method according to claim 12, characterized in that the raffinate that is taken to the second extraction stage is subjected to the neutralization of its sulfuric acid content of 60-70 g / 1 at a pH value of 1.6. -1.8 to neutralize the acid in the solution. A method according to claim 13, characterized in that the neutralization is carried out by means of lime or limestone. 15. A method according to claim 8 or 12, characterized in that the copper concentration of the raffinate leaving the second extraction stage is around 0.5 g / 1. 16. A method according to claim 1, characterized in that the step of leaching the ore is carried out in several closed reactors connected in series, in which a gas containing oxygen is fed below the reactor mixing element. and where said reactors are equipped with deflectors. 17. A method according to claim 16, characterized in that the temperature of the reactors is adjusted indirectly by means of an agent fed into the baffles. 18. A method according to claim 16, characterized in that the reactors of the leaching stage are equipped with a mixing element, which is composed of two mixers; placed on the same transmission shaft to form a suspension of solids, liquid and gas.