METHOD FOR SEPARATION AND LEACHING OF THE VALUABLE METALS IN METAL SULPHIDE MATERIALS

Abstract: This is a method for the complete leaching of the valuable metals in a metal sulphide material which con­¸ tains copper, zinc, lead, silver and iron by the use of a solution which essentially contains cupric chloride/­ sulphates. After the valuable metals have been recovered, the solution is regenerated whereby ferrous chloride and cuprous chloride/sulphate is oxidized to a ferric hydro­ xide solid and a cupric chloride solution respectively. The regenerated solution is split into two part-solutions and returned to the process. One part-solution goes to a metathesis stage where the fresh metal sulphide material is added in large ex­ cess with respect to the part-solution's content of cop­ per. The result is that only the valuable metals like zinc, lead and silver are leached while copper and iron remain in the residue. The other part-solution goes to a leach stage where the residue from the metathesis stage is added. The ratio between the residue and the solution is about stoichio­ metric, while the characteristic feature of this stage is how the leach operation is performed. This results in a well leached residue and an almost completely reduced solution in just one leach stage. The residue from this stage goes to a third leach stage where all remaining valuable metals are leached completely by the use of chlorine gas/oxygen gas coming from the zinc electrolysis stage. Iron is precipitated as a hydroxide. The ratio between the part-solution which goes to the metathesis stage and the part-solution which goes to the leach stage is between 1:1 and 1:100.

Description: This invention deals with a method for the separa­ tion of the valuable metals zinc, lead and silver from copper and iron in complex metal sulphides which contains one or more of these valuable metals. Normally this is about the impure chalcopyrite concentrates. Further this invention is about a complete leaching of the copper, and at the same time an almost fully reduced cuprous chloride and ferrous chloride solution is produced, from which the copper is recovered by electrolysis. The iron is re­ moved from the solution by oxidation using air in the presence of cuprous chloride applying well known methods. The new in this invention lies in the first separa­ tion technique, (the separation of zinc, lead and silver from copper and iron), and the following leaching of copper in a simplified effective leach operation. This excludes such operations as solvent extraction (Elkem) for zinc, and the leach operation for copper needs only one stage for 100% leaching, compared to others which needs 2 stages (Elkem) or only leaches 50-60 % (Duval). The separation and leaching is done by the cupric chloride/sulphate solution which is made by the oxidation of the solution coming from the copper electrolysis stage. This cupric chloride/sulphate solution is separated into two parts-solution. One part, and normally the smallest one (1-2% of the main part) goes to a metathesis stage where the copper in solution is exchanged with the zinc, the load and the silver in the fresh metal sulphide mate­ rial which is added. These reactions only proceed by deliberately con­ trolling the total chloride concentration in the solution to normally about 250 g/l, by injection of water or dilute filtrates to the metathesis stage, from washing opera­ tions of filter presses etc.. Then the zinc, the lead and the silver is dissolved as the copper in the solution is precipitated as a sul­ phide. The sulphur which the copper needs to make sul­ phides comes from the sulphur liberated when zinc, lead and silver is dissolved. It is important that at all time having an excess of elemental suphur (S o ) present for an effective precipitation of CuS. This can easiest be done by recycling some residue from the copper leach stage, a residue containing 70-80% elemental sulphur. The metals zinc, lead and silver can be separated from the solution by a number of different methods. Here an ordinary hy­ droxide precipitation is chosen. The leaching of copper and some of the iron from the chalcopyrite is in great contrast to the metathesis. The solution used in the me­ tathesis stage, containing some 250 g/l chorides cannot be used in the leaching. One has to increase this inten­ tionally to some 350 g/l for a complete leaching and re­ duction of the solution. The leaching can, of course, take place at lower choride concentrations, but then you do not get a reduced solution (Duval). Duval only manages 50-60% leaching in their main leach stage and does the rest of the leaching in oxidation autoclave. Elkem uses about 400 g/l chlorides and get a very re­ duced leach solution of ferrous chloride with some cuprous chloride. They need two leach stages for a complete leaching and simultaneously producing an almost fully reduced leach solution. Elkems ferric-chloride solution cannot be used for the metathesis reactions. The inven­ tors have found a new way of combining known chemistry and chemical reactions, by intentionally separating the strong cupric chloride/sulphate solution from the oxida­ tion/iron precipitation stage (containing some 350 g/l chlorides) into two part-solutions. The other part, and normally the largest part goes to the leach stage. Here the chloride concentration is kept on about 350 g/l by regulating the evaporation of water in an amount equal to the volume of water in the wash water/thin filtrates added in the metathesis stage. Thus the reaction between the copper in the leach stage and the copper in the leach residue forming a copper sulphide is avoided, and an almost fully reduced solution is obtained. Most of the known type of continuous reactors (stirred vessels) are concerned with what in terms may be called "shortening". This is a well documented phenomenon which means that fresh solution (here cupric chloride/sulphate solution) and concentrate (here chalcopyrite) travels right through the leach stage without reacting due to a too effec­ tive mixing in the tanks. Normal correction done to this "shortening" is the use of more leach stages. The inventors have found a unique metod to solve this problem. The stirrer and the leach tank is designed such that the unreacted chalcopyrite sinks to the bottom of the leach tank while the leach residue floats on top. This is based on the differences in the spesific gravity for the chalcopyrite and the leach residue. The strong,oxydized cupric chloride solution is fed into the lower chalcopy­ rite bed. There it reacts with fresh minerals all the time before entering the upper bed. This results in no "shorten­ ing" of solution and no unreacted chalcopyrite. The solu­ tion discharged from the overflow on the top of the tank is almost fully reduced. The chloride concentration in the leach solution is maintained on the desired level (about 350 g/l) by addi­ tions of non-jarosite forming materials, like MgCl₂. The concentration of magnesium will vary from 85 g/l in the metathesis stage (due to dilutions) to about 110 g/l in the leach solution. The process solution in the leach stage is also intentionally kept at about 100-150 g/l of sul­ phates, as it is expensive and complicated to remove the sulphates completely. The residue from the copper leach stage can be de­ posited and sulphur recovered if it is economically viable. However, the continued research has demonstrated that when treating very complex concentrates, where the zinc content is so large that zinc electrowinning should be used to recover the zinc, it is an advantage to treat the leach residue from the copper leach tank in the oxidation tank and at the same time use the chlorine gas produced by the zinc electrowinning (and from lead or other metals which produce chlorine gas by electrolysis) in the tank for a complete leaching of possible traces of metals that might be left in the residue. Such a chlorine leaching is very straight forward, and normally done at 500-600 mV (SCE). This creates the advantage that into this tank other re­ sidues and solutions from purification operations can be added if desired, when concerned with the total ion ba­ lance of the process for better economy. This last leach tank is therefore acting as a dump where all things are added, chlorine leached and out comes a cupric chloride/­ sulphate solution containing varying amount of ferric chlo­ ride dependent on the variation in the excess of anions in the process. The iron is precipitated as a hydroxide and reports together with the sulphur residue. This residue can easily be stored. This last chlorine leaching tank is a great advan­ tage, especially when treating very intricate mineralo­ gical complex concentrates. The process can, of course, also be used on pure con­ centrates, and therefore not limited to impure, complex concentrates. It is within the scope of this invention to use purification systems of different kinds in combination or separately. This includes as an example for the non-copper metals, precipitation as hydroxides, solvent extraction and cementation. The choice of which residues or solutions are returned to the chlorine leach stage may also be done singularly or in combinations. The process is further explained on the simplified flowsheet below (fig. 1), and the special operation of the leach tank for the copper leaching is illustrated in fig. 2. On the simplified flowsheet in fig. 1 (41) is the part-solution of cupric chloride/sulphate going to the cop­ per leach stage (26), as the other part-solution (42) goes to the metathesis stage (3) where fresh metal sulphide con­ taining material (1), leach residue (43) and water/thin filtrates (2) and returned anolyte (19) is also fed. After the reaction solid and solution are separated in (4). The residue (44) goes to the copper leach stage (26) while the solution goes to an oxidation stage (5) where chlorine gas (24) is used as an oxidant. After the oxidation the solu­ tion goes to an extraction system (6) where preferably about 90% of the total content of ferric chloride in the solution is removed by the use of an organic reagent (21). The organic reagent is stripped in (7) using anolyte (20), and a strip solution (22) is fed to the chlorine leach tank (36). The solution from the extraction goes to (8) where preferably lime is added (9) to make ferric hydroxide from the remaining ferric chloride in the solution. The hydroxide precipitate (11) is separated from the solution in (10) and the solution goes to a cementation (12) where metallic zinc (13) is added. The cemented copper (15) is separated from the solution in (14). The purified solu­ tion goes to the electrolysis stage (16) where zinc (17) is obtained. Chlorine gas (23) which is formed is sepa­ rated into two part streams (24) and (25), where (24) is returned to the oxidation of the metathese filtrate in (5), as (25) goes to the chlorine leach stage (36). The anolyte (18) is also separated into two part-solutions (19) and (20), where (19) is returned to the metathesis stage (3) as the other (20) goes to the strip stage (7). The residue (44) from the metathese stage goes to the copper leach stage (26) where also the part-solution of cupric chloride /sulphate (41) and the anolyte (34) is fed. The evaporation from this stage is (27). After ended reactions the residue and the solution are separated in (28). The residue is split into two part-residues (43) and (45) where part-residue (43) is recycled to the meta­ these stage as part-residue (45) goes to the chlorine leach stage (36). The solution goes to a purification stage (29) where metallic iron and sodium sulphide is added (30). The residue formed (46) is separated from the solution in (31) and the purified electrolyte goes to the copper electrolysis stage (32) where copper is produced (33). The anolyte from the copper electrolysis stage (34) is returned to the copper leach stage (26), as the ca­ tholyte (35) goes to the chlorine leach stage (36). The chlorine leach stage (36) receives residue (45) from the copper leach stage (26) and (28) together with catholyte (35), strip solution (22) and chlorine gas (25). The eva­ poration from this stage is (37). After completed reactions in the chlorine leach stage (36) the residue (39) and the solution (40) is separated in (38). The residue (39) is stored as the solution (40) is returned to the process by separating it into two part-solutions (41) and (42), and the process starts all over again. Fig. 2 shows a leach tank operation. The concentate from the metathese stage (1) (in fig. 1 shown as No. 44) is added to the leach tank (2), here shown as an open tank. The stirring is effected using an impeller/propeller type mixer (3) and (5) which stirs the content in the tank in such a manner that two phases occur . The upper phase (7) contains to the largest extent the leach re­ sidue (in fig. 1 named as No. 43) which contains 70-80% elementary sulphur. This residue together with the re­ duced solution is emptied in (8), as the residue (1) re­ mains (sinks) in the lower phase (4) where is is leached by the fresh, cupric chloride/sulphate solution (6) (in fig. 1 marked as No. 41), without reaching the outlet (8). Example 1 A chalcopyrite concentrate containing: was added to a continuously operating stirred leach tank with a vigorous stirring together with a strong magnesium chloride solution. This solution simulated the recycled filtrate from an ordinary hydroxide precipitation. The chalcopyrite was 97% -325 mesh (Tylor) grain size and it was added by vibration feeder. A strong cupric chloride/­ sulphate solution was added to obtain the desired level of red/ox in the reaction tank. The pump used was controlled by a red/ox control unit which caused the volum of the strong solution to vary in accordance with the desired red/ox in the filtrate from the leach tank. The tempera­ ture was all the time 100-102°C. All variables were con­ stant, except the red/ox value which was varied from about 200 mV (SCE) and up towards 400 mV (SCE) to show at which red/ox value the metathesis ended and when the ordinary leaching started. Table 1 below shows the results. Conclusions: The test shows that at chloride concentrations of 263 g/l and at red/ox of 310 mV (SCE) the metathesis ends, producing a secondary precipiate of CuS, ordinary leaching starts. This is indicated by the excess of elementary sul­ phur (S o ) in the residue. At the same time the percentage Cu in the residue is at a maximum at 310 mV. The main reaction happening in the metathesis is: Cu⁺⁺ + ZnS Zn⁺⁺ + CuS and in the leaching: Cu⁺⁺ + CuS 2 Cu⁺ + S o Example 2 This test was done in a strong chloride solution hav­ ing 352 g/l chlorides, to demonstrate the fact that at such high chloride concentrations no metathesis is done forming secondary precipitation of copper in accordance with the formula: 2 Cu⁺ + S o CuS + Cu⁺⁺ The test method was the same as the one mentioned in test No. 1. The concentrate used was the one which was made in test No. 1 at 310 mV. Conclusions: The test shows that the leaching was completed at about 330 mV and that no precipitation of CuS was occur­ ring at chloride concentrations of 352 g/l, indicated by the fact that elementary sulphur (S o ) was in excess all the time. Example 3 When test No. 1 and No. 2 had shown that the chloride concentration was important for the metathese reactions and the leach reactions and that the red/ox should be about 300-330 mV (SCE) for both operations, this test was designed to find the limits for the metathesis and the leaching reactions with respect to the chloride con­ centrations. This test was done as done in test 2 above using the residue from test No. 1 (310 mV). Elementary sulphur was added to 5 %. Conclusions: Test 3 shows that almost no leaching of copper occurs at chloride concentrations less than 248 g/l in the pro­ cess solution (i.e. full metathesis) is almost all the copper is leached at chloride concentrations higher than 346 g/l. Between these limits (at 310 mV), there is a more shaded zone where metathesis does happen, but to a limited extent. Example 4 This test was performed on such a leach operation as mentioned in test 3 above, except in this test a special reactor was used and the stirring varied with respect to the separation of the "phases" of chalcopyrite and leach residue containing 70-80 % elementary sulphur, thus avoid­ ing the "shortening". This was not considered in the pre­ vious tests. The added energy to the solution (the slurry) in the leach tank was measured directly on the current which the stirring motor was using, and calculated from this. Conclusions: The test shows that the reactor used here had a shortening energy of larger than 0.4 Hk/m³ solution. This shortening energy will, of course, vary from design to de­ sign, but the principle will be the same and be within the intentions of this invention. Further a well reduced solution and a good leaching was obtained. Example 5 A complex zinc/copper/lead concentrate being >97% -325 mesh grain size was leached in three batch tests in accordance with this invention. The three different leach stages - the metathesis stage, the copper leach stage and the oxidation leach stage was simulated by using a weaker cupric chloride/sulphate solution having 265 g/l chlorides for the metathesis and a stronger cupric chloride/sulphate solution having 350 g/l chlorides for the two other leaches. The chloride concentration was varied using dif­ ferent additions of magnesium chloride. The leaches was done at 102-110°C i 4 hours in a 10 litre stirred vessel for the metathesis and in a 30 litre stirred vessel for the two other leaches. After ended reactions, the slurry was filtered and solution and residue analysed. - In the metathesis (leach No. 1) the fresh material was added to the weaker CuCl₂/SO₄-solution. After ended reactions the slurry was filtered and residue and solution was analysed. - In the copper leach (leach No. 2) the residue from the metathesis was added to the stronger CuCl₂/SO₄-­ solution. After ended reaction the slurry was fil­ tered and the residue and the solution was analysed. - In the oxidation leaching (leach No. 3) the residue from the copper leach was chlorine gas leached in the stronger CuCl₂/SO₄-solution. After ended reac­ tion, the slurry was filtered and the residue and the solution were analysed. Conclusions. This example clearly shows the necessity of the third chlorine gas leach stage incorporated into the process in order to obtain a good leaching of the valuable metals when strongly complex (impure) concentrates are treated. At the same time the solutions were of satisfactory cha­ racter for further treatment by the process. Example 6 This test was done on the same concentrate as the one used in example 5, except that in this test the meta­ thesis (leach No. 1) was done in an autoclave at 140-142°C. After 2 hours reaction time, the slurry was cooled, fil­ tered and the residue analysed. This example shows that a higher reaction temperature makes a cleaner metathesis residue in a shorter time when compared to example 5. This is especially shown w.r.t. iron in the residue. At the same time the trace elements are well leached except selenium and tellurium. The silver is partly leached. Conclusions. An increase in the reaction temperature in the meta­ thesis stage from 105-110°C to 140-142°C increases the reaction rate and a cleaner metathesis residue is pro­ duced in a shorter time. The principle, however, concern­ ing this invention is not changed by increasing the reaction temperature.

Claims: 1. A method for the leaching of the valuable metals in metal sulphide materials which contains one or more metal sulphides of copper, iron, lead and silver by treating with one essentially all cupric chloride/sulphate solu­ tion where the solution after the recovery of the valu­ able metals is oxidized to cupric chloride/sulphate with a precipitation of dissolved iron to an iron residue and where the solution is reused in the process,characterized by the regenerated cupri chloride/sulphate solution is separated into two part-­ solutions where one part-solution is added to a meta­ thesis reaction stage where leach residue from the copper leach stage, which contains elementary sulphur and fresh metal sulphide material, is also added under controlled red/ox conditions, together with the chloride content of the solution in that stage is controlled by additions of di­ lute filtrates/water and return anolyte from the valuable metal electrolysis whereby the valuable metals zinc, lead and silver is dissolved and is recovered from the solu­ tion by electrolysis, as copper and iron remains undis­ solved and makes a residue together with the copper which was in the part-solution of cupric chloride/sulphate which is precipitated as a sulphide by using the liberated sulphur from the dissolution of zinc, lead and silver to­ gether with the sulphur existing in the recycled residue from the copper leach stage, as the other part-solution of cupric chloride/sulphate is added to a copper leach stage together with the total residue from the metathesis stage and anolyte from the copper electrolysis stage un­ der controlled red/ox conditions and stirring energy supplied to the solution in that copper leach stage, to­ gether with the chloride content of the solution in the stage being controlled by the evaporation of water, where­ by the residue from the metathesis stage is almost fully leached and at the same time an almost all cuprous chlo­ ride/sulphate- ferrous iron chloride/sulphate solution is produced which goes to a copper electrolysis stage which removes the copper metal values and where the solu­ tion from this stage is split into two part-solutions, where one part-solution is returned to the copper leach stage and the other goes to an oxidation leach stage, where also the leach residue from the copper leach stage is added together with residues and eluates from purifica­ tion stages of electrolytes together with anolyte and chlorine gas from the electrolysis of the metals zinc, lead and silver, under controlled red/ox conditions so that the remaining valuable metals in the leach residue from the copper leach stage is completely leached and the dissolved iron in the solution entering this stage is precipitated as a residue and reports together with the leach residue from this stage, as the oxidized solution which contains almost entirely cupric chloride/sulphate is recycled to the process. 2. A method as described in claim 1,characterized by the stirring energy sup­ plied to the copper leach stage is so small that the resi­ due which is added this copper leach stage sinks to below the design feature which necessitates the discharge of solution and residue from this copper leach stage, but at the same time such a large stirring energy added to the leach stage that the leach residue which is made and which essentially contains elementary sulphur having less spesific weight than the residue added, is kept in suspension in such a manner that it reaches the design feature which empties the stage. 3. A method as described in claim 1,characterized by the part-solution of cupric chloride/sulphate which is fed to the copper leach stage is fed under controlled red/ox conditions into that part of the stage where the fresh and heavier metal sul­ phide material is present. 4. A method as described in claim 1,characterized by the ratio between the volume cupric chloride/sulphate solution fed to the metathesis stage and to the copper leach stage is be­ tween 1:1 and 1:100. 5. A method as described in claim 1,characterized by the red/ox in the meta­ thesis stage is between 100 and 400 mV (SCE). 6. A method as described in claim 1,characterized by the red/ox in the copper leach stage is between 200 and 400 mV (SCE). 7. A method as described in claim 1,characterized by the red/ox in the oxida­ tion leach stage is between 450 and 650 mV (SCE). 8. A method as described in claim 1,characterized by the chloride content of the metathesis filtrate is between 200 and 300 g/l. 9. A method as described in claim 1,characterized by the chloride content of the filtrate of the copper leach stages is between 300 and and 400 g/l. 10. A method as described in claim 1,characterized by elementary sulphur is present in the metathesis residue, obtained by recycling the necessary amounts sulphur residue from the copper leach stage to the metathesis stage. 11. A method as described in claim 1,characterized by the solution out from the copper electrolysis stage is separated into two part-­ solutions, where one goes to the copper leach stage and the other goes to the oxidation leach stage, and that the ratio is between 10:1 and 1:10. 12. A method as described in claim 1,characterized by the sulphate content of the cupric chloride/sulphate solution is between 50 and 200 g/l. 13. A method as described in claim 1,characterized by the chloride concentra­ tions is adjusted to keep cuprous chloride in solution by the addition of magnesium chlorides. 14. A method as described in claim 1,characterized by the valuable metals in the solution from the metathesis stage is such as sinc, lead, silver, nickel and cobalt in a mixture,in different mixtures or singular. 15. A method as described in claim 1,characterized by the temperature in the metathesis stage is between 90 and 150°C.

Inventors: KOSTOL, CARL-OTTO, THOMASSEN, THOMAS
Applicants: CHEMINVEST A/S
Application year: 1985
Main classification: C22B3
IPC codes: C22B3, C22B15