An Environmentally Friendly Chalcopyrite Leaching Process And Theoretical Research

The researches and advances in the hydrometallurgical treatment of chalcopyrite at home and abroad are reviewed. Based on the thermodynamic analysis and explorative experiments, a novel process of weak acid leaching chalcopyrite with ammonium persulfate in the presence of silver ions or silver sulphide as the catalyst is put forward. This process is in possession of independent knowledge property right. The novel process realizes green leaching chalcopyrite concentrate. It is also an environmentally friendly improvement to the hydrometallurgical methods of treating complex sulphide copper ore. At the same times, this process was also an innovation in processing various grades of copper-bearing and nickel-bearing complex sulphide minerals.The main work and conclusions are as follows:â… , Systematic thermodynamics calculation and examination of the systems S-H₂O, Ag₂S-H₂O, Ag₂S-NH₃-H₂O, CuFeS₂-H₂O, CuFeS₂-NH₃-H₂O, Cu-S-O-H, ZnS-H₂O, FeS₂-H₂O and PbS-H₂OIn order to investigate the behaviors of chalcopyrite, sphalerite, chalcocite, pyrite and galena, the E-pH diagrams of the systems Ag₂S-H₂O, Ag₂S-NH₃-H₂O, CuFeS₂-H₂O, CuFeS₂-NH₃-H₂O, Cu-S-O-H, ZnS-H₂O, FeS₂-H₂O and PbS-H₂O are constructed, and the positions of S₂O₈^2- in these diagrams are determined for first time. The thermodynamics practicability of leaching Ag₂S, CuFeS₂, Cu₂S, ZnS, FeS₂ and PbS with S₂O₈^2- is studied. The E-pH diagrams of the system S-H₂O at ₂98K and ₃7₃K are also constructed to determine the stable ranges of S₂O₈^2- in the diagrams and the position of S₂O₈^2- in the system S-H₂O 373K is determined for first time. According to the principle of simultaneous equilibrium, the thermodynamics equilibrium calculation of the system Cu-NH₃-H₂O at 298/₃7₃K is carried out by use of VB computer program, and the points at which the solution are in equilibrium with solid Cu, Cu₂O and CuO were determined. These diagrams lay the theoretical foundation for application of ammonium persulfate to leaching sulphide minerals.â…¡, Systematic experimental study and mechanism-analysis of leaching chalcopyrite with ammonium persulfate under different leaching conditions1. The results of experiment show that the leaching efficiency of copper is only ₃0 pct in the absence of silver ion, but it is more than 97 pct in the presence of under the same leaching conditions, which suggests that silver ions ct as an active catalyst in leaching chalcopyrite with ammonium persulfate during leaching. The kinetics experiments indicates that the reaction of leaching chalcopyrite with ammonium persulfate is controlled by diffusion and the kinetics equation is derived as follows:l-|a-(l-a)l =0.0685fr.)"*. [Ag+]°-27[S2082f"The rate constants of leaching chalcopyrite with ammonium persulfate under the catalytic action of silver ions increases by 21.18times. The analysis of leaching mechanism indicates that the direct action of 52Og2" on chalcopyrite, producing Fe2+, Cu2+ and S;plays a dominant role in the dissolution of chalcopyrite, but S2Og can also oxidize Fe2+ to Fe3+ which can, in turn, oxidize chalcopyrite to produce Fe2+, Cu2+ and S. Thus, leaching of chalcopyrite with ammonium persulfate is the common results of the direct and indirect action between 52O82" and chalcopyrite, but the direct action between S2Oï¿¡ and chalcopyrite is prevailing during leaching.The analysis results of leach residue show that iron exists in the form of pyrite, which suggests that pyrite is not oxidized and dissolved during leaching process. The unleached chalcopyrite particles are wrapped in the elemental sulfur produced, being of porous and permeable texture, and the Ag2S produced from the added silver ions. The elemental sulfur produced during the leach is stable, and it is not oxidized further.The leaching experiment results show that leaching chalcopyrite with ammonium persulfate in the presence of silver sulfide is practicable and the leaching rate is high. The experiments are also carried out under the conditions of weak acid and relatively low temperature, and the satisfactory leaching rate obtained indicates that leaching chalcopyrite at ambient temperature is practicable. In addition, based on the results of mechanism-analysis of leaching chalcopyrite with ammonium persulfate in the presence of silver sulfide, the experiment of the catalyst replaced by the leach residue obtained from leaching of chalcopyrite with ammonium persulfate in the presence of silver ions was accomplished. The result show leaching chalcopyrite with ammonium persulfate by the leach residue as catalyst at low temperature was practical. 2.The experimental results of leaching chalcopyrite with ammonium persulfate in the presence of silver ion under the ultrasonic irradiation show that the leaching reaction is self-catalyzed reaction, and the rate equation is derived as follows:Under the ultrasonic irradiation, the apparent rate constants increase by 5.81 times. The analysis results of leach residue indicate that the elemental sulfur in the residue is discrete and surface-uneven, which suggests that the sulfur films on the surfaces of chalcopyrite particles are broken by the effect of ultrasonic cavitation effect and fall off the surfaces of unleached chalcopyrite cores <, As the result of that, the exposure of new surfaces of chalcopyrite contracts with oxidant and catalyst, and this facilitates the dissolution of chalcopyrite. 3.The experimental results of leaching chalcopyrite with ammonium persulfate in the presenceof silver ion under the microwave irradiation show that the leaching rate of copper reaches more than twice that under the conditions of conventional heat and in the absence of silver ions. The of results kinetic experiment show that the leaching reaction is chemical controlled, and the apparent rate constants increase by 2.79 times. The overall apparent rate equation is derived as follows:4>=1238.01X r/1The analysis of leaching mechanism shows that the stirring effect produced by microwave irradiation breaks the elemental sulfur films on the surfaces of chalcopyrite particles and makes the elemental sulfur films disperse discretely in the residue. The exposure of unreacted chalcopyrite cores facilitates the dissolution of chalcopyrite. IIIn Examination of treatment of the leach residue and leach solutionProcessing technologies for the leach residue and solution are carried out, and the technology to treat the leaching residue also determined. The cycle use of catalyst silver ions and the oxidant by regeneration is realized. IV > Application of this process to leaching other sulphide mineralsThe experimental results show that leaching complex copper -nickel sulfide ores of various grades with ammonium persulfate in the presence of silver ions at relative low temperature is practicable, which opens up wide prospect for the application of this process.In summary, a novel process of wet chemical leaching chalcopyrite and other sulphide minerals is researched. The advantages of this process are: high leaching rate, simple operation, short flowsheet, regeneration cycle of catalyst and oxidant, and high environmental acceptability. This process meets the requirements of green clean production, and is a new promising hydrometallurgical method of direct leaching sulfide ores.