Research On The Thermophilic Leaching And Mechanism Of Chalcopyrite

This paper researched the thermophilic bioleaching and mechanism of chalcopyrite. The purpose is to reveal the passivation process of chalcopyrite. Experiments were conducted to research the effect of thermophilic bacteria,initial pH,pulp density,particle size and temperature in the bioleaching of chalcopyrite. The copper leaching rate is65.35%in42days using moderate thermophilic bacteria and the copper leaching rate is98.40%in30days using extreme thermophilic bacteria. The changing process of products in the leaching of chalcopyrite is analyzed. The experimental results indicate that moderate thermophilic bacteria and extreme thermophilic bacteria can promote the leaching of chalcopyrite, the copper leaching rate is accelerated in high temperature, jarosite can hinder the leaching of chalcopyrite, the leaching products of chalcopyrite are the same in abiotic condition, moderate thermophilic bacteria condition and extreme thermophilic bacteria condition, and the products are ferric oxide, covellite, sulfur and jarosite.The bioleaching rate of chalcopyrite using extreme thermophilic bacteria is very high, so we conducted the open circuit potential and Tafel experiments in abiotic condition and extreme thermophlic condition. The electrochemical parameters of chalcopyrite in abiotic condition and extreme thermophilic condition were measured. The open circuit potential of chalcopyrite in abiotic condition is0.530V in343K and pH2.00. The open circuit potential of chalcopyrite in extreme thermophilic condition is0.574V. The results show that the open circuit potential of chalcopyrite in extreme thermophilic condition is0.044V higher than that in abiotic condition. The reason may be that the chalcopyrite surface in extreme thermophilic condition is adsorbed by extracellular polymeric substances which has high concentrate of Fe3+. The corrosion potential of chalcopyrite in abiotic condition is0.287V and the corrosion current density is9.39×10-3A·m-2in343K and pH2.00. The corrosion potential in extreme thermophilic condition is0.320V and the corrosion current density is1.55×10-2A·m-2. The results indicate that the corrosion potential in extreme thermophilic condition is0.033V higher than that in abiotic condition, and the corrosion current density in extreme thermophilic condition is6.11×10-3A·m-2higher than that in abiotic condition. The reason may be that the chalcopyrite surface in extreme thermophilic condition is adsorbed by extracellular polymeric substances. The extracellular polymeric substances lead to form oxygen concentration cell and ionic concentration cell which can enhance the leaching of chalcopyrite. The experiments indicate that the extreme thermophilic bacterial can enhance the leaching of chalcopyrite.In order to discuss the effect of redox potential on the leaching of chalcopyrite, the AC impedance spectrum experiments were conducted in abiotic condition and extreme thermophilic condition. The experiments show that high electrode potential is beneficial to the dissolution of chalcopyrite at the potential range of0.350V to0.850V. However, the diffusion impedance is increased rapidly with the rising of potential at the range of0.450V to0.650V in both abiotic condition and extreme thermophilic condition. The result indicates that the dissolution of chalcopyrite is hindered in the range of0.450V to0.650V. At the potential range of0.350V to0.450V, chalcopyrite may be oxidized and produces CuS, S0and Fe2+, and the diffusion impedance increases slowly in both abiotic condition and extreme thermophilic condition. These results show that CuS and S0have little effect on the dissolution of chalcopyrite. At the potential range of0.450V to0.650V, chalcopyrite may be oxidized and produces Fe2O3, CuO and S0, and the diffusion impedance increases rapidly in both abiotic condition and extreme thermophilic condition. These results show that Fe2O3and S0may be the passivation of chalcopyrite. At the potential range of0.650V to0.850V, the diffusion impedance decreases rapidly. The results show that the passivation layer of chalcopyrite may be destroyed. S0is not the passivation of chalcopyrite at the range of0.350V to0.450V, so S0may be not the passivation of chalcopyrite at the range of0.450V to0.650V. The AC impedance spectrum experiments show that Fe2O3may be the passivation of chalcopyrite.Combined with the results of leaching products of chalcopyrite, cyclic voltammetry experiments and thermodynamic calculation, this paper studies the electrochemical reactions of chalcopyrite in leaching. The potential-pH diagrams of CuFeS2-H2O system are plotted in298K,318K and343K under different ionic activity using the electrochemical reactions of chalcopyrite. The stability of substance on the potential-pH diagram is analyzed. The stability of products in the bioleaching of chalcopyrite using moderate thermophilic bacteria and extreme thermophilic bacterial are also analyzised. Before the optimal conditions of moderate thermophilic leaching of chalcopyrite, S0, CuS and Fe2O3/Fe(OH)3are unstable. After42days, S0and CuS are unstable, and Fe2O3/Fe(OH)3are stable in pH>2.01. Before the optimal conditions of extreme thermophilic leaching of chalcopyrite, S0, CuS and Fe2O3/Fe(OH)3are unstable. After30days, S0and CuS are unstable, and Fe2O3/Fe(OH)3are stable in pH>2.48. The experimental results show that the electrochemical reactions of chalcopyrite in low electrode potential and high electrode potential are different and Fe2O3/Fe(OH)3may be the passivation layer of chalcopyrite.To sum up, moderate thermophilic bacteria and extreme thermophiles can enhance the leaching of chalcopyrite, high temperature can accelerate the leaching rate of chalcopyrite, the electrochemical reactions of chalcopyrite in low electrode potential and high electrode potential are different, and jarosite and Fe2O3/Fe(OH)3may be the passivation layer of chalcopyrite. According to these results, this paper puts forward three methods to improve the copper leaching rate of chalcopyrite.The results of this paper provide a theoretic guidance in the bio leaching of chalcopyrite.