A Study Of Bioextraction And Electrochemical Performance On Chalcopyrite

Bioleaching of sulfide minerals was a complex process with the participation ofmicroorganisms, involving biooxidation, chemical reaction, electrochemical reaction,diffusion of reactant and product. In this paper, the increment of Acidianus brierleyiand the bioleaching of chalcopyrite were studied. The electrochemistry mechanismsof the chalcopyrite oxidation and sulfide anode behavior were studied using thechalcopyrite-carbon paste electrode.The application of thermophilic Acidianus brierleyi to leach chalcopyriteconcentrate had been investigated in shake flask. The results showed that84%ofcopper was leached which was more than that in the sterile. Controlling appropriateleaching system potential (400mV-500mV), the copper leaching rate can reach ashigh as98%and the copper almost released from chalcopyrite. Ferrous in the solutionwas oxidized to ferric by bacteria, and then a series of complex reactions of surplusferric occurs leading to the formation of jarosite. It can be inferred that theprecipitation formed on the surface of chalcopyrite caused the diffusion barrier andthe decomposition rate was decreased.Based on the character of carbon paste electrodes, which could detect thetransient reaction process, chalcopyrite-carbon paste electrodes was made. Theintermediate reactions of the anode process of chalcopyrite were measured by CV test.In presence of Acidianus brierleyi as well as the high temperature，the anodeoxidation process of chalcopyrite were enforced with the peak current increasing. TheAcidianus brierleyi attributed to the oxidation of polysulfide formed in theintermediate process. An oxidation peak of polysulfide appeared at0.45V. At thepotential of0.25V and0.43V, reduction peaks of the formation of bornite andchalcocite appeared respectively.Electrochemical impedance spectroscopy studied at open circuit potential(around0.32V vs. Ag/AgCl) proved the existence of a thin surface layer on theelectrode. This layer was assumed to be Cu1-xFe1-yS2-zbased on reports from previousstudies. By increasing the potential, the Cu1-xFe1-yS2-zlayer partially dissolved and asecond layer (Cu1-x-zS2or Cu2-xS) formed on the surface. Further increasing ofpotential caused the formation of an S layer which hindered the dissolution rate of the electrode. The thickness of passive film which roughly estimated by Mott–Schottkytechniques was between0.98nm and1.34nm. The corresponding equivalent circuitresulted from the electrochemical impedances measurements showed that thebioleaching of chalcopyrite was controlled by both the surface chemical reaction anddiffusion process.The polarize tafel cure proved that the exchange current increased and theoxidation rate was accelerated in the presence of Acidianus brierleyi. On the otherhand, the resistance of polarization decreased from102.068k to56.359k by usingthe linear polarization technique. The apparent activation energy of the electrodeprocess was12.917kJ/mol，and the electrochemical active energy was6.386kJ/molthrough calculation of Arrhenius plot. The electrode process was controlled by solidstate diffusion.