Chalcocite Surface Passivation During Bioleaching And Its Electrochemistry Studies

The oxidation of chalcocite was devided into two stages,during the initial stage,a passivation layer was formed on the surface which resulted in the slow dissolution rate of the later stage.At present,the passivating mechanisms during chalcocite bioleaching process and its remove mechanisms were proved inconclusive,therefore,the electrochemical studies of chalcocite would have a significant impact on the eliminating passivation and increasing the efficiency of chalcocite bioleaching.The research of passivating during chalcocite bioleaching was carried out in this article.Cyclic voltammetry and anode polarization curves were used for the electrochemical oxidation mechanism research of chalcocite in the absence and presence of Acidithiobacillus sp.and Leptospirillum sp.mixture.Tafel curves and the AC impedance maps and potentiostatic polarization curves were used for the electrochemical kinetics.The effects of bacteria,pH and temperature on the electrochemical behavior of chalcocite were studied.Based on the results of electrochemistry of chalcocite,the actual mineral bioleaching was carried out.The main oxidation product of chalcocite bioleaching was covellite,while there were other intermediate products which contained sulfur.In the later stage of bioleaching process of chalcocite,intermediate products transformed into(Sn2-)and(SO42-)gradually,and the(Sn2-)was the main passivation substance,which indicating that chalcocite bioleaching was a method of producing multisulfur substances.From the initial stage to the later stage of bioleaching process,the content of(S2-)in the biotic system was lower than in the abiotic system,the(S22-)and(S0)species stayed basically stable but the(Sn2-)increased to more than 20%.After the temperature raised to 40 ?,the passivating species(Sn2-)decreased to no more than 1%while(SO42-)accounted for 87.3%in the sulfur species.The potential in the later stage was lower than 0.4 V(vs Ag/AgCl),the bacteria strains were lack of activity,so high temperature would accelerate the dissolution of(Sn2-),the passivation effect on the chalcocite surface was declined,bacteria had a weak effect in this process..The optimization experiment which contained a normal temperature in the initial stage and an increase temperature in the later stage achieved a copper leaching rate of 82.08%.The High-throughput sequencing analysis showed the Leptospirillum sp.was the dominant bacteria in the initial stage,which accounted for 69.53%in the bacteria strains,and Acidithiobacillus sp.became the dominant bacteria in the later stage,which accounted for 81.83%in the bacteria strains.Regulating leaching conditions to make it more suitable for the growth of Acidthiobacillus sp.,it is beneficial to reduce the passivation effect of chalcocite surface and promote the dissolution of chalcocite.Cyclic voltammetry curves showed that the current density in the biotic system was higher than in the abiotic system.Anode polarization curves showed a wider potential zoom of active dissolution(biotic:0.236 V?0.933 V,abiotic:0.230 V?0.659 V),which indicated that bacteria enhanced the oxidation of chalcocite.Chalcocite was oxidized to mid products when the potential was higher than 0.230 V(vs Ag/AgCl).Reducing the pH or increasing the temperature would enhance the corrosion potential and corrosion current,and weaken the polarization resistance,From this aspect,the electrochemical corrosion rate of chalcocite was accelerated.The pH affected the initial stage while temperature affected the later stage leaching.