Study On Chemical Transformation On The Surface Of Chalcopyrite During The Bioleaching Process

The dissolution characteristics of different phase chalcopyrite and its mineralogical and chemical phase transformation were systematically investigated by electrochemical measurements, XRD, SEM and in situ Powder Diffraction of Synchrotron, during bioleaching by the adapted effective bacteria.The physiological characteristics of the adapted culture were studied. It was showed that the culture had a wide growth range of temperature (25-40℃) and pH (1.0-3.5), with the optimal temperature at30℃and pH at2.0. This culture had fairly high oxidative activity of ferrous ion and S0.96%ferrous ion were oxidized in60hours under the optimal condition in9K medium, and the pH of medium decreased to0.8cause of the oxidation of S0into SO42-. This culture could resist Cu2+, total Fe, Ni2+and Mg2+up to20g/L,25g/L,12g/L and20g/L respectively. And the optimal potential range was502-750mV vs. SCE.Eh-pH diagrams of Cu-H2O, Fe-H2O, S-H2O, Cu-S-H2O, Fe-S-H2O as well as Cu-Fe-S-H2O system for physical conditions and sulfide minerals-H2O were drew. It was obsevered that the iron mainly existed as Fe2+and Fe3+, of which the theoretical potential of transformation was0.771V. Cu2+was the stable component of copper in of bioleaching of copper sulphide, and Cu+might exist while the potential was below0.161V. S existed in multiple valence states, HSO4-and SO42-were stable components in higher potential, while pH=1.99was the equilibrium condition of transformation. At lower potential as well as higher pH, sulphur was reduced to H2S, H2S translated into HS-with the potential reduce and pH increase. Moreover, HS-was oxidized to SO42-with potential increased at pH above6. While less than6, H2S was oxidized to S0, S4O62-,S2O32-, SO2, HSO-and S2O62-. HS-would be oxidized to SO32-, and then to S2O62-at alkalic solution. In the bioleaching of copper sulfide, there was a relatively broad region for the existence of Cu2S and CuS which were the intermediate product in the dissolution of copper-iron sulfides. The CuFeS2could be dissolved by two ways as CuFeS2→CuS→Cu2+and CuFeS2→CuS-Cu2S→Cu2+. Preferential release of iron from sulfide minerals was the first step of copper-iron sulfide minerals dissolution.The chalcopyrite with different phase was obtained by quenching at desired temperature and the basic properties of the chalcopyrite weith different phase were also investigated. As shown from the result of XRD, when chalcopyrite was quenched below200℃, it existed in the stable form of phase a, the parameters of lattice was a=b=5.2894A, c=10.4221A, respectively. As for the sample quenched between200℃and420℃, the lattice size of the quenched chalcopyrite increases rapidly as long as the temperature increased. For the sample quenched at552℃, the lattice size of chalcopyrite increased significantly with the roasting time. Elemental sulfur played a pivotal role in the process of chalcopyrite phase modification. The in situ study of the phase transformation indicated that the phase modification of chalcopyrite could be divided into three stages:in the first stage, chalcopyrite presented as tetragonal crystal, the lattice size increased with the temperature. The second phase of the temperature ranging from490℃to550℃, chalcopyrite had accomplished the process of phase modification, in which chalcopyrite transferred from tetragonal crystal to cubic crystal with the lattice size increased. The last phase of the experiments, temperature ranging from550℃to600℃, chalcopyrite existed in form of cubic crystals in the zone. The mixed bacterial leaching test showed that, when chalcopyrite was roasted under the conditions of natural temperature,203℃,382℃and552℃, the leaching rate of copper were30.98%,32.99%,40.54%and60.95%, respectively. The high leaching rate mostly lies in the larger chalcopyrite lattice size and lower lattice energy.The electrochemical studies of the chalcopyrite with different phases showed that the Open Circuit Potential reduced as the quenched temperature increase. The Open Circuit Potential of nature chalcopyrite was214mV, and188mV at203℃,176mV at382℃and56mV at552℃. The anodic oxidation process of the different phase chalcopyrite was similar to nature chalcopyrite and three oxidation peaks was determined. However, with temperature increased, the cathodic peaks reduced. The corrosion potential of the different chalcopyrite modification electrode decreased and the corrosion current density increased with the roasting temperature. The corrosion current indensity of nature chalcopyrite was0.461μA·cm-2, and increased to0.457μA·cm-2and0.837μA·cm-2at203℃and382℃, respectively, finally reduced to2.221μA·cm-2at552℃. The corrosion resistance of nature chalcopyrite was80.31kΩ·cm2and it were54.03kΩ·m2and28.84kΩ·cm2quenched at203℃and382℃respectively. The corrosion resistance reduced to9.09kΩ·cm2at552℃In the bioleaching of chalcopyrite, Cu8S5and Cu3.39Fe0.61S4was observed as intermediate products. The ratio of Cu Fe S is5.5:1:6.5in Cu3.39Fe0.61S4which was the copper-iron sulphied with abundant sulpher. Preferential dissolution of iron was the first step of chalcopyrite dissolution. CuxFeySz was determined as the product of the first step of bornite dissolution caused by the preferential release from bornite. In addition, Cu8S5, CU7S4, Cu39S28, CuS, Cu2S and other intermediate substances formed during the bioleaching of bornite. The dissolution bornite could be described as followas:The bioleaching of chalcopyrite by mixed culture and A.f was carried out. It was indicated that the bioleaching process could be devided into two steps. At first step the preponderant bacteria was iron oxidation bacteria, furthermore, the leaching rate keep in high level and the redox potential increased rapidlly. However, at the second step the sulphur oxidation bacteria were preponderant. The redox potential keep at stable and the pH of solution reduce significantly because of the oxidation of sulpher by the sulphur oxidation bacteria. Furthermore, the copper extraction was enhached by inoculating the sulphur oxidation bacteria at the end of the fist step, resulting as the the copper extraction reached to43.78%after leaching for75days throuth inoculating the A.t and A.caldus into the leaching system.The extraction of copper reached43.64%after leaching75days by mixed culture B using the column reacter with the partical size of ore at-10+5mm, spraying intensity3ml/cm2·h and at natural temperature.