Author: Yang Yi
Yi, Yang, 2015 The Effect of Microorganisms on the Surface Properties of Chalcopyrite, Flinders University, School of Chemical and Physical Sciences
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To understand the chalcopyrite dissolution and passivation mechanism during bioleaching, the leaching kinetics, surface species, mineralogy and bacteria-mineral interaction under different conditions (temperature, Eh, pyrite, Ag+ and bacteria species) have been investigated. X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), Powder X-ray diffraction (XRD), Raman spectroscopy, X-ray fluorescence microscopy (XFM) and Electron backscatter diffraction (EBSD) have been applied in this study. The results indicate thermophiles significantly enhanced the leaching efficiency, which was mostly caused by the increased abiotic reaction rate. Cu K-edge XANES analysis indicated the formation of CuSn-like species in the early stages of leaching. XPS results show a sulfur-rich layer developed with time which is likely to be the rate limiting factor of the surface reaction. There is no significant difference on surface sulfur speciation between the chalcopyrite bioleached at 48 or 30 oC. The electrochemical studies show that there was an activated region in the middle of two passive regions for chalcopyrite dissolution. In the active region, between 550 to 630 mV (vs. Ag/AgCl), Sn2-/S0, S22- species and covellite were found by XPS and Raman. XPS study suggested a thin sulfur rich layer formed in the first passive region (530 mV). At 650 mV, S22- species and covellite started to dissolve, leaving a highly metal deficient polysulfide layer. Bacterial concentration at the mineral surfaces increased to about 5-7% coverage in 24 hrs. Raman spectroscopy showed the presence of organic species in the colourful film covered areas, which confirmed the formation of biofilm. From EBSD and optical images analysis, no significant difference in selectivity of bacterial attachment was found on crystal orientation of chalcopyrite. Low Eh (350-480 mV vs. Ag/AgCl) significantly promoted the chalcopyrite (bio)leaching. The leaching results and quantitative XRD and XANES analysis show jarosite and elemental sulfur did not primarily account for the passivation of chalcopyrite. Secondary mineral covellite was detected in chalcopyrite dissolution. Chalcopyrite leaching was significantly enhanced by pyrite addition. Chalcopyrite was selctively leached in chemical leaching as a result of galvanic effect. The favourable influence of galvanic effect and to chalcopyrite leaching is at least partially because of its function on Eh control. However, in bioleaching pyrite dissolution was significant which decreased the chalcopyrite leaching efficiency. μ-XRF and Raman studies suggest a sulfur-rich layer developed inhomogenously on mineral. The galvanic effect was also verified in column leaching of low grade chalcopyrite, which increased the yield of copper by a factor of about 3 in bioleaching. The bioleaching effeciency of chalcopyrite was enhanced at low concentration of Ag+ but decreased at high concentration of Ag+. AgCuS species was found in the leaching residue. The solution pH of the case with high concentration of Ag+ increased significantly in bioleaching but not in chemical leaching, which caused the formation of hematite.
Keywords: chalcopyrite,bioleaching,surface properties,passivation
Subject: Chemistry thesis, Physics thesis
Thesis type: Doctor of Philosophy
School: School of Chemical and Physical Sciences
Supervisor: Dr Sarah Harmer-Bassell