Studies On Bacterial Leaching Mechanism For Low-grade Chalcopyrite

This thesis discussed the bioleaching mechanism for chalcopyrite from the aspects of thermodynamics .electrochemistry and bacteriology. The bacteria strain used in this study is thiobacillus ferrooxidans. In the presence of Ag ion, the feasibility of bacterial leaching of chalcopyrite in thermodynamics also be debated. Meanwhile, the mechanism and principle of Ag ion catalyzing bacterial leaching of chalcopyrite are analyzed.The Pengzhou copper ore located in Sichuang Province is composed of chalcopyrite-quartz-pyrite. It is difficult to leaching from electrochemistry. The leaching rate is only 4-9% after 25 days leaching when there is only bacteria and without silver ions. The reasons of lower leaching rate locate in two sides: one is that the quartz impede the contact between chalcopyrite and pyrite from the electrochemistry view. So it is disadvantage to reaction by electrochemistry. On the other side, there is too higher iron ions concentration in the copper ores, and the ferric ions restrain the leaching of copper when the bacteria transform the ferrous ions into ferric ions. Under the optimized conditions, the leaching rate of copper significantly increases to 81% after 25 days leaching with Ag ions catalyzing. Therefore the Ag ions can remarkably improve the bioleaching rate of copper in chalcopyrite. When the Ag ions are added to the leaching system, it rapidly combine with sulfuric ores and form precipitated silver sulfide. During the ferric ion ceaselessly transform the silver sulfides into Ag ions, which reduce the ferric ions restraining to copper leaching. In the view of electrochemistry, the silver sulfide voltage is the highest positive in many kinds of sulfides. It can form a million of micro-cell with chalcopyrite, and the solubility of sulfuric silver is lower than other sulfides. Ag ions substitute the metallic ion in the chalcopyrite. So the many of tiny cells composed of silver sulfide with sulfides are produced on the surface of the copper ore, which promote the process of leaching of chalcopyrite.While the bacteria leaching chalcopyrite, the bacteria chiefly corrode the ore surface by direct adsorption, the mathematic model produced by bacterial direct leaching mechanism can well predict the bioleaching rate of chalcopyrite. In the presence of the Ag ions, it can circularly substitute metallic ions of chalcopyrite, the copper ions are produced continuously. So the Ag ions catalyzing bacterial leaching kinetic models produced by bacterial indirect leaching mechanism can well predict the rate of copper hi chalcopyrite.