Hanumantha Rao Kota
Norwegian University of Science and Technology, Norway
Title: Implications in sulphide mineral processing with new insights into metal sulphides oxidation during grinding by H2O2 generation
Biography
Biography: Hanumantha Rao Kota
Abstract
Recent studies reveal the formation of reactive, oxidizing oxygen species and H2O2 by sulfides interacting with water due to the catalytic activity of sulfide surfaces. The formation of hydrogen peroxide (H2O2) by sulfide minerals during grinding was investigated by us1-5. It was found that pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite (ZnS), and galena (PbS), which are the most abundant sulfide minerals on Earth, generated H2O2 in pulp liquid during wet grinding in the presence and absence of dissolved oxygen in water and also when the freshly ground solids were placed in water immediately after dry grinding. Pyrite generated more H2O2 than the other sulphide minerals and the order of H2O2 production by the minerals was found to be pyrite > chalcopyrite > sphalerite > galena. The amount of H2O2 formed also increases with increasing sulfide mineral loading and grinding time due to increased surface area and its interaction with water. The sulfide surfaces are highly catalytically active due to surface defects capable of breaking down the water molecule leading to hydroxyl free radicals. The type of grinding medium on formation of hydrogen peroxide by pyrite revealed that the mild steel produced more H2O2 than stainless steel grinding medium, where Fe2+ and/or Fe3+ ions played a key role in producing higher amounts of H2O2. The results of the amount of H2O2 production corroborate with the rest potential of the sulfide minerals; higher the rest potential, more is the formation of H2O2. Most likely H2O2 is responsible for the oxidation of sulfide minerals and dissolution of non-ferrous metal sulfides in the presence of ferrous sulfide besides the galvanic interactions reported in the literature. Studies have also been carried out to build correlation between percentage of pyrite in the concentrate, grinding conditions and concentration of OH•/ H2O2 in the pulp and as well of controlling the formation of these species through known chemical means for depressing the generation of the oxidant. The results demonstrate that the selectivity of metal sulphides against pyrite increases with increasing generation of H2O2 in the pulp liquid. These studies highlight the necessity of revisiting the electrochemical and/or galvanic interactions between the grinding medium and sulphide minerals, and interaction mechanisms between pyrite and other sulphide minerals in terms of their flotation behaviour, leaching and environmental degradation in the context of inevitable H2O2 existence in the pulp liquid.