| Mining tailing and waste residues prodced from the exploitation of sulfide minerals occupied a large amount of land, and acid soil and acid mine drainage (AMD) were formed due to their oxidation. Toxic heavy-metal elements, such as Cr, Hg and As, were leached and polluted waterway and lake, threatening ecological environments of human. Sulfide mineral resources are abundance, and have a wide distribution in China. The mineral products and consumption of China account for 50% of global production, and most of the metal and nonmetallic deposits contain iron sulfide minerals including pyrite (FeS2) and ferrous sulfide (FeS). Environmental problems resulted from the exploitation of sulfide minerals and the species, migration and transformation process of sulfide in environments attracted more and more attention of experts, and become a research focus and hot topics in the the field of envrionmental sicences and soil sciences.Manganese oxides with various crystal structures, such as layered structures including birnessite, vernadite and lithiophorite, tunnel structures including pyrolusite, cryptomelane and todorokite, and low valence state manganese oxides including manganite and hausmannite, were widely distributed in soils and minerls. Tunneled todorokite could be transformed from buserite under near room temperature and atmospheric pressure, and also could be directly formed by biology using Mn(II) sources. Therefore, todorokite would participate in redox of sulfide minerals in surface soils. Hwoever, the reported research mostly focused on the redox behaviors of birnessite and pyrolusite and sulfide minerals, and reaction between todorokite and sulfide minerals was less concerned. In this work, todorokite was prepared with different degrees of crystallinity in lab, and the redox mechanism and dynamics of todorokite and sulfides including S2- and FeS using x-ray diffraction (XRD), scanning electron microscope (SEM), ion chromatography (IC) and spectrophotography. The influence of crystallinity, the amount of todorokite and temperature on the redox process and kinetics was studied. The main topics and results of the research are summarized as follows:1. The redox process and kinetics of todorokites with higher crystallinity (Tod-25) and lower crystallinity (Tod-5) and sulfide (S2-=200 mg L"1, pH=12) were investigated with differnet quantity of minerals (0.06、0.12 and 0.24 g) and temperatures (20、30 and 40℃) under nitrogen and oxygen atmospere. These results suggested that elementary S and Mn(OH)2 were the main solid products, and a small amount of S2O32-、SO32- and SO42- in liquid phase was formed under nitrogen atmospere. The initial oxidation rate of S2+ followed a pseudofirst-order kinetic law, and the apparent rate constants (kobs) increased with elevating temperature, increasing the quantity of todorokite, a decrease in crystallinity. It was observed that the oxidation rate of S2- decreased with admission of oxygen atmosphere, and the content of S2O32-、SO32- and SO42- in the final products was increased.2. The pH affected the autocytolysis of FeS in the redox reaction between todorokite and FeS, and low pH facilitated the dissolve of FeS. It was observed that the admission of oxygen accelerate the oxidation of Fe2+ to Fe3+, and precipitate Fe(OH)3 was formed when pH was controlled at 3. The concentration of Fe3+ in reaction solution was remarkably decreased under oxygen atmosphere. Increasing of the quantity and lowering the crystallinity of todorokite accletrated the oxidation process between todorokite and FeS, when pH was controlled at 3. The admission of oxygen decrease the concentration of elementary S, S2- is possibly oxidized to form S2O32-、SO32- and SO42- in solution. |
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