10-水文地球化学-氧化还原反应.pptVIP

环境与土木工程学院 地质灾害防治与地质环境保护国家重点实验室 地下水科学研究与开发中心 成都理工大学 吴 勇博士教授 * * 黄铁矿的氧化 Model of pyrite oxidation ywu@cdut.edu.cn * 黄铁矿的氧化 Detailed reactions (1) FeS2 + 7/2 O2 + H2O = Fe 2+ + 2SO42- + 2H+ (2) Fe2+ + 1/4O2 + H+ = Fe3+ + 1/2 H2O (rate limiting step) (3) Fe3+ + 3H2O = Fe(OH)3 (yellow boy) + 3H+ (4) FeS2 +14Fe3+ + 8H2O = 15Fe2+ + 2SO42- + 16H+ BOTTOM LINE = Sulphides +water +oxygen (+ bacteria) give acidity (4H+) + sulphates If this is not neutralized it can result in heavy metal mobilisation which can have disastrous environmental consequences ywu@cdut.edu.cn * a unreacted pyrite b pyrite oxidation -oxygen consumed c oxygen diffuses to oxidation layer d liquid phase -oxygen concentration in equilibrium with the gas phase e Gas phase between the waste rocks - oxygen supply by diffussion and advection Sulphide Water film Product layer MODELS OF PYRITE OXIDATION- micro scale ywu@cdut.edu.cn * Influence of bacteria ywu@cdut.edu.cn * Influence of pH on Thiobacillus （硫杆菌）activity ywu@cdut.edu.cn * Oxygen dependence of bacteria ywu@cdut.edu.cn * Importance of bacterial catalysis（催化） on oxidation rate ywu@cdut.edu.cn * Outflow at a SA Coal Mine What kind of hydrochemical process occurred in this picture ? ywu@cdut.edu.cn * FeS2 + 2CaCO3 + 3, 75O2 + 1, 5H2O ? Fe(OH) 3 + 2SO42- + 2Ca2+ + 2CO2 ywu@cdut.edu.cn * Oxidation-Reduction Reactions redox reactions often mediated by organisms Without this catalysis these reactions would be very slow organisms use redox reactions as a source of energy, they are therefore usually autotrophic bacteria ywu@cdut.edu.cn * can be treated as electron transfer reactions free or solvated electrons (e-) do not exist in aqueous solutions. Oxidation is defined as an e- loss ( increase in oxidation state). Reduction is defined as an e- gain (decrease in oxidation state). (REG) These two always happen simultaneously because free electrons (e-) do not exist in aqueous solutions ywu@cdut.edu.cn * Redox reactions are written as two