不同来源腐殖酸对三价锑的光氧化作用及影响因素

三价锑是有毒金属锑生物地球化学循环中的不稳定还原态，其在腐殖酸体系中的光氧化过程可能是水体环境中Sb（Ⅲ）转化的重要途径.通过室内模拟实验，探讨了光照条件下不同来源腐殖酸对Sb（Ⅲ）的光氧化反应特征，并考察腐殖酸浓度、Sb（Ⅲ）初始浓度、溶液pH值、环境中普遍存在的阴阳离子等环境因素对光氧化作用的影响.结果表明：Sb（Ⅲ）在腐殖酸溶液中的光化学反应过程符合准一级动力学规律.反应体系中腐殖酸浓度的升高有利于促进Sb（Ⅲ）的光氧化作用，而Sb（Ⅲ）初始浓度增加则抑制其光氧化作用，Sb（Ⅲ）的光氧化速率常数随溶液pH值的升高而逐渐增大，褐煤来源腐殖酸对Sb（Ⅲ）的光氧化速率常数高于土壤来源腐殖酸.水环境中NO₃^-的存在促进了腐殖酸对Sb（Ⅲ）的光氧化作用，而Cl^-、SO₄^2-和Na⁺未对Sb（Ⅲ）的光氧化作用产生显著影响.羟基和超氧自由基是Sb（Ⅲ）光氧化反应中的主要活性基团，其中在酸性条件下，羟基自由基对Sb（Ⅲ）的光氧化反应起主导作用，而在中性和碱性条件下超氧自由基起主要作用.

Photoxidation of antimony(III) and influencing factors in the presence of humic acids with different origins

Antimony (Ⅲ) is the unstable reduced form involved in the biogeochemical cycling of toxic metals Sb. The photooxidation of Sb(Ⅲ) by humic acids may be the important means for environmental fates of Sb(Ⅲ) in aquatic ecosystem. In this study, the kinetic characteristics for Sb(Ⅲ) oxidation in the presence of humic acids with different origins were examined under photoirradiation. The photooxidation behaviors of Sb(Ⅲ) were investigated over a wide range of DOC concentrations, initial Sb(Ⅲ) concentrations, pH values and the occurrence of competitive ions. The mechanisms for the photoxidation of Sb(Ⅲ) by humic acids were discussed. The photooxidation of Sb(Ⅲ) by humic acids followed the pseudo-first-order kinetics model. The photooxidation rate constants increased rapidly with increasing pH values and DOC concentrations in the Sb(Ⅲ)-humic acids reaction systems. However, Sb(Ⅲ) photooxidation was inhibited with increasing initial Sb(Ⅲ) concentrations. The photooxidation rate constants of Sb(Ⅲ) under the humic acids with lignite origin were higher than that with soil origin. The occurrence of anionic NO₃^- enhanced the photooxidation of Sb(Ⅲ). However, there were no obvious effects of Cl^-、SO₄^2- and Na⁺ on Sb(Ⅲ) photooxidation. The ESR spectra suggest that hydroxyl radicals and superoxide free radicals induced by light are were reactive oxidants for Sb(Ⅲ) photooxidation. Hydroxyl radicals were the primary oxidants for Sb(Ⅲ) photooxidation under the acidic condition, and superoxide free radicals became the main photo-oxidants under the neutral and alkaline condition.