砷矿区变化环境条件下地表水胶体相砷形态转化过程与机理

Arsenic is a toxic element, arsenicals in the land surface can be high thread to human health. The mobility and toxicity of arsenic (As) in aquatic environments are largely dependent on the interaction between As, colloids and dissolved organic matter(DOM). At present, studies on such interactions have been conducted mainly on indoor controlled experiments, with spiked As, iron oxides and humic acids, and the related mechanisms were further elucidated, however, the actual behavior of As as related to such mechanisms in real earth conditions are rather complicated due to the impact of various factors, which still left much to be resolved. The project will be conducted on high As surficial watershed around Shimen Algar Mine area, with sample collections at different area, e.g., rivers and lakes, water depth, and seasons, the colloids and the dissolved solutions will be obtained in situ using cross-flow-fractionation method via accumulation. The colloids and solutions will be measured for As contents and speciation, mineral and elemental constitution, radical and functional groups, DOM constitutions and properties, using a series of instruments and methodologies, such as ATR-FTIR, XRD, SEM, stable isotope tracing, SR-XAS, etc.. Batch experiments will be performed according on the clue getting from the field studies, data will be simulated into theoretical calculations like thermodynamic and surface complexation models, to further resolve the potential mechanisms of the ternary formation of As-colloids-DOM in the surficial waters with high As levels. The results are expected to contribute to further understanding the environmental behavior of As in aquatic environments, and to provide basis on prevention of As contamination and treatment of As polluted waters.

水环境中砷的移动性和生物毒性很大程度上决定于其与胶体相的相互作用。目前对此认识多基于一些室内模拟实验结果，而对野外实际环境条件下的相关机理与过程则了解甚少，主要受环境条件复杂、现场分离富集难和不易达到室内仪器检出限等条件所限制。本项目拟选择石门雄黄矿区高砷地表水系，采集高砷河流、湖库不同区域、水深和不同季节水样，采用切向流超滤分离富集技术，获取矿区高砷地表水系变化环境条件下胶体相和真溶液相，应用红外光谱、X射线衍射、核磁共振等多种表征手段与方法，研究胶体中砷形态、无机胶体相组成、DOM组成性质与官能团特征，分析其中的相互关系；根据野外关键线索开展室内模拟实验，采用表面络合模型与地球化学热力学理论计算推断砷的结合形态；将模拟实验结果与野外结果对比进行综合分析，深入揭示变化环境下地表水系砷形态转化机理及其控制与影响因素。研究成果可为认识地表水砷的环境地球化学行为及控制地表水砷污染提供科学依据。

项目通过实地采集矿区不同位置、季节与类型（溪流、湖叉、湖库区）水体样品，现场采用切向流胶体提取分离装置分离富集不同分子量级别的胶体以及真溶液样本，在室内采用多种手段对各级胶体及真溶液中As的总量和赋存形态、DOM的组成和结构特征进行表征与分析，初步揭示了高砷区地表水体砷的结合形态、机理及其影响与控制因素。结果表明：矿区黄水溪和皂市水库水体不同分子量组分中理化参数呈现明显的季节性变化规律。石门雄黄矿区虽已经过五期的治理修复，但黄水溪和皂市水库仍继续受到过去砷矿开采和冶炼活动的影响，地表水体砷含量范围为24.2-1897 μg/L，是我国地表水环境质量标准I类标准值的0.5-38倍。矿区夏、秋季黄水溪和皂市水库地表水中DOC含量范围为2.9-9.2 mg/L和1.3-3.0 mg/L，主要分布在真溶态（68%-82%）中，胶体态DOC含量仅占18%-32%，且主要分布在较小分子量胶体组分中。矿区地表水中As主要以As(V)和As(III)形态存在，主要分布于真溶态（77%-96%），胶体态砷占过滤水砷含量的12%左右。地表水胶体态As(V)主要存在于3-10kDa组分中，与DOC含量呈现显著正相关，As(V)主要与较小的有机/金属有机胶体络合，而胶体态As(III)主要存在于100kDa-0.7μm组分中，As(III)主要与较大的无机胶体络合。FTIR光谱证明As与DOM和Fe的络合，其络合方式主要包括As-DOM二元和As-Fe-DOM三元形式。矿区地表水DOM呈现出空间差异，随上游黄水溪到下游皂市水库，外源贡献率逐渐减小，而内源贡献率逐渐增加。三维荧光组分分析显示，DOM的主要为陆源类腐殖质、微生物类腐殖质和类蛋白，由含不同C、H、O、N元素，少量含有S元素的分子组成，木质素类化合物是DOM最丰富的成分。地表水中As与DOM的紫外、荧光和质谱参数的相关性分析表明，高砷地表水DOM主要具有高腐殖化程度、不饱和度和芳香度以及低生物活性的特征。多元统计分析结果表明，研究区地表水体中，As与DOM的络合过程受到环境因素和DOM自身因素的影响。环境因子，如高Al3+、Fe3+和Mn2+，低EC和TDS环境有利于As与DOM的络合（p<0.05），而高Ca2+和Mg2+环境作用则相反。