草酸盐介导下含As(V)黄钾铁矾的相转化过程与As(V)的再分配行为

黄钾铁矾能够通过吸附和共沉淀作用固定酸性矿山废水（AMD）中的重（类）金属（如砷），降低其迁移性和生物可利用性.草酸盐广泛存在于天然水环境中，其具有的羧酸官能团能改变铁矿物的稳定性，进而影响吸持的重（类）金属的再分配行为.利用水热法合成含As（V）黄钾铁矾，探究其在不同草酸盐浓度与pH条件下的溶解、重结晶和共沉淀As（V）的行为.研究结果表明，草酸盐与含As（V）黄钾铁矾表面Fe（III）活性位点配位形成的可溶性强络合物是促进矿物溶解的第一步和关键；在pH 2.5时，含As（V）黄钾铁矾的溶解速率随草酸盐浓度增加而增加，伴随大量As（V）释放到溶液，反应过程中只有少量As（V）重新吸附到固相上，这是由于草酸盐与As（V）竞争矿物表面的同一活性位点；在pH 6.5条件下，草酸盐促进含As（V）黄钾铁矾的重结晶，经X射线衍射分析表明针铁矿和纤铁矿为主要产物，能有效地吸附释放的As（V）.研究结果有助于揭示在AMD环境下黄钾铁矾沉积物与含羧酸官能团有机酸共存时对As（V）的释放和固定机理，对AMD环境中As（V）污染控制有重要意义.

Phase transformation process of As(V)-bearing jarosite and redistribution behavior of As(V) under the oxalate mediating

Jarosite is considered as an effective scavenger for arsenic (As) under acid mine drainage (AMD) environment due to its strong adsorption capacity and ability to incorporate metal(loid)s. Oxalate is commonly found in natural water and exhibits a prominent contribution to the dissolution of iron minerals. In this study, the influences of oxalate on the dissolution and phase transformation of As(V)-bearing jarosite, as well as redistribution behavior of coprecipitated As(V) were investigated at pH 2.5 and 6.5 under aerobic condition. Results showed that the formation of Fe(III)-oxalate complex promoted the dissolution of As(V)-bearing jarosite and the release of As(V) under pH 2.5 condition. The insignificant re-adsorption of arsenate could be explained by the competition for Fe(III) active sites on the jarosite surface with oxalate. In addition, X-ray diffraction analysis result indicated that As(V)-bearing jarosite transformed to goethite and lepidocrocite at pH 6.5 and oxalate enhanced the crystallization of secondary minerals. After 60 d of reaction, almost all of the liberated As(V) re-adsorbed to the solid phase. It indicates that newly formed goethite and lepidocrocite play a vital role in controlling the fate of As(V). The reaction process involves that ligand promoted dissolution and recrystallization of As(V)-bearing jarosite, while As(V) is effectively immobilized by goethite and lepidocrocite. The present study reveals that carboxylic group in dissolved organic acid can exert great influence on the stability of jarosite and partitioning behavior of coprecipitated As(V) under AMD environment, which is of great significance for arsenic pollution control.