Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic.
Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic.
Sci Total Environ. 2022 May 1;819:152008. doi: 10.1016/j.scitotenv.2021.152008. Epub 2021 Nov 28.
Arsenic incorporation into newly formed As sulfides has recently been identified as an important As sequestration pathway in both laboratory experiments and natural As-wetlands. Here, we used an in situ experimental technique with double nylon experimental bags (10-μm mesh) to study the effect of low-cost organic materials (sawdust, wood cubes and hemp shives) on As sulfidation in three naturally As-enriched wetland soils under water-saturated (1 m depth) and neutral pH conditions. After 15 months of in situ incubation, all of the organic materials and their corresponding inner bags were covered by yellow-black mineral accumulations, dominantly composed of crystalline AsS polymorphs (realgar and bonazziite) and reactive Fe(II) sulfides (probably mackinawite); while the major fraction of As (80%) was sequestered as AsS minerals. The amount of As accumulation in the experimental bags varied significantly (0.03-4.24 g As kg) and corresponded with different levels of As (0.23-9.4 mg As L) in the groundwater. Our findings suggest an authigenic formation of AsS minerals in strongly reducing conditions of experimental bags by a combination of reduced exchange of solutes through the pores of the bag and comparatively fast microbial production of dissolved sulfide. Arsenic sulfide formation, as an effective treatment mechanism for natural and human-constructed wetlands, appears to be favored for As(III)-rich waters with a low Fe(II)/As(III) molar ratio. These conditions prevent the consumption of dissolved As and sulfide by their preferential incorporation into natural organic matter, and newly-formed Fe(II) sulfides, respectively.
砷与新形成的硫化物结合，最近被确定为实验室实验和天然砷湿地中砷固定的一个重要途径。在这里，我们使用原位实验技术，采用双层尼龙实验袋（10-μm 网眼），在水饱和（1 m 深度）和中性 pH 条件下，研究了三种天然富砷湿地土壤中廉价有机材料（木屑、木方块和麻纤维）对硫化砷的影响。原位孵育 15 个月后，所有有机材料及其相应的内袋都被黄色-黑色矿物覆盖，主要由结晶砷硫多形体（雄黄和钙铁辉砷矿）和反应性 Fe(II)硫化物（可能是磁黄铁矿）组成；而大部分砷（80%）被固定为砷硫矿物。实验袋中砷的积累量差异很大（0.03-4.24 g As kg），与地下水中不同水平的砷（0.23-9.4 mg As L）相对应。我们的研究结果表明，在实验袋强烈还原条件下，通过减少溶质通过袋孔的交换和相对较快的微生物产生溶解的硫化物，砷硫矿物的自生形成。砷硫化物的形成，作为天然和人工湿地的一种有效处理机制，似乎有利于富砷（III）、低 Fe(II)/As(III)摩尔比的水。这些条件可以防止溶解的 As 和硫化物被优先掺入天然有机物和新形成的 Fe(II)硫化物而消耗。
