Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment of Ministry of Education, Chongqing University, Chongqing, 400044, China.
Key Laboratory of the Three Gorges Reservoir Region's Eco-Environment of Ministry of Education, Chongqing University, Chongqing, 400044, China.
Chemosphere. 2020 Jul;251:126427. doi: 10.1016/j.chemosphere.2020.126427. Epub 2020 Mar 7.
Schwertmannite (Sch) is known to be an effective scavenger of arsenic (As) due to its strong binding affinity for toxic As species. However, the evolution of As-bearing schwertmannite under extreme pH conditions is poorly understood. In this study, we investigated the effects of extremely acidic and alkaline conditions on the stability of schwertmannite with structurally incorporated As(V) (CO-Sch) and schwertmannite with adsorbed As(V) (AD-Sch). The results show that both extremely acidic and alkaline conditions have significant effects on the evolution of minerals and liberation of iron and sulfate. At extremely acidic pH, the maximal release of ferric iron (Fe(III)) and sulfate from CO-Sch were greater than that from AD-Sch, whereas 6.2% and 0.3% of total As released from AD-Sch and CO-Sch, respectively. At extremely alkaline pH, aqueous Fe(III) was not observed, and Fe(III) was retained in As-bearing schwertmannite due to the chemical equilibrium between the dissolution of schwertmannite and re-precipitation of goethite; structurally incorporated As(V) promoted the liberation of sulfate. In addition, the adsorbed As on schwertmannite is more stable, which led to a minor release of As (0.8%) over a 30-d period, however, the liberated As(V) from CO-Sch accounts for up to 3.2%. Under extremely acidic and alkaline conditions, portions of AD-Sch and CO-Sch transformed from schwertmannite to goethite after 30 d, while schwertmannite was still the dominant mineral. Adsorbed As(V) inhibited the transformation of As-bearing schwertmannite to goethite more significantly than structurally incorporated As(V).
水铁矿是一种有效的砷（As）清除剂，因为它对有毒的 As 物种具有很强的结合亲和力。然而，结构上含有砷（V）的水羟铁锰矿（CO-Sch）和吸附砷（V）的水羟铁锰矿（AD-Sch）在极端 pH 条件下的砷行为变化还不太清楚。在这项研究中，我们研究了极端酸性和碱性条件对结构上含有砷（V）的水羟铁锰矿（CO-Sch）和吸附砷（V）的水羟铁锰矿（AD-Sch）稳定性的影响。结果表明，极端酸性和碱性条件对矿物的演化和铁和硫酸盐的释放都有显著影响。在极酸性 pH 下，CO-Sch 中释放的三价铁（Fe(III)）和硫酸盐的最大量大于 AD-Sch 中的释放量，而 AD-Sch 和 CO-Sch 中分别有 6.2%和 0.3%的总砷释放。在极碱性 pH 下，没有观察到水合三价铁（Fe(III)），由于水羟铁锰矿的溶解与针铁矿的再沉淀之间的化学平衡，含砷的水羟铁锰矿中保留了 Fe(III)；结构上含有的砷（V）促进了硫酸盐的释放。此外，吸附在水羟铁锰矿上的砷更稳定，在 30 天的时间内仅释放了 0.8%的砷（As），而 CO-Sch 中释放的 CO-Sch 中释放的砷（V）高达 3.2%。在极酸性和碱性条件下，AD-Sch 和 CO-Sch 的部分在 30 天后从水羟铁锰矿转化为针铁矿，而水羟铁锰矿仍然是主要的矿物。与结构上含有的砷（V）相比，吸附的砷（V）更能显著抑制含砷的水羟铁锰矿向针铁矿的转化。
