Southern Cross GeoScience, Southern Cross University, Lismore, New South Wales 2480, Australia.
Environ Sci Technol. 2010 Mar 15;44(6):2016-21. doi: 10.1021/es903424h.
In acid-mine drainage and acid-sulfate soil environments, the cycling of Fe and As are often linked to the formation and fate of schwertmannite (Fe(8)O(8)(OH)(8-2x)(SO(4))(x)). When schwertmannite-rich material is subjected to near-neutral Fe(III)-reducing conditions (e.g., in reflooded acid-sulfate soils or mining-lake sediments), the resulting Fe(II) can catalyze transformation of schwertmannite to goethite. This work examines the effects of arsenic(V) and arsenic(III) on the Fe(II)-catalyzed transformation of schwertmannite and investigates the associated consequences of this mineral transformation for arsenic mobilization. A series of 9-day anoxic transformation experiments were conducted with synthetic schwertmannite and various additions of Fe(II), As(III), and As(V). X-ray diffraction (XRD) and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy demonstrated that, in the absence of Fe(II), schwertmannite persisted as the dominant mineral phase. Under arsenic-free conditions, 10 mM Fe(II) catalyzed rapid and complete transformation of schwertmannite to goethite. However, the magnitude of Fe(II)-catalyzed transformation decreased to 72% in the presence of 1 mM As(III) and to only 6% in the presence of 1 mM As(V). This partial Fe(II)-catalyzed transformation of As(III)-sorbed schwertmannite did not cause considerable As(III) desorption. In contrast, the formation of goethite via partial transformation of As(III)- and As(V)-sorbed schwertmannite significantly decreased arsenic mobilization under Fe(III)-reducing conditions. This implies that the Fe(II)-catalyzed transformation of schwertmannite to goethite may help to stabilize solid-phase arsenic and retard its subsequent release to groundwater.
在矿山酸性排水和酸性硫酸盐土壤环境中，铁和砷的循环通常与水铁矿（Fe(8)O(8)(OH)(8-2x)(SO(4))(x)）的形成和归宿有关。当富含水铁矿的物质处于近中性的三价铁还原条件下（例如，在重新泛滥的酸性硫酸盐土壤或采矿湖沉积物中），由此产生的二价铁可以催化水铁矿向针铁矿的转化。这项工作研究了砷（V）和砷（III）对水铁矿在 Fe(II)催化下的转化的影响，并调查了这种矿物转化对砷迁移的相关影响。进行了一系列为期 9 天的缺氧转化实验，使用合成水铁矿和各种添加的 Fe(II)、As(III)和 As(V)。X 射线衍射 (XRD) 和 Fe K 边扩展 X 射线吸收精细结构 (EXAFS) 光谱表明，在没有 Fe(II)的情况下，水铁矿仍然是主要的矿物相。在无砷条件下，10 mM Fe(II)催化水铁矿迅速且完全转化为针铁矿。然而，在 1 mM As(III)存在的情况下，Fe(II)催化转化的幅度降低到 72%，而在 1 mM As(V)存在的情况下，仅降低到 6%。这种吸附有砷（III）的水铁矿的部分 Fe(II)催化转化并没有导致大量的砷（III）解吸。相比之下，通过部分转化吸附有砷（III）和砷（V）的水铁矿形成针铁矿，显著降低了三价铁还原条件下砷的迁移。这意味着水铁矿向针铁矿的 Fe(II)催化转化可能有助于稳定固相砷，并延缓其随后向地下水的释放。
