Aluminosilicate clay minerals are often a major component of soils and sediments and many of these clays contain structural Fe (e.g., smectites and illites). Structural Fe(III) in smectite clays is redox active and can be reduced to Fe(II) by biotic and abiotic processes. Fe(II)-bearing minerals such as magnetite and green rust can reduce Hg(II) to Hg(0); however, the ability of other environmentally relevant Fe(II) phases, such as structural Fe(II) in smectite clays, to reduce Hg(II) is largely undetermined. We conducted experiments examining the potential for reduction of Hg(II) by smectite clay minerals containing 0–25 wt% Fe. Fe(III) in the clays (SYn-1 synthetic mica-montmorillonite, SWy-2 montmorillonite, NAu-1 and NAu-2 nontronite, and a nontronite from Cheney, Washington (CWN)) was reduced to Fe(II) using the citrate-bicarbonate-dithionite method. Experiments were initiated by adding 500 µM Hg(II) to reduced clay suspensions (4 g clay L⁻¹) buffered at pH 7.2 in 20 mM 3-morpholinopropane-1-sulfonic acid (MOPS). The potential for Hg(II) reduction in the presence of chloride (0–10 mM) and at pH 5–9 was examined in the presence of reduced NAu-1. Analysis of the samples by Hg L_III-edge X-ray absorption fine structure (XAFS) spectroscopy indicated little to no reduction of Hg(II) by SYn-1 (0% Fe), while reduction of Hg(II) to Hg(0) was observed in the presence of reduced SWy-2, NAu-1, NAu-2, and CWN (2.8–24.8% Fe). Hg(II) was reduced to Hg(0) by NAu-1 at all pH and chloride concentrations examined. These results suggest that Fe(II)-bearing smectite clays may contribute to Hg(II) reduction in suboxic/anoxic soils and sediments.

中文翻译：

---

含Fe（II）的蒙脱石粘土矿物对Hg（II）的还原

硅铝酸盐粘土矿物通常是土壤和沉积物的主要成分，其中许多粘土都含有结构性的铁（例如绿土和伊利石）。蒙脱石粘土中的结构Fe（III）具有氧化还原活性，并且可以通过生物和非生物过程还原为Fe（II）。含铁（II）的矿物，例如磁铁矿和绿锈可以将Hg（II）还原为Hg（0）；然而，其他与环境有关的Fe（II）相（例如蒙脱石粘土中的结构Fe（II））还原Hg（II）的能力仍未确定。我们进行了实验，研究了含0-25 wt％铁的绿土粘土矿物减少Hg（II）的潜力。粘土中的Fe（III）（SYn-1合成云母-蒙脱土，SWy-2蒙脱土，NAu-1和NAu-2脱脱石，以及Cheney的脱脱石，使用柠檬酸氢盐-碳酸氢盐-连二亚硫酸盐方法将Washington（CWN）还原为Fe（II）。通过将500 µM Hg（II）添加到减少的粘土悬浮液（4 g粘土L^-1）在20 mM 3-吗啉代丙烷-1-磺酸（MOPS）中于pH 7.2缓冲。在存在还原的NAu-1的情况下，检查了在存在氯化物（0–10 mM）和pH为5–9时Hg（II）还原的潜力。通过Hg L _III边缘X射线吸收精细结构（XAFS）光谱对样品进行分析表明，SYn-1（0％Fe）几乎不还原Hg（II），而Hg（II）还原为Hg（II） 0）在还原的SWy-2，NAu-1，NAu-2和CWN（2.82.88％的铁）存在下观察到。在所有检测的pH和氯化物浓度下，NAu-1均可将Hg（II）还原为Hg（0）。这些结果表明，含Fe（II）的蒙脱石粘土可能有助于减少低氧/缺氧土壤和沉积物中的Hg（II）。