Schwertmannite(Sch)被认为是一种有效的铬(Cr)去除剂,因为它对有毒的Cr物种具有很强的亲和力。由于Sch的不稳定性,在Sch转变为更稳定的晶相过程中,Cr的环境命运值得关注。普遍存在的锰(II)(Mn(II))可能会影响Sch的转化,从而影响Cr的环境命运。因此,这项研究调查了Mn(II)对Cr吸收的Sch(Cr-Sch)的转化以及SO42-和Cr的相关行为的影响。我们揭示了Cr-Sch在pH3.0和7.0下的转化产物是针铁矿和Sch,分别。Mn(Ⅱ)的存在削弱了转化产物的结晶度,趋势与Mn(Ⅱ)浓度呈正相关。然而,Mn(II)在pH10.0时改变了Cr-Sch从赤铁矿到针铁矿的转化产物。Mn(II)取代矿物结构中的Fe(III)或形成具有表面羟基(-OH)的Mn-O配合物,从而影响Sch的转化途径。在pH3.0和7.0时,Mn(II)的存在增强了Cr在矿物上的固定。Sch很可能为Mn(II)和Cr(VI)之间的电子转移提供通道,这促进了Cr(VI)的还原。同时,Mn(Ⅱ)在次生矿物表面诱导产生更多的-OH,在提高Cr固色性方面发挥了重要作用。此外,在pH3.0和7.0条件下,部分Mn(Ⅱ)被氧化为Mn(Ⅲ)/Mn(Ⅳ)。这项研究有助于预测Mn(II)在环境中Cr-Sch转化中的作用,并设计Cr污染的修复策略。
Schwertmannite (Sch) is considered as an effective remover of Chromium (Cr) due to its strong affinity for toxic Cr species. Since the instability of Sch, the environmental fate of Cr deserves attention during the transformation of Sch into a more stable crystalline phase. The ubiquitous manganese(II) (Mn(II)) probably affects the transformation of Sch and thus the environmental fate of Cr. Therefore, this study investigated the impact of Mn(II) on the transformation of Cr-absorbed Sch (Cr-Sch) and the associated behavior of SO42- and Cr. We revealed that the transformation products of Cr-Sch at pH 3.0 and 7.0 were goethite and Sch, respectively. The presence of Mn(II) weakened the crystallinity of the transformation products, and the trend was positively correlated with the concentration of Mn(II). However, Mn(II) changed the transformation products of Cr-Sch from hematite to goethite at pH 10.0. Mn(II) replaced Fe(III) in the mineral structures or formed Mn-O complexes with surface hydroxyl groups (-OH), thereby affecting the transformation pathways of Sch. The presence of Mn(II) enhanced the immobilization of Cr on minerals at pH 3.0 and 7.0. Sch is likely to provide an channel for electron transfer between Mn(II) and Cr(VI), which promotes the reduction of Cr(VI). Meanwhile, Mn(Ⅱ) induced more -OH production on the surface of secondary minerals, which played an important role in increasing the Cr fixation. In addition, part of the Mn(Ⅱ) was oxidized to Mn(Ⅲ)/Mn(Ⅳ) at pH 3.0 and pH 7.0. This study helps to predict the role of Mn(II) in the transformations of Cr-Sch in environments and design remediation strategies for Cr contamination.