The influence of Mn(II) on transformation of Cr-absorbed Schwertmannite: Mineral phase transition and elemental fate

Hongmei Tang; Meiqing Chen; Pingxiao Wu; Yihao Li; Tianming Wang; Jiayan Wu; Leiye Sun; Zhongbo Shang

doi:10.1016/j.watres.2024.121656

The influence of Mn(II) on transformation of Cr-absorbed Schwertmannite: Mineral phase transition and elemental fate

Water Res. 2024 Apr 22:257:121656. doi: 10.1016/j.watres.2024.121656. Online ahead of print.

Authors

Hongmei Tang¹, Meiqing Chen², Pingxiao Wu³, Yihao Li⁴, Tianming Wang¹, Jiayan Wu¹, Leiye Sun¹, Zhongbo Shang¹

Affiliations

¹ School of Environment and Energy, Guangzhou Higher Education Mega Centre, South China University of Technology, Guangzhou 510006, PR China.
² School of Environment and Energy, Guangzhou Higher Education Mega Centre, South China University of Technology, Guangzhou 510006, PR China; School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, PR China. Electronic address: cmq20221@scut.edu.cn.
³ School of Environment and Energy, Guangzhou Higher Education Mega Centre, South China University of Technology, Guangzhou 510006, PR China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou 510006, PR China; Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling, Guangzhou 510006, PR China; Guangdong Engineering and Technology Research Center for Environmental Nanomaterials, Guangzhou 510006, PR China. Electronic address: pppxwu@scut.edu.cn.
⁴ South China Institute of Environmental Science, Ministry of Ecological Environment, Guangzhou 510655, PR China.

PMID: 38677110
DOI: 10.1016/j.watres.2024.121656

Abstract

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 SO₄^2- 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.

Keywords: Hexavalent chromium; Manganese; Schwertmannite; Secondary mineral; Transformation.