Arsenopyrite dissolution in circumneutral oxic environments: The effect of pyrophosphate and dissolved Mn(III)

Xingxing Wang; Zhipeng Shu; Haohua He; Ming Zhou; Xiaohan Lu; Jiajia Wang; Liwu Zhang; Zezhen Pan; Zimeng Wang

doi:10.1016/j.watres.2023.119595

Arsenopyrite dissolution in circumneutral oxic environments: The effect of pyrophosphate and dissolved Mn(III)

Water Res. 2023 Feb 15:230:119595. doi: 10.1016/j.watres.2023.119595. Epub 2023 Jan 9.

Authors

Xingxing Wang¹, Zhipeng Shu¹, Haohua He¹, Ming Zhou¹, Xiaohan Lu¹, Jiajia Wang¹, Liwu Zhang¹, Zezhen Pan², Zimeng Wang³

Affiliations

¹ Department of Environmental Science and Engineering, Fudan University, Shanghai, China.
² Department of Environmental Science and Engineering, Fudan University, Shanghai, China; National Observations and Research Station for Wetland Ecosystems of the Yangtze Estuary, Shanghai, China. Electronic address: zezhenpan@fudan.edu.cn.
³ Department of Environmental Science and Engineering, Fudan University, Shanghai, China; National Observations and Research Station for Wetland Ecosystems of the Yangtze Estuary, Shanghai, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, China.

PMID: 36642031
DOI: 10.1016/j.watres.2023.119595

Abstract

The oxidative dissolution of As from arsenopyrite, one important arsenic mineral in reducing conditions, poses an environmental hazard to natural aquatic systems. The dissolution of arsenopyrite occurs slowly due to the surface precipitates of iron oxides in circumneutral oxic environments. However, the presence of natural ligands and coexisting metals may change the release of Fe species, which would be of critical importance to the dissolution of arsenopyrite. Here, we investigated the oxidative dissolution of arsenopyrite induced by pyrophosphate (PP) and dissolved Mn(III) species as a natural occurring Mn species with strong complexation affinity to PP. With the presence of PP, the formation of Fe(II)-PP complexes and its rapid oxidation to dissolved Fe(III)-PP species resulted in a substantial increase in the generation of hydroxyl radicals (^•OH) under ambient dark conditions, contributing to faster dissolution of arsenopyrite and higher percentage of As(V) in the dissolved products. Dissolved Mn(III), though considered as an extra oxidant besides oxygen, unexpectedly acted as a radical scavenger for ^•OH and inhibited the production of As(V). Moreover, the oxidation of sulfur species differed in the two systems as significant formation of thiosulfate was observed with the presence of PP, which did not occur in the system with dissolved Mn(III). Overall, the effects of dissolved Mn(III) and PP on the dissolution of arsenopyrite and the subsequent transformation of Fe, As and S species have important implications for disentangling the interactions among these metastable elements, and for assessing their transport and environmental impacts in aquatic systems.

Keywords: Arsenate; Arsenite; Arsenopyrite; Dissolved Mn(III); Pyrophosphate; ROS.

MeSH terms

Arsenic*
Diphosphates
Ferric Compounds*
Minerals
Oxidation-Reduction
Solubility

Substances

arsenopyrite
Ferric Compounds
diphosphoric acid
Diphosphates
Minerals
Arsenic