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Influence of pH and sulfate concentration on hydrous ferric arsenate transformation behavior and As(v) mobilization

Xuedi Wang,Rui Su,Miao Xu,Yuyin Ma,Yanjiao Gao,Xu Ma

Published 2025 in RSC Advances

ABSTRACT

This study investigates the effect of various SO42− concentrations (0, 50, and 100 mM) on the phase transformation of hydrous ferric arsenate (HFA) and partitioning behaviors of As(v), Fe(iii), and SO42− under ambient (25 °C, 15 d) and subsequent elevated temperature (80 °C, 35 d) conditions. The results revealed that the primary factor controlling the transformation of HFA into crystalline scorodite was the pH, whereas the SO42− concentration played a secondary, pH-dependent role. More specifically, at pH 4 and under ambient temperature, SO42− enhanced the release of As(v) and Fe(iii) into the solution. By contrast, at pH 6 and 8, SO42− promoted the formation of basic ferric arsenate sulfate, which immobilized As(v), and later dissolved upon heating. SO42− incorporation into the solid phase occurred across all pH levels and was enhanced at higher concentrations and temperatures. Thus, SO42− modulates As(v) mobility via structural incorporation and ion competition, with distinct behaviors at acidic versus circumneutral pH. These findings offer guidance for risk assessment and design of sulfate-rich, mining-impacted remediation systems.

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