Fulvic acid induced the liberation of chromium from CrO42-substituted schwertmannite

The cycling of Fe and Cr is intimately linked to the fate of schwertmannite in acid mine drainage (AMD) and acid sulfate soil (ASS) environments. Dissolved organic matter (DOM) can affect the stability of minerals and speciation, mobility and toxicity of heavy metals via redox reactions and complexation. However, knowledge about the fate of Fe and Cr upon reduction and complexation of CrO42-substituted sehwertmannite by fulvic acid (FA) is poorly understood. In this study, experiments were devised to investigate the interaction between FA and schwertmannite, with major degeneration of the schwertmannite structure as well as the formation of secondary minerals. For CrO42-substituted schwertmannite, results indicated that the concentrations of total Fe and Cr in the solution were determined to be the maximum values at 360 h and 96 h, and then decreasing over the reaction time when FA was 10 mg/L at pH of 6.5. The characterization on the solid phase by X-ray diffraction, scanning electron microscopy and X-ray photo electron spectroscopy technologies revealed that goethite was the dominant newly secondary mineral phases which played a vital role in controlling the fate and transport of Fe and Cr. The possible mechanism was proposed to be synergistic effect including ligand-promoted and reduction. This study provides new insights into the understanding of trace element behavior in environments affected by DOM and also has guiding significance for Cr-contaminant remediation.