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<p>Arsenic (As) adsorption onto ferrihydrite (Fh) is an effective method for reducing As concentrations and is commonly used in passive mine drainage treatment. A model that predicts the removal of As(III) and As(V) is essential for designing treatment conditions. In this study, the mechanism of As removal in an As(III)-As(V) coexisting system by Fh at pH 7 was clarified. The presence of As(V) inhibited the surface complexation of As(III) on Fh. X-ray absorption fine structure (XAFS) analysis showed that surface precipitation of FeAsO<sub>4</sub> was suppressed at a low As/Fe ratio, while the proportion of surface-complexed As(III) increased. A geochemical model incorporating surface complexation and precipitation of As to Fh was developed using PHREEQC and reproduced experimental results by adjusting the solubility product (Ksp) of FeAsO<sub>4</sub> according to the As/Fe ratio. This model also reproduces the arsenic removal behavior observed at sites where As removal by Fh generation is being attempted. Because this model is based on equilibrium reactions, to manage field treatment using model predictions, it is desirable to avoid conditions where Fh redissolution and reprecipitation occur, and to design a hydraulic residence time (HRT) of 10&#xa0;h or more.</p>

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Experimental and geochemical modeling study of coexisting Arsenic(III) and Arsenic(V) removal by ferrihydrite

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月11日

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  • Hisanori Iwai,
  • Kaito Yamagata,
  • Y. K. Kong,
  • Keishi Oyama,
  • Yusei Masaki,
  • Takaya Hamai,
  • Yuki Semoto,
  • Chiharu Tokoro

摘要

Arsenic (As) adsorption onto ferrihydrite (Fh) is an effective method for reducing As concentrations and is commonly used in passive mine drainage treatment. A model that predicts the removal of As(III) and As(V) is essential for designing treatment conditions. In this study, the mechanism of As removal in an As(III)-As(V) coexisting system by Fh at pH 7 was clarified. The presence of As(V) inhibited the surface complexation of As(III) on Fh. X-ray absorption fine structure (XAFS) analysis showed that surface precipitation of FeAsO4 was suppressed at a low As/Fe ratio, while the proportion of surface-complexed As(III) increased. A geochemical model incorporating surface complexation and precipitation of As to Fh was developed using PHREEQC and reproduced experimental results by adjusting the solubility product (Ksp) of FeAsO4 according to the As/Fe ratio. This model also reproduces the arsenic removal behavior observed at sites where As removal by Fh generation is being attempted. Because this model is based on equilibrium reactions, to manage field treatment using model predictions, it is desirable to avoid conditions where Fh redissolution and reprecipitation occur, and to design a hydraulic residence time (HRT) of 10 h or more.