TY - JOUR
T1 - Removal mechanisms of cadmium by δ-MnO2 in adsorption and coprecipitation processes at pH 6
AU - Suzuki, Kohei
AU - Kato, Tatsuya
AU - Fuchida, Shigeshi
AU - Tokoro, Chiharu
N1 - Funding Information:
XAFS analysis was performed using the BL14B2 beamline of SPring-8, with the approval of the Japan Synchrotron Radiation Research Institute (Proposal No. 2018A1696 and No.2019B1867). Part of this work was performed within the activities of the Research Institute of the Sustainable Future Society, Research Institute for Science and Engineering, Waseda University. The authors thank the Japan Oil, Gas and Metals National Corporation (JOGMEC) for their corporation. We also thank Manohar Murthi, PhD, from Edanz Group (https://en-author-services.edanzgroup.com/) for editing a draft of this manuscript.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/9/20
Y1 - 2020/9/20
N2 - We elucidate the removal mechanism of Cd by birnessite (δ-MnO2) in adsorption and coprecipitation processes in the context of acid mine drainage (AMD) treatments. The removal mechanism was studied through batch removal experiments at different initial Cd/Mn molar ratios (0–2) by zeta potential measurements, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and X-ray absorption fine structure (XAFS) analysis. The sorption isotherm and zeta potential measurements suggest that surface complex formation is the dominant mechanism, and that surface precipitation and/or intercalation also occur in the coprecipitation process when the initial Cd/Mn molar ratio is high (1–2). Increasing the initial Cd/Mn molar ratio to above 0.5 decreased the particle size of δ-MnO2 and shifted its (001) XRD peak to lower angles, suggesting that the δ-MnO2 interlayer ((001) and (002) planes) was expanded and the growth of δ-MnO2 crystals was inhibited in the coprecipitation process. The results of XAFS analysis revealed the production of Mn(III) precipitates and surface complex formation with Cd at high Cd/Mn molar ratio condition (<1). No significant changes in the crystalline structures of δ-MnO2 over the entire range of initial Cd/Mn molar ratios were observed in the adsorption process, confirming that Cd could be adsorbed by triple-corner-sharing at neutral pH.
AB - We elucidate the removal mechanism of Cd by birnessite (δ-MnO2) in adsorption and coprecipitation processes in the context of acid mine drainage (AMD) treatments. The removal mechanism was studied through batch removal experiments at different initial Cd/Mn molar ratios (0–2) by zeta potential measurements, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and X-ray absorption fine structure (XAFS) analysis. The sorption isotherm and zeta potential measurements suggest that surface complex formation is the dominant mechanism, and that surface precipitation and/or intercalation also occur in the coprecipitation process when the initial Cd/Mn molar ratio is high (1–2). Increasing the initial Cd/Mn molar ratio to above 0.5 decreased the particle size of δ-MnO2 and shifted its (001) XRD peak to lower angles, suggesting that the δ-MnO2 interlayer ((001) and (002) planes) was expanded and the growth of δ-MnO2 crystals was inhibited in the coprecipitation process. The results of XAFS analysis revealed the production of Mn(III) precipitates and surface complex formation with Cd at high Cd/Mn molar ratio condition (<1). No significant changes in the crystalline structures of δ-MnO2 over the entire range of initial Cd/Mn molar ratios were observed in the adsorption process, confirming that Cd could be adsorbed by triple-corner-sharing at neutral pH.
KW - Acid mine drainage
KW - Cd removal
KW - Surface complex formation
KW - X-ray absorption fine structure
KW - δ-MnO
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U2 - 10.1016/j.chemgeo.2020.119744
DO - 10.1016/j.chemgeo.2020.119744
M3 - Article
AN - SCOPUS:85086502923
VL - 550
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 119744
ER -