TY - JOUR
T1 - Coprecipitation mechanisms of Zn by birnessite formation and its mineralogy under neutral pH conditions
AU - Tajima, Shota
AU - Fuchida, Shigeshi
AU - Tokoro, Chiharu
N1 - Funding Information:
XAFS analysis was performed using the BL5S1 beamline at the Aichi Synchrotron Radiation Center with the approval of the Japan Synchrotron Radiation Research Institute. 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. This work was also supported by the Research Institute of the Sustainable Future Society and Research Organization for Open Innovation Strategy, Waseda University, and a grant from the Japan Mining Industry Association. We thank the Kagami Memorial Research Institute for Materials Science and Technology, Waseda University for lending the XRD (SmartLab, Rigaku Corp. Japan). We thank Gabrielle David, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.
Funding Information:
XAFS analysis was performed using the BL5S1 beamline at the Aichi Synchrotron Radiation Center with the approval of the Japan Synchrotron Radiation Research Institute. 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. This work was also supported by the Research Institute of the Sustainable Future Society and Research Organization for Open Innovation Strategy, Waseda University, and a grant from the Japan Mining Industry Association. We thank the Kagami Memorial Research Institute for Materials Science and Technology, Waseda University for lending the XRD (SmartLab, Rigaku Corp. Japan). We thank Gabrielle David, PhD, from Edanz ( https://jp.edanz.com/ac ) for editing a draft of this manuscript.
Publisher Copyright:
© 2021
PY - 2022/11
Y1 - 2022/11
N2 - Birnessite (δ-Mn(IV)O2) is a great manganese (Mn) adsorbent for dissolved divalent metals. In this study, we investigated the coprecipitation mechanism of δ-MnO2 in the presence of Zn(II) and an oxidizing agent (sodium hypochlorite) under two neutral pH values (6.0 and 7.5). The mineralogical characteristics and Zn–Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis. Batch coprecipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0, which was similar to the result of adsorption experiments at pH 6.0 and 7.5. X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism on δ-MnO2 under these experimental conditions. A coprecipitation experiment at pH 6.0 produced some hetaerolite (ZnMn(III)2O4) and manganite (γ-Mn(III)OOH), but only at low Zn/Mn molar ratios (< 1). These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable. Woodruffite (ZnMn(IV)3O7•2H2O) was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5. This resulted in a Brunauer–Emmett–Teller (BET)-type sorption isotherm, in which formation was explained by transformation of the crystalline structure of δ-MnO2 to a tunnel structure. Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn–Mn compound formation on the δ-MnO2 surface, and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.
AB - Birnessite (δ-Mn(IV)O2) is a great manganese (Mn) adsorbent for dissolved divalent metals. In this study, we investigated the coprecipitation mechanism of δ-MnO2 in the presence of Zn(II) and an oxidizing agent (sodium hypochlorite) under two neutral pH values (6.0 and 7.5). The mineralogical characteristics and Zn–Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis. Batch coprecipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0, which was similar to the result of adsorption experiments at pH 6.0 and 7.5. X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism on δ-MnO2 under these experimental conditions. A coprecipitation experiment at pH 6.0 produced some hetaerolite (ZnMn(III)2O4) and manganite (γ-Mn(III)OOH), but only at low Zn/Mn molar ratios (< 1). These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable. Woodruffite (ZnMn(IV)3O7•2H2O) was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5. This resulted in a Brunauer–Emmett–Teller (BET)-type sorption isotherm, in which formation was explained by transformation of the crystalline structure of δ-MnO2 to a tunnel structure. Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn–Mn compound formation on the δ-MnO2 surface, and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.
KW - Surface complexation
KW - X-ray absorption fine structure
KW - Zinc removal
KW - δ-MnO
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UR - http://www.scopus.com/inward/citedby.url?scp=85123883659&partnerID=8YFLogxK
U2 - 10.1016/j.jes.2021.09.019
DO - 10.1016/j.jes.2021.09.019
M3 - Article
C2 - 35654505
AN - SCOPUS:85123883659
SN - 1001-0742
VL - 121
SP - 136
EP - 147
JO - Journal of Environmental Sciences (China)
JF - Journal of Environmental Sciences (China)
ER -