期刊
ENVIRONMENT INTERNATIONAL
卷 130, 期 -, 页码 -出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.envint.2019.104932
关键词
delta-MnO2; Mn(III)-rich delta-MnO2; Cadmium; Sorption complexes; Stability
资金
- National Key Research and Development Program of China [2018YFD0800302]
- National Natural Science Foundation of China [41771276, 21537002]
- Knowledge Innovation Program of the Chinese Academy of Sciences [ISSASIP1612]
Birnessite owing to its negative surface charge and defective structure exhibits high sorption affinities for Cd(II). However, Mn(II) can not only compete for the sorption sites with Cd(II), but also react with structural Mn(IV) in birnessite to form Mn(III), and thus, affect Cd(II) immobilization by birnessite. Herein, we investigate effects of Mn(II) on Cd(II) retention and remobilization on two birnessite delta-MnO2 and Mn(III)-rich delta-MnO2 (denoted as HE-MnO2). At pH 5.5, Cd(II) sorption to birnessite was inhibited by Mn(II) addition. Mn(II) addition to delta-MnO2 led to Cd(II) migration from vacant sites to edge sites, forming double-corner sharing (DCS) complexes. Mn(II) introduction to delta-MnO2 led to less stable Cd(II) species formed on birnessite, indicating that Cd(II) was more firmly bound to vacant sites than edge sites of birnessite. Cd(II) formed double-edge sharing (DES) and DCS complexes on HE-MnO2. Mn(II) addition to HE-MnO2 increased the Cd-Mn distance in DES complexes. The stability of adsorbed Cd(II) on HE-MnO2 was slightly elevated due to Mn(II) addition. At pH 7.5, Mn(II) had no effect on Cd(II) sorption and desorption amounts on birnessite. However, low concentration of Mn(II) added to delta-MnO2 induced partial migration of Cd(II) from vacant sites to edge sites while high concentration of Mn(II) added to birnessite led to the formation of amorphous Cd(II)-Mn(III) coprecipitate. These findings imply that aqueous Mn(II) is an important factor in influencing Cd(II) immobilization by birnessite in the environment.
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