Effect and mechanism of removing As from sediment by combination of LMB and oxygenating agent

In order to study the removal effect of lanthanum modified bentonite (LMB) and oxygenating agent CaO₂ on arsenic (As) pollution in the sediment of eutrophic lakes, and clarify the removal mechanism of combined technology on the sediment-water interface, a simulation test was carried out on the sediment of Meiliang Bay in Taihu Lake. The results show that the combined use of LMB and CaO₂ has a better removal effect on As in sediment than the use of LMB and CaO₂ alone. On the 45th day of the experiment, the maximum removal rate of dissolved As in sediment by the combination of LMB and CaO₂ was 39.31%. On the 90th day of the experiment, the combined use of LMB and CaO₂ showed poor removal efficiency for As. To achieve efficient removal of As in sediment, LMB and CaO₂ can be recovered after 45 days of adding covering agents. The main mechanism of As removal by the combination of LMB and CaO₂ is the complexation of La³⁺and Ca²⁺in LMB and CaO₂ with arsenate ions to form LaAsO₄ and Ca₃ (AsO₄) ₂ precipitates, as well as the synergistic adsorption of Fe (Ⅲ) and Mn (Ⅳ) oxides. The redox cycling of Fe and Mn plays a crucial role in controlling the release of As from sediment.