Mechanistic studies of arsenate sorption on lithium/aluminum layered double hydroxide intercalated by chloride

摘要

Layered double hydroxides (LDH), which consist of positively charged mixed-metal hydroxides layers and interlayer anions, were reported earlier than one and half centuries ago. In this study, Li/Al LDH-Cl was chosen as the sorbent to investigate arsenate sorption behavior. Extended X-ray absorption fine structure (EXAFS) analysis of arsenate sorbed on Li/Al LDH-Cl shows that As (V)-Li and As(V)-Al interatomic distances were 2.61±0.03 and 3.07±0.03A and the coordination number of As (V) Li and As(V)-Al were 1.5±0.3 and 2.5±0.5 atoms, respectively. These interatomic distances indicated that the inner-sphere bidentate mononuclear and bidentate binuclear bonding were the dominant arsenate sorption complexes on the planar surfaces and edges of Li/Al LDH-Cl, respectively. This biphasic arsenate sorption behavior was partially attributable to: (i) two different sorption sites of Li, exposing on planar surfaces, and Al, existing on edges of double hydroxyl layers, and (ii) micropore sorp tion sites within the Li/Al LDH-Cl surfaces.