title: Arsenate sorption on lithium/ aluminum layered double hydroxide intercalated by chloride and on gibbsite: sorption isotherms, envelopes, and spectroscopic studies.
abstract: The objective of this study was to provide fundamental knowledge of arsenate sorption on lithium/aluminum layered double hydroxide intercalated by chloride (Li/Al LDH-Cl) and further to reveal the contribution of exposed positive charge surface of Li/Al LDH-CI created by intercalating LiCl into Al(OH)3 layers to arsenate sorption. Therefore, sorption isotherms, envelopes and extended X-ray absorption fine structure (EXAFS) technique were employed to examine the reaction of arsenate on Li/Al LDH-Cl and on gibbsite. Based on an isotherm study, the sorption maximum of Li/Al LDH-Cl for arsenate was approximately six times higher than that of gibbsite. Sorption envelopes of arsenate on Li/Al LDH-Cl displayed a pH-sensitive behavior from pH 4.0 to 7.0, but it was insensitive to pH above pH 7.0, approaching to the pHpzc of Li/Al LDH-Cl (7.22). This transformation with shifted pHs illustrated that there were two types of reaction sites within Li/Al LDH-Cl that participate in arsenate sorption; one is pH-sensitive and the other is not. From EXAFS analysis, arsenate sorbed on Li/Al LDH, reacted not only with Al in the edges of Al-(OH)3 layers, but also with Li located in the vacant octahedral sites within Al(OH)3 layers; however, the decreasing intensity of As(V)-Al shells with increasing pH represented there were fewer As(V)-Al complex existed at higher pH, i.e., the complex between arsenate and Al is pH-sensitive. The superior sorption capability of Li/Al LDH-Cl to that of gibbsite could be attributed to the intercalated Li cations which served as the permanent sorption sites and made the surface of Al(OH)3 have high affinity to arsenate.
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, 10617.
authors.forename: Yu Ting
authors.initials: YT
authors.lastname: Liu
authors.forename: Ming Kuang
authors.initials: MK
authors.lastname: Wang
authors.forename: Tsan Yao
authors.initials: TY
authors.lastname: Chen
authors.forename: Po Neng
authors.initials: PN
authors.lastname: Chiang
authors.forename: Pan Ming
authors.initials: PM
authors.lastname: Huang
authors.forename: Jhy Fu
authors.initials: JF
authors.lastname: Lee
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D000536:Aluminum Hydroxide / Q000737:chemistry*; D001149:Arsenates / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D013816:Thermodynamics
chemical_list: D001149:Arsenates; D002712:Chlorides; D000536:Aluminum Hydroxide; D008094:Lithium; D000535:Aluminum; C025657:arsenic acid