Arsenate sorption on lithium/ aluminum layered double hydroxide intercalated by chloride and on gibbsite: sorption isotherms, envelopes, and spectroscopic studies.
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.
Liu
Yu Ting
YT
Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, 10617.
Wang
Ming Kuang
MK
Chen
Tsan Yao
TY
Chiang
Po Neng
PN
Huang
Pan Ming
PM
Lee
Jhy Fu
JF
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
D001149:Arsenates; D002712:Chlorides; D000536:Aluminum Hydroxide; D008094:Lithium; D000535:Aluminum; C025657:arsenic acid