Arsenate sorption on two Chinese red soils evaluated with macroscopic measurements and extended X-ray absorption fine-structure spectroscopy.
Arsenic sorption is the primary factor that affects the bioavailability and mobility of arsenic in soils. To elucidate the characteristics and mechanisms of arsenate, As(V), sorption on soils, a combination of sorption isotherms, zeta potential measurements, and extended X-ray absorption fine-structure (EXAFS) spectroscopy was used to investigate As(V) sorption on two Chinese red soils. Arsenate sorption increased with increasing As(V) concentration and was insensitive to ionic strength changes at pH 6.0. Arsenate, mainly as H2AsO4- in soil solution at pH 6.0, was strongly sorbed mainly through ligand exchange by the two soils. The sorption capacity was affected by the iron and aluminum mineral contents in the soils. The zeta potential measurements showed that As(V) sorption lowered the zeta potential and the points of zero charge of the soils. The EXAFS data indicate that adsorbed As(V) forms inner-sphere complexes with bidentate-binuclear configurations, as evidenced by an As-Fe bond distance of 3.28 +/- 0.04 A and an As-Al bond distance of 3.17 +/- 0.03 A. The two As(V) complexes were stable at different As(V) loadings, whereas the proportions were related to the aluminum and iron mineral contents in the soils. This study illuminated the importance of inclusion of microscopic and macroscopic experiments to elucidate sorption behavior and mechanisms.
Luo
Lei
L
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, PO. Box 2871, Beijing 100085, China.
Zhang
Shuzhen
S
Shan
Xiao-Quan
XQ
Jiang
Wei
W
Zhu
Yong-Guan
YG
Liu
Tao
T
Xie
Ya-Ning
YN
McLaren
Ronald G
RG
D000042:Absorption; D000535:Aluminum / Q000032:analysis / Q000737:chemistry; D001149:Arsenates / Q000032:analysis* / Q000737:chemistry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002681:China; D003116:Color; D007501:Iron / Q000032:analysis / Q000737:chemistry; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods*
D001149:Arsenates; D012987:Soil; D012989:Soil Pollutants; D000535:Aluminum; D007501:Iron; C025657:arsenic acid