TY - JOUR
T1 - Identifying the existence and molecular structure of the dissolved HCO3-Ca-As(V) complex in water
AU - Shi, Qiantao
AU - Zhang, Shujuan
AU - Korfiatis, George P.
AU - Christodoulatos, Christos
AU - Meng, Xiaoguang
N1 - Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/7/1
Y1 - 2020/7/1
N2 - Calcium (Ca2+) and bicarbonate (HCO3 −) ions co-exist with arsenic (As) in natural water systems, while Ca-based materials such as lime and cement are widely used to immobilize As(V) in contaminated solids. In this paper, a new dissolved ternary complex, HCO3-Ca-As(V), was discovered and its molecular structure was identified. The results from the batch experiments showed that adding As(V) to the solutions containing Ca2+ and HCO3 – increased the dissolved Ca concentration from 4.8 to 73.2 mg/L at pH 11. Both infrared and X-ray absorption spectroscopy indicated the presence of dissolved HCO3-Ca-As(V) complex. Based on the quantitative geometric information obtained from the spectroscopic results, the molecule of (OH)OC-O-(OH2)4Ca-O2-As(OH)2 was identified by the density functional theory (DFT) calculation. Although Ca2+ and As(V) can form complex without HCO3 −, the presence of HCO3 – further enhanced the stability of the dissolved Ca complex, as evidenced by the lower binding energy (BE) of HCO3-Ca-As(V) (−329.1959 kJ/mol) than Ca-As(V) (4.7171 kJ/mol). The discovery of dissolved HCO3-Ca-As(V) complex is important for understanding the mobility of As(V) in natural water, and the possible release of As(V) in contaminated solids treated with Ca-based materials.
AB - Calcium (Ca2+) and bicarbonate (HCO3 −) ions co-exist with arsenic (As) in natural water systems, while Ca-based materials such as lime and cement are widely used to immobilize As(V) in contaminated solids. In this paper, a new dissolved ternary complex, HCO3-Ca-As(V), was discovered and its molecular structure was identified. The results from the batch experiments showed that adding As(V) to the solutions containing Ca2+ and HCO3 – increased the dissolved Ca concentration from 4.8 to 73.2 mg/L at pH 11. Both infrared and X-ray absorption spectroscopy indicated the presence of dissolved HCO3-Ca-As(V) complex. Based on the quantitative geometric information obtained from the spectroscopic results, the molecule of (OH)OC-O-(OH2)4Ca-O2-As(OH)2 was identified by the density functional theory (DFT) calculation. Although Ca2+ and As(V) can form complex without HCO3 −, the presence of HCO3 – further enhanced the stability of the dissolved Ca complex, as evidenced by the lower binding energy (BE) of HCO3-Ca-As(V) (−329.1959 kJ/mol) than Ca-As(V) (4.7171 kJ/mol). The discovery of dissolved HCO3-Ca-As(V) complex is important for understanding the mobility of As(V) in natural water, and the possible release of As(V) in contaminated solids treated with Ca-based materials.
KW - Arsenate
KW - Bicarbonate
KW - Calcium
KW - Dissolved Ca complex
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U2 - 10.1016/j.scitotenv.2020.138216
DO - 10.1016/j.scitotenv.2020.138216
M3 - Article
C2 - 32272407
AN - SCOPUS:85082712797
SN - 0048-9697
VL - 724
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 138216
ER -