TY - JOUR
T1 - As(III) immobilization on gibbsite
T2 - Investigation of the complexation mechanism by combining EXAFS analyses and DFT calculations
AU - Duarte, Graziele
AU - Ciminelli, Virginia S.T.
AU - Dantas, Maria S.S.
AU - Duarte, Helio A.
AU - Vasconcelos, Igor F.
AU - Oliveira, Augusto F.
AU - Osseo-Asare, Kwadwo
PY - 2012/4/15
Y1 - 2012/4/15
N2 - The complexation of aqueous As(III) species on gibbsite was investigated as a function of pH. Theoretical calculations and X-ray absorption fine structure spectroscopy (XAFS) were combined to elucidate the structure of arsenite surface complexes on synthetic gibbsite. Several adsorption sites were evaluated using the self-consistent charge corrected density-functional based tight-binding (SCC-DFTB) method. The formation of bidentate-binuclear, bidentate-mononuclear, monodentate-mononuclear, and monodentate-binuclear complexes by means of both acid-base and non-dissociative mechanisms was studied in detail. The SCC-DFTB calculations showed the bidentate-binuclear/acid-base complex as the most thermodynamically stable geometry for As(III) bonding to gibbsite surface, estimating As-O and As-Al distances of 1.75 and 3.24å, respectively. EXAFS results also demonstrated As(III) complexation to three oxygen atoms in the first shell, at a distance of 1.77å, and to aluminum in the second shell at a distance of 3.21å, characteristic of bidentate-binuclear configuration, at pH 5.0, 7.0 and 9.0. Another As-Al interaction, attributed to the monodentate-binuclear complex due to its distance of 3.49å, was shown from EXAFS results to provide a minor contribution to As(III) sorption on gibbsite. Therefore, results from theoretical calculations and experimental measurements confirmed the occurrence of inner-sphere complexation during the As(III) adsorption on gibbsite, in a pH range of 5-9. Hence, the higher As(III) mobility in the environment, when compared to As(V), was suggested to be related to the protonation of the As(III) adsorbed complexes. This protonation would restore the neutral H 3AsO 3 molecule, which could be then released from the mineral surface. These results might be useful to predict and control arsenic mobility in aqueous environments, particularly where Al oxy-hydroxides are often found.
AB - The complexation of aqueous As(III) species on gibbsite was investigated as a function of pH. Theoretical calculations and X-ray absorption fine structure spectroscopy (XAFS) were combined to elucidate the structure of arsenite surface complexes on synthetic gibbsite. Several adsorption sites were evaluated using the self-consistent charge corrected density-functional based tight-binding (SCC-DFTB) method. The formation of bidentate-binuclear, bidentate-mononuclear, monodentate-mononuclear, and monodentate-binuclear complexes by means of both acid-base and non-dissociative mechanisms was studied in detail. The SCC-DFTB calculations showed the bidentate-binuclear/acid-base complex as the most thermodynamically stable geometry for As(III) bonding to gibbsite surface, estimating As-O and As-Al distances of 1.75 and 3.24å, respectively. EXAFS results also demonstrated As(III) complexation to three oxygen atoms in the first shell, at a distance of 1.77å, and to aluminum in the second shell at a distance of 3.21å, characteristic of bidentate-binuclear configuration, at pH 5.0, 7.0 and 9.0. Another As-Al interaction, attributed to the monodentate-binuclear complex due to its distance of 3.49å, was shown from EXAFS results to provide a minor contribution to As(III) sorption on gibbsite. Therefore, results from theoretical calculations and experimental measurements confirmed the occurrence of inner-sphere complexation during the As(III) adsorption on gibbsite, in a pH range of 5-9. Hence, the higher As(III) mobility in the environment, when compared to As(V), was suggested to be related to the protonation of the As(III) adsorbed complexes. This protonation would restore the neutral H 3AsO 3 molecule, which could be then released from the mineral surface. These results might be useful to predict and control arsenic mobility in aqueous environments, particularly where Al oxy-hydroxides are often found.
UR - https://www.scopus.com/pages/publications/84858288115
UR - https://www.scopus.com/pages/publications/84858288115#tab=citedBy
U2 - 10.1016/j.gca.2011.12.019
DO - 10.1016/j.gca.2011.12.019
M3 - Article
AN - SCOPUS:84858288115
SN - 0016-7037
VL - 83
SP - 205
EP - 216
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -