School of Environmental Science, South China Normal University
Supported by the National Natural Science Foundation of China (Nos. 41877038 and 42077016) and the Local Innovative and Research Teams Project of the Guangdong Pearl River Talents Program of China (No. 2017BT01Z176)
【Objective】pH is the most important environmental factor influencing the reactivity of heavy metals on mineral surfaces. The purpose of this study was to investigate the interfacial reactions between As(V) and Cd(II) adsorption/co-adsorption onto different mineral surface excluding the interference of pH.【Method】Three different minerals: Al2O3, TiO2, and kaolin, were chosen and passed through 100-mesh sieve. The experiments for As(V) and Cd(II) adsorption onto the different minerals were conducted in serum bottles (Effective volume = 2 mL) at pH 6.0. The bottles containing 0.02-1 mmol?L-1 As(V), 0.02-1 mmol?L-1 Cd(II), 28 mmol?L-1 4-Morpholineethanesulfonic acid sodium salt (MES), 100 mmol?L-1 NaCl and 2.0 mg of mineral powders were placed on a rotator at 200 r?min-1 and 25 oC. Batch studies were conducted to assess the adsorption kinetics, adsorption isotherm and the influence of molar ratio of As(V) and Cd(II) on the extent of As(V)and Cd(II) adsorption.【Result】The adsorption kinetics showed that As(V) and Cd(II) adsorbed onto different mineral interfaces followed the pseudo-second-order kinetics model, and chemical adsorption was the rate-controlling steps. Furthermore, the normalized adsorption capacities of Cd(II) and As(V) were ranked as TiO2 > Al2O3 > kaolin. The adsorption abilities of As(V) and Cd(II) were enhanced by the co-existing Cd(II) and As(V). Specifically, the addition of As(V) promoted the adsorption of Cd(II) onto Al2O3, while the addition of Cd(II) enhanced As(V) adsorption onto TiO2. The synergistic effect of As(V) and Cd(II) co-adsorption was mainly controlled by the electrostatic adsorption and the ternary complex formation. Moreover, with the increase of Cd(II)/As(V) concentration ratio, the regulation mechanism of Cd(II) adsorption gradually changed from the electrostatic adsorption to the synergy of the formation of interfacial - As(V) - Cd(II) ternary complex and electrostatic adsorption, and then changed to the formation of surface precipitate. Importantly, with the increase of As(V)/Cd(II) concentration ratio, the key regulation mechanism changed from adsorption controlling to surface precipitation controlling. 【Conclusion】Electrostatic adsorption, formation of interfacial - As(V) - Cd(II) ternary complex, and surface precipitation were the critical mechanisms controlling the interfacial reactions between As(V) and Cd(II) adsorption onto various mineral surfaces at various ratios.
HUANG Minxue, GUAN Yufeng, SU Zixian. Interfacial Reactions between As(V) and Cd(II) Co-adsorption onto Various Mineral Surfaces[J]. Acta Pedologica Sinica, DOI:10.11766/trxb202101140027,[In Press]