[Characteristics and Mechanism of Monothioarsenate Adsorption on Sand, Sediment, and Goethite]

Batch experiments were conducted to investigate the adsorption characteristics and mechanism of monothioarsenate (MTA) (>99%) on sand, soil sediment, and goethite under different pH and solid-liquid ratio conditions. Results showed the following. ① When MTA ranged from 0.14 to 23.59, 0.19 to 41.27, and 0.27 to 32.02 mg·L^-1 in solutions, its maximum equilibrium adsorption capacity (Q_m) in sand, soil sediment, and goethite was 21.54, 277.98, and 2607.42 mg·kg^-1, respectively. After its adsorption reached equilibrium, a small amount of the MTA in the solutions transformed into arsenite and arsenate. ② As pH increased from 4 to 10, the equilibrium adsorption capacity (Q_e) of MTA on sand decreased gradually, whereas Q_e first decreased and then increased for soil sediment and goethite. As the solid-liquid ratio increased, the Q_e of MTA in the three media gradually decreased. ③ X-ray powder diffraction (XRD), scanning electron microscope (SEM), and BET results further showed that the major factors controlling MTA adsorption on the three media included the low pore volume of sand, the high degree of crystallization of the soil sediment, and the large number of hydroxyl functional groups (-OH) on goethite.