Effects of S2- on arsenic adsorption to river sand and its mechanisms

Abstract

Sulfur (S2-) is closely related to the migration and enrichment of arsenic (As) in the water environment, but its mechanism of action in different aqueous medium is still unclear. To determine the adsorption characteristics of As by river sand, a common aqueous medium in the hyporheic zone, under the action of S2-, the adsorption kinetics experiment of As on river sand and the adsorption experiment of As by river sand under the action of S2- are designed and carried out. Combined with simulation calculation by PHREEQC and characterization tests based on XRD, SEM-EDS, XPS and FTIR, the mechanism of action is further identified. The results show that the adsorption of As by river sand reaches adsorption equilibrium at approximately 200 h and the adsorption capacity of As(Ⅴ) is significantly higher than that of As(Ⅲ) at the solid-to-liquid ratio of 25 g/L; with increasing S2- concentration, the adsorption capacity of river sand to As decreases gradually. The simulation and characterization test results show that a small amount of As is adsorbed on the surface of river sandandis mainly combined with Fe and Al on its surface. The adsorption of As (Ⅲ) may also be related to SiS2 that is formed after the fracture of the Si-O bondwith S2-. The main influence mechanism of S2- on the adsorption of As by river sand is as follows: ① the addition of S2- increases the pH of the solution and decreases Eh, thus inhibiting the adsorption of As; ②under the condition of adding S2-, Fe and Al on the surface of river sand can form compounds such as AlAs, AlAsO4, FeS2 and Fe4As2O11 with S and As, which reduces the active sites of As adsorption on the surface of river sand.

Keywords

• sulfur
• river sand
• characterization
• influence mechanism