Highly efficient in-situ purification of Fe(II)-rich high-arsenic groundwater under anoxic conditions: Promotion mechanisms of PMS on oxidation and adsorption

Abstract

Dissolved Fe(II) widely exists in high-arsenic (high-As) groundwater, whose concentration (12–518 µM) is positively correlated with that of As(III). In order to realize the environmental-friendly and highly efficient in-situ simultaneous oxidation and adsorption of As(III) under anoxic conditions, peroxymonosulfate (PMS) was directly dosed into Fe(II)-rich high-As groundwater. Compared with hydrogen peroxide (88.2%) and peroxydisulfate (66.6%), the involvement of PMS gave the best As(III) removal efficiency of 98.8% after 1 min treatment, owing to the dual aspects of the best oxidation of As(III) and the best adsorption of As(V). During As(III) oxidation process, more SO4•− and 1O2 generated and unactivated PMS in Fe(II)-PMS process were responsible for the most efficient oxidation. During the enhanced As(V) adsorption process, the presence of PMS changed the structure of the in-situ formed Fe(III) colloid to provide more adsorption sites. Besides, the higher PMS concentration caused better As(III) oxidation, As(III) immobilization, and As(V) adsorption efficiencies. A wide range of Fe(II) (125–500 µM) coupled with PMS (244 µM) could immobilize more than 90% of As(III) (C0 = 1000 µg/L), and As(III) ranging from 0.2 mg/L to 2.0 mg/L also could be removed over 90% in Fe(II)-PMS process. The coexistence of HCO3–, Cl−, and humic acid slightly affected As(III) immobilization. Furthermore, after treatment, residual Fe ions concentration, residual total arsenic concentration, sulfate ions concentration, and pH value met the drinking water standard. This study could provide a very promising and attractive technology for a fast and efficient in-situ purification of Fe(II)-rich high-As groundwater.