Bicarbonate-mediated enhanced successive oxidation and adsorption of As(III) in heterogeneous PMS activation process: Mechanism and practicability

Abstract

Successive oxidation and adsorption of arsenite (As(III)) for its immobilization are vital for purifying high-arsenic groundwater. Bicarbonate (HCO3ˉ), one of the most abundant anions in high-arsenic groundwater, usually inhibits As(III) immobilization in heterogeneous persulfate-based oxidation processes. In order to inhibit the negative effect of HCO3ˉ, we constructed a nanoscale MIL-100(Fe)-coupled peroxymonosulfate (NMIL-PMS) system. The results showed that when the initial concentration of HCO3ˉ increased from 0 to 1.2 mM, HCO3ˉ significantly accelerated the As(III) (C0 = 1000 µg/L) immobilization rate (k1, fitted by pseudo-first order model) from 0.018 min−1 to 0.409 min−1 and enhanced the As(III) immobilization capacity (calculated by Langmuir isotherm model) from 7962.7 µg/g to 12,082.6 µg/g. For the oxidation of As(III), HCO3ˉ shifted the dominant oxidation pathway from a 1O2-dominated one to the electron transfer-dominated non-radical pathway. As for the adsorption of evolved arsenate (As(V)), the process changed from chemisorption-driven to physical adsorption-driven, with hydrogen bonding and Van Der Waals interaction between NMIL and As(V) facilitated in the presence of HCO3ˉ. Furthermore, the NMIL-PMS-HCO3ˉ system exhibited excellent resistance towards complex water matrices as well as outstanding reusability and stability. This study could provide an avenue for the development of a very promising and economical technology for the purification of As(III)-contaminated groundwater.