Removal of dimethylarsinic acid (DMA) in the Fe/C system: roles of Fe(II) release, DMA/Fe(II) and DMA/Fe(III) complexation

Methylated arsenic species are ubiquitous in the environment and resistant to removal by conventional treatment technologies. This study addressed this challenge based on the examination of the removal of dimethylarsinic acid (DMA) in a system that combines zerovalent iron (ZVI) and powdered activated carbon (PAC). The removal of DMA in the ZVI/PAC system was compared to that by coagulation, adsorption, electrochemical and Fenton oxidations, and other conventional methods. While only the electrochemical oxidation using a PbO2/Sb-SnO2/Ti anode allowed removing up to 60% DMA at several hours-long treatment times, the removal of DMA in the ZVI/PAC system containing 10 g/L ZVI and 2.5 g/L PAC with an initial pH of 2.0 was 95% for a 30 min reaction time. Specific roles of PAC, ZVI and its oxidation products in DMA removal were examined based on the spectroscopic data and quantum chemical modeling for the DMA/Fe(II) and DMA/Fe(III) systems. These methods demonstrated the formation of moderately strong DMA/Fe(II) and DMA/Fe(III) complexation. These results and relevant kinetic data were interpreted to indicate that the removal of DMA is governed by the rapid generation of Fe2+ ions released as a result of accelerated ZVI corrosion in the galvanic ZVI/PAC microcells and ensuing formation of DMA/Fe2+ complexes that are readily adsorbed by PAC.

Automated summary

This study investigates the removal of dimethylarsinic acid (DMA) using a system combining zerovalent iron (ZVI) and powdered activated carbon (PAC). The results show that the ZVI/PAC system with 10 g/L ZVI and 2.5 g/L PAC can achieve a removal rate of 95% for DMA within 30 minutes, outperforming other conventional methods.