Zhuoyao Fang,Kaizhen Zhang,Xiaolin Zhang,Bingcai Pan
Methylated arsenic species, including monomethyl arsenate (MMA) and dimethyl arsenate (DMA), are frequently detected in natural waters due to the biochemical methylation of arsenic and various human activities. The presence of MMA/DMA may cause excess total arsenic (>10 μg/L) in drinking water, yet the efficient removal of methylated arsenic still remains challenging. Herein, we reported the utilization of a recently developed nanocomposite HZO@N201 for selective removal of MMA and DMA from water. HZO@N201 contains the gel-type anion exchanger N201, i.e. , quaternary ammoniated poly(styrene-co-divinylbenzene) beads, as the host, and the embedded sub-5 nm hydrated zirconium oxide (HZO) for specific adsorption. In comparison with the commercially available nanocomposite HZO@D201, which was prepared through in-situ growth of HZO inside the macroporous anion exchanger D201, the adsorption capacities of HZO@N201 toward MMA and DMA ascended by ∼ 1.9 and ∼ 2.2 times, respectively, mainly benefitting from the sub-5 nm nature of HZO@N201. The competing anions including sulfate, chloride and bicarbonate exerted negligible impact on the removal efficiency toward MMA/DMA, due to inner-sphere complex formation between HZO NPs and MMA/DMA, as verified by SEM-EDS and XPS Zr 3d analysis. The exhausted HZO@N201 was fully regenerated by alkaline treatment for cyclic utilization without obvious efficiency loss. In fixed-bed experiments, HZO@N201 column was able to successively produce ∼ 4000 and ∼ 160 bed volume (BV) clean water from the feeding solutions containing MMA and DMA, while the values for HZO@D201 column were merely ∼ 1600 BV and ∼ 70 BV, respectively.
Siqi Liu,Andrey M. Kuznetsov,Weiqing Han,Alexei N. Masliy,Gregory V. Korshin
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 PbO 2 /Sb-SnO 2 /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 Fe 2+ ions released as a result of accelerated ZVI corrosion in the galvanic ZVI/PAC microcells and ensuing formation of DMA/ Fe 2+ complexes that are readily adsorbed by PAC.
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