Uptake of methylated arsenic by a polymeric adsorbent: process performance and adsorption chemistry

Methylated arsenic in groundwater has caused a series of health problems to human beings. A N-methylglucamine modified chitosan polymeric adsorbent was successfully developed for efficient adsorption of methylated arsenic from water solution. Adsorption behaviors of two common methylated arsenic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), onto the adsorbent were investigated in this paper. The surface modification increased the adsorption capabilities for the arsenic. The uptake of MMA was higher than that of DMA throughout all pH values. The maximum adsorption capacities were 15.4 mg/g for MMA and 7.1 mg/g for DMA, exhibiting competitive advantages with other reported materials. The affinity of these arsenic species for the adsorbent followed a pattern of MMA > DMA. The adsorption equilibrium was achieved within 20 h. The uptake of MMA and DMA was dependent upon the concentration of background electrolytes, indicating the formation of outer-sphere complexes of both organoarsenic species with the adsorbent during the adsorption. The existence of natural organic matter and competitive anions cause decrease in the uptake of both arsenic species. Furthermore, the simultaneous uptake of organic contaminants such as humic acid was observed. The spectroscopic analysis demonstrated the strong attachment of both organic arsenic species onto the amine functional group of the adsorbent.