Removal of As(III) and As(V) by Using Magnetic Carbon Xerogels in Aqueous Solution and the Application in Groundwater

A problem in the availability of drinking water is the presence of contaminants in water bodies such as As(III) and As(V) due to their toxicities in the environment and public health. In arid northern Mexico, the high concentration of arsenic migrates to the groundwater by weathering processes of silica volcanic rock. The adsorption process by using magnetic nanoparticles is considered in water and wastewater treatment for sustainable environmental application due to their specific properties. Magnetic carbon xerogels (XMCs) were synthesized from sol–gel polymerization of a resorcinol-formaldehyde to remove As(III) and As(V) from an aqueous phase that facilitates recovery and possible reuse. The stoichiometric of resorcinol/water (R/W) ratios were modified in the design of materials to evaluate the adsorption capacity of As(III) and As(V) from aqueous solution and groundwater. The effect of pH, the initial concentration of arsenic and the adsorbent dose in the adsorption process were evaluated through an experimental design by using response surface methodology. After the carbonization at 600 °C 6 h by flowing inert nitrogen gas, the specific surface area from BET analysis of XMC5-600 increased to 579.2 m2/g. The XMCs with molar ratio of MNPs and resorcinol at 0.07, and containing 3.19–3.56% Fe content showed maximum adsorption capacity for the removal of arsenic from the aqueous solution. MNPs were incorporated into the structure of the RF gels corresponding to the SEM/EDX analysis. The reduction of the R/W ratio, the compactness and voidness of the RF gel structure decreased. The results of an experimental design by using response surface methodology indicate that the most significant variables of pH and dose play an important role in the adsorption of arsenic. The adsorption capacity for XMC5-600M and XMC10-600 was 66.35 μg/g As(III) and 76.40 μg/g As(V), respectively, at the initial concentration of 300 μg/L. The removal efficiency in groundwater using XMC5-600M and XMC10-600 was 88% of As(III) and 74.37% of As(V), respectively, with arsenic at levels lower than the Mexican and WHO standards.