Arsenate removal from synthetic wastewater by adsorption onto fly ash

In this work, the removal of arsenate from synthetic wastewater by adsorption onto a coal combustion fly ash (CCA) has been experimentally studied. To this aim, a multiple analysis that included the evaluation of metal releases in aqueous solution, the assessment of arsenate adsorption capacity and a possible beneficiation treatment has been performed. The release of different metallic ions (mainly Ca, Al, K, and Si) was observed, including arsenic itself whose total content on CCA resulted to be around 0.05 mg/g. Arsenate adsorption isotherms on raw CCA at constant temperature (20 °C) have been determined in two synthetic arsenic aqueous solutions, a distilled water and a mineral water simulating a groundwater. In both the experimental conditions, CCA shows almost the same arsenate adsorption capacities. In order to increase CCA adsorption capacity and to simultaneously remove the arsenic originally present on CCA, a HCl treatment has been performed; the treated sample showed a higher adsorption capacity, likely related to a surface oxidation. Finally, the effect of equilibrium pH on arsenate adsorption on both raw and treated CCA samples has been investigated. A speciation analysis of arsenate ions revealed that for each investigated pH, the treated CCA sample showed the highest adsorption capacity.