FeAl12-polyoxocations intercalated nano-bentonite fabrication in concentrated suspension using one-step ultrasonic-microwave irradiation for arsenic removal from alkaline wastewater

Abstract

Arsenic in alkaline wastewater often takes place from gold mining process and creates a major problem to ecosystems and human health. In alkaline condition for arsenic removal, the application of adsorbent with a high positive surface charge is necessary. The current study is focused on the synthesis and characterization of an eco-friendly FeAl12-polyoxocations intercalated nano-bentonite with a high positive surface charge for As(V) removal. Therefore, this pillared nano-bentonite was synthesized in different concentrations of clay suspension through a novel combination of the ultrasonic and microwave devices in one-step with decreasing water and time consumption. The characterization results showed that the incorporation of Al3+ and Fe3+ in pillared nano-bentonites increased the pH of zero point charge (pHZPC), d001 value, specific surface area, and micropore volume for arsenic removal. Various conditions such as the effect of coexisting anions and cations, arsenic concentration, adsorbent dosage, and contact time were investigated in the adsorption experiments. FeAl12-pillared samples represented the maximum adsorption capacity of 121.3 mg L−1 to remove 10–500 mg L−1 of As(V). The adsorbability of products was also evaluated by using the two, three, and four parameters adsorption isotherms. The presence of a heterogeneous surface with more active sites under endothermic reaction played an important role for immobilization of As(V) with ligand exchange reaction. In the regeneration study, the high removal efficiency of arsenic (more than 87%) was found even after four cycles.