Effects of calcination temperature on the adsorption ability of polyaluminum chloride (PAC) sludge-derived granules for As(V)

Abstract

The effect of calcination on the adsorption of As(V) by polyaluminum chloride (PAC) sludge-derived adsorbents in aqueous solution was investigated, and the As(V) adsorption ability of the adsorbent calcined at the optimal temperature was tested in batch and column modes. The characterization results for the calcined sludges indicated the formation of a porous framework and the transition of amorphous Al2O3 to its crystalline form in the sludge calcined at 500 °C. However, the adsorbents fabricated at temperatures >500 °C exhibited less adsorption of As(V) because of transformation of a crystalline phase. On the basis of the results of comparative As(V) adsorption experiments, the sludge calcined at 500 °C (PA500) was selected as the optimal adsorbent. The adsorption of As(V) by PA500 was terminated within 6 h, and its maximum adsorption capacity was 15.9 mg/g when the absorption data were fit to the Langmuir isotherm model. The adsorption of As(V) exhibited a low pH dependence and was strongly affected by the existence of P(V) in form of PO43−. The column results showed that a column filled with 7 g of PA500 maintained an As(V) concentration of <10 μg/L during 150 h of operation at 50 μg/L As(V) and a 1 mL/min flow rate. The stability of the sludge calcined at 500 °C was well demonstrated by a smaller amount of trace metals being leached from the sludge compared with that leached from other sludges. In conclusion, calcination of PAC sludge at an optimal temperature is a promising to fabricate As(V) adsorbents.