Adsorption of phosphate from aqueous solution onto modified palygorskites

In this study, the natural and modified palygorskites were tested to remove phosphate ions from aqueous solution. The modified palygorskites were prepared by being activated with hydrochloric acid and/or thermal treatments. The surface structure of the materials was investigated by means of X-ray diffraction (XRD), a N2 adsorption–desorption technique and Fourier transform-infrared (FT-IR) to understand the effect of surface properties on the adsorption behavior of phosphate. In the adsorption test, the adsorption isotherms, kinetics, pH effect, desorbability and selectivity were examined. The results showed that the modified palygorskites had faster kinetics and higher adsorption capacities than the natural palygorskite, which can be attributed to the surface structural changes of the materials, and the adsorbed amounts of phosphate tend to decrease with the increase of pH for all samples. The desorbability of P is about 10–13%, and it is relatively difficult for the adsorbed PO43− to be desorbed. Palygorskite could selectively adsorbed phosphate in complex solutions, and the selectivity of phosphate adsorption onto palygorskites was 1000–3000 times that of chloride. The relatively low cost and high capabilities of the natural and modified palygorskites make them potentially attractive adsorbents for the removal of phosphate from aqueous solution.