Research on the characteristics of red mud granular adsorbents (RMGA) for phosphate removal.

Red mud (RM), a waste tailing from alumina industry, was employed with bentonite and starch as the main raw materials for producing granular adsorbents in this study. The important parameters, which greatly affect the characteristics of red mud granular adsorbents (RMGA), such as the mass ratio of three raw materials, preheating time, preheating temperature, sintering time and sintering temperature (ST), were investigated. Adsorption capacities for various RMGA were described in terms of removal of phosphate from aqueous solution according to the adsorption experiments, in which certain operation parameters (like stirring speed, reaction time, adsorbent dosage, initial pH and initial phosphate concentration) at three different aquatic temperatures (AT) were applied. The results showed that the optimum ST, under which the largest adsorption capacity was achieved for RMGA with certain RM ratio, varied with different AT in adsorption process. Based on the further characterizations of RMGA, it was speculated that the performance above was caused by the competitive interactions of chemical adsorption and physical adsorption on RMGA, since the increase in ST could lead to qualitative diversification on the surface and quantitative decrease of effective components for adsorption simultaneously.