Phosphate removal from aqueous solution using ytterbium oxide supported mesoporous silicas (SBA-15, KIT-6 & MCM-41)

In this study, a series of ytterbium supported mesoporous silicas, SBA-15, KIT-6 and MCM-41 (containing different amounts of Yb) were studied for phosphate removal from aqueous solution. The prepared materials were characterized by X-ray diffraction, N2 adsorption/desorption (BET), HRTEM and XPS. All of the materials prepared were found to possess an ordered hexagonal mesoporous structure. The best performing materials under the conditions used (in terms of maximum adsorption capacity) for each of the silica supports were 0.3Yb SBA-15, 0.1Yb KIT-6, and 0.1Yb MCM-41 which had maximum adsorption capacities of 20.1 mg P/g, 20.9 mg P/g and 20.5 mg P/g respectively. The aforementioned best performing materials were found to have slightly higher maximum adsorption capacities at lower pH (pH 3 and 5, compared to pH 6) whilst the coexistence of chloride, sulphate and nitrate, were found to have no significant effect on phosphate adsorption. Bicarbonate ion was found to have a significant negative effect on adsorption capacity – this however was most likely due to this ion increasing the solution pH which in turn causes reduced adsorption. It was found that adsorbed phosphate could be readily desorbed from the materials studied using HNO 3 (5%) at room temperature. Reuse tests showed a slightly reduced adsorption capacity for the materials for which regeneration studies were conducted. • Influence of Ytterbium loading on maximum phosphorus adsorption capacity varied for the different silica supports studied (SBA-15, KIT-6 & MCM-41) • Phosphate adsorption most closely followed pseudo-second-order kinetics for all materials studied • The prepared materials had high selectivity for phosphate over some other common ions commonly found in water • Very good reusability of materials was demonstrated using a simple regeneration process