Synthesis of surface modified ceramsite from waste material and its application for phosphate removal from aqueous solutions

A novel ceramsite (MMSC) material was synthesised for phosphate removal from Municipal Solid Waste incineration bottom ash (MSWIBA) and Molybdenum tailings (MoT) as precursors with shell powders (SP) as an additive. The optimal process conditions and important parameters are the mass ratio of MSWIBA to MoT and the calcination temperature. The effects of the addition of SP on the composite (MMS) and the resultant ceramsite (MMSC) are characterised in terms of their apparent porosity and compressive strength. The optimal calcination temperature for the phosphorus adsorption capacity was established of MMSC. The optimum conditions for the synthesis of MMSC were as follows: MMS mass ratio, 4:6:0.9; preheating temperature, 700°C; preheating time, 30 min; calcining temperature, 1040°C; and calcining time, 25 min. MSSC is subjected to surface modification on treatment with Ca(OH)₂. The surface-modified MMSC, denoted as Ca-OC, exhibits a four-fold higher phosphorus adsorption capacity compared with virgin ceramsite (MMSC). Its phosphorus adsorption isotherms are generated over a temperature of 25 to 45°C. The Langmuir model and pseudo-second-order model fit the sorption process adequately, and demonstrate the chemical monolayer adsorption dominated process. The MMSC and the Ca-OC prepared under the optimal condition, had a compressive strength of 1.29 MPa, an apparent porosity of 42.2%, and a theoretical maximum phosphorus adsorption capacity of 7.79 mg/g at 45°C. X-ray diffraction analysis and analysis the adsorbed phosphate show that the chemical reaction between Ca²⁺ and PO₄^3-, which forms hydroxyapatite (Ca₅(PO₄)₃(OH)), is the main mechanism of phosphate removal.