Sorption kinetics of phosphates by a calcined sorbent from ash and slag waste

Abstract

This study investigates the sorption kinetics of phosphates onto a calcined sorbent derived from ash and slag waste generated by thermal power enterprises. The performance of the sorbent was also tested on water from an open discharge into the Kuban River, which contained a mixture of stormwater and domestic wastewater. The sorbent was prepared by drying and calcining ash and slag samples from the Novocherkassk State District Power Plant at 600 °C for 30 minutes. This paper details experiments on the static sorption removal of phosphates from both model aqueous solutions and wastewater. In the kinetic studies using model solutions, a sorbent dose of 1 g per 50 cm³ of solution was used. The optimal sorption parameters were determined experimentally: an agitation speed of 200 rpm, a pH of 7, and a contact time ranging from 10 to 120 minutes, with initial phosphate concentrations ranging from 2 to 300 mg/L. A high removal efficiency of 97–98% was achieved at initial concentrations of 10 and 20 mg/L. The experimental data were analyzed using pseudo-first-order (Lagergren) and pseudo-second-order (Ho – McKay) kinetic models. The pseudo-second-order model provided the best fit, with a coefficient of determination R² of 0.999, which is consistent with literature on phosphate sorption from aqueous solutions. A strong agreement was observed between the experimental and calculated values for phosphate removal efficiency.