Simultaneous adsorptive removal of fluoride and phosphate by magnesia–pullulan composite from aqueous solution

Abstract

This study is based on the use of MgOP to treat solution containing fluoride and phosphate for adsorption. The characteristics of MgOP before and after adsorption were analyzed by XRD, FTIR, SEM and EDX. The experimental parameters included adsorbent dose, contact time, initial pH of solution, initial concentration of ions and the adding order of ions. The optimized adsorbent dose and contact time are 2 g L⁻¹ and 60 min respectively. It is observed that the removal efficiency of fluoride and phosphate ions is hardly affected at the broad range of pH (2 to 12). The presence of fluoride and phosphate ions affects the adsorption rates of another one and the main existing forms of phosphate in domestic wastewater have no significant effects on the defluoridation capacity of MgOP. Besides, it is seen that the adding order of ions greatly influences the adsorption capacities of MgOP for fluoride and phosphate ions. The Langmuir isotherm and pseudo second-order kinetic models are observed to describe the adsorption processes of fluoride in the single- and multi-adsorbate systems. Intra-particle diffusion model with greater R² is showed to explain the process of the fluoride adsorption. Also, the negative values of ΔG⁰ reveal that the adsorption processes of fluoride and phosphate ions in the single- and multi-adsorbate systems are feasible and spontaneous.