Phosphorus removal from aqueous solution using Al-modified Pisha sandstone

Pisha sandstone (PS) can increase the ability of sandy soil to retain water and some nutrients due to the presence of montmorillonite, but its inadequate phosphorus adsorption capacity affects its phosphorus holding capacity. This study aims to determine whether Al modification can enhance the phosphate adsorption capacity of Pisha sandstone and to identify the adsorption mechanism. Batch adsorption kinetic and equilibrium isotherm experiments were conducted to investigate the phosphate adsorption behavior of Al-PS (Pisha sandstone modified with Al). The results showed that PS could be successfully modified with Al. As the Al modification ratio increased, the P adsorption capacities of Al-PS increased and the optimal Al-to-PS ratio was 0.81:1. Considering the modification cost and P removal efficiency, it was decided to apply 0.27:1 the Al-to-PS mass ratio in batch adsorption experiments and characterization. The phosphate adsorption capacity decreased but the removal rate increased with increasing amount of Al-PS. The temperature had no significant effect on the adsorption, and the adsorption kinetic and isothermal adsorption data could be well fitted by the pseudo-second-order and Temkin models, respectively. The phosphate adsorption mechanism of Al-PS for phosphate was proposed to be electrostatic adsorption. This study suggested that Al-PS could be considered to be an effective material for phosphate adsorption, and it could enhance the soil phosphorus content when added into sandy soil.