Effect of different wastewater composition on kinetics, capacities, and mechanisms of phosphorus sorption by carbonated bauxite residue

International audienceThis study aims at evaluating the effect of different wastewater composition on kinetics, capacities, and mechanisms of P sorption by carbonated bauxite residues (CBR). A series of batch experiments was performed to investigate P sorption behaviors from solutions prepared with different aqueous matrices (deionized water, tap water, and real wastewater) and different initial P concentrations (from 10 to 200 mg P/L). Also, a series of sequential P extractions was performed to investigate P fractionation of CBR before and after its use in P sorption experiments, and hence to elucidate the main P removal mechanisms. The results indicate that initial P concentration is the most influential parameter controlling kinetics, capacities, and mechanisms of P removal in batch experiments. Kinetic constant of P sorption increases exponentially with decreasing initial P concentration below 100 mg P/L, thus indicating a faster achievement of P sorption equilibrium. Equilibrium P sorption capacities increase linearly from about 0.2 to about 3.9 mg P/g CBR with increasing initial P concentration from 10 to 200 mg P/L, thus indicating that P saturation of CBR was not reached. Ca phosphate precipitation is the main P removal mechanism at higher initial P concentrations (> 10 mg P/L), whereas phosphate adsorption on CBR surface becomes more relevant over the total amount of P removed at lower initial P concentrations. Overall, the findings of this study allow to evaluate kinetic constants, sorption capacities, and removal mechanisms under different operating scenarios, thus providing crucial information for the design and operation of P treatment units