[Influence of Calcium Ion Pre-treatment on Phosphate Adsorption onto Magnetic Zirconium/Iron-modified Bentonite].

Two kinds of magnetic zirconium/iron-modified bentonites (ZrFeBTs), including magnetic zirconium/iron modified raw bentonite (ZrFeRBT) and magnetic zirconium/iron-modified Ca-pretreated bentonite, (ZrFeCaBT) were prepared and characterized. Their phosphate adsorption characteristics were compared to determine the effect of the Ca pre-treatment on the adsorption of phosphate onto ZrFeBTs. The results showed that the as-prepared ZrFeBTs contained FeO and Zr, and the content of exchangeable Ca in ZrFeCaBT was much higher than that in ZrFeRBT. The adsorption isotherm data exhibited good agreement with the Langmuir isotherm model, with maximum monolayer phosphate adsorption capacities of 8.70 mg·g and 11.5 mg·g for ZrFeRBT and ZrFeCaBT, respectively. The isotherm and kinetics studies showed that the adsorption of phosphate on ZrFeBTs was a chemisorption process. The phosphate adsorption capacities for ZrFeBTs decreased with increasing solution pH. The ZrFeBTs exhibited a high selective adsorption for phosphate in the presence of anions and cations, including Cl, HCO, SO, NO, Na, K, Mg, and Ca. Furthermore, coexisting Ca greatly enhanced the adsorption of phosphate onto ZrFeBTs. The pre-treatment of raw bentonite with Ca significantly improved the adsorption of phosphate onto ZrFeBTs.