The effect of heavy metal ions hydration on their sorption by a mesoporous titanium phosphate ion-exchanger

Abstract The sorption properties of a titanium phosphate ion-exchanger (Na-TiOP) towards Pb2+ Cd2+, Zn2+ and Co2+ have been investigated. The sorbent displays the highest Pb2+ uptake (1.95 mmol g–1) among other TiP ion-exchangers. To explore the ability of the titanium phosphate sorbent toward heavy metal ions the sorption equilibrium and kinetics parameters have been studied. To gain insight into some mechanisms of interactions between the sorbent and solute the radius and dehydration degree of the adsorbed ions have been calculated. The sorbent shows fast kinetics, the metal removal efficiency after 5−10 min of the sorption process is estimated to be 90–95 % for all metal ions studied. The equilibrium reached within 15−60 min, and the experimental data were best fitted to the pseudo-second-order kinetic model. Thermodynamic parameters of the sorption process were calculated, and it has been shown that the main factor determining the endothermic nature of the process is the partial destruction of the hydration shell of the sorbed ions. Titanium phosphate effectively removes metal ions from multi-component model and real wastewater solutions, resulting in the sorption capacity of heavy metal ions 2.03 mmol g–1. It makes this material an advanced sorbent for the selective isolation of toxic metals cations from sewage water. A competitive sorption phenomenon in favor of Pb2+ on titanium phosphate is shown for all studied complex solutions. The selectivity can be represented as Pb2+ > Cd2+ > Zn2+ > Co2+.