The influence of zeolite X ion-exchangeable forms and impregnation with copper nitrate on the adsorption of phosphate ions from aqueous solutions

Removal of phosphate ions from aqueous environment has become a global concern. Adsorption is one of the most efficient methods for removal of various pollutants. In this study, zeolite NaX derived from fly ash was modified by simple ion exchange with ammonium nitrate solution to obtain ammonium form (NH4X) and calcinated to proton form (HX) of zeolite X. The obtained materials were investigated as potential adsorbents of phosphate ions from aqueous solutions to find out the effect of zeolite form on adsorption capacity. Furthermore, zeolites NaX and NH4X were impregnated with copper nitrate solution and calcinated at 550 °C to obtain materials with Cu content of 3 wt% to simulate the potential utility of spent catalysts. The obtained results indicated that parent zeolite NaX has rather weak affinity towards phosphate ions — 4.38 mg (PO43−) g−1, only. The ammonium and proton forms of zeolite X showed significantly improved adsorption capacities of 12.09 and 35.33 mg (PO43−) g−1, respectively, implying the positive effect of ion exchange on removal of phosphate ions from aqueous solutions. Impregnated zeolites exhibited sufficient adsorption capacities of 11.86 and 26.53 mg (PO43−) g−1 for 3%[email protected] and 3%[email protected], respectively. However, no synergic effect of impregnation and zeolite form was observed due to partial pore blockage after preparation of zeolite 3%[email protected] To gain a deeper knowledge about the adsorption mechanisms, selected samples were subjected to kinetic adsorption studies and XPS measurements.