Preparation of new magnetic zeolite nanocomposites for removal of strontium from polluted waters

Efficient separation of strontium ions (Sr²⁺) from waters has become a critical technological requirement after the nuclear accident at Fukushima Daiichi power station. In the present investigation, new nanocomposites of zero valent iron nanoparticles–zeolite (nZVI–Z) and nano-Fe/Cu–zeolite (nFe/Cu–Z) were synthesized via a simple liquid-phase reduction approach and tested to determine their effectiveness in the sorptive removal of Sr²⁺ from aqueous solutions. The sorption of Sr²⁺ on both nanocomposites was studied in a batch sorption mode as a function of various environmental conditions such as initial Sr²⁺ concentration, contact time, pH, temperature, dosage of sorbent and competing cations (Na⁺, K⁺, Mg²⁺ and Ca²⁺). The results indicated that initial pH and temperature were significant for Sr²⁺ sorption on both nanocomposites. The Sr²⁺ sorption efficiency increases with the increase in nanocomposite dosage and decreases with the Sr⁺² concentration. It was also found that although the sorption of Sr²⁺ was decreased by the presence of coexisting cations, the nanocomposites still exhibited high uptake capacity of Sr²⁺ ions. The Sr²⁺ sorption kinetics can be satisfactorily fitted by a pseudo-second-order kinetic model. The sorption isotherm data were well predicted using the Langmuir model. The maximum sorption capacity for nFe/Cu–Z was found to be 88.74 mg/g, which was greater than that for nZVI–Z (84.12 mg/g). In addition to the high sorption capacity, the nanocomposites could be easily separated from aqueous media after Sr²⁺ sorption using an external magnetic field. The calculated thermodynamic parameters such as ∆H°, ∆S° and ∆G° revealed the endothermic and spontaneous nature of the sorption process. The nanocomposites were also applied in a real seawater medium. The present study confirmed that the prepared nZVI–Z and nFe/Cu–Z nanocomposites could be employed as promising methods for the removal of Sr²⁺ from wastewater streams.