Effective removal of radioactive 90Sr by CuO NPs/Ag-clinoptilolite zeolite composite adsorbent from water sample: isotherm, kinetic and thermodynamic reactions study

Abstract

In this research, the natural zeolite named clinoptilolite (NCp) was considered as an applicable base structure for subsequent preparation and modification by pre-selected chemical agents to use for removal/adsorption goals in progress. To make Na-clinoptilolite form, the mentioned zeolite undergoes variations by treating with NaCl salt. Ion exchange procedure was utilized to imprint silver ions (Ag+) from silver (Ι) nitrate solution as silver precursor on the modified clinoptilolite zeolite structure to attain Ag-clinoptilolite zeolite. Tenorite (CuO) NPs have been then dispersed and deposited on the external surface of the pre-prepared Ag-clinoptilolite zeolite through impregnation method to prepare the CuO NPs/Ag-clinoptilolite zeolite as a novel composite adsorbent. A series of analyses techniques including SEM-EDAX, XRD and FT-IR were applied for characterization and identification of crystal structure, morphology and elemental composition of the synthesized samples. The removal and adsorption process of radioactive strontium-90 (90Sr) by CuO NPs/Ag-clinoptilolite zeolite composite adsorbent was exploited under various experimental conditions including pH, amount of adsorbent and the contact time at room temperature and the final optimized procedure used for removal of probable presence of 90Sr in water sample of Bushehr city. Adsorption isotherm models including Langmuir, Freundlich, Temkin, D-R, H-J and Hasley have been applied and equilibrium adsorption data was better fitted to the Freundlich, Temkin, H-J and Halsey isotherms. The reaction kinetic information was studied by utilizing pseudo first and second orders, Elovich and Intra particle diffusion kinetic models. The adsorption kinetics is finely described by the pseudo second-order model. The energy of activation Ea calculated using the Arrhenius equation was found to be 44.75 kJ/mol. Further, the evaluation of the thermodynamic parameters such as ∆G0, ∆H0 and ∆S0, denoted that adsorption process of 90Sr was spontaneous and illustrates a chemical adsorption properties and exothermic nature of the adsorption. The obtained results revealed that 90Sr ions were removed by CuO NPs/Ag-clinoptilolite zeolite composite under optimized conditions after 6 h with a yield more than 97 %.