Nanocomposites and nanomaterials
Synthesis of nanocomposite adsorbent based on potassium nickel ferrocyanide-loaded clinoptilolite-rich tuff for selective removal of Cs-137 from contaminated waters

Yu.V. Bondar, S.V. Kuzenko
Institute of Environmental Geochemistry of the NAS of Ukraine. 34a Palladin ave.,  Kyiv 03142, Ukraine
E-mail: juliavad_peremoga@ukr.net

The selective removal of Cs-137 from liquid radioactive waste and their quantitative determination in the environment have a great importance in recent years. Inorganic adsorbents are the preferred materials for the removal of radionuclides from contaminated waters due to their high selectivity, radiation and thermal stability; and among them insoluble double ferrocyanides and zeolites are widely used in nuclear industry for selective removal of cesium radionuclides.
Clinoptilolite-rich zeolite tuff from the Sokirnytsky deposit (Ukraine) and synthesized potassium nickel ferrocyanide (KNi FC) grains were tested as adsorbents for selective removal of Cs ions from multicomponent model solutions (keeping the concentration of cesium ions constant - 135 mg/l, pH 6.5 - 7). 
It was found that adsorption efficiency of the zeolite samples (0.2-0.3 mesh) decreases from 99.9% to 68% with the increase in sodium ion concentration from 0 to 0.6M/L, and even to 42% when K and Ca ions in the solutions, while the adsorption efficiency of the ferrocyanide samples remains almost stable in the same conditions – 99.9 – 82%.
However, insoluble ferrocyanides are usually synthesized as fine or ultrafine grains which are difficult for practical applications due to their low mechanical stability and tendency to become colloidal in aqueous solution. In order to improve their mechanical properties the composite adsorbent has been synthesized by in situ loading nanosized KNi FC onto the surface and inside of pores of the clinoptilolite-rich zeolite tuff. 
Data of scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy confirmed the formation of KNi FC phase on the zeolite surface, which consisted of crystalline cubic-shaped nanoparticles. The efficiency of the synthesized adsorbent for removal of cesium ions was evaluated under various experimental conditions. It has demonstrated a rapid adsorption process, high adsorption capacity over a wide pH range, and selectivity in Cs ion removal from model solutions with high concentration of sodium and potassium ions.