Sorption and immobilization of cesium by natural clinoptilolite zeolite modified with nickel hexacyanoferrate

Advancement of nuclear technology has resulted in large scale release of radioactive cesium isotopes into environment since 137Cs is among the main fission products in radioactive wastes [1]. Often, the liquid radioactive wastes are managed by a two-step procedures: (1) removal of hazardous radionuclides by ion-exchange resins and (2) subsequent storage of the spent ion-exchanger resins in a cement matrix prior to encapsulation in stainless steel drums. A new strategy is sorption and stabilization them respectively in a natural or synthetic zeolite framework [2]. It was found that among organic and inorganic ion exchangers, the inorganic type has several superior qualities required for the treatment of waste streams compared to organic resins. These are their higher thermal stability and good compatibility with the final waste forms. Several inorganic ion exchanger such as zeolites, sodium titanates, silicotitanates, metal oxides, and hexacyanoferrates are in use for the treatment of wastes. Hexacyanoferrates have a high selectivity toward cesium [3]. Previous research pointed out that ceramization of zeolitic sludges entrapping polluting cations may be a possible alternative procedure to safely dispose harmful species. In particular, it has proven that pre-formed compacts of zeolitic sludge can be transformed by firing into stable alumino-silicate structures, which are highly resistant to leaching and possibly also of interest as ceramic materials [4]. The aim of this paper is to evaluate the zeolite uptake capacity of cesium, using clinoptilolite zeolite modified by Nickel hexacyanoferrate )NiHCF-Clino) as adsorbent. The effect of various parameter like the pH, contact time, temperature and initial concentration of the metal ion cesium adsorption efficiencies of NiHCF-Clino has been studied systematically by batch experiments. Then, the cesium-loaded adsorbents were heated at different temperature and the leach test carried out on all the heat-treated samples.