Metal hexacyanoferrates-based adsorbents for cesium removal

Metal hexacyanoferrates (MHCFs), as typical coordination polymers, are efficient adsorbents for the monovalent cesium ion, which is a major product of uranium fission and the most commonly existing radionuclide in radioactive wastewater. Due to the comparable sizes between their structure lattices and hydrated cesium ions, MHCFs can selectively adsorb cesium ions with a background of other coexisting ions by ion-exchange. The main drawback is associated with its microcrystalline structure, that leads to weak mechanical strength and high flow resistance. Modification is necessary to make it capable for large scale application. This review is mainly focused on MHCF-based adsorbents for the highly efficient removal of cesium ions. The physicochemical structure together with its pros and cons as adsorbents for cesium removal are discussed along with proposed modification methods, including size control, immobilization and magnetic modification. Among these methods, immobilization by various kinds of organic (e.g., alginate, chitosan, fibers and PAN) and inorganic supporters (e.g., silica and glass) by embedding or in-situ synthetic methods are highlighted. The adsorption mechanisms and regeneration methods are also discussed, and some suggestions are given for future research.