Inorganic ion exchangers for strontium removal from radioactive waste : a review

90Sr is the most hazardous radioactive isotope of strontium that is produced during the normal operation of nuclear reactors. It can also spread to the environment due to fallout from nuclear accidents and nuclear weapon testing. The removal of hazardous radionuclides and the safe management of radioactive waste are of vital necessity. Inorganic ion exchangers stand out with their thermal, chemical and radiation resistance. They also show remarkable selectivity for specific cations. This review focuses on the removal of 90Sr by natural and synthetic inorganic ion exchangers, viz. zeolites, clay minerals, hydroxyapatite, insoluble acid salts, hydrous oxides and metal sulfides.