[en] This paper reviews our work on the use of hexacyanocobaltate salts in the chemical treatment of radioactive waste solutions. The divalent cations of the 3d - block elements together with the hexacyanocobaltate moiety form insoluble polymeric coordination compounds. These compounds have been used as chemical precipitants or ion exchangers for the separation of radiocaesium from various simulated and actual waste solutions. Precipitation in situ has been performed by using various hexacyanocobaltate salts of the divalent cations of Mn, Fe, Co and Ni. The results showed that Co²⁺ and Ni²⁺ salts have high selectivity for caesium. The presence of monovalent cations and detergent has significant effect on the precipitation process. On the other hand Cd²⁺ salt has been found to be more stable than other salts in alkaline medium. The sorption properties of hexacyanocobaltate salts as ion exchangers were studied. Adsorption of caesium seems to proceed via an ion exchange mechanism. It has been used for the treatment of reprocessing medium active waste solution. A decontamination factor of about 10³ has been achieved. (author)