Abstract: To meet the needs of treatment of waste water containing low-level radioactive transition metal ions, using Co(Ⅱ) as a representative, the sorption ability of Co(Ⅱ) on calcium-silicate material, which is produced at the pre-desilication stage during the alumina extraction from the high-alumina fly ash by pre-desilication-soda-lime sintering technique, was studied. The results indicate that the calcium-silicate material, with hydration calcium silicate (C—S—H(Ⅰ)) as the main mineral, is one of those mesoporous materials with high specific surface area(733 m²/g) and developed void space structure. The material also has good acid and alkali buffer performance(pH=2  -10) and cation exchange capacity(Ca²⁺/H⁺). The adsorption capacity can reach 209-296 mg/g in the temperature range of 35-60℃ for Co(Ⅱ). The adsorption process is endothermic and consistent with Langmuir monolayer chemical adsorption. The adsorption equilibrium can be reached quickly within 3 h. Our results show that the main adsorption mechanism is most ion exchange(84.5%). Moreover, the adsorption results for nuclear power plant overhaul wastewater show that more than 98.6% of the radioactive cobalt as well as other radioactive transition metal ions are removed. Speaking from the perspective of practical application, the mesoporous calcium silicate material not only has high compatibility with cement which is good to the radionuclide stabilization, but also can replace part of cement to achieve the reduction of the radioactive solidification blocks. Because of the above mentioned environmental and economic benefits, the mesoporous calcium-silicate material evidently has potential application in radioactive transition nuclide removal of wastewater.