This work describes the sorption of Cs-134, Co-60 and Eu152+154 by crystals of unmodified and phosphoric acid modified silico-antimonates (SiSb). Equilibrium and selectivity sequence for co-exiting metal ions under strongly acidic conditions of HClO4, H2SO4, HNO3 and HCl were investigated. The results showed that the silico-antimonate either in the high Sb5+ content or in the phosphated form possesses acidic characters and shows cation-exchange properties more efficient in acidic media. Kinetic studies indicated that pseudo-second-order model gave better fitting parameters comparing to that of pseudo-first-order one. The thermodynamic parameters of the sorption processes revealed spontaneous and endothermic nature. High negativity of Delta G degrees values for the modified SiSb confirms the positive role of phosphoric acid impregnation in the sorption process. The break-through capacities of the studied ions were further calculated from a column investigation. (C) 2009 Elsevier B. V. All rights reserved.