[en] Preparation and use of tetra-C-alkyl cobalt dicarbollide for extraction of cesium and strontium into hydrocarbon solvents. Tetra-C-alkyl derivatives of cobalt dicarbollide, Co(C₂R₂B₉H₉)₂^-(CoB₂R₄^-; R=CH₃ and C₆H₁₃) are demonstrated to be significant cesium and strontium extractants from acidic and alkaline solutions into non-toxic organic solvent systems. Extractions using mesitylene and diethylbenzene are compared to those with nitrobenzene as the organic phase. CoB₂-hexyl₄^- in diethylbenzene shows improved selectivity (10⁴) for Cs over Na in acidic solution. In dilute alkaline solution, CoB₂-hexyl₄^- extracts Cs less efficiently, but more effectively removes Sr from higher base concentrations. A general synthesis of tetra-C-alkyl cobalt dicarbollides is described. 6 figs