Extraction of radio-strontium from acidic nuclear waste streams was studied by COSMO-RS in presence and in absence of strontium-selective crown ethers. The crown ethers studied in this work were dicyclohexano-18-crown-6 and di-tert-butyl-dicyclohexano-18-crown-6. The ionic liquids studied were [BuMeim] [PF₆], [HeMeim] [PF₆], [OcMeim] [PF₆], [BuMeim] [NTf₂], [HeMeim] [NTf₂] and [OcMeim] [NTf₂]. Two different strategies were used in our modeling approach. In the first approach, strontium was inserted in the crown ether whereas, in the second approach, an equimolar composition of crown ether and strontium nitrate was used. The former approach described the effects of crown ethers, alkyl chain length and presence of acidic medium successfully. The COSMO-RS model was further benchmarked by predicting the experimental trend of distribution coefficient of CsNO₃ in ionic liquid with respect to the length of alkyl chain.