MX-80 bentonite colloids’ effect on radionuclide sorption was studied by batch method and transport in flow using a granitic drill core column and Sr(II) as a radionuclide. Batch-type sorption and desorption experiments were conducted to determine Sr(II)’s distribution coefficients on bentonite colloids and metatexitic gneiss. Molecular modeling assessed the radionuclide’s sorption affinity and justified the differences in Sr(II)’s sorption behavior on biotite versus montmorillonite. The distribution coefficients were found to be a hundred times greater for colloids than for granitic rock. Strontium’s breakthrough from the column with bentonite colloids was successful without notable retardation on rock minerals.