Abstract <p>The interference of Sr(II) and Y(III) cations and of cationic (dodecyltrimethylammonium bromide), anionic (sodium dodecyl sulfate), and nonionic (polyoxyethylene laurate, tradename Brij-35) surfactants in competitive adsorption onto activated carbon prepared from lignin was studied. The radiotracers ⁹⁰Sr/⁹⁰Y and tritium were used for determining the equilibrium and surface concentrations of metal cations and surfactants, respectively. The tritium-labeled surfactants were prepared by thermochemical activation of tritium. The concentrations of all the sorbates in solution were determined by liquid scintillation spectrometry. The SpectraDec software was used in joint measurement of the ⁹⁰Sr/⁹⁰Y and tritium activity. Surfactants affect the sorption of strontium and tritium onto activated carbon prepared by thermochemical activation with orthophosphoric acid. The formation of a poorly soluble precipitate with the anionic surfactant enhances the adsorption and prevents the desorption of both cations and favors the sorption of the anionic surfactant itself. The nonionic surfactant containing the oxyethyl groups does not affect the adsorption value of the strontium and yttrium cations but favors their retention on the carbon surface, preventing the desorption. The cationic surfactant competes with the strontium and yttrium cations for the active sites on the activated carbon surface: The adsorption of all the components decreases, whereas the desorption of cations from the surface increases.</p>