A procedure was developed for conversion of spent UNEX solvent into a solid infusible resin, insoluble in aqueous alkali and acid solutions and organic solvents, by condensation with phenol and paraform. Incorporation of phenyl trifluoromethyl sulfone into the resin was confirmed by physicochemical methods. Resistance of the cured resin to high temperatures was proved by thermogravimetry. The developed procedure can also be applied to other organic wastes containing weakly reactive aromatic compounds such as nitrobenzotrifluoride, 1,2-dichlorobenzene, and nitrobenzene.