In this study waste polystyrene foam and virgin polystyrene as a reference materials were converted by chemical reactions under heterogeneous conditions into useful products. Polymeric flocculants were obtained from polystyrene during the sulfonation with sulfuric acid as the sulfonating agent and Ag2SO4 as the catalyst. The influence of temperature and time of reaction on the properties of the products were studied. The products were successfully used as flocculants in the treatment of the waste water. Solid silica sulfuric acid was also used to convert polystyrene. In comparison with the conventional sulfonation methods this sulfonating agent simplifies the reaction and makes easier separation of products from acid and solvent. The obtained products were cross-linked and exhibited cation-exchange properties. The batch method was used to study purification of solutions of Zn2+ and Cu2+ by the yielded resins. The performed study proved the usefulness of waste polystyrene derivatives for water treatment process.