Biosorption has been appearing as a useful alternative to conventional treatment systems for the removal of toxic metals from aqueous stream. The batch removal of chromate anions (CrO42-) from wastewater under different experimental conditions using a cationic surfactant-modified lichen (Cladonia rangiformis (L)) was investigated in this study. Cetyl trimethyl ammonium bromide (CTAB) was used for biomass modification. The results of the experiments showed that biomass modification substantially improved the biosorption efficiency. Effects of pH, biosorption time, initial CrO42- concentration, biosorbent dosage, and the existence of the surfactant on the biosorption of CrO42- anions were Studied. Studies up to date have shown that the biosorption efficiency of chromium increased as the pH of the solution decreased. In the present study, the removal of chromate anions from aqueous Solutions at high pH values with surfactant-modi fled lichen was investigated. From the results of the experiments it was seen that the removal of chromate anions by modified lichen was 61% at the solution natural pH (pH 5.11) but at the same pH value the removal of chromate anions by unmodified lichen was 6%. Also concentrations ranging from 30 to 150 mg/L Cr(IV) were tested and the biosorptive removal efficiency of the metal ions from aqueous solution at high pH was achieved more than 98%. (C) 2008 Elsevier B.V. All rights reserved.