Impregnated Activated Carbons with Binary Oxides of Iron-Manganese for Efficient Cr(VI) Removal from Water

Hexavalent chromium (Cr(VI)) is the most hazardous and toxic oxidation state of chromium and for this reason, its effective removal from water below the drinking water limits is a major issue. Adsorption is a very promising technology, among several techniques, and activated carbon is a common adsorbent material, used for water treatment, due to its extensive surface area and porosity. In the last years, emerging composite adsorbents containing two or more metal oxides have gained significant attention. However, there are few publications related to the application of modified activated carbon with a combination of iron and manganese or copper oxides, to remove Cr(VI) from water, which is why these materials are the focus of this research. The effect of pH value, contact time, and initial Cr(VI) concentration was examined with respect to Cr(VI) removal. The results indicated that the maximum Cr(VI) removal was observed at pH 3 with 3 h contact time. The most effective adsorbent was the NFM material (Fe–Mn modified carbon) where a substantial quantitative removal of Cr(VI) (99.7%) was observed. Langmuir isotherm and pseudo-second order kinetic models fitted the experimental data sufficiently. The maximum adsorption capacity for NFM found was 44.42 mg/g by using the Langmuir model. Finally, the structure of the formed modified adsorbents materials was studied by the application of BET and SEM characterization techniques.