Chromium(VI) removal with activated carbons

Several activated carbons, in powder and granular form, prepared from different raw materials and obtained by different activation procedures, were used to remove chromium(VI) from solution. The porous texture of the activated carbons was characterized by adsorption of N2/77 K and methylene blue/298 K. The Cr(VI)-adsorption experiments were carried out to analyze the influence of (i) pH, (ii) initial Cr(VI) concentration and (iii) carbon-solution contact time, on the efficiency of Cr(VI) retention by the activated carbons. The amount of Cr(VI) retained increased with increasing both pH and initial Cr(VI) concentration. At pH < 1, the retention of Cr(VI) was found to be affected by its reduction to Cr(III), the lower the pH the greater the facility to be reduced to Cr(III). The extent of adsorption and reduction processes depends on the porous texture, nature and preparation procedure of the activated carbons, the best performance being obtained with those prepared by physical activation.