Removal of methylene blue by carbons derived from peach stones by H3PO4 activation: Batch and column studies

Several activated carbons were obtained by H3PO4 at 500 degrees C, under increasing acid concentrations of 30-70%. Products were characterized by N-2 at 77 K, and proved to be highly microporous with high surface area and pore volume that increased with impregnation ratio. Two modified carbons were prepared by concurrently passing N-2 during pyrolysis of impregnated precursor with 50% H3PO4 at 500 degrees C, and post-heat treatment at 800 degrees C for one carbon. A low reduction in porosity accompanied this treatment. Equilibrium adsorption of methylene blue (MB) proved good uptake of the bulky dye, which improved considerably with impregnant concentration that was related to enhanced porosity. Dynamic removal of MB was carried out by running solutions of influent concentrations, of 100-200 mg/L, through a mini-column. Many column performance parameters were estimated at different stages on the typical S-shaped breakthrough curves: volume treated, amounts uptaken, bed service time, height of mass transfer zone, and column exhaustion characteristics. Increased impregnation ratio improved column performance, as well as forcing N-2 pyrolysis or extra heat-treatment. Activated carbon impregnated with 70% H3PO4 and carbonized at 500 degrees C exhibited the best properties which prevailed upon raising treated dye concentration to 150 and 200 mg/L, although degraded its capacity due to the limited mass of adsorbent and to the short contact time. (C) 2006 Elsevier Ltd. All rights reserved.