Enhanced Fenton removal of phenol catalyzed by a modified red mud derived from the reduction of oxalic acid and L-ascorbic acid.

Abstract

Red mud, a bauxite residue generated during alumina production through the Bayer process, contains oxides of Fe, Ti, Al, Mn, and rare earths, and has a latent performance for catalytic removal of phenol. We proposed a novel and facile approach for red mud modification by the reduction of oxalic acid and L-ascorbic acid in the acidic solution. By surveying characteristics of modified red mud and influencing factors of phenol removal, the optimum experiment conditions and the possible mechanism were explored, respectively. The results demonstrated that RO2V2 (treated red mud using 2 g of oxalic acid dehydrate and 2 g of L-ascorbic acid) and RO3V3 (treated red mud using 3 g of oxalic acid dehydrate and 3 g of L-ascorbic acid) showed the most efficient catalytic capacity for the phenol removal and removal efficiency of over 99.1% for the 200 mg/L of phenol solution within 5 min among investigated catalysts with the pH decreasing from 6.7 to 3. The excellent catalytic performance of modified red mud profited from the production of Fe3O4, Fe2O3, Mn2O3, Fe2SiO4, and FeTiO3 in the catalysts. It was motivating for removal of phenol to increase the dosage of catalyst and H2O2. The rate constants of the pseudo-first-order kinetics model of RO2V2 and RO3V3 were 1.0 and 1.073, respectively. The results of continuous experiments provided a positive reference for a future pilot scale test.