Study on decolorization of Rhodamine B by raw coal fly ash catalyzed Fenton-like process under microwave irradiation

Coal fly ash (CFA) catalyzed Fenton-like process was studied under microwave (MW) irradiation for the decolorization of Rhodamine B (RhB) wastewater. The physical-chemical properties of CFA were characterized, including the specific surface area, micromorphology, chemical and crystal components, and the distribution and chemical valence of metallic elements. The metallic oxidants in the CFA indicate CFA can work as Fenton-like catalyst and MW-absorbent simultaneously. The results reveal (OH)-O-center dot is more significant in the decolorization of RhB than HO2 center dot and O-2 center dot. The generation of more (OH)-O-center dot in the MW-Fenton-like process (293-326 K) than that in the conventional heated Fenton-like process (326 K) reflects the function of hot spot effect and possible non-thermal effect of MW. Under the optimum condition ([H2O2] 2 mmol L-1, [CFA] 15 g L-1, pH 3, P-MW 0.1 kW), the decolorization rate reaches 91.6% after 20 min. The intrinsic kinetic model of RhB decolorization is -dC(RhB)/dt = 1.76 x 10(-4). C-RhB center dot C-H2O2(1.89) center dot C-CFA(1.97) - dC(Rhodamine) (B)/dt = 1.76 x 10(-4) center dot C-Rhodamine (B) center dot C-H2O2(1.89) center dot C-coal fly ash(1.97). The loss of catalytic metallic elements causes the decline of catalytic capacity of CFA. The energy consumption (4313.3 kW.h kg(-1) RhB) is a limitation for the MW-Fenton-like process, which can be overcame by the safe application of nuclear energy. The intermediates and the path of RhB decolorization were detected and proposed, respectively. (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.