Study on preparation conditions of coal fly ash catalyst and catalytic mechanism in a heterogeneous Fenton-like process

Abstract

Coal fly ash (CFA) was transformed into three kinds of heterogeneous Fenton-like catalysts (MCFA powder, granular MCFA and Fe₂O₃/granular MCFA). The study results show that different types of CFA have different initial catalytic performances and acid modification can activate CFA better (64.3% of p-NP removal rate) than other methods (alkali (41.1%) and heat (44.9%) modification). Compared with kaoline, attapulgite can produce better granular MCFA (43.1% (attapulgite) versus 28.6% (kaoline)) by bonding MCFA powder together, and the optimal calcination temperature is 723 K. Supporting Fe₂O₃ on the surface of granular MCFA can promote the performance of granular MCFA significantly. The precursor solution (Fe(NO₃)₃) with pH pre-adjusted by oxalate can produce a relatively good Fe₂O₃/granular MCFA catalyst and 12 h of impregnation is recommended. Calcining the impregnated granular MCFA at 673 K for 2 h is the last necessary step in preparing Fe₂O₃/granular MCFA. The three MCFA catalysts could be reused at least 3 times, with a 57% removal rate of COD, even if real secondary effluent was treated. The CFA and three MCFA catalysts were characterized and their catalytic mechanism in a heterogeneous Fenton-like process was proposed.