Mineralization of refractory organics in oil refinery wastewater by the catalytic ozonation with magnetic praseodymium-catalysts: Catalytic performances and mechanisms

An efficient mineralization of refractory organics in oil refinery wastewater (ORW) was achieved from a novel magnetic Fe 2 O 3 /Pr 6 O 11 /g-C 3 N 4 (PFCN) based catalytic ozonation (O 3 /PFCN) method. O 3 /PFCN caused 80.4% of refractory organics mineralization within 120 min, which promoted the oxidization of soluble microbial metabolites and aromatic proteins. The kinetic constant of refractory organics mineralization was 0.01385 min −1 , almost twice that of single ozonation. Fe and Pr existed as the polyvalent oxidation states in PFCN, which not only increased the Lewis acid sites on the surface of catalyst, but also enhanced the electron transfer ability. Additionally, the formation of Fe-O-C between CN and ferric oxide could promote the electrons transfer between the aromatic ring of CN and iron ion. Electrons cycling between Fe(II)/Fe(III) and Pr(III)/Pr(IV) caused the decomposition of ozone to produce radicals ( OH, O 2 − ) and non-radicals ( 1 O 2 ), which attacked the organics to oxidize into small molecular intermediates and then further mineralized into CO 2 and H 2 O. 58–88.7% of low-carbon-number alkanes (nC11-nC21) and 76.7–94% of benzenes and alcohols in ORW can be removed easily in O 3 /PFCN, and the toxicity of organics degradation products was lower than that of the parent compound. PFCN with capacities of separation and catalytic oxidation provided a promising alternative for ozonation of recalcitrant tailwater.