The mechanism of enhanced diclofenac (DCF) mineralization by catalytic ozonation over iron silicate loaded pumice (FSO/PMC) was investigated. The results showed that FSO/PMC catalytic ozonation process significantly improved the DCF mineralization from 32.3% (sole-ozonation) to 73.3%. The adsorptive and catalytic properties of FSO/PMC effectively enhanced the oxidative capability of ozone and led to an excellent DCF mineralization. This is likely due to the presence of FSO/PMC that can improve the mass transfer of aqueous ozone, increase the solubility of aqueous ozone, and accelerate the generation of center dot OH radicals as verified in this study. The adsorption of DCF on FSO/PMC was low (7.3%), however, DCF could be rapidly decomposed into various intermediates, which have much higher adsorption on FSO/PMC surface than that of DCF. This is another critical finding to justify the higher and faster TOC removal, because the accumulation (i.e. adsorption) of various intermediates on the surface of FSO/PMC increases their contact probability with center dot OH radicals that derived from ozone decomposition. The ozone decomposition on the catalyst surface can further accelerate a benign cycling of the succeeding ozone gas transfer, H2O2 generation, and adsorption/decomposition of intermediates. (C) 2016 Elsevier B.V. All rights reserved.