Influence of pyrite on oxidative treatment of diclofenac with zero-valent iron/H2O2 system coupled with chemical precipitation under controlled and uncontrolled pH conditions

Batch experiments, combined with surface measurements, were conducted to elucidate the impact of pyrite on diclofenac treatment by zero-valent iron (ZVI)/H2O2 system. In binary systems with ZVI/H2O2, diclofenac removal was limited under controlled-pH conditions due to the agglomeration of ZVI particles and low rate of iron leaching. However, the use of pyrite in batch systems under uncontrolled-pH conditions drastically increased diclofenac removal by the ZVI/H2O2 system due to a significant drop in pH and enhanced iron dissolution. The diclofenac removal by the ternary ZVI/pyrite/H2O2 system could be explained through a combined effect of adsorption, oxidative degradation of diclofenac with hydroxyl radicals (*OH) and chemical precipitation of diclofenac and/or its intermediate species with the iron species dissolved from the ZVI/pyrite particles. While adsorption/chemical precipitation accounted for 75% of diclofenac removal in the initial stage, oxidative degradation achieved the remaining 25% diclofenac removal in the second stage. Surface analyses show that, in systems with diclofenac, the iron species dissolved from ZVI and pyrite particles complexed with diclofenac and/or intermediate species to form some spherical particles. Overall, this study sheds light on the reaction mechanism for the practical application of the ternary ZVI/pyrite/H2O2 system to diclofenac removal. [Display omitted] •The addition of pyrite enhanced diclofenac removal by zero-valent iron(ZVI)/H2O2 system.•Diclofenac removal was a collaborative effect of adsorption, *OH degradation and chemical precipitation.•Diclofenac complexed with iron dissolved from ZVI/pyrite particles to form spherical particles.