Insight into the mechanism of ferrate(VI) activation by mineral zincite for carbamazepine degradation: Role of Fe(V) species and free radical induction

This paper describes the ferrate(VI) (Fe(VI)) activation by mineral zincite for efficient micropollutants removal such as carbamazepine (CBZ). In the Fe(VI)-zincite activation system, the zincite stimulated the Fe(V) production and impelled the Fenton reaction by preventing the transformation of Fe(II), generated from the Fe(VI), to Fe(III). Furthermore, adducts formation between Lewis sites derived from zincite and Fe(VI) induced the generation of organic radical. The mechanism was unveiled via kinetic study, reactive species identification, Fe(VI)-zincite deposit characterization and CBZ degradation products detection. Results indicated that hydroxyl radical (•OH), Fe(V) and carboxyl radical (R-COO ) contribute to the CBZ degradation in Fe(VI)-zincite system and play different roles with pH change. The optimum application condition of [Fe(VI)]:[CBZ] = 5:1, [zincite] = 5 mg/L, the zincite particle size of 500–750 mesh and pH of 7.0 was further determined. Under this condition, 91% CBZ removal and 61% mineralization were achieved by the Fe(VI)-zincite system. The feasibility of Fe(VI)-zincite system for real condition was also evaluated. The CBZ removal and mineralization were decreased 6% and 8%, respectively, suggesting that Fe(VI)-zincite system was still highly effective for CBZ degradation in real natural water. Furthermore, amphoteric property of zincite contributed to the stability of pH in deficient buffering solution, ensuring the stability of reaction activity. Importantly, this study provided new insight into the Fe(VI) activation which was not achieved by the traditional introduced reducing substance, and has potential applications for micropollutant remediation in aquatic environment.