Mechanism and Efficiency of Tetracycline Removal by Ferrate and Ferrous-Enhanced Ferrate System

Ferrate fortified with ferrous iron can effectively improve the degradation of tetracycline (TC) in the coagulation process. Optimizing experiment conditions is investigated in the ferrate and ferrate-ferrous system. TC removing was up to 85% when the molar ratio of ferrate to TC was 2.5:1 under initial pH 4-9. Ferrate-ferrous performance is better than only ferrate or ferrous, and the morphology and composition of flocs formed by the ferrous and ferrate-ferrous systems are investigated. The initial pH has an influence on the coagulation process, whether in the ferrous or ferrate-ferrous system. The stability of flocs created by the ferrate-ferrous system under alkaline conditions was better than that under acidic conditions. Nevertheless, flocs formed by ferrous under acidic conditions were better than that under alkaline conditions. The flocs' stability is related to their composition and structure. The proportion of a-FeOOH formed by Fe(VI)-Fe(II) was approximately between 26% and 37.3%, and the proportion of gamma-FeOOH was 63 similar to 74%. The knowledge obtained in this research enhances the flocculation effect of ferrate and its ability for sustainable oxidative degradation of pollutants.