Enhanced degradation of tetracycline hydrochloride with in situ prepared ferrate supernatant based on calcium hypochlorite: Compare with purified and commercial ferrate

Abstract

Ferrate (Fe(VI)) salts are commonly regarded as green and high efficient oxidants to eliminate organic contaminants. Current studies mainly focused on develop homogeneous activation technology or heterogeneous catalysts to promote Fe(VI) performances in contaminants degradation. Interestingly, this study disclosed that the degradation performance of tetracycline hydrochloride (TC) was enhanced by using in situ prepared ferrate supernatant (Fe(VI)s), and the oxidation performance and degradation mechanism were systematically explored by comparing with the ferrate precipitation (Fe(VI)p) and the commercial ferrate (Fe(VI)c). Results showed that the degradation rate of TC by Fe(VI)s reached to 98.5 % within 5 min, while the degradation rate of Fe(VI)p and Fe(VI)c were obtained less than 20 % in 30 min. Although degradation process of TC in these three system were all conformed to the pseudo-first-order reaction kinetic, the rate of degradation (Kobs) obtained in Fe(VI)s was 5.30 and 37.2 times higher than that in Fe(VI)c and Fe(VI)p, respectively. Electron paramagnetic resonance (EPR), radical quenching and PMSO probe experiments proved that Fe(IV)/Fe(V) were the main active species for TC degradation with Fe(VI)s, while ∙OH and ⋅O2− were the main active substance of Fe(VI)c. On the basis of the intermediates detected by LC-MS/MS analysis, a pathway for TC degradation was proposed. In addition, the toxicity of TC and its degradation products was evaluated by using the toxicity evaluation software tool. This study demonstrated efficient organic contaminant oxidation with in situ prepared ferrate solution (Fe(VI)s) and provided a comprehensive understanding of degradation process for pollutants removal.