Degradation of tannic acid in heterogeneous Fenton system and persulfate system using iron(III) modified attapulgite: Influencing factors and degradation mechanism analysis

Abstract

The redox cycle of iron is a well-known rate-determining step for radical generation in advanced oxidation system. In this study, iron(III) modified attapulgite (Fe-ATP) was employed as a regulator to enhance the degradation of tannic acid (TA) in heterogeneous Fenton and persulfate (PS) systems. Results showed that under the conditions of pH 3 and 0.5 g·L−1 of Fe-ATP, the maximum removal rate of TA was 82.2% and the removal rate of total organic carbon (TOC) was 31.7% in heterogeneous Fenton system with 5 mM H2O2 and 90 min reaction, and the maximum removal rate of TA was 78.5% and removal rate of TOC was 28.9% in PS system with 1 g·L−1 Na2S2O8 and 60 min reaction. Among commonly inorganic anions (Cl-, NO3-, HCO3-, CO32-, SO42-, HPO42- and H2PO4-), only HPO42- and H2PO4- significantly inhibited the TA removal by Fe-ATP. Radical quenching tests indicated that hydroxyl radical (∙OH) and sulfate radical (SO4∙-) were the main active species in the heterogeneous Fenton system and PS system, respectively. Moreover, the TA removal rate could still reach 40% after four times of recycling. Hence, the Fe-ATP could be a good catalyzer for treating tannic acid contaminated waters in heterogeneous Fenton system and persulfate system.