Experimental and kinetic analysis of Hg0 removal by CoFe2O4 nanoparticles as an efficient activator of persulfate

Abstract

The sulfate radical (SO₄^•−) and hydroxyl radical (^•OH), derived from the oxidation of persulfate (PS), are significant active substances in the treatment of pollution. In this study, magnetic CoFe₂O₄ nanoparticles (CFO NPs) were synthesized by a hydrothermal method and applied to activate PS for Hg⁰ removal from the simulated flue gas. The results exhibited that the Hg⁰ removal efficiency can reach as high as 99.5% within 60 min under the optimal condition of 6 mM of PS, 0.8 g/L of CFO dose, 20 °C of reaction temperature and 7 of initial pH. The characterizations demonstrated that the large surface area and coexistence of Co/Fe mixed valence were generated after the formation of CFO nanostructure, improving the amount of active sites and facilitating the adsorption and activation of PS. Scavenging tests indicated that SO₄^•− and ^•OH were the main active radicals on Hg⁰ removal, where the ^•OH radicals primarily originated from the conversion of SO₄^•−. Moreover, the circulation of ≡Co(III)/≡Co(II) and ≡Fe(III)/≡Fe(II) resulted in a superior Hg⁰ removal activity. Based on the experiments and characterization analysis, the reaction mechanism was proposed. In addition, the kinetic model for Hg⁰ removal was systematically analyzed, and the role of SO₄^•− and ^•OH was further verified. This study provided new insights toward efficient activation of persulfate for removal of Hg⁰ from coal-fired flue gas.