Promotion effect of Cu doping on mercury removal properties of magnetic MnFe₂O₄ materials with high adsorption capacity

In this study, a simple method combining sol-gel and impregnation techniques was employed to synthesize magnetic Cu/MnFe₂O₄. The resulting material demonstrated outstanding efficiency in removing mercury, achieving over 90% at reaction temperatures ranging from 150 °C to 200 °C. Through Cu incorporation, the Hg⁰ removal performance of Cu_0.15MnFe was significantly enhanced, leading to a high adsorption capacity of 70.1 mg/g. This surpasses the capabilities of many previously reported adsorbents and holds great potential for enhancing the stability of Hg recovery efficiency. Furthermore, the presence of O₂, HCl, and NO further improved the Hg⁰ removal. Conversely, H₂O had an mild inhibitory effect on Hg⁰ removal. Additionally, the introduction of Cu noticeably mitigated the inhibitory impact of SO₂ on mercury removal characteristics and alleviated the issue of SO₂ poisoning in adsorbents. The primary active sites responsible for the oxidation of elemental mercury are the redox reaction between Cu²⁺/Cu⁺ and Mn³⁺/Mn²⁺, and adsorbed oxygen species. Through the oxidation process, Hg⁰ is primarily converted into various compounds, including HgO, Hg(NO₃)₂, HgCl₂, and HgSO₄. As a result, the prepared magnetic recyclable adsorbent, with its high mercury adsorption capacity, exhibits promising prospects for industrial application in the low-temperature removal of Hg⁰ from coal-fired flue gas.