Efficient mercury removal from flue gas using high-quality spinel mixed ferrites obtained from wastewater

Abstract High-quality spinel mixed ferrites (M-Fe) are obtained from the electroplating wastewater, which are then used as adsorbents for the removal of elemental mercury (Hg0) in the flue gas to simultaneously realize the purpose of waste resource utilization and pollution control. In the “ferrite process”, through adjusting the dosages of ferrous sulfate (FeSO4·7H2O), the chromium (Cr) in wastewater can be fully recycled to synthesize the M-Fe adsorbents with good crystal morphology and chemical stability, and they can be easily separated by applying a magnetic field. Hg0 removal experiments indicated that the feeding mass ratio of FeSO4·7H2O: Cr6+ and temperatures had great influence on mercury removal efficiency, and the M-Fe adsorbents with FeSO4·7H2O: Cr6+ mass ratio of 100: 1 (M-Fe (100)) had the highest Hg0 removal performance with nearly 100% at 100℃. In addition, M-Fe (100) presented good sulfur resistance, which remained above 90% Hg0 removal efficiency after SO2 injection, and it can recover activity when stopping SO2. The XPS and desorption dynamics analysis showed mercury existed in the form of physically and chemically adsorbed states. Adsorption kinetic studies manifested that surface active sites were the adsorption rate controlling step, and inner active sites played an important role in mercury adsorption process. Mercury equilibrium analysis indicated mercury amount during adsorption and desorption process was approximately identical, manifesting M-Fe (100) was well recyclable magnetic adsorbent.