Using rice-husk-derived porous silica modified with recycled cu from industrial wastewater and ce to remove Hg⁰ and NO from simulated flue gases

Resource-recovered CuO_x-CeO_x/SiO₂ samples were prepared by using rice-husk-derived silica modified with recycled copper ion from panel industry wastewater for controlling Hg⁰ and NO emissions from simulated flue gases. By using the silicate exfoliation method for sample preparation, the presence of Cu and Ce oxides could increase the specific surface area (S_BET) of SiO₂. 50%Cu-10%Ce/SiO₂ having the largest S_BET showed significant NO removal. XRD results indicated that significant CuO diffraction peaks were not detected among all the CuO_x/SiO₂ samples, suggesting that CuO_x was highly dispersed on the surface. SEM and TEM images showed that the uniform spherical SiO₂ particles have changed into plate-like structure, further confirming the occurrence of structural rearrangement after incorporated with Cu/Ce oxides via silicate exfoliation. XPS results showed that Cu²⁺ and Ce⁴⁺ were the major valence states presenting in the samples. H₂-TPR and NH₃-TPD indicated that the 50%Cu/SiO₂ and 50%Cu-10%Ce/SiO₂ had greater redox ability and stronger acidity as compared to those containing smaller amounts of CuO_x and CeO_x. Cu and Ce modification was shown to successfully improve the NO removal efficiency. 50%Cu-10%Ce/SiO₂ had the best NO conversion efficiency of 70–85% with a broad temperature window of 150–300°C. 50%Cu/SiO₂ exhibited the greatest total Hg removal efficiency of 88.2% among all the tested samples at 150°C and remained almost the same removal efficiency at 250°C. These results suggest that the recycled Cu modified rice-husk-derived SiO₂ is feasible for not only controlling Hg⁰ and NO emissions but also recovery of agricultural and industrial wastes.