Synergistic and competitive adsorption of NOx and SO2 using a microwave-assisted approach with industrial waste materials fly ash and carbide slag as sorbents

A novel catalytic adsorption approach for microwave-assisted synergistic utilization of coal fly ash (FA) and carbide slag (CS) as adsorbents and Na2O/Na2O2 as a catalyst was proposed as an efficient and low-cost De-SO2 and De-NOx technology. The highest SO2 and NOx adsorption capabilities under these circumstances were 0.55 and 0.06 mg/g under 2% Na2O/FA-CS adsorbent at 150 °C respectively. The experimental results shows that the loaded Na2O2 as adsorbent in the Na2O2/FA-CS was strongly oxidized and decomposed into reactive oxygen (O∗), in which the conversion behavior of NOx (ads) and SOx (ads) contributed to the catalytic activation and adsorption performance. In the synergistic adsorption process, both NOx (ads) and SOx (ads) were present on the adsorption interface of the X% Na2O/FA-CS adsorbent, which also facilitated the production of unstable nitrogen and sulfur compounds. In the competitive adsorption process, NOx and SOx readily occupied the active adsorption spots of CaO used as an adsorbent in FA-CS while also contaminating the active catalytic spots of the coexisting Na2+/Na1+ ions, thus reducing the activity and efficiency of the adsorbent. Environmental implications: Coal fly ash is the main solid waste discharged from coal-fired power stations. The large amount of coal fly ash occupies land resources, while solid fine particles and heavy metals pollute the surrounding air. In addition, calcium carbide slag is a kind of industrial waste slag mainly comprising calcium hydroxide. Calcium carbide slag exhibits the characteristics of high humidity and alkalinity, leading to stockpiling and land pollution. To achieve resource utilization and high-value utilization, synergistic microwave-assisted utilization of industrial waste materials coal fly ash and carbide slag was assessed for high-efficiency desulfurization and denitrification.