Simultaneous removal of NO and SO2 with a new recycling micro-nano bubble oxidation-absorption process based on HA-Na

Wet oxidation-absorption is a promising process for flue gas desulfurization and denitration due to its simple system and high removal efficiency. In comparison to the ordinary bubbles, micro-nano bubbles have some special properties such as spontaneous generation of hydroxyl free radicals and self-pressurized solution. Sodium humate (HA-Na), which is a cheap, easily accessible and recyclable reagent, can react with H+ to produce humic acid sediment so that it may promote the solution of NO2 and SO2 in the water. In this study, a new wet recycling micro-nano bubble oxidation-absorption process based on HA-Na was developed for the simultaneous removal of NO and SO2. A micro-nano bubble generator (MNBG) was utilized to generate the micro-nano bubble oxidation-absorption system (MNBOS) from HA-Na aqueous solution and the mixed gases, composed of N-2, NO, SO2 and/or other gases including O-2 and CO2. The MNBOS was recycled continuously from the MNBG to the reactor. The critical operation parameters, including operation time, initial pH and temperature of the absorbent, HA-Na concentration, NO concentration, SO2 concentration, presence of O-2 and/or CO2, were investigated to explore the simultaneous removal of NO and SO2 with the MNBOS. The results showed that hydroxyl free radicals generated by micro-nano bubbles played a critical role in the removal of NO and HA-Na promoted the removal of NO. All the investigated parameters affected NO removal. Only initial pH and temperature of the solution and concentrations of NO and SO2 affected SO2 removal, whereas the presence of O-2 and CO2 or HA-Na concentration had no significant effect on SO2 removal. This new process could achieve high removal efficiency which was respectively above 91.1% for NO and 99.7% for SO2 under the conditions of 0.5 g/L HA-Na, initial solution pH 7.47, initial solution temperature 298 K, 1250 ppm NO and 1650 ppm SO2. Moreover, according to the analysis of FTIR and XPS, the removal products were mainly HA, sulfate and nitrate, which are the components of fertilizer and can be recycled as compound fertilizer which has higher activity compared with the traditional HA fertilizer because HA from this system is subjected to oxygenolysis by nitric acid and sulfuric acid in solution.