The wastewater from the processes of desulfurization and denitration contained complex components, and the recovery of wastewater was limited by the co-existence of nitrates and nitrites. By now, this type of wastewater was mostly directly discharged after a simple treatment or was sent to the sewage treatment plant for further disposal, leading to series of environmental problems or causing instability of biochemical section in sewage treatment plants. Moreover, the cost of the recovery process will decrease via recovering the nitrogenous valuable salt. In this work, a low-cost process with high efficiency of desulfurization and denitration was developed. There were only nitrite ions as nitrogen-containing anions in the wastewater of desulfurization and denitration. Using steel slag slurry combined with ozone oxidation, this process achieved high desulfurization and denitration rate with accessory ingredient of Na2S2O3. There were cations such as Na+, Mg2+, Ca2+, Mn2+, Fe2+, etc. and anions such as NO2?, S2O32?, SO42?, etc. existing in the as-generated wastewater. The water pollution and marketable salt resources waste from wet flue gas desulfurization and denitration via a gas phase oxidation?wet absorption process was mainly solved in this work. A technology of pH adjustment?decalcification via adding sodium carbonate-evaporating crystallization to recovery NaNO2 from wastewater was proposed. The effects of pH, addition methods of sodium carbonate, concentrated total salt concentration, and crystallization temperature on the crystallization rate and purity of NaNO2 were discussed. The results indicated that the crystallization rate and the purity of NaNO2 from desulfurization and denitration wastewater were mainly affected by pH and total concentrated salt concentration. Under the optimal conditions, in which pH was 11, addition method of sodium carbonate was concentrated solution, total concentrated salt concentration was 70wt%, and crystallization temperature was 50℃, the crystallization rate of NaNO2 was greater than 60%. The products of NaNO2 met the quality requirement of national standard (GB/T 2367-2016).
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