Improving the quality of ammonium sulfate produced from the flue gas desulfurization process by using ammonium persulfate

Yellow ammonium sulfate, a by-product of flue gas desulfurization, has a lower product quality due to its chromaticity not meeting the chromaticity requirements for ammonium sulfate fertilizer. In this work, sulfur impurity was revealed to be the reason for the yellowing of ammonium sulfate products by studying the effects of organic pollutants, metal impurities, and sulfur-containing impurities on the chromaticity of ammonium sulfate products. A sulfur impurity was found to be generated when ammonium thiosulfate in the unqualified absorption mother liquor reacted with concentrated sulfuric acid, an oxidant in the ammonia desulfurization process. Subsequently, ammonium persulfate was proposed to replace concentrated sulfuric acid as an oxidant to solve the problem of abnormal chromaticity of ammonium sulfate. The experimental results show that under the optimized process conditions, the removal rates of thiosulfate and sulfite in the desulfurization mother liquor are as high as 90.1 % and 93.4 %, respectively, with ammonium persulfate as an oxidant. The ammonium sulfate product obtained is white with uniform particles. In addition, the effect degree of different oxidation components is S2O82−>SO4−∼OH in the oxidation process of ammonium persulfate to the absorption of the mother liquor. The ammonium persulfate oxidation technique provides benefits over the conventional ammonia acid process, including increased oxidation efficiency, decreased sulfur generation, and enhanced ammonium sulfate product quality.