Study On Sulfur Leaching And Separation Mechanism Of High Dust Desulfurization Gypsum And Utilization Of Tailings

With the rapid development of Chinese economic construction,industrial flue gas pollutant emissions are also increasing accordingly.In recent years,China has paid more and more attention on ecological environment protection and utilization of solid waste resources,and achieved great achievements in the control of SO₂ emission.Currently,the wet fuel gas desulfurization(FGD)technology is widely used for desulfurization from coal-fired flue gas.However,the utilization of its by product-FGD gypsum,especially the high dust FGD gypsum has also become an important issue to be solved urgently.At present,many studies have been carried out on the utilization of FGD gypsum,but the utilization ratio in China is still less than 80%,especially for the high dust FGD gypsum.Therefore,it is imperative to carry out researches on the properties of high dust FGD gypsum and its efficient resource utilization.In this paper,a series of researches were carried out to improve the utilization ratio of high dust FGD gypsum.According to the characteristics of high-sulfur and high-ash coal in China,the dust migration law in the wet FGD process was investigated.The dust properties and influence of structure of FGD gypsum on its properties were analyzed.The leaching mechanism of sulfur from the high dust FGD gypsum and the utilization of desulfurization tailings were further studied.With the increase of dust content in FGD gypsum,the crystal morphology of FGD gypsum changed from columnar to irregular.When it was used as building gypsum,the standard water consumption and the mechanical properties of FGD gypsum decreased with the increase of dust content.The main components of dust were Si O₂,Al₂O₃,Mg O,Fe₂O₃,K₂O and Ca CO₃,which were mainly from the flue gas.A small amount of dust was originated from the incompletely reacted desulfurizer and the impurities in the desulfurizer.The PM_2.5 content of the dust came from flue gas was 79.22%,while the PM_>2.5 content was 20.22%.After wet desulfurization,about 68.6%of PM_2.5 and 83.5%of PM_>2.5 dust entered the FGD gypsum.The Si and Fe contents were relatively high in the large particles,while the Al and Ca contents were higher in the small particles.During in the wet FGD process,the dust removal ratio decreased with the increase of gas flow rate and limestone slurry concentration.With the increase of the liquid-to-gas ratio,the dust removal efficiency increased first and then plateaued.The sulfur in high dust FGD gypsum can be effectively leached by oxalic acid solution.The sulfur leaching efficiency was higher than 97%under the optimal conditions i.e.oxalic acid concentration of 0.3 mol/L,solid-liquid ratio of 42.9 g/L,temperature of 30?,stirring rate of 500 rpm and leaching time of 10 min.The Avrami equation was suitable for describing the sulfur leaching process.The activation energy of the leaching reaction was calculated as 34.84 k J/mol based on Avrami equation.When the reaction temperature was lower than 20?,the sulfur leaching process was controlled by chemical reaction,otherwise was controlled by diffusion.The properties of desulfurization tailings obtained after sulfur leaching was studied,and the metallurgical utilization method of desulfurization tailings was investigated.The desulfurization tailings started to decompose into Ca O at 816.3?,which was much lower than that of pre-melting of the mold fluxes.The desulfurization tailings can replace the Ca O in the mold fluxes.The melting temperature and viscosity of the mold fluxes decreased with the increasing amount of desulfurization tailings added.When 70%of Ca O in the mold flux was replaced by the desulfurization tailings,the melting temperature of the mold flux dropped from 1192?to 1188?,and the viscosity dropped from 0.211 Pa·s to 0.193 Pa·s.Raman spectroscopy analysis showed that the Mg O,Fe₂O₃,K₂O in the desulfurization tailings could destroy the structure of the silicate melt to reduce the bridging oxygen content in the melt,resulting in lower melting temperature and viscosity of the mold fluxes.The addition of tailings can increase the crystallization temperature,crystallization rate,crystallization ability,and overall thermal resistance of the mold flux,while reduce the heat transfer capacity.The addition of tailings was beneficial to reduce the longitudinal cracks of the continuous casting slab,and it was more suitable for the manufacture of low-carbon steel with higher primary shell strength.For high-carbon steel with lower primary shell strength,the ratio of tailings should not be exceed to30%.With the addition of desulfurization tailings,there were no significant changes in the phase compositions and the C,S,and H contents of the mold flux.It's feasible to use the desulfurization tailings to prepare mold flux,which met the performance and design requirements for continuous casting production.In short,this study provided an effective method for the harmless resource disposal and utilization of high dust FGD gypsum.