The Desulfuration Process And Kinetics Of High Sulfur Coal By Using Ferric Salts As Leaching Agents

Abstract:In this paper, the samples originated from Liuzhi Coal Mine (Guizhou, China)contained sulfur3.79%(sulfate sulfur0.48%, pyritic sulphur2.31%, and organic sulfur1.00%) were used as raw material and their desulfuration process and kinetics were investigated by using ferric salts as leaching agents..The aim of this study is to understand the leaching process, and improve the efficient utilization of high-sulfur coal.Leaching desulfuration of coal by ferric sulfate and ferric chloride were studied respectively. The effects of leaching temperature, ferric concentration, liquid/solid ratio, stirring velocity and leaching time on the desulfuration efficiency were investigated. Samples dealed with optimized conditions were examined by IR, XRD and sulfur analysis. Contrasting analysis results of samples before and after desulfuration showed the basic structure of the coal was saved intactly, and sulfur was removed effectively.When ferric sulfate was used as oxidant, the optimum conditions were:leaching temperature87℃, ferric sulfate concentration1.0mol/L, solid-liquid ratio1:7.5, stirring velocity400rpm, leaching time16h. Under which the desulfuration efficiency was43.41%,86.15%sulfur in FeS2was removed, and67.74%of the sulfur in FeS2was oxidized into sulfate,32.26%was oxidized into elemental sulfur.When ferric chloride was used as oxidant, the optimum conditions were:leaching temperature87℃, ferric chloride concentration1mol/L, liquid-solid ratio1:5.0, stirring velocity400rpm, leaching time16h. Under which the desulfuration efficiency was49.69%,90.91%sulfur in FeS2was removed, and65.19%of the sulfur in FeS2was oxidized into sulfate,34.81%was oxidized into elemental sulfur.The thermodynamic results demonstrated that the pyritic sulfur was preferentially oxidized to SO42-.The results of Unreacted Shrinking Core Model (SCM) analysis showed that the leaching rate was dominated by internal diffusion. After8h leaching, the apparent activation energy of the leaching process was changed from12.59kJ/mol to20.96kJ/mol, which might owe to the inhibition of the elemental sulfur produced from the oxidation of pyrite. The elemental sulfur might have low diffusion rate and gradually enrich on the surface of pyrite unreacted with the extension of leaching time, resulting in decreasing active pyrite ranges, and then desulfuration rate.