Sulfur recovery from lignite coal and desulfurization solution for environmental sustainability

The presence of sulfur compounds in lignite coal results in environmental pollution. The investigation involves the coal sulfur extraction with 1 M sodium hydroxide solution or 1 M potassium hydroxide solution, with and without the treatment following 10% HCl solution, respectively, or with a mixture having a combination of the two alkaline solutions, with and without the treatment following 10% HCl solution. Optimal desulfurization results were achieved, with the use of 1 M NaOH with 73.62% sulfur removed at operating parameters of 50 degrees C, stirring speed of 300 RPM, and at a heating time of 75 min. The sulfur content of pre- and post-desulfurized coal was determined through carbon-sulfur analysis. The raw coal proximate and ultimate analysis was performed for the coal characteristics. Calorific value measurements of the coal were also conducted before and after the desulfurization. X-ray diffraction analysis of treated coal, gas chromatography-mass spectrometry, and scanning electron microscopy-energy dispersive spectroscopy of the desulfurized solution were performed to provide further comprehensive insights. Results revealed a maximum of 65% sulfur recovery during the sulfur regeneration step from the extracted solution. In this work, for the first time, we have highlighted a method for the regeneration of sulfur from coal desulfurized solutions.