Reclamation of elemental sulfur from flue gas biodesulfurization waste sludge

Perchloroethylene (PCE) extraction was used to reclaim elemental sulfur from flue gas biodesulfurization sludge. The sludge was generated from a biodesulfurization system that concurrently treated the flue gas scrubbing solution and wastewater of citric acid production. The sludge contained approximately 40-60% elemental sulfur; other components included flue gas dust, biomass, inorganic salts, and flocculants. The sulfur was extracted with PCE at 80 degrees C, and then separated from the sludge by hot filtration. The elemental sulfur was then recovered from the PCE solution by recrystallization and centrifugation. When the dried sludge with particle size less than 0.2 mm was used in the PCE extraction, more than 90% of the elemental sulfur in the sludge could be recovered with a contact time of 15 min and a PCE-to-sludge ratio of 5 mL PCE/g sludge. The recovered sulfur generally had purities of 98-99.9% and could be directly used in many industries. Reuse of the PCE solvent in the extraction protocol through four cycles did not adversely influence the sulfur recovery efficiency. The results indicated that the PCE extraction was an effective method for the sulfur recovery from the biodesulfurization sludge.