Recovery of ferrous sulfate and sulfuric acid from spent pickle liquor of the steel industry

Abstract

This paper demonstrates that spent sulfuric acid pickle liquor can be recycled by recovering sulfuric acid and ferrous sulfate. This is achieved by removing part of the water from the liquor followed by ferrous sulfate crystallization and separation of the ferrous sulfate from the resulting slurry. Depending on energy consumption, three cases of carrying out the process can be distinguished. The percentage of sulfuric acid recovered for these three cases was 92.4, 90.4 and 89.7, respectively, and the percentages of ferrous sulfate recovered were 69.7, 85.3 and 92.7, respectively. The sulfuric acid concentration in the respective filtrates increased from 7.62% in the spent pickle liquor to 17.7%, 19.5% and 35.5%. The ferrous sulfate concentration decreased from 15.1% to 11.5%, 6.31% and 5.75%, respectively. The crystals of recovered ferrous sulfate contained small amounts of occluded sulfuric acid.