Abstract
ABSTRACT In this study, calcium sulfate(gypsum) powder was obtained using waste sulfuric acid and stainless steel refinery sludge by-produced from chemical reagent and the iron industry, by the neutralization of waste sulfuric acid. As variables for the experiment, the molar ratio of the H2SO4: Ca(OH)2, the pH, the reaction temperature and time, the amount of catalyst were used. The crystal shape and microstructure of obtained powder were observed by XRD and SEM, and the thermal property was investigated by DTA. As the NaCl is added 0–20 wt.% as a catalyst to the H2SO4-Ca(OH)2 system, it can be found that the crystal shape goes through the processes as follows; gypsum dehydrate gypsum → gypsum hemihydrate + gypsum dihydrate → gypsum hemihydrate. And gypsum hemihydrate is δ-type as the result of DTA. As waste sulfuric acid and stainless steel refinery sludge were used, the pH of reacted solution (which was 0.8) was rapidly raised up to 8–9 by the addition of stainless steel sludge and gypsum dihydrate was produced as a by-product. Therefore, it was found that stainless steel refinery sludge is sufficiently applicable for the neutralization of waste sulfuric acid.
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