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 H 2 SO 4 : 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 02 0 wt.% as a catalyst to the H 2 SO 4 -Ca(OH) 2 system, it can be found that the crystal shape goes through the processes as follows ; gypsum dehydrate gypsum hemihydrate + gypsum dihydrate gypsum hemihydrate. And gypsum hemihydrate is β-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.

Stabilizing characteristics of heavy metals in the silicate glass (SD) and lead silicate glass(PD) containing Electric Arc Furnace(EAF) dust was studied by the toxic characterization leaching procedure(TCLP) test. Dependence of the amount of EAF dust upon structural changes of SD and PD glasses and TCLP results was also investigated by FT-IR spectroscopy. In the TCLP test, the concentration of heavy metals leached from a glass increased with the amount of EAF dust added. The SD series specimens showed heavy metal leaching lower than the PD series specimens, but the Pb leaching from the PD series specimens was the highest owing to the high Pb content in the PD glass composition. The value R(oxygen/network former ion ratio) was used to compare the leaching characteristics of glasses, and the SD had a higer R than PD series specimens to show a better chemical durability. Adding the EAF dust to the SD mother glass decreased the Si-O-Si symmetry and increased the non-bridging oxygen, which weakened the structure and decreased the chemical durability of glasses. It is concluded that SD is more effective in stabilizing the heavy metals of EAF dust than PD series glass.

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