Determination of Free Calcium Oxide in Steel Slags by Combination of Glycol-EDTA Titrimetry and Thermogravimetry-Differential Thermoanalysis (TG-DTA)

Glycol-EDTA titrimetry in combination with TG-DTA was applied to the determination of free CaO (f-CaO) in steel slag. It was shown that Ca(OH)2 co-existed with f-CaO in the sample reacts quantitatively with EDTA in the titrimetric process, hence the result obtained is the sum of contents of CaO and Ca(OH)2; and it was found that the TG-DTA pattern of Ca(OH)2 can be used to calculate the content of Ca(OH)2 in slag sample. Therefore, content of f-CaO of the sample was obtained by the difference of the results obtained by glycol-EDTA titrimetry and TG-DTA. In addition, it was found that the setting components in slag sample gave extra amount of Ca(OH)2 due to their hydration with water which was produced in the reaction of f-CaO with glycol to give soluble calcium glycollate. To overcome this interference, definite amount of silica gel was added to the reaction system to remove the water by adsorption, making accuracy of the method improved still further.