Determination of Free Magnesium Oxide in Steelmaking Slags by Microwave-Assisted-Hydration/Thermogravimetry

Over 10 million tons of steelmaking slags is produced every year in Japan.1) Steelmaking slag is a useful material to save natural resources2) and is expected to be used for a variety of purposes. The use of the slags as an aggregate for civil engineering has a long tradition and it comprises approximately 70% of all the products.1) In addition, steelmaking slag is recently used as fertilizer that enhances rice productivity in paddy fields damaged by seawater3) or constructs nursery ground in the sea.4) It is also used as a material for the development of biofuels.5) A steelmaking slag may contain appreciable amounts of free lime (f-CaO) and small amounts of free magnesia or periclase (f-MgO), which cause expansive self-destruction by about 100% volume increase due to their reactions with water.6) Consequently, f-CaO and f-MgO in the slag can be responsible for cracks of civil constructions or humps of roads. In order to make the efficient use of slags, it is thus very important to accurately and precisely determine the amounts of f-CaO and f-MgO in the slag. Various methods for determination of f-CaO in steelmaking slag have so far been proposed, e.g., the ethylene glycol extraction method,7,8) X-ray diffraction (XRD),9) and a combined use of the ethylene glycol extraction and thermogravimetry (TG),10) some of which have been validated through multi-laboratory studies.10) On the contrary, Determination of Free Magnesium Oxide in Steelmaking Slags by Microwave-Assisted-Hydration/Thermogravimetry