The chemistry and mineralogy of some granulated and pelletized blastfurnace slags

Humberside, collected over several years, vary somewhat in chemical composition reflecting differences in iron-making practice. All contain some melilite and oldhamite crystals and minor amounts of iron along with the glass. Granulated slag from Usinor, Dunkirk, France, has a little more CaO than the Scunthorpe material with crystals of merwinite and oldhamite. Pelletised slag from Redcar, Teeside, is much more vescicular than the granulated material and contains melilite and oldhamite. The melilite crystals contain many inclusions of old-hamite and iron. They span a wide range within the akermanite-gehlenite seri s and are non-stoichiometric in composition. The merwinite may have formed largely by quench crystallization. Oldhamite is probably the first phase to form in all the slags. The silicate mineralogy can be explained interms of the phase relationships within the CaO SiO 2 A12Oa-MgO quaternary system. The small difference incomposition ofthe French slags is sufficient for them to fall into the primary phase field of merwinite rather than melilite. Assuming that only a minor propor-tion of crystals i acceptable in slags for use in Portland Blastfurnace C ment, he present low A1 (< 11 ~ A1203) British and French slags are approaching an optimum composition