Physical chemistry of some slag and glass systems useful in recycling

The system CaO-SiO2-Fe2O3 serves as a useful base in examining the nature of glasses and mineral species found both in oxidized steelmaking slag and in glasses made using precipitator or baghouse dusts from electric are steelmaking furnaces. A study has demonstrated that by oxidizing steelmaking slag, normally containing Fe and FeO, to the higher oxidation state, Fe2O3, the slag has the potential to form both crystalline and glassy species which have cementitious properties. A second study has shown that dusts with high Fe2O3 contents and small percentages of hazardous heavy metals can be converted to glassy or crystalline silicates with enhanced leaching resistance. Steel slag has limited cementitious properties due to both a lack of tricalcium silicate and the presence of wustite solid solutions as a predominant mineral phase. By oxidizing the slag, ferrite phases which are cementitious can be formed. The effectiveness of these phases as cements can also be enhanced by rapid quenching to form a predominantly glass structure. The phases found can be compared to the phases and glasses found in common cementitious materials such as Portland cement and granulated blast furnace slag using the CaO-SiO2-Fe2O3 system. Steelmaking dusts containing zinc, lead, cadmium and chromium are an environmental problem because of the leaching of these heavy metals, particularly in acid rain. By melting these dusts in a fifty percent SiO2 matrix and quenching in water, it is possible to form glasses, occasionally containing some crystalline species, which have high resistance to acid leaching