MINERALOGY OF MODIFIED STEEL SLAGS

Abstract

Among the residues and by-products waiting for a sustainable valorisation, steel slags present the most interesting potential because of their chemical and mineralogical composition. In spite of that, the degree to which steel slag is used remains limited because of the quantity of free lime contained in this type of slag. Many processes have been tried to solve this problem but their economic balance has been limited by the quality of the final product and has prevented industrialization. Two processes, however, have a significant potential for indus- trial application. These involve treatments under oxidising or reducing conditions and a modification of the chemistry and the mineralogy by a mineral addition (addition of silica or alumina) between the converter and the slag discharge process step (‘Upstream’ process modification). With such modifications, it is possible to eliminate the free lime and to obtain sound aggregates or a product with cementitious properties similar to or better than a blast furnace slag. In this study, we compare the mineralogy of the final "modified slags" obtained by these processes and its impact on the reactivity. The best results are obtained by the addition of alumina and lime under oxidising conditions. The iron rich cement produced has a similar reactivity to that of a Portland cement with potential advantages in terms of durability thanks to the absence of alkalis