Experimental studies to overcome the recycling barriers of stainless-steel and BOF slags

Abstract: This thesis presents several studies aimed at improving the recycling of steel slag. The studies are based on a first evaluation of the state-of-the-artof the recycling applications both with respect to their possibilities and limitations. In addition, an analysis that highlights several properties of allkinds of ferrous slags, such as bulk chemical composition and common mineral phases, is presented to aid the discussion. Specifically, the studiespresented in this thesis cover two main topics: a new recycling application for stainless-steel slags and a theoretical study on the hydration offerropericlase, which is a mineral often present in basic oxygen furnace slags. Most of the studies presented in this thesis focus on the exploration of anew use of stainless-steel slags, aimed at increasing their recycling rate. In fact, this kind of materials are the most problematic slags to recycle, asmost are not viable for most of the state-of-the-art applications. Therefore, the potential to use them as a substitute for lime in the neutralization ofacidic waste waters is investigated. The studies cover a wide range of trials, from test performed at both laboratory and industrial scale with acidicwaste waters collected from stainless-steel plants, to more fundamental studies on the dissolution of slag minerals in acid environment. Overall,the substitution of lime with stainless-steel slags is proved to be successful both in terms of the obtained final pH values as well as in terms ofobtaining an efficient removal of metal ions dissolved in waters. In the last part of the thesis, a theoretical study on the hydration offerropericlase is conducted. This study proposes a possible technical solution to reduce the volumetric expansion of steel slags, which containhigh percentages of periclase. Specifically, it is seen that ferropericlase with high percentages of FeO adsorbs less water. Thus, they expand lesscompared to regular periclase. Therefore, the formation of such a phase during the solidification of slag can provide a higher volumetric stability,which is highly beneficial when the material later is employed in outdoors applications