Investigation of possible leaching control mechanisms for chromium and vanadium in electric arc furnace (EAF) slags using combined experimental and modeling approaches

In this study, possible leaching control mechanisms for Cr and V in electric arc furnace slags were investigated by using a multi-methodological approach. Aside from chemical and mineralogical bulk analyses, special emphasis was given to surface investigations of the slags prior to and after leaching. In addition, pH dependence leaching tests were performed and the obtained data were evaluated with hydrogeochemical models. Investigations revealed that Cr and V are mainly bound in spinel and wuestite as well as minor amounts of olivine. Spinel and wuestite do not dissolve during water leaching for 48 h, whereas, depending on the composition of olivine, this phase either dissolves and releases V and Cr congruently, or does not dissolve but may hydrate. Melilite may also hydrate, but neither V nor Cr were detected in this phase. It appears that leached V is subsequently adsorbed onto these newly hydrated phases. The combination of the applied methods further showed that the abundance of calcium silicates, spinel, and wuestite is influenced by the FeO/SiO2 and CaO/SiO2 ratio in the slag. Therefore, it is assumed that the leaching of V and Cr can be minimized by changing these ratios to favor the formation of Fe bearing calcium silicate and spinel instead of wuestite

Developing a new process to agglomerate secondary raw material fines for recycling in the electric arc furnace - the Fines2EAF project

Recent years have seen a worldwide change in the environmental policy towards circular economy approaches. It is estimated that steel-making activities in Europe produce about 80 million tonnes annually of by-products and waste, equivalent to half of the European steel production, of which more than 10 million tonnes is waste for disposal. This waste of resources and land area is not sustainable and has to be decreased in the future. The Fines2EAF project aims to increase the value of steelmaking residues by internal recycling and (re)use in the form of agglomerates. The benefit of this strategy is threefold: improved utilization of residues, internal recovery of valuable materials and reduction of the amount of dumped materials. The approach followed is the development of an innovative process to produce cement -free agglomerates based on primary and secondary raw material fines, alternative binder systems and a hydraulic stamp press. In addition, a new pre-treatment process for fines based on microwave heating is investigated. The first results of the lab-scale investigation of the fines pre-treatment to reduce the amount of zinc, volatiles and alkalis are presented. Six materials from two steel plants have been tested in a laboratory microwave furnace. Also presented are first results of the agglomeration of fines using a laboratory press