Investigation of Possible Leaching Control Mechanisms for Chromium and Vanadium in Electric Arc Furnace (EAF) Slags Using Combined Experimental and Modeling Approaches

Abstract

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.

Tailoring the FeO/SiO2 Ratio in Electric Arc Furnace Slags to Minimize the Leaching of Vanadium and Chromium

“…For the laboratory experiments, a collective EAF slag sample (sample A) from a previous study [9] was used, which showed high FeO and low SiO 2 abundances and increased V and Cr leaching compared to the other samples investigated. The sampling was performed in 2016 and was assigned to the production of one steel charge during standard operating conditions.…”

“…For comparison, this study also presented one EAF slag sample (sample C) from a second steel plant, which leached significantly lower amounts of V and Cr than sample A and was characterized by a FeO/SiO 2 ratio of approximately one [9].…”

“…All calculations were performed using the software FactSage TM (version 7.1) in equilibrium mode selecting the databases FToxid (FACT oxide database, 2017) and FactPS (FACT pure substances database, 2017). Based on the mineralogical characterizations [9], it was decided that the six-component-system CaO-SiO 2 -FeO-MgO-Al 2 O 3 -Cr 2 O 3 served as a good compromise between a simplified slag system and all necessary components for the formation of the main mineral phases of samples A, B and C, namely: spinel solid solutions, wuestite solid solutions, and different calcium silicate phases such as melilite, larnite, and olivine.…”

“…Therefore, further investigations are required on the leaching control mechanisms of, for example, V in electric arc furnace (EAF) slags. In a previously conducted research [9], a mineralogical and chemical characterization of EAF slags was combined with a hydrogeochemical model and a hypothesis was proposed that the FeO/SiO 2 ratio in the slag is decisive for the amount of V and Cr released. It was assumed that a higher amount of FeO compared to SiO 2 leads to a higher abundance of wuestite (Fe, Mg, Mn)O and impedes the formation of Fe bearing calcium silicate phases such as olivine (A 2 SiO 4 , A = Ca, Mg, Mn, Fe) and melilite (Ca 2 M(XSiO 7 ), M = Mg, Fe, Al and X = Si, Al) and also indirectly on the formation of spinel (AB 2 O 4 , A = Mg, Fe, Mn and B = Cr, Al, Fe, Mn).…”

“…It was also shown that olivine, enriched in Fe and Mn, spinel and melilite are less soluble than olivine (with comparable low Fe and Mn amount), wuestite, and larnite. In addition, it is assumed that hydrated Fe bearing calcium silicate phases may provide adsorption sites for V [9,10]. To minimize the V and Cr release, the formation of spinel must therefore be promoted and the formation of the highly soluble calcium silicate phases impeded.…”