Formation of Ta-rich magnetite phases in WEEE recycling slags through modification and controlled cooling

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During the last decades, the evolution of electronic devices push up the consumption of elements like Ta, In, Te, Ga, Se, and several Rare Earth Elements (REE), having a scarce presence in the technosphere. In most cases, the use of these strategic elements is in ppm, and thus, their recovery rate is smaller than 1%. Today, extract these raw materials from Waste Electrical and Electronic Equipment (WEEE) is one of the big challenges of process metallurgy. Typically found in pyrometallurgical slags from WEEE treatment, they are not recovered as their low concentration makes them economically unsuitable for further extraction under the conventional state of the art. Besides their scarcity, natural sources are found outside European borders and, due to their technological importance, are declared as Critical Raw Materials (CRM) by the European Union.Nonferrous metallurgy utilises fayalitic slag to treat several metal scraps such as lead, copper and WEEE because of their low viscosity, melting point and iron immobilisation in the slag. During cooling, fayalite partially decomposes into magnetite and silica. Magnetite share is inverse spinel structure with other compounds that under specific conditions show a magnetic behaviour and can be recovered using magnetic separators. Several authors have reported these strategies to concentrate Fe, Ti and V.This project aims to understand the formation and growing mechanism of artificial magnetitic mineral to concentrate and selectively capture CRM, focusing on Tantalum from WEEE. This phenomenon is strongly affected by the process conditions such as liquidus temperature, cooling rates, oxygen partial pressure in the melt, as well as the oxidation state of different ions in the slag. These different phenomena control the segregation and precipitation of Fe inversed spinel phases from fayalite and capturing several valuable elements during this process. The generation of data for modelling and setting the thermo-physical properties such as viscosity and density in a temperature-dependent system improves the possibilities to achieve control over the formation of the targeted structures.