PROJECT DESCRIPTION
BACKGROUND
Energy-intensive activities, including steel and aluminium production, use refractory or heat-resistant products as protective linings in furnaces. Refractory products are produced from industrial minerals including magnesite, graphite, dolomite and the critical raw material bauxite. For producing melted aluminium, bauxite-based refractory castables – or bauxite moulded into bricks or other shapes – are essential.
The European Union is heavily dependent on imports of refractory industrial minerals, including bauxite. The EU imports around half a million tonnes of refractory-grade bauxite each year, mainly from China. EU importers are therefore at the mercy of (restrictive) Chinese export policies.
Bauxite could be substituted by a secondary raw material that arises in the recycling of salt slag – the residue of salt used in aluminium refining. The European aluminium industry produces one million tonnes per year of salt slag from the secondary melting of aluminium scraps. Salt slag contains salts, aluminium oxide, aluminium metal and impurities and is classified in the EU as hazardous waste. It can be treated and separated into metals and non-metal residues, from which a substitute for bauxite could be derived.
OBJECTIVES
The LIFE BAUXAL-II project aimed to set up a pilot plant and use an innovative process to transform the non-metallic concentrate, which is a by-product from the recycling of aluminium salt slag, into a refractory material – known as BAUXAL. This product can be a suitable substitute for refractory-grade bauxites, therefore reducing the EU’s reliance on imports of bauxite. The project objective was to demonstrate resource efficiency and contribute to the implementation of circular economy policy by replacing natural minerals with a secondary material derived from a recycling process.
RESULTS
The project built a large hydrometallurgical plant (maximum processing capacity 1,500 t/y), leading to the final production of 205 t of new BAUXAL-based refractories (up to 50% BAUXAL, rest calcined bauxite) usable to cover ladles and furnaces in aluminium industry, which will continue to be operational after the project.
The validated transformation process involves a hydrometallurgical refining stage. In this stage, the unwanted compounds present in the secondary aluminium oxide are reduced, obtaining a new secondary material (so-called REFINAL) competitive with mineral-origin refractory-grade bauxites.
Then, this material is mechanically and thermally processed to obtain a product with properties equivalent to calcined bauxite, that can be used as refractory aggregate (so-called BAUXAL).
During the validation phase, up to eleven formulations of refractory castables incorporating BAUXAL were produced and validated in 20 different industrial trials between December 2022 and July 2024.
Overall, throughout the project up to 660 tonnes of aluminium salt slag were valorised for high added value applications, avoiding the extraction of 155 tonnes of mineral bauxite and preventing the generation of 139.5 tonnes of red mud.
However, the environmental and economic analyses revealed significant room for improvement in the environmental and economic performance of the process, which should still be further optimised to enhance the environmental benefits and reduce operation costs. In this context, the short-term market approach will focus on the Spanish market of refractories for the Aluminium industry.
