The recovery of rare earths and valuable metals from the red muds of the Eurallumina site in Porto Vesme, Sardinia, Italy

Red mud is generated during bauxite dissolution to produce alumina in the Bayer process. It contains both residual minerals of bauxite ore and products generated by the alkaline dissolution. Significant amounts of valuable metals are still contained in red mud, including major elements like Fe, Al, Si and Ti, and minor elements like Zr, Cr, V, Sc, Y and light rare earths. The current red mud management involves storage in artificial ponds/dams or dry stacked in open areas. This poses an environmental risk, especially for storage in ponds/dams which may and sometimes have collapsed releasing the material in the environment. Disposal processes are costly and not entirely defined and agreed upon. Recently, red mud has been utilized as a mineral addition in cement production or as a substrate for geopolymer manufacture by taking advantage of its alkalinity. This approach, however, results in the loss of valuable minerals, which could be strategically advantageous for resource-deficient nations. The extraction of valuable metals from red mud can significantly improve the efficiency of alumina production process, increase the economic sustainability of reclaim activities, reduce industrial liability and environmental impact. In the present work we deal with the red muds stored at the site of Eurallumina, near Porto Vesme in Sardinia, Italy. The material is ponded in lagoons, which have been sampled to determine the mineralogy and composition. Hematite is the main constituent in the red mud, along with an amorphous fraction constituted in majority by silica with minor alumina and titania. Other crystalline phases present in large amounts are sodalite, hydrotalcite and gibbsite, while minor phases are anatase, rutile, yttrium iron garnet and zircon. The extraction of valuable metals involves a leaching stage, to solubilize the elements of interest, and a recovery process by solid/liquid absorption. We present the optimization of the leaching process and the preliminary work to choose the most appropriate substrate for performing adsorption and extraction. The work is supported by the European project REMHub, and by the CAMEBAX Prin PNRR2022 project. REMHub is a four-year project funded under Horizon EU call HORIZON-CL4-2024-RESILIENCE-01-08 which started in October 2024 aiming to create a cutting-edge innovation hub propelling EU excellence for Rare Earth Elements (REEs) supply and permanent magnets manufacture. CAMEBAX is a two-year project started in November 2023 and funded by the Italian Ministry of University and Research, aimed at the recovery of critical raw materials from Eurallumina red muds via low-cost leaching and solid phase extraction methods.