Obtaining of rare earth elements from mining wastes

The group of rare earth elements consists of sixteen elements: scandium, yttrium, and the elements of the lanthanides group. These metals have a variety of applications in the areas of metallurgy, medicine, chemistry, electronics, and computation. China is the main rare earth producer in the world (>95%) and has a bigger resource in the world. As a way of seeking independence from the Chinese market, countries around the world are looking for alternatives to meet the growing demand for these elements.

Among the alternatives available, and also searching for sustainability in extractive processes, the residues generated in mineral processing are becoming even more important as rare earth element resources. As an example, there is the waste generated in the Bayer Process, used for alumina production from bauxite, known as red mud. It is estimated that the amount of this waste stored in the world is 4 billion tons. Furthermore, the bauxite is one of the most important scandium resources in the world, in which during the Bayer Process it is presented in the red mud, being this residue as one of the main resources not explored of scandium and other rare earth elements.

Although studies propose thermal processing as a way to remove impurities (as iron and silicon) from red mud and increase the scandium content, this route demands much energy and generates greenhouse gases. For this reason, the processing in aqueous media (hydrometallurgy) turns a better alternative for scandium extraction. Moreover, the use of thermodynamic computational (FactSage, HSC, and HydraMedusa) is an important tool to predict the compounds that will be formed during the process and then increase the process efficiency.

The main equipment used for the execution of this project are atomic absorption (AAS and GFAAS), inductively coupled plasma atomic emission spectrometry (ICP-OES), X-ray fluorescence by dispersive energy (EDXRF), scanning electron microscopy (SEM/EDS), organic and total carbon analyzer (TOC) and X-ray diffraction (XRD).