On January 23rd, 2018, Rodolfo Marin Rivera obtained his PhD degree in Chemical Engineering. He successfully defended his PhD thesis entitled ‘Innovative technologies for rare earth element recovery from bauxite residue‘. (Leuven, 23/01/2019)

The research was supervised by Prof. Tom Van Gerven (promoter), Prof. Koen Binnemans (co-promotor) and Dr. Ghania Ounoughene (co-promotor). Dr. Marin Rivera obtained his degree in the framework of the European Training Network for Zero-Waste Valorisation of Bauxite Residue (REDMUD). A list of the peer-reviewed papers published in the framework of his PhD can be found below. The full text of the thesis will become available once all research results have been officially published in the peer-reviewed literature. Dr. Marin Rivera is continuing his research career as a postdoc in the group of Prof. Tom Van Gerven, where he works on the synthesis of precipitated calcium carbonate from waste materials.

Abstract

Bauxite residue is a by-product in the Bayer process of alumina production from bauxite mineral ores. Disposal and long-term storage of this waste volumes occupy a lot of land. Additionally, the high alkalinity of bauxite residue is the main environmental concern. Some treatments already exist to further utilize this bauxite residue. However, bauxite residue also contains valuable metals such as rare-earth elements (REEs), in minor but non-negligible concentration.

Different studies have already been performed to consider a possible recovery of REEs, scandium in particular. Direct acid leaching is a commonly applied method with differences in the specific operational conditions. However, these methods have demonstrated low extraction yields and/or selectivity, which limit their application at an industrial scale. Thus, the main objective of this PhD Thesis was the development of innovative hydrometallurgical methods in order to overcome the main disadvantages of leaching processes reported in the literature, i.e. consumption of large amounts of acid during neutralization of the alkaline bauxite residue, the high co-dissolution of major metals that affects the efficiency of the separation process (e.g., solvent extraction or ion exchange), and the decomposition of silicate compounds that leads to the polymerization of amorphous silica.

The treatment of bauxite residue by dry digestion with multi-stage circulation of the leach solution appears to be economically the most interesting leaching alternative. The process allows to reduce significantly the volume of effluents due to the low amount of water required for the process. Gel formation does not occur and titanium can be recovered simultaneously with the REEs. High-pressure acid leaching of slag from bauxite residue smelting also avoids the polymerization of silica gel, but titanium remains in the solid residue after leaching. These processes must be studied further as part of an integrated extraction-separation process, so that a comprehensive cost analysis can be obtained to assess the feasibility and viability of the processes for the recovery of REEs from bauxite residue.

Publications by Rodolfo Marin Rivera in the framework of his PhD

  • M. Rivera, B. Xakalashe, G. Ounoughene, K. Binnemans, B. Friedrich, T. Van Gerven. High pressure acid leaching of slag from bauxite residue smelting in view of selective rare-earth elements recovery. Hydrometallurgy, In press.
  • R.M. Rivera, G. Ounoughene, A. Malfliet, J. Vind, D. Panias, V. Vassiliadou, K. Binnemans, T. Van Gerven. A study of the occurrence of selected rare-earth elements in neutralised-leached bauxite residue and comparison with untreated bauxite residue. Journal of Sustainable Metallurgy, In press.
  • R.M. Rivera, B. Ulenaers, G. Ounoughene, K. Binnemans, T. Van Gerven (2018). Extraction of rare earths from bauxite residue (red mud) by dry digestion. Minerals Engineering, 119, 82-92.
  • R.M. Rivera, G. Ounoughene, C.R. Borra, K. Binnemans, T. Van Gerven (2017). Neutralisation of bauxite residue by carbon dioxide prior to acidic leaching. Minerals Engineering, 112, 92-102.