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Ana Luiza Coelho Braga de Carvalho defends her PhD on reprocessing of sulfidic tailings through flotation

On August 14, 2023, Ana Luiza Coelho Braga de Carvalho successfully defended her PhD thesis entitled “Investigations on the reprocessing of fine particles from sulfidic tailings through flotation”. Ana Luiza did her PhD at the Institute of Mineral and Waste Processing, Recycling and Circular Economy Systems of the TU Clausthal and was one of the Early Stage Researchers of the MSCA-ETN SULTAN project.

Ana Luiza carried out her PhD in Environmental Process Engineering and Recycling under the supervision of Prof. Dr. Daniel Goldmann, from the TU Clausthal, and co-supervision of Prof. Dr. André Carlos Silva, from the Universidade Federal de Catalão, Brazil. Her PhD research was part of the H2020-MSCA-ETN SULTAN project, the EU Training Network targeting the remediation and reprocessing of sulfidic mining wastes. Ana Luiza continues her career at the Universidade Federal do Sul e Sudeste do Pará, Brazil, as a professor in in the Faculty of Mining Engineering.


The summary of the PhD research along with the list of publications are available below; the full text of the thesis will soon be made publicly available.


The mining industry generates large amounts of tailings every year. The most common destination for the tailings is deposition in tailings storage facilities (TSFs), which can have enormous dimensions. The management and storage of such large volumes of material pose many challenges in terms of dam stability and immobilization of hazardous contaminants that represent human-health and environmental risks, particularly for sulfide-containing materials. In addition, considerable amounts of precious and base metals can be lost in the tailings. Due to the economic value and growing industrial demand for precious and base metals, tailings may therefore be potential sources of secondary raw materials.

This research showed two case studies (from an active and a historical mine site) on the reprocessing of sulfidic mine tailings through flotation and the results obtained can contribute to the construction of knowledge about the reprocessing of sulfidic tailings. The approach adopted here focused on the removal of valuable and hazardous elements from the tailings and the generation of cleaner residues, with lower contaminant potential and with chemical and mineralogical characteristics more adequate for further applications (e.g. in the construction industry).

The tailings from the active mine site presented a broad particle size distribution, therefore the flotation approach combined classic flotation and floc flotation (flotation of flocs of targeted minerals). Flotation of the material as received, as well as after classification into two fractions was performed. The samples as received and the coarser fraction (+37 μm) underwent classic flotation, while the finer fraction (-37 μm) was processed either by using the classic or the floc flotation approach. The flotation of the coarser particles provided higher sulfide recoveries, higher combined Cu-Pb-Zn grades in the concentrate (3.66%), cleaner residues (1.6% S), faster flotation rates, and reduced reagent consumption. Likewise, the results from the fine particle flotation allowed lower S content in the residues (3.4% S) as compared to the flotation of the original material. The results of the use of floc flotation for the finer fraction showed an increase in the mass pull with a slight increase in the recovery of sulfides. Overall the development of a route to process the tailings proved to be promising and the use of a two-route approach indicates advantages as compared to a single route.

The tailings from the historical mine site, in addition to the sulfides, contained a relevant amount of barite. Therefore, flotation aiming for the separation of the barite was also performed after the sulfides removal. The tailings underwent classic flotation with several steps for the removal of sulfides and barite. Finally, trials in a pilot scale (100 L flotation cell) were performed to evaluate the transferability of the results to a larger scale. The results show that either the sulfides or the barite can be selectively recovered, with the barite posing more challenges than the sulfides. The flotation in the pilot scale enabled concentrates with higher grades and needed longer flotation times to achieve the same level of recovery as the bench-scale tests.

List of peer-reviewed publications in scientific journals

  • Silylated Thiol-Containing Cellulose Nanofibers as a Bio-Based Flocculation Agent for Ultrafine Mineral Particles of Chalcopyrite and Pyrite. J. Sustain. Metall. 7, 1506–1522 (2021). https://doi.org/10.1007/s40831-021-00439-y
  • de Carvalho, A.L.C.B., de Carvalho, V.A., Blannin, R., Escobar, A.G., Frenzel, M., Rudolph, M., Silva, A.C., Goldmann, D. A study on the desulfurization of sulfidic mine tailings for the production of a sulfur-poor residue. Minerals Engineering 202, 108285 (2023). https://doi.org/10.1016/j.mineng.2023.108285