A novel mechanically enhanced bioleaching process – BIOMECALIX

The methodology involved designing, building and operating a 4 L experimental reactor. An important part of the work consisted in studying certain aspects separately (abiotic attritive leaching efficiency, impact of fine particles on micro-organisms), before setting up an experimental protocol enabling study of the complete process.
The tests were carried out under biocompatible conditions (pH = 1, T = 42°C), on a chalcopyrite concentrate from a mining site. Interpretation of the tests was based on extensive physical (powder granulometry, solids mass), chemical (chemical and structural composition of solids and aqueous phase) and biological (biomass counting, bacterial analyses) characterizations carried out before, during and after the tests, enabling the most accurate possible material and biological balances to be established.

The major advances of the BIOMECALIX project are:
- Demonstration of the effectiveness of attritive leaching for chalcopyrite depassivation,
- A better understanding of the influence of parameters on passivation phenomena,
- Demonstration of the positive effect of the presence of fine particles (< 20 µm) on the growth and activity of bacterial populations used in bioleaching,
- Demonstration of operating conditions enabling bacteria to be active in the presence of beads, opening up the possibility of minimizing acid consumption and obtaining higher copper dissolution yields than in an abiotic process.

The prospects for this work, with a view to a better understanding of the hybrid attritive bioleaching process for chalcopyrite, include an in-depth study of the effect of these parameters and the ability of the bacteria to adapt to the attritive environment.

The study of the attritive leaching process will be pursued by LGC as part of the LULABAT project (PEPR «Recycling, recyclability and reuse of materials«) for the recycling of lithium batteries. Thanks to the synergy created by the collaboration between LGC and BRGM teams during the BIOMECALIX project, further collaborative work will be carried out as part of the PEPR «Sous-sol, Bien commun« (2 joint actions financed under this PEPR), focusing on the problems of sulfide ore leaching processes.

Journal article
A. Dakkoune, F. Bourgeois, A. Po, C. Joulian, A. Hubau, S. Touzé, C. Julcour, A.-G. Guezennec, L. Cassayre, Hydrometallurgical Processing of Chalcopyrite by Attrition-Aided Leaching, ACS Engineering Au. 3, 3, 195–209 (2023).
doi.org/10.1021/acsengineeringau.2c00051

Conferences (selected on abstract)

A. Po, A. Hubau, C. Joulian, A. Dakkoune, C. Julcour, F. Bourgeois, S. Touze, L. Cassayre, A-G. Guezennec, Bioleaching of chalcopyrite: the effect of particle size on passivation, bacterial growth and activity, 24th International Biohydrometallurgy Symposium (IBS), 20-23 Novembre 2022, Perth, Australie.
A. Dakkoune, A. Dufourny, C. Julcour, L. Cassayre, F. Bourgeois, Attrition et lixiviation : deux procédés synergiques pour les procédés hydrométallurgiques limités par la passivation, 18ème congrès de la Société Française de Génie des Procédés, 7-10 novembre 2022, Nantes, France.
A. Po, A. Hubau, C. Joulian, M. Assarra, G. Laurent, A. Dakkoune, C. Julcour, F. Bourgeois, L. Cassayre, A-G. Guezennec, Effet de l’attrition sur les communautés bactériennes dans un procédé de biolixiviation, 18ème congrès de la Société Française de Génie des Procédés, 7-10 novembre 2022, Nantes, France.

Communications

C. Laskar, A. Dakkoune, C. Julcour, F. Bourgeois, B. Biscans, L. Cassayre, Le procédé d'attrition-lixiviante en hydrométallurgie: Une synergie matériau-dépendante, Journées annuelles du GDR Prométhée, 15-16 juin 2023, Nîmes, France.
A. Dakkoune, F. Bourgeois, A. Po, C. Joulian, A. Hubau, S. Touzé, C. Julcour, A.-G. Guezennec, L. Cassayre, Amélioration de la dissolution de la chalcopyrite par le procédé d'attrition lixiviante, Journées annuelles du GDR Prométhée, 24-25 mars 2022, Toulouse, France.

A. Po, A. Hubau, C. Joulian, A. Dakkoune, C. Julcour, F. Bourgeois, S. Touze, L. Cassayre, A-G. Guezennec, Impact of particle size on chalcopyrite bioleaching, 8th PROMETIA Scientific Seminar, 1er Décembre 2021, Seville, Espagne.

In the context of hydrometallurgical processes dedicated to the recovery of metals, the leaching step consists of dissolving solid particles (ores, waste to be recycled) in an aqueous phase. With the aim of improving yields, a wiser use of resources and reducing effluents, the BIOMECALIX project aims to study the interest and feasibility of an innovative, competitive and eco-efficient leaching process. This hybrid process combines the advantages of bioleaching (moderate temperature and acidity, in situ production of the oxidizing reagent by microorganisms) and attrition leaching (in situ grinding, abrasion of passivation layers by agitated grinding media). The case of application is chalcopyrite, but the general framework is for leaching processes involving a redox reaction.
Such a coupling raises several scientific issues: (i) Does the lifting of the two major kinetic barriers (redox reaction thanks to bacteria and passivation thanks to attrition) make it possible to reach the yields predicted by thermodynamics? (ii) What is the impact of hydrodynamic and mechanical stresses on microorganisms? (iii) What is the limiting step: bacterial growth or activity, gas-liquid transfer (oxygen required for bacterial activity), dissolution reactions, attrition of passivation layers?
The proposed methodology combines experimental work in different types of reactors and modeling work. The project gathers a consortium of experts in process engineering, reactor engineering, thermodynamics, modeling, microbiology and hydrometallurgy, at the Chemical Engineering Laboratory (LGC) and at the Geological and Mining Research Bureau (BRGM). It is planned to recruit a doctoral student, a postdoctoral fellow and six trainees during the 42 months of the project.
The work program has four technical tasks. The first two tasks concern the adaptation of the uncoupled processes (currently developed by each of the partners) to the conditions of a hybrid reactor. Thus, the attrition leaching will be studied under biocompatible conditions (moderate pH, T between 40 and 55 ° C, oxygen supply) by the LGC, while the BRGM will evaluate the impact of the conditions inherent to the attrition process (high solid/liquid ratio, presence of grinding media, hydrodynamic stresses) on microorganisms. A third task will be to establish the proof of concept of the hybrid process, based on a reasoned selection of operating parameters, and by conducting experimental campaigns in a reactor developed for the project. In parallel, a fourth task will focus on proposing a leaching model integrating thermodynamic equilibria, kinetic laws related to different phenomena, and shear stresses. This model will support the establishment of the balance sheets of the process, and the development of a simulation tool of the hybrid process. This tool will be used for a techno-economic assessment and the establishment of a quantitative comparison (energy and environmental) of the hybrid process compared to existing processes for the treatment of chalcopyrite, in aqueous and pyrometallurgical ways.