Project Aims and Approach

The BIORECOVER project aims to produce a suite of versatile and flexible recovery processes applicable in several conditions (pH, mineral complex, raw materials), which obtain high recovery yields (≥90%), selectivity (>95%) and purity (≥99%) and delivers both environmental sustainability and cost-efficiency in safe conditions. The BIORECOVER strategy is based on research, integration and optimisation of the following stages at laboratory scale: pretreatment to remove major impurities in the raw materials, mobilisation of the target CRM into a bioleachate and recovery of metals with high selectivity and purity. Selection and integration of the best technologies will be carried out (one route for each type of raw material), and the selected processes will be optimised and validated, producing samples for end-user testing assuring the product quality requirements for their reuse in different applications (Figure 1).

To increase the efficiency and the sustainability of the BIORECOVER processes, valorisation of the byproducts and wastes generated will be studied towards a zero liquid discharge process. These BIORECOVER aims will be supported by applying tools such as interactive life cycle analysis and life cycle costing. Additionally, modelling of the overall process will be performed to develop a decision-making framework to maximise the performance. To obtain a competitive, secure, sustainable and publicly acceptable process, the project will be supported by socio-economic and health and safety analyses.

To achieve these goals, the BIORECOVER project has brought together an interdisciplinary consortium involving partners across the whole value chain from suppliers, scientific experts to the CRM end users, as well as two small-to-medium enterprises specialised in dissemination, communication, exploitation and social issues (Table I).

Supply of Raw Materials

MYTILINEOS SA, Metallurgy Business Unit (formerly known as Aluminium of Greece) is providing a REE-containing bauxite residue (BR) for the project. BR is the insoluble material generated during the extraction of alumina from bauxite ore using the Bayer process. When bauxite ore is treated with caustic soda, the aluminium hydroxides and oxides contained within are solubilised, leaving behind other bauxite oxides (mainly iron oxides, silica and titania) to form insoluble BR. The BR is washed then filter pressed to reduce storage volume and recover the alkaline solution (6). MYTILINEOS currently recycles ~10% of this residue as an additive for cement production, however the rest is stockpiled as a waste product. BR contains low amounts of some high value REE, such as scandium and yttrium, which are not currently recovered (7). BIORECOVER aims to recover these REE and, in doing so, reduce the build-up of and extract more value from the BR waste.

Magnesium-containing feeds are being supplied by Magnesitas de Navarra (MAGNA, Spain). Magnesite (magnesium carbonate) is mined, crushed, ground and enriched. Then the carbonate is either sintered at around 1800°C to produce magnesite sinter for the steel industry or calcined at around 1300°C to produce reactive magnesium oxide, used in agriculture, livestock farming and other industrial and chemical technologies (8). The waste streams of low-grade mineral and calcination byproducts (MgW) still contain some magnesium, which is currently not recovered. The low-grade mineral is deposited in mining dumps, while the calcination byproducts are used in different industrial and environmental applications due to their small particle size and basifying characteristics.

Johnson Matthey (UK) is supplying low-grade residues from its secondary pgm refineries. The feed intake is a mix of end-of-life pgm products and process residues, from spent catalysts to electronics and jewellery scrap. There are four main stages in the refinery process. In the smelting step, pgm‐containing bullions are produced, alongside a non-metallic stream which goes to second uses such as aggregates. The pgm-containing bullions then undergo chemical leaching processes to produce pgm solutions. In chemical separations, the pgm solutions are converted into separate pgm salts or high purity fine metal powder. These are then transformed into application-ready products, such as catalytic converters, which are fed back into the refinery at end-of-life (9). During the refining stages, lost material containing low levels of pgm is recovered and fed back into the smelting stage. This recovery is a highly energy intensive process relative to the low levels of pgm present and so recovering the precious metal through a bioprocess would be more sustainable and lower cost.

The final raw material is pgm-containing low grade material and concentrates which the University of the Witwatersrand (UWITS, South Africa) is sourcing from Anglo American Platinum in South Africa.

The BIORECOVER Technologies

Biometallurgy is a proven green and low-cost technology for the exploitation of metals through the application of different biocatalysts (microorganisms and metabolites) (10). These biocatalysts interact with metals by selectively concentrating or mobilising them. One crucial limitation of biometallurgy is the long retention times that are currently required. To address this, BIORECOVER will identify and develop new biocatalysts with improved performance. This approach, using microorganisms indigenous to mining and CRM storage sites, will assure fewer ecological distortions and less time consumption for adaptation. In terms of leaching efficiency, native strains usually achieve higher cell density and greater metal extraction rates than exogenous microbes. In addition, use of the following state-of-the-art technologies will facilitate the development of microbial consortia more competent for biometallurgy (11).

Another innovative approach to improve the biomining processes is the immobilisation of microorganisms onto supports that will enable the continuous supply of nutrients without competition, increase biomass, give protection from environmental stress and provide more control at a lower cost (12).

The first two biological steps in CRM recovery are pretreatment and CRM mobilisation. In both steps, BIORECOVER will isolate and cultivate microbial populations present in the feed. These would be expected to be naturally metal resistant and possess other valuable traits. BIORECOVER will use metagenomics and metatranscriptomics to identify and characterise these samples, as well as isolates from existing culture collections, that have the ability to remove impurities (for pretreatment) and leach CRM from samples (for CRM mobilisation).

For pretreatment, University of Copenhagen (UCPH, Denmark) and University of Coimbra (UC, Portugal) will screen microbial communities, present in either the unconditioned raw material or the UC culture collection, for the ability to remove impurities (iron, aluminium, calcium and titanium for BR; silicon, iron and calcium carbonate for MgW). For pgm‐containing material, UC will use selected mesophilic and thermophilic microbes and UWITS will isolate iron and sulfur-oxidising bacteria to test removal of copper, nickel, cobalt, zinc and iron from pgm‐containing Johnson Matthey refinery residues and Anglo American Platinum mining waste, respectively.

For CRM mobilisation, Linnaeus University (LNU, Sweden) will screen both indigenous microbial communities as well as fungal cultures known to excrete organic acids for the ability to mobilise REE in BR samples. LNU will also screen organisms in MgW for the ability to leach magnesium and in Johnson Matthey low-grade residues for the ability to leach pgm. Fundación Centro Tecnológico de Investigación Multisectorial (CETIM, Spain) will optimise CRM mobilisation conditions for microorganisms selected for BR and MgW. UWITS will sample soil around pgm deposits to isolate cyanide-producing bacteria that can mobilise pgm.

For both pretreatment and CRM mobilisation, the partners will perform further screening, testing relevant conditions such as co-cultivation for synergistic effects, and testing with different CRM concentrations to optimise activity.

In the third step, CRM recovery, BIORECOVER will develop five different sustainable technologies to bind CRM. Técnicas Reunidas (TR, Spain) will test and develop selective reusable polymeric microcapsules with ‘almost zero’ extractant consumption to recover a wide range of REE and platinum. ALGAENERGY, Spain, will cultivate and screen different microalgae species and develop microalgal-based biosorbents to recover mainly yttrium, magnesium, platinum and palladium. UC will screen planktonic cells that produce siderophores and immobilised systems to develop an adsorption process for yttrium and pgm. CETIM will screen fungi with known magnesium-binding activity to develop a biotransformation process to make magnesium nanoparticles. Johnson Matthey will design and synthesise different proteins and peptides to develop protein products that can adsorb magnesium and platinum.

For all three steps, data from all groups will be collected by University of Cape Town’s Centre for Bioprocess Engineering Research (CeBER, South Africa), who will develop kinetic models, that will be valuable in process optimisation. This will facilitate process improvement towards achieving a target recovery rate (>90%), selectivity (>95%) and purity (>99%).

In the second half of the project the best technology for each step will be selected, integrated into a complete process and scaled-up to 5 l bioreactors and columns. Along with the process modelling this will successfully optimise and validate the BIORECOVER strategy for the different CRM feeds. A technical, environmental and economic assessment of the selected process for each feedstock will be conducted to improve the performance and to facilitate further replicability and scaling up of the BIORECOVER technology.

Project Outputs

The CRM recovered through the BIORECOVER processes will be tested for end use by industrial project partners.

Francisco Albero SAU (FAE, Spain) will test the application of the recovered yttrium and platinum for brake pads and oxygen sensors, respectively. FAE fabricates brake pads by tape casting then sintering advanced ceramic slurries. Yttrium is added to the slurries to reduce the sintering temperature. FAE also produces oxygen sensors made of zirconia for exhaust gas monitoring. Conductive parts of the oxygen sensors are fabricated by screen-printing platinum inks on ceramic substrates.

The use of the recovered platinum, palladium and iridium for commercial catalysts will be tested by Johnson Matthey. Catalysts will be prepared and their catalytic activity will be tested on a range of reactions, including carbon monoxide and hydrocarbon oxidation, selective hydrogenation, selective nitro reductions and carbon-carbon bond forming reactions.

MAGNA will characterise the recovered magnesium nanoparticles and compare this with magnesium obtained through conventional technologies to assess their suitability for commercial applications such as agricultural fertilisers.

The dissemination of the project’s achievements to a wide range of stakeholders (policy makers, industry groups, potential markets and the academic community) will be key for the successful exploitation of the project. Diffusion actions will include conferences, seminars, workshops, scientific publications as well as engagement with other relevant projects on CRM recovery. Finally, a strategic plan to exploit the results generated during and after the end of the project will be accomplished in terms of business models and intellectual property rights strategy.