Our partners explain how the fourth stage of the BIORECOVER process “Post-treatment to recover targeted CRMs” has been going lately. Biorecover comprises different strategies for metal recovery:
Immobilisation of REE using bacteria, by the University of Coimbra
Rare Earth Elements (REE) are considered critical raw materials (CRM) with a wide application in modern technologies, highlighting the need for the development of specific recovering methodologies.
In this study, the ability of a bacterial strain, previously isolated from a contaminated environment, to immobilise REE (Rare Earth Elements) from multi-metal synthetic leachate was evaluated. This is in order to determine the effect of the inoculum cell density on the immobilisation process as well as the effect of supplementation with KH2PO4 (Potassium Phosphate).
It was possible to conclude that 1) higher cell density yielded better REE bioaccumulation, 2) phosphate was required to increment metal immobilisation and stabilise the metals in the cell biomass (Fig.1), and 3) the metal accumulation per biomass reached peak efficiency at 24h. The REE found in higher quantities in the cells grown under these conditions were Neodymium (17 µg/mg protein) followed by Yttrium (16 µg/mg protein) and Lanthanum (15 µg/mg protein).
Although not very specific, this method can recover REE into metal-dense biomass and other metals cheaply and sustainably. This can be useful for strategies aiming for water clean-up and/or broad metal concentration from complex leachates.
Figure 1. SEM-EDS of the bacterial strain incubated 24h in presence of REE and 1.2 mM KH2PO4, elements mass balance and spectrum quantification.
Immobilisation of PGM by modified biopolymers produced by bacteria, by the University of Coimbra
Platinum group metals (PGMs) are used for many purposes in different industries because of their unique properties. They belong to the European Union’s list of Critical Raw Materials since they have economical relevance but are mostly imported, which means there is a risk associated with their supply.
Within this 4th workstream, we tested a metallophore-modified bacterial polymer’s capacity to uptake metals from solutions compared to a control and a commercial metallophore-modified bacterial polymer. For this, the polymers were added to a PGM synthetic mixture and incubated at room temperature, with shaking.
After an hour, the control showed the lowest efficiency out of the three and among the modified polymers, the one modified with the metallophore extracted in our laboratory had the highest removal percentage for the metals present in the solution (94.5% and 92.0% for platinum and iridium, respectively) (Fig. 2).
This method is quite rapid and efficient, although somewhat demanding in terms of polymer preparation. Preliminary results have indicated a degree of specificity which makes it suitable for the extraction of platinum-group metals from complex solutions.
Figure 2. Iridium and Platinum relative immobilisation (%) using modified biopolymers (BB + Bacterial Ligand Pp) compared to unmodified controls and commercial alternatives.
Recovery of Scandium and Yttrium with polymeric microcapsules from bauxites residues, by Tecnicas Reunidas.
Different extractants micro encapsulated were evaluated to maximise the selectivity and extraction performance towards specific targets while preserving the physical integrity in harsh environments and the reuse of microcapsules and functional lifespan.
Variables such as temperature and reaction time were studied with synthetic solutions whose composition was agreed upon assuming REE leaching efficiencies from bauxite residues.
Preliminary laboratory testword was carried out in laboratory beakers. Once the best conditions were selected and demonstrated in laboratory beakers, the tests were carried out in adsorption columns that had previously been designed in TR.
Finally, testwork was performed with a synthetic solution that simulates the composition of the real bioleachates from bauxites residues.
The process was designed to separate Sc in a first stage and Y in a second stage from the rest of the elements present in the bioleachate such as Fe, Ca, Al, Ti.
Adsorption efficiencies of 85% for Scandium and 96% for Yttrium were achieved. Additionally, desorption tests using acid reached a recovery of up to 85% of Sc and 95% of Y. The results demonstrate the technical feasibility of the microcapsule rare earth recovery process.
AlgaEnergy investigated the development of microalgal biosorbents for the removal and recovery of CRMs in a safe, sustainable and efficient manner.
Four species of microalgae were evaluated, and their metal-adsorbing capacity was studied. The microalgal cells were used both as free cells as well as immobilised onto polyurethane foams (PUFs) as a support system for the removal of metals from monometallic solutions, synthetic leachates and real bioleachates obtained during previous work packages by other consortium partners.
Results showed that the biosorbents were highly efficient at adsorbing metals removing up to 98% of metals present in solution, with Y and Pd being the two metals that were more efficiently adsorbed. It was shown that adsorption of metals onto the microalgal surface took place mainly within the first minutes of treatment. Additionally, desorption tests using HCl as an eluting agent resulted in the recovery of up to 98% of the REEs that had been adsorbed onto the microalgae. Further studies using real bioleachates would be necessary to increase efficiency and selectivity of the biosorbent. However, it was evident that this type of technology could be used to efficiently remove and recover CRMs from waste materials.
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