Team:Bonn-Rheinbach/Proof Of Concept
Project
Proof of Concept
A Novel Extraction Method
To deliver an industry-ready rare earth element (REE) extraction protocol, precise experiments needed to be conducted validating the Biolan method.To access the suitability of our proposed extraction method, experiments were run validated through ICP-MS (Inductively coupled plasma mass spectrometry). ICP-MS is performing extremely well at detecting trace elements and unchallenged by other mass spectrometry techniques [1]. Apatite ore was acidified first. By applying Lanmodulin (LanM) and two ultrafiltration steps, REEs were then isolated from the leachate (see Figure 1). When LanM is added to the ore leachate in the first step LanM-REE-complexes form, as LanM is able to bind REEs at pH > 4. In the first ultrafiltration step (UF1) the REEs remain in the retentate (UF1-RET) as the LanM-REE-complexes are too big to pass through the filter. The retentate gets resuspended after which the pH gets reduced to less than 1.5. This leads to a conformational change of LanM by which the REEs get released into the solution. In the second ultrafiltration step (UF2), LanM gets separated from the REEs. LanM remains in the retentate (UF2-RET) and the now unbound REEs can pass through the filter and remain in the flow through (UF2-FT).
To assess the success of the extraction process, the amount of calcium ions was compared to that of all present REE-ions (Ca(II)/REE ratio). We chose calcium-ions for comparison as they are the most abundant cations in the utilized ore (apatite) [2]. Samples of the leachate before extraction as well as samples of the first ultrafiltration flow through (UF1-FT) and the second ultrafiltration flow through (UF2-FT) were compared (see Figure 2). In the leachate the ratio of calcium ions to REE-ions was 22.0. In the UF1-FT a neglectable amount of REEs were present as the ratio increased to 8,860.8. Finally, in the UF2-FT a high amount of REEs were present. The ratio of calcium-ions to REE-ions was 1.6.
The negative control where we ran the same experiments without the addition of LanM yielding neglectable amounts of REEs (see Figure 3) showed that the increase of REE purity was attributed to the chelating activity of LanM. These results demonstrate that by applying the Biolan extraction method, one is able to quickly and easily extract REEs from solutions like ore leachates as the ratio of cation-ions to REE-ions increased by the almost 14-fold.
Furthermore, we assessed whether the Biolan extraction method discriminates against certain REE elements. Our results indicate that at least for the here chosen ore (apatite) no discrimination against certain elements occurs (see Figure 4), as the share of individual REEs did not change significantly. This demonstrates that at least for Apatite Biolan is able to efficiently extract REEs without loss of certain elements.
To further improve the economic as well as ecological benefits of our projects, the loss of LanM during ultrafiltration was assessed via BCA-based protein determination. Of the original 26.3 mg LanM, 24.8 mg remained in the retentate of the second ultrafiltration (UF2-RET). 1.3 mg LanM were detected in the UF1-FT and only 0.3 mg in the UF2-FT (see Figure 5). Thus, the process guarantees quantitative recovery of the costliest compound, LanM. Previous studies verified that LanM retains its chelating ability throughout multiple capture-and-release cycles [3]. We confirmed those results by successfully applying LanM that has already been used in two capture-and-release-cycles to the final extraction process (data not shown). This further substantiates Biolan as an economic as well as environmentally friendly alternative to current REE-extraction methods.
Due to our specially developed purification technique of LanM, that utilizes its extreme pH stability, economical overhead costs can be cut down even more (more on that in Contributions). The last aspect to be noted is that the here utilized ore has a relatively low concentration of REEs compared to other industrial relevant sources. Our results with almost no loss of REEs in the UF1-FT (se Figure 1) demonstrate that LanM is highly efficient even at low REE-concentrations. And while the economical suitability for industrial ore refinement still has to be assessed, these results open up new alternative up until now barely utilized feedstock sources with very little concentrations of REEs. Some examples of these ressources are E-waste (for more on that check out our partner iGEM Calgary ), sewage and other production waste.
written by Alexander Schmatz
References:
[1] Ammann, A. A. (2007) ‘Inductively coupled plasma mass spectrometry (ICP MS): A versatile tool’, Journal of Mass Spectrometry, 42(4), pp. 419–427. doi: 10.1002/jms.1206.
[2] Stosch, H. G. et al. (2011) ‘Uranium-lead ages of apatite from iron oxide ores of the Bafq District, East-Central Iran’, Mineralium Deposita, 46(1), pp. 9–21. doi: 10.1007/s00126-010-0309-4.
[3] Deblonde, G.J.-P.; Mattocks, J.A.; Park, D.W.; Reed, D.W.; Cotruvo, J.A.; Jiao, Y. (2020): Selective and Efficient Biomacromolecular Extraction of Rare-Earth Elements using Lanmodulin. In Inorganic Chemistry 59: 11855-11867.