Team:Bonn-Rheinbach/Engineering
Project
Engineering Cycle
Advancing through trial and error
To tailor the process to industrial demands (e.g. potential for upscaling, low process costs, mild conditions), the approach shown in Figure 1 was first designed. It should initiate with the combination of REE-containing ore leachate and recombinant LanM purified from E. coli cell culture. At pH > 4.0, a LanM-REE complex form. By salting out with the kosmotropic salt ammonium sulfate, the complex precipitates from the leachate. Salting out is used to avoid costly affinity chromatography-based approaches which additionally might be sensitive to the highly complex ore leachate matrix. After removal of the REE-free supernatant and dissolving of the pellet (LanM-REE complex), the REE cations are released from the complex by acidification of the solution (pH < 1.5). Applying the acidic solution to an ultrafiltration unit with a molecular weight cut-off value of 3 kDa, apo-LanM (retentate/filter cake) is separated from highly pure REEs (flow-through). Apo-LanM is to be reused for further extraction cycles.
Salting out with ammonium sulfate requires a high concentration of salt to obtain precipitation of the LanM-REE complex. In a LanM-added extraction run, a pellet formed after 1h incubation with 100% ammonium sulfate (750 mg to 1 ml solution). To verify that this precipitation was indeed based on the salting-out of the LanM-REE complex, another extraction run was performed without LanM (no-protein control). After adding ammonium sulfate to 100% solubility, a precipitate with a similar texture and pellet size was observed again. Thus, we assume that the high concentration of ammonium sulfate does not lead to a salting-out of the LanM-REE complex but instead results in the undesired precipitation of mineral salts. Thus, the process selectivity was not ensured and another option for isolation of the LanM-REE complex was chosen.
After redesigning the REE extraction process (Figure 2), the salting-out-based isolation of the LanM-REE complex was replaced by an ultrafiltration step. This should separate the solution into ore leachate (flow-through) and the LanM-REE complex (retentate). Since the other process parts showed no unsuitability, no further modifications were made.
After running the redesigned process, 63% of the initially applied REEs were obtained in the flow-through of ultrafiltration 2 (UF2-FT) – showing first promising results. To investigate if this modified approach relied on the REE-chelating activity of LanM, a no-protein control run was performed again. The process was identical to the approach described in Figure 2, albeit without the addition of recombinant LanM. As shown in Figure 11, the protein-free control run (w/o LanM) yielded only a neglectable amount of REEs in the UF2-FT fraction (2.7 nmol) while the LanM-containing process run (w/ LanM) resulted in the presence of 502 nmol of REEs in the desired fraction (UF2-FT). Thus, it can be solidly stated that LanM contributed to the enrichment of REEs in the final solution.
Overall, an initial engineering design cycle revealed the necessity to improve the designed process with respect to extraction selectivity. After identifying the critical step that reduced process specificity, the approach was modified. The redesigned process was run, including quality controls, and showed improved performance considering the selectivity of REE extraction.
written by Friedrich Ehinger