1. The influence of the residence time of the REE ions in the microchannel on their enrichment efficiency
M. Luty-Błocho, K. Kolczyk, M. Wojnicki and P. Zabinski
Rare earth elements (REE) are interesting due to their magnetic, luminescence properties. They found an application in high technology e.g.: a radar, a sonar, a telescope, hybrid cars, as catalytic converters, television and computers screens, computer hard drives, wind turbines, etc. REE are produced both from primary and secondary sources. In hydrometallurgical processes, the most problematic step of those metals production is their separation. For this reason, it is desirable to improve the current processes via application of High Magnetic Gradient. It utilizes the different magnetic properties of rare earth metal ions to achieve separation by attraction or repulsion in an inhomogeneous magnetic field [1,2].
BR2018 – 2nd conference on Bauxite Residue Valorisation and Best Practices

2. Materials and methods
Materials: an aqueous solution of HoCl3 (Avantor), concentration of Ho3+ ions in the range 0.01 – 0.1M, pH =1, T=20ºC, Flow rates: 5 – 30mL/h.
Methods: Obtained solution were collected and analyzed using UV/Vis spectrophotometry and MP-AES (Microwave Plasma-Atomic Emission Spectrometer).
BR2018 – 2nd conference on Bauxite Residue Valorisation and Best Practices

3. Set up for separation two streams (enriched and depleted)
Figure 1. Set up
BR2018 – 2nd conference on Bauxite Residue Valorisation and Best Practices

4. Results
where Absλ is the absorbance value in a given  wavelength[nm], ελ is molar coefficient of absorption [dm3×cm-1×mol-1], l denotes path length [cm] and C is concentration of Ho(III) ions [mol×dm-3]
Lambert-Beer law shows relation between the absorbance of solution and the concentration of holmium ions: 〖𝐴𝑏𝑠〗_𝜆=𝜀_𝜆∙𝑙∙𝐶, where Absλ is the absorbance value in a given  wavelength [nm], ελ is molar coefficient of absorption [dm3×cm-1×mol-1], l denotes path length [cm] and C is concentration of Ho(III) ions [mol×dm-3]. The values ελ and l are constant and known [1], so it is possibility to define relation between concentration and absorbance as linear.
The differences of Ho (III) ions concentration from two outputs were calculated as follow: 〖∆𝐶〗_(𝑖,𝑗)=(〖𝐴𝑏𝑠〗_(𝑜𝑢𝑡𝑝𝑢𝑡1, 𝑖, 𝑗)−〖𝐴𝑏𝑠〗_(𝑜𝑢𝑡𝑝𝑢𝑡2,𝑖,𝑗))/〖𝐴𝑏𝑠〗_(𝑜𝑢𝑡𝑝𝑢𝑡1,𝑖,𝑗) ×100%
where 〖𝐴𝑏𝑠〗_𝑜𝑢𝑡𝑝𝑢𝑡1 and 〖𝐴𝑏𝑠〗_𝑜𝑢𝑡𝑝𝑢𝑡2 mean values of absorbance from output 1 and 2, i – number of samples, j – number of repetition of UV-Vis measurement.
Figure 2. Spectra for Ho(III) ions with different concentration (H0(0.1M)-H5(0.01M) (a); Dependency of A vs. concentration (b); An exemplary spectrum of UV-Vis of Ho(III), square markers-analyzed spectra maximums (A: 537nm, B: 641nm), rectangular marker – correction of the spectrum level (C: 590 – 610 nm) (c); Change of absorbance vs. flow rate for different concentration of Ho(III) ions in the solution.

5. Conclusions
The process of ions separation were carried out in inhomogeneous magnetic field;
For ions separation, the special cell (microreactor) was fabricated using 3D printing technology;
The differences of absorbance from outputs of microreactor were observed but the values were generally include the error bars;
The error bars were about the same or bigger range as the observed enrichment effect.
BR2018 – 2nd conference on Bauxite Residue Valorisation and Best Practices