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.

In this study, the using of elcectrochemical method combined with an inhomogeneous magnetic field allows for an enrichment of Ho³⁺ ions and then their separation from depleted aqueous solutions. The experiments were carried out in a microreactor produced by a 3D printing technology. The ions movement was carried out on a circular path due to the spiral arrangement of the microchannel. The inhomogeneous magnetic field in the channel was created by the placement of the microreactor in a laboratory electromagnet. During the flow conditions, the metal ions were exposed on the force coming from the gradient magnetic field and their separation into two streams was observed. First one consisting of the enrichment solution in magnetic ions and second one containing depleted solution. These solutions were collected and analyzed using UV/Vis spectrophotometry and MP-AES (Microwave Plasma-Atomic Emission Spectrometer).

In this work the influence of the applied current, direction of current field lines, residence time of the magnetic ions in the microchannel and their concentration on the efficiency of separation enrichment and depleted solution were examined.

Acknowledgment
The authors would like to thank Polish National Science Centre for the financial support provided by the grant: No UMO-2014/15/B/ST8/01528.