The demand for resources is increasing with increasing world population and technological and industrial development. Therefore, the European Union has defined a list of "critical raw materials" (CRM), which are economically important and have a high supply risk at the same time. CRM are often contained in relatively high concentrations in secondary sources, namely industrial by-products and wastes. Hence, the recovery of CRMs from secondary sources can help decreasing the supply risk, but also the ecological impacts of waste streams. Currently, CRM are recovered from secondary sources either by means of pyrometallurgical or hydrometallurgical processes. Hydrometallurgical processes may offer the advantage of being more energy / chemical efficient. Hydrometallurgical processing encompasses essentially ion exchange (IX) or solvent extraction (SX) for concentration and precipitation or electrolysis for recovery of metals. Although being efficient for many CRM, solvent extraction and ion exchange nevertheless rely on similar principles (i.e. complexation of ions) of separation. The application of advanced membrane separation processes represents a promising alternative for CRM recovery from secondary sources. More specifically, nanofiltration offers a separation based on both size and charge of the target ions, thus augmenting hydrometallurgical processing possibilities. Advanced membrane separation may offer some selectivity (different from SX or IX) and concentration of the target element, thus the amount of chemicals and energy used for recovery of the product may be considerably reduced.

This PhD project aims for the recovery of CRMs from secondary sources by means of advanced membrane processes. Thereby, different technologies, such as "conventional" nanofiltration, layer-by-layer (LbL) modified nanofiltration membranes and "enhanced" custom membranes (either enhanced tubular LbL or enhanced flat sheet coated) are applied and compared concerning their filtration properties, stability and scaling potential. Furthermore, the developed membrane filtration processes for the recovery of CRMs will be benchmarked with conventional hydrometallurgic processes concerning the overall energy- and chemical consumption as well as the purity of the product and large-scale feasibility of the process.