The separation of Nd(III) from mixed rare earth via hollow fiber supported liquid membrane and mass transfer analysis

Polymer-Based Extracting Materials in the Green Recycling of Rare Earth Elements: A Review

Rare earth elements (REEs) are becoming increasingly important in the development of modern and green energy technologies with the demand for REEs predicted to grow in the foreseeable future. The importance of REEs lies in their unique physiochemical properties, which cannot be reproduced using other elements. REEs are sourced through mining, with global exploration of additional commercially viable mining sites still ongoing. However, there is a growing need for recycling of REEs due to the current supply of REEs not matching the growing demand, the environmental impact of REE mining and processing (the so-called "balance problem"), and the generation of large volumes of harmful electronic waste (e-waste). Industrial REE processing is mainly carried out by hydrometallurgy processes, particularly solvent extraction (SX) and ion exchange (IX) technologies. However, these methods have a significant environmental impact due to their intensive use of harmful and nonsustainable reagents. This Review highlights the development of approaches involving polymer-based extracting materials for REE manufacturing as more sustainable alternatives to current industrial REE processing methods. These materials include supported liquid membranes (SLMs), solvent impregnated resins (SIRs), macro and micro capsules, polymer inclusion membranes (PIMs), and micro polymer inclusion beads (μPIBs). Polymer-based extracting materials have the advantage of more economical regent usage while applying the same extractants used in commercial SX, enabling applications analogous to the current industrial process. These materials can be fabricated by a variety of methods in a diverse range of physical formats, with the advantages and disadvantages of each material type described and discussed in this Review along with their applications to REE processing, including e-waste recycling and mineral processing.

Effect of solution chemistry on filtration performances and fouling potential of membrane processes for rare earth element recovery from red mud

Rare earth elements or REEs are a vital and irreplaceable part of our modern technological and digital industries. Among the REEs that are the most critical to be recovered are Ce, La, and particularly, Nd, and Y, due to high demand and at a potential future supply risk. Innovative techniques must be considered to recover REEs from secondary resources. In this study, REEs are extracted from iron mining sludge from Central Anatolia in Turkey. Two different acid solutions were compared, one with a higher acid content (120 ml HCl and 80 ml HNO₃ per liter) and one with lower acid content (20 ml HNO₃ per liter). Nanofiltration, as a process to concentrate the acidic leachate and increase the REE concentration, was carried out at pH levels of 1.5, 2.5, and 3.5 and under 12, 18, and 24 bar operating pressures. SLM studies had been carried out using a PVDF membrane with a pore diameter of 0.45 μm, with three different carriers to separate the REEs from other major elements in the concentrated leachate. Through this analysis, the optimum operating conditions for nanofiltration are at pH 3.5 at 12 bar, using the leach with low acidity, achieving about 90% recovery efficiency of the REEs. SLM studies using 0.3M D2EHPA, with a 3-h reaction time, showed the highest mass flux values for the REEs. Nanofiltration and SLM represent novel methods of REE concentration and extraction from iron mining sludge.