Electrodialytic recovery of rare earth elements from coal ashes

• Published in: Electrochimica acta 2020-11, Vol.359, p.136934, Article 136934
• Main Authors: Couto, Nazaré, Ferreira, Ana Rita, Lopes, Vanda, Peters, Stephen C., Mateus, Eduardo P., Ribeiro, Alexandra B., Pamukcu, Sibel
• Format: Article
• Language: English
• Subjects: Anolytes; Anthracite; Bituminous coal; Cation exchanging; Coal; Coal ash; Critical raw materials; Electrodialytic separation; Fly ash; HREE; Liquid phases; LREE; Neodymium; Periodic table; Rare earth elements; Raw materials; Recovering; Solubilization; Trace elements
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2020.136934

•Removal process regulated by 3 main steps dependent on REE position in the periodic table.•HREE removal more regulated by solubilization and LREE by mobilization.•EDR under the tested conditions allow >70% REE extracted from ash and up to ≈ 50% in the catholyte.•Criticality, concentration and EDR-removal puts the process in the path of Nd recovery. Rare earth elements (REE) are critical raw materials crucial for modern technologies and used in a variety of industries. There is a need of investment in REE recovery from secondary sources. The present work was designed to assess the potential of the electrodialytic process to recover REE from coal ash. The content of REE was evaluated in bituminous and anthracite ash. Anthracite presented higher REE concentration (447 ppm vs. 138 ppm) and a triple concentration of critical REE compared with bituminous ash. Anthracite ash was treated aiming to test the REE recover potential, including differences between light REE (LREE) and heavy REE (HREE) fractions as well as the specific recovery of REE with high criticality. A two-compartment electrodialytic cell was tested with the matrix placed in the anode compartment and a cation-exchange membrane separating the compartments. Experiments lasted a maximum of 7 days applying different current intensities and pH adjustment in the catholyte (≈ 2). Three main steps are observed in the removal process 1) REE solubilization - from the solid to the liquid phase (anolyte); 2) REE mobilization - movement from the anolyte towards the cathode end; 3) REE removal - presence in the catholyte. The extent of each step observed for the REE depends on their individual position in the periodic table with HREE removal being more regulated by step 1 and LREE by step 2. At the best tested conditions (50 mA, 3 days, pH adjustment), more than 70% of REE were extracted from the ash with the catholyte enclosing up to ≈ 50% of LREE and HREE. Combining the high criticality of neodymium with its high concentration in anthracite coal ash (65 ppm), the electrodialytic treatment is highly recommended to concentrate this REE in the catholyte. The results demonstrated the proof-of-concept for electro-assisted extraction of REE from anthracite coal ash, opening perspectives to a selective recovery of these elements from secondary sources. [Display omitted]