Selectivity potential of ionic liquids for metal extraction from slags containing rare earth elements

• Published in: Hydrometallurgy 2017-05, Vol.169, p.59-67
• Main Authors: Sahin, Ayfer Kilicarslan, Voßenkaul, Daniel, Stoltz, Nicolas, Stopic, Srecko, Saridede, Muhlis Nezihi, Friedrich, Bernd
• Format: Article
• Language: English
• Subjects: Hydrometallurgy; Ionic liquid; NiMH battery; QEMSCAN; Rare earth; Recovery
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2016.12.002

The recycling of rare earth elements and base metals from recycling slag powders of nickel metal hydride (NiMH) batteries by ionic liquid leaching was studied. Leaching tests were conducted by using the ionic liquid 1-methylimidazolium hydrogen sulfate (HmimHSO4) selected after some preliminary leaching tests on slag powders. The HmimHSO4 concentration of aqueous ionic liquid solution was 30% (v/v) in all tests. The slag powders were ground and sieved to obtain two different particle-size fractions namely 63–90μm and 90–125μm in order to evaluate the leaching behavior and the kinetics. The most important metals present in the initial slag powders are iron (35.70% w/w), aluminum (9.95% w/w), manganese (3.45% w/w) and rare earth elements (REEs) such as lanthanum, cerium, neodymium and yttrium (totally 22.50% w/w). In the leaching experiments three parameters were studied: temperature, particle size and time. The average dissolution ratios of 63–90μm particle size slag powder were 100% for iron, manganese and yttrium after 2h at a temperature of 80°C. However, the maximum leaching efficiencies were about 15% for lanthanide and cerium and 20% for neodymium under the same conditions. As an explanation for the low recovery rates, a phase analysis with QEMSCAN (Quantitative Evaluation of Materials by SCANning electron microscopy) indicated decomposition in the initial REE phases but a precipitation as sulfates. The kinetic study of Fe and Mn dissolutions showed that the leaching process follows the shrinking core model with an unchanged particle size controlling diffusion through the product layer. •NiMH batteries slag powders contain significant amount of Fe, Al, Mn and REEs.•Leaching of NiMH batteries slag powders by ionic liquid HmimHSO4 was proposed.•Generally, the particle size of slag powders has significant influence on leaching rate.•QEMSCAN has provided new insights for the dissolution behavior of base and REEs.•The leaching kinetics obey the shrinking core model for Fe and Mn.