The Diluent Effect on the Solvent Extraction of Rare Earth Elements from Neodymium Magnet Leachate
Licentiate thesis, 2016
The diluent effect on the solvent extraction of rare earth elements from neodymium magnet leachate
Industrial Materials Recycling
Department of Chemistry and Chemical Engineering
Chalmers University of Technology
Rare earth elements (REEs) have become vital components in a wide range of industrial applications. The demand for the REEs has grown significantly in the last few decades. This has led to increasing costs and supply chain risk. Today, despite lower prices than in 2011, they are classified as the highest supply risk elements in the EU; thus new incentives for recycling the REEs out of electronic scrap were brought forth. End-of-life neodymium magnets are a viable source for the recovery of some REEs. Although mainly iron alloys, these materials contain neodymium, dysprosium and small admixtures of praseodymium and terbium.
Leaching followed by solvent extraction of the REEs out of the leachate is an attractive and efficient way of recycling these elements out of end-of-life neodymium magnets. The issues that are encountered along this recycling path is the separation of the REEs from the other elements that are dissolved with the REEs into the leachate and achieving high separation factors between the REEs from each other. Extracting agents such as D2EHPA (di(2-ethylhexyl)phosphoric acid) and TODGA (tetraoctyl diglycolamide) have been previously used for achieving good separation of the REEs under specific extraction conditions.
This thesis has focused on the development and optimization of REE extraction from real commercial waste sources, the nitric acid and sulfuric acid media leachates of the neodymium magnet waste, using TODGA and D2EHPA as extracting agents, respectively. Selective REE extraction from the solution with minimal or no co-extraction of other elements in the leachate is hoped to provide a novel route to a commercially viable route to recyclable REE products. The composition of the organic phase was investigated in order to study the effect of the diluent on the overall extraction process, a well-known optimization parameter, however infrequently used. The effect of the diluent on the separation factors was also discussed as well as some characteristics of the aqueous phase on the overall extraction process. The named extractants were used at various concentrations in different diluents like solvent 70, hexane, octane, cyclohexanone, toluene, 1-octanol and chloroform. Both extractants demonstrated good selectivity concerning the extraction of the REEs out of the neodymium magnet waste leachates.
KEYWORDS : neodymium magnets, rare earth metals, recycling, solvent extraction, diluents, TODGA, D2EHPA