Rare earth elements recovery from e-wastes by solvent extraction and supported liquid membrane processes
- Autores: Sandra Pavón Regaña
- Directores de la Tesis: Ana María Sastre Requena (dir. tes.), Agustí Fortuny Sanromà (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: José Luis Cortina Pallás (presid.), Francisco José Alguacil Priego (secret.), Magdalena Regel Rosocka (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería de Procesos Químicos por la Universidad Politécnica de Catalunya
- Materias:
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- Resumen
Nowadays, rare earth elements (REEs) have gained importance due to their indispensable and critical use in many high-tech industries like hybrid cars, fluorescent lamps, flat screen televisions, mobile phones, disc drives and wind turbines. Since these metals are needed to supply the required functionality in advanced technologies development and the lack of alternative materials, the REEs recovery from urban mining seems to be promising. Moreover, being the ores mines and their strip mining to REEs production placed in a few specific countries such as China, United States and Australia, the stable supply of such metals is becoming a concern. The absence of economical and operational primary deposits in other territories is making many countries consider the REEs recycling from pre-consumer scrap, industrial residues and end-of life products. However, about only 12.5% of e-waste is currently being recycled for all metals due to technological problems, inefficient collection and a lack of incentives and pilot-scale feasible testing to be industrially implemented.
In this thesis, different routes to recover and separate these elements from end-of-life products like NdFeB magnets and fluorescent lamps have been developed considering the relevance of these applications in the REEs field and the feasibility of the complete industrial implementation.
Regarding NdFeB magnet, it was demonstrated that Nd, the most REE representative component found in magnet wastes, was separated from an Nd/Tb/Dy mixture by using solvent extraction process and intensified processes like liquid membranes in flat sheet configuration. To avoid the inter-step pH conditioning in a continuous industrial process when cationic extractants are used, an ionic liquid such as Primene 81R.Cyanex 572 was proposed in an industrial counter-current extraction process. The results disclosed that two stages were required to separate Nd from the mixture with a purity of 99.7% removing =99% of the initial Tb and Dy. Although both cationic extractants, Cyanex 272 and Cyanex 572, were able to separate the Nd, the transport through the liquid membrane using the former is about 35% slower than using Cyanex 572. Hence, to obtain similar results to those got with Cyanex 572, the membrane area or the working time should be increased when Cyanex 272 is used.
REEs from fluorescent lamp wastes were recovered and selectively separated with purities =99.9% by using a process that can be industrially implemented and combines acidic leaching treatments, liquid membranes and cross-flow solvent extraction process. Two successive acidic leachings were needed: (L1) to remove the Ca avoiding its precipitation in following stages of the process and (L2) to recover the REEs present in the waste. Unfortunately, a REEs amount, mainly Y and Eu, was also dragged in the liquid fraction from L1 and these REEs were recovered using Cyanex 923 as carrier by a hollow fibre renewal liquid membrane module. Furthermore, a transport modelling was developed to foresee the permeability coefficient values for Y and Eu depending on the organic solution viscosity and the membrane characteristic parameters. A mathematical modelling was developed using D2EHPA to predict the Y/Eu/Ce mixture extraction behaviour to investigate the optimal separation conditions of the REEs found in the leachate coming from the L2. Once the REEs behaviour was studied in the extraction modelling, the recovery and separation of the REEs were experimentally achieved obtaining purities =99% by four stages cross-flow solvent extraction process using two ionic liquids, Primene 81R.02EHPA and Primene 81R.Cyanex 572.
In this sense, REEs recycling processes of both wastes promote potential circular economy based on solutions where a waste is turned into a resource.
