Guilhem ARRACHART1, Cyril MICHEAU1, Micheline DRAYE2, Sophie LEGEAI3, Stéphane PELLET-ROSTAING1
1ICSM, CEA, CNRS, ENSCM, Univ Montpellier, Marcoule, France
2LCME, Univ. Savoie Mont Blanc, Le Bourget du Lac, France
3IJL-UMR CNRS 7198, Univ. Lorraine, Metz, France
Liquid-liquid extraction is one of the most powerful technic to separate and purify compounds. Despite its efficiency, this methodology suffers some drawbacks particularly the use of organic diluents which are environmentally questionable. They are often toxic, flammable and responsive of the emission of VOCs in the atmosphere. Due to the growing environmental awareness and the development of green chemistry, intense researches have been devoted to develop alternative processes limiting the use of volatiles and one of the most promising concerns the use of ionic liquids. These compounds are today considered as an alternative to common solvents mainly due to their very low vapor pressure, their non-flammability limiting thus the atmospheric pollution and increasing by the same time the safety for workers.
An eco-friendly process was proposed based on ionic liquids (ILs) or functionalized task specific ionic liquids (TSILs) for the extraction and stripping of tantalum from sulfuric acidic medium that may come from of the dissolution of bottom ash and by-products of industrial activities, as well as from secondary sources such as waste electrical and electronic equipment (WEEE).
The study of the key parameters of the IL-based process was investigated including the effect of Ta concentration, H2SO4 concentration, equilibration time, temperature, IL partitioning…. The IL phase is selective to tantalum with respect to all other cations considered in the simulated solution of an e-waste leachable slag, with separation factors higher than 250. As shown with the extraction-stripping cycles, the recycled IL phase exhibits the same extractive behaviours as the initial IL phase, allowing the recyclability of the IL phase. The recovery of the Ta in its oxide form is easily performed after the stripping using water followed by a precipitation step with ammonia and thermal treatment. From the different statement obtained in batch mode, experiments have been conducted using centrifuge mixer in a semi-batch mode for the implementation of the process.
The recovery of other valuable metals such as Au and Pd from aqua regia leachate of e-waste was also demonstrated and a global flowsheet was proposed.