Refining of Palladium, Platinum, and Rhodium from a Pregnant Leach Solution of Spent Automotive Catalysts by Continuous Counter-Current Solvent Extraction with Ionic Liquids in Mixer-Settlers
Industrial & engineering chemistry research(2023)
摘要
Assessment of solvent extraction in continuous mode iscrucialto determine the feasibility of upscaling the processes. At the moment,limited information is publicly available on how to operate counter-currentsolvent-extraction equipment and how to tackle problems that may emergeduring the use of these contactors with real feeds. In this work,the performance of a solvent-extraction process in mixer-settlersis evaluated. The extractant Aliquat 336 iodide was synthesized inmixer-settlers by contacting the commercially available Aliquat 336diluted in p-cymene with an aqueous solution of potassiumiodide in a counter-current mode. Next, palladium(II) and platinum(IV)were extracted by Aliquat 336 iodide from a highly impure pregnantleach solution of spent automotive catalysts. Selective strippingwas achieved with solutions of aqueous ammonia and thiourea. In total,12 L of pregnant leach solution from spent automotive catalysts wasprocessed in mixer-settlers using two stages for the extraction ofpalladium(II) and platinum(IV) and four stages for each strippingstep. The chosen organic to aqueous (O/A) ratios allowed to enrichthe solutions of palladium and platinum up to 6 and 2.5 times, respectively,whereas rhodium remained in the raffinate. The output solutions obtainedduring solvent extraction were further treated downstream to producehighly pure (>99%) platinum group metal (PGM) nitrate solutions.Themain challenges of running a solvent-extraction process using ionicliquids at a minipilot scale are critically discussed.
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