(214a) Silver Recovery from Catalysts Using a Leaching and Emulsion-Liquid-Membrane Hybrid Process
This paper introduces a hybrid process for an efficient silver recovery from the deactivated industrial catalysts. The hybrid process combines leaching and ELM processes. Leaching first transfers silver from a catalyst to an aqueous solution. In a single separation step, ELM then extracts silver ions from the leach solution. 2-ethylhexyl phosphoric acid ester (MEHPA, a mixture of 55% mono- and 45% di-esters) is used as the carrier in membrane phase (facilitated transport) to extract silver ions from the aqueous solution. A paraffinic and naphthenic solvent is used as the diluent. As a major problem with ELM is emulsion instability resulting from poor surfactants like Span 80, a new surfactant, polypropylene glycol (PPG)-PEG-PPG triblock copolymer, is synthesized. Two stability methods are used to evaluate the ELM stability and the compatibility of the ELM process components (diluent, surfactant, and carrier). Finally, effects of process operating conditions such as carrier, surfactant and internal phase (receiving phase) concentrations, pH of the external phase (feed phase), striping speed, volume ratio of the internal phase to the membrane phase, and volume ratio of the emulsion phase to the external phase (emulsion phase holdup) on the silver recovery are investigated to arrive at the optimal operating conditions that maximize the silver recovery.
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