Electrodeposition of metal cations from the wet ionic liquid [EMIM][TFSI]

Abstract

We investigated the deposition of silver, copper, and lead from the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI] under potentiostatic conditions in the presence of water. This was part of a larger project involving the extraction of metal ions from mining waste into an ionic liquid followed by electrodeposition so that the ionic liquid could be recycled. All three elements were deposited in metallic form by electrolysis in the ionic liquid, and the process was enhanced rather than hindered by the presence of water. The deposited metals did not adhere strongly to the cathode of the electrochemical cell, especially when Ebonex® was used as the cathode. The deposition of silver showed little temperature dependence, and at temperatures close to ambient, the ionic liquid was not adversely affected. The deposits of copper and lead gradually re-dissolved after electrodeposition, suggesting that chemical re-oxidation of these metals by air is more facile in the ionic liquid than in water. Copper showed strong evidence of formation of a Cu+ species upon reduction of Cu2+ (not seen in water); lead (Pb2+) showed evidence of a time-dependent complexation with the anions of the ionic liquid.