Gold(III) extraction and recovery and gold(III)/copper(II) separation using micelles

• Micellar enhanced ultrafiltration approach enables Au recovery and Au/Cu separation.
• DTAC(+) micelles extract AuCl4− with excellent yields.
• Gold(III) can be recovered from DTAC with good yields using NH3/NaCl mixtures.
• SDS(−) micelles extract the [PADA–AuCl2]+ complex with excellent yields.
• Excellent AuCl4−/Cu2+ separation is achieved using either DTAC or SDS.

Gold extraction from aqueous solutions has been performed by micellar enhanced ultrafiltration (MEUF), using SDS and DTAC micelles. DTAC entraps 92–100% of the metal, which is present in form of AuCl4−, owing to electrostatic interaction. Using SDS the extraction of gold is unsuccessful. However, addition of PADA, as a metal extractor agent, according to the ligand modified micellar enhanced ultrafiltration (LM-MEUF) procedure, makes the extraction yield to approach 100% also with SDS. The recovery of gold entrapped in the micellar pseudo-phase has also been investigated. Different stripping agents have been used, the most efficient of them being a mixture of NaCl and NH3 which allowed the metal to be expelled from the micelle with a yield of 85%. Finally, Au(III)/Cu(II) separation is achieved with DTAC or SDS between pH 3 and 5. Almost 100% of Au(III) is retained on DTAC micelles while all Cu(II) remains in the aqueous medium, while the opposite occurs in SDS.

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