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

Abstract

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 AuCl<inf>4</inf>^-, 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 NH<inf>3</inf> 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

The mechanism of the reaction between Au(III) and PADA in sodium dodecylsulphate

“…The commercially available ligand PADA ( Figure 1) is totally adsorbed on a variety of surfactants, including SDS [4] and has proven to be an excellent metal extractor, being able to transfer metal ions from water to micellar phases with yields approaching 100% [5][6][7] Moreover, we have found that PADA is able to complex Au(III) with great affinity even if the coordination shell of the metal is occupied, as in AuCl4 - [8,9]. In this case, a molecule of PADA replaces two chloride ions forming a strong chelate.…”

“…The stock solutions of these reactants were prepared by dissolving appropriate amounts of the relevant solid material in water. The gold content was determined by direct UV absorption spectrometry exploiting the absorption band of AuCl4ion centred at 233 nm whose maximum absorption is proportional to the gold concentration [8,9]. Water, purified by pumping deionized water through a Milli-Q apparatus, was used to prepare the solutions and also as the reaction medium.…”

pH-Responsive Polyketone/5,10,15,20-Tetrakis-(Sulfonatophenyl)Porphyrin Supramolecular Submicron Colloidal Structures

“…Then, 10 mL of every solution was passed across the membrane (cutoff 1000 Da) under 60 bar of nitrogen pressure. When 8 mL of the initial solution has been filtered, the concentration of TPPS in the filtrate was measured by UV–vis spectroscopy (PerkinElmer Lambda 650 spectrophotometer—San Francisco, CA, USA), and then the percentage of retention ( R %) was calculated by the following equation [ 86 ]: where Ap and Ai are the absorbance of TPPS in the permeate and in the initial solution, respectively, at a given wavelength. R % were calculated at different wavelengths (corresponding to signal maxima) and averaged.…”

“…Then, 10 mL of every solution was passed across the membrane (cutoff 1000 Da) under 60 bar of nitrogen pressure. When 8 mL of the initial solution has been filtered, the concentration of TPPS in the filtrate was measured by UV-vis spectroscopy (PerkinElmer Lambda 650 spectrophotometer-San Francisco, CA, USA), and then the percentage of retention (R%) was calculated by the following equation [86]:…”

Nanofiltration Mediated by Surfactant Micelles: Micellar- Enhanced Ultrafiltration

“…Cu(II) removal could not be achieved by cationic DTAC micelles. But they could provide gold-copper separation by MEUF to a large extent utilizing charge effect of SDS micelles: oppositely charged Cu(II) ions bound to micelles retained on the membrane, while AuCl 4 − ions of the same charge with micelles passed through the permeate [52].…”