Synergistic extraction of gold(I) from aurocyanide solution with the mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide in supported liquid membrane

Abstract

Utilization of supported liquid membrane (SLM) for the extraction of Au(I) from alkaline cyanide solution was investigated. The SLM consisted of a synergistic mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide (BESO) in kerosene as carrier and a hydrophobic microporous polyvinylidene fluoride (PVDF) membrane as the solid support. The presence of both BESO and N1923 extractants in the liquid membrane induces an evident synergistic effect, allowing the latter to transfer Au(I) from the highly alkaline solution (pH>9.21). The fundamental parameters influencing the gold transport, such as stirring speed, composition of the liquid membrane, feed pH, NaOH concentration in stripping solution, and initial gold concentration in the feed solution were explored. The gold transport is almost quantitative after 7h under the optimum process conditions: a mixture of (0.50mol/L N1923 + 0.75mol/L BESO) in kerosene as membrane phase, stirring rate of 1000rpm in both phases, 5.0mg/L gold in 0.20mol/L NaCl solution with a pH of 9.60, and 0.10mol/L NaOH as stripping agent. The parameters defining the mass transfer model of Au(I) through the SLM are experimentally determined as: maximum permeability coefficient, P = 31.45 × 10−6m/s, the diffusion coefficient for [Au(CN)2−·RNH3+ ·2BESO] complex across the liquid membrane, Dorg = 1.42 × 10–12m2/s, and the thickness of the aqueous diffusion layer, daq = 2.07 × 10−5 m. Selectivity of this SLM system was evaluated by performing the permeation test of Au(CN)2- with other metal cyanide species in aqueous solution and it was found that the gold ions were preferred over other impurity ones. Finally, stability of this SLM system has also been examined on a continuous run mode and satisfactory stability was observed for five runs.