Selective recovery of gold(III) via continuous counter-current foam separation from hydrochloric acid solution – Effects of foam and column sizes on separation performance

• Novel method of foam separation was applied to gold recovery.
• The effect of an average foam diameter was investigated on the separation performance.
• A parameter chart of the operational conditions on the separation performance was presented.
• The effect of a bubble column diameter was also investigated on the separation performance.

Continuous counter-current foam separation with simultaneous injections of metal and surfactant solutions into rising foam bed was applied to Au(III) recovery from hydrochloric acid solutions containing binary metals of Au(III) and Cu(II). A nonionic surfactant, poly(oxyethylene) nonylphenyl ether, used in this study showed a strong affinity to Au(III) and played a double role of foam-producer and metal collector. The effect of an average foam diameter (from 0.026 to 0.28 cm) was investigated on the separation performance. It is noteworthy that a larger foam enhances gravitational drainage dramatically while decreasing of the adsorption capacity for Au(III). Increasing the foam diameter from 0.07 to 0.22 cm improves Au(III)/Cu(II) separation factor successfully from 64 to 1060 under keeping the complete recovery of Au(III). Based on the results obtained, a parameter chart of the operational conditions on the separation performance was presented. Usage of a larger foam is essential for the metal separation under the optimized counter-current flow balance in the foam bed. Furthermore, enlargement of a bubble column diameter from 3.0 to 6.0 cm enhances the separation factor as much to 3840 while keeping the complete recovery of Au(III), indicating that the size of the column is also crucial to the separation.