Cloud-Point Extraction of Gold(lll) with Nonionic Surfactant—Fundamental Studies and Application to Gold Recovery from Printed Substrate

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Abstract
An aqueous solution of a nonionic surfactant, polyoxyethylene nonyl phenyl ether, having an average of 7.5 oxyethylene units, provides an aqueous two-phase system that is surfactant-rich and surfactant-lean at ambient temperature. The system found use as a separation field. Au(III) was effectively partitioned into the small surfactant-rich phase from hydrochloric acid solutions; thus such operational factors as the concentrations of the surfactant, HCl, and NaCl were investigated. Partitioning of other heavy metals was depressed, and selective extraction of Au(III) could be attained. Such a cloud-point extraction technique has been applied to the recovery of gold from an aqua regia leaching solution of a printed substrate, and an overall process scheme, including stripping and reduction steps, was proposed. By introducing scrubbing stages using a dilute HCl solution, satisfactory recovery of gold with a high yield and purity from undesirable metals could be obtained.