Leaching behaviour of gold from computer circuit board components in acidic thiourea solutions was investigated. Characterization of the solutions has been done through determination of solution stability, oxidation-reduction potential (ORP) and pH dependence on time, as well as by following gold leaching without any ORP control. Effects of thiourea concentration, ORP and leaching time on gold leaching have been studied under controlled ORP. Results show that acidic thiourea solutions are not stable. Decomposition of thiourea constitutes not only a cost problem, but also retards further leaching due to formation of a thin film of sulphides or elemental sulphur on circuit components. Minimum requirements must be met regarding thiourea concentration and ORP to achieve effective gold leaching.
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