Recovery of surface-plated metals from lead frame scrap using selective leaching and solvent extraction

The selective leaching of surface-plated metals from lead frame scrap followed by metal separation and enrichment through solvent extraction has been investigated. The leaching of lead frame scrap using H2SO4 solution under non-oxidizing and oxidizing conditions could efficiently and selectively dissolve Ni, leaving majority of Cu-substrate in the leach residue for further processing. The leaching carried out in a 1.0 M H2SO4 solution at 400 rpm agitation speed, 90 °C temperature and 15 g/L pulp density yielded a Ni leaching efficiency of 98.6% for 240 min (non-oxidative), but required only 60 min to reach the Ni efficiency of 96.4% while supplying 1.0 L/min O2 (oxidative). For both leaching systems, Cu dissolution was found to be <7% only without any dissolution of precious metals contained in the scrap. The kinetic study showed that the Ni leaching under non-oxidizing conditions proceeded by a single rate-controlling step following film diffusion model with activation energy of 12.6 kJ/mol in the temperature range 50–90 °C.The Ni leaching in oxidative system was however, controlled by a mixed control model comprising film diffusion and chemical reaction with the activation energy of 40.0 kJ/mol in the same temperature range. These results were corroborated by SEM analysis of the leach residue. Subsequently, leach liquor obtained from the oxidative leaching (0.84 g/L Cu2+ and 0.32 g/L Ni2+) was subjected to solvent extraction using LIX 84-I. Based on the extraction data, a two-stage counter-current extraction at A/O ratio = 10/1 was required using 20% LIX 84-I to quantitatively extract and enrich Cu2+ from the solutions (equilibrium pH 2.5). The stripping of Cu-loaded organic phase indicated that a three-stage counter-current stripping using 200 g/L H2SO4 at O/A ratio of 5/1 was required. Nickel(II) from the copper free aqueous solution was extracted and enriched using 20% LIX 84-I at an A/O ratio of 5/1, and was stripped from the loaded organic phase using 20 g/L H2SO4 at O/A ratio of 5/1. The hydrometallurgical route of selective leaching-SX results in not only Cu- and Ni-rich solutions suitable for recovery of final products, but also Ni-free lead frame scrap for further processing by smelting. Finally, a flowsheet has been proposed for the total recycling of lead frame scrap.