Leaching of metals from printed circuit boards using ionic liquids

The rise in the electronics industry has impacted the environment through the large volumes of waste that are improperly disposed of and the growing demand for precious and rare metals from natural sources. Leaching of copper, cobalt, gold, and silver from printed circuit boards of waste cellular phone has been carried out using imidazolium cation-based ionic liquids (ILs). For the studied metals, the obtaining of selective leaching obtained is reported for the first time, where acidic ionic liquids ([Bmim]HSO₄ and [Hmim]HSO₄) leached copper and cobalt, while basic ionic liquids ([Bmim]Cl and [Bmim]Br) extracted gold and silver. The effect of temperature has been studied by testing at 60 and 80 °C, where the highest extraction was obtained at the lowest temperature. The concentration of the ionic liquid was also studied through a test without ionic liquid and then varying from 20 to 60%, where at higher concentration the extraction is more efficient ratifying the use of ionic liquids as leaching solutions for metals. Ionic liquids have demonstrated the ability to leach metal ions as the primary reagent in the leaching solution. The following extraction percentages were obtained for each metal: 86.2% copper, 99.5% cobalt, 40.8% gold, and 44.6% silver.