Metal recovery from non-mounted printed wiring boards via hydrometallurgical processing

Hydrometallurgical processes have been proposed for selectively leaching nickel, then copper from non-mounted printed wiring boards, which contain considerable amounts of heavy metals, such as copper, nickel and gold in metal strips printed on the resin substrates, while at the same time recovering solid flakes of gold in high purity. Among the leaching reagents examined, nitric acid showed a great possibility of recovering gold flakes and its leaching performance was evaluated in terms of such experimental parameters as concentration, temperature, time and solid–liquid ratio. With the advance of the leaching of the base metals, gold flakes were detached spontaneously from the boards and recovered easily in high yield with excellent purity. For the separation of copper and nickel, both two-step leaching and solvent extraction have been examined. In the former process, nickel was selectively leached with 0.1 M HNO3 solution in the first step of leaching, and the remaining copper was transferred into 1.0 M HNO3 solution in the second step of leaching. In the latter process, copper could be selectively extracted from the leach solution with LIX984 reagent as extractant, while leaving nickel in the raffinate solution. Stripping was carried out successfully with 4.0 M HNO3 solution, giving pure copper solution of over 10 000 mg/L. An overall separation scheme has been proposed.