Removal of iron from waste printed circuit board dust: surfactant assisted magnetic separation versus selective leaching routes

Iron content in printed circuit board (PCB) dust consumes complexing agents, compromises recovery and contaminates leach solution during precious metals recovery from this waste stream. This study evaluated the prospects of iron removal from PCB dust via wet magnetic separation (WMS) versus sulphuric acid leaching. Chemical conditioning of the PCB pulp is required to make WMS effective in this case; this is a factor still new to magnetic separation technology. This was studied as a function of surface tension variation to optimize magnetic separation. For selective leaching route, the PCB dust was first treated with ammonia to selectively pre-remove copper, followed by sulphuric acid treatment of the residue for iron removal. After these investigations, the best performance from WMS gave a separation efficiency of 87%, whilst selective leaching efficiency for iron removal was 98%. Both routes compromise zinc and nickel into their ferrous streams, but the WMS route also compromised gold and silver. Though wet magnetic separation efficiency was greatly enhanced by pulp surfactant conditioning investigated herein, the selective leaching route is still more effective for iron removal from the PCB dust for this assorted material fraction, considering the risk of compromising gold loss to the ferrous fraction.