Leaching of base metals in PCBs and copper cementation by iron powder

When dealing with electronic waste, printed circuit boards (PCBs) are some of the most important materials in terms of recovery possibilities, because of their high content of precious metals and base metals, notably copper (> 20% w/w), in addition to organic resins and ceramic materials. Efficient hydrometallurgical metals recovery from electronic waste is an important on-going research topic, and the present study consisted in the development of a process for the concentration of precious metals by leaching and recovery of major base metals mainly copper.

A fraction of crushed PCBs concentrated in metals with more than 50 % copper was used for the leaching tests for two types of components: processor cards and mobile phone cards. For the leaching process, two steps were carried out. A first step consisted in leaching the concentrate three times with sulfuric acid and hydrogen peroxide, a second step consisted in lead removal by nitric acid leaching.

The obtained results exhibit that, for processor cards, the first stage of leaching allowed the extraction of about 98 % of copper. Other base metals, zinc (99.8 %) and nickel (96 %) were also significantly leached. Precious metals were less leached except Ag with 88 % of release. The second stage of leaching with nitric acid allowed significant removal of lead (66 %). For mobile phone cards, the first stage of leaching led to an almost complete extraction of Cu (>98 %) and some other base metals (Fe, Ni, Sn, and Zn > 90 %). Al, Co and Mn were also extracted at 76 %, 78 % and 81 % respectively. Precious metals remained in the residue, except Pd which was leached at 16 %. The second stage of leaching with dilute nitric acid solution was not necessary for mobile phone cards, as it was responsible of an important Ag release from residue (80 %).