Recovery of Gold, Silver, Copper and Niobium from Printed Circuit Boards Using Leaching Column Technique

Nowadays, over 300 tons of Au are used in electronic equipment each year with other precious and strategic metals such as Ag, Pt, Pd, Cu, Nb, Ta, etc.. After the use-phase, the electronic devices become electronic waste (e-waste); consequently it is important to consider e-waste as a secondary supply for the recovery of these metals. This paper presents the recovery of Au, Ag, Cu and Nb from PCBs (printed circuit boards) of discarded computers using leaching column technique. The PCBs were crushed with a hammer mill until reaching a particle size between 3.33 mm to 0.43 mm. Then, it was leached with a sodium cyanide solution in a glass column using the following conditions: sodium cyanide concentration 4 g/L, flux 20 L/d kg PCBs day, pH between 10.5 to 11 and leaching time 15 days. Every day, after leaching, the pregnant solutions passed through a column with activated carbon to complete the closed loop system. The following recoveries were obtained: Au 46.6%, Ag 51.3%, Nb 47.2% and Cu 62.3%. A preliminary technical-economic study shows the feasibility to create a small-scale PCBs recycling plant. The initial investment is on the order of US$155,639, considering the recovered metals from the loaded carbon. The internal rate of return for a 10 years period IRR (internal rate of return) and NPV (net present value) estimated are 27% and US$105,926 respectively.