Recovery of copper and the deportment of other base metals from alkaline glycine leachates derived from waste printed circuit boards (WPCBs)

E-waste has become a global risk to the environment and humans due to the improper disposal. Recently, a novel approach has been reported to effectively extract copper (Cu) from waste printed circuit boards (WPCBs) using environmentally friendly glycine solutions, with the co-extraction of other base metals. This process step is ideally positioned after the bulk of the aluminium, copper and iron is removed using conventional dry physical processes, but before hydrometallurgical recovery of precious metals. To recover Cu and other minor base metals from glycine leachate of WPCBs and release the glycine for reuse, this study investigates three options, i.e. hydrazine reduction, sulphide precipitation, and solvent extraction. During the hydrazine reduction, it was found that Cu recovery was sensitive to the leachate pH, and copper recovery increases with the increase of initial pH, Cu concentration and temperature. The obvious co-precipitation of lead and tin was also found while no coprecipitation of nickel, zinc and aluminium was observed. At the Cu/hydrazine molar ratio of 1:0.7 and 1:1, the products were identified as cuprite (Cu2O) and native Cu with 96.9% and 98.6% recoveries, respectively. During sulphide precipitation, >= 99.5% Cu could be easily precipitated at Cu/HS- molar ratio <= 1:1.2 in only 5 min. Lead, tin and zinc in the alkaline glycinate leachate also precipitated to a significant extent (>65%), whereas aluminium and nickel co-precipitation was limited (<= 3%) in the sulphide. XRD analysis of precipitates verifies that Cu was recovered as covellite (CuS). During solvent extraction from the polymetallic leachate, Mextral 84H showed better performance than Mextral 54-100 but requires higher H2SO4 concentration for stripping. Mextral 84H also showed higher selectivity than Mextral 54-100 with no zinc, aluminium and nickel co-extractions detected. The overall Cu recoveries of 91.6% for 15% Mextral 84H extraction followed by 200 g/L H2SO4 stripping, and 86.7% for 30% Mextral 54-100 extraction followed by 80 g/L H2SO4 stripping were achieved. Finally, discussion and comparison of the three methods were made with a suggested conceptual process of WPCBs recycling.

Automated summary

A novel approach for extracting copper from waste printed circuit boards using glycine solutions was reported, with the investigation of three recovery options: hydrazine reduction, sulphide precipitation, and solvent extraction. Each method showed different levels of copper recovery and effectiveness in metal extraction.