Advances in Recovering Noble Metals from Waste Printed Circuit Boards (WPCBs)

Abstract

An extensive investigation on the noble metal (NM) content in different classes of waste printed circuit boards (WPCBs: random access memories, RAMs; network interface controllers, NICs; motherboards; TV, DVD/CD player, hard-drive, and mobile phone PCBs) has been performed to define the most appropriate case study and provide a robust database useful for workers in the waste valorization field. Following accurate selection, mechanical comminution, representative sampling, quantitative digestion, and analytical characterization (ICP-AES), RAMs and mobile phone PCBs confirmed to be the “richest” source, while TV PCBs are the “poorest” one in term of NM content. Accordingly, the RAM case study has been employed for the application of a new NMs recovery method, previously set up on finely comminuted waste electric and electronic equipment underwent materials enrichment by mechanical separation. Despite the very large amount of vitreous-plastic and metallic materials present in the mixture, satisfactory NM recovery yields (Cu 70%, Ag 92%, Au 64%) with limited byproduct formation have been obtained using safe and recyclable reagents in mild conditions: citric acid for base metal leaching, ammonia in oxidizing environment for Cu and Ag separation and recovery, triiodide aqueous solution for gold recovery, at room pressure, and 25–100 °C. The reported results provide useful quantitative parameters for assessing the profitability of an industrial scale-up of the new sustainable NMs recovery method.

Evaluation of Simple Amides in the Selective Recovery of Gold from Secondary Sources by Solvent Extraction

“…7 8 WEEE is recognized as the fastest-growing global waste stream (>5% annual growth) and comprises both critical and hazardous materials for which new separation and recycling technologies are required to provide impetus to global circular economy visions. [9][10][11][12][13] Currently around 90% of the world's gold supply is derived from mining processes that exploit cyanidation. This process forms, through heap leaching, solutions of the water-soluble Au(CN)2complex, which is recovered from solution by precipitation, adsorption, and reduction.…”

Global occurrence, chemical properties, and ecological impacts of e-wastes (IUPAC Technical Report)

“…As a number of precious metals are used in the manufacturing of EEE components (e. g., silver, gold, palladium, and platinum), they provide additional incentives to recover these materials. Furthermore, gold and other valuable elements that are in relatively short supply are usually found in WEEE as high purity and quality materials, which make these secondary sources highly attractive for recovery [54]. It was estimated that the resource perspective for secondary raw materials of e-waste is worth 55 × 10 9 € [2] and the gold content present in e-waste was projected to represent 11 % of the global gold production from mines in 2013 [5].…”

Bioelectrochemical recovery of silver from wastewater with sustainable power generation and its reuse for biofouling mitigation

“…Hybrid cyanidation and high-pressure membrane processes have been employed to recover silver from mining wastewater (Koseoglu and Kitis, 2009;Lei et al, 2018). Besides, industries have adapted various hydrometallurgical processes integrated with pyrolysis to recover precious metals from the waste printed circuit boards (Niu et al, 2017;Rigoldi et al, 2018). Unfortunately, hydrometallurgical processes are based on dissolving noble metals by acids and caustic leachates, which is not a cost effective process.…”

“…Unfortunately, hydrometallurgical processes are based on dissolving noble metals by acids and caustic leachates, which is not a cost effective process. Several other technologies, like cementation, may involve the use of toxic thiocyanate and subsequent production of secondary pollutants may limit their applications on a larger scale (Rigoldi et al, 2018). Thus, more efficient and eco-friendly strategies must be developed for sustainable silver recovery from the wastewater.…”