HYDROMETALLURGICAL METAL EXTRACTION FROM PCBs

There are many valuable metals hidden inside printed circuit boards (PCBs for short), such as copper, aluminum, lead, iron, tin, and even noble metals like gold, silver, and platinum. To be exact, approximately 49% of all metals in PCBs are copper, 21.8% zinc, 11.6% iron, 6.5% nickel, 5.5% aluminum, 1.9% lead, 1.7% tin, 1.5% silver, 0.5% chromium, 0.1% gold, and less than 0.1% palladium. As technology advances rapidly, old devices are being discarded, yet only about 17.4% of all electronic waste was officially recycled in 2019 [1]. This leads us to believe that roughly 82.6% of all electronic waste was left untreated. This also includes PCBs, which (depending on the production year and manufacturer) can contain approximately 340 g of gold, 3.5 kg of silver, 140 g of palladium, and 130 kg of copper per ton of PCBs [2]. These numbers quickly add up, and many of the lost metals can heavily pollute the environment — including soil and water — if not properly treated. One of the ways to treat and extract these metals is by using hydrometallurgy (metal extraction using aqueous solutions) [3]. It is still widely used to extract various metals, either selectively or broadly. The entire process consists of three main stages: selective leaching, solution purification, and recovery of specific elements (usually via precipitation). In this study, we focus on extracting metals from waste using different acids and reagents. We decided to test traditional methods (such as Aqua Regia and Piranha Solution) and compare them to less commonly used alternatives (such as thiosulfate and salt solutions). Aqua Regia usually consists of 3 parts concentrated HCl and 1 part concentrated HNO₃. It is capable of dissolving noble metals like gold and silver. Piranha solution consists of 3 parts concentrated H₂SO₄ and 1 part H₂O₂. Other less common methods used in this work include: Salt solution, consisting of 10 parts saturated NaCl solution, 1 part concentrated HCl, and 2 parts concentrated H₂O₂.