Hydrometallurgical recovery of high-purity copper from waste printed circuit boards: an experimental study and life cycle assessment

Abstract

Due to their complex structure and high metal content, printed circuit boards (PCBs) represent both a major challenge and opportunity for recycling. By weight, copper represents the main metallic fraction of PCBs. Thus, the selective removal and recovery of high-purity copper is crucial for efficient recycling, in addition to the extraction of minor, precious metal components, such as gold, silver, and palladium. This paper presents an integrated study of detailed characterization, process development, and the environmental impact of copper recycling from virgin PCBs using hydrometallurgical approaches – rather than the well-established pyrometallurgical route. Thorough mineral liberation analysis helped us understand specific processing and metallurgical approaches based on the accessibility of the target metal phases. Near quantitative copper leaching was achieved with H₂SO₄/H₂O₂ and HNO₃, whereas heterotrophic bioleaching with citric acid and polyglutamic acid resulted in <13% of copper leaching. In a two-stage process, >98% of the leached copper was selectively transferred to the organic phase by solvent extraction with a LIX 84-I-kerosene/CuSO₄–H₂SO₄ system. With the exception of Ni²⁺, co-extraction of further metal ions was not detected. Subsequently, up to 98% of the copper was recovered from the organic phase via stripping with a model electrolyte containing copper(II) sulfate in H₂SO₄. From the enriched electrolyte solutions, metallic copper with a purity of 99.64–99.84% was electrodeposited on a stainless steel cathode, with a current efficiency of 98.66–99.85%. Residual copper obtained by washing the leaching residue was recovered by cementation with an iron powder according to a stoichiometric ratio of Fe/Cu²⁺ of 1.5 : 1. According to life cycle assessment, based on the energy and chemical consumption of the copper recycling process, the global warming potential of the tested approaches lies in the range 13.0 kg CO₂ eq. per (kg Cu) – 40.3 kg CO₂ eq. per (kg Cu). The greatest contributors to environmental impact are leaching and solvent extraction processes, which can be substantially improved by operating on a larger scale and recycling process ingredients. The proposed approach demonstrates end-to-end high-purity metal recovery with direct application to various circuit boards and copper-rich electronic components.