Environmental Technologies for Contaminated Solids, Soils and Sediments
4st cohort

Arda Işıldar

Two-step Biological and Chemical Leaching for the Recovery of Copper and Gold from Electronic Waste

The well-being of the society depends on several metals, including base metals, precious metals, and increasingly rare earth elements (REE). The usage of these metals increased in numerous applications, including electrical and electronic equipment (EEE), and their interrupted supply is at stake. Modern electronic devices contain up to 60 metals. There is an increasing interest in the secondary sources of these metals, particularly waste electrical and electronic equipment (WEEE) in order to compensate their potential supply deficit. This PhD thesis demonstrates the advantages and bottlenecks of biological and chemical approaches, as well as the advances and perspectives in the development of sustainable processes for metal recovery from WEEE. Furthermore, a novel process for the recovery of metals from WEEE is described, and a techno-economic assessment is given. Discarded printed circuit boards (PCB) from personal computers (PC), laptops, mobile phones and telecom servers were studied. Following an extensive literature review, a novel characterization and total metal assay method was introduced and applied to the
waste board materials. Discarded PCB contained metals in the range of (%, by weight): copper (Cu) 17.6 – 39.0, iron (Fe) 0.7 – 7.5, aluminum (Al) 1.0 – 5.5, nickel (Ni) 0.2 – 1.1, zinc (Zn) 0.3 – 1.2, as well as gold (Au) (in ppm) 21 – 320. Multi-criteria analysis (MCA) using the analytical hierarchical process (AHP) methodology was applied for selection
of the best-suited metal recovery technology. A proof-of-concept for a two-step bioleaching extraction is given, in which 98.4% and 44.0% of the Cu and Au, respectively, were extracted. The two-step extraction procedure was also applied in the chemical leaching of metals from discarded PCB. Cu leaching was carried in an acidic oxidative mixture of H2SO4 and H2O2, whereas Au was leached by in a medium, catalyzed by CuSO4. Under the optimized conditions, 99.2% and 92.2% of Cu and Au, respectively, were extracted from the board material.
Selective recovery of Cu from the bioleaching leachate using sulfidic precipitation and electrowinning was studied. Cu was selectively recovered on the cathode electrode at a 50 mA current density in 50 min., with a 97.8% efficiency and 65.0% purity. The technoeconomic analysis and environmental sustainability assessment of the new technology
at an early stage of development was investigated.