Approach on recycling of printed circuit boards (PCB) via hydrometallurgical procedures: Principle and methodology

Abstract

Recent mankind demand for electronic devices is in constant upgrowth, those devices always contain printed circuit boards (PCB) which are mainly constructed of plastics, semiconductors and decent content of various metals. Hence, in the end-of-life of those products, it is highly recommended to recover those materials or functionalize those waste into other products or feed materials, in order to lessen their harmful impact on the environment. One of the promising processing procedures is hydrometallurgical treatment, since it is cost-effective and simple. In order to recover metals as aqueous soluble salts, crushed and milled PCB is air-pyrolyzed and obtained powder is processed as start material in leaching experiments. The use of concentrated aqua regia led to the passivation of solid material and consequently impede the leaching process. Dry-digestion leaching using concentrated sulfuric acid partially leached some metals. The highest leaching rate (≥70 %) has been achieved using diluted sulfuric acid (for Al, Ni, Fe, Co, and rare-earth) and copper yield was highest utilizing 2 M H2SO4 + 3 M H2O2; S/L = 0.1 g/ml. While sulfuric acid has accomplished some results for enumerated leachates, it achieved limited success for leaching Ba, Pb, Ag, Au, Pt and Pd. Overall findings imply that hydrometallurgical procedures may be used but only together with previous separation techniques. That approach would increase overall leaching with oxidizing agents and enable leaching of noble metals.