THE EFFECT OF PRE-TREATMENT AND PARAMETERS FOR BIOLEACHING OF PRINTED CIRCUIT BOARDS

摘要

Waste electrical and electronic equipment (WEEE) is one of the largest growing waste streams in the world. Especially printed circuit boards (PCB) contain plenty of valuable metals, like Au, Ag, Pd, Cu and REE but also harmful contaminants like halogens, flame retardant chemicals and plastics. Currently, WEEE treatment and metal recovery methods are incomplete. In this paper, bioleaching with mixed acidophilic culture was utilised as a process step for overall treatment and metal recovery process for printed circuit boards (PCB). Flotation, conducted after crushing and sieving of PCB produced two fractions: a metal concentrate to be more suitable for pyro or hydrometallurgical treatment, and metal-poor, but plastics-rich froth, suitable for bioleaching. It was seen that especially low pH (1.6), high initial Fe~(2+) concentration (7.8 g/1) and low froth concentration in solution (50 g/1) were beneficial for rapid and selective dissolution of copper. With these parameters, 88-99 % of Cu was solubilized from PCB froth in bioreactor treatment, with Cu and Fe being the only major metallic elements in solution. High selectivity improves later Cu recovery from liquids, and simplifies also later Au, Ag, Pd and REE recovery from residual solids.