Continuous production of a biogenic ferric iron lixiviant for the bioleaching of printed circuit boards (PCBs)

Ferric iron is a low-cost oxidant frequently used in hydrometallurgy and is particularly suitable to leach various metals from printed circuit boards (PCBs). This paper presents the use of the BRGM-KCC acidophilic consortium to generate ferric iron solution in a bubble column run in continuous mode. The influence of influent ferrous iron concentration, ranging from 1 to 9 g L−1 on the bio-oxidation rate was studied in the presence of a solid support. The impacts of the quantity of solid support, the hydraulic residence time (HRT), the culture medium and the type of support were established. Stable performance was achieved over an extended period with a Fe2+ oxidation rate of 1400 mg L−1 h−1. Cryogenic scanning electron microscopy was used to observe the attachment of cells on the solid support in different operating conditions and showed that the clogging of the solid support with jarosite precipitates influenced its colonization by the micro-organisms and the stability of the bioprocess. The operating conditions, and especially the influent ferrous iron concentration and nutritive medium composition, also influenced the structure and the abundance of the microbial community.