Metal recovery from printed circuit boards (PCBs) by acidophilic bioleaching
Résumé
During bioleaching, the use of bacteria allows the dissolution of metals with markedly reduced amount of reagents and mild pressure and temperature conditions, compared to usual operating conditions. In our study, acidophilic bioleaching was applied to comminuted spent printed circuit boards (PCBs). These wastes contain various metals, including precious and base metals, with concentrations that are generally higher than those found in primary resources. Some studies already demonstrated the efficiency of PCBs bioleaching but significant variations are observed between reported bioleaching rates. In the present study, a double-stage bioreactor has been designed and used in order to bioleach comminuted PCBs in continuous mode. The first stage of the continuous bioreactor was a bubble column in which the acidophilic consortium BRGM-KCC mainly composed of Leptospirillum ferriphilum and Sulfobacillus benefaciens was used to oxidize Fe(II) into Fe(III). The resulting leaching solution was employed to leach the metals contained in PCBs under mechanical stirring in the second stage of the bioreactor. Such a configuration was particularly relevant to reduce the impact of PCBs toxicity on bacterial growth and to maximize bioleaching rates. The culture was able to slowly adapt to PCBs (1% w/v). Consequently , with 48 hours residence time, main metals were dissolved with high yields : 96% Cu, 85% Zn, 73% Ni and 93% Co. When the solid concentration was increased up to 1.8%(w/v), it resulted in higher dissolution rates.
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