Recovery of metals in a double-stage continuous bioreactor for acidic bioleaching of printed circuit boards (PCBs)

Abstract

Many studies are now focusing on bioleaching methods to recover metals from WEEE. The efficiency of this process is highly dependent on microorganisms but also on the solid-liquidgas mass transfer, which is controlled by the reactor design. In this study, bioleaching of comminuted spent printed circuit boards (PCBs) was performed in a stirred tank reactor operated in batch mode and in a double-stage continuous bioreactor. The metal dissolution kinetics were compared. The first stage of the continuous bioreactor was a bubble column in which a BRGM-KCC acidophilic consortium comprising Leptospirillum ferriphilum and Sulfobacillus benefaciens was used to oxidise Fe(II) into Fe(III). The resulting liquor was used to leach out metals contained in PCBs in the second stage of the bioreactor with mechanical stirring. The use of two distinct stages allowed the bacteria to adapt gradually to the PCBs and reach high dissolution yields, i.e. 96% Cu, 73% Ni, 85% Zn and 93% Co when 1% (w/v) PCB scraps were added into the bioleaching reactor, with a hydraulic residence time of 48 hours. By using the double-stage bioreactor, the concentration of PCB scraps could be increased up to 1.8% (w/v) without reducing bioleaching performance. Biomass concentration in the second stage and adaptation of the microorganisms to the toxicity of the metals were sufficient for only the second stage to be used. Under these conditions, the dissolution kinetics were stable, even when iron was provided only by the comminuted PCBs.

Microbial Processing of Waste Shredded PCBs for Copper Extraction Cum Separation—Comparing the Efficacy of Bacterial and Fungal Leaching Kinetics and Yields

“…Thus, the PCBs slurry pH was lowered to <1.5 before adding the microbial inoculum by using 2N sulfuric acid. A. ferrooxidans oxidizes ferrous to ferric form and A. thiooxidans has the inherent ability to oxidize the elemental sulfur (S°) to produce H2SO4 [20,[37][38][39][40]. It was reported earlier that A. niger produces different kinds of organic acids like citric acid, oxalic acid, gluconic acid when the growth medium is enriched with sucrose as the source of energy [41][42][43].…”

Preliminary Bioleaching Experiment of E-Waste

“…Biohydrometallurgy or bio-metallurgy is a biological method for metal recovery. It is based on the same mechanism of hydrometallurgical process and uses microorganisms for production of reagents to extract metals [14,15] from primary (natural ores) or secondary resources (e-waste, i.e., PCBs) [11,16,17]. The recovery of metals via bio-metallurgy includes five different mechanisms -biotransformation, biosorption, bioaccumulation, bioleaching, biomineralization [16].…”

“…Bioleaching, also known as microbial leaching [18], is a specialized biohydrometallurgical process which utilizes either metabolic activities or products of microorganisms [17] under soft operating conditions, i.e. low temperatures and a mild pHs [15]. Bioleaching methods are based on the application of the sulphur compounds oxidizing bacteria and microorganisms.…”

Elemental Copper Recovery from e-Wastes Mediated with a Two-Step Bioleaching Process

“…However, it has been reported that the bacteria could be affected by toxic compounds which could be found in the e-waste treated [21][22][23]. For this reason, a bioleaching process carried out in two steps could be very suitable in order to avoid toxicity issues and thus, improve the extraction of metals during the bioleaching [24,25]. The goal of the first step is to obtain the Fe (III) ions required in the second step to extract the copper from the PCB waste (Eq 1).…”