Bioleaching of Gold and Silver from Waste Printed Circuit Boards by Pseudomonas balearica SAE1 Isolated from an e-Waste Recycling Facility

Abstract

Indigenous bacterial strain Pseudomonas balearica SAE1, tolerant to e-waste toxicity was isolated from an e-waste recycling facility Exigo Recycling Pvt. Ltd., India. Toxicity tolerance of bacterial strain was analyzed using crushed (particle size ≤150 µm) waste computer printed circuit boards (PCBs)/liter (L) of culture medium. The EC value for SAE1 was 325.7 g/L of the e-waste pulp density. Two-step bioleaching was then applied to achieve the dissolution of gold (Au) and silver (Ag) from the e-waste. To maximize precious metal dissolution, factors including pulp density, glycine concentration, pH level, and temperature were optimized. The optimization resulted in 68.5 and 33.8% of Au and Ag dissolution, respectively, at a pH of 9.0, a pulp density of 10 g/L, a temperature of 30 °C, and a glycine concentration of 5 g/L. This is the first study of Au and Ag bioleaching using indigenous e-waste bacteria and its analysis to determine e-waste toxicity tolerance.

Enhancement of gold and silver recovery from discarded computer printed circuit boards by Pseudomonas balearica SAE1 using response surface methodology (RSM)

“…KU053282) was taken from the author's laboratory, previously isolated from e-waste recycling facility, Haryana, India. The bacterial strain has ability to produce cyanide and showed a higher tolerance to e-waste toxicity, i.e., the EC 50 = 325.7 g/L of PCBs (Kumar et al 2017b). To culture P. balearica SAE1, 5 mL of inoculum was added to 100 mL Luria broth (LB) followed by incubation at 30 °C and 150 rpm in an incubator shaker (MaxQ 8000; Thermo Fisher Scientific).…”

“…In the first step, cells of P. balearica [5% (v/v) of inoculum having 2 × 10 8 CFU/mL] were inoculated to LB media in the absence of CPCBs in Erlenmeyer flasks of 250 mL capacity. The flaks were inoculated at respective temperature (as per CCD-RSM software) and 150 rpm for 48 h. After 48 h in the second step, sterilized CPCBs were added to LB medium followed by incubation at 150 rpm for additional time period of 7 days (Kumar et al 2017b;Pradhan and Kumar 2012). After 7 days of bioleaching, the cell biomass and ground CPCBs were removed by filtration (Grade 1, Whatman filter paper) followed by 10-min centrifugation (Eppendorf, 5804 R) at 7000 rpm.…”

“…However, these processes are expensive, energy intensive, generates large amount of spent acid, toxic gases, sludge, liquid waste, fumes of heavy metals (metals with low melting point like mercury, lead and cadmium), and may lead to formation of mixed halogenated dioxins and furans [especially, if the scrap contains plastic with brominated flame retardants (BFRs)] (Kaya 2016;Sahni et al 2016). The hydrometallurgical/pyrometallurgical methods are rapid but low metal recovery rate, loss of precious metals during recovery, environmental impacts and high cost have push the development of alternative methods of metal recovery from e-waste (Kumar et al 2017b;Priya and Hait 2017;Sun et al 2017). In this context, bioleaching process recovers metals from e-waste and low-grade ores in an ecofriendly, cost economic and energy conservative way (Priya and Hait 2017).…”

“…Although bioleaching process is slow and time consuming yet increases the metal recovery due to higher extraction rate from low-grade ores/complex sources like e-waste where thermal and physico-chemical methods are not economical (Brandl et al 2001). Other than this, the low energy requirement, minimum sludge generation, environmental compatibility and low cost of bioleaching process make it suitable from industrial point of view (Kumar et al 2017b;Priya and Hait 2017). Bioleaching using cyanogenic microorganisms (C. violaceum; B. megaterium; Pseudomonas sp.)…”

Effect of Graphite on Copper Bioleaching from Waste Printed Circuit Boards

“…This is because friction between particles was promoted with the increase of pulp concentration, hindering bacterial growth. In fact, the bacteria's tolerance was reduced in the presence of a large quantity of heavy-metal species [19,20]. On the other hand, Figure 7b and Equations (2) and (3) [21] indicate that the redox potential initially decreased with increasing bioleaching time due to the presence of Figure 7 shows the bacterial-growth curve, redox potential (E h ), and copper leaching for assays with up to 10% (w/v) pulp density.…”