Bio-Assisted Leaching of Non-Ferrous Metals from Waste Printed Circuit Boards—Importance of Process Parameters

Abstract

The effect of varying process parameters during bio-catalyzed leaching of metals from end-of-life printed circuit boards (PCBs) was investigated. Fragmented PCBs (under 2 mm) were subjected to an indirect bioleaching in a stirred tank reactor while pulp density, pH and initial ferric iron content were varied. An iron oxidizing Acidithiobacillus ferrooxidans 61 microbial strain was used to generate the lixiviant through oxidizing Fe(II) to Fe(III). Chemically generated Fe(III) was tested as lixiviant under the same conditions as the biological one for comparative purposes. Cell enumeration during leaching and microscopic observations of the input and leached PCBs were conducted in parallel to shed light on the observed phenomena. The degree of bringing metals in solution was found to depend mainly on ferric iron concentration and pH. For the entire duration being always kept as 24 h, substantial portion of Cu (~87%) was extracted respectively at 1% pulp density (PD), 15.5 g/L Fe3+ and pH 1. For Zn and Ni, nearly 100% recovery was observed at 5% PD, 18 g/L Fe3+ and pH 1.1. The achieved results offer possibilities for further studies at higher pulp density, to ultimately render the bioleaching approach as enabling economical and environmentally friendly technology for urban mining of non-ferrous metals.

Biotechnological Recycling and Recovery of Metals from Waste Printed Circuit Boards and Spent Li-Ion Batteries—Selected Results from the ERAMIN EU BaCLEM Project

“…In the case of PCBs prior to bioleaching, the input samples were pre-treated by boiling with NaOH to remove the organic coating. The chemical assay for the PCBs reported the following main metals content for a representative sample: Cu (21.53%), Al (6.95%), Ni (5.12%), Pb (3.2%) and Fe (3.86%) [10].…”

“…In this study, leaching with Fe 3+ derived from Acidithiobacillus ferrooxidans 61 biogenic solution at different pH was investigated at 1% pulp density [10]. Figure 3a,b shows the results of Cu and Ni recoveries at 1% pulp density under different pH and Fe 3+ concentrations for 24 h. The optimum recovery of Cu (87%) was reached at 15.5 g/L Fe 3+ , whereas, the maximum Ni (100%) recovery was reached at 13.5 g/L Fe 3+ (Figure 3a).…”

Bioleaching of Metals from E-Waste Using Microorganisms: A Review

“…Other factors that affect metal bioleaching include the effectiveness of the leaching methods: one-step, two-step, or spent medium bioleaching; and the mode of operation: heap, column, shake-flask, or bioreactor operation [6,123]. These parameters influenced bioleaching efficiency autonomously or as combined [124,125]. Some of the various factors that affect bioleaching are discussed below.…”

“…The pH of the bioleaching medium is a crucial factor that influences the mobilization of metals from e-waste, since it affects the growth of microorganisms and biolixiviant production. However, a deviation in the optimum pH requirement of the organisms can have a detrimental effect on their growth, metabolic activities, and leaching efficiency [125]. The pH requirements differ among different groups of microbes.…”

“…It is the amount of a solid matrix (e-waste) present in a solution. A higher liquid-to-solid ratio signifies a low pulp density [125]. A higher pulp density contributes to the toxicity of the e-waste, affecting the growth and metabolic activity of organisms [130].…”