Integrated bioleaching of copper metal from waste printed circuit board-a comprehensive review of approaches and challenges

Recovery of precious metals from waste printed circuit boards though bioleaching route: A review of the recent progress and perspective

The rapid proliferation of electronic waste (e-waste), including waste printed circuit boards (WPCBs), has exerted immense pressure on the environment. The recovery of precious metals from WPCBs not only serves as an effective means of alleviating this environmental burden but also generates economic value. This review focuses on bioleaching, an environmentally friendly method for extracting precious metals from WPCBs. Under various conditions, this method has achieved leaching rates of 30%-73% for Au and 33.8%-90% for Ag. However, there is a relative scarcity of studies on the bioleaching of precious metals from WPCBs. In this paper, we provide an overview of the current status of bioleaching for precious metals from WPCBs and describe the underlying mechanisms. We also briefly outline the influence of various process factors on leaching efficiency. While this review underscores the considerable potential of bioleaching in WPCBs applications, certain limitations hinder the engineering-scale application of the technology. Consequently, this paper describes the current enhanced processes for enhancing leaching efficiency. Overall, this review can serve as a valuable reference for future research endeavors, ultimately promoting the widespread utilization of bioleaching for the recovery of precious metals from WPCBs.

Thermally Reduced Graphene Oxide Membranes Revealed Selective Adsorption of Gold Ions from Mixed Ionic Solutions

The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au3+ and other ions by rGO membranes. The maximum adsorption capacity for Au3+ ions was about 16 times that of Cu2+ ions and 10 times that of Fe3+ ions in a mixture solution with equal proportions of Au3+/Cu2+ and Au3+/Fe3+. In a mixed-ion solution containing Au3+:Cu2+:Na+:Fe3+:Mg2+ of printed circuit board (PCB), the mass of Au3+:Cu2+:Na+:Fe3+:Mg2+ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector.

Potential and current practices of recycling waste printed circuit boards: A review of the recent progress in pyrometallurgy

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated.

Fungal bioleaching of e-waste utilizing molasses as the carbon source in a bubble column bioreactor

Mobile phones are known as the most widely used electronic instruments, and an enormous number of discarded mobile phones are generated. The present work used a pure culture of Penicillium simplicissimum in a bubble column bioreactor to extract Cu and Ni from mobile phone printed circuit boards (MPPCBs) waste. Molasses was used as an efficient carbon source to enhance bioleaching efficiency and increase the cost benefits. The adaptation phase was done at Erlenmeyer flasks to reach 40 g/L of MPPCBs powder. The most significant parameters, including the mass of MPPCBs powder, aeration, molasses concentration, and their interaction, were optimized in order to leach the maximum possible Cu and Ni using central composite design in response surface methodology (RSM). The model p-values for Cu and Ni recovery were 0.0030 and 0.0348, respectively, emphasizing the model's accuracy. 96.94% of Cu was recovered under 8.8% (v/v) of molasses, aeration rate of 0.29 (l/min), and MPPCBs powder of 10 g/L. The optimized condition of Ni leaching was 1.9% (v/v) of molasses, aeration rate of 0.37 (l/min), and MPPCBs powder of 10 g/L, resulting in 71.51% recovery. The present article demonstrated the great potential of P. simplicissimum to improve metal recovery from e-waste utilizing molasses and bubble column bioreactors.

Electrochemical oxidation of copper-clad laminate for manufacturing printed circuit boards via bioleaching by the fungus Phanerochaete chrysosporium

The leaching and electrochemical oxidation of the copper-clad laminate for manufacturing printed circuit boards were investigated in systems with and without the fungus P. chrysosporium, which yielded the copper-leaching efficiencies of 54% and 7.0%, respectively. In particular, the formation of a biofilm on the electrode surface reduced the open-circuit potential and increased the corrosion level, and the degree of increase and the rate of change of the current density in the fungal leaching system were higher than those of the sterile system. In addition, the cyclic voltammetry curves showed oxidation peaks that correspond to the oxidation of Cu to Cu²⁺. Further, for the fungal leaching system, the peak potential was highly negative and the curve area and peak current density were relatively high. Moreover, the electrochemical polarization parameters and the impedance characteristics were affected by the fungus, and the leaching systems were controlled by charge transfer and diffusion. In summary, P. chrysosporium can accelerate the leaching of copper as a result of the formation of extracellular electron transfer-induced microbiologically influenced corrosion (EET-MIC) and metabolite-induced microbiologically influenced corrosion (M-MIC). The enzymes and organic acids, which act as fungal metabolites, participate in the leaching of copper.

Recovery of valuable metals from waste printed circuit boards using organic acids synthesised by Aspergillus niveus

Organic acids such as citric acid, itaconic acid and oxalic acid synthesised by Aspergillus niveus were used for the bioleaching of metals from waste printed circuit boards. Bioleaching of valuable metals was performed in one‐step, two‐steps and spent medium approaches using A. niveus. In the absence of waste printed circuit boards (WPCBs), the dry cell weight of A. niveus was higher when compared with the presence of WPCBs. Variations in the dry cell weight were observed for the presence of different particle sizes. The increase in itaconic acid and oxalic acid synthesis was found at a reduced particle size (60–80 mesh) and reached the maximum titre of itaconic acid (22.35 ± 0.87 mM) and oxalic acid (12.75 ± 0.54 mM) in 12 days during the two‐step bioleaching. The maximum recovery of 75.66% Zn, 73.58% Ni and 80.25% Cu from WPCBs was achieved in 15 days in two‐step leaching with particle sizes of the mesh being 60–80.

Bioleaching of critical metals from waste OLED touch screens using adapted acidophilic bacteria

The mobile phone is a fast-growing E-waste stream that includes hazardous substances and valuable metals. Smartphone touch screens (SPTS) contain a considerable amount of critical metals, such as indium and strontium that can be recovered from end of life devices as a secondary resource. Bioleaching is an emerging and environmentally friendly method for metal recovery from electronic waste. In the present study, bioleaching was assessed for the extraction of indium and strontium from organic light emitting diode type smartphone touch screens. A statistical approach based on the response surface methodology was successfully applied. The effects of influential variables: pH, ferrous sulfate, elemental sulfur, and solid content and their interactions on indium and strontium recovery using adapted Acidithiobacillus ferrooxidans were evaluated. Under optimum conditions (ferrous sulfate: 13.0 g/L; solid content; 3.0 g/L; elemental sulfur: 5.6 g/L; and initial pH of 1.1), a complete indium extraction was observed, with a concentration in solution of about 200 mg/L indium. As concerns strontium, a 5% extraction efficiency was observed, which, even if quite low, resulted in a relatively high strontium concentration in solution, around 3000 mg/L, due to its high content in the solid (2%). This work opens new perspectives in the application of clean technologies for the extraction of valuable metals, such as indium and strontium from smartphone screens.

Studies on leaching characteristics of electronic waste for metal recovery using inorganic and organic acids and base

In this paper, we report leaching of precious and scattered metals such as gold (Au), copper (Cu), nickel (Ni), zinc (Zn), iron (Fe), and lead (Pb) from printed circuit boards of scrap mobile phones by hydrometallurgical process using inorganic acid, organic acid and base. The amount of metals leached by different leachants are quantified using atomic absorption spectroscopy. Among various inorganic acids, aqua regia (mixture of nitric acid (HNO₃) and hydrochloric acid) is found to be the strongest leachant for most of the metals such as Zn (2.04 wt %), Fe (17.90 wt %), Ni (0.66 wt %), Pb (5.86 wt %) and Au (0.04 wt %). The basic leachant, ammonium thiosulphate is found to be very effective in leaching of Au (0.03125 wt %). The dissolution of Cu in HNO₃ gives the highest amount of Cu in the solvent, that is, ∼ 7.52 wt %. The metallic phases present in the electronic waste before and after leaching are identified by X-ray diffraction analysis. The microscopic structure has been studied using a scanning electron microscope which depicts erosion of the structure after leaching.

Biohydrometallurgy as an environmentally friendly approach in metals recovery from electrical waste: A review

Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.

Bench scale microbial catalysed leaching of mobile phone PCBs with an increasing pulp density

The study reports the effect of increasing pulp density on the bio-catalyzed leaching of metals from waste mobile phone printed circuit boards. Mixed microbial consortia of iron and sulfur-oxidizing microorganisms were used for batch bioleaching at varying pulp density of 7%, 10% and 15% (w/v). The copper content in the feed material was 26.3% (w/w) and the prime focus was to recover maximum copper along with other minor metals, such as zinc, aluminum, and nickel. All the bioleaching experiments resulted with 98-99% of copper recovery together with reasonable extraction Zn, Al, and Ni. The optimum copper recovery from bioleaching experiments demonstrates the possibility of scaling up with high pulp density, which could be economical as well as eco-friendly.

A visualized investigation on the intellectual structure and evolution of waste printed circuit board research during 2000-2016

Waste printed circuit boards (WPCBs) containing various metals and hazardous materials are considered as a secondary resource and an environmental pollution source. A systematic overview of WPCB study was conducted by using CiteSpace. The relevant knowledge of 242 documents was collected from SCI-Expanded database (SCIE) and saved as txt files. A 556-node and 636-link network and 17 clusters were obtained. Based on co-citation network, nonmetallic material treatment and recycling, metal recovery, pyrolysis treatment, and new technology development were successively the most attractive fields in the study period. Timeline pattern showed that mechanical processing attracted great attention in the initial period and profitability assessment was the latest hot spot in WPCB study. The results could provide a reference for future work in WPCB field.

Separation of metals from metal-rich particles of crushed waste printed circuit boards by low-pressure filtration

In recent years, recovery of metals from electronic waste (e-waste) within China has become increasingly important due to potential supply risk of strategic raw material and environmental concerns. Printed circuit boards (PCBs) contain lots of valuable metals together with plenty of hazardous materials, which are considered both an attractive secondary resource and an environmental contaminant. Pressure filtration is an effective and environmentally friendly method for separating and recycling comminuted PCBs. Present work is focused on the recovery of metals from PCBs by low-pressure filtration separation. A two-stage separation process was adopted to selectively recover Pb-Sn and Cu alloys at different temperatures. The results showed that the temperature and pressure had great influence on the recovery of metals in the separation process. After the two-stage separation process, the total recoveries of Pb, Sn, Cu and Zn were 79.96%, 89.91%, 88.80% and 68.57% respectively, when the temperature is 1350 °C and the pressure is 0.30 MPa. This is a high-efficiency, short-flow, clean-production, and environmental-friendliness that can improve the recovery of metals and realize the reuse of waste resources.

Bioleaching of metals from WEEE shredding dust

A bioleaching process developed in two separate steps was investigated for the recovery of base metals, precious metals and rare earth elements from dusts generated by Waste Electrical and Electronic Equipment (WEEE) shredding. In the first step, base metals were almost completely leached from the dust in 8 days by Acidithiobacillus thiooxidans (DSM 9463) that lowered the pH of the leaching solution from 3.5 to 1.0. During this step, cerium, europium and neodymium were mobilized at high percentages (>99%), whereas lanthanum and yttrium reached an extraction yield of 80%. In the second step, the cyanide producing Pseudomonas putida WSC361 mobilized 48% of gold within 3 h from the A. thiooxidans leached shredding dust. This work demonstrated the potential application of biohydrometallurgy for resource recovery from WEEE shredding dust, destined to landfill disposal, and its effectiveness in the extraction of valuable substances, including elements at high supply risk as rare earths.

Interaction between Diethyldithiocarbamate and Cu(II) on Gold in Non-Cyanide Wastewater

A surface-enhanced Raman scattering (SERS) detection method for environmental copper ions (Cu2+) was developed according to the vibrational spectral change of diethyldithiocarbamate (DDTC) on gold nanoparticles (AuNPs). The ultraviolet-visible (UV-Vis) absorption spectra indicated that DDTC formed a complex with Cu2+, showing a prominent peak at ~450 nm. We found Raman spectral changes in DDTC from ~1490 cm-1 to ~1504 cm-1 on AuNPs at a high concentration of Cu2+ above 1 μM. The other ions of Zn2+, Pb2+, Ni2+, NH₄⁺, Mn2+, Mg2+, K⁺, Hg2+, Fe2+, Fe3+, Cr3+, Co2+, Cd2+, and Ca2+ did not produce such spectral changes, even after they reacted with DDTC. The electroplating industrial wastewater samples were tested under the interference of highly concentrated ions of Fe3+, Ni2+, and Zn2+. The Raman spectroscopy-based quantification of Cu2+ ions was able to be achieved for the wastewater after treatment with alkaline chlorination, whereas the cyanide-containing water did not show any spectral changes, due to the complexation of the cyanide with the Cu2+ ions. A micromolar range detection limit of Cu2+ ions could be achieved by analyzing the Raman spectra of DDTC in the cyanide-removed water.

Recovery of precious metals from waste streams

As there is a high potential for microbe‐based technologies to bring the recovery of metals from waste streams to an ecologically friendly and financially reasonable level, it is worth to invest efforts into the advancement of these biotechnologies in the future.

Bioleaching of electronic waste using bacteria isolated from the marine sponge Hymeniacidon heliophila (Porifera)

The bacteria isolated from Hymeniacidon heliophila sponge cells showed bioleaching activity. The most active strain, Hyhel-1, identified as Bacillus sp., was selected for bioleaching tests under two different temperatures, 30°C and 40°C, showing rod-shaped cells and filamentous growth, respectively. At 30°C, the bacteria secreted substances which linked to the leached copper, and at 40°C metallic nanoparticles were produced inside the cells. In addition, infrared analysis detected COOH groups and linear peptides in the tested bacteria at both temperatures. The Hyhel-1 strain in presence of electronic waste (e-waste) induced the formation of crust, which could be observed due to bacteria growing on the e-waste fragment. SEM-EDS measurements showed that the bacterial net surface was composed mostly of iron (16.1% w/w), while a higher concentration of copper was observed in the supernatant (1.7% w/w) and in the precipitated (49.8% w/w). The substances linked to copper in the supernatant were sequenced by MALDI-TOF-ms/ms and identified as macrocyclic surfactin-like peptides, similar to the basic sequence of Iturin, a lipopeptide from Bacillus subtilis. Finally, the results showed that Hyhel-1 is a bioleaching bacteria and cooper nanoparticles producer and that this bacteria could be used as a copper recovery tool from electronic waste.

Evaluating waste printed circuit boards recycling: Opportunities and challenges, a mini review

Rapid generation of waste printed circuit boards has become a very serious issue worldwide. Numerous techniques have been developed in the last decade to resolve the pollution from waste printed circuit boards, and also recover valuable metals from the waste printed circuit boards stream on a large-scale. However, these techniques have their own certain specific drawbacks that need to be rectified properly. In this review article, these recycling technologies are evaluated based on a strength, weaknesses, opportunities and threats analysis. Furthermore, it is warranted that, the substantial research is required to improve the current technologies for waste printed circuit boards recycling in the outlook of large-scale applications.