Computer Printed Circuit Boards Research Articles

Investigation of the Impact of Electrochemical Hydrochlorination Process Parameters on the Efficiency of Noble (Au, Ag) and Base Metals Leaching from Computer Printed Circuit Boards

The development of environmentally friendly and energy-saving processes for recycling electronic waste (e-waste) is still relevant today. The research presented in this work relates to hydrometallurgy, namely, the electrochemical leaching of metals from e-waste under the action of alternating current (AC) into hydrochloric acid solutions of electrolytes, and can be used for leaching both noble and non-ferrous metals from secondary raw materials. The main object of the study was disintegrator-crushed mixed computer PCBs metal-rich powders with a particle size (d) of <90 µm. The impact of such leaching process parameters as temperature (Tel) and composition of the electrolyte solution, AC density (i) on the electrodes, experiment duration (tex) while maintaining a constant electrolyte temperature (60 °C, 70 °C, and 80 °C) on the metal (Au, Ag, Cu, Al, Ni, Pb, Sn, Ti, Zn, and Fe) leaching efficiency has been studied. In addition, under similar experimental conditions, but without external control of Tel, the kinetics of metal leaching from raw material powders obtained via PCBs single and double crushing in a disintegrator has been also presented. Comparison of raw material powders obtained from different batches of the source material showed both the variability of its chemical composition and the different kinetics of Au and Ag leaching under the same experimental conditions. The optimal conditions for pretreatment of the raw material obtained by single crushing in a disintegrator (CHCl = 6 mol·L−1, i = 0.88 A·cm−2, tex = 1 h, solid-to-liquid ratio—8.6 g·L−1 and without external control of Tel) were determined. It has been shown that this electrochemical pretreatment is accompanied by transition of only base metals into the electrolyte solution, making it possible to significantly reduce their concentration in the final solution. Under pretreatment conditions, the following degree of metal leaching (RMe) has been established: RCu = 98.2%, RAl = 62.8%, RNi = 53.4%, RPb = 93.2%, RSn = 98.0%, RTi = 88.5%, RZn = 61.6%, and RFe = 78.8%. As a result of a subsequent two-hour electrochemical treatment of a solid residue, the degree of leaching of gold and silver was 73.6% and 86.7%, respectively. The presented results provide a broader understanding of the possibility of using the proposed electrochemical hydrochlorination method for noble and base metals leaching from waste PCBs. The novelty and practical value of this research is a validation of the developed technology in laboratory conditions using the real batch of the PCBs. This approach may also be useful to researchers involved in the recycling of other types of secondary raw materials.

Statistical Optimization of Bioleaching for Simultaneous Recovery of Cu, Sn, Pb, and Zn from Computer-Printed Circuit Boards

Electronic garbage is one of the fastest-growing waste streams. Its disposal and appropriate management are a worldwide concern. Printed circuit boards (PCBs) are critical components in contemporary electronic gadgets that contain toxic elements. Bioprocessing of PCBs for metal recovery employing microbial methods has evolved as a green solution in metallurgical operations. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were used in this study to leach metals from powdered waste PCBs. The RSM is used for optimizing the leaching conditions. The optimal conditions obtained were a bacterial activation period of 28 days, a pulp density of 23 g/L, and a temperature of 31°C. A confirmatory experiment under these optimal circumstances yielded recovery rates of Cu2+, Sn2+, Pb2+, and Zn2+ of 95.62%, 96.27%, 95.6%, and 98.25%, respectively.

Biolixiviation of Metals from Computer Printed Circuit Boards by Acidithiobacillus ferrooxidans and Bioremoval of Metals by Mixed Culture Subjected to a Magnetic Field.

Crushed and ground printed circuit board (PCB) samples were characterized to evaluate copper, lead, and aluminum using X-ray fluorescence spectroscopy (XRF) and the morphology was done by scanning electron microscopy (SEM). The XRF characterizations showed 0.12% lead, 3.72% copper, and 12.73% aluminum in the PCBs. The metal solubilization experiments using Acidithiobacillus ferrooxidans indicated higher values of total metal solubilization when the initial pH of the inoculum was adjusted. However, these experiments did not show higher metal solubilization by bioleaching. The sequential bioremoval experiments using mixed culture after bioleaching assays with A. ferrooxidans with initial adjustment of inoculum pH and without applying a magnetic field removed 100% of Al, 27.34% of Cu, and 96.43% of Pb from the lixiviate medium; with magnetic field application, 100% of Al, 83.82% of Cu, and 98.27% of Pb were removed. A similar bioleaching experiment without inoculum pH adjustment and without field application achieved 99.74% removal for Cu and 91.92% for Pb. When the magnetic field was applied, 100% of Cu and 95.76% of Pb were removed. Bioreactors with a magnetic field do not show significantly better removal of any of the metals analyzed.

Exploring bioleaching potential of indigenous Bacillus sporothermodurans ISO1 for metals recovery from PCBs through sequential leaching process.

The low efficiency and selectivity limitations of biohydrometallurgy technique compel the researchers to explore novel microbial strains acclimated to metal existence site with higher toxicity tolerance and bioleaching capability in order to improve the role of bioleaching process for e-waste management. The current study aimed to explore bioleaching potential of indigenous Bacillus sporothermodurans ISO1; isolated from metal habituated site. The statistical approach was utilized to optimize a variety of culture variables including temperature, pH, glycine concentration and pulp density that impact bio-cyanide production and leaching efficiency. The highest dissolution of Cu and Ag, 78% and 37% respectively, was obtained at 40 °C, pH 8, glycine concentration 5 g L-1, and pulp density 10 g L-1 through One Factor at a Time (OFAT), which was further increased up to 95% Cu and 44% Ag recovery through the interactive effect of key factors in the Response Surface Methodology (RSM) approach. Furthermore, Chemo-biohydrometallurgy approach was utilized to overwhelm the specificity limitation; as higher concentration of Cu in computer printed circuit boards (CPCBs) causes interference to recover other metals. The sequential leaching through ferric chloride (FeCl3), recovered Cu prior to bio-cyanidation by B. sporothermodurans ISO1 and resulted in the improved leaching of Ag (57%), Au (67%), Pt (60%), etc. The current work reports on B. sporothermodurans ISO1, a new Bacillus strain that exhibits highest toxicity tolerance (EC50 = 425 g L-1) than earlier reported stains and has higher leaching potential that can be implemented to large-scale biometallurgical process for e-waste treatment to achieve the agenda of sustainable development goal (SDG) under the strategies of urban mining.

Leaching of Gold and Copper from Printed Circuit Boards under the Alternating Current Action in Hydrochloric Acid Electrolytes

Modern technologies for recycling electronic waste (e-waste) have high economic efficiency and environmental safety requirements. Among the existing technologies, hydrometallurgy is considered to be the most promising technology for e-waste recycling. Increasing attention paid to the chlorination method is associated with the complex recycling of low-grade ores containing noble metals and the raw materials of secondary polymetallic. In this paper, we propose a new scheme for leaching metals from computer printed circuit boards (PCBs) pre-crushed in a disintegrator: The processes of chlorine production and hydrochlorination are implemented in one reactor under the action of an alternating current (AC) of industrial frequency (50 Hz). Three fine fractions of raw material powders with particle size d < 90 µm, d = 90–180 µm, and d = 180–350 µm were used as research objects and the finest fraction of the raw material (d < 90 µm) was studied in more detail. It was found that complete leaching of gold is achieved from fractions of raw materials with a particle size d = 90–180 µm and d = 180–350 µm, containing 277 ppm and 67 ppm of the gold, respectively, at an experiment duration (tex) of 2 h, a current density (i) of 0.66 A·cm−2, and a solid/liquid (S/L) ratio of 8.6 g·L−1. Under the same conditions of the electrochemical leaching process from the fraction of raw materials with a particle size of d < 90 µm and a gold content of 824 ppm, the degree of metal leaching is 80.5%. At the same time, with an increase in particle size in the raw material fractions from d < 90 µm to d = 180–350 µm and a copper content in the raw material from 1.40% to 6.13%, an increase in the degree of its leaching from 81.6% to 95.2%, respectively, is observed. In the framework of the preliminary study presented in this work, for the finest raw material fraction with d < 90 μm the highest gold leaching degree (86.3%) was achieved under the following experimental conditions: tex= 4 h, CHCl = 6 M, i = 0.88 A·cm–2, S/L ratio—8.6 g·L–1 and the highest copper leaching degree (94.2%) was achieved under the following experimental conditions: tex = 2 h, CHCl = 6 M, i = 0.64 A·cm–2, and S/L ratio—2.9 g·L–1.

Extraction of silver from computer printed circuit boards wastes by supercritical fluids: pretreatment study

Extraction of silver from computer printed circuit boards wastes by supercritical fluids: pretreatment study

Simultaneous leaching of Cu, Al, and Ni from computer printed circuit boards using Penicillium simplicissimum

A short lifespan and increased consumption patterns make e-waste the world's fastest-growing waste stream. Computers are one of the most significant parts of e-waste. Recycling of e-waste has been introduced as the main solution to deal with environmental problems and to save natural mines. This research aims to investigate the bioleaching of Cu, Ni, and Al from computer printed circuit boards (CPCBs) using Penicillium simplicissimum. The adaptation phase began at 1 g/l CPCBs powder with 107 spores and final pulp density was reached at 30 g/l. The most effective parameters including pulp density, initial pH, and the sucrose concentration were optimized to achieve maximum simultaneous leaching efficiency of Cu, Ni, and Al. The results showed the main mechanism of Al and Ni leaching was acidolysis, while complexoysis was the main mechanism for leaching of Cu. The optimal conditions of 60 g/l sucrose concentration, 16 g/l pulp density, and initial pH 6 led to leaching of 100% Cu, 70% Ni, and 98% Al. Additionally, the initial CPCBs sample and the bioleaching residue were analyzed using XRD, HPLC, SEM, and FTIR. The HPLC results confirmed that gluconic and oxalic acids were the main metabolites produced by P. simplicissimum. The SEM micrograph revealed the effectiveness of the bioleaching process in metal leaching. FTIR spectra validated conversion of the molecular structure to simpler materials, as well as the presence of HIPS, PC, and PPO in CPCBs waste powder.

Investigating critical parameters for bioremoval of heavy metals from computer printed circuit boards using the fungus Aspergillus niger

In this article, bioleaching of computer printed circuit boards (CPCBs) was examined using Aspergillus niger with one-step, two-step, and spent-medium bioleaching methods. Four effective parameters were optimized using response surface methodology (RSM) to achieve maximum recovery of Cu and Ni. Under optimal conditions – pH of 5.15, pulp density of 10 g/l, 1E+007 spores of A.niger, and 4.5 days for the sample adding time − 97% and 74% of Cu and Ni were recovered, respectively. Two-step bioleaching and spent medium bioleaching were respectively identified as the best methods for maximizing Cu and Ni recovery. Fungi deteriorate the sample mainly by it is chemical action like producing acids. Surface morphology results confirmed the metabolites produced by the fungus—corrosive chemicals—eroded the particles of the e-waste sample during the bioleaching time. The mapping and energy dispersive X-ray (EDAX) of the initial sample and the processed sample validated that bioleaching was quite effective. The overall results indicate that Cu and Ni from e-waste can be recovered through the bioleaching process using A. niger. The addition time (day) of the sample to the solution plays an important role in metal recovery using A. niger. Acid production by the fungi increases the metal recovery, while biocrystallization of heavy metals decreases the recovery. This paper proved the great potential of the biohydrometallurgical route mediate by Aspergillus niger strain for recovering heavy metals from electronic wastes under defined optimal condition, two-step process, 30 °C, and shaking rate of 130rpm.

Multivariate study of a novel hydrometallurgical route employing chloride/hypochlorite for leaching silver from printed circuit boards

The rapidly expanding use of electronic products has led to the generation of very large quantities of waste electrical and electronic equipment (WEEE). This waste essentially consists of polymeric, ceramic, and metallic materials, with the metal fraction including noble and base metals, which may be toxic. It is therefore important to recycle printed circuit boards (PCBs) for both economic and environmental reasons, especially since this solid waste contains noble metals (gold and silver). Given this background, the aim of the present work was to develop a hydrometallurgical route for leaching of the silver present in computer PCBs, using a combination of sodium chloride and calcium hypochlorite as the lixiviants. Optimization was performed of the following independent variables: (i) pulp density, (ii) calcium hypochlorite concentration, (iii) sodium chloride concentration, and (iv) leaching time. Multivariate experimental designs were employed, consisting of a 24 full factorial design and response surface methodology with a spherical central composite design (CCD). The operational conditions were varied according to the mathematical equation obtained from the CCD, in order to find their best values which resulted in the maximum Ag extraction. The optimal conditions for the leaching of silver were a pulp density of 48 g L−1, calcium hypochlorite concentration of 165 g L−1, sodium chloride concentration of 65 g L−1, and extraction time of 200 min, resulting in 95.29 ± 0.72% extraction of silver. Silver was dissolved by forming complexes with chloride, being AgCl4 aq3− the predominant specie. In summary, the hydrometallurgical route employed in this work enabled satisfactory and environmentally favorable extraction of silver.

Evaluating the optimal digestion method and value distribution of precious metals from different waste printed circuit boards

Knowing the metal content of electronic waste is essential to evaluate metal recovery. Lack of a standard method for digestion of precious metals from electronic waste has resulted in difficulty in comparison to the efficiency of recovery. In this study, different precious metal digestion methods and economic value of precious metals from different types of waste printed circuit boards in different fraction sizes, including computer printed circuit boards, mobile phone printed circuit boards, television printed circuit boards, fax machine printed circuit boards, copy machine printed circuit boards, and central processing unit were examined. The optimal digestion method using aqua regia, hydrogen peroxide, hydrofluoric acid, and boric acid was adopted. The precious metal content was analyzed to answer what precious metals and types of printed circuit boards is preference. The results presented the following order of total value of precious metals ( $$\sum {W_{ti} \Pr_{ti} }$$ ): central processing unit > Mobile phone > Copy > Fax > Computer > Television. Among the precious metals, gold and palladium were, respectively, attributed to the highest value distribution. The average values of the precious (gold and palladium) and all of the metals of electronic waste are about 19 and 21 times higher than the average cost of the world’s top ten mines.

Neural network prediction of bioleaching of metals from waste computer printed circuit boards using Levenberg‐Marquardt algorithm

AbstractThe applicability of artificial neural network (ANN) to predict the bioleaching of metals using from computer printed circuit boards (CPCB) and the influence of process parameters were studied. The influence of process parameters initial pH (1.6‐2.4), pulp density (2%‐13%), and the initial volume of Inoculum (5%‐25%) were investigated on the rate of bioleaching of metals from CPCB. Network inputs were fed as initial pH, pulp density, and inoculum volume and with the extraction of Cu, Ag, and Au as output. The ANN was developed using the Levenberg‐Marquardt algorithm and trained for modeling and prediction. The most fitting architectures for Cu, Ag, and Au were [4‐5‐5‐2‐1], [4‐7‐5‐2‐1], [4‐7‐1‐1‐1] trained with Levenberg‐Marquardt algorithm, respectively. The R values were observed to be 0.996, 0.997, and 0.993 for Cu, Ag, and Au extraction predictions, respectively. The genetic algorithm model defined by ANN was used to achieve maximum extraction rates for Cu, Au, and Ag. The predicted data showed that there is a great capability of using ANN for the prediction of Cu, Ag, and Au extraction from CPCB through bioleaching process. Hence, the ANN model can be used to control the operational conditions for improved metals extraction through bioleaching.

ZnO/CuO nanocomposites from recycled printed circuit board: preparation and photocatalytic properties.

Cost-effective recycling of e-waste (from computer printed circuit boards, PCB's) for the synthesis of metal oxide nanocomposites is demonstrated. Metals in electronic components of waste memory slots were leached out using nitric acid (HNO3). Compositional analyses of the filtrate obtained after leaching were 66wt.% Cu, 27.7wt.% Zn, and 6.2wt.% Ni. The leached out metal salt solutions were subjected to alkaline hydrothermal treatment to synthesize nanocomposites. Two nanoparticle samples were prepared, one without any stabilizing agent and another sample with PVP as a stabilizing agent. XRD, HR-XRD, HR-TEM, UV-DRS, UV-visible spectroscopy was used to characterize the as-prepared metal oxide nanoparticles. The analysis showed the formation of ZnO/CuO nanocomposites only. No nickel oxide component was precipitated under the studied hydrothermal experimental conditions. Most of the ZnO/CuO nanocomposite particles obtained by this route consisted of fine ZnO nanostructures precipitated on CuO cores. The ZnO and CuO components exhibit both direct and indirect band gaps in the visible range. The nanocomposites demonstrate good visible light photo-Fenton methyl orange (MO) degradation by pseudo-zero order kinetics.

Content evaluation of different waste PCBs to enhance basic metals recycling

This research aims to expand the body of information that researchers require before starting electronic waste (E-waste) recovery experiments. With this purpose, the basic metal contents, alkalinity, polymer components, iron magnetic separation, metal recovery priority and economic values of different types of waste printed circuit boards (PCBs) were investigated. The selected wastes were computer PCBs (CPCBs), CPCBs with wires, mobile phone PCBs (MPPCBs), television PCBs (TVPCBs), fax machine PCBs (FPCBs), copy machine PCBs (COPCBs) and central processing units (CPUs). These E-wastes were prepared in the three fraction sizes of F1<1 mm, 1 < F2<3 mm, and 3 < F3<8 mm to evaluate the metal contents of different PCB fractions. The plastics of some samples were separated through the shaking table method. Magnetic separation of the iron particles attributed the highest amounts of separated iron to the CPCBs (84%) and MPPCBs (76%). Among the investigated E-wastes, the TVPCBs and CPCBs had the highest percentages of plastic (68 and 57%, respectively). Fourier transform infrared (FTIR) spectroscopy declared the presence of polyphenylene oxide (PPO) and polycarbonate (PC) in all evaluated PCBs. The highest quantities of Cu, Ag, Ni and Ti corresponded to the F1 fraction for all E-waste samples while the economic values of the E-wastes were as follows: CPU > FPCBs > MPPCBs > COPCBs > TVPCBs > CPCBs. Accordingly, FPCBs and COPCBs were determined as the high value E-wastes for metal recovery. In addition, Cu, Ag and Sn respectively were found to be the most economic basic metals that should be recovered from most PCBs. Finally, pH analysis of the samples demonstrated that E-waste alkalinity is due to the presence of alkaline metals not plastics.

Influence of Thermal Treatment on Copper Extraction from Electronic Wastes

The results of studying the influence of the preliminary thermal treatment of crushed electronic waste (EW) at a temperature of 450°C on the copper extraction degree during the subsequent leaching of materials by solutions of nitric acid are presented. The waste of the electronic industry, in particular, automobile microcircuits and computer printed circuit boards, is chosen as a research object. It is experimentally determined that the percentage of the organic phase in the composition of the research object varies within the range of 20–25% of the mass of the crushed raw material. The results of thermogravimetric analysis (TGA) and X-ray fluorescence analysis (XRF) show that the maximum degree of organic removal and formation of oxide forms of metals are observed in the temperature range 400–450oC. A mathematical model of the copper leaching process from EW with nitric acid solutions is obtained. The optimum parameters for the process are found: the temperature in the system is 75°C, the duration of leaching is 150 min, and the concentration of acid is 4 M with the maximum copper extraction to the solution being 98%. A comparative analysis of leaching processes of two types of materials (after thermal treatment and without thermal treatment) was carried out. It is experimentally confirmed that, for materials after preliminary thermal treatment, more completed copper leaching from EW with nitric acid solutions of lower concentration is provided when compared to the leaching of raw materials without thermal treatment. It is proved that, due to the preliminary thermal treatment of the materials, phase changes occur in the composition of the research object, namely, the transition of metals to their oxide forms, which positively affects the degree of copper extraction from EW at the subsequent nitric acid leaching.

THERMAL TREATMENT INFLUENCE ON COPPER EXTRACTION FROM ELECTRONIC WASTE

The paper provides the results of studying the influence of preliminary thermal treatment of crushed electronic waste at a temperature of 450 °C on the copper extraction degree during subsequent material leaching by nitric acid solutions. Electronic industry waste, in particular automobile microcircuits and computer printed circuit boards, was chosen as a research object. It was experimentally determined that the percentage of the organic phase in the research object composition varies within 20–25 % of the crushed raw material mass. The results of thermogravimetric analysis (TGA) and X-ray fluorescence analysis (XRF) show that the maximum degree of organic removal and formation of metal oxides are observed in a temperature range of 400–450 °C. A mathematical model of copper leaching from electronic waste by HNO3 solutions was obtained. The optimum parameters for the process were found – the temperature in the system is 75 °C; leaching duration is 150 min; acid concentration is 4 M with a maximum copper extraction to the solution of 98 %. A comparative analysis of leaching processes for two types of materials (after thermal treatment and without it) was carried out. It was experimentally confirmed that copper leaching from electronic waste by nitric acid solutions with lower concentrations is more complete for materials after preliminary thermal treatment as compared to raw material leaching without thermal treatment. It was proved that preliminary thermal treatment leads to phase changes in the composition of the research object, namely, the transition of metals to their oxide forms, which positively affects the degree of copper extraction from electronic waste at subsequent nitric acid leaching.

INVESTIGATION OF ABILITY LIBERATION OF METALS FROM PRINTED CIRCUIT BOARDS BY MECHANICAL PROCESSES FOR PHYSICAL SEPARATION PROCESSES

Physical separation process was widely applied for the separation of metallic component from Printed Circuit Boards (PCBs) due to their advantages as friendly-environment, facilitated control, and low-cost. However, the efficiency of physical separation depends on a level of the liberation between the metallic and non-metallic components which is conducted by mechanical processing.In this study, the liberation of metals from computer PCBs was conducted in detail by mechanical processes including cutting and crushing. The obtained results demonstrate the distribution metallic and non-metallic component weighs as a function of particle sizes. The separation efficiency of metals was conducted by air separation using vacuum sorter equipment. The results showed that the comminution processes using hammer mill for reach the highest efficiency with 92 % recovery and 87 % grade of metallic components in the heavy fraction with particle size 1.0 - 1.4 mm by air separation process.

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

Two-step bioleaching was applied using a cyanogenic bacterium Pseudomonas balearica SAE1 to recover gold (Au) and silver (Ag) from the computer printed circuit boards (CPCBs) via central composite design of a response surface methodology (CCD-RSM). To enhance Au and Ag recovery, factors like pH level, pulp density, temperature and glycine concentration were optimized and their interactions were studied. CCD-RSM optimization resulted in 73.9 and 41.6% dissolution of Au and Ag, respectively, at initial pH 8.6, pulp density 5g/L, temperature 31.2°C, and glycine concentration 6.8g/L, respectively. Two quadratic models were proposed by RSM which can be utilized as an efficient tool to predict Au and Ag recovery through bioleaching. The experimental results are in line with the predicted results, indicating reliability of RSM model in enhancing the Au and Ag recovery from CPCBs. The increased bioleaching yield of Au and Ag from discarded CPCBs has its importance in industrial e-waste recycling and safe disposal.

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

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 ≤150µm) waste computer printed circuit boards (PCBs)/liter (L) of culture medium. The EC50 value for SAE1 was 325.7g/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 10g/L, a temperature of 30°C, and a glycine concentration of 5g/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.

Total Recovery of Gold Contained in Computer Printed Circuit Boards. Leaching Kinetics of Cu, Zn and Ni

In this study a thorough characterization of certain printed circuit boards has been carried out; it was found that they are made up of a polymer layer, a metal layer of Cu, Zn and Ni, and a gold substrate. A kinetic study of the acid dynamic leaching of copper, zinc and nickel has been carried out, finding out that these elements’ dissolution allows the gold substrate to be physically separated; then, the gold particles are separated from the polymer by filtration. The reaction orders were calculated vs. H2SO4 concentration, and the activation energy was calculated as well; reaction orders of n = 0.265, n = 0.247 and n = 0.245 were found for Cu, Zn and Ni respectively, while Ea = 86.3, Ea = 95.3 and Ea = 11.2 kJ/mol were found for Cu, Zn and Ni respectively. When the attack time is over, a shiny, solid product has been obtained; it was characterized by SEM-EDS and AAS, confirming that it is metallic gold, with a purity of 100 and 99.9% according to the respective technique.

Selective thermal transformation of old computer printed circuit boards to Cu-Sn based alloy

This study investigates, verifies and determines the optimal parameters for the selective thermal transformation of problematic electronic waste (e-waste) to produce value-added copper-tin (Cu-Sn) based alloys; thereby demonstrating a novel new pathway for the cost-effective recovery of resources from one of the world's fastest growing and most challenging waste streams. Using outdated computer printed circuit boards (PCBs), a ubiquitous component of e-waste, we investigated transformations across a range of temperatures and time frames. Results indicate a two-step heat treatment process, using a low temperature step followed by a high temperature step, can be used to produce and separate off, first, a lead (Pb) based alloy and, subsequently, a Cu-Sn based alloy. We also found a single-step heat treatment process at a moderate temperature of 900 °C can be used to directly transform old PCBs to produce a Cu-Sn based alloy, while capturing the Pb and antimony (Sb) as alloying elements to prevent the emission of these low melting point elements. These results demonstrate old computer PCBs, large volumes of which are already within global waste stockpiles, can be considered a potential source of value-added metal alloys, opening up a new opportunity for utilizing e-waste to produce metal alloys in local micro-factories.