Circuit Boards Of Mobile Phones Research Articles

Towards circular economy of wasted printed circuit boards of mobile phones fuelled by machine learning and robust mathematical optimization framework

Estimating the operating conditions using conventional process analysis techniques for the maximum metal extraction from the wasted printed circuit boards (WPCB) can provide sub-optimal solutions leading to the low yield of the process. In this paper, we present a closed-loop methodological framework built on machine learning and robust mathematical optimization technique, that offers the mathematical rigour, to determine the optimum operating conditions for the maximum Cu and Ni recovery from the WPCB. Alkali leaching based novel metals recovery process from the WPCB is designed, and the experiments are conducted to collect the data on the percentage recovery of Cu and Ni against the operating levels of the process input variables (ammonia concentration (NH3 conc. (g/L)), ammonium sulfate concentration ((NH4)2SO4 conc. (g/L)), H2O2 concentration (H2O2 conc. (M)), time (h), liquid to solid ratio (L/S ratio, (mL/g)), temperature (Temp. (°C)), and stirring speed (rpm)). The experimental data is deployed to construct the functional mapping between the nonlinear output variables of metals recovery process with the hyperdimensional input space through artificial neural network (ANN) based modelling algorithm – a powerful universal function approximator. Well-predictive ANN models for Cu and Ni recovery are developed having co-efficient of determination (R2) value more than 0.90. Partial derivative-based sensitivity analysis is then carried out to establish the order of the significance of the input variables that is backed by the domain knowledge, thus promotes the interpretability of the trained ANN models. The hybridization of ANN with NLP (nonlinear programming) framework is implemented for the determination of optimized operating conditions to extract maximum Cu and Ni under separate and combined model of metal extraction. The robustness of the determined solutions is verified, the determined optimized solutions for the metal recovery are validated in the lab, and the maximum metal recovery, i.e., 100 % Cu and 90 % Ni is extracted from the WPCB. This research demonstrates the effective utilization of ANN model-based robust optimization approach for the metal recovery from the WPCB that supports the circular economy for the metal extraction industry.

Electrolyte circulation: Metal recovery from waste printed circuit boards of mobile phones by alkaline slurry electrolysis

Alkaline slurry electrolysis has been verified as an effective method for metal recovery from waste printed circuit boards (WPCBs). However, the electrolyte that remains after slurry electrolysis contains high concentrations of metal, which can cause pollution without suitable treatment. Most importantly, the metals in the electrolyte are not completely recovered, resulting in wasted resources and increased costs. Here, the feasibility of circulating this electrolyte and its effect on copper recovery, current efficiency, and purity, is discussed. We also describe in detail the migration and transformation of copper and other metals, such as nickel, zinc, and lead, during the preparation of high-purity cathode copper from mobile phone WPCBs (WPCB-MPs) using an ammonia-ammonium chloride slurry electrolysis system. Experimental results from 19 cycles of electrolyte reuse show that copper is mainly distributed in the cathode products, whereas other metals are mainly distributed in the electrolyte and anode residues. With an increase in the number of cycles, the concentration of other metals in the electrolyte gradually increased, showing metal enrichment. The current efficiency fluctuates but is usually >90%. In addition, the copper recovery rate and purity were essentially unaffected, being >99% and >99.9% for all 20 runs, respectively, and all the cathode copper foils were easily peeled off. This study demonstrated that electrolytes can be reused for metal recycling from WPCB-MPs by alkaline slurry electrolysis without decreasing Cu purity, Cu recovery rate, and current efficiency. Thus, this study provides a green and cost-effective process for recycling resources from e-waste.

Synthesis of AgNPs from waste mobile phone circuit boards using an emulsion liquid membrane method

The disposal of mobile phone print circuit boards (WMPCBs) has now been a problem because of the continually increasing production of mobile phones. It could be considered a new source of precious metal but may jeopardize the environment and human health without proper management. An emulsion liquid membrane (ELM) method is applied and improved to recover silver from WMPCBs and prepare AgNPs. The effects of significant operating parameters were studied for a better understanding of the ELM process. Under the optimized conditions i.e., 0.25 % (v/v) Cyanex 302, 6 % (v/v) Span 80, 5 % (w/v) ASC, 3500 rpm emulsification speed, 10 min emulsification time, 300 rpm extraction stirring speed, 10 min extraction stirring time and 3 (v/v) phase ratio, 98.7 % silver was extracted. AgNPs produced were flower structures assembled by a group of individual nanosheets with a diameter of 800–1400 nm and a thickness of 10–14 nm. The purity was 98.7 % and the yield was 96.6 %. AgNPs of oblate spheroidal structure with a diameter of 30–50 nm could be synthesized by controlling the concentration of Span 80 in ELM. The current study intends to fulfill the gap by exploring the recovery of silver from WMPCBs by the ELM method.

Gold recovery from waste printed circuit boards of mobile phones by using microwave pyrolysis and hydrometallurgical methods

Recycling of waste printed circuit boards (PCBs) has attracted increasing attention because of its high annually produced amount and high content of gold. In this study, gold recovery from waste PCBs was carried out by using the processes including microwave pyrolysis, acid leaching, solvent extraction and oxidative precipitation. The leaching efficiency of copper was approximately 95% when using a lixiviant composed of sulfuric acid and hydrogen peroxide, and the leaching efficiencies of gold were approximately 59, 95 and 95% by using thiourea, thiosulfate and aqua regia, respectively. The gold ions contained in the leachate previously produced by the leaching processes were not satisfactorily extracted by using organic solvents including di-(2-ethylhexyl)phosphoric acid, tributyl phosphate, dibutyl carbitol and trioctylamine, so the leachate was decided to bypass solvent extraction and directly apply to the oxidative precipitation process. By using the oxidants of hydrogen peroxide and perchloric acid, the precipitation efficiencies of gold were approximately 95 and 99%, and the final recovery rates were approximately 90 and 93%, respectively. The high recovery rates of gold can be attributable to the use of microwave pyrolysis that prevents the loss of gold caused by shredding and grinding processes. In addition, perchloric acid can provide higher selectivity for gold recovery than hydrogen peroxide. The maximum processing capacity of microwave pyrolysis of waste PCBs would be approximately 1.23 kg. The gold recovered from 1 t of waste PCBs can be sold for approximately USD 10,000, and thus the return on investment can be as high as approximately 1400%.

Recovery of high purity copper from waste printed circuit boards of mobile phones by slurry electrolysis with ammonia-ammonium system

Waste printed circuit boards (WPCBs) are identified to be the most complex recycling materials among waste electrical and electronic equipment (WEEE). Slurry electrolysis with acidic system can directly separate and recover copper from WPCBs while current efficiency and purity were generally reduced due to deposition of impurity metals and the hydrogen evolution during recovery process. In ammonia-based system, copper can be selectively extracted and copper (II) ammine complexes generally react with metallic copper to form copper (I) ammine complexes, promoting current efficiency and purity. Therefore, an efficient ammonia-ammonium carbonate slurry electrolysis system is proposed for high purity copper recycling from waste printed circuit boards of mobile phones (WPCB-MPs). The factors affecting copper current efficiency and recovery rate are systematically discussed. These results indicate that appropriate increasing NH3·H2O, (NH4)2CO3, Cu2+, NaCl concentration, solid-to-liquid ratio, current density and reaction time could effectively increase copper recovery rate and current efficiency. The current efficiency and recovery rate of copper are 95.2 and 90.4%, respectively under the optimum test conditions of 20 g/L Cu2+, 0.25 mol/L (NH4)2CO3, 4 mol/L NH3·H2O, 30 g/L solid-to-liquid ratio, 1 mol/L NaCl, 20 mA/cm2, 3 h. Moreover, copper could be recovered at the cathode with a purity of 99.97%. Compared with acidic system, this study provides an efficient approach to recover high purity copper from WPCB-MPs, showing a prospective future for WEEE resource recycling.

Design-of-experiment analysis of non-destructive detachment of electric parts from printed circuit boards of mobile phones using a cross-flow shredder

For minor metal recycling from electric parts, detachment without breakage (non-destructive detachment) of the electric parts from printed circuit boards (PCBs) is required. A cross-flow shredder (CFS), a drum-type chain mill, is often used in PCB recycling, but the effects of its individual features (e.g., chain thickness) on the non-destructive detachment of the PCB parts have yet to be understood. In this study, a CFS suited to the design-of-experiment (DoE) approach was developed; 27 different experimental conditions were evaluated, with three repetitions under each condition for a single PCB crushing, and the effect of nine CFS factors on the non-destructive detachment of parts from the PCBs of mobile phones was investigated. It was revealed that two factors (rotation rate and vent screen) have a statistically significant influence on such non-destructive detachment, and two other factors (chain-wall distance and crushing time) have a significant influence on related results such as the overcrushing of boards (PCBs after parts detachment) and powder generation. Based on these results, a future perspective on CFS improvement is presented.

Recovery of gold from waste mobile phone circuit boards and synthesis of nanomaterials using emulsion liquid membrane

In recent years, waste mobile phones have become popular as electronic waste due to the huge amount, serious pollution with improper disposal and high resource value. It is imperative to realize the recycling of resources in waste mobile phones. The application of emulsion liquid membrane in the recovery of gold and synthesis of nanomaterials from waste mobile phone printed circuit boards (WMPCBs) was studied. The components of the emulsion liquid membrane, effects of 7 factors on the extraction rate and the morphology of the synthesized nanomaterials were explored. The results show that it is possible to extract 99.79% of Au(III) from WMPCBs leachate with kerosene as diluent, Span80 as surfactant, methyl isobutyl ketone(MIBK) as carrier, ascorbic acid solution as stripping agent and liquid paraffin as membrane stabilizer. The external phase pH and the internal phase concentration had a greater influence on the extraction efficiency of Au(III) among 7 factors. The morphology of the synthesized product was affected by the concentration and type of the surfactant. It provides a new idea to connect recovery from waste with deep processing, extending the waste mobile phone recycling process chain and achieving high-value utilization of waste mobile phone secondary metal resource products.

Improving Hydrometallurgical Methods for Processing Tin-containing Electronic Waste

This article provides an overview of methods for processing electronic waste (mobile phones, smartphones, printed circuit boards). The possibility of extracting tin from the waste of printed circuit boards of mobile phones using hydrochloric acid is shown. Established that the deposition of tin from the productive solution occurs due to cementation - an electrochemical displacement reaction between a cementing metal (aluminum) and a cemented ion (tin). The possibility of intensification of the process using a vibrating installation is evaluated. An environmentally friendly and efficient method for processing tin-containing electronic waste is proposed.

Ni and Cu recovery by bioleaching from the printed circuit boards of mobile phones in non-conventional medium

There is a substantial volume of mobile phone waste every year. Due to the disadvantages of traditional methods, it is necessary to look for biological processes that are more eco-friendly and economical to recover metals from e-waste. Fungi provide large amounts of organic acids and dissolve metals but using sucrose in the medium is not economical. In this paper, the main objective is to find a suitable alternative carbon substrate instead of sucrose for fungi bioleaching of Ni and Cu in printed circuit boards (PCBs) of mobile phones using Penicillium simplicissimum. Four kinds of carbon sources (including sucrose, cheese whey, sugar, and sugar cane molasses) were selected. Also, pH and number of spores in inoculum were optimized by response surface methodology (RSM) for all carbon sources. The results showed the simultaneous maximum recovery of Cu and Ni is not possible. For Cu recovery, sugar is the best economical and simplistic medium instead of sucrose. Maximum recovery of Cu (90%) gained at the pH of 7, 3.3 × 107 spores, and in sugar. The amount of Ni recovery (89%) was highest in molasses, at the pH of 2, and 106 spores. The results proved non-conventional carbon sources improve bioleaching efficiency and the possibility of industrialization.

Gold Bioleaching from Printed Circuit Boards of Mobile Phones by Aspergillus niger in a Culture without Agitation and with Glucose as a Carbon Source

Hydrometallurgical and pyrometallurgical processes to recover gold (Au) from cell-phone printed circuit boards (PCBs) have the disadvantage of generating corrosive residues and consuming a large amount of energy. Therefore, it is necessary to look for biological processes that have low energy consumption and are friendly to the environment. Among the biological alternatives for the recovery of Au from PCB is the use of cyanogenic bacteria and filamentous fungi in cultures with agitation. Considering that it is important to explore the response of microorganisms in cultures without agitation to reduce energy expenditure in the recovery of metals from PCB, the present investigation evaluated the capacity of Aspergillus niger MXPE6 and a fungal consortium to induce Au bioleaching from PCB in a culture medium with glucose as a carbon source and without agitation (pH 4.5). The results indicate that the treatments with PCB inoculated with the fungal consortium showed a considerable decrease in pH (2.8) in comparison with the treatments inoculated with A. niger MXPE6 (4.0). The fungal consortium showed a significantly higher Au bioleaching (56%) than A. niger MXPE6 (17%). Finally, the use of fungal consortia grown without agitation could be an alternative to recover metals from PCB, saving energy and material resources.

Microbial Bioleaching of Ag, Au and Cu from Printed Circuit Boards of Mobile Phones.

Electronic waste (E-Waste) is consumed at high speed in the world. These residues contain metals that increase their price each year, generating new research on the ability of microorganisms to recover the metals from these wastes. Therefore, this work evaluated the biologic lixiviation of Cu, Ag and Au from printed circuit boards (PCB) of mobile phones by three strains of Aspergillus niger, Candida orthopsilosis, Sphingomonas sp. and their respective consortia, in addition to leaching with citric acid. The microorganisms were cultured in mineral media with 0.5g of PCB, and the treatments with 1M citric acid were added the same amount of PCB. All treatments were incubated for 35days at room temperature. The results showed that Sphingomonas sp. MXB8 and the consortium of C. orthopsilosis MXL20 and A. niger MXPE6 can increase their dry biomass by 147% and 126%, respectively, in the presence of PCB. In the bioleaching of metals, the inoculation of A. niger MXPE6, the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 and Sphingomonas sp. MXB8 leached 54%, 44.2% and 35.8% of Ag. The consortium of A. niger MX5 and A. niger MXPE6 showed a leaching of 0.53% of Au. A. niger MX5 leaching 2.8% Cu. Citric acid increased Cu leaching by 280% compared to treatments inoculated with microorganisms. Although further research is required, A. niger MXPE6 and the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 could be an alternative to recover Ag from PCB of mobile phones.

Closing the Loop on E‐waste: A Multidisciplinary Perspective

SummaryThis paper describes the challenges faced, and opportunities identified, by a multidisciplinary team of researchers developing a novel closed loop system to recover valuable metals and reduce e‐waste, focusing on mobile phones as a case study. This multidisciplinary approach is contrasted with current top‐down approaches to making the transition to the circular economy (CE). The aim of the research presented here is to develop a product service system (PSS) that facilitates the recovery of valuable functional components and metals from mobile phone circuit boards. To create a holistic solution and limit unintended consequences, in addition to technological solutions, this paper considers appropriate component lifetimes; the (often ignored) role of the citizen in the circular economy; customer interaction with the PSS; environmental life cycle assessment; and social impacts of the proposed PSS. Development of enabling technologies and materials to facilitate recovery of components and metals and to provide an emotionally durable external enclosure is described. This research also highlights the importance of understanding value in the CE from a multifaceted and interdisciplinary perspective.

Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment

Precious metals are the most attractive resources in waste printed circuit boards (PCBs) of mobile phones. In this work, an alternative process for recovering Au, Ag, and Pd from waste PCBs of mobile phones by supercritical water oxidation (SCWO) pre-treatment combined with iodine–iodide leaching process was developed. In the process, the waste PCBs of mobile phones were pre-treated in supercritical water, then a diluted hydrochloric acid leaching (HL) process was used to recovery the Cu, whose leaching efficiency was approximately 100%, finally the resulting residue was subjected to the iodine–iodide leaching process for recovering the Au, Ag, and Pd. Experimental results indicated that SCWO pre-treatment temperature, time, and pressure had significant influence on the Au, Ag, and Pd leaching from (SCWO+HL)-treated waste PCBs. The optimal SCWO pre-treatment conditions were 420°C and 60min for Au and Pd, and 410°C and 30min for Ag. The optimum dissolution parameters for Au, Pd, and Ag in (SCWO+HL)-treated PCBs with iodine–iodide system were leaching time of 120min (90min for Ag), iodine/iodide mole ratio of 1:5 (1:6 for Ag), solid-to-liquid ratio (S/L) of 1:10g/mL (1:8g/mL for Ag), and pH of 9, respectively. It is believed that the process developed in this study is environment friendly for the recovery of Au, Ag, and Pd from waste PCBs of mobile phones by SCWO pre-treatment combined with iodine–iodide leaching process.

RADIATION ACCIDENT DOSIMETRY ON ELECTRONIC COMPONENTS BY OSL

In the event of large-scale radiation accidents and considering a growing terrorism concern, non-invasive and sufficiently accurate retrospective dosimetry methods are necessary to carry out a fast population triage in order to determine which radiation-exposed individuals need medical treatment. Retrospective dosimetry using different electronic components such as resistors, capacitors, and integrated circuits present on mobile phone circuit boards have been considered. Their response has been investigated with luminescence techniques (OSL, IRSL, and TL). The majority of these electronic components exhibit radiation-induced luminescence signals, and the OSL technique seems the most promising for these materials. Results concerning three types of components that present the most interesting OSL characteristics (in terms of signal annealing and sensitivity) and that are the most often present on mobile phone circuit boards are presented. Preheating effects on OSL signal, sensitization, and dose-response curves from 0.7 to 27 Gy for resistors and from 0.7 to 160 Gy for capacitors and integrated circuits, dose recovery tests, and signal stability 10 h after irradiation have been studied and interests and limits of their use evaluated.