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Electro dynamic fragmentation of printed wiring boards as a preparation tool for their recycling
Abstract
The use of Electro Dynamic Fragmentation (EDF) enables selective fragmentation of materials through generating electrical discharges as a means of fracturing. Liberated materials can be thus processed downstream in a more efficient way especially when value-added End-of-Life (EoL) electronic equipment is recycled. The aim of this study was to assess the benefits of the EDF technology towards processing of EoL printed wiring boards (PWBs) in view their recyclability. Printed wiring boards were comminuted using EDF at three different settings and with a hammer mill for comparative experiment. The products coming out were characterized by optical microscopy, SEM and liberation oriented leaching. Subsamples from the various EDF stages were inspected to investigate the progress of cracks and degree of copper layers exposure. The different energy levels used during the EDF processing have resulted in different degrees of PWBs damages, starting from components removal to entire structure perturbation and size reduction. EDF has resulted in generation of a lesser amount of fines, however the optimal approach in view energy efficient post-processing of the studied PWBs was the combination between single-stage EDF for components removal only with subsequent shredding of the depopulated boards.
... A significant metal liberation can also be achieved when coarse PCBs are treated with high voltage electrical pulse (HVEP) comminution. The use of electro dynamic fragmentation in the pre-treatment of PCBs is analogous to the HVEP comminution [89]. HVEP comminution does not result in size reduction to a greater extent since most of the applied electrical energy is allocated at the hetero-component interface for delamination (Figure 2). ...
... Comparison studies are performed to investigate the crushing impacts of HVEP comminution and hammer mill [89]. Delamination is observed on HVEP-treated PCBs with a negligible size reduction effect, which is absent for the hammer mill products. ...
... Martino et al. [89] performed HVEP comminution using populated motherboards and reported the sequential damage on the boards under increased electrical energy ( Table 2). This technique thus possesses the added advantage of electrical component removal in advance, which is one of the requirements for hydrometallurgical operations. ...
Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals.
... The researcher showed that hammering and shredding electronic waste reduced it to a suitable size, enhancing the efficiency of the recovery process (Kaya 2016). However, recent research by Martino et al. (2017) showed that reduction of the size and liberation using electrodynamic fragmentation is an unconventional process for the recovery of the metal due to fine grinding (typically < 200 mm) of the electronic waste (Martino et al. 2017). ...
... The researcher showed that hammering and shredding electronic waste reduced it to a suitable size, enhancing the efficiency of the recovery process (Kaya 2016). However, recent research by Martino et al. (2017) showed that reduction of the size and liberation using electrodynamic fragmentation is an unconventional process for the recovery of the metal due to fine grinding (typically < 200 mm) of the electronic waste (Martino et al. 2017). ...
The demand for rare earth elements (REEs) has significantly increased due to their indispensable uses in integrated circuits of modern technology. However, due to the extensive use of high-tech applications in our daily life and the depletion of their primary ores, REE’s recovery from secondary sources is today needed. REEs have now attracted attention to policymakers and scientists to develop novel recovery technologies for materials’ supply sustainability. This paper summarizes the recent progress for the recovery of REEs using various emerging technologies such as bioleaching, biosorption, cryo-milling, electrochemical processes and nanomaterials, Siderophores, hydrometallurgy, pyrometallurgy, supercritical CO2. The challenges facing this recovery are discussed comprehensively and some possible improvements are presented. This work also highlights the economic and engineering aspects of the recovery of REE from waste electrical and electronic equipment (WEEE). Finally, this review suggests that greener and low chemical consuming technologies, such as siderophores and electrochemical processes, are promising for the recovery of REEs present in small quantities. These technologies present also a potential for large scale application.
... PCBs have a complex multicomponent composition. Using the electric discharge method for PCB disintegration is interest because PCB have significant differences in density and electrical conductivity [9,10]. ...
The results of the electric discharge crushing of PCB (printed circuit boards) to millimeter-sized fractions suitable for separation of the metal from the dielectric are presented. The crushing was performed on a high-voltage repetitively pulsed generator with varying the number of pulses. It was determined the dependences of the fractional composition of crushing products on the number of pulses in the cycle. Crushing products were studied for definition separation of metal from the dielectric with optical microscope. The results of the work confirm the possibility of electric discharge crushing various types of PCB, including fiberglass PCB with four layers. Keywords: high voltage fragmentation, waste printed circuit board, recycling
... This method was used by scientists from Belgium and Switzerland in the innovative crushing of electronic components. Researchers found that there is a possibility of obtaining the grain size of recycled material, similar to the grain size obtained in hammer mills [14]. After appropriate modifications, the method could be introduced to crumble existing concrete structures. ...
The article presents selected problems connected with the accomplishment of the research grant ‘Application of reclaimed materials’ as part of the joint project Development of Road Innovations (RID) co-financed by the National Centre of Research and Development as well as the General Directorate for National Roads and Motorways. The main aim of the project was to analyse possibilities of application of reclaimed concrete obtained from the demolition waste from the existing roads to produce new layers of road pavements. The article presents selected test results which show the influence of the reclaimed concrete content on the strength parameters of the MCE mixtures. Significant variation of the tested MCE mixtures properties depending on the percentage of the reclaimed material has been indicated. It has been suggested that new tests should be implemented in the process of MCE mixtures design process. An optimal content of reclaimed concrete has been determined in order to obtain required values of the analysed parameters. The application of reclaimed concrete in conventional MCE mixtures made it possible to achieve positive economical and environmental effects.
... Shredders and hammer mills are extensively used for size reduction of WEEE (Dalrymple et al., 2007;Kaya, 2016). In a recent study, Electro Dynamic Fragmentation of PCB was demonstrated as an unconventional method for size reduction and liberation of components (Martino, Iseli, Gaydardzhiev, Streicher-Porte, & Weh, 2017). ...
Waste electrical and electronic equipment (WEEE) contains economically significant levels of precious, critical metals and rare earth elements, apart from base metals and other toxic compounds. Recycling and recovery of critical elements from WEEEs using a cost-effective technology are now one of the top priorities in metallurgy due to the rapid depletion of their natural resources. More than 150 publications on WEEE management , leaching and recovery of metals from WEEE were reviewed in this work, with special emphasize on the recent research (2015-2018). This paper summarizes the recent progress regarding various hydrometallurgical processes for the leaching of critical elements from WEEEs. Various methodolo-gies and techniques for critical elements selective recovery (using ionic liquids, solvent extraction, electrowinning, adsorp-tion, and precipitation) from the WEEEs leachates are discussed. Future prospects regarding the use of WEEEs as secondary resources for critical raw materials and its techno-economical and commercial beneficiaries are discussed.
The liberation of components from multi-component waste such as printed circuit boards during recycling is associated with the crushing process. High-voltage electric pulse (HVEP) crushing is considered as an alternative to traditional mechanical crushing methods. This study presents research on the possibility of optimising HVEP crushing for printed circuit boards using high-voltage pulses of microsecond and sub-microsecond durations. Four generators were used for crushing with an output voltage of 40–260 kV and a stored energy of 40–500 J. The similarity criterion K was applied to determine the optimal ratio between the generator parameters and the channel parameters. The generators used attained the best distribution of the fractional composition for a sub-microsecond pulse duration and minimal energy costs (11–12 kJ/g) for both pulse durations. The energy costs for high-voltage pulse crushing were still higher than that for mechanical crushing. HVEP crushing produces a lower over-grinding fraction which was confirmed by sieve analysis.
Printed circuit boards (PCBs) are an essential and central component of electronic waste. The rapid depletion of natural resources, massive generation of end-of-life PCBs and inherently metal-loaded values inevitably call for recycling and recovery. This review critically discusses the systematic and sequential processes adopted for PCB metallic recoveries via physical, pyrometallurgical, hydrometallurgical, and combined technologies. Pre-treatments play a decisive and significant role in upgradation and efficient metal extraction. A novel combination of different pre-treatments and hybrid thermal-chemical routes are often reported for improved separation efficiency and performance. Selective recovery (using solvent extraction, precipitation, polymer inclusion membrane, adsorption, ion exchange) of high purity product from multi-elemental leach solution has recently gained interest and is reviewed. Current recycling techniques at a commercial scale are preferably based on pyrometallurgy (smelting-refining), where electronic waste is only a fraction of the total feed stream. Electronic components such as monolithic ceramic capacitors, tantalum capacitors, integrated circuits, and central processing units mounted on the PCBs are important due to precious metals' presence. The futuristic recycling perspective should treat base and precious metal-rich components separately with minimal environmental effect, end product usage, and maximum economic benefit. Sustainable processing routes for converting discarded PCBs into value-added products should also be attempted, as amplified in this review. An integrated, definite framework for full resource recovery from waste PCBs was proposed.
Mining companies are actively looking for new and innovative techniques which can significantly reduce operational costs and processing carbon footprint. The high voltage pulse (HVP) is a novel technology with the potential to be applied in the mineral processing industries which provides enhanced liberation, pre-weakening and pre-concentration benefits for raw material. This paper reviews in detail the HVP working principles and the work devoted to the aforementioned three applications. In addition, major challenges affecting the industrial uptake of the HVP technique are also discussed in the context of HVP fragmentation specific energy consumption, machine wear, cost of water processing and machine throughput limitations. HVP selectivity in between particles is accentuated in this review and believed to have good prospects for industrial uptake due to its capability to achieve selective fragmentation and selective weakening effects for the mineralised particles. Finally, the paper is enclosed with an outlook of HVP future development.
This chapter explains the aim and importance of size reduction in e-waste recycling. Shredding, crushing, pulverizing, and grinding are general comminution methods used in WPCB recycling. Industrial-size shredders, which are hammer mill pulverizers, are covered in detail. Emerging fractionation and electrodynamic fragmentation with high-voltage pulse technologies are introduced for WPCB recycling. Industrial plant application flowsheets are demonstrated. Industrial-scale material classification methods and equipment are presented. Plant-scale conveyor belts for material transport between equipment and working principles of filtration and dust collection systems for high filtration efficiency are also covered in this chapter.
Reliability and lifetime are the two most relevant design considerations in the production of safety critical assemblies. For example in a modern automobile dozens of electronic assemblies are integrated in which thousands of solder joints are mounting the electronic components to the printed circuit boards. There exists no standardised and universal observation method for characterising the fine microstructure of such solder joints. Previously we have developed a new method for the quantitative characterization of lead-free solder alloys and in present study the validity of the proposed method is demonstrated. Microstructure of Sn-3.5Ag lead free solder alloy was investigated by electrochemical impedance spectroscopy. Solder samples were solidified with different cooling rates in order to induce differences in the microstructure. Microstructure of the ingots was revealed by selective electrochemical etching. Electrochemical impedance spectra (EIS) were measured before and after the selective etching process. The complex impedance spectra contain information about microstructure of the solder alloys. Comparison and modelling of two EIS spectra allowed obtaining a characteristic parameter of surface structure of the etched specimens. The EIS measurements were complemented with small angle neutron scattering measurements and scanning electron microscopy, in order to correlate the EIS parameter with the magnitude of the interface of the β-Sn and Ag3Sn phases.
Electronic components (ECs) disassembling from waste printed circuit boards (WPCBs) is the first and essential step in WPCBs recycling chain. Over the past decades, primitive methods like simply heating WPCBs on a coal-heated plate to melt solders are dominated in practice, causing serious environmental pollution and also putting a real threat to the human health. In order to solve this problem, in this article, an automatic system in pilot-scale for ECs disassembling from WPCBs is designed, manufactured, and investigated. This system contains two parts: ECs automatic disassembly and off-gas purification. Meanwhile, WPCBs from television (i.e., TV-WPCBs) and personal computer (i.e., PC-WPCBs) are used for disassembling tests, respectively. When the disassembling temperature, rotating speed, and incubation time are 265±5°C, 10rpm, and 8min, respectively, the solder can be completely removed from both TV-WPCBs and PC-WPCBs. No pollutant is discharged from this system. Finally, the disassembling procedures for ECs from both TV-WPCBs and PC-WPCBs are suggested to promote WPCBs disassembling in an environment-friendly way, without threaten the environment and human health.
SELFRAG AG has developed a flexible pilot scale Pre-Weakening Testing Station (PWTS) using high voltage pulses (HVP). This provides a unique opportunity to investigate the machine setting conditions on ore breakage behaviour. A joint campaign was undertaken by the Julius Kruttschnitt Mineral Research Centre and SELFRAG AG to investigate the breakage behaviour of two copper-gold ores and one iron ore in the PWTS. The effects of specific energy, pulse voltage, cumulative discharges, feed particle size and ore particle breakage pattern (body breakage or surface breakage) were investigated. The investigation revealed that the mass-specific energy of HVP was the most significant factor affecting the breakage behaviour in the PWTS. This effect was compounded with the effects of ore properties and particle size. Comparison between the PWTS and a laboratory HVP machine indicates that there is considerable scope for optimisation of HVP performance based on processing zone design.
A method based on single-particle tests has been developed to characterise the pre-weakening effect of high voltage pulses on ores. A pre-weakening index, PWI, defined as the percentage change in ore breakage resistance indicator (A*b) per unit of specific energy, is used to evaluate the energy efficiency of an electrical comminution machine, and to assess an ore's amenability to pre-weakening by high voltage pulses. A reduced JKRBT (JK Rotary Breakage Tester) testing procedure using five tests (instead of the standard 12 tests per sample) to determine the ore breakage parameters, makes characterisation by high voltage pulse pre-weakening more practical. A gold-copper ore sample treated by high voltage pulses, based on single-particle tests with a specific energy of 1.6 kWh/t, achieved an A*b change from 31 to 84 at a nominal particle size of 30 mm, representing a 171% pre-weakening result. X-ray tomography images show the induced cracks/microcracks in the pulses-treated rocks. The pre-weakening effect was found more pronounced for larger fragments, suggesting that the use of high voltage pulses to pre-weaken AG/SAG mill feed may result in more significant benefits in terms of energy savings or increased throughput than pre-weakening ball mill feed.
Comparative comminution between high voltage pulses and conventional grinding, at the same specific energy levels, shows that the electrical comminution generates a coarser product with significantly less fines than the mechanical breakage. However, minerals of interest in the electrical comminution product are better liberated than in the conventional comminution with an over 95% statistical significance. There is a potential to use less energy in the electrical comminution to generate the similar degree of mineral liberation as in the mechanical comminution. Distribution of the liberated minerals demonstrates that, in the electrical comminution product, a large percentage of the liberated minerals appear in size fractions coarser than 53 gm; while in the mechanical comminution product, the liberated minerals are accumulated in fine and very fine size fractions. Therefore there may be potential benefits in recovering the coarse liberated minerals in the electrical comminution product, prior to further grinding.
Mechanical size reduction processes in the mineral processing industry are energy intensive. In this study, a novel High Voltage Electric Pulses Crusher (HVEPC) was designed and developed to pre-weaken and crush a phosphate ore. To compare the effectiveness of the new HVEPC in crushing with the conventional crushers, several rock samples of a phosphate ore were used and the effect of the capacitor, the voltage level and voltage rise time on the phosphate ore breakage was investigated. Comparing the particle size distribution of the crushed samples using both the HVEPC and the conventional crushers revealed the difference between their breakage mechanisms. The final results showed that applying the high voltage pulses at specific energy of 3-5 kWh/t could significantly increase and extend the cracks and microcrakcs inside the rocks and consequently lead to decline in the Bond crushability and Abrasion indices of the crushed samples by 10.6% and 28.1%, respectively.
A new comminution method has been developed by applying high voltage pulses at specific energy 1–3kWh/t to pre-weaken mineral particles, leading to reduction in energy consumption in the downstream grinding process. Four ore samples were tested using high voltage pulses and conventional crushing in parallel for comparison. Evidence of cracks and microcracks measured with X-ray tomography and mercury porosimetry supported the principle of high voltage pulses induced damage on rocks in the electro-comminution process, which resulted in energy saving up to 24% found in this study. Ore surface texture and mineral properties affected the efficiency of high voltage pulse breakage. The feasibility of the electro-comminution and its benefits need to be investigated case by case.
a b s t r a c t Waste of electric–electronic equipment (WEEE) with an annual growth rate of about 3–5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydromet-allurgical processes were reviewed in this study. With their relatively low capital cost, reduced environ-mental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treat-ment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes.