Recovery of metals from waste printed circuit boards by a mechanical method using a water medium

Research on the recycling of waste printed circuit boards (PCB) is at the forefront of environmental pollution prevention and resource recycling. To effectively crush waste PCB and to solve the problem of secondary pollution from fugitive odors and dust created during the crushing process, a wet impacting crusher was employed to achieve comminution liberation of the PCB in a water medium. The function of water in the crushing process was analyzed. When using slippery hammerheads, a rotation speed of 1470 rpm, a water flow of 6 m³/h and a sieve plate aperture of 2.2 mm, 95.87% of the crushed product was sized less than 1 mm. 94.30% of the metal was in this grade of product. Using smashed material graded −1 mm for further research, a Falcon concentrator was used to recover the metal from the waste PCB. Engineering considerations were the liberation degree, the distribution ratio of the metal and a way to simplify the technology. The separation mechanism for fine particles of different densities in a Falcon concentrator was analyzed in detail and the separation process in the segregation and separation zones was deduced. Also, the magnitude of centrifugal acceleration, the back flow water pressure and the feed slurry concentration, any of which might affect separation results, were studied. A recovery model was established using Design-Expert software. Separating waste PCB, crushed to −1 mm, with the Falcon separator gave a concentrated product graded 92.36% metal with a recovery of 97.05%. To do this the reverse water pressure was 0.05 MPa, the speed transducer frequency was set at 30 Hz and the feed density was 20 g/l. A flow diagram illustrating the new technique of wet impact crushing followed by separation with a Falcon concentrator is provided. The technique will prevent environmental pollution from waste PCB and allow the effective recovery of resources. Water was used as the medium throughout the whole process.     

Recovery of high purity precious metals from printed circuit boards

Waste printed circuit boards (WPCB) have an inherent value because of the precious metal content. For an effective recycling of WPCB, it is essential to recover the precious metals. This paper reports a promising method to recover the precious metals. Aqua regia was used as a leachant and the ratio between metals and leachant was fixed at 1/20 (g/ml). Silver is relatively stable so the amount of about 98 wt.% of the input was recovered without an additional treatment. Palladium formed a red precipitate during dissolution, which were consisted of Pd(NH(4))(2)Cl(6). The amount precipitated was 93 wt.% of the input palladium. A liquid-liquid extraction with toluene was used to extract gold selectively. Also, dodecanethiol and sodium borohydride solution were added to make gold nanoparticles. Gold of about 97 wt.% of the input was recovered as nanoparticles which was identified with a high-resolution transmission electron microscopy through selected area electron diffraction and nearest-neighbor lattice spacing.     

Recovery of metal fractions from waste printed circuit boards via the vibrated gas-solid fluidized bed

The vibrated gas-solid fluidized bed based on fluidized separation technology was used to recycle the metallic fraction of waste printed circuit boards (WPCBs). The size fraction composition and element distribution of the crushed products were analyzed by sieving and X-ray fluorescence, respectively. The contents of Cu, Zn, Fe and Ti in various size fractions had significant differences, resulting in preliminary enrichment. The performance of vibration on the fluidization characteristics of WPCBs powder was described. With fluidization number, vibration frequency and vibration amplitude as variables, the separation performance of WPCBs powder under various operational conditions was studied. With the optimum operated conditions, the optimal recovery rates of metallic fraction of the three size fractions of 1–0.5 mm, 0.5–0.25 mm and 0.25–0.125 mm were 88.53%, 95.61% and 82.28%, respectively. The vibrated gas-solid fluidized bed can effectively enrich and recover the metallic fraction of WPCBs, providing convenience for subsequent separation.     

Leaching copper from shredded particles of waste printed circuit boards

Leaching copper from shredded particles of waste printed circuit boards (PCBs) was carried out in sulfuric acid solution using hydrogen peroxide as an oxidant at room temperature. The influence of system variables on copper recovery by leaching was investigated, such as sulfuric concentration, amount of hydrogen peroxide addition, waste PBCs particle size, presence of cupric ion, temperature and time. The results shown that the optimum addition amount was 100mL 15 (wt%) sulfuric acid solution and 10 mL of 30% hydrogen peroxide for leaching 10 g waste PCBs powder with a solid/liquid ratio of 1/10 for 3h at room temperature (～23 °C). Moreover leaching temperature and initial copper ion concentration had insignificant effect on the leaching recovery of copper. The effect of different particle size of shredded waste PCBs on leaching of copper was investigated under the optimum leaching condition. The results revealed that shredding pieces of waste PCBs smaller than 1mm was efficient and suitable for copper leaching. Then the leaching solution was concentrated to crystallize CuSO(4)·5H(2)O, and crystal liquor was reused for the next cycles.     

Recovery of copper from printed circuit boards scraps by mechanical processing and electrometallurgy

The constant growth in generation of solid wastes stimulates studies of recycling processes. The electronic scrap is part of this universe of obsolete and/or defective materials that need to be disposed of more appropriately, or then recycled. In this work, printed circuit boards, that are part of electronic scrap and are found in almost all electro-electronic equipments, were studied. Printed circuit boards were collected in obsolete or defective personal computers that are the largest source of this kind of waste. Printed circuit boards are composed of different materials such as polymers, ceramics and metals, which makes the process more difficult. However, the presence of metals, such as copper and precious metals encourage recycling studies. Also the presence of heavy metals, as Pb and Cd turns this scrap into dangerous residues. This demonstrates the need to search for solutions of this kind of residue, in order to have it disposed in a proper way, without harming the environment. At the first stage of this work, mechanical processing was used, as comminution followed by size, magnetic and electrostatic separation. By this process it was possible to obtain a concentrated fraction in metals (mainly Cu, Pb and Sn) and another fraction containing polymers and ceramics. The copper content reached more than 50% in mass in most of the conductive fractions and significant content of Pb and Sn. At the second stage, the fraction concentrated in metals was dissolved with acids and treated in an electrochemical process in order to recover the metals separately, especially copper. The results demonstrate the technical viability of recovering copper using mechanical processing followed by an electrometallurgical technique. The copper content in solution decayed quickly in all the experiments and the copper obtained by electrowinning is above 98% in most of the tests.     

废弃电路板真空热解产物特性分析

采用真空热解对废弃电路板进行热解实验,利用FT-IR分析、GC/MS、SEM等技术对真空热解液体、固体及气体产物进行了分析表征,研究了不同真空条件和温度下对热解产物的组成和理化特性.结果表明,液体产物的密度会随着真空度的变化发生改变;在不同真空条件下,产物的组成也有不同,并分析其产生的原因.为进一步探讨废弃电路板的真空热解产物特征提供参考.     

Bioleaching of metal concentrates of waste printed circuit boards by mixed culture of acidophilic bacteria

Metal concentrates of printed circuit boards (PCBs) are the residue valuable metals from which non-metallic components are removed. The non-metallic components show bacterial toxicity in bioleaching process and can be recycled as well. In this study, the effects of initial pH, initial Fe(II) concentration, metal concentrate dosage, particle size, and inoculation quantity on the bioleaching were investigated so as to determine the optimum conditions and evaluate the feasibility of bioleaching of metal concentrates of PCBs by mixed culture of acidophilic bacteria (MCAB). The results showed that the initial pH and Fe(II) concentration played an important role in copper extraction and precipitate formation. Under the optimized conditions of initial pH 2.00, 12 g/L initial Fe(II), 12 g/L metal concentrate dosage, 10% inoculation quantity, and 60-80 mesh particle size, 96.8% the copper leaching efficiency was achieved in 45 h, and aluminum and zinc 88.2% and 91.6% in 98 h, respectively. All findings demonstrated that metals could be efficiently leached from metal concentrates of waste PCBs by using the MCAB, and the leaching period was shorten from about 8 days to 45 h.     

Application of glass-nonmetals of waste printed circuit boards to produce phenolic moulding compound

The aim of this study was to investigate the feasibility of using glass-nonmetals, a byproduct of recycling waste printed circuit boards (PCBs), to replace wood flour in production of phenolic moulding compound (PMC). Glass-nonmetals were attained by two-step crushing and corona electrostatic separating processes. Glass-nonmetals with particle size shorter than 0.07 mm were in the form of single fibers and resin powder, with the biggest portion (up to 34.6 wt%). Properties of PMC with glass-nonmetals (PMCGN) were compared with reference PMC and the national standard of PMC (PF2C3). When the adding content of glass-nonmetals was 40 wt%, PMCGN exhibited flexural strength of 82 MPa, notched impact strength of 2.4 kJ/m(2), heat deflection temperature of 175 degrees C, and dielectric strength of 4.8 MV/m, all of which met the national standard. Scanning electron microscopy (SEM) showed strong interfacial bonding between glass fibers and the phenolic resin. All the results showed that the use of glass-nonmetals as filler in PMC represented a promising method for resolving the environmental pollutions and reducing the cost of PMC, thus attaining both environmental and economic benefits.     

A novel approach to recycling of glass fibers from nonmetal materials of waste printed circuit boards

The printed circuit boards (PCBs) contain nearly 70% nonmetal materials, which usually are abandoned as an industrial solid-waste byproduct during the recycling of waste PCBs. However those materials have abundant high-value glass fibers. In this study, a novel fluidized bed process technology for recycling glass fibers from nonmetal materials of waste PCBs is studied. The recycled glass fibers (RGF) are analyzed by determination of their purity, morphology and surface chemical composition. This process technology is shown to be effective and robust in treating with nonmetal materials of waste PCBs. The thermoset resins in the nonmetal materials are decomposed in the temperature range from 400 °C to 600 °C. And the glass fibers are collected at high purity and recovery rate by the cyclone separators without violating the environmental regulation. This novel fluidized bed technology for recycling high-value glass fibers from nonmetal materials of waste PCBs represents a promising way for recycling resources and resolving the environmental pollutions during recycling of waste PCBs.     

基于废弃印刷线路板中非金属的复合板材制备

随着废弃电子电器产品的快速增长带来的环境问题日趋严重,废弃印刷线路板的资源化问题一直成为关注的焦点。着重研究了气流分选后得到的废弃印刷线路板非金属粉碎料的资源化再生制板材的可行性,探讨了不同填料粒径、投加量和改性剂下所得复合材料拉伸强度、弯曲和冲击强度的变化。研究表明以马来酸酐接枝聚丙烯（MAH-g-PP）作为改性剂,聚丙烯S700为基体树脂,在粒径范围为0.125～0.3mm的非金属粉碎料添加量为20%的条件下,板材力学性能较优,具有广泛的应用前景。     

The reuse of nonmetals recycled from waste printed circuit boards as reinforcing fillers in the polypropylene composites

The feasibility of reusing nonmetals recycled from waste printed circuit boards (PCBs) as reinforcing fillers in the polypropylene (PP) composites is studied by using both mechanical and vicat softening temperature (VST) tests. The concentration of Cu leaded from the composites is also tested. The mechanical test shows that both tensile and flexural properties of the nonmetals/PP composites can be significantly improved by adding the nonmetals into PP. The maximum increment of tensile strength, tensile modulus, flexural strength and flexural modulus of the PP composites is 28.4%, 62.9%, 87.8% and 133.0%, respectively. As much as 30 wt% nonmetals recycled from waste PCBs can be added in the PP composites without violating the environmental regulation. The VST test shows that the presence of nonmetals can improve the heat resistance of the nonmetals/PP composites for their potential applications. The optimum particle is the fine or medium nonmetals recycled from waste PCBs, and the optimum content of the nonmetals is 30 wt% basing on the comprehensive consideration. All the above results indicate that the reuse of nonmetals as reinforcing fillers in the PP composites represents a promising way for recycling resources and resolving the environmental pollutions.     

The ultrasonically assisted metals recovery treatment of printed circuit board waste sludge by leaching separation

This paper provides a practical technique that realized industrial scale copper and iron separation from printed circuit board (PCB) waste sludge by ultrasonically assisted acid leaching in a low cost, low energy consumption and zero discharge of wastes manner. The separation efficiencies of copper and iron from acid leaching with assistance of ultrasound were compared with the one without assistance of ultrasound and the effects of the leaching procedure, pH value, and ultrasonic strength have been investigated in the paper. With the appropriate leaching procedure, a final pH of 3.0, an ultrasonic generator power of 160 W (in 1 l tank), leaching time of 60 min, leaching efficiencies of copper and iron had reached 97.83% and 1.23%, respectively. Therefore the separation of copper and iron in PCB waste sludge was virtually achieved. The lab results had been successfully applied to the industrial scaled applications in a heavy metal recovery plant in city of Huizhou, China for more than two years. It has great potentials to be used in even the broad metal recovery practices.     

Manufacturing process of reproduction plate by nonmetallic materials reclaimed from pulverized printed circuit boards

The aim of this study was to present a new method for resource utilization of nonmetallic materials reclaimed from pulverized waste printed circuit boards. A reproduction nonmetallic plate (RNMP) was prepared by adding resin paste, glass fiber and additives into nonmetallic materials using self-made hot-press former. Principle of manufacturing process and effects of mould temperature and moulding time on the mechanical properties of RNMP were studied. The results showed that when moulding pressure was fixed at 6 MPa, the optimum conditions for the RNMP were as follows: 140/135 degrees C for top/bottom mould temperature, 5 min for moulding time. The maximum content of nonmetallic materials in RNMP was up to 40 wt%. When nonmetallic material content was 20 wt%, the RNMP moulded at optimum conditions had excellent mechanical properties, with impact strength of 5.8 kJ/m(2) and flexural strength of 65.1 MPa.     

A new two-roll electrostatic separator for recycling of metals and nonmetals from waste printed circuit board

The electrostatic separation is an effective method for recycling waste electrical and electronic equipment (WEEE). The efficiency of electrostatic separation processes depends on the ability of the separator. As a classical one, the roll-type corona-electrostatic separator has some advantages in recycling metals and plastics from waste printed circuit board (PCB). However, its industry application still faces some problems, such as: the further disposal of the middling products of the separation process; the balance of the production capacity and the good separation efficiency; the separation of the fine granular mixture and the stability of the separation process. A new "two-roll-type corona-electrostatic separator" was built to overcome the limitation of the classical one. The experimental data were discussed and the results showed that the outcome of the separation process was improved by using the new separator. Compared with the classical machine, the mass of conductive products increases 8.9% (groups 2 and 3) and10.2% (group 4) while the mass of the middling products decreases 45% (groups 2 and 3) and 31.7% (group 4), respectively. The production capacity of the new machine increases, and the stability of the separation process is enhanced.     

A model for computing the trajectories of the conducting particles from waste printed circuit boards in corona electrostatic separators

A model for computing the trajectory of conducting particle from waste printed circuit board (PCB) scraps in corona electrostatic separator is established. Using analytical expression for computing non-uniformity of the electric field in the active zone of the separator and the differential method were used for computing the trajectories of conducting particles in the air, after detachment. The result shows that the trajectory of conducting particle can be computed under various initial parameters (R, r, L, alpha, U, n; rho, r0) by the computing model and the computing results have a good agreement with the actual separating process. This model offers a possible for designing the new corona electrostatic separator.     

Recycling of waste printed circuit boards: a review of current technologies and treatment status in China

From the use of renewable resources and environmental protection viewpoints, recycling of waste printed circuit boards (PCBs) receives wide concerns as the amounts of scrap PCBs increases dramatically. However, treatment for waste PCBs is a challenge due to the fact that PCBs are diverse and complex in terms of materials and components makeup as well as the original equipment's manufacturing processes. Recycle technology for waste PCBs in China is still immature. Previous studies focused on metals recovery, but resource utilization for nonmetals and further separation of the mixed metals are relatively fewer. Therefore, it is urgent to develop a proper recycle technology for waste PCBs. In this paper, current status of waste PCBs treatment in China was introduced, and several recycle technologies were analyzed. Some advices against the existing problems during recycling process were presented. Based on circular economy concept in China and complete recycling and resource utilization for all materials, a new environmental-friendly integrated recycling process with no pollution and high efficiency for waste PCBs was provided and discussed in detail.     

The inspection of solder joints on printed circuit boards by phase-shift holographic interferometry

The principle of inspecting solder joints on printed circuit boards (PCBs) by phase-shift holographic interferometry is described. By using this technique, defective solder joints can be easily distinguished from good ones without analysing complicated holographic interferograms. Experiment shows that most defects in solder joints, such as breaks and voids, can be detected successfully.     

Optimizing the operating parameters of corona electrostatic separation for recycling waste scraped printed circuit boards by computer simulation of electric field

The printed circuit board (PCB) has a metal content of nearly 28% metal, including an abundance of nonferrous metals such as copper, lead, and tin. The purity of precious metals in PCBs is more than 10 times that of rich-content minerals. Therefore, the recycling of PCBs is an important subject, not only from the viewpoint of waste treatment, but also with respect to the recovery of valuable materials. Compared with traditional process the corona electrostatic separation (CES) had no waste water or gas during the process and it had high productivity with a low-energy cost. In this paper, the roll-type corona electrostatic separator was used to separate metals and nonmetals from scraped waste PCBs. The software MATLAB was used to simulate the distribution of electric field in separating space. It was found that, the variations of parameters of electrodes and applied voltages directly influenced the distribution of electric field. Through the correlation of simulated and experimental results, the good separation results were got under the optimized operating parameter: U=20-30 kV, L=L(1)=L(2)=0.21 m, R(1)=0.114, R(2)=0.019 m, theta(1)=20 degrees and theta(2)=60 degrees .