Crushed Waste Printed Circuit Boards Research Articles

Eddy current separation can be used in separation of non-ferrous particles from crushed waste printed circuit boards

Waste printed circuit boards are produced greatly due to the wide application of electronic devices, in which non-ferrous metals are valuable resources. Without effective recovery processes, it can cause serious heavy metal pollution. Traditional recover technologies will cost too much energy, materials, manpower together with producing secondary ecological and environmental pollution. Eddy current separation is a green and low-cost technology to separate non-ferrous metals from others. However, it was well reported that there was a certain particle size limitation for the separated non-ferrous metals. Was it a truth or unbreakable principle for eddy current separation? In this paper, we researched the causes of the size limitation for eddy current separation. Meanwhile, the eddy current separation mechanism was detailed explained in a new comprehension related to the change of magnetic flux density, generation of eddy current force and particles’ motor behaviors. We consider that there is no size limitation for the separated non-ferrous metals in eddy current separation as long as the size of magnetic pole is enough big or small. This paper brings a new recognition about the traditional eddy current separation and will expand new application area for this environment-friendly and low-cost technology.

Bromine removal from resin particles of crushed waste printed circuit boards by vacuum low-temperature heating

Uncontrolled dumping and incineration of resin particles of waste printed circuit boards had caused serious pollution due to the contained brominated flame retardants. High-temperature vacuum pyrolysis was proposed to treat the resin particles. However, due to the generation of brominated gases and solid floc, high-temperature vacuum pyrolysis reproduced more hazardous wastes. In this paper, resin particles of crushed waste circuit board were processed by vacuum heating at the temperature of 300 °C and condensation at 180 °C. Resin particles were converted into residue and oil with the mass ratios 84.0 wt% and 16.0 wt% respectively. Content of organic bromine in residue was reduced to 0.082 wt%. Meanwhile, morphology of resin in residue was basically unchanged, which could be directly recycled as the filler for building materials. About 95.4 wt% of bromine in resin particles was transferred to oil. These results achieved the reduction of the hazardous wastes. Compared with the high-temperature vacuum pyrolysis, low-temperature heating not only reduce energy consumption, but also reduce the generation of toxic products. This paper might be the first time to report low-temperature heating of resin particles of waste printed circuit boards. This study contributed a novel technology to remove bromine from brominated substrates.

Ecological influences of the migration of micro resin particles from crushed waste printed circuit boards on the dumping soil

About 0.8 million tons of resin particles, which were generated from the recovery of waste printed circuit boards, were dumped on soil at Qingyuan city of China. Resin particles not only belong to micro plastic but also contain brominated flame retardants and heavy metals. There is little information about soil pollution caused by the dumped resin particles. This study found resin particles would transfer from soil surface into soil at least 10 mm downward for six months. Average content of bromine in soil within 10 cm exceeded 2500 mg/kg. The highest content of Pb, Zn, and Cu was 3450, 1143 and 1450 mg/kg, which were approximately 6.9, 2.3 and 3.6 times as much as Grade Ⅲ soil standard of China. Micro plastic, brominated flame retardants, and heavy metals made significant effects on soil bacterial community. Bacterial diversity was destroyed and the number of resistant bacteria increased obviously such as Acinetobacter, Pseudomonas and Paracoccus. This paper presented the ecological destroy of soil when the resin particles were deposited on soil surface. It also suggested the government to urgently manage the resin particles produced in the recovery of waste printed circuit boards.

Directional concentration of bromine from nonmetallic particles of crushed waste printed circuit boards by vacuum-gasification-condensation

Nonmetallic particles of crushed waste printed circuit boards usually contain 8.0–12.3 wt% of brominated flame retardants, which are harmful to humans and environment. Some articles proposed the method of pyrolysis to treat nonmetallic particles, but the pyrolysis products were still hazardous wastes. In this study, a novel process of vacuum-gasification-condensation was proposed to directionally concentrate bromine from the nonmetallic particles. Organic components of nonmetallic particles were completely gasified at the temperature of 700 °C and then cooled at 200 °C and 50 °C. Oils, floc, gases and residue were obtained and the bromine were concentrated in different products. Residue contained 0.19 wt % bromine and was no longer hazardous waste. Meanwhile, another breakthrough was that bromine migrated directionally to floc (36.15% of total bromine) and gases (46.37% of total bromine), which would be beneficial for the reduction of hazardous wastes. Additionally, we forecasted the future work about the treatment of the nonmetallic particles. To maximize the reuse of the nonmetallic particle, the key is to keep the bonds of other macromolecular organics stable and break C–Br bond only. This paper contributed a novel technology to collect bromine from the brominated wastes.

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

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

Elements in the Crystals Determine the Distribution of Bromine in Nonmetallic Particles of Crushed Waste Printed Circuit Boards

The recovery of waste printed circuit boards (WPCBs) has been a hot topic in the area of environmental science. WPCBs contain heavy metals (Cu, Zn, Pb, etc.) and nonmetals (fiberglass, plastics, an...

Low-temperature melting and centrifugation of lead and tin from metal-rich particles of crushed waste printed circuit boards

The rapid growth of electronic devices, their subsequent obsolescence and disposal has resulted in electronic waste being one of the fastest increasing waste streams worldwide. Printed circuit boards (PCBs) contained substantial quantities of metals in concentrations significantly higher than those typically found in corresponding ores. The high value of valuable metals in the e-waste makes the recycle process attractive economically. The study was focused on an effective process to selectively recycle lead and tin from metal-rich particles of crushed PCBs by melting and centrifugation in low temperature. Centrifugal separation is an efficient technology to strengthen the transmission of multiphase flow and reaction process. The temperature had a great influence on the composition of Pb-Sn alloy, while the gravity coefficient only affected the Pb and Sn recovery values, and had little effect on the mass ratio of Pb and Sn in the obtained alloy. At an optimized temperature of 420 °C and a gravity coefficient of 1000, the recovery values of Pb and Sn were 57.16% and 59.49%, respectively. The total mass fraction and mass ratio of Pb and Sn were 93.58 wt.% and 0.87, respectively. This process provides an effective method to recycle valuable metals from PCBs.

Effect of Milling Parameters on the Concentration of Copper Content of Hammer-Milled Waste PCBs: A Case Study

The current study reports optimization of hammer milling parameters to achieve crushed waste printed circuit boards (WPCBs) of − 16 BSS (British Standard Specification) sieve size. The WPCBs, having 22 wt% copper, have been crushed to − 16 BSS sieve size by means of a hammer mill. The result showed that initial milling takes place rapidly and then decreases gradually. Approximately 94% feed material is ground to − 16 BSS sieve size within 7 min, and further increase in the time does not affect the milling rate. It is also revealed that with the increasing feed rate, lower milling rate is experienced due to the distribution of impact energy among more pieces of WPCBs. Study of the size distribution of milled WPCBs (− 16 BSS sieve size) revealed that it follows the similar trend, and the crushed material is mostly concentrated in − 240 BSS and + 72 to − 52 BSS sieve size range. Further, 50–55% crushed fraction attains + 100 BSS sieve size, while the rest is smaller than this sieve size. Chemical analysis of the crushed material of various size fractions elucidated that a fraction above 100 BSS sieve size is copper rich (43 wt%), while − 100 BSS sieve size fraction has lesser copper because the nonmetals which account for majority concentration in WPCBs are milled to a finer size. Microscopic examinations of crushed fraction showed that copper has metallic luster and ruptured foil-type morphology. The fibrous structure of glass fiber and gray/black-colored polygon morphology of nonmetals were also visible.

Heat Transfer in Vacuum Pyrolysis of Decomposing Hazardous Plastic Wastes

Vacuum pyrolysis has been widely used to decompose plastic wastes for obtaining purity chemicals or remove hazardous organic pollutants. The pyrolysis temperature determined the variety of pyrolysis products. The final (highest) temperature was the most investigated factor. However, temperatures used in vacuum pyrolysis were not equally distributed. The lowest temperature also determined the variety of the products. Regrettably, this vital factor has not been researched and reported. In this paper, the heat transfer process of vacuum pyrolysis was fully analyzed. The models for computing the lowest temperature were constructed. The models were certified by the vacuum pyrolysis of novolac epoxy particles collected from crushed waste printed circuit boards. According to the models, we found the heat transfer coefficient of the crucible and the inner diameters of the crucible and alundum tube were the key factors for controlling the lowest temperature. The models can help us to modify and adjust the lowest a...

Review on Chromobacterium Violaceum for Gold Bioleaching from E-waste

Electronic waste, such as printed circuit boards, are an important secondary resource if processed with environment-friendly technologies for obtaining precious metal, such as gold. The gold bioleaching from electronic waste was recently getting paid attractive attention because its available deposit is limited. This review was focused on Chromobacterium violaceum (C. Violaceum), which was a mesophilic, gram-negative, and facultative anaerobe. C. violaceum has the ability of producing CN− which can dissolve gold from the metallic particles of crushed waste printed circuit boards. This article also provided an overview of cyanide-generation mechanism and the optimal conditions for C. violaceum to achieve maximum amount of cyanide generation. The past achievements and recently scenario of recovery studies carried out on the use of some other microorganisms were compared with C. violaceum. And recently some researchers proposed that combined C. violaceum with chemical methods or other mechanism such as iodide, Pseudomonas aeruginosa and Pseudomonas fluorescens which can reinforce the cyanide generation and improve gold-leaching efficiency. The factors affected the microorganisms on cyanide generation were summarized and the proper conditions were also discussed in this article. And present researches of C. violaceum in gold bioleaching had made good progress which the reported leaching efficiency of gold was over 70%.

A new strain for recovering precious metals from waste printed circuit boards

A new strain, Pseudomonas Chlororaphis (PC), was found for dissolving gold, silver, and copper from the metallic particles of crushed waste printed circuit boards (PCBs). The optimized conditions that greatly improved the ability of producing CN− (for dissolving metals) were obtained. Dissolving experiments of pure gold, silver, and copper showed that the metals could be changed into Au+, Ag+, and Cu2+. PC cells and their secreta would adsorb metallic ions. Meanwhile, metallic ions destroyed the growth of PC. Dissolving experiments of metallic particles from crushed waste PCBs were performed by PC. The results indicated that 8.2% of the gold, 12.1% silver, and 52.3% copper were dissolved into solution. This paper contributed significance information to recovering precious metals from waste PCBs by bioleaching.

An impact crushing dynamic model of waste printed circuit board particles

In order to obtain optimal particle size and distribution of crushed waste printed circuit boards (PCBs) for high-quantify separation of Cu and nonmetal, different distribution models are used to describe waste PCBs particles impact crushing distribution characteristics. The results showed that: Rosin–Rammler distribution can more accurately describe waste PCBs impact crushing distribution regularity, and can be used to predict waste PCBs particles impact crushing distribution characteristics. Based on this, a new dynamic model for impact crushing waste PCBs particle size and distribution was established. It was used to analyze the impact crushing distribution characteristics of the waste PCBs particles with the same mass and different size grades, and with the same size grades and different mass. The results have a good agreement with the actual crushing results. This model has some significance for the processing of waste PCBs impact crushing, and this research possibly offers a basis for the design of waste PCBs recycling production lines.

Separating and Recovering Pb from Copper-Rich Particles of Crushed Waste Printed Circuit Boards by Evaporation and Condensation

Waste printed circuit boards (WPCBs) are treated by crushing and electrostatic separation to obtain the copper-rich particles. However, the copper-rich particles contain a certain content of solder, which may cause Pb contamination if improperly treated. The separation behaviors of Pb from single solder and solder mixed with Cu particles under vacuum are studied in this work. Due to the presence of Cu particles in the copper-rich particles, it becomes much easier to separate Pb from mixed particles than from single solder. On the basis of the experiments, the rules and phenomena different from previous studies are concluded, including the multilayer evaporation effect, the formation of Cu-Sn intermetallic compound and so on. Mechanisms of these phenomena are also explored. Pb is separated and recovered from copper-rich particles of crushed WPCBs at 1123 K for 90 min under 0.1-1 Pa. The metals including Cu, Pb, Sn in WPCBs are all efficiently recovered. This work enriches separating rules for recovering Pb by evaporation and condensation, and also points out an efficient and promising method for recovering toxic heavy metals from WPCBs.

Size distribution of wet crushed waste printed circuit boards

A wet impact crusher was used to breakdown waste printed circuit boards (PCB’s) in a water medium. The relationship between the yield of crushed product and the operating parameters was established. The crushing mechanism was analyzed and the effects of hammerhead style, rotation speed, and inlet water volume on particle size distribution were investigated. The results show that the highest yield of −1 + 0.75 mm sized product was obtained with an inlet water volume flow rate of 5.97 m 3/h and a smooth hammerhead turning at 1246.15 r/min. Cumulative undersize-product yield curves were fitted to a nonlinear function: the fitting correlation coefficient was greater than 0.998. These research results provide a theoretical basis for the highly effective wet crushing of PCB’s.

Quadratic nonlinear models for optimizing electrostatic separation of crushed waste printed circuit boards using response surface methodology

The electrostatic separation has proved to be an effective and environment-friendly treatment for the recovery of crushed waste printed circuit boards (PCBs). In this paper a more sophisticated response surface methodology was applied to build quadratic models and optimize the three main factors on a roll-type electrostatic separator. The sample of granular mixture got from crushed PCB wastes (size 0.3–0.45 mm, containing 25% metal and 75% nonmetal). According to the analysis of the experiment data, some quadratic effects were found, and two quadratic models for conductor production ( C) and middling production ( M) were established. The results indicated that the high voltage level and roll speed are the most important factors for the process. Because of the existence of the quadratic effect, the highest efficiency can also be achieved at a lower voltage level (27–29 kV) compared with a maximum voltage level.

Application of Vacuum Metallurgy to Separate Pure Metal from Mixed Metallic Particles of Crushed Waste Printed Circuit Board Scraps

The principle of separating pure metal from mixed metallic particles (MMPs) byvacuum metallurgy is that the vapor pressures of various metals at the same temperature are different As a result, the metal with high vapor pressure and low boiling point can be separated from the mixed metals through distillation or sublimation, and then it can be recycled through condensation under a certain condition. The vacuum metallurgy separation (VMS) of MMPs of crushed waste printed circuit boards (WPCBs) has been studied in this paper. Theoretical analyses show that the MMPs (copper, zinc, bismuth, lead, and indium, for example) can be separated by vacuum metallurgy. The copper particles (0.15-0.20 mm) and zinc particles (<0.30 mm) were chosen to simulate the MMPs of crushed WPCBs. Experimental results show that the separated efficiency of zinc in the copper-rich particles achieves 96.19 wt % when the vacuum pressure is 0.01-0.10 Pa, the heating temperature is 1123 K, and the heating time is 105 min. Under this operation condition, the separated efficiency of zinc in the copper-rich particles from crushed WPCBs achieves 97.00 wt % and the copper purity increases from 90.68 to 99.84 wt %.