Distribution behavior of valuable elements in oxygen-enriched top-blown smelting process of waste printed circuit boards

Oxygen-enriched top-blown smelting is a promising technology for processing waste printed circuit boards(WPCBs).The distribution behavior of valuable elements in WPCBs during smelting was investigated by varying the oxygen-enriched concentration,oxygen volume,CaO/SiO_(2)(mass ratio),and Fe/SiO_(2)(mass ratio).The optimal operating conditions were obtained by implementing a one-factor-at-a-time method.X-ray diffractometer,scanning electron microscopy−energy dispersive spectrometer,and inductive coupled plasma-atomic emission spectroscopy methods were utilized to detect the chemical composition,occurrence state as well as elemental contents of alloy and slag.It is found that the elements of Cu,Sn and Ni are mainly accumulated in the alloy while Fe is mainly oxidized into the slag.The direct yields of Cu,Sn and Ni are 90.18%,85.32%and 81.10%under the optimal conditions of temperature 1250℃,oxygen-enriched concentration 30%,oxygen volume 24 L,CaO/SiO_(2) mass ratio 0.55,and Fe/SiO_(2) mass ratio 1.05.The results show that the valuable metals are mainly lost in the slag through mechanical entrainment.

Effect of copper content on the pyrolysis process of organic components in waste printed circuit boards:Based on experimental and quantum chemical DFT simulations

In recent years,scientists have become increasingly concerned in recycling electronic trash,particularly waste printed circuit boards(WPCBs).Previous research has indicated that the presence of Cu impacts the pyrolysis of WPCBs.However,there may be errors in the experimental results,as printed circuit boards(PCBs)with copper and those without copper are produced differently.For this experiment,we blended copper powder with PCB nonmetallic resin powder in various ratios to create the samples.The apparent kinetics and pyrolysis properties of four resin powders with varying copper concentrations were compared using nonisothermal thermogravimetric analysis(TG)and thermal pyrolysis-gas chromatography mass spectrometry(Py-GC/MS).From the perspective of kinetics,the apparent activation energy of the resin powder in the pyrolysis reaction shows a rise(0.1<a<0.2)-stable(0.2<a<0.4)-accelerated increase(0.4<a<0.8)-decrease(0.8<a<0.9)process.After adding copper powder,the apparent activation energy changes more obviously when(0.2<a<0.4).In the early stage of the pyrolysis reaction(0.1<a<0.6),the apparent activation energy is reduced,but when a?0.8,it is much higher than that of the resin sample without copper.Additionally,it is discovered using thermogravimetric analysis and Py-GC/MS that copper shortens the temperature range of the primary pyrolysis reaction and prevents the creation of compounds containing bromine.This inhibition will raise the temperature at which compounds containing bromine first form,and it will keep rising as the copper level rises.The majority of the circuit board molecules have lower bond energies when copper is present,according to calculations performed using the Gaussian09 software,which promotes the pyrolysis reaction.

Optimization of low-temperature alkaline smelting process of crushed metal enrichment originated from waste printed circuit boards

A novel low-temperature alkaline smelting process is proposed to convert and separate amphoteric metals in crushed metal enrichment originated from waste printed circuit boards. The central composite design was used to optimize the operating parameters,in which mass ratio of Na OH-to-CME, smelting temperature and smelting time were chosen as the variables, and the conversions of amphoteric metals tin, lead, aluminum and zinc were response parameters. Second-order polynomial models of high significance and3 D response surface plots were constructed to show the relationship between the responses and the variables. Optimum area of80%-85% Pb conversion and over 95% Sn conversion was obtained by the overlaid contours at mass ratio of Na OH-to-CME of4.5-5.0, smelting temperature of 653-723 K, smelting time of 90-120 min. The models were validated experimentally in the optimum area, and the results demonstrate that these models are reliable and accurate in predicting the smelting process.

Pyrolysis kinetics and TG-FTIR analysis of waste epoxy printed circuit boards

Thermal decomposition of waste epoxy PCBs was performed in different atmospheres （nitrogen, argon, air and vacuum） at a heating rate of 10 ℃/rain by DSC-TGA, and the pyrolysis characteristic was analyzed. The gases volatilized from the experiment were qualitatively analyzed by TG-FTIR. Kinetics study shows that pyrolysis reaction takes place between 300 and 400℃, and the activation energies are 256, 212 and 186.2 kJ/mol in nitrogen, argon and vacuum, respectively. There are two mass-loss processes in the decomposition under air atmosphere. In the first mass-loss process, the decomposition is the main reaction, and in the second process, the oxidation is the main reaction. The activation energy of the second mass-loss process is 99.6 kJ/mol by isothermal heat-treatments. TG-FTIR analysis shows carbon dioxide, carbon monoxide, hydrogen bromide, phenol and substituent phenol are given off during the pyrolysis of waste epoxy PCBs.

Efficient recovery of valuable metals from waste printed circuit boards by microwave pyrolysis

The recycling of waste printed circuit board(WPCBs) is of great significance for saving resources and protecting the environment. In this study, the WPCBs were pyrolyzed by microwave and the contained valuable metals Cu, Sn and Pb were recovered from the pyrolyzed WPCBs. The effect of pyrolysis temperature and time on the recovery efficiency of valuable metals was investigated. Additionally, the characterization for morphology and surface elemental distribution of pyrolysis residues was carried out to investigate the pyrolysis mechanism. The plastic fiber boards turned into black carbides, and they can be easily separated from the metals by manual. The results indicate that 91.2%, 96.1% and 94.4% of Cu, Sn and Pb can be recovered after microwave pyrolysis at 700 °C for 60 minutes. After pyrolysis, about 79.8%(mass)solid products, 11.9%(mass) oil and 8.3%(mass) gas were produced. These gas and oil can be used as fuel and raw materials of organic chemicals, respectively. This process provides an efficient and energy-saving technology for recovering valuable metals from WPCBs.

Pyrolysis behaviour and combustion kinetics of waste printed circuit boards

The effective recycling of waste printed circuit boards(WPCBs)can conserve resources and reduce environmental pollution.This study explores the pyrolysis and combustion characteristics of WPCBs in various atmospheres through thermogravimetric and Gaussian fitting analyses.Furthermore,this study analyses the pyrolysis products and combustion processes of WPCBs through thermogravimetric and Fourier transform infrared analyses(TG-FTIR)and thermogravimetry-mass spectrometry(TG-MS).Results show that the pyrolysis and combustion processes of WPCBs do not constitute a single reaction,but rather an overlap of multiple reactions.The pyrolysis and combustion process of WPCBs is divided into multiple reactions by Gaussian peak fitting.The kinetic parameters of each reaction are obtained by the Coats-Redfern method.In an argon atmosphere,pyrolysis consists of the overlap of the preliminary pyrolysis of epoxy resin,pyrolysis of small organic molecules,and pyrolysis of brominated flame retardants.The thermal decomposition process in the O_(2) atmosphere is mainly divided into two reactions:brominated flame retardant combustion and epoxy combustion.This study provided the theoretical basis for pollution control,process optimization,and reactor design of WPCBs pyrolysis.

Stress Analysis of Printed Circuit Board with Different Thickness and Composite Materials Under Shock Loading

In this study,the deformation and stress distribution of printed circuit board(PCB)with different thickness and composite materials under a shock loading were analyzed by the finite element analysis.The standard 8-layer PCB subjected to a shock loading 1500 g was evaluated first.Moreover,the finite element models of the PCB with different thickness by stacking various number of layers were discussed.In addition to changing thickness,the core material of PCB was replaced from woven E-glass/epoxy to woven carbon fiber/epoxy for structural enhancement.The non-linear material property of copper foil was considered in the analysis.The results indicated that a thicker PCB has lower stress in the copper foil in PCBs under the shock loading.The stress difference between the thicker PCB(2.6 mm)and thinner PCB(0.6 mm)is around 5%.Using woven carbon fiber/epoxy as core material could lower the stress of copper foil around 6.6%under the shock loading 1500 g for the PCB with 0.6 mm thickness.On the other hand,the stress level is under the failure strength of PCBs with carbon fiber/epoxy core layers and thickness 2.6 mm when the peak acceleration changes from 1500 g to 5000 g.This study could provide a reference for the design and proper applications of the PCB with different thickness and composite materials.

Distribution of heavy metals during pyrolysis of waste printed circuit boards

The volatilization behavior of Cu, Pb, Sn, Sb, Ni, Zn, Mn, Co, Cr, Cd during pyrolysis of waste printed circuit boards was investigated in a bench-scale fixed-bed pyrolysis system. It was found that volatility of heavy metals increases with operating temperature elevating, and bromine and vacuum have an obvious promoting effect on volatility of most of heavy metals. Over 99% weight of Cu and Ni are still remained in solid residue after pyrolysis, about 20% weight of Sb, Zn and Cd are transfered into liquid and gas during a pyrolysis process at 600 ℃, volatilization fractions of Pb, Sn, Mn, Co, Cr are less than 10% at the same conditions. The contents of heavy metals in liquid and gas products depend on not only volatility of metals, but also their initial contents in printed circuit boards, pyrolysis liquid and gas are primarily contaminated by Cu, Pb, Sn, Sb and Zn, their contents in liquid vary from 10^2 to 10^3 pg/mL, Mn, Co, Cr, Cd were detected only at very low level, less than 10 μg/mL.

Research on Selective Shredding of Wasted Printed Circuit Boards

Electronic scrap, especially wasted printed circuit boards (PCBs), is regarded as an environmental challenge. At present, the physical separation is thought to be the environmental friendly and economical method of treating and reutilizing electronic waste. An effective liberation of metals from non metallic components is a crucial step towards mechanical separation and recycling of wasted PCBs. In this paper, the selective shredding theory and mechanics characteristics of wasted PCBs were analyzed, and the shredded experiments of wasted PCBs by hammer mill were investigated. The result shows that the selective shredding exists in the wasted PCBs shredded process by hammer mill. The shredding velocity of non metallic components is far greater than that of metals in the wasted PCBs shredding, which makes the metals concentrate in the coarser fraction. And the impact force of hammer mill is superior to metal liberation from non metallic components, a satisfied metal liberation degree can be achieved in the wasted PCBs shredding by hammer mill.

Review: Current Status of Recycling of Waste Printed Circuit Boards in India

Printed Circuit Boards (PCBs) are an integral part of any electronic equipment. The growth of e-waste as end-of-life electronic equipments at an exponential rate is producing large quantities of discarded PCBs. In India, current recycling and processing of PCBs is managed almost entirely by the informal sector or the unskilled labor (95%). The crude recycling activities cause irreversible health and environmental hazards and the loss of valuable materials due to the poor recovery of base and precious metals. With the disclosures of the recycling being done by unskilled labor, alternative recycling strategies are being sought with the aim of higher recovery of materials in an environment friendly manner. There is an urgent need to establish effective and efficient methods for recycling the metals presented in the waste PCBs. In this study, the existing methods practiced for recycling of waste PCBs in India and the management strategies for handling them are assessed.

Vacuum pyrolysis of waste print circuit board

Waste print circuit board containing 11.38% Br was pyrolyzed in vacuum. Thermal stability of waste print circuit board was studied under vacuum condition by thermo-gravimetry(TG). Vacuum pyrolysis of WPCB was studied emphasizing on the kinetics of WPCB pyrolysis reactions. Based on the TG results, a kinetic model was pro- posed. Kinetic parameters were calculated for reaction with this model including all stages of decomposition. The average activation energy is 68 kJ/mol with reaction order 3. These findings provide new insights into the WPCB thermal decomposition and useful data for rational design and operation of pyrolysis.

Metals Recovery from Fine Printed Circuit Boards Using Falcon SB Concentrator

Physical methods show great potential and advantages on comprehensive reutilization of waste printed circuit boards (PCBs) because of lower investment and operation cost, higher efficiency and environment friendliness. However, metals contained in fine fraction of PCBs cannot be recovered effectively by conventional equipments such as high tension electrostatic separator or shaking table. In the paper, this conundrum was resolved successfully with the enhanced Falcon SB concentrator. The separation mechanism of Falcon SB concentrator was analyzed and main factors affecting separation efficiency such as magnitude of rotation frequency of bowl, water counter pressure and slurry concentration of feed were studied and interaction of factors above also were investigated using Design-Expert software. Experiment results show that complete liberation degree and great difference of density between metals and nonmetals are suitable to recover metals from -74 μm PCBs using enhanced Falcon SB concentrator and 80.77 % integration efficiency can be achieved when slurry concentration of feed is 40 g/L with the water counter pressure of 0.01 MPa and rotation frequency of 50 Hz.

Modeling of Micropores Drilling Force for Printed Circuit Board Micro-holes Based on Energy Method

The quality of printed circuit board(PCB)micro-hole processing directly determines the stability of the inner and outer circuit connections.Micro-hole drilling technology is a typical method for PCB micro-hole processing.The problem of optimal control of its drilling force is one of the main factors affecting the quality of micro-hole machining.To address this problem,the thrust forces and torques in PCB drilling were first modeled and analyzed,and the corresponding prediction models were established.The drilling force analysis was carried out through the micro-hole drilling experiment,the specific cutting energy under different feed rates was calculated,the influence of the size effect was clarified,and the accuracy of the prediction model was verified.The result shows that during the drilling of glass fiber cloth,changes in the material removal mechanism are induced as the feed per revolution is varied.When the feed per revolution is less than the tool edge radius,the glass fiber is not cut by the main cutting edge,but is crushed and broken.When the feed per revolution is greater than the radius of the tool edge,the glass fiber is cut by the main cutting edge.At the same time,the established analytical model can accurately reflect the influence of the size effect on the drilling torque in PCB micro-hole drilling,and the error is within 10%.This method has certain practical application value in controlling PCB micro hole processing quality.

Products Made from Nonmetallic Materials Reclaimed from Waste Printed Circuit Boards

Printed circuit boards （PCBs） are in all electronic equipment, so with the sharp increase of electronic waste, the recovery of PCB components has become a critical research field. This paper presents a study of the reclaimation and reuse of nonmetallic materials recovered from waste PCBs. Mechanical processes, such as crushing, milling, and separation, were used to process waste PCBs. Nonmetallic materials in the PCBs were separated using density-based separation with separation rates in excess of 95%. The recovered nonmetals were used to make models, construction materials, composite boards, sewer grates, and amusement park boats. The PCB nonmetal products have better mechanical characteristics and durability than traditional materials and fillers. The flexural strength of the PCB nonmetallic material composite boards is 30% greater than that of standard products. Products derived from PCB waste processing have been brought into industrial production. The study shows that PCB nonmetals can be reused in profitable and environmentally friendly ways.

Methodology for Precious Metal Recovery in Computer Printed Circuit

The life of electronic equipment is becoming increasingly shorter and its replacement always generates a quantity of waste increase, giving rise to a problem of environmental character and still needed new options of solid waste management that will contribute to global sustainable development. Parts of these waste are TCI （the card＇s printed circuit） which containing dangerous elements and turns them into a polluting material from the soil, water and air, being harmful to human health if there is to proper and responsible way, so the recycling of TCI to obtain precious metals is an example of industrial materials that can be recycled. Despite this, large quantities of these are not recycled and some others are not considered. The objective of this work is to present a systematic and ecological methodology for the recovery of valuable materials contained in parts of used in computers, circuit boards using a leaching process. The method determines a set of variables to evaluate the kinetics of the reaction and the leaching of metals that form the substrate of metal and to establish the parameters that affect the rate of leaching of metals through a sensitivity analysis, to identify design alternatives. It determines the quantity and percentages that constitutes the motherboard, processor, video cards, accelerator graphics, network and memory cards RAM, among others and its content of metals such as Cu, Fe, Ag, Au and Pt.

Preparation of pure SnO_2 powders from tin slag of printed circuit boards waste

The recycling method and principle of SnO2 from the tin slag of printed circuit boards（PCB） waste were investigated. In this study, pure SnO2 powders were obtained through a multi-step process including ball-milling, roasting, dissolving, precipitating, and pickling. The total recovery rate of tin can be up to 91 %. The SnO2 powders obtained is the single phase, and the content of SnO2 is up to 99.9 %. However, the SnO2 particles are easier to agglomerate during the precipitation process. The agglomerate SnO2 particles are about 7.778 lm in mean particle size（D50）. This preparation method presents a viable alternative for the tin slag recycling. The tin is not only recycled, but also reused directly to prepare pure SnO2 powders.

Self-catalytic pyrolysis thermodynamics of waste printed circuit boards with co-existing metals

Waste printed circuit boards(WPCBs)are generated increasingly recent years with the rapid replacement of electric and electronic products.Pyrolysis is considered to be a potential environmentally-friendly technology for recovering organic and metal resources from WPCBs.Thermogravimetric analysis and kinetic analysis of WPCBs were carried out in this study.It showed that the co-existing metals(Cu,Fe,Ni)in WPCBs have positive self-catalytic influence during the pyrolysis process.To illustrate their catalytic effects,the apparent activation energy was calculated by differential model.Contributions of different reactions during catalytic pyrolysis process was studied and the mechanism function was obtained byŠesták-Berggren model.The results showed that Cu,Fe,Ni can promote the reaction progress and reduce the apparent activation energy.Among the three metals,Ni plays better catalytic role than Cu,then Fe.This work provides theoretical base for understanding the three metals’catalytic influence during the pyrolysis of non-metal powders in WPCBs.

Copper recovery from waste printed circuit boards concentrated metal scraps by electrolysis

Copper recovery is the core of waste printed circuit boards （WPCBs） treatment. In this study, we proposed a feasible and efficient way to recover copper from WPCBs concentrated metal scraps by direct electrolysis and thctors that affect copper recovery rate and purity, mainly CuSO4.5H2O concentration, NaCI concentration, H2SO4 concentration and current density, were discussed in detail. The results indicated that copper recovery rate increased first with the increase ofCuSO4- 5H2O, NaCI, H2SO4 and current density and then decreased with further increasing these conditions. NaCI, H2SO4 and current density also showed a similar impact on copper purity, which also increased first and then decreased. Copper purity increased with the increase of CuSO4.5H2O. When the concentration of CuSO4-5H2O NaCI and H2oSO4 was respectively 90, 40 and 118 g/L and current density was 80 mA/cm-, copper recovery rate and purity was up to 97.32% and 99.86%, respectively. Thus, electrolysis proposes a feasible and prospective approach for waste printed circuit boards recycle, even for e-waste, though more researches are needed for industrial application.

Preparation of Pure Copper Powder from Acidic Copper Chloride Waste Etchant

The method for the recycling of copper from copper chloride solution was developed. This process consists of extraction of copper, purification and particle size reduction. In the first step, reductive metal scraps were added to acidic copper chloride waste enchants produced in the PCB industry to obtain copper powder. Composition analysis showed that this powder contained impurities such as Fe, Ni, and water. So, drying and purification were carried out by using microwave and a centrifugal separator. Thereby the copper powder had a purity of higher than 99% and spherical form in morphology. The copper powder size was decreased by ball milling.

微波强化嗜酸氧化硫硫杆菌浸出废线路板中铜的条件优化

为提高电子废弃物中金属铜的生物浸出率,用微波强化嗜酸氧化硫硫杆菌(Aidithiobacillus thiooxidan)对废线路板中铜的浸出,采用Plackett-Burman法和Box-Behnken法优化强化浸出条件。Plackett-Burman法表明微波功率、辐照时间和浸出时间能够显著影响废线路板中铜的生物浸出率。最陡爬坡实验确定3因素的中心值为微波功率340 W、辐照时间3.60 min和浸出时间6.80 d。采用Box-Behnken法优化浸铜条件。研究发现,微波功率、浸出时间、微波功率和浸出时间及辐照时间和浸出时间的交互作用对浸铜有显著影响,辐照时间有影响但不显著。模型预测最优条件为微波功率336.10 W、辐照时间3.59 min和浸出时间6.82 d,预测最优浸出率为75.69%。调整微波强化废线路板中铜的生物浸出条件为微波功率336 W、辐照时间3.60 min和浸出时间6.80 d,实际铜浸出率为75.41%±0.76%,与模型预测结果相近。表明所得最优条件真实有效,可用于后续研究。