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.

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 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 °C/min 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 °C,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.

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.

Distribution of heavy metals during pyrolysis of waste printed circuit boards

<正> 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 μg/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.

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.

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.

基于298/77 K循环处理回收PCB中非金属组分

为解决废印制电路板(PCB)中非金属组分回收难且二次污染率大的问题,引入298/77 K循环处理技术,首先分析温度改变对PCB内部结构所造成的影响及PCB内部力学性能的变化,测试静电分选和离心分选对PCB非金属组分回收率的实际影响,之后引入CaF_(2)作为精炼过程中的强氧化剂,测试PCB内部结构发生改变后的硅组分回收率,最后测定回收后硅元素的实际纯度。结果表明:PCB在经过298/77 K循环处理后,内部结构受温度循环影响发生明显变化;各项力学性能均实现明显下降;PCB非金属组分实际产出量和硅组分回收率,相比于传统处理方式实现了明显提升,且对原PCB中各项杂质有较好的去除效果,硅元素占比在97%以上。

废旧线路板综合回收利用技术研究进展

为了提高电子固体废弃物等二次资源综合利用水平,针对目前废旧线路板存量大,增速快的特点,以及暴力拆解、强酸浸出、污染严重、回收率低等问题,对其物理分选、火法处理、湿法处理等技术手段进行了综述,并分析了不同工艺技术优缺点。最后指出,废旧线路板等电子固废应当在高效拆解的基础上,使不同组分最大限度解离,再通过火法处理手段利用其中有机组分,通过湿法处理技术回收其中有价金属,最终实现全组分回收以及过程中使用的药剂都循环利用的目的。废旧线路板综合利用未来可在热解设备、新型萃取剂研发等方面进行更加深入的研究。

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。

基于网络层次分析法的废电路板树脂粉典型利用处置技术综合评价

面对产量快速增长的废电路板(WPCBs),通过机械物理等方法得到的废树脂粉若不能妥善利用处置会造成资源浪费和二次污染等一系列问题,亟须对现有WPCBs树脂粉典型利用处置技术进行综合评价。本研究运用基于网络层次分析法结合专家打分的综合评估方法,从资源、环境、经济、技术和社会五个方面构建网络层次关系,以确定其准则和指标间的联系与反馈,同时对WPCBs树脂粉三种典型利用处置技术填埋、焚烧和物理法进行优劣排序。研究结果表明,物理法以优异的环境、资源和经济准则获得最高的综合评价水平。最后以苏州某资源再生利用企业为例,应用本研究建立的评价模型对其开展在准则和指标方面的综合评价,验证了该模型的有效性,以期为WPCBs树脂粉工业化利用处置技术路线选择提供理论依据和参考。

基于深度学习的废旧电路板表面缺陷分类

针对废旧电路板表面缺陷识别,提出了一种利用深度学习进行分类的方法。在ResNet34模型的基础上,增加了CBAM注意力机制。通过将ResNet34架构与注意力机制相结合,旨在增强模型关注输入图像中重要特征并对其进行优先排序的能力,从而提高分类的准确性。结果表明提出的方法在提高废旧电路板表面缺陷分类方面的有效性。

添加剂对WPCB非金属组分树脂分离物热解脱溴的影响

研究了不同添加剂对废旧印刷线路板非金属组分(NMFs)中树脂分离物热解脱溴的影响,结果表明,以尿素为添加剂可以促使NMFs树脂分离物中含溴阻燃剂以HBr、溴甲烷和溴乙烷的形式脱除,同时,使热解油中苯酚和其他酚类物质的含量增加,而固体残碳中的溴含量减少;对对′-二氨基二苯甲烷对废旧印刷线路板NMFs树脂分离物中含溴成分的脱除无促进作用,但可使热解油中苯酚和其他酚类物质的含量增加,同时使生成的气体量减少,液体和固体产物量增加;六亚甲基四胺尽管可以促使NMFs树脂分离物中含溴阻燃剂以HBr和溴甲烷、溴乙烷的形式脱除,但显著降低了热解油中苯酚和其他酚类物质的含量,同时有较多的N-甲基乙酰胺和N,N-二甲基甲酰胺生成,此外使得液体和固体产物量增加,但气体产物量减少。

WPP/NWPCB/POE复合材料的制备及其热解特性

以废旧汽车保险杠(WPP)为基体,废弃线路板非金属粉(NWPCB)为填料,通过熔融共混的方法制备了系列WPP/NWPCB复合材料。在此基础上,用乙烯-辛烯共聚物(POE)和马来酸酐接枝聚丙烯(PP-g-MAH)对复合材料进行了协同改性,以增强复合材料的性能。力学性能测试和冲击断面微观形貌分析表明,POE显著提高了WPP/NWPCB复合材料的韧性,当POE用量为15 g·(100 g)-1时,冲击强度较改性前提高129%;PP-g-MAH能够有效改善复合材料中填料与基体相容性,当添加量为9 g·(100 g)-1时,复合材料的机械性能达到最佳,冲击强度、弯曲强度和拉伸强度较改性前分别提高7.8%、23.4%和20%。通过热重-红外联用研究了WPP/NWPCB/POE复合材料的热解过程,结果表明,复合材料在热解过程中除产生烷烃、烯烃及CO2外,还产生了少量的苯酚类芳香族化合物与HBr等有害气体,同时NWPCB填料的添加提高了复合材料中WPP的热稳定性。

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.

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.