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.

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.

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.

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.

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。

粉末压片-波长色散型X射线荧光光谱法测定废弃印刷线路板中10种金属元素的含量

测定废弃印刷线路板(WPCBs)中金属元素含量的方法均需对样品进行消解,操作复杂耗时;X射线荧光光谱法无需样品消解,但由于缺少相似基体的标准样品而定量不准确。基于此,以与WPCBs在元素组成上较为相似的地质类标准物质作为本底物,按不同比例添加环氧树脂及铜粉制备一系列校准样品并绘制校准曲线,提出了题示研究。取WPCBs研磨,过200目(0.074 mm)筛,于105℃烘干,取上述样品5 g置于不锈钢模具中,加入硼酸镶边,用压片机(压力200 kPa,保压时间20 s)制成直径40 mm圆片,采用波长色散型X射线荧光光谱法(WD-XRF)测定其中银、钡、铬、铜、铁、锰、镍、铅、硅、钛等10种金属元素的含量。结果表明:各元素的质量分数在一定范围内与响应强度呈线性关系;方法用于分析其他校准样品,测定值的相对误差的绝对值不大于20%;方法用于测定2个实际WPCBs样品分析,硅的测定结果与氟硅酸钾容量法的基本一致,其他元素测定结果与电感耦合等离子体原子发射光谱法(ICP-AES)的基本一致。

废电路板资源化利用研究动态及展望

巨大的环境压力和循环经济发展需求推动了废电路板资源化利用产业的快速发展,但该产业目前面临废电路板有价组分回收缺乏系统性的瓶颈。详细介绍废电路板资源化利用技术,展望废电路板资源化回收的发展趋势,提出废电路板“全利用、零污染、高增值”的新发展思路,明确系统地回收利用废电路板全组分,实现回收过程零污染,助力可持续循环经济是废电路板发展的方向。

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。

废线路板利用过程重金属污染特征、迁移及风险评估

电子工业的发展和电器电子产品更新换代的加速使得废线路板产生量逐年增加.废线路板虽然资源回收价值高,但伴随其利用,重金属等污染物的释放会对生态环境和人体健康造成严重危害.因此,研究废线路板利用过程重金属的污染特征和迁移规律可为精准防控利用过程的重金属污染,保障人民群众健康和生态环境安全提供依据.本研究以采用机械分选工艺利用报废印刷线路板的企业为研究对象,通过采集车间内外不同环境介质样品,运用富集因子法和地累积指数法评价了废线路板利用过程重金属的富集和污染特征,并结合Pearson相关性分析、主成分分析等统计分析方法,阐明利用过程重金属的迁移规律,使用潜在生态风险指数法(RI)分析了潜在生态风险.结果表明,废线路板利用车间内灰尘和总悬浮颗粒物(TSP)中Cu浓度最高,Cd浓度最低;Sn、Cu、Pb、Cd、Zn在灰尘和TSP中表现出不同程度的富集;Sn、Cd、Pb在车间内主要分布于TSP中,但在车间外的富集程度和污染水平明显降低,表明其对车间外区域的影响范围有限.Cu、Pb、Sn、Cd等元素性质和在颗粒中的存在形态不同,其迁移特征也有所差异,但废线路板利用过程重金属的迁移规律总体可以总结为:破碎的小颗粒物料—车间内TSP—车间内灰尘/车间外—地表灰尘或土壤—扬尘—TSP.车间内灰尘和TSP的RI值分别为386、1706,Cu、Cd、Pb均是贡献最高的因子.因此,妥善处置定期清理的灰尘,保持车间相对密闭和微负压状态,并对收集的废气进行处理可有效控制废线路板利用过程重金属污染.

基于超声强化硫氰酸盐体系的废旧电路板中贵金属回收研究

电子废弃物中含有大量的稀贵金属,已经成为了重要的城市矿产资源。从电子废弃物中回收贵金属,可以在一定程度上缓解资源短缺问题。目前,对于废旧电路板中金的回收大多采用氰化法,该方法存在严重的环境污染风险。本文提出了一种环境友好、反应速率快的超声强化硫氰酸盐体系用于回收废旧电路板中的金。通过对浸金过程的因子设计和响应曲面设计,建立浸金过程的二阶非线性模型,得到的最佳浸出条件为:硫氰酸钠浓度0.23 mol/L、过氧化氢体积0.96 mL、试验温度41.3℃、固液比188片/25 mL,在此条件下反应90 min,浸金率为94.65%。该体系浸出过程主要受混合模型控制,遵循动力学模型(1-2/3X)-(1-X)^(2/3)+k_(r)/k_(d)(1-(1-X)^(1/3))=kmt。研究成果可为电子废弃物中贵金属资源化回收及其工业化应用提供理论依据。

微生物浸出技术应用于废线路板金属资源化利用的研究进展

废线路板(WPCBs)由有机环氧树脂、贱金属和贵金属组成,具有回收价值高、污染重、处理难度高等特点,因此其资源化处理处置备受关注。以废线路板为例,本文综述了微生物浸出技术在其金属回收方面的应用研究,包括微生物种类(嗜酸菌、真菌和产氰微生物)、浸出机理和优化浸出工艺方法等。微生物浸出技术是未来值得深入研究和工程应用的技术,能有效回收稀贵金属,降低治理成本,提高工艺的经济性。

废旧电路板压力氧化—氰化提金试验研究

对市面购买的废旧电路板进行压力氧化—氰化提金试验研究,考察了物料细度、物料质量分数、氧化温度、氧化时间等对压力氧化预处理效果的影响。试验结果表明:在物料细度-0.25 mm占80%、物料质量分数30%、氧气分压2.0 MPa、氧化温度200℃、氧化时间3.0 h、硫酸用量90 kg/t、氧化剂用量25 kg/t条件下进行压力氧化预处理试验,而后在适宜条件下进行氰化提金试验,平均金浸出率可达92.52%。

废弃电路板中金属的含量与溶出规律研究

电子废弃物中金属引起的环境问题日益增加,采用微波消解法对电子废弃物印刷电路板中金属分布及其构成进行研究,并通过配制仿真酸雨溶液对电路板中金属溶出规律进行分析。结果表明:采用原子吸收光谱仪对电路板中金属含量进行测试,在废弃电路板中一共检测到12种金属,总量约占电路板总质量的37.3%。其中,7种金属在p H值等于1的强酸性环境下表现出了良好的溶出性能,其溶出程度从高至低依次是铜、铁、锌、铅、镍、铬和镉,其中镉的溶出比例最大并且溶出速度最快。研究结果为评估酸雨条件下金属从废弃电路板中溶出的潜在能力提供依据,为分析废弃电路板的环境危害以及衡量废弃电路板的生态风险提供基础数据。