Examining the technology acceptance for dismantling of waste printed circuit boards in light of recycling and environmental concerns

The dismantling of printed circuit board assemblies (PCBAs) and the recovery of their useful materials can lead to serious environmental impacts mainly due to their complicated physical structure and the variety of toxic elements contained in their material composition. So far, less attention has been paid to their responsible recycling compared to that of bare printed circuit boards. Combined with other materials recovery process, proper dismantling of PCBAs is beneficial to conserve scarce resources, reuse the components, and eliminate or safely dispose of hazardous materials. In analyzing the generation, resources potential and hazardous risk of scrap PCBAs, technologies used for the dismantling of waste PCBAs have been widely investigated and reviewed from the aspects of both industrial application and laboratory-scale studies. In addition, the feasibility of PCBA dismantling has been discussed, the determinants of which, including the heating conditions and mechanical properties have been identified. Moreover, this paper evaluates the environmental consequences caused by the dismantling of PCBAs.     

Recovery of valuable materials from waste liquid crystal display panel

Associated with the rapid development of the information and electronic industry, liquid crystal displays (LCDs) have been increasingly sold as displays. However, during the discarding at their end-of-life stage, significant environmental hazards, impacts on health and a loss of resources may occur, if the scraps are not managed in an appropriate way. In order to improve the efficiency of the recovery of valuable materials from waste LCDs panel in an environmentally sound manner, this study presents a combined recycling technology process on the basis of manual dismantling and chemical treatment of LCDs. Three key processes of this technology have been studied, including the separation of LCD polarizing film by thermal shock method the removal of liquid crystals between the glass substrates by the ultrasonic cleaning, and the recovery of indium metal from glass by dissolution. The results show that valuable materials (e.g. indium) and harmful substances (e.g. liquid crystals) could be efficiently recovered or separated through above-mentioned combined technology. The optimal conditions are: (1) the peak temperature of thermal shock to separate polarizing film, ranges from 230 to 240 °C, where pyrolysis could be avoided; (2) the ultrasonic-assisted cleaning was most efficient at a frequency of 40 KHz (P = 40 W) and the exposure of the substrate to industrial detergents for 10 min; and (3) indium separation from glass in a mix of concentrated hydrochloric acid at 38% and nitric acid at 69% (HCl:HNO₃:H₂O = 45:5:50, volume ratio). The indium separation process was conducted with an exposure time of 30 min at a constant temperature of 60 °C.     

建筑废物填海处置过程重金属浸出特性及环境影响

填海处置已成为滨海城市建筑废物的重要消纳途径,而海水侵蚀导致重金属浸出可能加剧环境风险.为探究不同类型建筑废物中重金属受海水侵蚀的浸出特性及环境影响,于深圳市的城中村拆除作业现场、建筑装饰装修工程现场、建筑废物资源化利用厂、建筑垃圾堆填场开展不同来源建筑废物样品采集,分析样品中w（Zn）、w（Pb）、w（Cu）、w（Cd）,评价其潜在环境风险并解析其产生源;在此基础上,参考固体废物毒性浸出方法开展海水浸出模拟试验.结果表明:①建筑废物中重金属的潜在环境风险程度依次表现为Zn > Pb > Cu > Cd,w（Zn）、w（Pb）、w（Cu）、w（Cd）的最大值依次为197.8、82.6、67.1、0.22 mg/kg,分别为广东省土壤环境背景值的3.8、2.2、3.7和2.2倍,且来源于砖块、瓷砖、砂浆块、墙面涂料和玻璃的重金属含量超过了围填海工程填充物质成分限值要求.②海水对废物中重金属浸出影响显著,在液固比为10:1、浸出时间为18 h条件下,Zn、Pb、Cu、Cd浸出率分别高达15.9%、82.0%、10.4%和57.4%.③随着液固比和浸出时间的增加,重金属浸出量呈明显的上升趋势,其中Pb的浸出量最高.鉴于此,一方面应完善海水侵蚀对建筑废物中重金属浸出给沿海环境带来的生态风险分析;另一方面在填海处置前应加强建筑废物的风险管理如分类收集和安全处置等,并建立相应的控污机制.      

Thermal cracking of waste printed wiring boards for mechanical recycling by using residual steam preprocessing

Mechanical waste-processing methods, which combine crushing and separation processes for the recovery of valuable materials, have been widely applied in waste printed wiring board (PWB) treatment. However, both the high impact toughness and the tensile and flexural strengths of whole PWB with a laminated structure result in great energy consumption and severe abrasion of the cutters during multi-level crushing. In addition, the high temperatures occurring in continual crushing probably cause the decomposition of the polymer matrix. A thermal-crack method using residual steam as the heating medium has been developed to pre-treat waste PWBs. This treatment reduces the mechanical strength in order to improve the recovery rate of valuable materials in subsequent mechanical recycling. The changes of the PWBs’ macro-mechanical properties were studied to evaluate thermal expansion impacts associated with changes in temperature, and the dynamic dislocation micro-structures were observed to identify the fracture mechanism. The results showed that thermal cracking with steam at the temperature of 500 K can effectively attenuate the mechanical properties of waste PWBs, by reducing the impact, tensile and flexural strengths respectively, by 59.2%, 49.3% and 51.4%, compared to untreated PWB. Thermal expansion can also facilitate the separation of copper from glass fiber by reducing peel resistance by 95.4% at 500 K. It was revealed that the flexural fracture was a transverse cracking caused by concentrated stress when the heating temperature was less than 500 K, and shifted to a vertical cracking after exceeding 500 K.     

Enhancement of municipal sludge dewaterability by electrochemical pretreatment

Electrolysis is a promising technology to improve sludge dewaterability efficiently with negligible environmental impact. To intensify the electrolytic efficiency, the effect of electrolytes (NaCl, Na₂SO₄, NaNO₃, and NaClO₄) on electrolysis pretreatment of municipal sludge and its mechanisms was investigated using Ti/PbO₂ electrodes. The electrolytes, which enhanced the production of oxidative radicals, showed a significant synergetic effect in reducing the capillary suction time (CST) of sludge. NaCl was distinguished from the other electrolytes since it formed a large amount of active chlorine species, which oxidized the sludge cells to improve the sludge dewaterability. The surface morphologies as well as the soluble proteins and polysaccharides were analyzed to unravel the underlying mechanisms of sludge dewaterability. Additionally, an economic assessment showed that NaCl addition in the electrolysis pretreatment can be a suitable technique for enhancing municipal sludge dewaterability.     

An evaluation on the environmental consequences of residual CFCs from obsolete household refrigerators in China

Chlorofluorocarbons (CFCs) contained in household refrigerators consist mainly of CFC-11 and CFC-12, which will be eventually released into the environment. Consequentially, environmental releases of these refrigerants will lead to ozone depletion and contribute significantly to the greenhouse effect, if waste refrigerators are not disposed of properly. In the present paper, the potential release of residual CFCs and their substitutes from obsolete household refrigerators in China is examined, and their contributions to ozone depletion and greenhouse effect are compared with those of other recognized ozone-depleting substances (ODS) and greenhouse gases (GHGs). The results imply that annual potential amounts of released residual CFC-11 and CFC-12 will reach their maximums at 4600 and 2300 tons, respectively in 2011, and then decrease gradually to zero until 2020. Meanwhile, the amounts of their most widely used substitutes HCFC-141b and HFC-134a will keep increasing. Subsequently, the contribution ratio of these CFCs and their substitutes to ozone depletion will remain at 25% through 2011, and reach its peak value of 34% by 2018. The contribution to greenhouse effect will reach its peak value of 0.57% by 2010. Moreover, the contribution ratio of these CFCs to the total global release of CFCs will steadily increase, reaching its peak of 15% by 2018. Thus, this period from 2010 to 2018 is a crucial time during which residual CFCs and their substitutes from obsolete household refrigerators in China will contribute significantly to ozone depletion.     

钡盐共沉法处理酸性含铅废水

硫酸盐、氯化物复杂体系含铅酸性废水对环境的污染比较严重,并且不易处理.采用钡盐共沉法对含铅废水的处理进行研究,结果表明,钡盐共沉法可有效除去废水中的铅,但除铅效果受铅与废水中氯离子络合程度的影响,而受反应时间、温度、陈化时间的影响较小,容易实现工业化.采用钡盐共沉法处理硫酸盐氯化物复杂体系酸性废水.处理后的废水中含铅量远低于0.5 mg/L.     

建筑装修施工过程环境污染特征

为系统探明装修施工过程存在的环境污染问题及其潜在人体健康影响,以深圳市典型装修项目为例,研究了不同装修装饰工序中噪声污染及室内典型空气污染物浓度水平,同时展开了装修过程废物产生特性及其重金属污染特征和潜在的健康风险方面的研究.结果表明:①拆改、木工与金属切割作业会产生较为严重的噪声污染,其严重影响了周边居民的正常生活与装修工人的职业健康,其中金属切割过程噪声最为严重,平均强度是GB 3096-2008《声环境质量标准》昼间2类限值的1.6倍;②拆除工程产生的粉尘污染（PM_2.5）、涂饰作业产生的甲醛以及油漆作业产生的TVOC（总挥发性有机物）严重超标,其中,ρ（PM_2.5）是GB 3095-2012二级标准24 h平均浓度限值的2.1倍,ρ（甲醛）和ρ（TVOC）分别是GB/T 18883-2002标准值的2.6、2.5倍;③装修垃圾中不同重金属元素的污染水平表现为Cd > Zn > Pb > Cu > Ni > Cr > As > Hg,Pb是产生健康风险的主要污染物,其中塑料中w（Cd）、瓷砖中w（Zn）、PVC线管中w（Pb）与玻璃中w（Cr）平均值分别为1.5、432.2、6 026.0和288.0 mg/kg,分别是广东省土壤背景值的11.5、5.6、104.6与3.3倍.研究显示,PVC线管中的Pb是产生健康风险的主要污染物,应加强环境管理.      

Take back and treatment of discarded electronics: a scientific update

This paper indicates that the performance of tack-back and treatment of electronic waste (e-waste) system can be improved substantially. This can be reached by better taking into account in a better way the big variety in material composition and potential toxicity of electrical and electronic products - from a technical, organizational and regulatory perspective. Realizing that there is no ‘one size fit for all’ and combining smart tailor made solutions with economic of sale will result in the best environmental gain/cost ratio. Several examples show how science and engineering have supported or will support this approach.