超临界CO2回收线路板工艺研究

用正交试验设计进行了超临界CO2回收废弃印刷线路板的实验。以温度、压强、时间和夹带剂为实验因素,通过对实验前后样本在重量、厚度、弯曲强度和断裂强度四方面变化的分析考察了各实验因素对实验效果的影响。实验结果表明,影响超临界CO2法回收印刷线路板的最主要因素为温度、时间和夹带剂,超临界CO2法回收废弃印刷线路板的最佳工艺条件：温度270℃,压强大于7．38MPa,时间3h,夹带剂（水）160mL。实验进一步验证了压强对实验结果的非显著性影响。     

超临界CO2回收线路板工艺研究

采用正交试验设计进行了超临界CO₂回收废弃印刷线路板的实验。以温度、压强、时间和夹带剂为实验因素,通过对实验前后样本在重量、厚度、弯曲强度和断裂强度四方面变化的分析考察了各实验因素对实验效果的影响。实验结果表明,影响超临界CO₂法回收印刷线路板的最主要因素为温度、时间和夹带剂,超临界CO₂法回收废弃印刷线路板的最佳工艺条件：温度270℃,压强大于7.38 MPa,时间3 h,夹带剂(水)160 mL。实验进一步验证了压强对实验结果的非显著性影响。     

废弃印刷线路板最佳分离参数的实验研究

为研究废弃印刷线路板的热解特性,确定金属和非金属分离的热解最佳参数,用差热-热重联用分析仪对FR-4型印刷线路板进行了热失重分析,并对影响废弃印刷线路板中金属和非金属分离效果的升温速率、颗粒尺寸、热解终温和保温时间等主要因素进行了实验研究。结果表明,FR-4型线路板在320~360℃区间热失重速率达到最大值;升温速率越高,热解起始温度、终止温度和失重峰温也越高,显著失重过程持续的时间越长;当热解终温相同时,升温速率对FR-4型线路板的热失重率影响很小。综合考虑FR-4型废弃印刷线路板中金属和非金属的分离效果、热解装置的设计、热解过程的能耗以及运行过程的控制等因素,最佳热解参数建议设定为升温速率为10℃/min,热解终温为500℃,保温时间取30 min为宜。     

废弃印刷线路板非金属热解动力学

废弃印刷线路板非金属材料现有处理方式存在较大的环境风险,其热分解特性是对其进行安全处理处置及资源化再利用的关键所在。结合热重实验数据,分别运用Kissinger法、Flynn-Wall-Ozawa法及Freeman-Carroll法对动力学参数E、A、n进行了求解和讨论,结果表明,动力学参数E近似等于125.875 kJ/mol;A近似等于3.825×1010min-1;废弃印刷线路板非金属材料热解的动力学机理函数假设不宜表示为:f(α)=(1-α)n。运用atava-esták法对最概然机理函数进行了探讨,结果表明,废弃印刷线路板非金属材料的热分解动力学机理函数为:f(α)=[-ln(1-α)]4。研究结论为废弃印刷线路板非金属材料资源化再利用工业化设计与应用提供重要的实验数据和理论依据。     

化学溶胀法分离废弃线路板中金属与基板

废弃线路板的粉碎和所含金属组分的高效解离是后续分选回收的前提条件。本研究分别使用乙二胺等10种溶剂浸泡废弃线路板,比较对线路板中铜箔与基板间剥离强度的影响,从而筛选出4种有代表性的溶剂,即溶剂D、溶剂F、丙酮和水, 比较废弃线路板经化学溶胀后的单体解离度和获得一定粒径分布的颗粒所需的破碎时间。研究结果表明,化学溶胀后破碎能大幅提高金属的单体解离度,浸泡效果的优良排序为：溶剂D>溶剂F>丙酮>水;浸泡时间越长,浸泡温度越高,对剥离强度的降低越有利;使用溶剂D在150℃、3 h或140℃、5 h的工艺下浸泡废弃线路板,可以使铜箔与基板自动脱落。研究结果为后续的分选提供了便利的条件。     

废印刷线路板回收利用的现状与存在的问题

从分析印刷线路板材料构成的复杂性人手,论述了国内外在废印刷线路板回收处理技术方面的研究现状和进展。找出目前我国在处理废印刷线路板方面存在的问题与差距．并提出切实可行的建议。分析表明,干法分离分选技术应是今后的发展方向。     

浮选处理＜0.25mm粒级废弃印刷电路板的试验研究

从废弃印刷电路板微细颗粒中富集有用金属是目前环境污染防治领域中的前沿课题,采用浮选方法对废弃印刷电路板破碎后的微细物料进行探索性浮选试验研究.借助Design-Expert7.0软件进行了废弃印刷电路板金属回收的4因素3水平浮选试验设计和结果分析,讨论了搅拌速度、充气量、矿浆温度及矿浆质量浓度对浮选效果的影响,给出了金...     

液-固流化床回收印刷线路板中金属的研究

根据废弃印刷线路板中材料密度不同,采用水介质流化床对印刷线路板粉末中的金属进行回收,对0.25～0.177、0.177～0.104、0.104～0.074和-0.074 mm 4个粒级范围内的物料进行分选试验。试验结果表明,在上述4个粒级范围内,随介质流速的增大,金属回收率降低;金属回收率η与实际操作速度（ua）和颗粒终端沉降速度（ut）的比值φ（ua/ut）存在一定线性关系,分析模拟了η与φ之间的相关性方程,外推试验的结果证明了相关性方程的可靠性;在合适的操作条件下,各粒级范围内金属的回收率分别为95.02%、90.07%、87.5%和92.68%。     

氧化亚铁硫杆菌浸出废弃线路板中铜的研究

对废弃线路板中的铜进行了细菌浸出、只有硫酸亚铁环境下的浸出及酸浸出实验,研究了不同条件对比浸出效果,研究结果表明,细菌浸出比只有硫酸亚铁存在的浸出和酸浸要快得多。研究了在线路板粉末浓度12、24、40、60和120 g/L下浸出速率的变化,结果表明, 在考察范围内,浸出速度随着加入的废弃线路板粉末浓度的升高而降低,当线路板粉末的浓度＞60 g/L时,浸出速度维持在较低水平,选取24 g/L作为浸出的线路板粉末的浓度。分别在细菌培养0、24、48和72 h时加入线路板粉末24 g/L进行浸出实验,结果表明,细菌培养时间长,使得浸出过程进行得也更快。     

废弃印刷线路板碘化法浸金研究

针对碘化法从废弃印刷线路板中提取金的工艺设计,分别考察了碘的质量分数、n(I₂)/n(I^-)比值、固液比、双氧水的质量分数、pH值、浸出时间和浸出温度对金浸出率的影响。结合正交设计优化实验方法,提出了从废弃印刷线路板中碘化法浸取金的最佳工艺条件：碘的质量分数为1.1％,n(I₂)∶n(I^-)=1∶10,双氧水的质量分数为1.5％,浸出时间4 h,固液比为1∶10,浸出温度为常温（25℃）,溶液pH值为中性,此时金浸出率可达97.5％。     

Characterization and risk assessment of polychlorinated biphenyls in soils and vegetations near an electronic waste recycling site, South China

This study aimed at identifying the levels of PCBs generated from e-waste recycling, and their potential impacts on the soils and vegetations as well. The ΣPCBs concentrations in soil and plant samples ranged from 7.4 to 4000 ng g(-1) and from 6.7 to 1500 ng g(-1), respectively. For the plant samples, Chrysanthemum coronarium L. from vegetable field and the wild plant Bidens pilosa L. from the burning site showed relatively higher PCB concentrations than other species. For the soil samples, the e-waste burning site had relatively higher PCB concentrations than the adjacent areas, and vegetable soils had higher PCB concentrations than paddy soils. The PCB concentrations showed a clear decreasing trend with the increasing distance from the e-waste recycling site. PCB 28, 99, 101, 138, 153, and 180 were the predominant congeners. Principal component analysis results showed a potential fractionation of PCB compositions from the burning site to the surroundings. The PCB congener pattern at the burning site was similar to Arochlor 1260, pointing to an input of non-domestic e-waste. Similar PCB congeners were found in soils and related vegetables, indicating they derived from the same source. The consumption of vegetables grown in soils near e-waste recycling sites should be strictly avoided due to the high PCBs in the plant tissues.     

Hazardous substances in indoor dust emitted from waste TV recycling facility

Various hazardous substances contained in waste TV sets might be released into environment via dust during recycling activities. Two brominated flame retardants (BFRs), polybrominated diphenyl ethers (PBDEs), and tetrabromobisphenol A (TBBPA), and five kinds of heavy metals (Cu, Pb, Cd, Cr, and Ni) were detected in indoor dust collected from two workshops (TV dismantling workshop and subsequent recycling workshop). PBDEs concentrations in dust from waste wires recycling line (722,000 ng/g) were the highest among the studied sites, followed by those in manual dismantling–sorting line (117,000 ng/g), whereas TBBPA concentrations were the highest in manual dismantling–sorting line (557 ng/g) and printed circuit board (PCB) recycling line (428 ng/g). For heavy metals, Cu and Pb were the most enriched metals in all dust samples. The highest concentration of Pb (22,900 mg/kg) was found in TV dismantling workshop-floor dust. Meanwhile, Cu was the predominant metal in dust from the PCB recycling line, especially in dust collected from electrostatic separation area (42,700 mg/kg). Occupational exposure assessment results showed that workers were the most exposed to BDE-209 among the four PBDE congeners (BDE-47, BDE-99, BDE-153, and BDE-209) in both workshops. The hazard quotient (HQ) indicated that noncancerous effects were unlikely for both BFRs and heavy metals (HQ?<?1), and carcinogenic risks for Cd, Cr, and Ni (risk?<?10^?6) on workers in two workshops were relatively low.     

废印刷电路板的静电分选实验研究

金属与非金属材料的分离是回收利用废印刷电路板的关键环节。对废印刷电路板物料的静电分选进行了实验研究。实验以电压、辊筒转速、电晕电极与辊筒之间的距离、静电极位置、电晕电极位置、电晕电极数量等为考察因素,研究各因素对电选效果的影响规律。结果表明,影响金属与非金属材料分离的主要因素是电压、辊筒转速和电晕电极与辊筒之间的距离,对于-0.9 0.45mm的破碎物料,当电压为24kV,辊筒转速为15Hz(54.6r/min),电晕电极与辊筒之间的距离为5.2cm时,得到最大静电分选综合效率67.37%。     

超临界CO_2流体环境中线路板分层实验分析

在超临界CO2流体环境下,当温度达到240℃以上时,印刷线路板就会发生分层现象。同时,在实验中发现在非超临界流体环境下,当温度达到260℃以上时,线路板也会发生分层现象。从线路板粘接材料发生热解反应的角度出发,在对比超临界CO2流体环境下与非超临界流体环境下的线路板分层效果的基础上,对超临界CO2流体环境下的线路板分层做出合理分析,最后发现临界CO2流体对线路板分层过程有促进作用,并对其分层效果有优化作用。     

Mussels as bioindicators of PCB pollution: a case study on uptake and release of PCB isomers and congeners in green-lipped mussels (Perna viridis) in Hong Kong waters

The uptake and release of PCB isomers and congeners were examined in green-lipped mussels (Perna viridis) through a transplantation experiment in two locations in Hong Kong waters. Rapid rates of uptake and release of relatively less lipophilic lower-chlorinated PCBs were observed in the mussels, indicating that the primary mechanism of bioaccumulation of lipophilic pollutants in P. viridis complies with the concept of equilibrium partitioning. Thus, data for contaminant concentrations are most appropriately based upon lipid weights of samples when using mussels as bioindicators of aquatic PCB pollution. Considering the kinetic parameters of PCBs based on lipid weight-related data, it is concluded that P. viridis has the ability to respond rapidly to changes in ambient levels of PCBs. This is significant in determining the usefulness and limitations of mussels as bioindicators for monitoring programmes investigating aquatic pollution by PCBs.     

Assessing the potential for rhizoremediation of PCB contaminated soils in northern regions using native tree species

Rhizosphere bioremediation of polychlorinated biphenyls (PCBs) offers a potentially inexpensive approach to remediating contaminated soils that is particularly attractive in remote regions including the Arctic. We assessed the abilities of two tree species native to Alaska, Salix alaxensis (felt-leaf willow) and Picea glauca (white spruce), to promote microbial biodegradation of PCBs via the release of phytochemicals upon fine root death. Crushed fine roots, biphenyl (PCB analogue) or salicylate (willow secondary compound) were added to microcosms containing soil spiked with PCBs and resultant PCB disappearance, soil toxicity and microbial community changes were examined. After 180 d, soil treated with willow root crushates showed a significantly greater PCB loss than untreated soils for some PCB congeners, including the toxic congeners, PCB 77, 105 and 169, and showed a similar PCB loss pattern (in both extent of degradation and congeners degraded) to biphenyl-treated microcosms. Neither P. glauca (white spruce) roots nor salicylate enhanced PCB loss, indicating that biostimulation is plant species specific and was not mediated by salicylate. Soil toxicity assessed using the Microtox bioassay indicated that the willow treatment resulted in a less toxic soil environment. Molecular microbial community analyses indicated that biphenyl and salicylate promoted shifts in microbial community structure and composition that differed distinctly from each other and from the crushed root treatments. The biphenyl utilizing bacterium, Cupriavidus spp. was isolated from the soil. The findings suggest that S. alaxensis may be an effective plant for rhizoremediation by altering microbial community structure, enhancing the loss of some PCB congeners and reducing the toxicity of the soil environment.     

Effects of dietary wheat bran on absorption and accumulation of PCBs in rats

Polychlorinated biphenyls (PCBs) are toxic environmental contaminants, which tend to accumulate in the food chain. Since dietary intake is the most important exposure route, PCB body burden may be affected by taking proper dietary measures. In the present study, diets were supplemented with either wheat bran or its cellulose based placebo in order to study the effect of bran consumption on the absorption of dietary PCBs and the excretion of initially stored PCBs. During the period of PCB intake, faecal PCB excretion was elevated by consumption of wheat bran as compared to the placebo. Hence, apparent faecal PCB digestibilities as well as PCB retentions in the whole body were lower in the wheat bran consuming rats. After ending PCB consumption, dietary wheat bran had only a minor effect on faecal PCB output while accumulation in the body was not affected. When PCBs were consumed for a longer time, a small but significant reduction of apparent faecal PCB digestibility was found. However, PCB content in the body kept increasing while PCB retention as percent of intake remained almost constant. Furthermore, differences among individual PCB congeners in metabolic susceptibility and hydrophobic characteristics had an impact on their accumulation in the body.     

Exposure to PCBs, through inhalation, dermal contact and dust ingestion at Taizhou, China--a major site for recycling transformers

Air samples containing gaseous and particulate phases were collected from e-waste workplaces and residential areas of an intensive e-waste recycling area and compared with a reference site. The highest total concentration of PCBs was detected at transformer recycling workshops (17.6 ng m(-3)), followed by the residential area (3.37 ng m(-3)) at Taizhou, and the lowest was obtained at the residential area of the reference site, Lin'an (0.46 ng m(-3)). The same trend was also observed with regards to PCB levels in dust samples. The highest average PCBs level of 2824 ng g(-1) (dry wt) was found in the transformer recycling workshops, and was significantly higher than that of residential areas of Taizhou (572 ng g(-1) dry wt) and Lin'an (42.4 ng g(-1) dry wt). WHO-PCB-TEQ level in the workshops of Taizhou was 2216 pg TEQ(1998)g(-1) dry wt or 2159 pg TEQ(2005)g(-1) dry wt, due to the high abundance of PCB 126 (21.5 ng g(-1) dry wt), which contributed 97% or 99% of WHO-PCB-TEQs. The estimated intake of PCBs via dust ingestion and dermal absorption by transformer recycling workers were 77.5×10(-5) and 36.0×10(-5) pg WHO-PCB-TEQ(1998)kg(-1)d(-1), and 67.3×10(-5) and 31.3×10(-5) pg WHO-PCB-TEQ(2005)kg(-1)d(-1), respectively.     

The pathway of dechlorination of PCB congener by a photochemical chain process in 2-propanol: the role of medium and quenching

As part of a program aimed at developing a field process for cleanup of PCB contaminated soils using photochemistry in basic 2-propanol, additional details of the dechlorination pathway are presented. The mechanism involves a chain reaction with both homolytic photochemical C-Cl bond fission and electron transfer steps producing PCB anion radicals. Kinetics of dechlorination of various congeners show patterns of relative rates associated with the basic 2-propanol medium that are not found in other media because both electron transfer and photochemical homolysis steps determine overall rates of dechlorination and govern the pathways and relative concentrations of intermediates. The electron transfer steps display opposite structure-reactivity correlations to the photo-homolysis, C-Cl bond fission steps. Oxygen quenching is shown to differentially affect both types of steps. In contrast to the suggestion that inter system crossing can be highly efficient with reaction originating from a PCB triplet, oxygen quenching data suggest that a significant minimum of the quantum yield is non-quenchable, presumably because of a reaction path from the PCB singlet. This may help to explain why exclusion of air is not entirely necessary in practice.