【作者】 詹路；

【导师】 许振明；

【作者基本信息】 上海交通大学 ， 环境工程， 2011， 博士

【摘要】 废弃印刷电路板（WPCBs）是电子垃圾的重要组成部分,其中蕴含的金属的含量是天然矿藏品位的几十倍甚至几百倍,具有重要的回收价值。目前,WPCBs的资源化利用主要集中在回收铜和贵金属,铅、镉等有毒重金属则得不到有效处理和处置。在回收铜和贵金属的同时,铅、镉等有毒重金属释放到空气、土壤、水等环境中,造成重金属污染,危害人类健康。本论文将废弃印刷电路板经破碎-分选后得到的混合金属颗粒作为研究对象,自行研制真空分离设备一台,根据混合金属中各组分在同一温度下蒸气压不同,在真空中通过蒸发与冷凝,实现各组分的相互分离。研究各金属颗粒蒸发-冷凝的热力学和动力学条件,得出混合金属颗粒中高蒸气压、低熔点金属的蒸发分离机制,揭示多元混合金属在真空分离过程中的相互影响作用,使废弃印刷电路板中的多元混合金属得到分离和回收,避免了在回收铜冶炼过程中有毒、有害金属（铅、镉等）挥发到大气中,并实现了铅、镉等金属的分离与回收。发现混合金属颗粒中锌、镉由固态直接升华,蒸发过程受到表面氧化膜的阻碍,粒径越小,阻碍作用越大;铅、铋颗粒由固态熔化为液态进而蒸发,粒径越小,形成的液滴蒸气压越大,蒸发速率也越大,蒸发速率可以用Langmuir-Knudsen公式描述。结合各种金属元素的蒸气压差异和纯金属颗粒的蒸发率差别,得出混合金属颗粒中锌、镉、铅、铋真空冶金的分离判据,根据判据,将易挥发金属颗粒进行分离,混合物中目标金属的分离率达90 %以上。从动力学角度,混合金属颗粒的真空分离过程分为金属颗粒蒸发/升华、金属蒸气扩散I（即颗粒间扩散）、金属蒸气扩散II（即炉膛内扩散）以及冷凝四步。扩散I阶段,铜颗粒料层厚度对混合物中金属的蒸发分离起到阻碍作用,扩散II阶段,高真空有利于高蒸气压金属的分离。对于多元混合金属颗粒,由于铜颗粒的阻碍作用,各种易挥发金属蒸发率之间的差异缩小,很难实现依次分离。当金属混合颗粒中同时含有铋和铅时,铋与铅形成负偏差合金——铅铋合金,蒸气压小于铅或铋,使铅的蒸发分离更为困难,在1123 K下,需要较长的加热时间（135 - 150 min）才能使分离率达90 %以上,但镉等高蒸气压金属可以在低温下优先与铜分离,在1023 K下加热60 min,镉的分离率接近100 %,然后再分离铅和铋;当同时含有锌和铅时,锌和铅在1123 K下加热90 min,利用锌和铅的冷凝位置和冷凝形貌不同,实现了铜富集体中铅、锌的共同蒸发分离与分别回收。根据各种金属蒸发与冷凝特性的差异,将优先分离与共同蒸发分离相结合,可以实现混合金属颗粒中易挥发金属的分离与回收。焊锡-铜混合颗粒的铅分离率高于单纯焊锡,大量铜颗粒的存在使得焊锡中的铅更易于蒸发分离,存在多层蒸发效应和铜-锡合金化效应,当真空度维持在0.1 - 1 Pa,在1123 K下加热90 min,铅分离率可达到95 %以上。真空分离铜富集体中的焊锡,得到的青铜色聚集体富含金属锡,使原本分散分布的锡得到富集,有利于进一步资源化再利用。在研究基础上,利用Labview软件建立了混合金属颗粒分离工艺的人机交互界面,将含有各种高蒸气压金属铜富集体的真空分离工艺参数进行可视化显示,便于制定混合金属颗粒的真空冶金分离流程,指导实际生产。对真空分离车间内的噪声、总悬浮颗粒物（TSP）、可吸入颗粒物(PM₁₀)及TSP中铅和镉的浓度进行监测评价,结果表明:真空分离车间内的主要噪声源为机械泵和水泵,噪声声级分别为71.2和69.5 dB（A）,符合国家标准,在该环境下工作,不会对工人的听力造成损害;TSP和PM₁₀浓度符合我国《环境空气质量标准》规定的空气二级标准;采用美国EPA人体暴露风险评价方法对TSP中所含的铅和镉进行健康风险评价显示,铅和镉浓度均低于风险阈值,不会对工人造成健康伤害。本文采取的真空分离法对WPCBs经破碎-分选后的铜富集体进行分离回收,在整个真空分离过程中,铜颗粒没有熔化,铜富集体中的铅、镉等重金属在低于铜熔点的温度下实现了固态分离。与传统的金属熔体真空冶金分离相比,具有分离温度低,能耗低的特点。本研究为分离回收WPCBs中的重金属提供了理论依据,为WPCBs的资源化回收和再利用提供一种高效、环保、经济可行的方法,同时也为回收其它电子废弃物中的铅、镉等重金属提供了技术储备。更多还原

【Abstract】 Waste printed circuit boards （WPCBs） are the main component of waste electrical and electronic equipments. The content of metals contained in WPCBs is about more than ten or hundreds times of natural mineral. Therefore, the recycling of WPCBs is of great value. At present, the resource utilization of WPCBs mainly focuses on the recycling of copper and precious metals. However, the toxic and hazardous metals such as lead and cadmium are released into air, soil and water, which may result in heavy metal contamination and bring potential risk to human health. The mixed metallic particles obtained after crush and separation of WPCBs are the research objects in this study. An exploratory vacuum separation equipment is fabricated. Based on the different vapor pressures of metals at the same temperature, the metals can be separated from each other through vacuum evaporation and condensation. This paper studies the separation mechanism of metals with high vapor pressure and low boiling point and finds out the interaction effects of mixed metallic metals during the vacuum separation process. The mixed metallic particles of WPCBs are separated and recovered, which can avoid the release of toxic and hazardous metals （Pb, Cd et al） during the copper smelting and realize the separation and recover of lead and cadmium.Zn and Cd in the mixed metallic particles sublimate and come into gaseous phase directly. Due to the metal oxide layer covering on the surface of Zn and Cd particles, there exists resistance blocking the free evaporation of Zn and Cd atoms. The smaller the particles, the bigger resistance there is. By contrast, Pb and Bi particles both melt first and then evaporate. The evaporation rates become bigger with smaller particles as a result of bigger vapor pressure of the liquid droplet. The evaporation rates of Pb and Bi particles can be described by the Langmuir-Knudsen equation. The criterion of separating the high-vapor-pressure metals （Pb, Zn, Cd and Bi） from each other is obtained by combining both the differences of vapor pressures and evaporation efficiencies. Under the instruction of separation criterion, different kinds of mixed metallic particles are successfully separated with the separation efficiency of the target metal more than 90 wt %.The vacuum separating process of the mixed metallic particle can be divided into four steps from the dynamics point of view: evaporation/sublimation of metallic particles, diffusion I （diffusing among the particles） of the metal vapor, diffusion II （diffusing in the furnace chamber） of the metal vapor and condensation. During the diffusion I step, the layer height of copper particles can block the separation of metals. During the diffusion II step, higher vacuum degree is helpful for separating the high-vapor-pressure metals.For the multi-metal mixture, the difference of the evaporation efficiency of each high-vapor-pressure metal becomes narrower due to the blocking effect of copper particles, which makes separating metals one by one impossible. When both lead and bismuth exist in the mixed metallic particles, Pb-Bi alloy （a kind of negative-deviation alloy） can form. Due to lower vapor pressure of Pb-Bi alloy, the separation of Pb becomes more difficult. It requires heating for 135-150 min at 1123 K to realize 90 % of Pb evaporation. However, nearly 100 % of Cd can be separated from the mixed metallic particles with priority at a lower temperature （1023 K for 60 min） and then Pb and Bi can be separated subsequently at a higher temperature. When both Zn and Pb exist, hearting for 90 min at 1123 K, Zn and Pb can simultaneously evaporate and be respectively condensed according to the different condensation positions and morphologies of Zn and Pb. Based on the difference of evaporation and condensation of each metal, the high-vapor-pressure metals can be separated and recovered by combining the priority separation and simultaneous separation.In the presence of a large amount of Cu particles, Pb separation efficiency of solder-copper mixed particles becomes higher than that of single solder. It becomes much easier to separate Pb due to the multi-evaporation effect and Cu-Sn inter-metallic effect. When the vacuum degree maintains 0.1 - 1 Pa, Pb separation efficiency can attain to over 95 % at 1123 K for 90 min. After the vacuum separation of solder-copper mixed particles, the obtained aggregates contain a certain content of Sn, which plays an important part of enrichment of dispersed Sn and is in favor of further resource utilization.Based on the research, the human-computer interface of the vacuum separation flowchart is built using Labview. The corresponding parameters for separating various kinds of copper-rich particles containing high-vapor-pressure metals can be visualized, which is greatly convenient for establishing the flowchart and guiding the practical production.The noise level, TSP, PM₁₀ as well as the Pb and Cd concentrations in TSP are monitored inside and outside the vacuum separation workshop. The results show that the noise source is mainly the mechanical pump and water pump. Their noise levels are 71.2 and 69.5 dB （A） respectively, in accordance with the national standard. The working environment will not bring any hearing injury for workers. The contents of TSP and PM₁₀ accord with the second level of air standard regulated by national ambient air quality standard. The use of risk assessment strategies given by US EPA indicates that the concentrations of Pb and Cd in TSP are lower than the risk threshold value, and that they will not do harm to the workers’health.In this study, vacuum metallurgy separation is adopted to separate and recover the copper-rich particles of WPCBs after crushing and separating. During the whole vacuum separation process, the copper particles do not melt. Pb, Cd and other metals are separated from the solid copper particles, which realizes the solid separation. Compared with the traditional vacuum metallurgy separation of the metal melt, the solid separation needs lower separation temperature and consumes less energy. This research provides the theoretical foundation for separating and recovering the metals with high vapor pressure and points out an efficient, environmentally-friendly, economic feasible method for the resource recycling and utilization of WPCBs. Meanwhile, this thesis supplies the technical storage for recovering Pb, Cd and some other metals from other kinds of waste electrical and electronic equipments.更多还原