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随着电子产品更新速度的加快,导致其使用周期缩短,产生了大量的电子垃圾。据统计,2020年全球产生了5.36×107 t电子垃圾,比上一年增加近2×106 t,电子废弃物已成为世界上增长最快的固体废物;预计到2030年将达7.4×107 t,2050年增至1.2×108 t [1]。手机的平均使用寿命约为2~3 a,2020年中国废旧手机已超过5×108 台[2]。线路板是手机中核心部件之一,废旧手机的产生伴随着大量的废手机板(Waste Printed Circuit Boards of Mobile Phones, WPCB-MPs)。WPCB-MPs中含有大量的铜、锡、铅、镍等有色金属,是手机元器件中最具价值的二次资源[3]。因此,WPCB-MPs中金属的回收一直是研究的热点。
目前,WPCB-MPs金属回收方法主要有机械物理法、生物冶金、湿法冶金等[4]。机械物理法包括WPCB-MPs的拆解、破碎、分选等,一般可作为其他处理方式的预处理[5]。生物冶金法是利用某些微生物或其代谢产物与电子废弃物中的金属发生作用,产生氧化、还原、溶解、配位等反应,从而实现电子废弃物中有价金属(尤其是贵金属)的回收[6]。传统湿法冶金主要是利用强酸或强碱浸出废线路板中的金属,然后再对浸出液进行分离和除杂,利用净化、沉淀、过滤、萃取、离子交换等方法得到目标金属[7-8]。
矿浆电解不同于传统的湿法冶金,它是指在一个装置中同时实现金属浸出、部分溶液净化及电沉积的技术,因此具有流程短、能耗低、金属分离效果好、环保等优势。在我国,利用矿浆电解法第一次成功实现分离的是金属铋,并且阴极上析出的金属锑纯度可达99%以上,含铅小于0.04%,首次实现了矿浆电解工业化[9-10]。近年来,矿浆电解法也逐步用于电子垃圾资源化。例如,在酸性条件下,利用矿浆电解法回收废弃CPU插槽中的金属,在最佳实验条件下,总金属的分离率可高达93%以上[11]。随后,为了促进其工业应用,进行了5 000 mL规模实验,铜的回收率达94.5%[12-13];此外,还证实了酸性体系下矿浆电解液循环使用的可行性[14]。虽然这些研究可以获得较高的铜回收率,但其他金属,如Fe、Al等也存在于电解质和阴极产物中,因而降低了电流效率和产物纯度[15]。有研究发现,在氨-氯化铵碱性矿浆电解体系中,Cu可以形成低价态的[Cu(NH3)]+铜氨络合物从而在阴极沉积,而铁和锰等金属几乎不能形成此类络合物,这有助于提高电流效率和铜纯度[16]。实验结果显示,在最佳条件下,WPCB-MPs中铜的回收率为97.48%、纯度为99.992 1%,电流效率达106.76%[17]。
电解液循环可以降低化学试剂的使用量以及减少废液的产生,节约成本、保护环境,对工业化生产有着重要作用。因此,在前期氨-氯化铵碱性矿浆电解体系的研究基础上,探讨电解液循环对Cu的回收率、电流效率和纯度以及Cu和Ni、Zn、Pb等金属迁移转化的影响,以期为后期工业化应用奠定基础。
电解液循环对废手机线路板碱性矿浆电解回收的影响
Influence of electrolyte circulation on recycling waste printed circuit boards of mobile phones by alkaline slurry electrolysis
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摘要: 针对废手机线路板碱性矿浆电解资源化过程中电解液带来的污染问题,采用氨-氯化铵碱性矿浆电解液循环回收废手机线路板中金属,以降低能耗、减少污染。研究了氨-氯化铵碱性矿浆电解体系从废手机板制备阴极铜的过程中,电解液循环对Cu的回收率、电流效率、Cu纯度以及Cu和Ni、Zn、Pb等金属迁移转化的影响。经过7次电解液循环实验,结果表明,电解液循环对Ni、Zn、Pb等金属分布及电流效率的影响十分显著,但Cu的分布、纯度及回收率基本不受影响。Cu主要分布在电解液和沉积物中,其他金属则主要在电解液与阳极渣中;8组实验获得的沉积物中Cu的纯度和回收率分别高于99.9%和90%。基于碱性矿浆电解回收废手机板中金属工艺中,完全可以实现电解液的循环利用。本研究可为碱性矿浆电解废线路板提供参考。Abstract: Aiming at the pollution problems caused by electrolyte in the process of alkaline slurry electrolysis of waste printed circuit boards of mobile phones, ammonia-ammonium chloride alkaline slurry electrolyte circulation was used to recover the metal in waste printed circuit boards of mobile phones (WPCB-MPs), so as to reduce energy consumption and pollution. The effect of electrolyte circulation on Cu recovery, current efficiency and purity, as well as the migration and transformation of Cu and other metals such as Ni, Zn and Pb in the process of preparing cathode copper from waste printed circuit boards of mobile phone by ammonium-ammonium chloride slurry electrolysis system was studied. The results of seven electrolyte cycles showed that the electrolyte circulation had a significant effect on the distribution and current efficiency of Ni, Zn, Pb and other metals, while the distribution, purity and recovery rate of Cu were hardly affected. Cu was mainly distributed in electrolyte and cathodic copper, while other metals were mainly in electrolyte and anode residues; the purity and recovery of Cu in the 8 groups were higher than 99.9% and 90%, respectively. The recycling of metal from waste printed circuit boards of mobile phones by alkaline slurry electrolysis could realize the recycling of electrolyte. This study can provide a reference for the high value resource recycling of alkaline slurry electrolysis in waste circuit board.
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Key words:
- WPCB-MPs /
- slurry electrolysis /
- alkaline electrolyte /
- metal recovery
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表 1 废手机板主要成分
Table 1. Main compositions of WPCB-MPs
Cu Ba Fe Al Ni Zn Pb Sn Mg Cr 34.30% 2.40% 1.59% 1.40% 1.42% 0.89% 0.55% 0.73% 0.28% 0.24% 表 2 电解液循环体系实验安排
Table 2. Experimental arrangements of the electrolyte circulation system
循环次数 电流密度/
(mA∙cm−2)固液比/
(g∙L−1)时间/h 调节前电解液中
Cu2+质量浓度/
(g∙L−1)调节后电解液中
Cu2+质量浓度/
(g∙L−1)反应前pH 反应后pH 电解液/mL 氨水加入量/
mL1 20 30 3 − 20 10.20 9.5 200 − 2 20 30 3 20.75 20 10.00 9.2 205 19 3 20 30 3 21.63 20 9.90 9.10 210 28 4 20 30 3 20.47 20 9.90 9.10 209 18 5 20 30 3 20.34 20 9.90 9.10 200 15 6 20 30 3 19.63 20 9.90 9.00 200 20 7 20 30 3 21.08 20 9.90 9.30 208 17 8 20 30 3 20.47 20 9.90 9.10 206 13 注:“−”表示该数值不存在。 表 3 阴极产物主要金属的质量分数
Table 3. Cathode products mass fraction of major metals
阳极产物 Cu Fe Ni Zn Pb Mg Sn Cr Y1 99.984 0% ND ND ND 0.016 0% ND ND ND Y2 99.981 8% ND ND ND 0.018 1% ND 0.000 1% ND Y3 99.980 1% ND ND ND 0.019 7% ND 0.000 2% ND Y4 99.976 9% ND ND ND 0.022 0% ND 0.001 1% ND Y5 99.976 2% ND ND ND 0.022 4% ND 0.001 4% ND Y6 99.971 7% ND ND ND 0.026 4% ND 0.001 9% ND Y7 99.969 9% ND ND ND 0.027 4% ND 0.002 7% ND Y8 99.968 0% ND ND ND 0.029 0% ND 0.003 0% ND 注:ND表示未检出;Y1~Y8分别表示第1组~第8组电解得到的阴极产物。 表 4 阴极产物最强峰的半峰宽、晶粒尺寸
Table 4. Half peak width and grain size of the strongest peak of the cathode product
阴极产物 Cu(111)晶面半峰宽/(°) 晶粒尺寸/nm Y1 0.181 44.189 Y2 0.301 26.572 Y3 0.253 31.613 Y4 0.215 37.201 Y5 0.253 31.614 Y6 0.216 37.029 Y7 0.232 34.475 Y8 0.207 38.639 注:Y1~Y8分别表示第1组~第8组电解得到的阴极产物。 -
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