Acta Metall  2019, Vol. 55 Issue (6): 751-761    DOI: 10.11900/0412.1961.2018.00486
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Liquid-Liquid Phase Separation of Fe-Cu-Pb Alloy and Its Application in Metal Separation and Recycling of Waste Printed Circuit Boards
Bin CHEN1,2,Jie HE1,2(),Xiaojun SUN1,2,Jiuzhou ZHAO1,2,Hongxiang JIANG1,Lili ZHANG1,Hongri HAO1
1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2. School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Abstract

The pyrolysis processing was carried out on the waste printed circuit boards (WPCBs) of mobile phones to dissociate metals from non-metals and obtain mixed metals with Fe, Cu and Pb as main components. Based on the main compositions of Fe, Cu and Pb, the liquid-liquid phase separation behavior of (Fe0.4Cu0.6)100-xPbx ternary alloy has been studied experimentally. The results show that the liquid-liquid phase separation of L→L(Fe)+L(Cu, Pb) may occur during the ternary Fe-Cu-Pb alloy melt cooling in the miscibility gap. After the liquid L(Fe) solidified, the secondary liquid-liquid phase separation L(Cu, Pb)→L(Cu)+L(Pb) takes place in the residual L(Cu, Pb) liquid phase, finally resulting in a three-zone separation structure. On the basis of the behavior of the liquid-liquid phase separation, a self-organized hierarchical separation system has been designed to separate and recycle these mixed metals from WPCBs. The enrichment behavior of the minor components like Cr, Au and Cd in the separation system was explored. The effect of super-gravity level on the metal separation and recycling rates has been discussed. As a result, a new harmless route has been established to recycle metal resources in WPCBs.

Received:  30 October 2018      Published:  21 March 2019
 ZTFLH: X705
Fund: National Natural Science Foundation of China(Nos.51574216);National Natural Science Foundation of China(51774264);National Natural Science Foundation of China(51374194);Key Project of Innovation Foundation of IMR-CAS(No.SCJJ-2013-ZD-03);Natural Science Foundation of Liaoning Province(No.2015020172)
Corresponding Authors:  Jie HE     E-mail:  jiehe@imr.ac.cn
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 Fig.1  Thermogravimetric (TG) profiles of waste printed circuit boards (WPCBs) at different heating rates Fig.2  Waste mobile phone PCBs (a) and mixed metals of WPCBs after pyrolysis (b) (PCBs—printed circuit boards) Table 1  Metal composition of the waste mobile phones PCBs Fig.3  Macroscopic separation morphologies of (Fe0.4Cu0.6)100-xPbx (atomic fraction, %) ternary alloy (a~c) and the enlarged images of Figs.3a~c respectively (d~f) Fig.4  Calculated miscibility gap of the Fe-Cu-Pb alloy with different concents of Pb additions (xCu—atomic fraction of Cu) Fig.5  Schematics of solidification process of ternary (Fe0.4Cu0.6)72Pb28 alloy (a~e) Table 2  The enthalpy of mixing (ΔHA-B) between various metals[41] Fig.6  Logarithm values of the estimated molar distribution ratio of minor metals between Fe-rich and Cu-rich liquids $lgKMCu/Fe$ at 1473 K and distribution ratios obtained in different literatures[27,48] (a), and logarithm values of the estimated molar distribution ratio of minor metals between Cu-rich and Pb-rich liquids $lgKMCu/Pb$ at 1233 K without and with the collecting agent Al (b) Fig.7  OM images of the sections of MFeC-MPCB-MPb-MAl (mass ratio MFeC∶MPCB∶MPb∶MAl=0.8∶1∶1.1∶0.1) (a), MFeC-MPCB (mass ratio MFeC∶MPCB=0.8∶1) (b), MCu-rich zone-MPb-MAl (mass ratio MCu-rich zone∶MPb∶MAl=1∶1.1∶0.1) (c) ingots solidified in super-gravity field (rotation rate n=4500 r/min); and Cu dendrites (d) and Pb-rich substance (e) obtained by centrifugal separation Fig.8  Effect of rotation rate (n) on Cu content of Fe-rich zone and Fe content of Cu-rich zone Fig.9  The motion rates ($νS$, $ν'S$) of the Fe-rich droplets at 1473 K and the Pb-rich droplets in Cu matrix at 1233 K at different rotation rates Table 3  The recycling rate (H) of various minor metals in different separated substance