Extraction Of Zinc And Lead From E-waste And Preparation Of Nanoparticles

At the present stage, most of the resource recovery technologies from e-waste are over-emphasized in recycling precious metals like Au, Ag, Pt, Pd, Rh and Cu with a relatively higher price, while some toxic and hazardous metals like zinc (Zn) and lead (Pb) cannot be recovered efficiently. These metals can either be oxidized or evaporated easily during the pyro-metallurgy process and released into the atmosphere with fly ash or goes into slime during hydro-metallurgy process which may result in serious environmental risk.In this work, vacuum evaporation and inert gas condensation methods were used to extract zinc and lead which had low boiling points and volatile characteristics from e-waste and simultaneously prepare Zn, Pb and PbO nanoparticles with high added values. The main contents and results are presented as follows:1. Zinc cathodes dismantled from waste AA/R6c zinc manganese batteries were used for experiments. Vacuum separation and inert gas condensation were integrated to recycle zinc and prepare zinc nanoparticles from spent zinc manganese batteries. As a result of the relatively high vapor pressure, zinc could be easily separated from the other metals in zinc manganese batteries by vacuum evaporation with a high separation efficiency. Simultaneously, morphology controlled zinc nanoparticles were prepared by inert gas condensation. The results showed that inert gas pressure, heating and condensing temperature and condensation distance away from the evaporation source and condensation substrates were significant factors influencing nanoparticles preparation. Higher inert gas pressure was beneficial for preparing inerratic nanoparticles because of the diffusing effects. At higher heating temperature and lower condensing temperature, more inerratic nanoparticles could be prepared. With more collisions and cementations, the particles became irregular at the places far away from the heater. It was also observed that nanostructured particles with different morphologies including hexagonal prisms, fiber and sheet shapes were prepared on different substrates. Uniform zinc nano hexagonal prisms with the diameter of 100-300 nm and the purity of more than 99 wt.%were successfully prepared on the quartz substrate under the optimized conditions as follows:10000 Pa inert pressure,1073 K heating temperature, lower than 473 K condensing temperature and 10-30 cm condensation distance. The zinc separation efficiency can attain to 99.68%.2. Pb contained solders of waste printed circuit boards (WPCBs) were studied to recovery Pb with high added values. Highly dispersed spherical Pb nanoparticles were prepared by combining vacuum evaporation and forced flow inert gas condensation methods. With a relatively high vapor pressure, Pb could be easily separated from waste Pb/Sn solders by vacuum evaporation, while Sn still remained in the residues. Simultaneously, Pb nanoparticles were prepared by the dynamic inert gas condensation. Agglomeration and size inhomogeneity phenomena was eliminated to the maximum extent by sharp quenching using forced flow inert gas and optimizing operation Parameters like dynamic nitrogen gas pressure, heating and condensation temperatures and condensation distance away from the heating chamber. Highly dispersed spherical Pb nanoparticles were prepared under the optimized conditions of 1223 K heating temperature,1000 Pa dynamic nitrogen gas pressure,413 K condensation temperature and 60 cm condensation distance away from the heating chamber. The separation efficiency of Pb from waste solders could reach to higher than 98.2 wt.% with the product purity of more than 98 wt.% and the size distribution ranging from 20 to 100 nm.3. Air was innovatively applied as oxidizing agent and carrier gas to prepare PbO nanoparticles from waste solders by high temperature oxidation, evaporation and condensation and simultaneously pure SnO2 powder remained in the crucible as by product. The oxidation, separation, nucleation, growth mechanism and influencing factors related to the formation of PbO nanoparticles are investigated in detail. Experimental results indicated that the condensation temperatures had great effects on PbO growth stage. Hexagonal PbO nanosheets with thickness of about 10-20 nm. length of about 150-200 nm and width of about 100-150 nm were prepared at 573 K condensation temperature and 90 cm condensation distance away from the heating chamber. Uniform PbO nanorods with dimensions of 10-15 nm in diameter and 50 nm in length were collected at 373 K condensation temperature and 60 cm condensation distance. Furthermore, the as prepared nanosheets and nanorods were applied for constructing Li-ion batteries to test their electrochemical performance. The Cyclic Voltammetry (CV) measurements indicated that PbO particles were transformed to Pb and resulted in the formation of LixPb alloys during the first discharge. The galvanostatic cycling tests of Li-ion batteries made by the PbO nanosheets showed an initial specific capacity of 917.9 mAh/g and could maintain at 202.2 mAh/g after 100 cycles. The PbO nanorods had a much higher initial specific capacity of 1869.6 mAh/g and could maintain at 190.2 mAh/g after 100 cycles.This work provides the theoretic foundation for recycling Zn and Pb from e-waste with high added values. The results can also be important references for industrialized application in the future.