Experimental Study On Separation Of E-Waste Plastics By Froth Flotation With Microwave Pretreatment

With the rapid development of economy,all kinds of electronic products and household appliances have been introduced constantly.At the same time,a large amount of waste plastics has also been produced,resulting in serious environmental pollution and waste of resources.The recycling after separation and purification has become a research focus in the field of plastics flotation and environmental protection.A novel process,wetting reagent modification combined with microwave pretreatment,was applied to the froth floatation separation of ABS from waste electronic communication equipment plastics?ABS/PC/PET?.With Fenton combined with microwave treatment,froth flotation was evaluated for separation of waste household appliance plastics?PC/ABS/PP/PVC?.The effects of pretreatment on flotation recovery were examined in detail and the optimum flotation separation parameters were obtained.Contact angels?CA?,adsorption kinetics experiments and Fourier transform infrared spectrometry analysis?FT-IR?were examined to investigate the mechanism of pretreatment.The results provide technical insights into the industrial separation of E-waste plastics.A surface pretreatment method of microwave treatment combining with wetting agent was proposed in froth floatation process to separate the ABS from the waste electronic communication equipment plastics?ABS/PC/PET?.The effects of the type and concentration of wetting reagent,treatment time,microwave irradiation power,irradiation time,stirring rate,frother concentration,and flotation time were examined in detail.Plastic mixtures of ABS,PC and PET with different mixing ratios was also investigated.The optimum conditions are wetting reagent CMC concentration,25 mg/L;treatment time,5 min;microwave irradiation power,700W;irradiation time,3 min;stirring rate,1800 rpm;frother concentration,40 mg/L;and flotation time,4 min.ABS was efficiently separated from PC and PET under the optimum conditions.The recovery and purity of the separated ABS was 97.68%and 99.86%,respectively.Contact angle of ABS remains almost unchanged while the contact angle of PC and PET has a significant decrease after pretreatment,which indicates that the surface wettability of PC and PET has increased.Adsorption kinetics experiments shows that the increase of the wettability of PC and PET is due to the adsorption of CMC on the surface and it is found that the adsorption is physical adsorption by the adsorption kinetic model fitting.No obvious changes are observed from the FT-IR spectrum of untreated and treated ABS,PC and PET,which indicates that the molecular structure and functional groups of the plastic samples don't change before and after treatment,and no chemical reaction occurs on the surface of plastics.In order to separate PC,ABS,PP and PVC from waste household appliance plastics,a surface pretreatment method of microwave treatment combined with Fenton was proposed in the froth floatation process.PC can be separated from ABS/PP/PVC by one-stage flotation under the optimum conditions of microwave power 350 W,irradiation time 5 min,H₂O₂concentration 0.2 mol/L,molar ratio(H₂O₂/Fe²⁺)50:1,pH 4,frother concentration 20 mg/L,stirring rate 1800 rpm and flotation time 6min.The recovery and purity of PC were 97.63%and88.95%,respectively.By second-stage flotation,ABS can be separated from ABS/PP/PVC with recovery and purity of 91.82%and 90.51%,respectively.The optimum condition was microwave power 560 W,irradiation time 7 min,H₂O₂ concentration 0.4 mol/L,molar ratio(H₂O₂/Fe²⁺)20:1,pH 4,frother concentration 20 mg/L,stirring rate 1400 rpm and flotation time4 min.Under the optimal conditions of aeration flow 0 L/h,frother concentration 5 mg/L,stirring rate 600 rpm and flotation time1min,PP can be separated from PVC by flotation.PP was the floated product with recovery and purity of 99.70%and 100%,respectively.The recovery and purity of PVC as sink product were 100%and 99.70%.,respectively.The contact angles of PP and PVC didn't have obvious changes before and after microwave combined with Fenton treatment,but the contact angles of PC and ABS decreased rapidly,indicating that the wettability of PC and ABS surfaces have enhanced.By FT-IR analysis,it was found that the surface hydrophilicity of PC was enhanced by the increase of oxygen-containing groups on the surface of PC.And the stretching vibration of oxygen-containing group?C—O?appears in the spectrum of treated ABS which increased the hydrophilicity of ABS surface and decreased the floatability of ABS.