| With the rapid development of economy and technology,plastic products are widely used in various industries,but plastic products are susceptible to aging and rapid replacement,resulting in a large amount of waste plastics,causing serious waste plastic disposal crisis and environmental problems.Recycling waste plastics is an effective way to dispose them.However,it is difficult to separate them from each other because of the mixed composition of waste plastics,and the development of recycling of waste plastics is limited.Plastic flotation is an economic and efficient separation method,which can separate waste plastics with similar density and charging properties.In this paper,the effects of potassium permanganate pretreatment,different particle sizes and potassium permanganate combined with wetting agent pretreatment on the flotation results of acrylonitrile-butadiene-styrene(ABS)and high impact polystyrene(HIPS)waste plastics with high recycling value and difficult separation were investigated by using self-made flotation equipment.The surface properties of ABS and HIPS before and after treatment were studied by characterization test,and the reaction mechanism was explored.The main research contents and results of this paper are as follows:(1)The permanganate oxidation method is an environmentally friendly process,which occupies an important position in green chemistry.By using potassium permanganate pretreatment method,the flotation separation of waste ABS and HIPS was carried out.Attenuated total internal reflectance Fourier transform infrared spectroscopy(ATR-FTIR)and X-ray photoelectron spectroscopy(XPS)test results showed that potassium permanganate pretreatment can oxidize the butadiene and nitrile groups in ABS to form oxygen-containing hydrophilic groups.Although butadiene in HIPS can also be oxidized to form oxygencontaining hydrophilic groups,the increase of these hydrophilic groups is less than that of ABS.The results of scanning electron microscopy(SEM)showed that the surface morphology of the pretreated ABS changed,and the surface roughness increased significantly,while the HIPS surface did not changed significantly.The surface wettability of ABS increased with the increase of surface roughness.The contact angle test results showed that the increase of contact angle of ABS,after pretreatment,is significantly higher than that of HIPS,and the surface wettability of ABS and HIPS after potassium permanganate pretreatment is significantly different,which provides conditions for subsequent flotation separation.It is found that the optimum pretreatment conditions for ABS and HIPS are potassium permanganate solution concentration of 50 m M/L,pretreatment temperature of 60 ℃,pretreatment time of 30 min.The best frother concentration is 35 mg/L.The flotation experiment results showed that under the optimum conditions,the recovery and purity of ABS reached 97.64% and 95.41%,respectively;the recovery and purity of HIPS reached 95.40% and 97.64%,respectively.(2)Through the study on the flotation separation of ABS and HIPS with different particle size groups,it is found that the flotation separation effect of small particle size group(0.2-0.4cm)ABS and HIPS with potassium permanganate pretreatment was not as good as that of large particle size group(0.5-1.0 cm).This is because the smaller size of plastic only need to absorb a small amount of bubbles,which would lead to the density of plastic and bubble aggregates less than the flotation medium.At the same time,the small particle size of plastic particles increased the specific surface area than that of the big particle size,improved the adhesion probability of bubbles and increased the floatation recovery rate of ABS.As the pretreatment temperature increased,which had a great influence on the floatation recovery rate of ABS and HIPS,the floatation recovery rate of ABS was restrained and a large number of HIPS sank(at80 ℃ of pretreatment temperature,the floatation recovery rate of HIPS is only 77.91%).It is difficult to achieve the ideal separation effect.(3)In order to improve the flotation separation effect of waste ABS and HIPS with small particle size group,the flotation separation of waste ABS and HIPS with small particle size group was further studied by using potassium permanganate combined with wetting agent pretreatment method.Through the previous study,it is found that the floatation recovery rate of HIPS was higher when the potassium permanganate pretreatment temperature is 50 ℃,which was conducive to the follow-up experiment.At the same time,the SEM test results showed that the surface of ABS could get rougher when the potassium permanganate pretreatment temperature is 50 ℃,which is conducive to the flotation separation of ABS and HIPS.Thus,the optimum pretreatment conditions for ABS and HIPS are potassium permanganate solution concentration of 50 m M/L,pretreatment temperature of 50 ℃,pretreatment time of 30 min.It was found that the optimal wetting agent pretreatment conditions were as followed: the wetting agent concentration is 5 mg/L,the wetting time is 4 min,and the best frother concentration is 35 mg/L.The results of flotation experiments showed that under the optimum conditions,the recovery and purity of ABS were 90.07% and 95.34%,respectively;the recovery and purity of HIPS were 95.48% and 90.45%,respectively.The flotation experiment results showed that potassium permanganate combined with wetting agent pretreatment could improve the flotation separation effect of ABS and HIPS with small particle size group.At the same time,the flotation experiments of ABS and HIPS with 5:5 mixture of small particle size group and large particle size group were carried out.The flotation results showed that the pretreatment method of potassium permanganate combined with wetting agent could effectively separate ABS and HIPS with mixed particle size.The recovery and purity of ABS were 93.25% and 91.76%,respectively;the recovery and purity of HIPS were 91.45% and 92.99%,respectively. |
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