Study On Separation Techniques Of Electronic Waste Plastic Shell

There was 4.18×1010 kg of electronic waste (E-waste) produced all over the world in 2014 and China was the main producer. E-waste contains heavy metals, polychlorinated biphenyls, polybrominated diphenyl ethers and other organic pollutants, which will cause secondary pollution in resource process seriously affecting the ecological environment. E-waste is an important part of the "urban minerals", from which non-ferrous and rare metals can be extracted by chemical, physical and biological methods and techniques, realizing environmental and economic value of e-waste. Therefore, electronic waste plays an important role in the circular economy of China. Household appliances and electronic equipment contain a wide variety of plastics, accounting for 11-60% of the total weight. For a long time, heavy metals rather than plastics are paid much attention in China, because the price of plastics is much lower than that of metals. Recycling of plastics has great benefits on resource and environment, not only reducing energy consumption in the producing process of original plastics, but also saving oil and other resources, and recycled products itself has a certain economic value.Different kinds of plastics have different melting temperatures, chemically incompatible with each other, which will lead to the poor material properties of the mixed plastics and affect the recycling of plastic waste. As there is a variety of E-waste plastic shell, reprocessing them directly will affect the quality and characters of the products. Therefore the utilization of E-waste plastic shell in high value only can be achieved on condition that the mixed plastics are separated into single plastic of high-purity by separation techniques. Wetting agents can reduce the surface tension of the separating medium, and can be adsorbed on plastic surface to change its surface chemistry properties, making the plastic selectively wetted. Processing the mixed plastics that contain PET with lye and additives, the difference of PET and other plastics in their hydrophilicity or hydrophobicity can be expanded. In this study, by separating mixed plastics with density separation and flotation techniques, impacts of media and wetting agents on density separation efficiency were deeply discussed, and parameters of the density separation process were further optimized; impacts of assistant agents such as wetting agents and additives on flotation results were discussed, and the system of assistant agents for flotation were established as well as the separation system, providing the industrialization of separation techniques of E-waste plastic shell with technical supports.Nine kinds of common plastics were selected to mix in groups and separated with density separation in this study. The groups are Group 1 PVC (or POM or PET)/PC, Group 2 PC/PA6, Group 3 PA6/PS (or ABS), group 4 PS (or ABS)/HEPE, group 5 HDPE/PP. Impacts of the types of media, density, and wetting agents on density separation results were discussed, and it was shown that PVC (or POM or PET), PC, PA6, PS (or ABS), HDPE and PP can be separated step by step by CaCl2 solution (1.30 g/mL), NaCl solution (1.16 g/mL), NaCl solution (1.09 g/mL), water (1.00 g/mL) and C2H5OH solution (0.90 g/mL). And the sorting rates of PVC, POM, PC and PS were improved by 30 mg/L of nonylphenolethoxylates-7 (NP-7), with all the sorting rates of plastics reaching 100%.Under the optimized system of assistant agents for density separation, through adjusting the parameters of separating tank,90% of the target plastic sunk into the collecting area of the tank, thus achieving continuous density separation. The best water flow for mixed plastics Group 1 to Group 5 was respectively 8.5 L/min,8.0 L/min,5.0 L/min,9.0 L/min and 11.0 L/min, while the best stirring speed for Group 1 to Group 5 was respectively 500 rpm/min,400 rpm/min,500 rpm/min,250 rpm/min and 500 rpm/min. By these means the density separation system has been established.When separating the two groups of mixed plastics, PET/PC/PS and PET/PVC/PS with flotation, the first step was to separate PS from the mixture. The sorting rate of PS reached 100% by using the floating solution,60 mg/L of sodium laurylsulfonate (SDS) solution, after 30min of wetting under appropriate conditions of floating device. The second step was to separate PET/PC or PET/PVC. Reprocessing the mixture for 30min and 15min respectively with 1-3 mol/LNaOH solution and 8 mmol/L of dibutyl sebacate (DBS) solution, and under appropriate floating conditions, PET/PC or PET/PVC were successfully separated with the floating rates of PC and PVC being 97% and 93% respectively and sinking rate of PET 96%.