Studies On Separation Techniques Of Waste Plastic

With the rapid depletion of resource and initiatives of energy conservation and emission reduction today, the study on urban minerals developing tecnology has become the focus. As an important part of urban minerals, waste plastic can not only create considerable economic value by recycling but also reduce plastic polution in the environment, which has obvious environmental and economic benefits. However, it is always a difficulty to separate different kinds of plastics in the recycling process. This paper studied plastics from packaging, End-of-life vehicle and electronic waste with experimental flotation equipment, and achieved efficient separation of various types of plastic mixture, and established the flotation technological process of waste plastics by optimizing equipment parameters and selectively regulating plastic floatability with different reagents, which provided tecnical support for waste plastic recycling.It is difficult to separate interior plastic components of end-of-life vehicles (ELVs) due to their complex types. As flotation has been considered as one of most efficient plastic separation technologies, efficiency of separating interior plastic components of ELVs with flotation technique was exploringly studied in this paper. Aiming at separating four kinds of interior plastic components of ELVs, a designed flotation column was used in laboratory to investigate the effects of parameters, such as flotation fluid flow, dissolved-air tank pressure and wetting agent concentration, on the flotation behaviors. The results showed that the primary flotation of PP/ABS/PC/PVC achieved the optimal effect with PP/ABS as floating materials and PC/PVC sinking materials under 15mg/L of tannic acid as wetting agent. 0.22MPa of dissolved-air tank pressure and 10L/min of flotation fluid flow. Floating rates of PP/ABS were 100% and 98.63% respectively while sinking rates of PC/PVC were 98.95% and 100% respectively. In secondary flotation, PP and ABS were separated completely under 10mg/L of tannic acid as wetting agent, 0MPa of dissolved-air tank pressure and 6L/min of flotation fluid flow. PC/PVC separation in the secondary flotation achieved the optimal effect with PC floating rate being 92.87% and PVC sinking rate being 91.41% respectively, under 10mg/L of tannic acid and 10mmol/L dibutyl sebacate as wetting agent,0.24MPa of dissolved-air tank pressure and lOL/min of flotation fluid flow. After two stages of flotation screening, the separating rates of PP, ABS,PC and PVC finally reached 100%,98.63%, 92.87% and 91.41% respectively, which indicated that the two-stage flotation process developed could achieve effectively separate the four kinds of mixed plastics. The two-stage flotation process developed has broad application prospects in separating interior plastic components of ELVs.Flotation, as one efficient waste plastic separation technology, is an effective method to improve the recycling rate of packaging waste. Polyethylene terephthalate (PET) widely used in packaging industry, has a large number of consumption and high recovery value. Aiming at separating PET from plastic packaging wastes, a designed flotation column was used in laboratory to investigate the effects of parameters, such as wetting agent species and wetting agent concentration, on the flotation behaviors. The results showed that the primary flotation of PET/polyvinyl chloride(PVC)/polycarbonate(PC)/polystyrene(PS)achieved the optimal effect with PS as floating materials and PET/PC/PVC sinking materials under 70mg/L of sodium dodecyl sulfate as wetting agent. When 3mol/L sodium hydroxide used to modify the mixed plastics and 8mmol/L of dibutyl sebacate (DBS) used as wetting agent, PET/PC/PVC separation in the secondary flotation achieved the optimal effect with PET floating rate being 3.56% and PC/PVC floating rate being 97.45% and 92.91% respectively. After two stages of flotation screening, the purity of recycled PET finally reached 90.91%, which indicated that the flotation process developed could effectively separate PET from four kinds of mixed plastics.To separate plastic mixture of PS/ABS, impacts of different wetting reagents at different concentrations on flotation effect of three kinds of mixture were researched. The results showed that, the type and concentration of wetting reagents effected the separation of PS/ABS mixture very much. When the p (tannic acid) in wetting solution was 40 mg/L, floating rates of recycled PS and ABS were 1.08% and 100% respectively. When the p(sodium dodecyl sulfate) was 30mg/L in wetting solution. PS/ABS from electronic waste plastic shell achieved optimum separation, with the PS sink rate 100% and ABS floating rate 98.5%. According to the infrared spectroscopy spectra, similar molecular structures of three kinds of ABS resulted in a similar floating rate. While compared with the molecular structure of virgin PS, molecular structures of recycled PS and PS from electronic waste plastic shell changed much leading to higher floatability.which is the key factor to efficiently separate recycled PS/ABS and PS/ABS from electronic waste plastic shell.