Separation Of PVC And PET By Froth Flotation With Chemical Pretreatment

With the rapid development of plastics industry in China,the Consumption of plastic products had been grown as well.Although plastic gave much convenience to our lives,however,it also bringed a series of environmental problems.Recycling of plastics played an important role in solving these problems,the only difficulty was how to sort out the plastic.This study selected two components(PVC and PET)which make up a huge market share and have sorting values.With the help of modern characterization methods,we focused on conditions which maked a difference in separation of plastics and major factors of plastic separation.Moreover,the present study also investigated the best separation process parameters and discussed the related mechanism.The experimental results showed as follows:The natural flotability of plastics are not only related to the density of samples,but also to the hydrophobicity.The flotation effect increases after adding frother terpineol(TP)which may optimize the gas phase in flotation system.The wetting agent(sodium carboxymethyl cellulose(CMC))can be used for the separation of the PET if collocated with frother TP,The best parameters of separating PET are: flotation time,impeller speed,aerated flow,TP concentration,CMC concentration and adjustment time are 6 min,2200 RMP,200 L/h,25 mg/L,450 mg/L and 11 min,respectively.The recovery rate and purity in sediment product are 79.97%,80.72%,respectively.The optimal process parameters of alkali pretreatment are that the concentration of a solution of sodium hydroxide(NaOH)is 2 wt %,pretreatment time and temperature are 15 min and70?,respectively,frother TP concentration and flotation time are 35 mg/L and2 min,respectively.For potassium permanganate pretreatment(KMnO4)solution,the optimal process parameters were: KMnO4 solution concentration of 300 mg/L,the pretreatment time of 40 min,pretreatment temperature of 60?,frother TP concentration and flotation time were 15 mg/L,1 min,respectively.Using both two surfactants can achieve desired separation efficiency: After dealing with NaOH,recovery of PVC reachs 83.15% and purity reachs 100%,then the PVC recovered can use directly.As for the sediment,PET can be harvested totally,and its recovery and purity are 100% and 86.05%,respectively.After dealing with KMnO4,as for the sediment,recovery and purity of PVC are 96.75% and 70.89%,respectively.By contrast,PET is on the top and its recovery and purity are 60.25% and 94.98%.Comparing the purity of PVC and PET before and after treating with alkaline solution,treating with KMnO4 can get higher purity for PET,while treating with NaOH can make the PVC have a better behavior in harvesting.In contrast to conventional approaches,this method has an ideal separation efficiency and less dosage of chemical agent that facilitates the management for the recycling water.It is no doubt that the method has a great significance in the field of plastic flotation.