Abstract
The U.S. Bureau of Mines investigated a simultaneous elutriation and flotation technique for separating polyethylene terephthalate (pet) from polyvinylchloride (pvc). The Tuscaloosa Research Center, through a cooperative agreement with a recycling company, devised an elutriation-flotation method for beneficiating the mixed heavy plastics portion of municipal solid wastes, which is composed of polystyrene (ps), pet, and pvc. A sodium carbonate brine was used to remove the lighter ps from the heavier pet and pvc. Over 98 pct of the ps was recovered in a high-purity ps concentrate containing 99.7 pct ps. The remaining pet and pvc mixture was washed to remove the brine salts that would be harmful to the flotation process. The clean pet and pvc mixture was conditioned in a solution of 45 g/t gelatine and floated in a short (1-m) column flotation cell in an upward flow of water. In a single flotation step, over 75 pct of the pet was recovered in a high-purity product containing 99.8 pct pet. The bubbles attached to the pet lowered the effective density of the pet-bubble agglomerate and allowed successful separation of these agglomerates from the pvc plastic pieces. This method separated two-thirds of the mixed plastics fraction into high-purity ps and pet products suitable for recycling and left only one-third of the plastics in the mixed plastics product.
