Development of a restraining wall and screw-extractor discharge system for continuous jig separation of mixed plastics

Abstract Batch and continuous jig experiments were compared using plastic mixtures with different light and heavy particle ratios. The purity of bottom layer products of continuous jig was lower than those of batch jig because of light particle entrainment induced by the screw-type extractor. To minimize entrainment, a new discharge system consisting of a vertical restraining wall and a screw-type extractor was developed. The restraining wall was installed close to the “product-end” to separate the jig chamber into two and allow particles to transfer from one part to the other via the gap under the wall. The experimental results showed that this proposed discharge system could improve the purity of heavy particles in bottom layer products because of two reasons: (1) higher material mass ratio of heavy plastic close to product-end, and (2) changes in the flow of water and particles. Moreover, the purity of bottom layer products during continuous jig separation was influenced by the difference of material mass ratio in feed; that is, purity was higher when the ratio of heavy plastic was high. In addition, an estimation procedure based on multi-step treatment using separation curves is proposed to achieve the target purity of bottom layer products.