Feasibility of Flotation to Separation of Waste Plastics

• Published in: Shigen to sozai Vol. 112; no. 3; pp. 177 - 184
• Main Authors: SHIBATA, Junji, MATSUMOTO, Shigeno, KUSAKA, Eishi, YAMAMOTO, Hideki, MORIMOTO, Yoshio
• Format: Journal Article
• Language: Japanese; English
• Published: The Mining and Materials Processing Institute of Japan 1996
• Subjects: Flotation; Gravity Separation; Plastics; Recycling; Wetting Agent
• ISSN: 0916-1740; 1880-6244
• DOI: 10.2473/shigentosozai.112.177

As part of studies on the development of separation process for efficiently separating waste plastics, the applicability of flotation method to the separation of inherently hydrophobic plastics has been investigated. For optimizing the flotation operation conditions, floatability measurements of plastics was carried out in solutions including wetting-agent, and flotation separation using two plastics mixture as well. Moreover, the dense media separation and flotation process, which has been proposed in this investigation, were examined in terms of the plastic grade and percent recovery. Polyvinyl chloride (PVC), polycarbonate (PC), polyacetal (POM) and polyphenylene ether (PPE) were used as test polymers, and tannic acid, sodium ligninesulfonate, polyoxyethylene lauryl ether, Aerosol OT and saponin as wetting-agents. The floatability measurements showed that the increased concentration of wetting-agent brings about the decrease in percent floatability of each of polymers; this might be explained in line with adsorption behavior of surface-active species. Separation flotation using two plastics mixture indicated that one plastic is sufficiently separated from another in an optimum concentration of wetting-agent. Furthermore, the wetting-agent mixture was found to improve the efficiency of the separation flotation. Finally, according to the results obtained from the flotation tests, a dense media separation and flotation process was proposed and applied to the differential separation of the four plasticsmixture. It was found that the proposed process satisfactorily separated one plastic from others with high grade and recovery at each of the operations; the 100% PPE floats is obtained with 100% recovery in the dense media separation, the 95.7% PVC sinks with 90.7% PVC recovery in the first flotation, and the 87.6 % POM floats and the 90.3% PC sinks with 99.2% POM and 83.6% PC recoveries, respectively, in the second flotation. We suppose this separation process to be feasible for recycling waste plastics.