Leaching of aluminium from post-consumer beverage packaging residual PolyAl using biogenic organic acids: Towards low-cost, sustainable recycling

Abstract

Plastic packaging provides enormous benefits for preservation and transportation of food and beverage products. However, recycling the multilayered packaging materials represents a challenge due to the complexity of separating the components making up the different layers. The drinks packaging, having aluminium (Al) as a light barrier placed between polyethylene layers inside the paperboard carton, comprises a significant category of post-consumer waste in need of complete recycling. Microbially produced organic acids are gaining attention for recovery of metals from industrial residues. This report presents a study on evaluation of acetic- and gluconic acid, which are known to be produced by acetic acid bacteria, for leaching out the Al from Tetra Pak PolyAl material remaining after removal of the paperboard. By using Taguchi design technique L₉ (3)⁴, optimal conditions for 100 % Al leaching from 1 % (w/v) PolyAl (0.4 cm²) were determined to be treatment at pH 1 and 50 °C with 0.25 M acetic acid for 6 days or 1 M gluconic acid for 15 days. Increasing the PolyAl concentration to 2 % w/v and particle size to 4 cm² resulted in increase in the time for maximal Al leaching. Various microscopic, spectroscopic and thermal analyses techniques confirmed the removal of Al and revealed no notable change in the properties of the residual PE. The metal released was recovered nearly quantitatively (99.5 %) by precipitation as Al(OH)₃ only from the acetic acid leachate. The results indicate the potential of the leaching method in providing a greener route for recycling the Al containing packaging material using biogenic organic acids.