Effective recovery of pure aluminum from waste composite laminates by sub- and super-critical water

An innovative and environment-friendly sub- and super-critical water processes have been proposed for successful recovery of aluminum from composite laminated wastes. The effects of reaction temperature (190-400 °C) and residence time (10 and 30 min) were mainly investigated to recover aluminum in an intact form from two commercially available packaging materials, which were made by dry and extrusion lamination methods (samples A and B), respectively. After the reaction, carbon and oxygen contents in the solid-phase were measured by CHNS/O analyzer and the aqueous-phase was subjected for TOC, ICP and ethylene glycol analyses. The results suggested that, the dry laminated ‘sample A’ exhibited a gradual decrease in carbon and oxygen level with increase in reaction temperatures indicating separation of polymers from aluminum. At 10 min, temperature ranges from 340 to 400 °C and at 30 min, from 310 to 340 °C were optimum for the aluminum recovery, showing the lowest percentage of carbon and oxygen in the solid-phase. The aluminum was oxidized above the optimum temperatures. On the other hand, the extrusion laminated ‘sample B’ showed resistance to separation of polymers and the carbon and oxygen level decreased drastically only near the critical point of water. At 30 min, 370-400 °C led to an efficient recovery of aluminum. The results revealed that, temperature, reaction time and the lamination method were the key parameters that determined the recovery of aluminum. This study provides a framework for the effective material cycling of huge wastes of laminated composites using sub- and super-critical water technology.