Development of a new process to recover aluminium from thin complex aluminium scrap to employ for primary aluminium alloys

Abstract

Current thermal processes for the treatment of metals contaminated with impurities, especially with high contents of organic compounds, present problems in obtaining the metal fraction: the metal fraction oxidises with increasing pro cess temperature and the contact with organic compounds. Often, the quality of aluminium obtained from "dirty" raw materials does not allow using it for applications requiring high metal purity or low metal oxidation (alloying tablets, aluminium shots, ...), or for HPDC structural parts. Some aluminium scrap streams cannot be recovered with existing processes and new developments are needed. A new two-step continuous process has been developed. It consists of a heating process at 300°C in a controlled oxi dising atmosphere furnace, followed by a second heating process at 400-550°C in an inert atmosphere, which results in a combined thermo-mechanical action. The obtained clean material can be continuously sintered under pressure, obtaining a product with a density close to 2.7 g/cc. Several "dirty" materials with initial contents up to 15% wt. C and up to 1.5% wt. O have been studied, reaching to final products containing as low as 0.15% wt. C and 0.3% wt. O. An exam ple with a filter dust from shredding of aluminium profiles is described. The final composition of the product obtained after the treatment allows using the recycled aluminium as a high quality secondary raw material for aluminium alloying tablets, aluminium powder and high-performance aluminium casting alloys.