TECNALIA is a pioneer in developing a process that eliminates 99% of the organic load from complex aluminium scrap.
Waste generated from processing aluminium as fine particles, foil and shavings is one of the most difficult materials to recover by smelting. For this reason, TECNALIA has developed a new two-stage continuous process. It consists of a heating process at 300°C in a furnace with a controlled oxidising atmosphere, followed by a second heating process at 400-550°C in an inert atmosphere, resulting in a combined thermo-mechanical action that ultimately removes impurities from the metal.
For this purpose, several 'complex' materials with different particle sizes, thicknesses and origins have been studied, including lacquered cans from the food industry, lacquered shavings and others. Aluminium scrap contaminated with up to 15 % by weight of C, and up to 1.5 % by weight of oxygen were treated with this new technology. It resulted in a material containing only 0.15 % by weight of C and 0.3 % by weight of O.
Structural die castings
Primary aluminium alloys are the most widely used alloys in the industry to produce structural die castings (HPDC). These alloys contain very low percentages of alloying elements considered as harmful. In contrast, secondary aluminium alloys are mainly produced from recovered scrap and aluminium dross, which reduces the energy required to produce primary alloys by electrolysis by up to 95 %.
Current thermal processes for the treatment of metals contaminated with impurities, especially with high contents of organic compounds (mainly paints, lacquers and plastics), present problems in obtaining the metal fraction: the metal fraction oxidises with increasing process temperature and contact with organic compounds.
Because of all these problems, some currents aluminium scrap streams cannot be recovered with existing processes and new developments are needed to solve these problems.
Further information
This development has been carried out in recent years by TECNALIA's Iron and Steel and Biorefinery and Waste Recovery areas. It has been presented at the international congress HIGH TECH DIE CASTING (HTDC 2021), with the paper 'Development of a new process to recover aluminium from contaminated granulated or thin complex materials to employ for primary aluminium alloys'. The authors of the paper were I. Vicario, J. Antoñanzas Gonzalez, L. Yurramendi Sarasola, J.C. Múgica Iraola and A. Abuin Ariceta.
