Direct collection and reuse of dispersed aluminum chips through salt flux and supergravity enrichment: less salt consumption and circular economy

Abstract

Machining chips are considered to be the most promising secondary aluminum resource for achieving a circular economy, as it only has to face the challenge of high surface-to-volume ratios. While salt flux technology has been recognized as the optimal strategy for recycling chips due to its outstanding oxidation suppression and impurity removal during melting, its sustainable value is constrained by excessive salt costs and potential environmental risks. This study introduces an innovative supergravity-enhanced technique that works synergistically with salt fluxes for extracting high cleanliness metals from chips, achieving higher yields of same-level aluminum while significantly reducing flux consumption. According to the investigation of enrichment mechanism under salt flux and supergravity, the oxide film covering the chips surface was rapidly stripped off by the erosion and adsorption of molten salt, and subsequently the coalesced melt and salt-slag clusters were accelerated to enrich and gradually stratified under supergravity enhancement. Ultimately, more than 99.5 % clean aluminum was collected in a short period of time, while residues were completely captured in the surface salt layer. Subsequently, over 99 % of salts were extracted and reused, successfully achieving harmless treatment of salt slags. Furthermore, a scaled-up continuous enrichment device was developed, with its economic and environmental costs evaluated through feasibility tests. This strategy demonstrated potential to increase profits by no less than 0.4 $/kg compared to conventional technologies, enhancing the economic viability of chip-to-metal conversion. Meanwhile, it amplified environmental benefits through closed-loop flux and waste minimization, effectively preventing the loss of valuable resources and the production of hazardous salt cakes.