Manipulation of reactivity based on metallic adsorption in magnesium alloy scraps for rare-earth recycling by liquid metal extraction

Abstract

Magnesium (Mg) is widely applied in various fields because of its excellent properties, such as its light weight, high oxidation efficiency and good pharmacological properties. Recently, based on the highly selective reactivities between Mg and certain rare earth elements (REEs), liquid metal extraction, which is a representative eco-friendly process for recovering REEs from permanent magnets, has been regarded as an innovative application of Mg. As an industrial paradigm is shifted to management systems that considers the sustainability of resources, the generation of stockpiled wastes from the die casting process to fabricate Mg alloys is urgently needed for application in reindustrialization. In this work, waste AZ91 alloy (Mg-aluminum (Al)-zinc (Zn)) is an extraction agent based on its ability to manipulate the reactivity of the system. Moreover, the extraction behavior of waste AZ91 is investigated via liquid metal extraction to address supply risks. The main challenge faced by REE recovery is the presence of intermetallic compounds between Al in waste AZ91 and REE in permanent magnets. Based on the different affinities between elements, the phase of Al-iron (Fe)-REE is controlled by adding the absorbing agent zirconium (Zr). Finally, the recovery efficiency of each REE is 91.2%. This value is close to that of pure Mg, and it is approximately 16% greater than that of waste Mg. It is suggested that technology for enhancing the sustainability of resources to address supply risk for circular economy is feasible. Waste resources can be used to optimize additional parameters affecting the absorbing agent.