Aluminum and aluminum-based alloys have been used for many years. In view of the increase in material purity requirements of advanced technology products, research regarding high-purity aluminum has gained significant attention in recent years. In this review, we seek to describe the fundamental purification principles and the mechanisms of various segregation techniques used to produce high-purity aluminum. Moreover, we aim to provide an overview of high-purity aluminum production, with particular emphasis on: (a) principles on how to produce high-purity aluminum by layer- and suspension-based segregation methods; (b) discussion of various influencing process parameters for each technique, including three-layer electrolysis, vacuum distillation, organic electrolysis, suspension-based segregation, zone melting, Pechiney, Cooled Finger, and directional solidification; as well as (c) investigations of fundamental working principles of various segregation methods and corresponding reported end-purification for the production of HP-Al. Eventually, the end-reported product purity, and advantages and disadvantages of various purification methods and technologies are summarized. By analyzing and comparing the characteristics of different methods, we put forward suggestions for realizing efficient and environmentally friendly production of high-purity aluminum in the future.

Magnesium-based materials with exceptional properties are being widely used in the automotive and aerospace industries, as well as in electronic equipment and Mg-based implants. The development of many advanced engineering structures and precision devices prompts the demand for high-purity Mg with better performance and service. However, the current purification methods meet challenges such as the complex equipment, potential dangers due to the powdery condensed products, and the lack of systematic analysis of the impurity behavior. Here, we report the purification of commercial raw materials into 99.9958% (± 0.0034%) pure magnesium products through one-step vacuum distillation. The process adopts a vertical distillation device, which has the advantages of high recovery efficiency, lumpy condensation products, easy cleaning, and reusability. Experimental results confirm that vacuum evaporation is more effective than vacuum sublimation for the purification of magnesium. Then, the behavior of eight impurities is analyzed theoretically and experimentally. The results significantly verify the difficulty sequence of impurity separation from the Mg base, which is Zn > Ca > Pb > Al > Cu > Ni. The similar equilibrium vapor pressure of Zn and Mg and the separation coefficient close to unity are the reasons that cause zinc to be the most difficult one to be separated. Graphical Abstract

The increasing demand for magnesium as a next-generation structural material highlights the significance of incorporating CaF₂ as a catalyst to enhance the efficiency of vacuum carbothermal reduction of magnesium (VCTRM). This study investigates the thermodynamic theory and catalytic mechanism of CaF₂ in the VCTRM process. Catalytic reduction experiments and molecular dynamics simulations were conducted to gain a comprehensive understanding of the process. Thermodynamic calculations indicate that in vacuum carbothermal reduction, the primary reaction occurs between MgO and C. Analysis shows that CaF₂'s catalytic action primarily involves F⁻, Ca²⁺, and melt eutectic. Our experiments demonstrate that the addition of CaF₂ significantly increases the reduction rate. Furthermore, the mass loss rate increases with both the quantity of CaF₂ added and the holding time, stabilizing at additions over 5%. Experiments conducted at temperatures above the melting point of CaF₂ exhibited a pronounced catalytic effect. The resultant magnesium showed optimal structure and crystallization, with a purity of 87.84%. Notably, while CaF₂ remained in the residue, it was not detected in the condensate, confirming its catalytic role. Molecular dynamics simulations revealed that molten CaF₂ sabotages the structure of magnesium oxide, with F⁻ dispersing onto the surface of MgO, thus enhancing the reaction between MgO and C to form CO. However, no chemical reaction was observed between C, MgO, and CaF₂. The occurrence of the carbothermal reduction reaction at high temperatures depends on the concentration of the reducing agent C, with CaF₂ influencing the reaction rate. This research elucidates the theoretical and mechanistic foundations of CaF₂-catalyzed VCTRM, aligning with the green energy-saving concept and significantly advancing the green and efficient VCTRM process.