Mechanical, electrodynamic, and magnetic particle-size classification of lunar regolith for in-situ resource utilization: A review

To facilitate large-scale and long-term human lunar exploration, it is indispensable to establish technologies such as excavation, beneficiation, and chemical processing of lunar regolith to achieve efficient in-situ resource utilization (ISRU) on the Moon. Because particle-size classification is one of the most essential technologies required for ISRU, various methods based on mechanical, electrodynamic, and magnetic forces have been developed: (1) The first mechanical method involves the application of conventional technologies, namely sieve and centrifugal classifiers, which are widely employed in the terrestrial powder processing industry and are anticipated to be effective in the lunar low-gravity field. Both classifiers have demonstrated high performance; nevertheless, their necessity for airflow to facilitate the transportation of particles is a significant disadvantage for space applications. The second mechanical method leverages the Brazil nut effect in an inclined vibrating tube. Large particles contained in the regolith float on the vibrated regolith layer are tend to fall downward, while small particles are transported upward. A considerable quantity of regolith can be classified using this vibration system. The low-gravity field on the Moon is advantageous for this system. (2) The electrodynamic method leverages the balance between electrostatic and gravitational forces. Small regolith particles agitated or conveyed in an electrodynamic field are lifted to higher altitudes than large particles in a vacuum. As a result, the classified particles are collected in boxes placed at an upper position. Five types of such electrodynamic classification systems have been developed, demonstrating high classification performance. The low-gravity field on the Moon is also advantageous for these systems. A unique method that leverages an electrodynamic travelling wave for lifting regolith particles has demonstrated both high classification accuracy and high yield. Although the amount of classified regolith is small, these systems are compatible with the lunar environment because of their simple configuration, no need for consumables, and intrinsically low power consumption. (3) Magnetic force is used for beneficiation and classification of regolith. Because the usage of real lunar regolith is limited, further studies are required to evaluate the feasibility of magnetic classification and beneficiation using real lunar regolith or an improved simulant featuring magnetic properties similar to those of real regolith. In this paper, the author offers an overview of the recent progress on classification technologies for efficient ISRU on the Moon. • Particle-size classification technologies of lunar regolith for in-situ resource utilization are reviewed. • Reviewed technologies are categorized as mechanical, electrodynamic, and magnetic methods. • The unique mechanical method, which leverages the Brazil nut effect, is suitable for space applications. • The electrodynamic method is well-suited for the lunar low-gravity field and vacuum environment. • The magnetic method is used for beneficiation and classification of regolith.