Advances in Monazite Decomposition Technologies: Proposed Potential Direction for the Sodium Hydroxide Leaching Context

Abstract: The current understanding and development of monazite decomposition technology using sodium hydroxide are examined. Most previous assessments have primarily focused on the post-leaching processing of monazite using sodium hydroxide, including processing steps to produce the total rare earth oxide product. However, the initial leaching process of monazite with alkali solution proves to be highly significant in practice. It presents numerous problems, such as the requirement for fine grinding of the ore down to below 45 microns, substantial alkali excess, and extended reaction times to achieve the desired efficiency. These requirements result in increased energy, chemical, and equipment costs. This article is focused on discussing the leaching conditions of monazite with alkali solution based on published literature, the problems associated with this process, the underlying reasons, newly proposed variations such as sodium hydroxide leaching under pressure and sodium hydroxide leaching in a heated ball mill, limitations of these variations, and unresolved issues. Furthermore, the manuscript introduces a novel technique, high-intensity ultrasound, to support the leaching process, which has been applied in technological cases. The discussion delves into the mechanisms of high-intensity ultrasound and its applicability in the monazite leaching process using sodium hydroxide.