Ammonium sulfate leaching of NaOH-treated monazite. (October 2022)

• Record Type: Journal Article
• Authors: Liu, Wei; Feng, Xu; Noble, Aaron; Yoon, Roe-Hoan
• Is Part Of: Minerals engineering. Volume 188(2022)
• Publication Date: 2022-10
• Subjects: Rare earth elements -- NaOH pretreatment -- Monazite leaching -- Ammonium sulfate -- Ion-exchange leaching -- Enthalpy of hydration; Mines and mineral resources -- Periodicals; Ressources minérales -- Périodiques; Mines and mineral resources; Periodicals; Electronic journals; 622
• DOI: 10.1016/j.mineng.2022.107817
• Languages: English
• ISSNs: 0892-6875

Abstract

Highlights: Methods of decomposing monazite under mild conditions have been studied. The decomposition product can be leached using ammonium sulfate as lixiviant. The ammonium sulfate leaching is controlled by an ion-exchange mechanism. The ion-exchange mechanism is controlled by the hydration enthalpies. A conceptual model for the ion-exchange mechanism has been proposed. Abstract: Rare earth elements (REEs) can be extracted from monazite under aggressive decomposition and leaching conditions. Much of the waste rocks are removed prior to the extraction process to minimize the costs and waste generation, which is difficult with coal byproducts. The possibility of extracting REEs from low-grade monazite concentrates under relatively mild conditions has been explored to simulate the extraction of REEs from coal byproducts. It has been found that monazite can be decomposed in 10 to 50 % NaOH solutions at 80 °C, with the resulting hydrous oxide being subjected to the ammonium sulfate leaching at pH 4. The ς-potential measurements conducted in the presence of the lixiviant suggest that the NH4 + ions displace the hydrated Ln 3+ ions from the surface of Ln(OH)3 (s) by an ion-exchange mechanism, which may be driven by the large differences in the hydration enthalpies between the charged species involved. This approach may be advantageous over acid leaching, including the regeneration of spent lixiviant, lower chemical consumption, and leaching at higher pH.