Pyrometallurgy and Electrometallurgy of Rare Earths – Part A: Analysis of Metallothermic Reduction and Its Variants

ABSTRACT

Rare earths are classified as most important and critical material for US economy and defense by Congress, and a mandate has been set to increase their in-house production, domestic resource utilization and decrease reliance on foreign resources and reserves. They are widely available in earth crust as ore (bastnaesite (La, Ce)FCO₃, monazite, (Ce, La, Y, Th)PO₄, and xenotime, YPO₄), but their so-called economic reserves are sparsely located geographically. They may be produced by various means such as beneficiation (physical, chemical, mechanical, or electrical), reduction (direct or indirect), electrolysis (of aqueous or molten/fused single or mixed salt systems) at high temperature or hydrometallurgy. Out of these, direct reduction, also known as metallothermic reduction (La and Ca reduction), is mostly utilized. Its variant, high temperature electrowinning of fused salts, is also practiced widely. These processes are material- and application-specific. In this study, the author will employ thermodynamics (Ellingham diagrams, free energy of formation, reduction potential, Nernst equation, Pourbaix (E_h-pH) diagrams, E-pO⁻² diagrams), kinetics, and energetic of a chemical reaction (chemical metallurgy) to reduce rare earth oxide/salt to rare earth metals (REO/RES – REM). It is shown that materials and energy requirement vary greatly depending on the type of mineral ore, production facility, and beneficiation/mineral processing method selected. The aim is to reduce dependence on coal deposits. It is anticipated this route will be able to produce rare earths with >35% yield and >98% purity which will be described in subsequent studies and patents.

KEYWORDS:

• Metallothermic
• thermodynamics
• Ellingham diagrams
• Nernst equation
• Pourbaix (E_h-pH) diagrams
• E-pO⁻² diagrams

Disclosure statement

No potential conflict of interest was reported by the author.