Thermal Pretreatment and Selective Leaching of Mineral-Bearing Industrial Residues for Domestic Critical-Material Recovery: A Process-Engineering Framework January 2021

Abstract

Critical materials, including rare earth elements, lithium, cobalt, nickel, scandium, and vanadium, are essential to energy, defense, electronics, and transportation technologies, yet refining and midstream processing remain concentrated in a small number of foreign suppliers. Large volumes of mineral-bearing industrial residues, such as mine tailings, coal combustion ash, bauxite residue, and metallurgical slags, contain recoverable concentrations of these materials, but they are difficult to process because the target elements are locked in refractory or glassy phases and are diluted by large amounts of iron, aluminum, silica, and other matrix constituents. This paper presents a portable process-engineering framework that pairs controlled thermal pretreatment with selective leaching to upgrade heterogeneous residues into purified critical-material intermediates. The framework defines feedstock classes and screening criteria, specifies a feedstock-to-product pathway built from standard unit operations, and provides decision rules for selecting pretreatment and leaching conditions by feedstock type rather than for a single plant. Thermal pretreatment is used to modify mineralogy, remove carbon and moisture, and convert refractory phases into acid-soluble forms, which raises leaching selectivity and lowers reagent demand. Selective leaching, impurity removal, and downstream precipitation or solvent extraction then recover the target elements while suppressing matrix dissolution. Mass-balance, yield, and energy-intensity templates are included to support bench-scale and pilot evaluation. The framework is presented as a transferable protocol that several categories of domestic processors can apply to expand midstream processing capacity from existing residue streams. Limitations and a staged validation program are discussed.