The process mineralogy of leaching sandstone-hosted uranium-vanadium ores

Abstract

In the United States, sandstone-hosted ore deposits of the Paradox Basin (Colorado Plateau) are major resources of uranium and vanadium, two metals important to green energy among other applications. Despite historic and current mining interest, and their significance as major domestic resources of critical elements, the geometallurgy of these deposits has received little study. This article documents the geometallurgy and process mineralogy of the U-V ores and identifies the principal barriers to optimal recovery by acid leaching. Most of the metals occur as pitchblende (mixed uranium oxide-silicate), V-hydroxides, V-bearing phyllosilicates, and diverse vanadates of U, Pb, Cu, and other metals. Commercial extraction is by two-stage heated tank leaching with H2SO4 and NaClO3, yielding high U but lower V recovery (70–75% in the industrial operation). Laboratory leaching experiments coupled with comparisons of head and residue mineralogy indicate that the unrecovered U consists of micron-scale pitchblende grains locked within quartz and other insoluble minerals. The principal cause of suboptimal V recovery is the V-phyllosilicates, which show variable but generally poor solubility at room temperatures. An ancillary cause is locking of a small amount of fine-grained V-hydroxide and pitchblende by authigenic quartz and V-phyllosilicates. Comparison with other global V resources suggests that variable solubility of V-phyllosilicate ore minerals may also diminish recovery from more common ore deposit types, such as V hosted in black shales or stone coal, particularly in heap leaching of low-grade ores at coarse grain sizes.