In-Situ Leaching of South Texas Uranium Ores - Part 1: Laboratory Studies of Ore Composition and Leaching Performance

This paper presents data on mineralogy and laboratory chemical-leaching tests for ore samples from several areas of the south Texas tertiary Catahoula formation. Optical microscope, electron microprobe, spectroscopic, X-ray diffraction (XRD), and various chemical analyses were performed. Batch screening tests gave qualitative estimates of leach rate and potential recovery. Packed column tests using hydrogen peroxide or pressurized oxygen gave more quantitative recovery estimates. The frequently friable sandstones contained highly variable amounts of quartz, feldspar, calcite, and clay, and in some cases, zeolite or mica. Clays were mainly mixed layer illite/smectite type. High cation exchange capacities (CEC's) correlated. with clay (and zeolite) content, while high reducing capacities were often associated with pyrite level. Coffinite, in various environments, was pyrite level. Coffinite, in various environments, was the main uranium mineral. With batch tests using pseudo-first-order rate constants, ore leach rates were pseudo-first-order rate constants, ore leach rates were generally characterized as "fast" on a scale of fast, intermediate, and slow. However, there was variability in leach rates, both in samples from different areas and in samples taken at different depths in the same well. Fast rates and recoveries greater than 80% were observed in most column pack tests, but there was variation with leachate composition and sample source. The chemistry and kinetics of leaching are also discussed. Introduction In-situ leaching has become an important alternative to open-pit and shaft-mining recovery of uranium. It has the potential of recovering reserves not presently minable by conventional techniques with minimal disturbance of the surface environment. Water requirements of in-situ leaching can be up to 30 times less than a comparable mine, and there are no undesirable tailings ponds. It is physically less hazardous than conventional mining methods. The increasing number of commercial scale in-situ operations is evidence of the emerging potential of this mining method. As more forms of alternative energy are sought to offset shortages and dependency on imported oil, increased production of uranium is inevitable. Current uranium production from in-situ mining is estimated to be 9% of the U.S. total. Considerable uranium reserves are found in south Texas in the Oakville (Miocene) and Catahoula (Oligocene) formations and the Jackson formation (Eocene). The importance of this resource is evidenced by the number of leaching permits issued by the State of Texas in the past 6 years. Larson reviewed early leaching activities in south Texas and other areas of the U.S. Many leaching studies have been reported for south Texas, including laboratory kinetics of leaching, case histories of field operations, and commercialsize projects. The existence of about 12 pilot and commercial-scale; in-situ leaching operations in south Texas indicates the great interest in this technology. The distribution of these sites parallels the Texas coast. They are also generally located in arid, gently rolling terrain. P. 377