Sequential Chemical Extraction as a Method to Determine Uranium Mineral Leachability and Speciation

Improved exploitation of the remaining uranium in the Grants Mineral District, New Mexico, hinges on the development of a mineral-element speciation determination method. Understanding the mobility and leachability of uranium in mine wastes and ores has importance in both industrial and environmental applications. To this end, we are evaluating the applicability of a previously established sequential chemical extraction method (where a sample is exposed to a series of increasingly aggressive reagents) for copper mine waste on three uranium minerals common to New Mexico: the primary ore mineral uraninite (uranium oxide) and the secondary ore minerals meta-autunite (hydrated calcium uranyl phosphate) and meta-tyuyamunite (calcium uranyl vanadate). We evaluated changes to mineral structure and composition via X-ray powder diffractometry and analysis of the leachate via ICP-MS. Sequential exposures to deionized water, 1 M NH4-acetate, 0.2 M NH4-oxalate, heated 0.2 M NH4-oxalate, and 35% H2O2 resulted in appreciable changes to mineral composition and abundance and yielded detectable amounts of uranium, molybdenum, vanadium, selenium, and calcium in the leachate as a result of mineral dissolution and/or desorption. With further refinement (i.e., testing on ore samples of mixed mineralogical composition), this method may be of use in evaluating the leachability and mineralogical makeup of uraniferous material (e.g., ore, waste rocks, tailings).