In-situ leaching of Crownpoint, New Mexico, uranium ore: V. Laboratory study of strong leaching systems--oxidant-heat

While some fractions of the uranium ores from Crownpoint, New Mexico are amenable to leaching with mild chemical reagents such as hydrogen peroxide or high pressure oxygen in sodium bicarbonate solution, other ores are refractory to this treatment, possibly because the uranium mineral is embedded in a kerogenic organic matrix. Such refractory ore occurs only in selected areas of the general Crownpoint properties. Previous papers have described the use of chemically severe leaching systems (sodium hypochlorite, oxygen/sulfuric acid) to recover uranium from such refractory ore. This paper reports an experimental study on the effects of heating refractory Crownpoint ore at moderate temperatures in the presence of a mild (O/sub 2//NaHCO/sub 3/ or H/sub 2/O/sub 2// NaHCO/sub 3/) chemical leaching system. When a composite sample of refractory ore from Mobil's Crownpoint uranium properties was leached with high pressure (600-800 psig) O/sub 2//NaHCO/sub 3/ at ambient temperature in batch or pack tests, only 30 - 40% recovery and slow reaction rates were observed. However, this same leachate, when heated to 140/sup 0/F, gave 60-65% recovery in batch, pack, and core studies at much more rapid rates. Several other temperatures were also studied, but 140/sup 0/F appears to be close to the optimum more » for the group of ore samples tested. Using rough kinetic approximations, relatively low apparent energies of activation--typical of those encountered in diffusion-limited systems--were observed. Reservoir heat balance estimations suggest that the concept of utilizing heated leachate for in-situ leaching can be technically feasible in reservoirs such as Crownpoint, particularly if injection rates are high and ore bodies are reasonably thick. « less