Reactive Transport of U and V from Abandoned Uranium Mine Wastes

摘要

The reactive transport of uranium (U) and vanadium(V) from abandoned mine wastes collected from the Blue Gap/Tachee Claim-28 mine site in Arizona was investigated by integrating flow-through column experiments with reactive transport modeling, and electron microscopy. The mine wastes were sequentially reacted in flow-through columns at pH 7.9 (10 mM HCO_3~-) and pH 3.4 (10 mM CH_3COOH) to evaluate the effect of environmentally relevant conditions encountered at Blue Gap/Tachee on the release of U and V. The reaction rate constants (km) for the dissolution of uranyl— vanadate (U—V) minerals predominant at Blue Gap/Tachee were obtained from simulations with the reactive transport software, PFLOTRAN. The estimated reaction rate constants were within 1 order of magnitude for pH 7.9 (k_m = 4.8 × 10~(-13) mol cm~(-2) s~(-1)) and pH 3.4 (km = 3.2 × 10~(-130) mol cm~(-2) s~(-1)). However, the estimated equilibrium constants (K_(eq)) for U—V bearing minerals were more than 6 orders of magnitude different for reaction at circumneutral pH (K_(eq) = 10~(-38.65)) compared to acidic pH (K_(eq) = 10~(-44.81)). These results coupled with electron microscopy data suggest that the release of U and V is affected by water pH and the crystalline structure of U—V bearing minerals. The findings from this investigation have important implications for risk exposure assessment, remediation, and resource recovery of U and V in locations where U—V-bearing minerals are abundant.