Reactive Transport of U and V from Abandoned Uranium Mine Wastes.

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) and pH 3.4 (10 mM CHCOOH) to evaluate the effect of environmentally relevant conditions encountered at Blue Gap/Tachee on the release of U and V. The reaction rate constants (k) 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 = 4.8 × 10 mol cm s) and pH 3.4 (k = 3.2 × 10 mol cm s). However, the estimated equilibrium constants (K) for U-V bearing minerals were more than 6 orders of magnitude different for reaction at circumneutral pH (K = 10) compared to acidic pH (K = 10). 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.