Reactive Transport of U and V from Abandoned Uranium Mine Wastes

Abstract

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 HCO3−) and pH 3.4 (10 mM CH3COOH) 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 (km = 4.8 × 10−13 mol cm−2 s−1) and pH 3.4 (km = 3.2 × 10−13 mol cm−2 s−1). However, the estimated equilibrium constants (Keq) for U–V bearing minerals were more than 6 orders of magnitude different for reaction at circumneutral pH (Keq = 10−38.65) compared to acidic pH (Keq = 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.

Framework Polymorphism and Modular Crystal Structures of Uranyl Vanadates of Divalent Cations: Synthesis and Characterization of M(UO2)(V2O7) (M = Ca, Sr) and Sr3(UO2)(V2O7)2

“…[53] Increasing of the amount of large alkaline-earth cations to the ratio Sr : U = 3:1 in the system [preserving the ratio (M 2+ +U) : (V 2 O 7 ) = 2:1] leads to formation of a differentiated structure with two kinds of modules. The detailed crystal chemical formula of Sr 3…”

“…Uranium production in the USA peaked between the 1940s and 1980s during operation of thousands of uranium mines mostly in the western United States, leaving abandoned mines with potential hazards to the environment and humans . Uranium reacts with hydroxide, carbonate, or alkaline earth metals in oxidizing conditions affecting the mobility of uranium in water . Uranium and vanadium species can form solid phases including vanadate, phosphate, silicate, and carbonate minerals .…”

“…Uraninite (UO 2+ x ), davidite [La(Y,U)Fe 2 (Ti,Fe,Cr,V) 18 (O,OH,F) 38 ], and montroseite [(V 3+ ,V 4+ ,Fe 2+ )O(OH)] are major minerals that can alter to form uranyl vanadate minerals , . Studies of the crystal chemistry and various properties of uranium‐containing minerals and compounds are helpful for understanding the influence of radionuclides on human health and the environment , …”

“…[1] Uranium reacts with hydroxide, carbonate, or alkaline earth metals in oxidizing conditions affecting the mobility of uranium in water. [2][3][4] Uranium and vanadium species can form solid phases including vanadate, phosphate, silicate, and carbonate minerals. [5][6][7][8] Uraninite (UO 2+x ), davidite [La(Y,U)Fe 2 (Ti,Fe,Cr,V) 18 (O,OH,F) 38 ], and montroseite [(V 3+ ,V 4+ ,Fe 2+ )O(OH)] are major minerals that can alter to form uranyl vanadate minerals.…”

“…[9,10] Studies of the crystal chemistry and various properties of uranium-containing minerals and compounds are helpful for understanding the influence of radionuclides on human health and the environment. [3,[11][12][13] Carnotite-group minerals are uranyl vanadates with a layer structure [9] that are commonly found in abandoned mine sites 6.891(3) Å, b = 7.171(3) Å, c = 14.696(6) Å, α = 85.201 (4), β = 78.003 (4), γ = 89.188(4); V = 707.9(5) Å 3 ; space group P1, Z = 2. The framework structure of Sr(UO 2 )(V 2 O 7 ) is related to that of Pb(UO 2 )(V 2 O 7 ) reported previously, while that of Ca(UO 2 )(V 2 O 7 ) has a different topology.…”