CO2和O2共注入下方解石溶解对黄铁矿氧化固铀的影响

我国大型可地浸砂岩型铀矿床普遍存在黄铁矿和方解石与铀矿物密切共生现象。中性地浸采铀过程中O₂和CO₂的共注入会诱导黄铁矿氧化和方解石溶解，目前针对二者共存体系中方解石溶解对黄铁矿氧化固铀的影响尚不明确。本文通过静态批实验和数值模拟的方法对比研究了CO₂和O₂条件下方解石溶解对黄铁矿氧化固铀的影响。结果表明：无CO₂分压下中性Tris缓冲体系中黄铁矿氧化对U(VI)的吸附率高达90%,有CO₂分压下碳酸铀酰体系中铀的固定率明显降低，约有32%的铀被吸附。在方解石和黄铁矿共存体系中，单独通O₂条件下铀的吸附率为27%,CO₂和O₂共通时黄铁矿氧化对铀的吸附率仅为2%,结合数值模拟结果表明O₂+黄铁矿+方解石体系和CO₂+O₂+黄铁矿+方解石体系中Ca₂(UO₂)(CO₃

Effect of Calcite Dissolution on Uranium Fixation by Pyrite Oxidation Under CO2 and O2 Co-injection Conditions

Pyrite and calcite are closely associated with uranium minerals in large in-situ leachablesandstone-type uranium deposits in China. The co-injection of O₂ and CO₂ in the process of neutral in-situ leaching of uranium will induce pyrite oxidation and calcite dissolution. At present, the effect of calcite dissolution on pyrite oxidation and uranium fixation in the coexistence system of the two is not clear. In this paper, the effect of calcite dissolution on uranium fixation by pyrite oxidation under CO₂ and O₂ conditions was comparatively studied by static batch experiments and numerical simulations. The results showed that the adsorption rate of U(VI) by pyrite oxidation in neutral Tris buffer system without CO₂ partial pressure was as high as 90%. The fixation rate of uranium in the uranyl carbonate system was significantly reduced under CO₂ partial pressure, and about 32% of uranium was adsorbed. In the coexistence system of calcite and pyrite, the removal rate of uranium was 27% under the condition of O₂ alone, and the removal rate of uranium by pyrite oxidation was only 2% when CO₂ and O₂ are combined. The numerical simulation results showed that Ca₂(UO₂)(CO₃)₃ accounted for 80% and 95% of the O_2+pyrite+calcite and CO₂₊O_2+pyrite+calcite systems, respectively. X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and Fourier transform infrared (FT-IR) results showed that the formation of goethite and lepidocrocite on the surface of pyrite increased the adsorption of U(VI). The dissolution of calcite promoted the formation of Ca-UO₂-CO₃ complex, which affected the fixation of U(VI) by pyrite and its oxidation products and improved the migration ability of U(VI).