Uranium leaching was influenced by multiphase flow and geological structure during in-situ recovery of uranium (ISRU). In this study, the characteristics of multiphase flow and pore structure responding to the alkaline ISRU was investigated, using a real-time triaxial coupling nuclear magnetic resonance experiment system. The component of leaching solute, flow regime and pore structure evolution was monitored online through the T spectrum and magnetic resonance imaging (MRI), and corresponding coupling correlation of uranium recovery and pore conductivity was analyzed. The result demonstrates that the uranium sandstone was composed of micropore (1–10 ms), mesopore (10–100 ms), and macropore (>100 ms) corresponding to different relaxation times (ms). The uranium migration was mainly dominated by mesopore, and mineral dissolution and precipitation were influenced by micropore and macropore. Uranium recovery based on colloidal tetravalent and hexavalent uranium particles was exponentially correlated with the volume of leaching solution passed through the solute (solid phase/pores) and slightly contributed by the seal pore and matrix-bearing uranium. The physical migration, mineral dissolution, carbonate precipitation, and alternation by reactive transport occurred and was influenced by the hydrodynamic pressure. The dissolution of U, Ca, and Si experienced a dynamic period (0–5 PV), buffer period (5–37 PV), transition period (37–200 PV), and stable period (200–319 PV); peak concentration of U occurred at 5 PV, and 73.4% of uranium was recovered in the scope of 0–37 PV. Here, 1 PV represents the sample pore volume of 3.95 cm. The porosity and permeability were enlarged under the influence of the chemical dissolution and physical migration, but decreased with the precipitation of CaCO and SiO colloids. Permeability and porosity exhibited a positive correlation with the volume of solution passed through in the range of 0–100 PV, but a negative correlation was observed in the range of 100–319 PV. The findings provide significant insight into ISRU engineering practice.

中文翻译：

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低渗透砂岩中铀的碱性原位浸出：利用在线低场核磁共振（LF-NMR）光谱多相响应的实验研究

铀原位回收（ISRU）过程中，铀浸出受到多相流和地质结构的影响。本研究利用实时三轴耦合核磁共振实验系统研究了碱性ISRU响应的多相流特征和孔隙结构。通过T谱和磁共振成像（MRI）在线监测浸出溶质成分、流态和孔隙结构演化，并分析相应的铀回收率和孔隙电导率的耦合相关性。结果表明，铀砂岩由对应不同弛豫时间（ms）的微孔（1~10 ms）、中孔（10~100 ms）和大孔（>100 ms）组成。铀的运移主要以中孔为主，矿物的溶解和沉淀则受微孔和大孔的影响。基于胶体四价和六价铀颗粒的铀回收率与通过溶质（固相/孔隙）的浸出液体积呈指数相关，并且由密封孔隙和基质含铀贡献较小。发生物理迁移、矿物溶解、碳酸盐沉淀和反应输运交替，并受到流体动力压力的影响。U、Ca、Si的溶解经历了动态期（0~5PV）、缓冲期（5~37PV）、过渡期（37~200PV）和稳定期（200~319PV）；U的峰值浓度出现在5 PV，并且在0-37 PV范围内回收了73.4%的铀。这里，1 PV 代表样品孔体积 3.95 cm。孔隙度和渗透率在化学溶解和物理迁移的影响下增大，但随着CaCO3和SiO2胶体的沉淀而减小。渗透率和孔隙度在0~100PV范围内与通过的溶液体积呈正相关，但在100~319PV范围内呈负相关。这些发现为 ISRU 工程实践提供了重要的见解。