低渗透含铀砂岩振动耦合场增渗浸出机理研究

Sandstone type uranium reserves in China have proved to be the low permeability of sandstone uranium. Whether efficient mining by CO2+O2 in-situ leaching can achieve low permeability sandstone deposit depends on how to improve the permeability of low permeability sandstone uranium, as to obtain largest uranium leaching rate. Vibration induced permeability has been widely used in oil and gas mining, but few researches has been focused on how to increase permeability in uranium sandstone. Previous studies of this research have found that the low frequency mechanical vibration increases the porosity of coal, and established the coupled mathematical model of stress and seepage. The new research, by using the vibrating processes like mechanical vibration of low frequency and ultrasonic vibration, of low permeability uranium sandstone for CO2+O2 test, analyzes the porosity change of uranium, and ion concentration change in solution, to explore the vibration effects of uranium hydro-chemical damage mechanism of sandstone, to establish mathematical modeling of stress-seepage-chemical coupling field for low permeability and chemical field the sandstone uranium elastic-plastic constitutive model and numerical simulation. The study has obtained permeability change, migration and leaching solution of uranium ion leaching under the condition of stress, seepage and chemical coupling field of sandstone uranium. It has found out the largest combination of uranium leaching rate, and identified the vibrating enhancement mechanism of leaching. It is of great theoretical significance and practical value for the efficient exploitation of low permeability sandstone uranium.

我国已探明的砂岩型铀资源储量以低渗透含铀砂岩为主，采用CO2+O2地浸采铀能否实现低渗透含铀砂岩矿床的高效开采，关键取决于如何提高低渗透含铀砂岩的渗透性，获得最大的铀浸出率。振动增渗已广泛应用于石油、天然气开采，但针对低渗透含铀砂岩振动增渗浸出方面研究较少。申请者前期研究发现低频机械振动增加了煤岩孔隙率，建立了振动作用下煤岩应力-渗流耦合数学模型。以此为基础，本课题通过振动（低频机械振动、超声振动）低渗透含铀砂岩CO2+O2浸出试验，分析浸出后含铀砂岩孔隙率变化、溶液内离子浓度变化，探究振动影响含铀砂岩水化学损伤机理，建立应力-渗流-化学耦合场振动低渗透含铀砂岩弹塑性本构模型并进行数值模拟，获得振动作用下应力-渗流-化学耦合场含铀砂岩渗透率变化、溶浸液运移及铀离子浸出状况，找出振动作用下铀浸出率最大的条件组合，阐明振动增渗浸出机理。对低渗透含铀砂岩高效开采具有重要的理论意义与实际价值。

我国70%以上铀资源赋存于低渗透砂岩，低渗透砂岩中提取铀是核工业长期面临的挑战。因此，提高砂岩渗透率已成为提高铀浸出效果的一个重点研究方向。在这项研究中，使用一种新型设备对低渗透砂岩样品进行了振动浸出实验，针对振动作用下砂岩孔隙率、渗透率以及浸出率展开研究。结果表明：低频振动显著提高了低渗透砂岩样品的铀浸出性能。30W低频振动作用8h后溶液中检测到铀离子，相比100W超声振动作用14小时后溶液中才检测到铀离子，而未经振动处理的试样在试验22小时内都未检测到铀离子，在试验时间内低频振动作用下铀浸出量最高达2.36mg/L，超声振动作用下铀浸出量最高达0.468mg/L。低频振动处理后，试样渗透率由初始值0.05–1.98 md增加了0.098–3.265 md。振动频率越大或振动时间越长，试样孔隙率越大，渗透率越高，浸出液获得的能量越大，对样品产生的冲击力越大。这使得更多的离子溶解到溶液中，增加了离子交换率，从而提高了浸出铀的含量。本研究为利用CO2+O2从低渗透砂岩中有效地浸出更多的铀提供了一种新方法，并为更好地了解低频振动对铀浸出过程的影响提供了新的思路。