An experimental device and method for simulating semi-closed column leaching of sandstone uranium ore

Abstract

This invention provides an experimental apparatus and method for simulating semi-closed column leaching of uranium ore from sandstone. The invention eliminates any stirring structure within the reactor body and uses a quartz container to hold the core, allowing the leaching agent to diffuse naturally within the core pores solely through its concentration gradient. This preserves the original pore structure of the sandstone and avoids interference from forced flow on the leaching process. Secondly, through the coordinated operation of a gas compensation component and a bottom-mounted first sampling valve, a pressure sensor monitors the pressure drop within the reactor in real time during sampling. The control unit drives a back-pressure valve to replenish the reactor with isobaric gas, maintaining pressure fluctuations within ±0.10 MPa. This achieves dynamic sampling without depressurization or disruption of the gas-liquid-solid balance, and the obtained leaching kinetic data accurately reflects the in-situ leaching process. Finally, this invention uses uranium leaching rate and a comprehensive potential ecological risk index as dual objectives. Through normalized weighting and response surface methodology, it minimizes environmental risk while ensuring leaching efficiency.

Description

Technical Field

[0001] This invention relates to mineral resource leaching and environmental protection technologies, and in particular to an experimental apparatus and method for simulating semi-enclosed column leaching of sandstone uranium deposits. Background Technology

[0002] In-situ leaching technology for sandstone-type uranium deposits is an important method for uranium resource development. The leaching process is influenced by a variety of factors, including underground temperature, pressure, pore structure, and redox environment. To optimize the leaching process and elucidate the leaching mechanism, column leaching experiments are usually conducted under laboratory conditions to simulate the water-rock reaction process in the underground in-situ environment.

[0003] Currently, existing experimental setups and methods still have the following shortcomings when simulating in-situ static leaching of sandstone uranium ore: First, existing experimental setups disrupt the in-situ equilibrium of the system during sampling. When conducting staged sampling under high temperature and high pressure conditions, existing setups typically require significant depressurization or complete reactor opening to obtain the leachate. This causes the reaction system to instantly transform from a closed system to an open system, resulting in rapid gas overflow, drastic pH fluctuations, and a sharp drop in pore pressure. This disrupts the multiphase equilibrium of the underground reservoir, making the measured kinetic data unable to accurately reflect the in-situ leaching process.

[0004] Second, there is a lack of comprehensive assessment of the ecological risks associated with heavy metals during the leaching process. Harmful heavy metals are commonly found in sandstone uranium deposits. During in-situ leaching, these elements enter the leachate along with the target elements, potentially posing risks to the groundwater environment. However, existing leaching experimental methods mostly focus on improving uranium leaching rates, failing to incorporate the ecological risks of associated elements into the evaluation system, and lacking optimization methods for leaching schemes based on both leaching efficiency and ecological risk indicators. More importantly, this evaluation and optimization process relies on experimental equipment capable of stably and continuously providing leachate samples. If the sampling process disrupts the system equilibrium, the data basis for subsequent ecological risk assessments will be distorted.

[0005] In view of this, the inventors have specifically designed an experimental apparatus and method for simulating semi-enclosed column leaching of sandstone uranium ore, which leads to this invention. Summary of the Invention

[0006] To solve the above problems, the technical solution of the present invention is as follows: The reactor includes a main body and a heating unit for heating the main body. The main body has a solvent injection port at its top and a gas inlet and a leachate sampling port at its bottom. The reactor is characterized by further comprising: The pressurization and regulation unit includes a mixed gas source, a pressurization device, and a gas compensation component. The output end of the pressurization device is connected to a gas interface to pressurize the mixed gas of CO2 and O2 to the experimental set value before it is introduced into the main body of the reactor. The input end of the gas compensation component is connected to the pressurization device, and its output end is connected to the top of the main body of the reactor through a back pressure valve. A pressure sensor, installed on the upper part of the reactor body, is used to monitor the pressure inside the reactor body in real time; The sampling unit includes a first sampling valve connected to the leachate sampling port; The control unit is electrically connected to the pressure sensor, heating unit, back pressure valve, first sampling valve and gas compensation component. When the control unit receives the sampling signal that the first sampling valve is open, it controls the back pressure valve to open according to the pressure signal fed back by the pressure sensor, so that the gas compensation component can supplement gas into the reactor body to maintain the pressure fluctuation inside the reactor body within a preset range during the sampling process.

[0007] Preferably, a first gas source valve, a three-way valve, and a second gas source valve are sequentially provided between the pressurization device and the gas interface. The gas compensation component includes a one-way valve with a unidirectional conduction direction toward the inside of the reactor body. The inlet end of the one-way valve is connected to the three-way valve, and its outlet end is connected to the back pressure valve.

[0008] Preferably, the mixed gas source includes a CO2 cylinder, an O2 cylinder, and a mixed gas tank. The inlet end of the mixed gas tank is connected to the CO2 cylinder and the O2 cylinder respectively, and its outlet end is connected to a pressurization device. The volume fraction of O2 in the mixed gas tank is in the range of 10% to 50%.

[0009] Preferably, the heating unit includes a heating steel sleeve, the top of which is provided with a heating tube insertion hole. The heating steel sleeve is located in a cavity and has a quartz container inside that holds a columnar sandstone uranium ore core. The heating steel sleeve is wrapped with a vacuum insulation sleeve. The main body of the reactor is wrapped with an external insulation layer. The top of the main body of the reactor is also provided with a temperature sensor for detecting temperature changes inside the main body of the reactor.

[0010] Preferably, the sampling unit further includes a condenser, a sampling collector, a constant temperature circulating water cooler, a leachate collection bottle, a drainage gas collection bottle, and a measuring cylinder. The leachate sampling port is connected in sequence to a first sampling valve and a condenser. The sampling collector is connected to the condenser to perform sampling. The input end of the leachate collection bottle is connected to the condenser through a second sampling valve. The output end of the leachate collection bottle is connected in sequence to a drainage gas collection bottle and a measuring cylinder. The leachate collection bottle is located inside the constant temperature circulating water cooler.

[0011] Preferably, the present invention also provides an experimental method for simulating semi-closed column-leached sandstone uranium deposits, comprising the following steps: The sandstone uranium ore core, which retains its original pore structure, is processed into a columnar core sample, placed inside the main body of the reactor, and leaching agent is injected through the leaching agent injection port. The main body of the reactor is then sealed. A mixture of CO2 and O2 is introduced into the reactor body through a gas interface via a pressurization device to pressurize it to the target pressure; the heating unit is then activated, and the reactor body is heated to the target experimental temperature using a segmented heating method, so that the leaching agent undergoes static diffusion leaching through the core pores under conditions of no stirring and no forced flow. At the preset leaching time point, sampling is initiated. Simultaneously, the control unit controls the back pressure valve to replenish gas into the reactor body based on the pressure signal fed back by the pressure sensor, so that the pressure fluctuation inside the reactor body is maintained within ±0.10MPa during the sampling process. The leachate after cooling in the condenser is collected at different time points. Based on the collected data on multiple sets of leachate and pressure changes, the concentrations of uranium and associated elements in the collected leachate were analyzed, and the uranium leaching rate and comprehensive potential ecological risk index were calculated. With the dual objectives of maximizing uranium leaching rate and minimizing potential ecological risks, the leaching temperature and pressure were adjusted.

[0012] Preferably, the segmented heating is performed from room temperature to 250°C at a rate of 10°C / min; after reaching 250°C, the temperature continues to rise at a rate of 1°C / min to 5°C / min until the target leaching final temperature is reached, wherein the target leaching final temperature does not exceed 650°C; and the target pressure is 0.5MPa to 40MPa.

[0013] Preferably, the method for calculating the comprehensive potential ecological risk index includes: First, the concentration of each associated metal element in the leachate was measured, and the background concentration of the element in the original sandstone uranium ore sample was obtained; the pollution index of the element was obtained by dividing the measured concentration of the leachate by its background concentration. Then, based on the toxicity level of the metal element, a corresponding toxicity response coefficient is assigned to it. The pollution index of the element is multiplied by the toxicity response coefficient to obtain the single potential ecological risk index of the element. Finally, the individual potential ecological risk indices of all detected associated metal elements are summed to obtain the comprehensive potential ecological risk index.

[0014] Preferably, the dual-objective optimization specifically includes: The uranium leaching rate and the comprehensive potential ecological risk index were normalized to their minimum and maximum values, respectively, with the comprehensive potential ecological risk index being negatively standardized. Calculate the overall evaluation score; Using different leaching agent concentrations as independent variables and uranium leaching efficiency as the response variable, a nonlinear quadratic polynomial regression model was constructed using response surface methodology, and a multivariate response surface was plotted. By solving for the extreme points of the response surface regression model, the optimal operational experimental parameters are obtained under the constraint that the comprehensive potential ecological risk index is below the safety threshold.

[0015] The technical solution provided by this invention has the following beneficial effects: This invention eliminates the need for any stirring structure within the reactor body and uses a quartz container to hold the core, allowing the leaching agent to diffuse naturally within the core pores solely through its concentration gradient. This preserves the original pore structure of the sandstone and avoids interference from forced flow during leaching. Secondly, through the coordinated operation of the gas compensation component and the bottom first sampling valve, a pressure sensor monitors the pressure drop within the reactor in real time during sampling. The control unit drives the back pressure valve to replenish the reactor with isobaric gas, maintaining pressure fluctuations within ±0.10 MPa. This achieves dynamic sampling without depressurization or disruption of the gas-liquid-solid balance, resulting in leaching kinetic data that accurately reflects the in-situ leaching process. Finally, this invention uses uranium leaching rate and a comprehensive potential ecological risk index as dual objectives. Through normalized weighting and response surface methodology, it minimizes environmental risk while ensuring leaching efficiency. In summary, this invention represents a significant advancement in protecting the core structure, maintaining in-situ equilibrium, and ensuring ecological safety. It is suitable for high-fidelity simulation and optimization studies of in-situ leaching processes for sandstone uranium deposits. Attached Figure Description

[0016] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0017] in: Figure 1 This is a schematic diagram of the experimental apparatus in this invention; Figure 2 This is a schematic diagram of the main body of the reaction vessel in this invention; Figure 3 This is a three-dimensional surface diagram illustrating the combined effects of citric acid and oxalic acid on uranium leaching efficiency in this invention.

[0018] Label Explanation: 1. Reactor body; 11. Gas interface; 12. Leachate sampling port; 2. Heating steel sleeve; 21. Quartz container; 22. Vacuum insulation sleeve; 3. Mixing gas source; 31. CO2 cylinder; 32. O2 cylinder; 33. Mixing gas tank; 4. Pressurization device; 41. First gas source valve; 42. Three-way valve; 43. Second gas source valve; 5. Gas compensation component; 51. Back pressure valve; 52. One-way valve; 6. Sampling unit; 61. Condenser; 62. Sampling collector; 621. Constant temperature circulating water cooler; 622. Leachate collection bottle; 623. Drainage gas collection bottle; 624. Measuring cylinder; 63. First sampling valve; 64. Second sampling valve; 7. Control unit; 71. Temperature sensor; 72. Pressure sensor; 8. Cleaning unit; 81. Cleaning tank; 82. Exhaust valve. Detailed Implementation

[0019] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0020] Please see Figures 1 to 3 This is a simulated semi-enclosed column-leached sandstone uranium ore experimental apparatus, which is a preferred embodiment of the present invention, comprising: The reaction unit includes a reactor body 1, which is used to contain columnar sandstone uranium ore cores and provide a sealed reaction environment. This reactor body 1 is a high-temperature, high-pressure reactor body 1, capable of achieving a temperature of 650 ℃, a pressure of 40 MPa, and a volume of 200 ml. The inner diameter of the reactor body 1 is φ50 mm, and the net height of the reactor body 1 is 105 mm. The reactor body 1 is made of GH4169 nickel-based alloy material, and also features temperature and pressure testing interfaces on its upper part. The reactor body 1 is columnar with an internal cavity. The top of the reactor body 1 has a leaching agent injection port, and the bottom has a gas inlet 11 and a leaching solution sampling port 12.

[0021] The heating unit includes a heating steel sleeve 2, with a heating tube insertion hole at the top. The heating steel sleeve 2 is externally wrapped with a vacuum insulation sleeve 22, and the reactor body 1 is externally wrapped with an additional insulation layer. The sealing structure adopts a self-tightening thermal balance structure, which effectively solves the problem of leaks caused by screw expansion due to high temperature. The screws are made of high-strength, heat-resistant material and will not stick at high temperatures. Heating is done in a split manner. This design allows for stepped heating of the reactor body 1, preventing artificial cracks in the core due to uneven thermal stress, which could affect experimental results. The heating steel sleeve 2 is located inside a cavity and contains a quartz container 21 for holding the columnar sandstone uranium ore core. This quartz container 21 prevents direct contact between the core and the metal reactor wall and facilitates easy handling.

[0022] The pressurization and regulation unit includes a mixed gas source 3, a pressurization device 4, and a gas compensation component 5. The output end of the pressurization device 4 is connected to the gas interface 11, which is used to pressurize the mixed gas of CO2 and O2 to the experimental set value and then introduce it into the reactor body 1. The input end of the gas compensation component 5 is connected to the pressurization device 4, and its output end is connected to the top of the reactor body 1 through the back pressure valve 51. The back pressure valve 51 is used to maintain a constant pressure environment for the leaching experiment. The pressurization device 4 is used to pressurize the mixed gas of CO2 and O2 to the experimental set value, with a pressurization ratio of 100:1, a maximum outlet pressure of 400 Bar, and a maximum flow rate of 40 L / min.

[0023] The temperature and pressure detection unit includes a temperature sensor 71 and a pressure sensor 72 installed on the upper part of the reactor body 1. These sensors are used to monitor the temperature and pressure inside the reactor body 1 in real time. To meet the requirements of high-temperature and high-pressure leaching conditions, a high-temperature pressure sensor 72 is selected. This imported pressure sensor 72 transmits pressure to the downstream acquisition module through an internal capillary tube. The sensor body is designed with multiple heat dissipation devices to prevent damage to the acquisition module from high temperatures. The measurement range is 0-50 MPa, and the entire unit is made of 316L stainless steel. The pressure value can be directly displayed on a digital secondary instrument and communicates with the control unit 1 via an interface. Temperature measurement uses a high-temperature sensor, and the data is converted and displayed on the instrument via a data interface.

[0024] The sampling unit 6 includes a condenser 61, a sampling collector 62, and a first sampling valve 63. The leachate sampling port 12 is connected to the first sampling valve 63 and the condenser 61 in sequence. The sampling collector 62 is connected to the condenser 61 to realize sampling. The condenser 61 is a straight tube cooler used to pre-cool the high-temperature fluid flowing out of the reactor body 1 to realize real-time leachate sampling and protect the sealing system of the back pressure valve 51. The control unit 1 is electrically connected to the temperature sensor 71, the pressure sensor 72, the heating steel sleeve 2, the back pressure valve 51, and the gas compensation component 5. According to the signal fed back by the pressure sensor 72, when the fine-tuning sampling valve is opened for sampling, the control unit 1 opens the back pressure valve 51 and controls the gas compensation component 5 to replenish gas into the reactor body 1, so as to maintain the pressure fluctuation inside the reactor body 1 within the preset range during the sampling process.

[0025] Using a first gas fine-tuning valve, the gas flow control is highly precise, ensuring minimal pressure fluctuations during experimental sampling. While maintaining mass exchange (sampling) between the reaction system and the external environment, real-time pressure compensation in the top gas phase space ensures that the fluid inside the reactor body 1 is always under pressure constraints equivalent to the overlying formation pressure of the underground reservoir. This state guarantees continuous sampling requirements while preserving the physicochemical continuity of the deep geological environment to the greatest extent, achieving a high-fidelity simulation of in-situ leaching behavior of sandstone uranium ore. The input end of the pressurization device 4 is connected to the gas interface 11 of the high-pressure reactor body 1; the top gas interface 11 has a gas compensation component 5, which connects to the gas phase space at the top of the high-pressure reactor body 1; the control end of the gas compensation component 5 is connected to the control unit 1 to receive pressure compensation commands and precisely adjust the gas inlet rate. Through condensation cooling, fine-tuning valves, and pressure loss compensation, staged continuous sampling under non-pressure relief conditions is achieved.

[0026] The pipes and valves in this embodiment are all made of 316L stainless steel and can withstand pressures of over 100MPa.

[0027] Please see Figures 1 to 3 A first gas source valve 41, a three-way valve 42, and a second gas source valve 43 are sequentially provided between the pressurizing device 4 and the gas interface 11. The first gas source valve 41 controls the gas flow at the output of the pressurizing device 4, the second gas source valve 43 controls the gas flow into the gas interface 11 at the bottom of the reactor body 1, and the three-way valve 42 enables gas flow diversion and switching. The gas compensation assembly 5 includes a one-way valve 52, which is unidirectionally directed towards the interior of the reactor body 1. Its inlet is connected to one port of the three-way valve 42, and its outlet is connected to the back pressure valve 51. With the above-described gas path structure, the experimental operation can be carried out as follows: In the initial pressurization stage of the experiment, the first gas source valve 41 and the second gas source valve 43 are opened, and the back pressure valve 51 is closed. The high-pressure CO2 and O2 mixture output by the pressurization device 4 enters the reactor body 1 through the first gas source valve 41, the three-way valve 42, the second gas source valve 43, and the gas interface 11, so that the pressure inside the reactor quickly reaches the target value. During the pressure compensation process in the sampling stage, the second gas source valve 43 is closed, and the back pressure valve 51 is opened. The gas enters the top of the reactor body 1 through the first gas source valve 41, the three-way valve 42, the one-way valve 52, the back pressure valve 51, and the gas interface 11. The one-way valve 52 ensures that the compensation gas can only flow into the reactor in one direction, and the high-temperature, high-pressure mixture containing acidic solvent volatiles inside the reactor cannot flow back to the gas compensation component 5 or the pressurization device 4, thereby avoiding pipeline corrosion, back pressure valve 51 failure, and sampling contamination. Meanwhile, the combined use of the first gas source valve 41 and the second gas source valve 43 allows the pressurization pipeline and the pressure replenishment pipeline to be controlled independently or work together, ensuring both the efficiency of initial pressurization and accurate pressure compensation during sampling.

[0028] Please see Figures 1 to 3 The mixed gas source 3 includes a CO2 cylinder 3231, an O2 cylinder 32, and a mixed gas tank 33. The inlet of the mixed gas tank 33 is connected to both the CO2 cylinder 3231 and the O2 cylinder 32 via independent pipelines, while the outlet of the mixed gas tank 33 is connected to the pressurization device 4. The volume fraction of O2 in the mixed gas tank 33 is controlled within the range of 10% to 50%, and the specific ratio can be dynamically adjusted according to the content of reducing minerals (such as pyrite and organic matter) in the sandstone uranium ore and the target redox potential. When simulating a specific strong oxidative leaching environment, the partial pressure ratio of CO2 to O2 is set to 1:1.

[0029] Please see Figures 1 to 2 The sampling collector 62 consists of a constant-temperature circulating water cooler 621, a leachate collection bottle 622, a drainage gas collection bottle 623, and a measuring cylinder 624. The input end of the leachate collection bottle 622 is connected to the output end of the condenser 61 via a second sampling valve 64. The output end of the leachate collection bottle 622 is sequentially connected to the drainage gas collection bottle 623 and the measuring cylinder 624. The leachate collection bottle 622 is entirely housed inside the constant-temperature circulating water cooler 621. During the experiment, the leachate, after pre-cooling by the condenser 61, first enters the leachate collection bottle 622 through the second sampling valve 64. The constant-temperature circulating water cooler 621 continuously maintains a low temperature in the leachate collection bottle 622 to prevent further escape of volatile components from the leachate during collection, while also avoiding thermal shock to subsequent pipelines and the collection bottle caused by the high-temperature liquid. The gas generated in the leachate collection bottle 622, as well as the gas originally dissolved in the leachate, enters the water displacement gas collection bottle 623 through the output end of the leachate collection bottle 622. The overflow gas is collected by water displacement gas collection method, and the gas volume is read and recorded through the measuring cylinder 624. The liquid portion remains in the leachate collection bottle 622 for subsequent ICP analysis.

[0030] Please see Figures 1 to 2The system also includes a cleaning unit 8, used to clean the reactor body 1 and sampling pipelines after the experiment. The cleaning unit 8 includes a cleaning tank 81 and an vent valve 82, connected via pipelines to the solvent injection port, leachate sampling port 12, and gas interface 11 of the reactor body 1. After the experiment, the reactor body 1 is first cooled to room temperature and then slowly depressurized to atmospheric pressure before the core sample is removed. Then, the cleaning unit 8 is activated: the pressurization device 4 and gas compensation component 5 are shut off, and the vent valve 82 is opened, allowing the cleaning solution (such as deionized water or dilute acid solution) in the cleaning tank 81 to be pressurized by the cleaning pump and injected into the reactor body 1 through the solvent injection port. Simultaneously, cleaning solution can be alternately introduced from the gas interface 11 and the leachate sampling port 12 to circulate and flush the inner wall of the reactor, the core fixing support, and all pipelines and valves. The waste liquid after flushing is discharged through the leachate sampling port 12 and collected in a waste liquid tank. For the sampling pipeline, the cleaning solution can be made to flow fully through the condenser 61, the leachate collection bottle 622 and the drainage gas collection bottle 623 by repeatedly opening and closing the second sampling valve 64, so as to effectively remove secondary precipitates (such as iron hydroxide, calcium sulfate, organic acid complexes, etc.) attached to the inner wall of the pipeline.

[0031] Please see Figures 1 to 3 The present invention also provides a method for simulating a semi-enclosed column-leached sandstone uranium deposit, comprising the following steps: The sandstone uranium ore core, which retains its original pore structure, is processed into a columnar core sample and placed in a quartz container 21 inside the main body 1 of the high-pressure reactor. The leaching agent is then injected through the leaching agent injection port, and the reactor is sealed.

[0032] Evacuate the main body of the reactor to 0.1 MPa to remove residual air from the system. Then, introduce a mixture of CO2 and O2 to bring the pressure back to normal. Repeat the evacuation and purging process 2 to 3 times.

[0033] A mixture of CO2 and O2 is introduced into the reactor body 1 via the pressurization device 4 and gas interface 11, pressurizing it to the target pressure. The heating unit is then activated, and the reactor body 1 is heated to the target experimental temperature using a segmented heating method. This allows the leaching agent to undergo static diffusion leaching through the core pores without stirring or forced flow. The segmented heating involves increasing the temperature from room temperature to 250°C at a rate of 10°C / min. After reaching 250°C, the temperature continues to increase at a rate of 1°C / min to 5°C / min until the target final leaching temperature is reached, which does not exceed 650°C. The target pressure is 0.5 MPa to 40 MPa. In this high-temperature, high-pressure, and sealed environment, the differential thermal expansion of the various mineral components can easily generate enormous local thermal stress. If the temperature rises too quickly, this thermal stress can induce microcracks inside the core. This not only damages the original pore structure of the core, but also causes the leaching agent to "short-circuit the dominant channel" during subsequent leaching (i.e., the leaching agent is lost directly without uniform static diffusion), thus causing the experimental data to deviate significantly from the actual underground in-situ leaching behavior.

[0034] At the preset leaching time point, the condenser 61 and the first sampling valve 63 are turned on. At the same time, the control unit 1 controls the back pressure valve 51 to supplement gas into the reactor body 1 according to the pressure signal fed back by the pressure sensor 72, so that the pressure fluctuation inside the reactor body 1 is maintained within ±0.10MPa during the sampling process. The leachate after the condenser 61 is cooled is collected in stages. The staged collection is the collection of leachate at different time points (12h, 24h, 48h, 72h, 96h, 120h, 144h, 168h). Based on the collected data on multiple sets of leachate and pressure changes, the concentrations of uranium and associated elements in the collected leachate were analyzed, and the uranium leaching rate and comprehensive potential ecological risk index were calculated. The leaching scheme is optimized with the dual objectives of maximizing uranium leaching rate and minimizing potential ecological risks.

[0035] Based on the collected data on leachate and pressure changes, inductively coupled plasma atomic emission spectrometry (ICP) was used to analyze the release behavior of uranium and associated elements. In combination with temperature and pressure changes, the leaching kinetics and mechanism were studied, and a leaching rate function K = f (T,P,C) based on the coupling of temperature (T), pressure (P), and solvent concentration (C) was established.

[0036] Where, k c k is the apparent chemical reaction rate constant. dLet be the apparent diffusion rate constant, and x be the leaching rate. The comprehensive apparent rate constant K (K being a function of kc and kd) obtained by fitting under different temperature (T), pressure (P), and solvent concentration (C) conditions is used to establish a relationship between T, P, and C.

[0037] According to Arrhenius's law, the comprehensive apparent rate constant can be expressed as: Where A is the pre-exponential factor, Ea is the apparent activation energy, R is the ideal gas constant, 8.314 J / (mol·K), and n and m are the reaction orders for pressure and concentration, respectively.

[0038] By performing nonlinear multiple regression fitting on multiple sets of phased sampling data under different T, P, C conditions, the comprehensive apparent rate constant K under different conditions is obtained, and then the functional expression of K = f(T,P,C) is established.

[0039] To enhance the ecological risk assessment model for leaching data analysis, a single risk index is introduced. The potential ecological risk index (RI) is used to evaluate the environmental impact of uranium and associated elements (V, As, Ni, etc.). Following the principle of "toxicity response coefficient × pollution index" (as shown in Tables 1 and 2), the elemental concentrations of the original sandstone uranium deposit are used as background values. The calculation method is as follows:

[0040] Among them, CF i C i and C b,i These represent the pollution index of a certain metal, the concentration of a certain metal in the leachate, and the concentration of a certain metal in the leachate of the blank control group, respectively. TR i These represent the RI value of a metal and the toxicity response coefficient of the target metal, respectively; PERI is the total risk index. Among them, uranium leaching efficiency (U,%) reflects the leaching capacity of the leaching agent; the total risk index (PERI) reflects the environmental impact caused by the leaching and migration of PTEs.

[0041] To eliminate dimensions and facilitate comparisons between indicators, all variables are normalized to [0,1] using a minimum-maximum normalization process. Specifically, the PERI index is negatively standardized according to equation (7), so that the closer the values ​​of U* and PERI* are to 1, the better the performance.

[0042] A comprehensive evaluation index was calculated based on the above two indicators: Given that leaching efficiency is the primary objective, and further consideration is given to ensuring the sustainable and safe application of the leaching agent in static column leaching of sandstone uranium deposits, the weight is assigned as w. U = 0.7,w PERI = 0.3.

[0043] Table 1 Toxicity Response Coefficients Table 2 Assessment of the potential ecological risk index of harmful metals Using both the RI index and leaching rate data as evaluation indicators, and with the constraints of maximizing leaching efficiency and minimizing ecological risk, the optimal leaching scheme is predicted and optimized.

[0044] Using different leaching agent concentrations as independent variables and uranium leaching efficiency as the response variable, a nonlinear quadratic polynomial regression model was constructed using response surface methodology (RSM), and multivariate response surfaces were plotted. Specifically, RSM utilized central composite design (CCD) to design the response surface. Design-Expert13 was used to construct a uranium leaching CCD model with different leaching agents as independent variables (x) and leaching efficiency as the response variable (Y). The quadratic polynomial regression equation was fitted using the least squares method. Analysis of variance (ANOVA) was used to evaluate the contribution of each factor and its interaction terms to the leaching efficiency. Three-dimensional response surface plots and contour plots were plotted to visually demonstrate the interaction effects between different variables, thus identifying the optimal leaching system.

[0045] By solving for the extreme points of the response surface regression model, the optimal operational experimental parameters are obtained under the constraint that the comprehensive potential ecological risk index is below the safety threshold.

[0046] This embodiment utilizes Figure 1 The experiment shows a simulated semi-enclosed column leaching experimental device for sandstone uranium ore, and conducts an evaluation experiment on the leaching performance of sandstone uranium ore by small molecule organic acids (citric acid and oxalic acid).

[0047] Experimental parameter settings The sample was a sandstone-type uranium deposit core (25 mm in diameter and 25 mm in height) from a certain location in China. The leaching agents used were 0.1 mol / L citric acid solution and 0.1 mol / L oxalic acid solution. The gas environment was a CO2 to O2 partial pressure ratio of 1:1.

[0048] Experimental Procedure and Sampling Core samples were placed in a high-pressure reactor and injected with citric acid solution. The reactor was pressurized via gas inlet 11 using a pressurization system. The leaching cycle lasted 7 days, maintaining a static diffusion state without any stirring device to simulate the natural migration of groundwater. Sampling valves were opened at 12h, 24h, 48h, 72h, 96h, 120h, 144h, and 168h. Upon opening, the gas source panel synchronously compensated for pressure fluctuations, ensuring the pressure fluctuation within the reactor was less than ±0.1MPa. The sampled liquid was collected after being cooled to room temperature via condenser 61.

[0049] Ecological risk assessment ICP was used to determine the concentrations of U and associated elements V, As, and Ni in the leachate at each stage. A single-risk index and a potential ecological risk index (PERI) were introduced to evaluate the dynamic environmental impact of the leaching process. Experimental data and results are shown in Table 3.

[0050] Table 3 Comparison of Static Column Impregnation Experiment Results for Different Organic Acid Systems Experimental conclusions According to Table 3 and Figure 3 As shown, citric acid exhibited a higher uranium leaching rate (90.47%) at 168h, but the associated release of heavy metals resulted in a higher PERI index than the oxalic acid system. Experiments demonstrated that the device can perform online, staged sampling while maintaining stable system pressure, providing reliable data support for leaching kinetics research and leaching scheme optimization.

[0051] In summary, this invention does not incorporate any stirring structure within the reactor body 1 and uses a quartz container 21 to hold the core, allowing the leaching agent to diffuse naturally within the core pores solely through its concentration gradient. This preserves the original pore structure of the sandstone and avoids interference from forced flow in the leaching process. Secondly, through the coordinated operation of the gas compensation component 5 and the bottom first sampling valve 63, the pressure sensor 72 monitors the pressure drop within the reactor in real time during sampling. The control unit 1 drives the back pressure valve 51 to replenish the reactor with isobaric gas, maintaining pressure fluctuations within ±0.10 MPa. This achieves dynamic sampling without depressurization or disruption of the gas-liquid-solid balance, ensuring that the obtained leaching kinetic data accurately reflects the in-situ leaching process. Finally, this invention uses uranium leaching rate and a comprehensive potential ecological risk index as dual objectives. Through normalized weighting and response surface methodology, it minimizes environmental risk while ensuring leaching efficiency. In summary, this invention represents a significant advancement in protecting core structure, maintaining in-situ equilibrium, and ensuring ecological safety. It is suitable for high-fidelity simulation and optimization studies of in-situ leaching processes for sandstone uranium deposits.

[0052] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A simulated semi-enclosed column leaching experimental apparatus for sandstone uranium ore, comprising a reactor body and a heating unit for heating the reactor body, wherein the reactor body has a solvent injection port at the top and a gas inlet and a leaching solution sampling port at the bottom, characterized in that, Also includes: The pressurization and regulation unit includes a mixed gas source, a pressurization device, and a gas compensation component. The output end of the pressurization device is connected to a gas interface to pressurize the mixed gas of CO2 and O2 to the experimental set value before it is introduced into the main body of the reactor. The input end of the gas compensation component is connected to the pressurization device, and its output end is connected to the top of the main body of the reactor through a back pressure valve. A pressure sensor, installed on the upper part of the reactor body, is used to monitor the pressure inside the reactor body in real time; The sampling unit includes a first sampling valve connected to the leachate sampling port; The control unit is electrically connected to the pressure sensor, heating unit, back pressure valve, first sampling valve and gas compensation component. When the control unit receives the sampling signal that the first sampling valve is open, it controls the back pressure valve to open according to the pressure signal fed back by the pressure sensor, so that the gas compensation component can supplement gas into the reactor body to maintain the pressure fluctuation inside the reactor body within a preset range during the sampling process.

2. The experimental device for simulating a semi-closed state column leaching of sandstone-type uranium ore according to claim 1, characterized in that, The pressurization device and the gas interface are sequentially provided with a first gas source valve, a three-way valve and a second gas source valve. The gas compensation component includes a one-way valve with a unidirectional conduction direction toward the inside of the reactor body. The inlet end of the one-way valve is connected to the three-way valve and its outlet end is connected to the back pressure valve.

3. The experimental device for simulating a semi-closed state column leaching of sandstone-type uranium ore according to claim 1, characterized in that, The mixed gas source includes a CO2 cylinder, an O2 cylinder, and a mixed gas tank. The inlet of the mixed gas tank is connected to the CO2 cylinder and the O2 cylinder respectively, and its outlet is connected to a pressurization device. The volume fraction of O2 in the mixed gas tank is in the range of 10% to 50%.

4. The experimental device for simulating a semi-closed state column leaching of sandstone-type uranium ore according to claim 1, characterized in that, The heating unit includes a heating steel sleeve with a heating tube insertion hole at the top. The heating steel sleeve is located inside a cavity and contains a quartz container for holding columnar sandstone uranium ore cores. The heating steel sleeve is wrapped with a vacuum insulation sleeve. The reactor body is wrapped with an additional insulation layer. The top of the reactor body is also equipped with a temperature sensor for detecting temperature changes inside the reactor body.

5. The experimental device for simulating a semi-closed state column leaching of sandstone-type uranium ore according to claim 1, characterized in that, The sampling unit further includes a condenser, a sampling collector, a constant temperature circulating water cooler, a leachate collection bottle, a drainage gas collection bottle, and a measuring cylinder. The leachate sampling port is connected to the first sampling valve and the condenser in sequence. The sampling collector is connected to the condenser to perform sampling. The input end of the leachate collection bottle is connected to the condenser through the second sampling valve. The output end of the leachate collection bottle is connected to the drainage gas collection bottle and the measuring cylinder in sequence. The leachate collection bottle is located inside the constant temperature circulating water cooler.

6. An experimental method for simulating a semi-closed state column leaching sandstone uranium ore experimental device according to any one of claims 1 to 5, characterized in that, Includes the following steps: The sandstone uranium ore core, which retains its original pore structure, is processed into a columnar core sample, placed inside the main body of the reactor, and leaching agent is injected through the leaching agent injection port. The main body of the reactor is then sealed. A mixture of CO2 and O2 is introduced into the reactor body through a gas interface via a pressurization device to pressurize it to the target pressure; the heating unit is then activated, and the reactor body is heated to the target experimental temperature using a segmented heating method, so that the leaching agent undergoes static diffusion leaching through the core pores under conditions of no stirring and no forced flow. At the preset leaching time point, sampling is initiated. Simultaneously, the control unit controls the back pressure valve to replenish gas into the reactor body based on the pressure signal fed back by the pressure sensor, so that the pressure fluctuation inside the reactor body is maintained within ±0.10MPa during the sampling process. The leachate after cooling in the condenser is collected at different time points. Based on the collected data on multiple sets of leachate and pressure changes, the concentrations of uranium and associated elements in the collected leachate were analyzed, and the uranium leaching rate and comprehensive potential ecological risk index were calculated. With the dual objectives of maximizing uranium leaching rate and minimizing potential ecological risks, the leaching temperature and pressure were adjusted.

7. The method according to claim 6, wherein the method is an experimental method for simulating a semi-closed state column leaching of sandstone-type uranium ore, characterized in that, The segmented heating process involves increasing the temperature from room temperature to 250°C at a rate of 10°C / min; after reaching 250°C, the temperature continues to increase at a rate of 1°C / min to 5°C / min until the target leaching final temperature is reached, which does not exceed 650°C; the target pressure is 0.5MPa to 40MPa.

8. The method according to claim 6, wherein the method is an experimental method for simulating a semi-closed state column leaching of sandstone-type uranium ore, characterized in that, The calculation method for the comprehensive potential ecological risk index includes: First, the concentration of each associated metal element in the leachate was measured, and the background concentration of the element in the original sandstone uranium ore sample was obtained; the pollution index of the element was obtained by dividing the measured concentration of the leachate by its background concentration. Then, based on the toxicity level of the metal element, a corresponding toxicity response coefficient is assigned to it. The pollution index of the element is multiplied by the toxicity response coefficient to obtain the single potential ecological risk index of the element. Finally, the individual potential ecological risk indices of all detected associated metal elements are summed, and the resulting total value is the comprehensive potential ecological risk index.

9. The method according to claim 8, wherein the method is an experimental method for simulating a semi-closed state column leaching of sandstone-type uranium ore, characterized in that, The dual-objective optimization specifically includes: The uranium leaching rate and the comprehensive potential ecological risk index were normalized to their minimum and maximum values, respectively, with the comprehensive potential ecological risk index being negatively standardized. Calculate the overall evaluation score; Using different leaching agent concentrations as independent variables and uranium leaching efficiency as the response variable, a nonlinear quadratic polynomial regression model was constructed using response surface methodology, and a multivariate response surface was plotted. By solving for the extreme points of the response surface regression model, the optimal operational experimental parameters are obtained under the constraint that the comprehensive potential ecological risk index is below the safety threshold.

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