Method for in-situ leaching mining of sandstone uranium ore

Abstract

The invention discloses a method for in-situ leaching mining of sandstone uranium ore, the concentration of bicarbonate radical ions in ore bed water of the sandstone uranium ore is lower than 0.5 g / L, uranium in the sandstone uranium ore mainly exists in a uranium stone form, and the carbonate content is higher than 2%. The critical pH value of uranium stone corrosion is determined based on laboratory conditions, the required injection pressure of carbon dioxide is determined based on the critical pH value, the proper required injection pressure of oxygen is determined, and then the corresponding flows of carbon dioxide and oxygen during on-site leaching are determined according to the liquid injection flow of a liquid injection well. In this way, by controlling the pressure and flow of carbon dioxide and the pressure and flow of oxygen, the pH value of ore bed water is controlled, advantageous dissolution and leaching are achieved, the leaching time is shortened, the leaching efficiency is improved, and the uranium concentration of leachate is improved.

Description

Technical Field

[0001] This invention relates to the field of sandstone uranium mining technology, specifically to a method for in-situ leaching mining of sandstone uranium. Background Technology

[0002] Sandstone uranium deposits are my country's most important natural uranium resources. However, in recent years, sandstone uranium deposits with high carbonate content, where uranium mainly occurs as refractory uranium minerals (including yttrium uranium), and low bicarbonate ion concentration in the ore water have encountered difficulties in in-situ leaching using existing acid leaching methods (sulfuric acid + oxidant, with oxygen or hydrogen peroxide as the main oxidant) and neutral carbon dioxide + oxygen leaching processes. These processes result in long leaching times, low leaching rates, and low uranium concentrations in the leachate.

[0003] Therefore, how to shorten the leaching time, increase the leaching rate, and improve the uranium content of leached uranium in sandstone uranium ore has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for in-situ leaching mining of sandstone uranium deposits. The sandstone uranium deposit has a bicarbonate ion concentration in the ore bed water below 0.5 g / L, and uranium is primarily found in the form of uranium ore, with a carbonate content exceeding 2%. The method involves determining the critical pH value for uranium ore dissolution under laboratory conditions, determining the required carbon dioxide injection pressure and the appropriate oxygen injection pressure based on this critical pH value, and then determining the corresponding flow rates of carbon dioxide and oxygen during in-situ leaching based on the injection flow rate of the injection well. By controlling the pressure and flow rates of carbon dioxide and oxygen, the pH value of the ore bed water can be controlled, resulting in superior dissolution leaching, shortening the leaching time, improving leaching efficiency, and increasing the uranium concentration in the leachate.

[0005] This application provides a method for in-situ leaching mining of sandstone uranium ore, wherein the concentration of bicarbonate ions in the ore seam water is less than 0.5 g / L; the sandstone uranium ore includes yttrium-bearing uranium and has a carbonate content greater than 2%; the method includes:

[0006] The sandstone uranium ore was prepared into thin section samples;

[0007] Using the mineral water as a solvent, leaching agents with different pH values ​​adjusted by sulfuric acid were prepared, and the hydrogen peroxide concentration in the leaching agents was 2 g / L.

[0008] Using different leaching agents, stirring leaching experiments were conducted on the thin-slice samples to determine the pH value of the leaching agent when uranium minerals in the thin-slice samples were dissolved; based on the maximum pH value of the leaching agent when uranium minerals were dissolved, the critical pH range was determined.

[0009] Based on the aforementioned critical pH range, the required injection pressure and critical pH value for carbon dioxide are determined.

[0010] Based on the required carbon dioxide injection pressure, determine the required oxygen injection pressure;

[0011] Based on the critical pH value and the required oxygen injection pressure, the carbon dioxide injection flow rate and oxygen injection flow rate are determined according to the injection flow rate of the injection well; and based on the required carbon dioxide injection pressure, the lowering depth of the gas injection pipeline is determined.

[0012] At the leaching site, the gas injection pipeline is lowered into the injection well according to the specified lowering depth;

[0013] Carbon dioxide and oxygen are mixed according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and the mixed carbon dioxide and oxygen are injected into the injection well through the gas injection pipeline.

[0014] In some embodiments, the step of performing a stirring leaching experiment on the sheet sample using different leaching agents includes:

[0015] The thin-film samples were placed in different leaching agents and stirred for 8 hours. After removing the thin-film samples from the different leaching agents, washing and drying them, it was determined whether the uranium minerals in the thin-film samples were dissolved.

[0016] In some embodiments, the step of determining the required carbon dioxide injection pressure based on the critical pH range includes:

[0017] For multiple pH values ​​within the target pH range, the corresponding carbonic acid concentration is calculated using the carbonic acid ionization equilibrium constant.

[0018] Based on the carbonic acid concentration value, Henry's Law is used to determine the required injection pressure of the carbon dioxide to be selected.

[0019] One of the multiple required injection pressures for carbon dioxide is selected as the required injection pressure for carbon dioxide.

[0020] In some embodiments, before determining the required oxygen injection pressure based on the required carbon dioxide injection pressure, the calculated carbon dioxide injection pressure is experimentally verified; wherein the step of experimentally verifying the calculated carbon dioxide injection pressure includes: placing the sheet sample in a high-pressure reactor and then adding a 2 g / L hydrogen peroxide solution prepared with mineral water as a solvent.

[0021] Carbon dioxide is introduced into the hydrogen peroxide solution in the high-pressure reactor according to the required carbon dioxide injection pressure, and stirred for seven days; then it is determined whether the uranium minerals in the thin-film sample have dissolved.

[0022] If the uranium minerals in the thin-film sample are dissolved, then the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure is performed.

[0023] In some embodiments, the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure includes:

[0024] Oxygen at different preset injection pressures is mixed with carbon dioxide to obtain different mixed gases, wherein the partial pressure of carbon dioxide in the mixed gas is the required injection pressure of carbon dioxide;

[0025] The thin-film sample and the mineral layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor, and the thin-film sample is stirred and leached in the high-pressure reactor for seven days; the degree of uranium mineral dissolution is observed under a scanning electron microscope using the thin-film sample, and the preset pressure corresponding to the uranium mineral dissolution in the thin-film sample is used as the required oxygen injection pressure;

[0026] or,

[0027] A powder sample prepared from sandstone uranium ore and ore layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor to stir and leach the powder sample for seven days; the leaching rate is determined; and the preset pressure corresponding to the highest leaching rate is selected as the required oxygen injection pressure.

[0028] In some embodiments, the step of determining the carbon dioxide injection flow rate and oxygen injection flow rate based on the critical pH value and the required oxygen injection pressure, according to the injection flow rate of the injection well, includes:

[0029] The concentration of carbon dioxide in the mineral water is determined based on the critical pH value.

[0030] The carbon dioxide injection flow rate is determined based on the concentration of carbon dioxide in the mineral water and the injection flow rate of the injection well.

[0031] Based on the required oxygen injection pressure, the oxygen concentration in the mineral water is determined using Henry's Law.

[0032] The oxygen injection flow rate is determined based on the oxygen concentration in the mineral water and the injection flow rate of the injection well.

[0033] In some embodiments, the step of mixing carbon dioxide and oxygen according to carbon dioxide injection flow rate and oxygen injection flow rate, and then introducing the mixed carbon dioxide and oxygen into the injection well through an injection pipeline includes: using pressure reducing valves to reduce the pressure of carbon dioxide and oxygen to the corresponding carbon dioxide injection pressure and oxygen injection pressure.

[0034] Carbon dioxide and oxygen are mixed according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and the mixed carbon dioxide and oxygen are introduced into the injection well through the gas injection pipeline.

[0035] In some embodiments, the step of determining the lowering depth of the gas injection line based on the required carbon dioxide injection pressure includes:

[0036] Subtract the injection pressure from the required carbon dioxide injection pressure and then subtract the preset difference to obtain the water pressure corresponding to the lowering depth of the gas injection pipeline;

[0037] The lowering depth of the air injection pipeline is determined based on the water pressure.

[0038] This invention provides a method for in-situ leaching mining of sandstone uranium ore. The concentration of bicarbonate ions in the ore bed water of this sandstone uranium ore is less than 0.5 g / L, and uranium in the sandstone uranium ore mainly exists in the form of uranium ore with a carbonate content higher than 2%. Based on laboratory conditions, the critical pH value for uranium ore dissolution is determined. Based on the critical pH value, the required injection pressure for carbon dioxide and the appropriate injection pressure for oxygen are determined. Then, the corresponding flow rates of carbon dioxide and oxygen during in-situ leaching are determined according to the injection flow rate of the injection well. By controlling the pressure and flow rate of carbon dioxide and oxygen, the pH value of the ore bed water is controlled, resulting in superior dissolution leaching, shortening the leaching time, improving leaching efficiency, and increasing the uranium concentration in the leachate. Attached Figure Description

[0039] Figure 1 An exemplary flowchart illustrates a method for in-situ leaching mining of sandstone uranium ore according to some embodiments;

[0040] Figure 2 An exemplary schematic diagram of a sample stage provided according to some embodiments is shown;

[0041] Figure 3 Exemplary illustrations show before-and-after comparisons of etched sheet samples in three groups of acid leaching experiments at pH 3, 4, and 5, provided according to some embodiments;

[0042] Figure 4 An exemplary diagram is shown showing a before-and-after comparison of uranium mineral dissolution under conditions of 3 MPa carbon dioxide + 2 g / L hydrogen peroxide, according to some embodiments. Detailed Implementation

[0043] Sandstone uranium deposits are my country's most important natural uranium resources. However, in recent years, sandstone uranium deposits with high carbonate content, where uranium mainly occurs as refractory uranium minerals (including yttrium uranium), and low bicarbonate ion concentration in the ore water have encountered difficulties in in-situ leaching using existing acid leaching processes (sulfuric acid + oxidant, with oxygen or hydrogen peroxide as the main oxidant) and neutral carbon dioxide + oxygen leaching processes. These processes result in long leaching times, low leaching rates, and low uranium concentrations in the leachate.

[0044] After careful research, the inventors discovered that the aforementioned problems with acid leaching and neutral carbon dioxide + oxygen leaching processes stem primarily from a lack of understanding of the leaching reaction mechanism. For instance, the theories of acid leaching and neutral carbon dioxide + oxygen leaching posit that the oxidant is the most crucial factor controlling leaching. Many studies focus on enhancing the oxidizing performance of the oxidant, such as increasing the dissolved oxygen content in the ore bed water through nanobubbles. Other studies focus on complexes with high coordination stability constants, attempting to achieve efficient uranium mining by developing ligands that can form more stable complexes with uranyl, such as some multidentate ligands. Secondly, the key parameters controlling leaching in acid leaching and carbon dioxide + oxygen leaching studies lack a clear understanding. Especially under neutral carbon dioxide + oxygen leaching conditions, carbon dioxide is often considered primarily to provide a complexing agent. Finally, in the in-situ leaching mining of sandstone uranium deposits, the material composition and structure of the ore, as well as the composition of the ore bed water, also significantly influence the selection of the leaching process; existing acid leaching and neutral carbon dioxide + oxygen leaching processes do not consider this factor. Therefore, identifying the key parameters controlling leaching in such deposits and establishing relevant leaching processes is of great significance for their development. Existing neutral carbon dioxide + oxygen leaching methods suffer from mild reagent conditions, resulting in poor leaching effects on refractory deposits.

[0045] Therefore, how to shorten the leaching time, increase the leaching rate, and improve the uranium content of leached uranium in sandstone uranium ore has become a technical problem that urgently needs to be solved by those skilled in the art.

[0046] To address the aforementioned technical problems, this application provides a method for in-situ leaching mining of sandstone uranium deposits. The concentration of bicarbonate ions in the ore water of this sandstone uranium deposit is below 0.5 g / L, and uranium is primarily found in the form of uranium silicate with a carbonate content exceeding 2%. The method involves determining the critical pH value for uranium silicate dissolution under laboratory conditions, determining the required injection pressure for carbon dioxide and oxygen based on this critical pH value, and then determining the corresponding flow rates for carbon dioxide and oxygen during in-situ leaching based on the injection flow rate of the injection well. By controlling the pressure and flow rates of carbon dioxide and oxygen, the pH value of the ore water can be controlled, resulting in superior dissolution leaching, shortening the leaching time, improving leaching efficiency, and increasing the uranium concentration in the leachate.

[0047] This application provides a method for in-situ leaching mining of sandstone uranium ore. Figure 1 A flowchart of a method for in-situ leaching mining of sandstone uranium ore according to some embodiments is illustrated. The method includes steps S100-S800.

[0048] S100. Prepare the sandstone uranium ore into thin section samples.

[0049] In this embodiment, a leaching process is determined for sandstone uranium ore where the concentration of bicarbonate ions in the ore bed water is less than 0.5 g / L, and where the sandstone uranium ore includes yttrium-bearing uranium and has a carbonate content higher than 2%. Sandstone uranium ore mainly occurs as yttrium-bearing uranium, which is more difficult to leach than pitchblende or crystalline uranium ore.

[0050] In this embodiment of the application, preparing the sandstone uranium ore into a thin-slice sample may include: preparing the massive sandstone uranium ore into a thin-slice sample consisting only of a glass slide, and using epoxy resin to adhere the mineral layer to the glass slide.

[0051] To ensure the smooth progress of the experiment, it is first necessary to determine whether uranium minerals, i.e., whether yttrium-bearing uranium minerals, are present in the thin-section sample before the experiment begins. Specifically, scanning electron microscopy is used to observe the thin-section sample to locate the uranium minerals, observe their morphology, and determine their composition. Once it is confirmed that uranium minerals are present in the thin-section sample, step S200 is then performed.

[0052] S200. Using the mineral water as a solvent, leaching agents with different pH values ​​adjusted by sulfuric acid are prepared respectively, wherein the hydrogen peroxide concentration in the leaching agent is 2 g / L.

[0053] In one example, leaching agents with hydrogen peroxide concentrations of 2 g / L and pH values ​​of 1, 2, 3, 4, 5 and 6 were prepared using mineral water as a solvent. The pH value was adjusted using sulfuric acid.

[0054] S300. Using different leaching agents, a stirring leaching experiment is conducted on the thin-film sample to determine the pH value of the leaching agent when the uranium minerals in the thin-film sample are dissolved; based on the maximum pH value of the leaching agent when the uranium minerals are dissolved, the critical pH range is determined.

[0055] For example, when leaching agents with pH values ​​of 1, 2, and 3 can all dissolve the thin-film sample, while leaching agent with pH = 4 cannot dissolve the uranium mineral, the maximum pH value among the pH values ​​of the leaching agent at which the uranium mineral is dissolved is determined to be 3.

[0056] The step of determining the critical pH range based on the maximum pH value of the leaching agent during uranium mineral dissolution may include: determining a value that is 1 greater than the maximum pH value; and determining the critical pH range based on the value and the maximum pH value. The maximum value of the critical pH range is the value itself, and the minimum value is the maximum pH value. For example, if the maximum pH value is 3, the critical pH range is 3–4. In this embodiment, the critical pH range can be used as a reference for subsequent calculations of the amount of carbon dioxide added.

[0057] In some embodiments, the step of performing a stirring leaching experiment on the sheet sample using different leaching agents includes:

[0058] The thin-film samples were placed in different leaching agents and stirred for 8 hours. After removing the thin-film samples from the different leaching agents, washing and drying them, it was determined whether the uranium minerals in the thin-film samples were dissolved.

[0059] In some embodiments, the uranium mineral-containing side of the thin-slice sample is placed face up in the leaching agent. The leaching agent is stirred using a stirrer at a speed of 60-80 rpm to avoid agitation of the thin slice in the aqueous solution. The experiment is conducted for 8 hours. After the leaching experiment, the thin-slice sample is removed from the leaching agent, rinsed with distilled water, and dried. Scanning electron microscopy is then used to re-observe the uranium mineral regions observed before the leaching experiment, and to analyze whether the uranium minerals have been dissolved.

[0060] In other embodiments, the leaching agent is poured into the sample stage, and the sheet sample is placed in the slot of the sample stage with one side of the sheet sample facing the center of the sample stage and in contact with the leaching agent. Figure 2 A schematic diagram of a sample stage according to some embodiments is shown as an example. The sample stage is made of acrylic material. The sample stage includes a housing with five sides and a bottom surface; the five sides are sequentially connected to and connected to the bottom surface, and multiple slots are provided on the sides, with the projections of the multiple slots on the same side overlapping on the bottom surface. Figure 2 The yellow graphic represents a thin sample that has been placed into multiple slots on one side.

[0061] S400. Based on the critical pH range, determine the required carbon dioxide injection pressure.

[0062] In some embodiments, the step of determining the required carbon dioxide injection pressure based on the critical pH range includes:

[0063] For multiple pH values ​​within the target pH range, the corresponding carbonic acid concentration is calculated using the carbonic acid ionization equilibrium constant.

[0064] Based on the carbonic acid concentration value, Henry's Law is used to determine the required injection pressure of the carbon dioxide to be selected.

[0065] One of the multiple required injection pressures for carbon dioxide is selected as the required injection pressure for carbon dioxide.

[0066] In the experiment, the critical pH range was 3–4. The following example details the steps of calculating the corresponding carbonic acid concentration for multiple pH values ​​within the target pH range using the carbonic acid ionization equilibrium constant; determining the required injection pressure of the carbonic acid candidate using Henry's Law based on the carbonic acid concentration; and selecting one of the required injection pressures from among the multiple candidate carbonic acid injection pressures as the required injection pressure for the carbon dioxide.

[0067] Specifically, in this embodiment, multiple pH values ​​selected from the target pH range are 3.1, 3.2, 3.3, and 3.4. Based on the ionization equilibrium of carbonic acid in water, since the second ionization of carbonic acid is very weak compared to the first ionization, the H+ produced by its ionization... + The particles ionized in the first step are negligible compared to the first step.

[0068] H2CO3=H + +HCO3 - Ka1 = 4.3 × 10 -7 ;

[0069] If the concentration of hydrogen ions is equal to the concentration of bicarbonate ions, then the concentration of carbonic acid is:

[0070]

[0071] Calculate the hydrogen ion concentrations corresponding to pH values ​​of 3.1, 3.2, 3.3, and 3.4, and determine the carbonic acid concentration based on the hydrogen ion concentrations.

[0072] According to Henry's Law, the concentration of carbon dioxide in mineral water is... for:

[0073]

[0074] KH =0.33mol / L·MPa

[0075] in, The required injection pressure for carbon dioxide. Based on the carbonic acid concentration, the required carbon dioxide injection pressures for pH values ​​of 3.1, 3.2, 3.3, and 3.4 were calculated to be 4.4 MPa, 2.8 MPa, 1.8 MPa, and 1.1 MPa, respectively. In this embodiment, one required carbon dioxide injection pressure was selected from the first four pressure values, and the corresponding pH value was determined as the critical pH value. The selection principle was to ensure that the required carbon dioxide injection pressure would not be too high while keeping the pH value as low as possible; therefore, 2.8 MPa was chosen as the required carbon dioxide injection pressure. The required carbon dioxide injection pressures for pH values ​​of 3 and 4 were 7 MPa and 0.07 MPa, respectively. It can be seen that although the pH values ​​differ by 1, the carbon dioxide pressures differ by an order of magnitude.

[0076] In some embodiments, after determining the required injection pressure of the carbon dioxide to be selected based on the carbon dioxide concentration value using Henry's Law, a target required injection pressure of carbon dioxide is selected from a plurality of the selected required injection pressures. A range of required injection pressures for carbon dioxide is determined based on the target required injection pressure. For example, the target required injection pressure can be 2.8 MPa. The selection principle is the same as that in the previous embodiment, and the required injection pressure range can be 1.8 MPa to 3.8 MPa. A pressure is selected from the required injection pressure range as the required injection pressure for carbon dioxide.

[0077] In some embodiments, before the step of determining the required oxygen pressure based on the required carbon dioxide injection pressure, the method further includes: experimentally verifying the calculated carbon dioxide injection pressure; wherein the step of experimentally verifying the calculated carbon dioxide injection pressure includes: placing the thin-film sample in a high-pressure reactor, and then adding a 2 g / L hydrogen peroxide solution prepared with mineral water as a solvent; according to the required carbon dioxide injection pressure, bubbling carbon dioxide into the hydrogen peroxide solution in the high-pressure reactor and stirring for seven days; determining whether the uranium mineral in the thin-film sample has dissolved; if the uranium mineral in the thin-film sample has dissolved, then performing the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure.

[0078] In this embodiment, to verify whether the required carbon dioxide injection pressure meets the leaching requirements, a 2 g / L hydrogen peroxide solution with mineral water as the solvent can be used first. Using hydrogen peroxide solution as the leaching agent avoids the difficulty of adding oxygen. During the experiment, the thin-film sample is first placed in a high-pressure reactor, then 1000 ml of the prepared hydrogen peroxide solution is added. Carbon dioxide gas is then introduced into the hydrogen peroxide solution in the high-pressure reactor at the required carbon dioxide injection pressure, and the mixture is stirred. This experiment needs to be conducted for one week. If the uranium minerals in the thin-film sample dissolve, it is determined that the required carbon dioxide injection pressure meets the leaching requirements. Then, the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure is performed.

[0079] S500. Based on the required carbon dioxide injection pressure, determine the required oxygen injection pressure;

[0080] In some embodiments, the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure includes:

[0081] Oxygen at different preset injection pressures is mixed with carbon dioxide to obtain different mixed gases, wherein the partial pressure of carbon dioxide in the mixed gas is the required injection pressure of carbon dioxide.

[0082] For example, different preset injection pressures can be 1MPa, 1.5MPa, 2MPa, etc.

[0083] The thin-film sample and the mineral layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor, and the thin-film sample is stirred and leached in the high-pressure reactor for seven days; the degree of uranium mineral dissolution is observed under a scanning electron microscope using the thin-film sample, and the preset pressure corresponding to the uranium mineral dissolution in the thin-film sample is used as the required oxygen injection pressure;

[0084] or,

[0085] A powder sample prepared from sandstone uranium ore and ore layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor to stir and leach the powder sample for seven days; the leaching rate is determined; and the preset pressure corresponding to the highest leaching rate is selected as the required oxygen injection pressure.

[0086] Leaching rate = Leaching residue grade / Grade of powder sample before leaching; or, Leaching rate = Uranium concentration in leaching solution × Volume of leaching solution / Grade of powder sample before leaching × Mass of powder sample.

[0087] S600. Based on the critical pH value and the required oxygen injection pressure, determine the carbon dioxide injection flow rate and oxygen injection flow rate according to the injection flow rate of the injection well, and determine the lowering depth of the gas injection pipeline based on the required carbon dioxide injection pressure.

[0088] In some embodiments, the step of determining the carbon dioxide injection flow rate and the oxygen injection flow rate based on the critical pH value and the required oxygen injection pressure, according to the injection flow rate of the injection well, includes:

[0089] The concentration of carbon dioxide in the mineral water is determined based on the critical pH value.

[0090] The carbon dioxide injection flow rate is determined based on the concentration of carbon dioxide in the mineral water and the injection flow rate of the injection well.

[0091] Based on the required oxygen injection pressure, the oxygen concentration in the mineral water is determined using Henry's Law.

[0092] The oxygen injection flow rate is determined based on the oxygen concentration in the mineral water and the injection flow rate of the injection well.

[0093] The following example details the steps of determining the carbon dioxide concentration in the formation water based on the critical pH value; determining the carbon dioxide injection flow rate based on the carbon dioxide concentration in the formation water and the injection flow rate of the injection well; determining the oxygen concentration in the formation water based on Henry's Law according to the required oxygen injection pressure; and determining the oxygen injection flow rate based on the oxygen concentration in the formation water and the injection flow rate of the injection well.

[0094] Specifically, taking the injection flow rate of the injection well as 5m³ / h as an example... 3 / h, the critical pH is 3.2. According to the ionization equilibrium of carbonic acid in water, since the second ionization of carbonic acid is very weak compared to the first ionization, the H₂ produced by its ionization... + The particles ionized in the first step are negligible compared to the first step.

[0095] H2CO3=H + +HCO3 - Ka1 = 4.3 × 10 -7

[0096] If the concentration of hydrogen ions is equal to the concentration of bicarbonate ions, then the concentration of carbonic acid is:

[0097]

[0098] The hydrogen ion concentrations at pH 3.2 were 10 -3.2 mol / L. The calculated carbonic acid concentration at pH = 3.2 is 0.93 mol / L.

[0099] The injection flow rate of the injection well is 5m³. 3 / h, where the carbonic acid concentration equals the carbon dioxide concentration in the mineral water, and based on Henry's Law, to maintain the pH at 3.2, the carbon dioxide injection flow rate is:

[0100] in, The calculated carbon dioxide injection flow rate is 77.5 mol / min.

[0101] According to Henry's Law, the solubility of carbon dioxide in mineral water, i.e., the concentration of carbon dioxide in mineral water, is:

[0102]

[0103] K H =0.33mol / L·MPa

[0104] The partial pressure of carbon dioxide at pH = 3.2 was calculated. The values ​​are 0.93 ÷ 0.33, which is approximately 2.8 MPa.

[0105] Assuming the optimal oxygen concentration in the mineral water obtained from experiments is 1.5 MPa, corresponding to the highest leaching rate, according to Henry's Law (K... H =6.85×10 -6 mol / L·MPa):

[0106]

[0107] At an oxygen pressure of 1.5 MPa, the oxygen concentration in the mineral water is approximately 10. -5 Based on the oxygen concentration in the mineral water and the injection flow rate of the injection well, the oxygen injection flow rate is calculated to be approximately 0.17 × 10⁻⁶ mol / L. -3 mol / min.

[0108]

[0109] In some embodiments, the step of determining the lowering depth of the gas injection line based on the required carbon dioxide injection pressure includes:

[0110] Subtract the injection pressure from the required carbon dioxide injection pressure and then subtract the preset difference to obtain the water pressure corresponding to the lowering depth of the gas injection pipeline;

[0111] The lowering depth of the air injection pipeline is determined based on the water pressure.

[0112] In one example, the preset difference is 0.3 MPa.

[0113] Taking an injection pressure of 1 MPa as an example, the water pressure corresponding to the lowering depth of the air injection pipeline is 2.8 - 1 - 0.3 = 1.2 MPa.

[0114] According to the water pressure p = hgρ, where h is the water depth, g is the acceleration due to gravity, and ρ is the water density, a water pressure of 1.2 MPa is calculated to be approximately 120 m deep. The air injection pipeline is then lowered to a depth of 120 m.

[0115] In this embodiment, since the injection pressure required for carbon dioxide is relatively high, adding it to the surface system will cause air blockage on the one hand, and on the other hand, since the injection pressure required for carbon dioxide is much higher than the injection pressure, the leaching agent is difficult to inject. In order to enable carbon dioxide to be successfully injected into the mineral water, the insertion depth of the pipeline is determined by the water pressure at the end being 0.3 MPa lower than the liquid pressure.

[0116] S700. At the leaching site, the gas injection pipeline is lowered into the injection well according to the insertion depth.

[0117] S800. Mix carbon dioxide and oxygen according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and introduce the mixed carbon dioxide and oxygen into the injection well through the gas injection pipeline.

[0118] In some embodiments, the step of mixing carbon dioxide and oxygen according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and then introducing the mixed carbon dioxide and oxygen into the injection well through the gas injection pipeline includes:

[0119] The pressure reducing valves are used to reduce the pressure of carbon dioxide and oxygen to the corresponding carbon dioxide injection pressure and oxygen injection pressure, respectively.

[0120] Carbon dioxide and oxygen are mixed according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and the mixed carbon dioxide and oxygen are introduced into the injection well through the gas injection pipeline.

[0121] In this embodiment, a pressure reducing valve is used to reduce the pressure of carbon dioxide and oxygen to the corresponding carbon dioxide injection pressure and oxygen injection pressure, respectively. A gas flow meter is installed after the pressure reducing valve to control the injection flow rate of oxygen and carbon dioxide.

[0122] The methods described in this application are further illustrated below with examples of the Traobao uranium deposit.

[0123] The Teraobao uranium deposit has a high carbonate content (over 2% wt), with uranium mainly existing in the form of yttrium uranium-bearing ore. The concentration of bicarbonate in the ore water is approximately 0.23 g / L.

[0124] Currently, it has been confirmed that leaching using traditional neutral carbon dioxide + oxygen (0.2 MPa carbon dioxide for 4 hours, followed by 2 MPa oxygen until the end of the experiment) is ineffective, with a leaching rate of only 11.78% after ten days of leaching. For the same deposit, leaching with a 15 g / L H₂SO₄ + 2 g / L H₂O₂ solution for 24 hours resulted in a leaching rate of only 46.56%.

[0125] Using the method in the embodiments of this application, leaching under carbon dioxide + oxygen conditions was successfully achieved by determining the critical pH range of the suitable sulfuric acid solution for leaching.

[0126] First, three acid leaching experiments were designed with pH values ​​of 3, 4, and 5. Sulfuric acid was used to adjust the pH, and hydrogen peroxide was used as the oxidant at a concentration of 2 g / L. After preparing the leaching solution, the observed thin-section samples were placed in 500 ml of the solution, and the stirrer speed was set to 60 rpm for 8 hours. After leaching, the thin-section samples were removed, washed with distilled water, and air-dried. Finally, they were observed under a scanning electron microscope. Figure 3 As shown in the figure. The results show that uranium minerals can be effectively dissolved at pH=3, but no dissolution occurs at pH=4, thus determining the critical pH range to be 3–4.

[0127] Based on the first-order ionization equilibrium of carbon dioxide and Henry's Law, the corresponding carbon dioxide pressures at pH values ​​of 3.1, 3.2, 3.3, and 3.4 were calculated to be 4.4 MPa, 2.8 MPa, 1.8 MPa, and 1.1 MPa, respectively. In this experiment, 2.8 MPa carbon dioxide was chosen as the leaching condition to ensure the pH value was as low as possible while preventing excessively high carbon dioxide pressure. The specific experimental procedure is as follows: First, a 2 g / L hydrogen peroxide solution was prepared. Then, the thin film was placed in the hydrogen peroxide solution, and both were placed in a high-pressure reactor. The high-pressure reactor was closed, and 2.8 MPa carbon dioxide was introduced for leaching. The experiment lasted for 7 days. After the experiment, the thin film was removed, washed with distilled water, dried, and then observed under a scanning electron microscope. The results showed that uranium minerals were significantly dissolved under the conditions of 2.8 MPa carbon dioxide + 2 g / L hydrogen peroxide. Figure 4 The left image shows the leaching process before and after dissolution, and the right image shows the leaching process after dissolution, confirming the feasibility of carbon dioxide + oxygen leaching in the Tela Aobao deposit.

[0128] The core of the method in this application lies in the discovery, through a series of studies, that in the carbon dioxide + oxygen leaching process, carbon dioxide not only provides ligands, but more importantly, for such refractory deposits, the amount of carbon dioxide added can adjust the pH value of the ore bed water, thereby dissolving and leaching the refractory uranium minerals. This is significantly different from the traditional carbon dioxide + oxygen method with a pH around 7, where carbon dioxide mainly provides bicarbonate ligands and does not provide hydrogen ions to induce acidolysis. The method mainly includes how to conduct laboratory experiments to determine the pressure of carbon dioxide and oxygen, how to inject carbon dioxide and oxygen during actual mining, and how to determine the amount of carbon dioxide and oxygen added. This method of controlling the in-situ leaching of sandstone uranium ore by adjusting the pH of the ore-bearing aquifer with carbon dioxide can, on the one hand, avoid the problem of chemical precipitation (calcium sulfate) blockage during acid leaching of high carbonate content deposits; on the other hand, since the key parameter for controlling leaching has been identified as pH, effective leaching of refractory deposits can be achieved by injecting a large amount of carbon dioxide into the ore-bearing aquifer.

[0129] This application provides a method for in-situ leaching mining of sandstone uranium ore. The concentration of bicarbonate ions in the ore bed water of the sandstone uranium ore is less than 0.5 g / L, and uranium in the sandstone uranium ore mainly exists in the form of uranium ore with a carbonate content of more than 2%. Based on laboratory conditions, the critical pH value for uranium ore dissolution is determined. Based on the critical pH value, the required injection pressure for carbon dioxide and the appropriate injection pressure for oxygen are determined. Then, the corresponding flow rates of carbon dioxide and oxygen during in-situ leaching are determined according to the injection flow rate of the injection well. By controlling the pressure and flow rate of carbon dioxide and oxygen, the pH value of the ore bed water is controlled, resulting in superior dissolution leaching, shortening the leaching time, improving leaching efficiency, and increasing the uranium concentration in the leachate.

[0130] It will be readily understood by those skilled in the art that the above-described advantageous methods can be freely combined and superimposed without conflict. The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application. The above are merely preferred embodiments of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the protection scope of this application.

Claims

1. A method for in-situ leaching mining of sandstone uranium ore, characterized in that, The concentration of bicarbonate ions in the ore water of the sandstone uranium deposit is less than 0.5 g / L; the sandstone uranium deposit includes yttrium-bearing uranium and has a carbonate content greater than 2%; the method includes: The sandstone uranium ore was prepared into thin section samples; Using the mineral water as a solvent, leaching agents with different pH values ​​adjusted by sulfuric acid were prepared, and the hydrogen peroxide concentration in the leaching agents was 2 g / L. Using different leaching agents, stirring leaching experiments were conducted on the thin-slice samples to determine the pH value of the leaching agent when uranium minerals in the thin-slice samples were dissolved; based on the maximum pH value of the leaching agent when uranium minerals were dissolved, the critical pH range was determined. Based on the aforementioned critical pH range, the required injection pressure and critical pH value for carbon dioxide are determined. Based on the required carbon dioxide injection pressure, determine the required oxygen injection pressure; Based on the critical pH value and the required oxygen injection pressure, the carbon dioxide injection flow rate and oxygen injection flow rate are determined according to the injection flow rate of the injection well; and based on the required carbon dioxide injection pressure, the lowering depth of the gas injection pipeline is determined. At the leaching site, the gas injection pipeline is lowered into the injection well according to the specified lowering depth; Carbon dioxide and oxygen are mixed according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and the mixed carbon dioxide and oxygen are injected into the injection well through the gas injection pipeline.

2. The method according to claim 1, characterized in that, The steps of conducting the stirring leaching experiment on the thin film sample using different leaching agents include: The thin-film samples were placed in different leaching agents and stirred for 8 hours. After removing the thin-film samples from the different leaching agents, washing and drying them, it was determined whether the uranium minerals in the thin-film samples were dissolved.

3. The method according to claim 1, characterized in that, The step of determining the required carbon dioxide injection pressure based on the critical pH range includes: For multiple pH values ​​within the target pH range, the corresponding carbonic acid concentration is calculated using the carbonic acid ionization equilibrium constant. Based on the carbonic acid concentration value, Henry's Law is used to determine the required injection pressure of the carbon dioxide to be selected. One of the multiple required injection pressures for carbon dioxide is selected as the required injection pressure for carbon dioxide.

4. The method according to claim 1, characterized in that, Before the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure, the calculated carbon dioxide injection pressure is experimentally verified. The step of experimentally verifying the calculated carbon dioxide injection pressure includes: placing the sheet sample in a high-pressure reactor and then adding a 2 g / L hydrogen peroxide solution prepared with mineral water as a solvent; Carbon dioxide is introduced into the hydrogen peroxide solution in the high-pressure reactor according to the required carbon dioxide injection pressure, and stirred for seven days; then it is determined whether the uranium minerals in the thin-film sample have dissolved. If the uranium minerals in the thin-film sample are dissolved, then the step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure is performed.

5. The method according to claim 1, characterized in that, The step of determining the required oxygen injection pressure based on the required carbon dioxide injection pressure includes: Oxygen at different preset injection pressures is mixed with carbon dioxide to obtain different mixed gases, wherein the partial pressure of carbon dioxide in the mixed gas is the required injection pressure of carbon dioxide; The thin-film sample and the mineral layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor, and the thin-film sample is stirred and leached in the high-pressure reactor for seven days; the degree of uranium mineral dissolution is observed under a scanning electron microscope using the thin-film sample, and the preset pressure corresponding to the uranium mineral dissolution in the thin-film sample is used as the required oxygen injection pressure; or, A powder sample prepared from sandstone uranium ore and ore layer water are placed in a high-pressure reactor; the mixed gas is introduced into the high-pressure reactor to stir and leach the powder sample for seven days; the leaching rate is determined; and the preset pressure corresponding to the highest leaching rate is selected as the required oxygen injection pressure.

6. The method according to claim 1, characterized in that, The step of determining the carbon dioxide injection flow rate and oxygen injection flow rate based on the critical pH value and the required oxygen injection pressure, according to the injection flow rate of the injection well, includes: The concentration of carbon dioxide in the mineral water is determined based on the critical pH value. The carbon dioxide injection flow rate is determined based on the concentration of carbon dioxide in the mineral water and the injection flow rate of the injection well. Based on the required oxygen injection pressure, the oxygen concentration in the mineral water is determined using Henry's Law. The oxygen injection flow rate is determined based on the oxygen concentration in the mineral water and the injection flow rate of the injection well.

7. The method according to claim 1, characterized in that, The step of mixing carbon dioxide and oxygen according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and then introducing the mixed carbon dioxide and oxygen into the injection well through the gas injection pipeline includes: using pressure reducing valves to reduce the pressure of carbon dioxide and oxygen to the corresponding carbon dioxide injection pressure and oxygen injection pressure. Carbon dioxide and oxygen are mixed according to the carbon dioxide injection flow rate and the oxygen injection flow rate, and the mixed carbon dioxide and oxygen are introduced into the injection well through the gas injection pipeline.

8. The method according to claim 1, characterized in that, The step of determining the lowering depth of the gas injection pipeline based on the required carbon dioxide injection pressure includes: Subtract the injection pressure from the required carbon dioxide injection pressure and then subtract the preset difference to obtain the water pressure corresponding to the lowering depth of the gas injection pipeline; The lowering depth of the air injection pipeline is determined based on the water pressure.

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