A leaching method and leaching apparatus for preventing the reduction of uranium permeability in in-situ leaching.

Abstract

This invention provides a leaching method and apparatus for preventing the reduction of permeability in in-situ uranium leaching, relating to the field of in-situ uranium leaching technology. Based on the conventional CO2+O2 in-situ uranium leaching process, this invention adds a CO2-to-bicarbonate generator system before the CO2-rich adsorption tailings enter the ore layer. The treated adsorption tailings then enter the underground ore layer. The CO2-to-bicarbonate generator provides the bicarbonate required for uranium leaching, avoiding the direct addition of carbonates that could alter the ore layer's chemical environment, or the introduction of easily precipitated ions such as calcium and magnesium into the ore layer's water system through ore carbonate conversion, which could cause secondary chemical precipitation and block seepage channels. This invention stabilizes the ore layer's permeability, thereby ensuring the injection and extraction cycle of uranium in in-situ leaching.

Description

Technical Field

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

[0002] CO2+O2 in-situ leaching uranium mining has become one of the important methods for low-cost and environmentally friendly natural uranium mining. Showalter first proposed carbon dioxide as a leaching agent (William E. Showalter, Seal Beach Calif. Process for recovery of mineral values ​​from underground formations: US05 / 767788 [P]. 1978-8-8.), which mainly involves CO2+O2 underground mining technology for a series of precious metals such as uranium, nickel, copper, molybdenum, rhenium, and vanadium, thus opening the era of neutral underground leaching of CO2+O2. Regarding the application of leaching agents CO2 and O2, ZL200910125409.5 proposes using different oxygen concentrations to prepare the leaching solution based on different stages of underground leaching progress. The dissolved oxygen concentration of the leaching solution should be controlled at 300–400 mg / L, with a residual oxygen concentration of 7–10 mg / L within this range. CO2 should be added to the uranium-bearing leaching solution at a concentration of 100–300 mg / L to maintain a stable pH value in the underground mineralized aquifer. The CO2+O2 in-situ leaching process can create an environment similar to the reverse mineralization process of sandstone-type uranium deposits to the greatest extent possible in mineralized aquifers. It exhibits strong leaching selectivity, low reagent consumption, low production costs, and minimal impact on the groundwater environment, and is highly adaptable to uranium deposits with high carbonate content, high mineralization, low permeability, and low grade.

[0003] However, the CO2+O2 in-situ leaching process for uranium mining also affects the permeability of the ore layer. Jiao Xueran et al., through mechanism analysis, found that during the leaching process, CO2 reacts with carbonates to generate bicarbonate ions, while also producing calcium, magnesium, and iron ions. When the concentration reaches a certain level, these ions can easily precipitate and block the ore layer (Jiao Xueran et al. Study on the blocking mechanism of in-situ leaching mining of a high-mineralization sandstone-type uranium deposit [J]. Nonferrous Metals (Smelting Section), 2013(8):25-28). Ji Hongbin et al., through PHREEQCI software, calculated the composition of the leaching solution of the CO2+O2 process in the Mengqiguer uranium deposit and determined that the main blockage material was calcite, which would block the pores and reduce the permeability of the deposit (Ji Hongbin et al. Analysis and discussion on the CO2+O2 in-situ leaching process in the Mengqiguer uranium deposit [J]. Nonferrous Metals (Smelting Section), 2018(3):55-59). Wang Liang et al. demonstrated through experiments that when CO2 is introduced into pure water, the pH value of the solution decreases significantly, but the HCO3- content in the solution remains high. -The concentration of bicarbonate did not change significantly, indicating that CO2 cannot be directly converted into bicarbonate ions. However, the introduction of CO2 into a supersaturated CaCO3 solution showed that CO2 can effectively dissolve calcium carbonate and release bicarbonate ions (Wang Liang et al. Research on CO2+O2 leaching technology of high bicarbonate-carbonate sandstone uranium ore [J]. Uranium Mining and Metallurgy, 2016(4)). The sandstone system contains a certain amount of carbonate, which enables the application of the CO2+O2 process. The dissolution of non-uranium easily precipitable ions leads to the precipitation of crystals when the solubility reaches saturation. The accumulation of precipitated crystals to a certain extent will inevitably block the seepage channels and reduce the permeability of the ore layer. Since the optimal leaching conditions for uranium have certain requirements for bicarbonate, especially for ore deposits with low bicarbonate content in the ore-bearing and aquifer layers, directly adding bicarbonate will increase the pH of the solution and make the blockage more serious. Alternatively, the conversion of carbonates in the ore deposit will also affect the permeability. In order to address the above problems, a suitable method is needed to reduce the formation of ore layer precipitates and maximize the permeability of the seepage channels. Summary of the Invention

[0004] The purpose of this invention is to provide a leaching method and apparatus for preventing the reduction of uranium permeability during in-situ leaching. This invention can be applied to sandstone uranium deposits with low bicarbonate concentrations in mineralized aquifers, effectively inhibiting the occurrence of chemical blockage, meeting the bicarbonate requirements for uranium leaching, minimizing the decrease in ore layer permeability, and reducing pollution to the groundwater environment of the mining area.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a leaching method for preventing the reduction of permeability in uranium mining, comprising the following steps:

[0007] (1) Perform a pumping and injection cycle, and pass the pumped liquid into a CO2 conversion bicarbonate generator to obtain a solution with high bicarbonate content; the bicarbonate concentration of the solution with high bicarbonate content is ≥1.2g / L.

[0008] (2) The solution with high bicarbonate content is injected into the underground mineral layer. After the concentration of bicarbonate in the mineral layer water rises to more than 1.2 g / L, the pumped liquid is stopped from flowing into the CO2 conversion bicarbonate generator and oxygen is injected into the mineral layer water.

[0009] (3) When the uranium concentration in the leachate is negatively correlated with the sulfate concentration, reduce or stop the injection of oxygen, inject carbon dioxide gas, and continue leaching; when the uranium concentration in the leachate is positively correlated with the sulfate concentration, continue the operation by injecting oxygen.

[0010] (4) When the concentration of bicarbonate in the leachate is less than 800 mg / L, the leachate is passed into the CO2 conversion bicarbonate generator again, and the resulting high bicarbonate content solution is injected into the underground mineral layer, repeating steps (2) to (4).

[0011] Preferably, the CO2 to bicarbonate generator comprises a carbon dioxide gas mixer and a carbonate packed tower connected in sequence.

[0012] Preferably, the carbonate packed tower comprises carbonate packing; the carbonate packing comprises one or more of sodium carbonate, calcium carbonate, and magnesium carbonate.

[0013] Preferably, the CO2 to bicarbonate generator further includes a cation exchange resin adsorption tower; the inlet of the cation exchange resin adsorption tower is connected to the outlet of the carbonate packed tower.

[0014] Preferably, in step (1), no leaching agent is added during the injection cycle and the cycle is performed empty. After the injection volume stabilizes, the extracted liquid is introduced into the CO2 to bicarbonate generator.

[0015] Preferably, the concentration of oxygen injected in step (2) is 200-500 mg / L.

[0016] Preferably, the concentration of carbon dioxide gas in the leachate of step (3) is 100-300 mg / L.

[0017] Preferably, step (4) further includes: passing the obtained leachate into an anion exchange tower to extract uranium.

[0018] The present invention provides a leaching device for the leaching method described in the above technical solution, comprising an underground well site and an above-ground CO2 to bicarbonate generator; the pumping port of the well site is connected to the inlet of the CO2 to bicarbonate generator.

[0019] Preferably, it also includes an anion exchange tower located on the ground; the inlet of the anion exchange tower is connected to the leachate outlet of the well site.

[0020] This invention provides a leaching method to prevent the reduction of permeability in uranium leaching. Based on the conventional CO2+O2 uranium leaching process, this invention adds a CO2-to-bicarbonate generator system before the CO2-rich adsorption tailings enter the ore layer. The treated adsorption tailings then enter the underground ore layer. The CO2-to-bicarbonate generator provides the bicarbonate required for uranium leaching, avoiding the direct addition of carbonates that could alter the ore layer's chemical environment, or the introduction of easily precipitated ions such as calcium and magnesium into the ore water system through ore carbonate conversion, which could cause secondary chemical precipitation and block seepage channels. This invention stabilizes the ore layer's permeability, thereby ensuring the uranium injection and extraction cycle in uranium leaching. Attached Figure Description

[0021] Figure 1 A schematic diagram of a leaching device used to prevent reduced permeability in uranium mining. Detailed Implementation

[0022] This invention provides a leaching method for preventing the reduction of permeability in uranium mining, comprising the following steps:

[0023] (1) Perform a pumping and injection cycle, and pass the pumped liquid into a CO2 conversion bicarbonate generator to obtain a solution with high bicarbonate content; the bicarbonate concentration of the solution with high bicarbonate content is ≥1.2g / L.

[0024] (2) The solution with high bicarbonate content is injected into the underground mineral layer. After the concentration of bicarbonate in the mineral layer water rises to more than 1.2 g / L, the pumped liquid is stopped from flowing into the CO2 conversion bicarbonate generator and oxygen is injected into the mineral layer water.

[0025] (3) When the uranium concentration in the leachate is negatively correlated with the sulfate concentration, reduce or stop the injection of oxygen, inject carbon dioxide gas, and continue leaching; when the uranium concentration in the leachate is positively correlated with the sulfate concentration, continue the operation by injecting oxygen.

[0026] (4) When the concentration of bicarbonate in the leachate is less than 800 mg / L, the leachate is passed into the CO2 conversion bicarbonate generator again, and the resulting high bicarbonate content solution is injected into the underground mineral layer, repeating steps (2) to (4).

[0027] This invention employs a pumping-injection cycle, passing the extracted liquid into a CO2-to-bicarbonate generator to obtain a solution with a high bicarbonate content. Preferably, this invention performs an empty circulation without adding a leaching agent during the pumping-injection cycle. Once the pumping liquid volume stabilizes, the extracted liquid is then passed into the CO2-to-bicarbonate generator. This invention utilizes an empty circulation system to clear the ore layer.

[0028] In this invention, the CO2 to bicarbonate generator preferably includes a carbon dioxide gas mixer and a carbonate packed tower connected in sequence.

[0029] In this invention, the carbonate packed tower preferably comprises carbonate packing; the carbonate packing preferably comprises one or more of sodium carbonate, calcium carbonate and magnesium carbonate.

[0030] In this invention, the CO2 to bicarbonate generator preferably further includes a cation exchange resin adsorption tower; the inlet of the cation exchange resin adsorption tower is connected to the outlet of the carbonate packed tower. In this invention, when the carbonate packing includes calcium carbonate or magnesium carbonate, it is preferable to connect the outlet of the carbonate packed tower to the inlet of the cation exchange resin adsorption tower. When the calcium ion concentration in the resulting high bicarbonate content solution is less than 30 mg / L, it is injected into the underground mineral layer. In this invention, the cation exchange resin used in the cation exchange resin adsorption tower is preferably a weakly acidic cation exchange resin, specifically preferably D152 weakly acidic cation exchange resin, D113 weakly acidic cation exchange resin, 111 weakly acidic cation exchange resin, or 112 weakly acidic cation exchange resin.

[0031] In this invention, the bicarbonate concentration of the high bicarbonate content solution is ≥1.2 g / L, preferably 1.2 g / L. In this invention, when the bicarbonate concentration in the solution discharged from the CO2 to bicarbonate generator is lower than 1.2 g / L, the discharged solution is returned to the CO2 to bicarbonate generator.

[0032] After obtaining a solution with a high bicarbonate content, this invention injects the solution into the underground mineral layer. Once the concentration of bicarbonate in the mineral layer water rises to above 1.2 g / L, the pumped-out solution is stopped from flowing into the CO2-to-bicarbonate generator, and oxygen is injected into the mineral layer water. In this invention, the concentration of the injected oxygen is preferably 200–500 mg / L. Preferably, this invention uses oxygen dissolved in water at maximum pressure for saturation oxygen injection.

[0033] In this invention, when the uranium concentration in the leachate is negatively correlated with the sulfate concentration, oxygen injection is reduced or stopped, and carbon dioxide gas is injected to continue leaching; when the uranium concentration in the leachate is positively correlated with the sulfate concentration, oxygen injection continues. In this invention, the concentration of carbon dioxide gas in the leachate is preferably 100–300 mg / L. In this invention, the sulfate ions are derived from the oxidation of pyrite or sulfide minerals.

[0034] In this invention, when the concentration of bicarbonate in the leachate is less than 800 mg / L, the extract is passed into the CO2 conversion bicarbonate generator again, and the resulting solution with high bicarbonate content is injected into the underground mineral layer, repeating steps (2) to (4).

[0035] In this invention, step (4) preferably further includes: passing the obtained leachate into an anion exchange tower to extract uranium.

[0036] This invention provides a leaching apparatus for the leaching method described in the above-mentioned technical solution, comprising an underground well site and an above-ground CO2-to-bicarbonate generator; the pumping port of the well site is connected to the inlet of the CO2-to-bicarbonate generator. In this invention, the well site is the location where the leaching agent reacts chemically with the minerals in the ore layer.

[0037] As an embodiment of the present invention, the leaching device further includes an anion exchange tower located on the ground; the inlet of the anion exchange tower is connected to the leaching liquid outlet of the well site.

[0038] Figure 1 A schematic diagram of a leaching device used to prevent reduced permeability in uranium mining. Figure 1 In the diagram, the solid line represents the pretreatment stage for increasing the bicarbonate concentration in the mineralized aquifer, namely steps (1) and (2). The well site pumped fluid is converted from CO2 into a solution with high bicarbonate content via a carbonate packed tower and a cation exchange resin adsorption tower, and then reinjected into the well site. Figure 1 In the diagram, the dashed path represents the leaching stage, namely steps (2) and (3). When the uranium concentration reaches 1 mg / L or higher, the leaching solution is introduced into an anion exchange tower to adsorb uranium. The adsorption tail liquid is returned to the well site. When the leached uranium concentration begins to decrease or is negatively correlated, the oxygen concentration is reduced and a low concentration of CO2 is added to continue leaching.

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1

[0041] The experimental setup employed a CO2+O2 pressurized column leaching system. A constant flow pump and back pressure valve controlled the leaching agent's migration velocity within the core column to 0.2 m / d. Daily measurements were taken of the leachate volume, pH, and Eh (redox potential), and analysis of U and HCO3- content was performed. - Ca 2+ Mg 2 + Composition of mineral water: ρ(HCO3) - )=242mg / L, ρ(Ca 2+ ) = 6.2 mg / L, ρ(Mg 2+ <1 mg / L, ρ(Cl) -)=360mg / L, ρ(SO4) 2- The concentration of the mineral sample was 45 mg / L, pH = 8.6, and the main components were: U = 0.13 wt%, total iron = 5.82 wt%, Ca = 2.57 wt%, Mg = 0.83 wt%, and Al = 7.65 wt%.

[0042] (1) First, perform two separate pore volumes of distilled water without reagent circulation and uranium leaching from the mineral layer water. Stop adding water when the uranium concentration is less than 10 mg / L.

[0043] (2) CO2 and sodium carbonate were added to the ore bed water to prepare ore bed water with a bicarbonate concentration of 1.2 g / L. The ore bed water was then pumped to the ore pillar using a constant flow pump. Once the bicarbonate concentration of the effluent reached 1.2 g / L, 400 mg / L CO2 was introduced to continue operation. The results showed that the seepage velocity began to decrease when the liquid-to-solid ratio was 10.7. When the liquid-to-solid ratio was 16.3, the seepage velocity decreased by 11.2%, and the decrease in seepage velocity was not significant in the later stages.

[0044] Comparative Example

[0045] The same test apparatus as in Example 1 was used.

[0046] Uranium leaching was first performed using distilled water without reagents in two pore volumes, followed by uranium leaching in ore seam water. Uranium leaching began when the uranium concentration was less than 10 mg / L. 600 mg / L CO2 was introduced into the ore seam water and transported to the ore pillar. After multiple cycles, the bicarbonate concentration in the leaching solution reached 1.2 g / L, at which point CO2 injection was stopped, and 400 mg / L O2 was introduced to continue the process. The results showed that the seepage velocity began to decrease at a liquid-to-solid ratio of 7.6, decreased by 34% at a liquid-to-solid ratio of 9.3, and decreased by 86% at a liquid-to-solid ratio of 12.1.

[0047] The results of the examples and comparative examples show that the present invention can suppress the decrease in the permeability of the ore layer and maintain the permeability of the seepage channel to the maximum extent.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A leaching method for preventing the reduction of uranium permeability during in-situ leaching, comprising the following steps: (1) A pumping and injection cycle is performed, and the extracted liquid is passed into a CO2-to-bicarbonate generator to obtain a solution with a high bicarbonate content; the bicarbonate concentration of the solution with a high bicarbonate content is ≥1.2 g / L; the CO2-to-bicarbonate generator includes a carbon dioxide gas mixer and a carbonate packed tower connected in sequence, and the CO2-to-bicarbonate generator also includes a cation exchange resin adsorption tower; the inlet of the cation exchange resin adsorption tower and the outlet of the carbonate packed tower are connected. (2) The solution with high bicarbonate content is injected into the underground mineral layer. After the concentration of bicarbonate in the mineral layer water rises to more than 1.2 g / L, the pumped liquid is stopped from flowing into the CO2 conversion bicarbonate generator and oxygen is injected into the mineral layer water. (3) When the uranium concentration in the leachate is negatively correlated with the sulfate concentration, reduce or stop the injection of oxygen, inject carbon dioxide gas, and continue leaching; when the uranium concentration in the leachate is positively correlated with the sulfate concentration, continue the operation by injecting oxygen. (4) When the concentration of bicarbonate in the leachate is less than 800 mg / L, the leachate is passed into the CO2 conversion bicarbonate generator again, and the resulting high bicarbonate content solution is injected into the underground mineral layer, repeating steps (2) to (4).

2. The leaching method according to claim 1, characterized in that, The carbonate packed tower includes carbonate packing; The carbonate filler includes one or more of sodium carbonate, calcium carbonate, and magnesium carbonate.

3. The leaching method according to claim 1, characterized in that, In step (1), no leaching agent is added during the injection cycle and the cycle is empty. After the injection volume stabilizes, the extracted liquid is introduced into the CO2 to bicarbonate generator.

4. The leaching method according to claim 1, characterized in that, The concentration of oxygen injected in step (2) is 200-500 mg / L.

5. The leaching method according to claim 1, characterized in that, The concentration of carbon dioxide gas in the leachate of step (3) is 100-300 mg / L.

6. The leaching method according to claim 1, characterized in that, The step (4) is followed by: passing the obtained leachate into an anion exchange tower to extract uranium.

7. The leaching apparatus used in the leaching method according to any one of claims 1 to 6 includes an underground well site and an above-ground CO2 to bicarbonate generator; the pumping port of the well site is connected to the inlet of the CO2 to bicarbonate generator.

8. The leaching apparatus according to claim 7, characterized in that, It also includes an anion exchange tower located on the ground; the inlet of the anion exchange tower is connected to the leachate outlet of the well site.

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