Method for intensifying in-situ leaching uranium mining through external electric field

Abstract

The invention provides a method for intensifying in-situ leaching uranium mining through an external electric field. The method comprises the steps that a liquid extraction well and a liquid injection well are arranged on a uranium deposit; an inert cathode is mounted at the liquid injection well; an inert anode is mounted at the liquid pumping well; a CO2 + O2 neutral leaching system or an acid leaching system is adopted as the leaching liquid, the leaching liquid is injected into the liquid injection well to conduct in-situ leaching on the uranium ore layer, and the obtained leaching liquid is extracted from the liquid extraction well; the in-situ in-situ immersion is carried out under the assistance of an external electric field; the external electric field is a direct-current pulse voltage applied between the inert cathode and the inert anode. The in-situ leaching uranium mining is enhanced by adding the pulsed electric field, the production efficiency is high, good leaching of uranium ore is effectively achieved, the cost is low, the influence on the environment is small, implementation is easy, and the industrial application value is high.

Description

Technical Field

[0001] The invention belongs to the field of in-situ leaching of uranium, and in particular relates to a method for intensifying in-situ leaching of uranium through an external electric field. Background Art

[0002] Since the 19th century, humans have begun to mine uranium for the production of ceramics and dyeing. Later, with the discovery of X-rays by Roentgen and the proposal of the mass-energy equation by Einstein, nuclear energy officially appeared in human history, and uranium gradually became an important strategic material.

[0003] Relevant data show that my country's uranium resources are divided into four categories: sandstone, granite, volcanic rock and carbonaceous siltstone. Among them, sandstone uranium ore accounts for 45.51% of the total proven uranium resources (2020), ranking first among the four categories. At the same time, my country's uranium deposits are generally small in scale, low in grade and complex in composition. Among them, uranium resources with an average grade of less than 0.1% account for more than 50% of the total resource reserves, and those with a grade of less than 0.3% account for more than 96% of the total resource reserves. These low-grade uranium deposits are mostly considered to be dead mines in other uranium-producing countries, that is, minerals that are not worth mining.

[0004] Low-grade uranium ore often leads to problems such as slow leaching speed, incomplete leaching, and high mining costs. Therefore, my country has long faced technical difficulties in uranium mining and extraction. For example, CN108411130A uses iron as an anode and graphite as a cathode, passes direct current to oxidize the anode iron to trivalent iron, and uses the strong oxidizing property of trivalent iron to oxidize uranium to hexavalent. This method is simple in process, but requires the use of an electrolytic cell to process uranium ore, and the single processing volume is small and inefficient. Another example is CN106930747A, which focuses on optimizing the well network reorganization method for in-situ leaching uranium, and reduces the dead corner of leaching by adjusting the injection and extraction system of the borehole, thereby improving the efficiency of secondary recovery of uranium resources, but it fails to solve the problem of difficult leaching of low-grade uranium ore. For the field of in-situ leaching uranium, the existing process is often difficult to solve the problems of low efficiency and difficult leaching at the same time, which seriously restricts my country's ability to ensure the safe supply of uranium resources. Therefore, it is urgent to develop a method for strengthening in-situ leaching uranium that takes into account efficiency and leaching rate. Summary of the invention

[0005] It is difficult for existing processes to simultaneously solve the problems of low production efficiency and difficulty in leaching uranium ore. The present application provides a method for intensifying in-situ leaching of uranium by applying an external electric field. The method can significantly increase the production efficiency of in-situ leaching of uranium, and increase the uranium concentration of the output leaching solution, thereby solving the problem of difficulty in leaching uranium ore.

[0006] To achieve the above objectives, this application proposes the following technical solutions: A method for enhancing in-situ leaching of uranium by applying an external electric field is provided, comprising: Arranging a liquid extraction well and a liquid injection well on the uranium ore bed; installing an inert cathode at the liquid injection well; installing an inert anode at the liquid extraction well; The leaching solution adopts a CO2+O2 neutral leaching system or an acidic leaching system, and the leaching solution is injected into the injection well to carry out in-situ leaching of the uranium ore layer, and the obtained leaching solution is extracted from the extraction well; the in-situ leaching is carried out with the assistance of an external electric field; the external electric field is a DC pulse voltage applied between an inert cathode and an inert anode.

[0007] Furthermore, the maximum voltage of the DC pulse voltage ranges from 100 to 300 V, the minimum voltage ranges from 0 to 100 V, and the pulse period is 12 h to 5 d.

[0008] Furthermore, the inert anode is one of a graphite electrode, a metal ceramic electrode, and a metal electrode.

[0009] Furthermore, the inert cathode is one of a glassy carbon electrode, a graphite electrode, and a metal electrode.

[0010] Furthermore, the inert cathode and the inert anode are both subjected to insulation treatment; the insulation treatment is to coat an insulation layer on the surface of the inert cathode and the inert anode.

[0011] Furthermore, the leaching solution contains an anionic oxidant; the concentration range of the anionic oxidant in the leaching solution is 0.5~1.5 g / L.

[0012] Furthermore, the anionic oxidant is at least one of sodium chlorate, sodium hypochlorite and sodium percarbonate.

[0013] Furthermore, the well types of the extraction wells and injection wells for in-situ leaching of uranium are at least one of a linear arrangement, a grid arrangement, and a radial arrangement.

[0014] Furthermore, the well types of the extraction wells and injection wells for in-situ uranium leaching are selected and arranged according to the physical and chemical properties of the mining body.

[0015] Furthermore, during the in-situ leaching of the uranium ore layer, the liquid extraction and injection system is adjusted according to the progress of in-situ leaching of uranium.

[0016] Furthermore, the adjustment of the extraction and injection system according to the progress of in situ uranium leaching includes: within the range of 100-200 days, the uranyl ion concentration in the leachate is tested once every 2 days, and the uranyl ion concentration and time are plotted as axes to analyze the trend of the uranyl ion concentration and determine the peak value; within the range of 200-400 days, the uranyl ion concentration in the leachate is tested once every 5 days; if the uranyl ion concentration obtained by the test is lower than 30% of the historical peak value, the in situ leaching operation is deemed to have entered the final stage, and at least part of the injection wells surrounded by the extraction wells are shut down, and the injection rate of at least part of the injection wells surrounding the extraction wells is simultaneously reduced by 30%-60%.

[0017] Furthermore, the injection rate of the injection well during the in-situ leaching of uranium is 0-5 m / s. 3 / h, the pumping rate of the pumping well is 5~25m 3 / h.

[0018] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: (1) The method for in-situ leaching of uranium by applying an external electric field provided by the present invention has high production efficiency and can effectively achieve good leaching of uranium ore. It has low cost, little impact on the environment and is easy to implement, and has high industrial application value.

[0019] (2) By inserting electrodes in the pumping and injection wells and insulating them, a pulsed electric field is created in the ore layer, which promotes the reactant ions to reach the reaction point as soon as possible to start the reaction, and promotes the directional migration of the reaction product uranyl anion toward the pumping well. It can also increase the concentration of the leaching agent on the mineral surface, reduce the thickness of the product layer, and help increase the leaching reaction rate, ultimately effectively reducing the production cycle and increasing the concentration of the leachate. Based on the directional electric field pointing from the pumping well to the injection well, the electromigration effect is used to suppress the large accumulation of elements such as Ca, Mg, Al, and Fe in the pores of the ore body near the pumping well, and the occurrence of chemical blockage is effectively reduced by reducing the hydrolysis of the precipitated elements, thereby improving the leaching rate and shortening the leaching cycle.

[0020] (3) By periodically changing the voltage of the cathode and anode, the electric field intensity in the ore layer fluctuates in a pulsed manner. High and low field intensities promote the mass transfer process and leaching reaction respectively, and simultaneously improve the utilization rate of the leaching solution and the uranium concentration in the leaching solution. The electrocapillary mechanism brought about by the high field strength stage can promote the seepage of the solution into the micropores, while the low field strength stage can reduce this seepage, which is conducive to the release of the leaching solution in the micropores; this cycle can maximize the mineral leaching rate, ultimately significantly improve the leaching rate, shorten the leaching cycle and reduce the subsequent concentration cost.

[0021] (4) By adding anionic oxidants to the leaching solution, the effect of external electric field to enhance migration and the effect of external oxidants to enhance leaching are effectively combined, which is beneficial to avoid the phenomenon of high concentration accumulation of anionic oxidants, reduce the occurrence of oxidant side reactions, give full play to the strengthening effect of anionic oxidants, significantly improve the utilization rate of raw materials, increase the concentration of leaching solution and shorten the production cycle.

[0022] (5) By changing the extraction and injection system in a timely manner, it is possible to avoid excessive leaching solution flowing into the part of the ore body that has almost reacted completely, avoid waste of resources, and reduce the dilution of the leaching solution, thereby increasing the uranium concentration in the leaching solution and effectively reducing the cost of subsequent purification treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 Schematic diagram of the "thirteen injections and three extractions" in-situ leaching of uranium established for the present invention.

[0025] Figure 2 The uranium concentration of the leaching solution of Example 1 and Comparative Example 1 changes with time.

[0026] Figure 3 The uranium concentration of the leaching solution of Example 1 and Example 2 changes with time.

[0027] Figure 4 The curves of uranium concentration in the leaching solution of Example 1 and Comparative Example 2 changing with time are shown.

[0028] Figure 5 The curves of uranium concentration in the leaching solution of Example 3 and Example 1 changing with time are shown. DETAILED DESCRIPTION

[0029] The present invention provides a method for intensifying in-situ leaching of uranium by applying an external electric field, comprising: Investigate the physical and chemical properties of the uranium ore to be mined, select a reasonable well type, and arrange pumping wells and injection wells at appropriate locations on the uranium ore bed according to the selected well type; An inert cathode is inserted in the injection well, and an inert anode is inserted in the extraction well. During the in-situ leaching of uranium, a DC pulse voltage is applied between the inert cathode and the inert anode. The leaching liquid adopts an acid leaching system or a CO2+O2 neutral leaching system. The leaching liquid is injected into the ore body from the injection well to fill the pore structure in the ore body and fully react with the mineral. The leaching liquid is subjected to the positive pressure of the injection well and the negative pressure of the extraction well to flow in a directional manner and is extracted from the extraction well.

[0030] During the in-situ leaching of uranium, a DC pulse voltage is applied between the cathode and anode electrodes. During the low voltage stage, due to the weak electric field in the ore body, the migration rate of the leaching reactant components in the leaching solution is low, which is conducive to increasing the concentration of reactants in the pores, thereby promoting the leaching reaction rate. During the high voltage stage, the electric field in the ore body is at a high level, which can effectively promote the migration of the reaction product uranyl anion and improve the production efficiency of in-situ leaching of uranium; at the same time, it can also avoid the accumulation of reaction products on the surface of the mineral. According to Le Chatelier's principle, reducing the concentration of reaction products can promote the forward reaction and prepare for the next leaching cycle; further, the electrocapillary mechanism brought about by the high voltage stage can promote the behavior of solution seepage into micropores, while the low voltage stage can reduce this seepage, which is conducive to the release of leachate in micropores. This cycle is repeated to maximize the mineral leaching rate. In the neutral or acidic leaching pH range, the uranium element in the leachate mainly exists in the form of negative divalent uranyl complex ions, with a small amount of negative tetravalent uranyl complex ions and zero-valent uranyl molecules, and basically no positive divalent uranyl ions. Therefore, inserting a cathode at the injection well and an anode at the pumping well can create a negative electric field from the injection well to the pumping well, promote the migration of negatively valent uranyl polymer ions to the pumping well, and improve production efficiency.

[0031] In some preferred embodiments, the inert anode is connected to a DC pulse voltage; the maximum voltage range of the DC pulse voltage is 100~300V, for example, 100V, 120V, 150V, 180V, 200V, 220V, 250V, 280V, 300V, etc., the minimum voltage range is 0~100V, for example, 0V, 20V, 40V, 60V, 80V, 100V, etc., and the pulse period is 12h~5d, for example, 12h, 18h, 24h, 1.5d, 2d, 2.5d, 3d, 3.5d, 4d, 4.5d, 5d, etc.

[0032] The physical and chemical properties of different ore bodies are suitable for different well types. For example, ore bodies with higher porosity and permeability are suitable for linear or sparse grid well types; on the contrary, ore bodies with lower porosity and permeability are suitable for radial or dense grid well types. The selection needs to be made according to the actual situation. The ultimate goal is to minimize the dead corners of leaching, simplify construction and operation costs, and improve leaching efficiency. In some preferred embodiments, the well type is at least one of a linear arrangement, a grid arrangement, and a radial arrangement.

[0033] In some preferred embodiments, the leaching solution contains an anionic oxidant; the concentration range of the anionic oxidant in the leaching solution is 0.5~1.5g / L, for example, 0.5g / L, 0.6g / L, 0.7g / L, 0.8g / L, 0.9g / L, 1.0g / L, 1.1g / L, 1.2g / L, 1.3g / L, 1.4g / L, 1.5g / L, etc.

[0034] In some preferred embodiments, the anionic oxidant added to the leaching solution is at least one of sodium chlorate (NaClO3), sodium hypochlorite (NaClO), and sodium percarbonate (2Na2CO3·3H2O2). When an appropriate amount of anionic oxidant is added to the injected leaching solution, the oxidant is also affected by the electric field to accelerate the migration rate, so that it reaches the mineral surface faster and undergoes oxidation reaction on the tetravalent uranium element, thereby improving the efficiency of in-situ leaching of uranium and avoiding the long-term accumulation of the oxidant and the occurrence of a large number of side reactions.

[0035] In some preferred embodiments, the inert anode is one of a graphite electrode, a metal ceramic electrode, a metal electrode (such as a platinum electrode, a titanium-based coating anode, an iridium-tantalum alloy anode, an iron-nickel-copper alloy anode, etc.).

[0036] In some preferred embodiments, the inert cathode is one of a glassy carbon electrode, a graphite electrode, and a metal electrode (such as a platinum electrode, a titanium-based coating anode, an iridium-tantalum alloy anode, an iron-nickel-copper alloy anode, etc.).

[0037] In some preferred embodiments, the inert cathode and the inert anode are both insulated, that is, they are only used to generate a directional electrostatic field; the insulation treatment is to coat the surface of the inert cathode and the inert anode with an insulating layer, such as epoxy resin. The insulation treatment can reduce energy consumption and cost on the one hand, and can also prevent the cathode from producing alkali at the injection well and causing chemical blockage in the ore body on the other hand.

[0038] In some preferred embodiments, the injection rate of the injection well during the in situ leaching of uranium is 0-5 m / s. 3 / h, the pumping rate of the pumping well is 5~25m 3 / h. During in-situ leaching of uranium, ensure that the number of injection wells*injection rate ≤ the number of extraction wells*extraction rate.

[0039] During the process of in-situ leaching of uranium, the reaction degree of different positions in the ore body at the same time is different. Generally, the distance between the mineral and the injection well is inversely proportional to the reaction degree of the mineral, that is, the farther the mineral is from the injection well, the lower the reaction progress. The reason is that the uneven concentration of the leaching solution in the ore layer leads to different leaching rates of minerals at different positions, which leads to the phenomenon that some ore bodies have reacted completely at a certain moment but continue to be injected with leaching solution. Therefore, during the in-situ leaching process, the leaching solution should be regularly sampled to obtain its uranyl ion concentration data, and the extraction and injection system should be changed at a certain time point under the premise of ensuring the full reaction of the mineral, so as to optimize the utilization rate of the leaching solution and increase the concentration of the leaching solution.

[0040] In some preferred embodiments, when uranium is in situ leached, the method further includes changing the uranium in situ leaching liquid injection system in a timely manner according to the progress of the uranium in situ leaching operation to optimize the efficiency of the uranium in situ leaching operation. In some preferred embodiments, the extraction and injection system is adjusted with the progress of in situ leaching of uranium. Specifically, within the range of 100-200 days, the uranyl ion concentration in the leachate is detected once every 2 days, and the uranyl ion concentration and time are plotted as axes to analyze the uranyl ion concentration trend and determine the peak value; within the range of 200-400 days, the uranyl ion concentration in the leachate is detected once every 5 days; if the uranyl ion concentration at this moment is lower than 30% of the historical peak value, it is considered that the in situ leaching operation has entered the final stage, and at least part of the injection wells surrounded by the extraction wells are routinely shut down according to experience and working conditions, and the injection rate of at least part of the injection wells surrounding the extraction wells is synchronously reduced by 30%-60%, for example, by 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, etc.

[0041] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Example 1 The method for in-situ leaching of uranium in an applied electric field provided by the present invention comprises the following steps: (1) Drilling extraction wells and injection wells on the ore body according to the "13 injection and 3 extraction" well pattern, such as Figure 1 As shown, the depth of the pumping well and injection well is 250~300m, and the well radius is 0.5m; (2) A CO2+O2 neutral leaching system is used to inject the leaching solution into the ore body from the injection well. The leaching solution fills the pore structure in the ore body and fully reacts with the minerals. The leaching solution is subjected to the positive pressure of the injection well and the negative pressure of the extraction well, and flows in a directional manner. The leaching solution is extracted from the extraction well. The injection rate is 2m 3 / h, the pumping rate is 10m 3 / h; (3) Insert a graphite cathode with an epoxy resin insulation layer on the surface into the injection well, and insert a graphite anode with an epoxy resin insulation layer on the surface into the extraction well, and apply a DC pulse voltage between the cathode and the anode with a pulse period of 2 days. The peak potential of the anode is 250V, the trough potential is 50V, and the cathode potential is 0V.

[0043] The average uranium concentration in the extracted leaching solution was detected and recorded every 20 days, and a graph was drawn with time (d) as the horizontal axis and uranium concentration (mg / L) as the vertical axis. The results are shown in the figure below: Figure 2 shown.

[0044] Comparative Example 1 The difference between this comparative example and Example 1 is that step (3) is omitted, and the other conditions remain unchanged.

[0045] Comparative Example 1 Comparison of uranium concentration in leaching solution at different times Figure 2 .

[0046] from Figure 2 It can be seen that under the same conditions, the maximum uranium concentration of the leaching solution obtained in Example 1 of the external electric field enhanced in-situ leaching is increased by 12.45% compared with that in Comparative Example 1 of the direct in-situ leaching.

[0047] Example 2 The difference between the process steps of this embodiment and that of embodiment 1 is that in step (2), 1.4 g / L sodium hypochlorite (10% NaClO) is additionally added to the CO2+O2 neutral leaching system to assist oxidative leaching.

[0048] The comparison of uranium concentration in the leaching solution at different times between Example 1 and Example 2 is shown in FIG. Figure 3 The results show that under the same conditions, the maximum uranium concentration of the leaching solution obtained in Example 2 with the addition of an oxidant to assist the leaching is 4.51% higher than that in Example 1 without the addition of an oxidant to assist the leaching, and the time interval of the maximum uranium concentration is significantly widened.

[0049] Comparative Example 2 The only difference between this comparative example and Example 1 is that the external electric field is a DC constant voltage, wherein the anode potential is 250V and the cathode potential is 0V.

[0050] Comparison of uranium concentration in the leaching solution at different times between Example 1 and Comparative Example 2 Figure 4 The results show that under the same conditions, the maximum uranium concentration of the leaching solution obtained by the comparative example 2 of direct current electric field enhanced in-situ leaching is 16.3% lower than that of the example 1 of pulse electric field enhanced in-situ leaching.

[0051] Example 3 according to Figure 2 As shown in the results of Example 1, the uranium concentration of the leaching solution of Example 1 has a significant downward trend at around 300 days. Figure 1 The well structure shown can be guessed that around 300 days Figure 1 The uranium ore in the central area has reacted completely, and there is no need to continue injecting liquid into the central injection well.

[0052] Therefore, Example 3 continues the process steps of Example 1, with the only difference being that: at 300 days, the injection of the central injection well is stopped, the injection rate of the other injection wells is reduced by 50%, and the extraction rate of the extraction well is changed to 5m / s. 3 / h.

[0053] The comparison of uranium concentration in the leaching solution at different times between Example 3 and Example 1 is shown in Figure 2. Figure 5The results show that under the same conditions, timely changes in the pumping and injection system can prevent excessive leaching solution from flowing into the ore body that has almost completely reacted, thereby increasing the uranium concentration in the solution extracted from the pumping well. After the system change, the uranium concentration of the leaching solution increased by an average of about 31%.

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for intensifying in-situ leaching of uranium by applying an electric field, characterized in that: include: Arranging a liquid extraction well and a liquid injection well on the uranium ore bed; installing an inert cathode at the liquid injection well; An inert anode is installed at the liquid extraction well; The leaching solution adopts a CO2+O2 neutral leaching system or an acidic leaching system, and the leaching solution is injected into the injection well to carry out in-situ leaching of the uranium ore layer, and the obtained leaching solution is extracted from the extraction well; the in-situ leaching is carried out with the assistance of an external electric field; the external electric field is a DC pulse voltage applied between an inert cathode and an inert anode.

2. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The maximum voltage of the DC pulse voltage ranges from 100 to 300 V, the minimum voltage ranges from 0 to 100 V, and the pulse period is 12 hours to 5 days.

3. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The inert anode is one of a graphite electrode, a metal ceramic electrode and a metal electrode.

4. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The inert cathode is one of a glassy carbon electrode, a graphite electrode and a metal electrode.

5. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The inert cathode and the inert anode are both subjected to insulation treatment; the insulation treatment is to coat an insulation layer on the surface of the inert cathode and the inert anode.

6. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The leaching solution contains an anionic oxidant; the concentration range of the anionic oxidant in the leaching solution is 0.5-1.5 g / L.

7. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 6, characterized in that: The anionic oxidant is at least one of sodium chlorate, sodium hypochlorite and sodium percarbonate.

8. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: The well type of the extraction well and injection well for in-situ leaching of uranium is at least one of a linear arrangement, a grid arrangement, and a radial arrangement; The well types of the pumping wells and injection wells are selected and arranged according to the physical and chemical properties of the mining body.

9. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1, characterized in that: During the in-situ leaching of the uranium ore layer, the pumping and injection system is adjusted according to the progress of uranium in-situ leaching; The adjustment of the extraction and injection system according to the progress of in-situ uranium leaching includes: within the range of 100-200 days, the uranyl ion concentration in the leachate is tested once every 2 days, and the uranyl ion concentration trend is analyzed and the peak value is determined by plotting the uranyl ion concentration and time as the axes; within the range of 200-400 days, the uranyl ion concentration in the leachate is tested once every 5 days; if the uranyl ion concentration obtained by the test is lower than 30% of the historical peak value, it is regarded that the in-situ leaching operation has entered the final stage, and at least part of the injection wells surrounded by the extraction wells are shut down, and at the same time, the injection rate of at least part of the injection wells surrounding the extraction wells is synchronously reduced by 30%-60%.

10. The method for in-situ leaching of uranium by applying an electric field as claimed in claim 1 or 8, characterized in that: The injection rate of the injection well in the in-situ leaching process is 0~5m 3 / h, the pumping rate of the pumping well is 5~25m 3 / h.

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