Method for enhancing in-situ leaching of uranium by applying an electric field

Abstract

The application provides a method for enhancing in-situ leaching of uranium by an applied electric field, comprising the following steps: arranging a liquid pumping well and a liquid injection well on a uranium deposit; installing an inert cathode at the liquid injection well; installing an inert anode at the liquid pumping well; using a CO2+O2 neutral leaching system or an acid leaching system as a leaching liquid; injecting the leaching liquid into the liquid injection well to perform in-situ leaching on the uranium ore layer; and pumping the obtained leaching liquid from the liquid pumping well; wherein the in-situ leaching is performed under the assistance of an applied electric field; and the applied electric field is a direct current pulse voltage applied between the inert cathode and the inert anode. The method for enhancing in-situ leaching of uranium by an applied pulse electric field not only has high production efficiency, effectively realizes good leaching of the uranium ore, but also has low cost, small environmental impact and easy implementation, and has high industrial application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of in-situ leaching mining of uranium deposits, and particularly relates to a method for enhancing in-situ leaching of uranium by applying an electric field. BACKGROUND

[0002] Low-grade uranium deposits often result in slow leaching, incomplete leaching, high mining costs and other problems. For example, CN108411130A uses iron as an anode and graphite as a cathode, and applies direct current to oxidize the anode iron to trivalent iron, which is used to oxidize uranium to hexavalent iron by virtue of the strong oxidizing property of trivalent iron. This method is simple, but it needs to use an electrolytic cell to process uranium ore, and the single processing capacity is small and the efficiency is low. CN106930747A focuses on optimizing the well network reorganization method for in-situ leaching of uranium, and adjusts the liquid injection and extraction system of the drill hole to reduce the leaching dead angle, thereby improving the efficiency of secondary recovery of uranium resources. However, it fails to solve the problem of difficult leaching of low-grade uranium deposits. For the field of in-situ leaching of uranium, existing processes often cannot simultaneously solve the problems of low production efficiency and difficult leaching of uranium deposits, and therefore there is an urgent need to develop a method for enhancing in-situ leaching of uranium that takes into account both efficiency and leaching rate. SUMMARY

[0003] Existing processes cannot simultaneously solve the problems of low production efficiency and difficult leaching of uranium deposits, and the present application provides a method for enhancing in-situ leaching of uranium by applying an electric field, which can significantly increase the production efficiency of in-situ leaching of uranium and improve the uranium concentration of the resulting leaching solution, thereby solving the problem of difficult leaching of uranium deposits.

[0004] To achieve the above-mentioned object, the present application proposes the following technical solutions:

[0005] The present application provides a method for enhancing in-situ leaching of uranium by applying an electric field, which comprises:

[0006] arranging a liquid extraction well and a liquid injection well on a uranium deposit; installing an inert cathode at the liquid injection well; and installing an inert anode at the liquid extraction well;

[0007] using a CO2+O2 neutral leaching system or an acid leaching system for the leaching solution, injecting the leaching solution into the liquid injection well to perform in-situ leaching of the uranium deposit, and extracting the leaching solution from the liquid extraction well; the in-situ leaching is performed under the assistance of an applied electric field; and the applied electric field is a direct current pulse voltage applied between the inert cathode and the inert anode.

[0008] Further, the highest voltage of the direct current pulse voltage ranges from 100 to 300 V, the lowest voltage ranges from 0 to 100 V, and the pulse period ranges from 12 h to 5 d.

[0009] Further, the inert anode is one of a graphite electrode, a metal ceramic electrode, and a metal electrode.

[0010] Further, the inert cathode is one of a glassy carbon electrode, a graphite electrode, and a metal electrode.

[0011] Further, the inert cathode and the inert anode are both subjected to insulation treatment; the insulation treatment is coating an insulation layer on the surface of the inert cathode and the inert anode.

[0012] Further, the soaking solution contains an anionic oxidant; the concentration of the anionic oxidant in the soaking solution ranges from 0.5 to 1.5 g / L.

[0013] Further, the anionic oxidant is at least one of sodium chlorate, sodium hypochlorite and sodium percarbonate.

[0014] Further, the well type of the liquid extraction well and the liquid injection well for in-situ leaching of uranium is at least one of linear arrangement, grid arrangement and radial arrangement.

[0015] Further, the well type of the liquid extraction well and the liquid injection well for in-situ leaching of uranium is arranged according to the physical and chemical properties of the ore body.

[0016] Further, during the in-situ leaching of the uranium ore layer, the extraction and injection system is adjusted according to the progress of the in-situ leaching of uranium.

[0017] Further, the adjustment of the extraction and injection system according to the progress of the in-situ leaching of uranium includes: in the interval of 100 to 200 days, the concentration of uranyl ions in the leaching solution is detected once every 2 days, and the concentration trend of uranyl ions is analyzed and the peak value is determined with uranyl ion concentration and time as the axes; in the interval of 200 to 400 days, the concentration of uranyl ions in the leaching solution is detected once every 5 days; if the detected concentration of uranyl ions is lower than 30% of the historical peak value, it is considered that the in-situ leaching operation enters the end stage, at least part of the injection wells around the extraction well are shut down, and the injection rate of at least part of the injection wells around the extraction well is simultaneously reduced by 30% to 60%.

[0018] Further, the injection rate of the injection well during the in-situ leaching of uranium is 0 to 5 m 3 / h, and the extraction rate of the extraction well is 5 to 25 m 3 / h.

[0019] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0020] (1) The method for enhancing in-situ leaching of uranium by applying an electric field provided by the application has high production efficiency, can effectively realize good leaching of uranium ore, has low cost, has less impact on the environment, is easy to implement, and has high industrial application value.

[0021] (2) By inserting electrodes in the injection and extraction well and insulating treatment, a pulse electric field is created in the ore bed to promote the ions of reactants to reach the reaction point as soon as possible to start the reaction, promote the directed migration of the reaction product uranyl anion towards the extraction well, and increase the concentration of leaching agent on the mineral surface to reduce the thickness of the product layer, which is conducive to improving the leaching reaction rate, ultimately effectively reducing the production cycle and increasing the concentration of leaching solution. Based on the directed electric field from the extraction well to the injection well, the electric migration effect is used to inhibit the accumulation of elements such as Ca, Mg, Al and Fe in the pores of the ore body near the extraction well, effectively reducing the occurrence of chemical plugging by reducing the hydrolysis of precipitated elements, thereby improving the leaching rate and shortening the leaching cycle.

[0022] (3) By periodically changing the voltage of the anode and cathode, the electric field intensity in the ore bed presents a pulse fluctuation, and high and low field strength promotes mass transfer process and leaching reaction respectively, which synchronously improves the utilization rate of leaching solution and the concentration of uranium element in the leaching solution. The electric capillary mechanism brought by high field strength can promote the seepage behavior of the solution into the micropore, while the low field strength can reduce the seepage, which is conducive to the release of leaching solution in the micropore; such a cycle realizes the maximization of mineral leaching rate, ultimately significantly improves the leaching rate, shortens the leaching cycle and reduces the subsequent concentration cost.

[0023] (4) By adding anionic oxidants to the leaching solution, the effects of external electric field strengthening migration and external oxidant strengthening leaching are effectively combined, which is conducive to avoiding the accumulation of high-concentration anionic oxidants and reducing the occurrence of oxidant side reactions, fully exerting the strengthening effect of anionic oxidants, significantly improving the utilization rate of raw materials, increasing the concentration of leaching solution and reducing the production cycle.

[0024] (5) By timely changing the extraction and injection system, it can avoid too much leaching solution flowing into the part of the ore body that has approached complete reaction, avoid resource waste and reduce the dilution of the leaching solution, thereby increasing the concentration of uranium element in the leaching solution and effectively reducing the cost of subsequent purification treatment. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0026] Figure 1 The "thirteen injection and three extraction" in-situ leaching of uranium is schematically shown.

[0027] Figure 2 The leaching solution uranium concentration-time curve of Example 1 and Comparative Example 1.

[0028] Figure 3 Uranium concentration versus time curves for the leachate of Example 1 and Example 2.

[0029] Figure 4 Uranium concentration versus time curves for the leachate of Example 1 and Comparative Example 2.

[0030] Figure 5 Uranium concentration versus time curves for the leachate of Example 3 and Example 1. DETAILED DESCRIPTION

[0031] The present application provides a method for enhancing in-situ leaching of uranium by an applied electric field, comprising:

[0032] According to the physical and chemical properties of the uranium ore to be mined, a reasonable well type is selected, and a liquid extraction well and a liquid injection well are arranged at appropriate positions on the uranium ore deposit according to the selected well type.

[0033] An inert cathode is inserted into the liquid injection well, and an inert anode is inserted into the liquid extraction well. During the in-situ leaching of uranium, a direct current pulse voltage is applied between the inert cathode and the inert anode.

[0034] The leaching solution adopts an acidic leaching system or a CO2+O2 neutral leaching system. The leaching solution is injected into the ore body from the liquid injection well, fills the pore structure in the ore body, and fully reacts with the minerals. The leaching solution flows directionally under the action of the positive pressure of the liquid injection well and the negative pressure of the liquid extraction well, and is extracted from the liquid extraction well.

[0035] During the in-situ leaching of uranium, a direct current pulse voltage is applied between the cathode and the anode. During the low-voltage stage, the migration rate of the leaching reactant components in the leaching solution is small due to the weak electric field in the ore body, which is beneficial to increasing the concentration of the reactants in the pores and thus 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 the in-situ leaching of uranium. At the same time, it can also avoid the accumulation of the reaction product on the surface of the minerals. According to the Le Chatelier principle, reducing the concentration of the reaction product can promote the forward reaction and prepare for the next leaching cycle. Further, the electro-osmosis mechanism brought by the high-voltage stage can promote the seepage of the solution into the micropores, while the low-voltage stage can reduce this seepage, which is beneficial to the release of the leaching solution in the micropores. In this way, the mineral leaching rate is maximized. In the neutral or acidic leaching pH range, the uranium element in the leaching solution mainly exists in the form of negative divalent uranyl complex ions, a small amount of negative tetravalent uranyl complex ions and zero-valent uranyl molecules, and basically no positive divalent uranyl ions. Therefore, the insertion of the cathode at the liquid injection well and the anode at the liquid extraction well can create a negative electric field from the liquid injection well to the liquid extraction well, promote the migration of the negative-valent uranyl polymer ions to the liquid extraction well, and improve the production efficiency.

[0036] In some preferred embodiments, the inert anode is connected to a direct current pulse voltage; the highest voltage of the direct current pulse voltage ranges from 100 to 300 V, for example, 100 V, 120 V, 150 V, 180 V, 200 V, 220 V, 250 V, 280 V, 300 V, etc., and the lowest voltage ranges from 0 to 100 V, for example, 0 V, 20 V, 40 V, 60 V, 80 V, 100 V, etc., and the pulse cycle ranges from 12 h to 5 d, for example, 12 h, 18 h, 24 h, 1.5 d, 2 d, 2.5 d, 3 d, 3.5 d, 4 d, 4.5 d, 5 d, etc.

[0037] The physical and chemical properties of different ore bodies are suitable for different well types. For example, ore bodies with high porosity and permeability are suitable for linear or sparse grid well types; conversely, ore bodies with low porosity and permeability are suitable for radial or dense grid well types. The actual situation needs to be considered, and the ultimate goal is to minimize the leaching dead angle, simplify the construction and operation cost, and improve the leaching efficiency. In some preferred embodiments, the well type is at least one of linear arrangement, grid arrangement, and radial arrangement.

[0038] In some preferred embodiments, the leaching solution contains an anionic oxidizing agent; the concentration of the anionic oxidizing agent in the leaching solution ranges from 0.5 to 1.5 g / L, for example, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L, 1.0 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, etc.

[0039] In some preferred embodiments, the anionic oxidizing agent added to the leaching solution is at least one of sodium chlorate (NaClO3), sodium hypochlorite (NaClO), and sodium percarbonate (2Na2CO3·3H2O2). The addition of an appropriate amount of anionic oxidizing agent to the injected leaching solution accelerates the migration rate of the oxidizing agent under the action of the electric field, so that the oxidizing agent reaches the mineral surface faster and reacts with tetravalent uranium elements, thereby improving the efficiency of in-situ leaching of uranium and avoiding the occurrence of a large number of side reactions due to the long-term accumulation of the oxidizing agent.

[0040] In some preferred embodiments, the inert anode is one of a graphite electrode, a metal ceramic electrode, and a metal electrode (for example, a platinum electrode, a titanium-based coated anode, an iridium-tantalum alloy anode, and an iron-nickel-copper alloy anode).

[0041] In some preferred embodiments, the inert anode is one of a graphite electrode, a metal ceramic electrode, and a metal electrode (for example, a platinum electrode, a titanium-based coated anode, an iridium-tantalum alloy anode, and an iron-nickel-copper alloy anode).

[0042] In some preferred embodiments, the inert cathode and the inert anode are both insulated, i.e., only for generating a directional electrostatic field; the insulation treatment is to coat an insulating layer on the surface of the inert cathode and the inert anode, for example, to coat epoxy resin. The insulation treatment can reduce energy consumption and cost, and can also avoid chemical clogging in the ore body caused by the cathode producing alkali at the injection well.

[0043] In some preferred embodiments, the injection rate of the injection well in the in-situ leaching of uranium is 0-5 m 3 / h, and the pumping rate of the pumping well is 5-25 m 3 / h. In the in-situ leaching of uranium, the product of the number of injection wells and the injection rate should be less than the product of the number of pumping wells and the pumping rate.

[0044] In the process of in-situ leaching of uranium, the reaction degree at 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, i.e., the farther the mineral is from the injection well, the lower the reaction progress is. The reason is that the concentration of the leaching solution in the ore bed is not uniform, resulting in differences in the leaching rate of the minerals at different positions, thus causing the phenomenon that part of the ore body has been completely reacted at a certain moment but the leaching solution is still continuously injected. Therefore, during the in-situ leaching process, the leaching solution should be regularly sampled to obtain the uranyl ion concentration data, and the injection and pumping system should be changed at a certain time node to optimize the utilization rate of the leaching solution and improve the concentration of the leaching solution under the premise of ensuring sufficient reaction of the mineral.

[0045] In some preferred embodiments, during the in-situ leaching of uranium, the injection and pumping system is also changed in time according to the progress of the in-situ leaching of uranium to optimize the working efficiency of the in-situ leaching of uranium. In some preferred embodiments, the injection and pumping system is adjusted according to the progress of the in-situ leaching of uranium, and the specific method is as follows: in the interval of 100-200 days, the uranyl ion concentration in the leaching solution is detected once every 2 days, and the uranyl ion concentration trend is analyzed and the peak value is determined based on the uranyl ion concentration and time as the axis; in the interval of 200-400 days, the uranyl ion concentration in the leaching solution is detected once every 5 days; if the uranyl ion concentration at this moment is less 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 around the pumping well are routinely shut down according to experience and working conditions, and the injection rate of at least part of the injection wells around the pumping well is also reduced by 30%-60% at the same time, for example, by 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, etc.

[0046] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments. However, the scope of protection of the present application is not limited to the following specific embodiments.

[0047] Example 1

[0048] The method for enhanced uranium extraction by external electric field leaching provided by this invention includes the following steps:

[0049] (1) Drill pumping wells and injection wells on the ore body according to the "thirteen injections and three extractions" well type, such as Figure 1 As shown, the depth of the pumping well and the injection well is 250~300m, and the well radius is 0.5m;

[0050] (2) A CO2+O2 neutral leaching system is adopted. The leaching solution is injected into the ore body from the injection well. The leaching solution fills the pore structure of the ore body and reacts fully with the minerals. The leaching solution is directionally flowed under the positive pressure of the injection well and the negative pressure of the pumping well, and is pumped out from the pumping well. The injection rate is 2m. 3 / h, pumping rate 10m 3 / h;

[0051] (3) Insert the graphite cathode with an epoxy resin insulating layer on its surface into the injection well, and insert the graphite anode with an epoxy resin insulating layer on its surface into the extraction well. Apply a DC pulse voltage between the cathode and the anode, with a pulse period of 2d. The peak potential of the anode is 250V and the trough potential is 50V; the potential of the cathode is 0V.

[0052] The average concentration of uranium in the extracted leachate was measured and recorded every 20 days. A graph was plotted with time (d) on the x-axis and uranium concentration (mg / L) on the y-axis. The results are shown below. Figure 2 As shown.

[0053] Comparative Example 1

[0054] The only difference between this comparative example and Example 1 is that step (3) is omitted, while the other conditions remain unchanged.

[0055] Comparison of uranium concentration in leaching solution at different times in Example 1 is shown in Figure 1. Figure 2 .

[0056] from Figure 2 It can be seen that, under the same conditions, Example 1, which uses an external electric field to enhance ground leaching, has a 12.45% higher maximum uranium concentration in the leachate than Comparative Example 1, which uses direct ground leaching.

[0057] Example 2

[0058] The difference between this embodiment and the process steps of embodiment 1 is that in step (2), an additional 1.4 g / L sodium hypochlorite (10% NaClO) is added to the CO2+O2 neutral leaching system to assist in oxidative leaching.

[0059] Comparison of uranium concentration in leaching solutions at different times between Example 1 and Example 2 is shown in the figure. Figure 3The results show that, under the same conditions, the maximum uranium concentration of the leaching solution obtained in Example 2 is increased by 4.51% than that of Example 1 without adding oxidant assisted leaching, and the time interval of the maximum uranium concentration is significantly widened.

[0060] Comparative Example 2

[0061] The difference between the present comparative example and Example 1 is that the applied electric field is a direct current constant voltage, in which the anode potential is 250 V and the cathode potential is 0 V.

[0062] The comparison of the uranium concentration in the leaching solution at different times between Example 1 and Comparative Example 2 is shown in Table 2. Figure 4 The results show that, under the same conditions, the maximum uranium concentration of the leaching solution obtained in Comparative Example 2 is reduced by 16.3% than that of Example 1 with pulse electric field enhanced leaching.

[0063] Example 3

[0064] According to the results of Example 1 shown in Table 1, the uranium concentration of the leaching solution of Example 1 has a relatively obvious decreasing trend at about 300 d, and in combination with the well type structure shown in Table 2, it can be guessed that the uranium ore in the central region has been completely reacted at about 300 d, and the central injection well does not need to continue to inject liquid. Figure 2 Figure 1 Figure 1

[0065] Therefore, Example 3 continues the process steps of Example 1, and the only difference is that the central injection well stops injecting liquid at 300 d, and the injection rate of the remaining injection wells is reduced by 50%, and the pumping rate of the pumping well is changed to 5 m 3 / h.

[0066] The comparison of the uranium concentration in the leaching solution at different times between Example 3 and Example 1 is shown in Table 3. Figure 5 The results show that, under the same conditions, timely changing the pumping and injection system can avoid too much leaching solution flowing into the part of the ore body that has been close to complete reaction, thereby increasing the uranium concentration of the solution pumped out by the pumping well. After the system is changed, the average uranium concentration of the leaching solution is increased by about 31%.

[0067] The above only describes the preferred embodiments of the present application, and it should be noted that, for ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.​​​

Claims

1. A method of enhancing in-situ leaching of uranium by an applied electric field, characterised in that, The application relates to a method for in-situ leaching of uranium ore. The method comprises the following steps: a liquid extraction well and a liquid injection well are arranged on a uranium deposit; an inert cathode is arranged at the liquid injection well; 2. The method of enhancing in-situ leaching of uranium by an applied electric field as claimed in claim 1, wherein, an inert anode is arranged at the liquid extraction well; 3. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1, wherein, a leaching solution is injected into the liquid injection well to in-situ leach the uranium ore layer, and the obtained leaching solution is extracted from the liquid extraction well; the in-situ leaching is assisted by an applied electric field; the applied electric field is a direct current pulse voltage applied between the inert cathode and the inert anode; the highest voltage of the direct current pulse voltage ranges from 100 V to 300 V, the lowest voltage ranges from 0 V to 100 V, and the pulse period ranges from 12 h to 5 d.

4. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1 wherein, The inert anode is one of a graphite electrode, a metal ceramic electrode and a metal electrode.

5. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1 wherein, The inert cathode is one of a glassy carbon electrode, a graphite electrode and a metal electrode.

6. The method of enhancing in-situ leaching of uranium by an applied electric field as claimed in claim 5, wherein, Both the inert cathode and the inert anode are subjected to insulation treatment; the insulation treatment is to coat an insulation layer on the surface of the inert cathode and the inert anode.

7. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1 wherein, The leaching solution contains an anionic oxidant; the concentration of the anionic oxidant in the leaching solution ranges from 0.5 g / L to 1.5 g / L. The anionic oxidant is at least one of sodium chlorate, sodium hypochlorite and sodium percarbonate.

8. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1 wherein, The well type of the liquid extraction well and the liquid injection well for in-situ leaching of uranium is at least one of a straight line type, a grid type and a radial type. The well type of the liquid extraction well and the liquid injection well is selected according to the physical and chemical properties of the ore body. During the in-situ leaching of the uranium ore layer, the liquid extraction and injection system is adjusted according to the progress of the in-situ leaching of uranium; The adjustment of the liquid extraction and injection system according to the progress of the in-situ leaching of uranium comprises the following steps: in a period of 100-200 days, the concentration of uranyl ions in the leaching solution is detected once every 2 days; the concentration of uranyl ions is plotted against time to analyze the trend of the concentration of uranyl ions and determine the peak value; in a period of 200-400 days, the concentration of uranyl ions in the leaching solution is detected once every 5 days; if the detected concentration of uranyl ions is lower than 30% of the historical peak value, it is considered that the in-situ leaching operation enters the final stage, at least part of the liquid injection wells around the liquid extraction well are shut down, and the injection rate of at least part of the liquid injection wells around the liquid extraction well is simultaneously reduced by 30%-60%.

9. The method of enhancing in-situ leaching of uranium by applied electric field as claimed in claim 1 wherein, The injection rate of the injection well in the in-situ leaching uranium process is 0-5 m 3 / h, and the pumping rate of the pumping well is 5-25 m 3 / h.

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