Method for concentrating uranium in uranium-containing solution

Abstract

The invention relates to hydrometallurgy. A method of concentrating uranium in a uranium-containing solution includes separating the uranium-containing solution by nanofiltration, and concentrating uranium in a concentrate. The used uranium-containing solution is uranium-rich eluent. The uranium-containing solution is first fed into a fine filter to remove suspended particles before separation by nanofiltration. And the solution is separated by using a membrane assembly in the third-stage or fourth-stage nano-filtration. The membrane module is a module having a selective membrane. A portion of the concentrate obtained after the last nanofiltration membrane module is sent back to the starting point of the nanofiltration process. As a result, the efficiency of enriching uranium from the initial uranium-containing solution is improved.

Description

[0001] The invention is applicable to the hydrometallurgy of metals and can be used to increase the concentration of available components, in particular uranium, obtained after desorption of a uranium-containing solution and to reduce the sulfuric acid content relative to uranium in the concentrate (retentate) compared to the initial uranium-containing solution.

[0002] There is a known method for treating a uranium-containing solution (Patent of the Republic of Kazakhstan No. FG4A(12), classification C22B 3 / 26, C22B 3 / 22, published on November 4, 2015, electronic bulletin No. 13, 2017), which comprises leaching uranium from an ore, concentrating and purifying the uranium-containing solution, regenerating the leaching agent, and further concentrating the uranium from the process solution by multi-stage nanofiltration, wherein the solution is initially diluted before the nanofiltration. The uranium concentration and leaching agent regeneration are carried out using three nanofiltration stages, and the retentate from the first nanofiltration stage is diluted with water at a dilution rate of 10% to 50%. The permeates from the first nanofiltration stage and the second nanofiltration stage are combined and fed to the third nanofiltration stage.

[0003] A disadvantage of this method is the use of water to dilute the first-stage retentate during the nanofiltration process, which results in relatively high water consumption when operating under practical industrial conditions. The use of water also increases the total volume of solution sent for nanofiltration, which results in a greater load on the pumping equipment and, therefore, higher energy consumption. The inclusion of water for dilution in the nanofiltration process reduces the potential for reducing the volume of solution sent for processing and fed to the refinery.

[0004] A known method for extracting metals using multi-stage filtration is a hydrometallurgical process (Russian Federation Patent No. 2626112, Classification C22B060 / 02, published on July 21, 2017, Publication No. 12). The method comprises leaching the metal using a lixiviant to obtain a leachate containing the metal and impurity solids, and concentrating and purifying the leachate to obtain a metal-rich solution stream. The leachate concentration and purification stage involves extracting the metal from the leachate using an organic solvent, resulting in a metal-rich organic solution and a metal-depleted raffinate. After the metal is extracted using the organic solvent, the organic solution and raffinate are fed to a first nanofiltration subsystem to produce a first retentate and a first permeate stream. The permeate from the first subsystem is combined with the rich solution stream and processed in a second nanofiltration subsystem to produce a second retentate and a second permeate stream, which can be used for leaching or for concentrating and purifying the resulting leachate.

[0005] A disadvantage of this method is that it cannot substantially increase the concentration of uranium from the rich eluent solution to the resulting retentate (concentrate) by nanofiltration. Combining the entire volume of the permeate from the first subsystem with the rich solution will significantly reduce the potential for enrichment of uranium in the retentate (concentrate) after the second nanofiltration subsystem.

[0006] The method closest to the present invention is a method for enriching uranium from a solution (Patent No. 33914 of the Republic of Kazakhstan, C22B 60 / 02C22B 3 / 24, October 25, 2019, Publication No. 43). This method includes the possibility of increasing the uranium enrichment level in a solution (concentrate) obtained by nanofiltration. According to this method, the retentate (concentrate) obtained during the nanofiltration of a uranium-containing solution is divided into two parts, one of which is combined with the initial solution and fed back to the nanofiltration process. The second part is removed from the nanofiltration process as a finished product along with the permeate. Combining part of the retentate (concentrate) with the initial uranium-containing solution allows its content in the nanofiltration feed to be continuously increased, and therefore, its content in the retentate (concentrate) obtained from the combined feed is increased.

[0007] The disadvantages of this approach are a reduction in the effective productivity of the nanofiltration unit and a concurrent increase in the uranium content of the permeate, which negatively impacts the overall efficiency of the rich eluent nanofiltration technology.

[0008] The object of the present invention is to develop a method for increasing the uranium concentration in the concentrate obtained after nanofiltration of a uranium-containing solution (rich eluent or product solution) while reducing the sulfuric acid content relative to the uranium. The method also aims to reduce the uranium content in the permeate obtained after nanofiltration of a uranium-containing solution (rich eluent or product solution) and the consumption of reagents for precipitating the concentrate obtained after nanofiltration of a uranium-containing solution (rich eluent or product solution).

[0009] The technical result of the invention is to increase the efficiency of concentrating uranium from an initial uranium-containing solution (rich eluent or product solution) into a retentate (concentrate) by nanofiltration, to return part of the sulfuric acid together with the permeate obtained after nanofiltration of the uranium-containing solution (rich eluent or product solution), thereby increasing the productivity of the refining process by reducing the volume of solution sent for refining, and to adjust the degree of uranium enrichment in the concentrate obtained after nanofiltration of the uranium-containing solution (rich eluent or product solution) according to the technical requirements of the production.

[0010] This technical result is achieved by a method for concentrating uranium in a uranium-bearing solution, which includes separating the uranium-bearing solution by nanofiltration, with the uranium being concentrated in a concentrate. According to the invention, the rich eluate or production solution is used as the uranium-bearing solution, which is purified from mechanical suspended solids by passing the uranium-bearing solution through a fine filter before separation by nanofiltration. Separation is performed in three or four nanofiltration stages using membrane modules, with modules having high-selectivity and low-selectivity membranes as the membrane modules, and a portion of the concentrate obtained after the last nanofiltration module is returned to the starting point of the nanofiltration process.

[0011] Additional technical results are achieved by concentrating the uranium in the uranium-bearing solution using high-selectivity membranes in the first two nanofiltration membrane modules and low-selectivity membranes in the subsequent one or two nanofiltration membrane modules, depending on the selected three-stage or four-stage scheme for separating the uranium-bearing solution.

[0012] The advantages of this method are due to the use of multiple uranium-containing solution nanofiltration process complexes and the proposed scheme of using multiple types of nanofiltration membranes, in which the flow ratio of the uranium solution in the nanofiltration process is optimized.

[0013] A method for concentrating uranium in a uranium-containing solution is shown in the accompanying drawing, which shows a schematic diagram of the claimed method, the components of which are as follows:

[0014] 1-Uranium-containing solution

[0015] 2-Pipeline

[0016] 3-Storage tank

[0017] 4-Pipeline

[0018] 5-nanometer filtration unit

[0019] 6-Filter

[0020] 7-First membrane module

[0021] 8-Permeate

[0022] 9-Concentrate

[0023] 10-Sand trap for production solution

[0024] 11-Second nanofiltration module

[0025] 12-Second module permeate

[0026] 13-Second Module Concentrate

[0027] 14-Third nanofiltration module

[0028] 15-Third Module Permeate

[0029] 16-Third Module Concentrate

[0030] 17-Fourth nanofiltration module

[0031] 18-Part of the fourth module permeate

[0032] 19-Part of the fourth module permeate

[0033] 20-4th Module Concentrate

[0034] 21 - Part of the fourth module concentrate

[0035] 22 - Part of the fourth module concentrate

[0036] The method with reference to the accompanying drawings is performed as follows.

[0037] The average content of 62 g / dm2 obtained as a result of treating the uranium-containing solution was 3 of uranium and 28.6 g / dm 3 The rich eluate 1 of sulfuric acid is fed to a dedicated storage tank 3 through a pipeline 2, from which the rich eluate is pumped as feed solution through a pipeline 4 to a 3.5m 3 / h nanofiltration unit 5. The initial rich eluate is delivered via a low-pressure pump to a fine filter 6. There, it is purified of mechanically suspended solids. After the fine filter, the rich eluate is delivered to a high-pressure pump and then to a first membrane module with a highly selective membrane 7 (NF90-400 / 34i). As the rich eluate passes through the membrane of the first nanofiltration module, it is separated into two parts: one part, the solution that has passed through the membrane—the "permeate" 8, and the second part, the solution that has not yet passed through the membrane—the "concentrate" 9. The permeate from the first nanofiltration module is removed from the process and fed to a post-processing stage or to a process solution (hereinafter referred to as PS) sand trap 10, from which it is sent along with the process solution for adsorption. The concentrate obtained from the first nanofiltration module is fed to a second nanofiltration module with a highly selective membrane 11 (NF90-400 / 34i). The permeate 12 obtained from the second membrane module is combined with the permeate 8 from the first module, removed from the process, and sent to a post-capture stage or to a PS sand trap 10, from which it is sent along with the process solution for adsorption. The concentrate 13 from the second module is sent to a third nanofiltration module with a less selective membrane 14 (NF270-400 / 34i). The permeate 15 obtained in the third module is combined with the permeates from the first module 8 and the second module 12 and sent to a post-processing stage or to a PS sand trap 10, from which it is sent along with the process solution for adsorption. The concentrate 16 obtained in the third module is fed to a fourth nanofiltration module with a less selective membrane 17 (NF270-400 / 34i). A portion of the permeate 18 obtained in the fourth module is combined with the permeates from the first module 8, the second module 12, and the third module 15 and removed from the process to a recovery stage or PS sand trap 10, from which it is sent along with the process solution for adsorption. Another portion 19 of the permeate obtained at the fourth module is returned to the pipeline 4 supplying the initial solution and, after mixing with the initial solution, fed to the first nanofiltration module. Recirculation of a portion of the permeate from the fourth module, which has a less selective membrane, serves to return a portion of the permeate that is most enriched in uranium (compared to the other membrane modules) to the nanofiltration process. This allows for a reduction in the total U content in the permeate removed from the process while also reducing the U content in the initial uranium-containing solution by mixing it with the permeate. The concentrate 20 obtained at the fourth module is divided into two parts. One portion 21 of the concentrate is removed from the process as a finished product, while the other portion 22 is returned to the initial stage of the nanofiltration process (recirculation), where it is fed along with the original rich eluate to the first membrane of the first nanofiltration module 7.In this case, the concentrate is recycled to increase the solution flow through the membranes 7, 11, 14, 17, which helps prevent the formation of precipitates on the membrane surfaces. The volume of the retentate (concentrate) returned to the circulation during the recycling process can be 10% to 30% of the initial solution. The concentrate yield is 50% to 70% of the permeate yield.

[0038] The results of the implementation of this method and the comparative analysis results of the uranium and acid contents in the concentrate and permeate products are shown in Table 1.

[0039] Table 1. Experimental results of the prototype and the proposed method

[0040]

[0041] Based on the results obtained, returning a portion of the permeate from the last nanofiltration module with a low selectivity membrane to the nanofiltration process allows obtaining a permeate with a uranium content not exceeding 1 g / dm3 while maintaining the uranium enrichment level in the retentate (concentrate).

[0042] The uranium concentration in the concentrate obtained after three or four membrane modules is adjusted by varying the flow rate of the concentrate relative to the permeate, and a smaller portion of the concentrate is returned to the process after the last nanofiltration module to increase the flow of solution through the membranes, which helps prevent the formation of precipitates on the membrane surface.

[0043] Using this method also reduces the acid content in the concentrate by an average of 1.66 times relative to uranium, compared to the original uranium-containing solution.

Claims

1. A method for concentrating uranium in a uranium-containing solution, said method comprising separating said uranium-containing solution by nanofiltration, wherein the uranium is concentrated into a concentrate, characterized in that Rich eluate or production solution is used as the uranium-bearing solution, which is treated for mechanical suspension purification by feeding it through a fine purification filter before separation by nanofiltration. The uranium-bearing solution is then separated in three or four nanofiltration stages using membrane modules, wherein membrane modules with high and low selectivity membranes are used and a portion of the concentrate obtained after the last nanofiltration module is returned to the beginning of the nanofiltration process.

2. The method for concentrating uranium in a uranium-containing solution according to claim 1, characterized in that: Highly selective membranes are used in the first two nanofiltration membrane modules and low selective membranes are used in the subsequent one or two nanofiltration membrane modules, depending on whether a three-stage or four-stage separation scheme is selected for the uranium-containing solution.

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