Method for extracting metal oxyacid radical by imidazole type ionic liquid

Abstract

The invention discloses a method for extracting metal oxyacid radicals by using imidazole type ionic liquid. Comprising the following steps: adding an ionic liquid into alkaline wastewater containing metal oxyacid radicals, mixing to form two aqueous phases, and separating the aqueous phase to realize extraction of the metal oxyacid radicals; the structural formula of the ionic liquid is shown in the specification, wherein R is C6-12 straight-chain or branched-chain alkyl. The ionic liquid alkaline aqueous two-phase system adopted in the method retains the advantages of no volatilization, safety, stability and low viscosity, is high in extraction rate of target metal oxyacid radicals and high in selectivity, and has wide application prospects in the fields of spent fuel treatment, non-ferrous metallurgy and the like. According to the present invention, the nitric acid can be adopted to perform reverse extraction on the ion-rich liquid phase containing the metal oxyacid radical so as to recover the metal oxyacid radical, and the ionic liquid adopted as the extraction agent can be recycled, such that the problem of difficult reverse extraction of the extraction system in the prior art is solved, the cost is substantially reduced, and the industrial promotion is easily achieved. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of spent fuel post-processing, and in particular to a method for extracting metal oxygen-containing acid radicals using imidazole-type ionic liquid. Background Art

[0002] The separation of metal oxygen-containing acid radicals is a core technical problem in the field of metallurgy and environment. The existing nuclear fission technology will produce spent fuel containing a large amount of radioactive elements, including 235 U fission products 99 Tc half-life is long (2.13×10 5 Years), the main ion state is TcO4 - It is highly water-soluble, has weak interactions with soil and rock formations, and is highly mobile. During long storage processes, it can easily leak into the environment with the migration of groundwater, posing a long-term potential hazard to the ecosystem. [1] Currently TcO4 - There are three main separation technologies: reduction precipitation, solid phase adsorption and liquid-liquid extraction. Among them, liquid-liquid extraction is relatively mature in technology. This technology has a high degree of automation, a large processing capacity, and can process raw material solutions with low Tc concentrations. The core of liquid-liquid extraction technology is to develop an extraction system that is highly selective for the target metal oxyacids. In order to improve the selectivity of the liquid-liquid extraction process and solve environmental problems such as the volatility of organic solvents in traditional extraction processes, it is currently necessary to develop a new green extraction system with high efficiency and selectivity for metal oxyacids.

[0003] In recent years, many new green systems are being developed and applied in the field of metal oxygen acid extraction, such as ionic liquids, aqueous two-phase, deep eutectic solvents, etc. Among them, the aqueous two-phase based on polyethylene glycol polymer (Rogers RD, Bond AH, Bauer CB, et al. Partitioning behavior of 99 Tc and 129 I from simulated Hanfordtank wastes using polyethylene-glycol based aqueous biphasic systems [J]. Solvent Extraction & Ion Exchange, 1995, 13 (4): 689-713.), and low eutectic solvents based on quaternary phosphonium salts and quaternary ammonium salts (Phelps TE, Bhawawet N, Jurisson SS, et al. Efficient and Selective Extraction of 99m TcO4 -from Aqueous Media Using Hydrophobic Deep EutecticSolvents[J].ACS Sustainable Chemistry&Engineering,2018,6(11):13656-13661.) The extraction effect was good, but the system after extraction was different from TcO4 - The binding energy is too strong, making it difficult to strip-extract, and a reducing agent needs to be added to achieve stripping. The reagent consumption is large, the stripping is incomplete, the extraction agent is seriously lost, and it is difficult to recycle, which hinders the industrialization of related technologies. Summary of the invention

[0004] Aiming at the problem that metal oxyacids such as pertechnetate or perrhenate are difficult to extract, the present invention provides a method for extracting metal oxyacids using imidazole-type ionic liquids. The method can be applied to a two-phase aqueous system of high-salinity alkaline wastewater to achieve highly selective separation and extraction of metal oxyacids, and the extraction rate of metal oxyacids is high and the selectivity is strong.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for extracting metal oxygen-containing acid radicals with imidazole-type ionic liquids comprises the steps of: adding ionic liquids to alkaline wastewater containing metal oxygen-containing acid radicals, mixing to form a two-phase aqueous solution, and separating the aqueous phase to extract the metal oxygen-containing acid radicals;

[0007] The structural formula of the ionic liquid is as follows:

[0008]

[0009] Wherein, R is a C6-12 straight chain or branched chain alkyl group.

[0010] In the present invention, imidazole chloride-containing ion liquid is used as an amphipathic solute, and the aqueous solution will be separated due to temperature changes. Within a certain ionic liquid and hydroxide concentration range, it is a uniform single-phase solution at room temperature (25°C), and as the temperature rises, a mutually incompatible two-phase solution is formed. The metal oxygen-containing acid radicals in the wastewater are replaced with the anions in the ionic liquid through an anion exchange mechanism and enter the organic phase. During the temperature change process, the ionic liquid particles loaded with the metal oxygen-containing acid radicals agglomerate to form a hydrophobic micelle group, and continue to grow to form a two-phase water. Since anions such as perrhenate and pertechnetate are highly hydrophobic, even under the condition that a large number of competitive anions are present in the solution, anion exchange can preferentially occur according to the Hofmeister lyophilic sequence to enter the hydrophobic phase.

[0011] Preferably, the ionic liquid is 1-hexyl-3-methylimidazolium chloride (C6MImCl), 1-octyl-3-methylimidazolium chloride (C8MImCl), 1-decyl-3-methylimidazolium chloride (C 10 MImCl), 1-dodecyl-3-methylimidazolium chloride (C 12 The hydrophilicity and hydrophobicity of the above ionic liquids can be adjusted by the length of their alkyl chains. When the alkyl chain length is too large, the ionic liquid has strong hydrophobicity and high viscosity, and becomes an organic phase-aqueous phase system, losing the advantage of a two-phase aqueous system; when the alkyl chain length is too small, it is too hydrophilic and difficult to form a two-phase aqueous system.

[0012] Preferably, the ionic liquid is C8MImCl and / or C 10 MImCl, these two ionic liquids have moderate viscosity, and the concentration of salting-out agent required to form a two-phase solution is relatively small; further preferably, the ionic liquid is C8MImCl, which maintains a high extraction rate for perrhenate and pertechnetate in a relatively large concentration range.

[0013] The metal oxygen-containing acid radical is pertechnetate and / or perrhenate, such as water-soluble metal salts such as sodium salts or ammonium salts thereof. In the present invention, the extraction rate of the alkaline ionic liquid two-phase system for such metal oxygen-containing acid radicals is above 95%. Most of such anions have small hydration enthalpy and strong hydrophobicity, so even under the condition that a large number of competitive anions exist in the solution, anion exchange can occur preferentially according to the Hofmeister lyophilic sequence and enter the hydrophobic phase, without affecting the extraction efficiency.

[0014] The alkaline wastewater also includes any one or more inorganic salts of sodium hydroxide, potassium hydroxide, potassium nitrate, sodium nitrite, sodium aluminate, sodium nitrate, trisodium phosphate, sodium sulfate, sodium carbonate, sodium citrate, disodium EDTA, sodium iodide, and sodium chloride. When the alkalinity of the solution of the metal oxygen-containing acid radical to be extracted is not strong enough, the pH of the solution can be appropriately adjusted according to the phase diagram to ensure that the entire system can form a two-phase aqueous system at the phase transition temperature.

[0015] The mass concentration of the ionic liquid in the two-phase water is 5-40wt%. The concentration of hydroxide in the two-phase water is 1-10mol / L. The higher the concentration of the ionic liquid, the higher the extraction rate. In the present invention, the ionic liquid at 5wt% can basically achieve an extraction rate of more than 90%.

[0016] The temperature for mixing to form a two-phase water solution is between the melting point and boiling point of the ionic liquid used. Preferably, the mixing temperature is 25-60°C, and more preferably, the temperature is 55°C. At this temperature, the viscosity of the ionic liquid is low, which is conducive to phase separation.

[0017] The alkaline wastewater also contains one or more impurity anions selected from sulfate, carbonate, nitrate, chloride, iodide, nitrite and aluminate, and the total molar concentration of the impurity anions is less than 3000 times that of the metal oxyacids. Even in the case of containing multiple competitive impurity anions, the extraction rate of the metal oxyacids by the system of the present invention is very high and is hardly affected by any factors, and can reach an extraction rate of more than 90%, or even more than 94%.

[0018] Preferably, the method further comprises the step of adding nitric acid to the water phase for stripping to achieve the regeneration cycle of the ionic liquid and the recovery of the metal oxygen-containing acid radicals.

[0019] The stripping process also follows the anion exchange mechanism. The metal anions carried in the organic phase can combine with the hydrogen ions in the stripping acid and re-enter the aqueous phase to achieve stripping. Therefore, nitric acid can be used to strip the ionic liquid phase containing metal oxygen-containing acid radicals, and the ionic liquid used as the extractant can be recycled and reused. This solves the problem of the difficulty of stripping in the extraction system in the prior art, greatly reducing the cost.

[0020] The nitric acid concentration in the stripping solution formed by adding nitric acid is above 4 mol / L; the stripping temperature is 25-55°C.

[0021] The mass fraction of the dehydrated phase in the stripping solution is 4-20wt%, the mass fraction of nitric acid is 15-50wt%, and the remainder is water. The higher the nitric acid concentration, the higher the stripping rate. Since nitrate has a smaller hydration enthalpy and hydrophobicity than sulfate and chloride, it is suitable for stripping. The metal oxygen acid radicals in the ionic liquid phase exchange anions with nitrate radicals and combine with hydrogen ions in the acid to form metal oxygen acids, which are more water-soluble and then redissolved in the dehydrated phase.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The ionic liquid alkaline two-phase aqueous system used in the present invention retains the advantages of non-volatilization, safety, stability and low viscosity, has a high extraction rate and strong selectivity for the target metal oxygen-containing acid radicals, and has broad application prospects in the fields of spent fuel treatment, non-ferrous metal metallurgy, etc.

[0024] (2) The ionic liquid alkaline two-phase aqueous system used in the present invention can use nitric acid to strip the ionic liquid-rich phase containing metal oxyacids, thereby recovering the metal oxyacids, and the ionic liquid used as the extractant can be recycled and reused. It also solves the problem of difficult stripping of the extraction system in the prior art, greatly reduces the cost, and is conducive to industrial promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 11 is the alkaline aqueous two-phase phase diagram of different ionic liquids in Example 1.

[0026] Figure 2 This is a diagram showing the extraction rate effects of each competitive anion pair in Example 2.

[0027] Figure 3 This is a diagram showing the relative stripping rate effects of different concentrations of sodium nitrate and water in Example 5.

[0028] Figure 4 This is a diagram showing the effect of different concentrations of nitric acid on the stripping rate in Example 5. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0030] C6MImCl (98%, AR), C8MImCl (98%, AR), C 10 MImCl(96%,AR),C 12 MImCl (99%, AR) and sodium sulfate (99.5%, AR) were purchased from Shanghai Bid Pharmaceutical Co., Ltd.; sodium aluminate (98%, AR), trisodium phosphate (98%, AR), sodium citrate (99.5%, AR), and disodium EDTA (99.99%, AR) were purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; sodium nitrate (>99.0%, AR), concentrated nitric acid (65-68%, GR), sodium hydroxide (98%, AR), potassium nitrate (99%, AR), and sodium iodide (99.0%, AR) were purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium carbonate (99.8%, AR) and sodium nitrite (98.5%, AR) were purchased from Shanghai Anage Chemical Co., Ltd.; sodium chloride (99.5%, AR) was purchased from Shanghai Titan Technology Co., Ltd.; and sodium perrhenate was purchased from Alfa Aesar (China) Chemical Co., Ltd.

[0031] Example 1 Phase change experiment

[0032] The ionic liquids C6MImCl, C8MImCl, and C 10 MImCl, C 12 Phase diagram of the two-phase aqueous system of MImCl. The specific operation steps are as follows:

[0033] First, weigh the mass of a 3ml empty culture bottle, and prepare a series of 1g ionic liquid solutions with concentrations of 50-2wt% in it, and record the total mass of each culture bottle. Prepare a 40wt% NaOH solution, and place both the ionic liquid solution and the NaOH solution in an oven at the phase diagram temperature for one hour.

[0034] Use a pipette to drop 200 μL of NaOH solution into each strain bottle, put it back into the oven and let it stand for 30 minutes to observe whether the solution remains clear. If it is clear, continue to repeat the above steps of dropping NaOH solution and letting it stand; if the solution becomes turbid, take it out and weigh it, and calculate the mass of the added NaOH solution by the mass change. Calculate the mass fraction of each component in the solution at this time based on the recorded mass data and draw a phase diagram.

[0035] The results are as follows Figure 1 As shown, it can be seen that when the phase transition temperature of the above-mentioned ionic liquid is between 25 and 55°C, the alkali concentration of the system needs to be higher, preferably maintained above 1 mol / L. For raw material liquids with insufficient concentration, alkalis such as sodium hydroxide and potassium hydroxide need to be added for adjustment.

[0036] Example 2 Extraction experiment

[0037] With non-radioactive ReO4 - Replacement of TcO4 - To test the extraction performance of each ionic liquid, a NaReO4 solution with a concentration of 100 ppm was prepared as the extraction solution. After diluting it by a certain multiple, it was measured using inductively coupled plasma spectroscopy (ICP-OES) to calculate its actual concentration.

[0038] Competitive experiment: A system with a total solution mass of 1g was prepared in a 2ml centrifuge tube, of which 0.3g was ReO4 - The concentration of the extract is 100ppm, the concentration of the ionic liquid is fixed at 15wt%, the concentration of NaOH is fixed at 15wt%, and different sodium salts of competitive anions (including sodium nitrate, sodium sulfate, sodium chloride, sodium phosphate, sodium iodide, sodium carbonate) are added according to the maximum solubility, and the remaining mass is made up with deionized water. After the centrifuge tube is sealed, it is shaken at 2000rpm for 20min on a multi-tube vortex mixer to fully mix it, and it is placed in a 55℃ oven for more than 3h. After the phases are separated, the lower phase (hydrophilic salt-rich phase) of the two-phase water is sucked with a syringe, its mass is weighed and diluted according to a certain ratio, and the ReO4 in the salt-rich phase is determined by ICP-OES. - The content of ReO4 in the salt-rich phase is calculated - The concentration of is the molar ratio of the competing anion.

[0039] The specific extraction rate of perrhenate is calculated as follows: E = (w Re,o ×m o -wRe,a ×m a ) / (w Re,o ×m o );Where E is the extraction rate, w Re,a is the mass concentration of rhenium in the aqueous phase after extraction, m a w is the mass of the aqueous phase after extraction; Re,o is the mass concentration of rhenium in the original solution, m o is the mass of the raw material liquid. The extraction results are shown in Table 1 and Figure 2 As shown, in the presence of different competing anions, the extraction rate of perrhenate is above 94%, and impurity ions have almost no effect on the extraction effect.

[0040] Table 1 Extraction rate of perrhenate by [C8MIm]Cl in the presence of different impurity anions

[0041] Anion type <![CDATA[Impurity anions and ReO4 - molar ratio]]> <![CDATA[ReO4 - Extraction rate (%)]]> <![CDATA[NO3 - ]]> 3000 96.6 <![CDATA[SO4 2- ]]> 1500 94.35 <![CDATA[Cl - ]]> 3000 95.25 <![CDATA[PO4 3- ]]> 600 99.9 <![CDATA[I - ]]> 3000 97.59 <![CDATA[CO3 2- ]]> 1800 96.49

[0042] Example 3

[0043] Simulating Hanford tank waste liquid experiment: The spent fuel waste liquid with the composition shown in Table 2 was used as the simulated liquid for extraction experiment. A system with a total solution mass of 1 g was prepared in a 2 ml centrifuge tube, of which 0.5 g was the simulated waste liquid. The concentration of the ionic liquid [C8MIm]Cl was not fixed, the concentration of NaOH was fixed at 15wt%, and the remaining mass was supplemented with deionized water. The experimental steps of Example 2 were repeated, and the extraction rate of perrhenate was calculated. The results are shown in Table 3. It can be seen that a higher extraction effect can be achieved when the concentration of the ionic liquid is above 5wt%.

[0044] Table 2. Composition of spent fuel simulated waste liquid

[0045] Element Molar concentration (mol / kg) Sodium hydroxide 1.9738 Sodium aluminate 0.2304 Sodium nitrate 2.9454 Potassium Nitrate 0.0770 Sodium Nitrite 0.1997 Sodium sulfate 0.0500 Sodium carbonate 0.5977 Sodium Citrate 0.0510 Disodium EDTA 0.0239 Trisodium phosphate <![CDATA[5.293×10 -3 ]]>

[0046] Table 3 Extraction rate of perrhenate in spent fuel simulated waste liquid by ionic liquids of different concentrations

[0047]

[0048]

[0049] Example 4

[0050] A NaReO4 solution with a concentration of 10 to 10000 ppm is prepared as the extraction solution, which is first diluted by a certain multiple, and then measured by inductively coupled plasma spectroscopy (ICP-OES) to calculate its actual concentration. A system with a total solution mass of 1g is prepared in a 2ml centrifuge tube, of which 0.5g is the extraction solution, the concentration of the ionic liquid [C8MIm]Cl is fixed at 25wt%, the concentration of NaOH is fixed at 15wt%, and the remaining mass is supplemented with deionized water. Repeat the subsequent experimental steps of Example 2 to calculate the extraction rate of perrhenate. The results are shown in Table 4. It can be seen that regardless of the perrhenate concentration, an extraction effect of 99.5% can be achieved.

[0051] Table 4 Extraction rate of different perrhenate concentrations

[0052] <![CDATA[Feed solution ReO4 - Concentration (ppm)]]> Extraction rate E% 10 100 100 99.78 500 99.83 1000 99.88 6000 99.98 10000 99.99

[0053] Example 5 Stripping Experiment

[0054] In a 25mL separatory funnel, prepare a solution with a total mass of 15g with 25wt% ionic liquid [C8MIm]Cl, 15wt% NaOH, and 100ppm to be extracted. Add 5g of water and oscillate on a shaker at 200rpm for 1h to fully mix. Place it in a 55℃ oven for more than 3h. After phase separation, release the salt-rich phase from the lower end of the separatory funnel, record the mass, and use ICP-OES to detect the concentration. Pour out the ionic liquid-rich phase from the upper end of the separatory funnel and record the mass to calculate the ReO4 loaded in the ionic liquid-rich phase. - concentration.

[0055] A certain amount of ion-rich liquid phase was added to a 2 ml centrifuge tube, and a certain amount of various inorganic acids and corresponding salting-out agents (such as HNO3 and NaNO3, H2SO4 and Na2SO4, HCl and NaCl, etc.) were added. The centrifuge tube was sealed and then oscillated at 2000 rpm for 20 minutes on a multi-tube vortex mixer to fully mix them. The mixture was placed in a 55°C oven to observe whether the phases were separated. Among them, sulfuric acid, hydrochloric acid, and phosphoric acid did not form a two-phase aqueous solution at extremely high concentrations, so these systems could not be used for back extraction.

[0056] A system with a total solution mass of 1 g was prepared in a 2 ml centrifuge tube. The amount of ionic liquid-rich phase, concentrated HNO3, NaNO3 added, and the type of ionic liquid were changed respectively. The centrifuge tube was sealed and oscillated at 2000 rpm for 20 min on a multi-tube vortex mixer to fully mix it. It was placed in a 55 ° C oven for more than 3 h. After the phases were separated, the lower phase (salt-rich phase) of the two-phase water was sucked out with a syringe, its mass was weighed and diluted according to a certain ratio, and ReO4 in the salt-rich phase was determined by ICP-OES. - The stripping rate is calculated based on the content of rhenate. The specific stripping rate of perrhenate is calculated as follows: S = (w Re,s ×ms ) / (w Re,IL ×m IL );Where S is the stripping rate, w Re,s is the mass concentration of rhenium in the inorganic acid after stripping, m s w is the mass of inorganic acid after stripping; Re,IL is the mass concentration of rhenium in the aqueous phase to be stripped, m IL is the mass of the aqueous phase to be stripped.

[0057] The results are as follows Figure 3 and Figure 4 The specific data are shown in Table 5 and Table 6. The higher the nitric acid concentration, the better the stripping rate; the addition of salting-out agent sodium nitrate will promote the formation of a two-phase aqueous system, but inhibit the stripping effect; the stripping rate is different for different types of ionic liquids in the ionic liquid-rich phase, and C8MImCl is higher than C 10 The stripping rate of MImCl is higher, and the stripping rate reaches 77.75% under the optimal conditions.

[0058] Table 5 Stripping rate of [C8MIm]Cl under different conditions

[0059]

[0060] Table 6 Stripping rate under different ionic liquid types and nitric acid concentrations

[0061]

Claims

1. A method for extracting metal oxyacid radicals using imidazole-type ionic liquids, characterized in that: The method comprises the following steps: adding ionic liquid to alkaline wastewater containing metal oxygen-containing acid radicals, mixing to form a double aqueous phase, and separating the aqueous phase to realize extraction of the metal oxygen-containing acid radicals; The structural formula of the ionic liquid is as follows: Wherein, R is a C6-12 straight chain or branched chain alkyl group.

2. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The metal oxygen-containing acid radical is pertechnetate and / or perrhenate.

3. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The alkaline wastewater also includes any one or more inorganic salts of sodium hydroxide, potassium hydroxide, potassium nitrate, sodium nitrite, sodium aluminate, sodium nitrate, trisodium phosphate, sodium sulfate, sodium carbonate, sodium citrate, disodium EDTA, sodium iodide, and sodium chloride.

4. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The mass concentration of the ionic liquid in the aqueous two-phase is 5-40wt%.

5. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The hydroxide concentration in the aqueous two phase is 1-10 mol / L.

6. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The temperature for mixing to form a two-phase aqueous solution is 25-60°C.

7. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The alkaline wastewater also contains one or more impurity anions selected from sulfate, carbonate, nitrate, chloride, iodide, nitrite and aluminate, and the total molar concentration of the impurity anions is less than 3000 times that of the metal oxygen-containing acid radicals.

8. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 1, characterized in that: The method also includes the steps of adding nitric acid to the water phase for stripping to achieve the regeneration cycle of the ionic liquid and the recovery of the metal oxygen-containing acid radicals.

9. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 8, characterized in that: The nitric acid concentration in the stripping solution formed by adding nitric acid is above 4 mol / L; the stripping temperature is 25-55°C.

10. The method for extracting metal oxyacid radicals with imidazole-type ionic liquids according to claim 8, characterized in that: The mass fraction of the water phase in the stripping solution is 4-20wt%, the mass fraction of nitric acid is 15-50wt%, and the rest is water.

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