Method for separation of zirconium and hafnium by centrifugal extraction based on MIBK method

Abstract

The invention relates to the technical field of hydrometallurgy, and discloses a method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method, comprising the following steps: S1 extraction section: centrifugal extraction is performed after mixing an extractant, a feed liquid and an auxiliary extractant, and the extracted loaded organic phase formed after the extraction enters the next step, and the residual water phase is then converted and calcined to form nuclear-grade zirconium oxide; S2 washing section: centrifugal washing is performed after mixing the extracted loaded organic phase and a detergent, and the washed loaded organic phase formed after washing enters the next step, and the washed water phase returns to the S1 extraction section together with the feed liquid; S3 stripping section: centrifugal stripping is performed after mixing the washed loaded organic phase and a stripping agent, and the stripping water phase formed after stripping is precipitated and calcined to obtain hafnium oxide; the blank organic phase formed after stripping is neutralized and regenerated to recover thiocyanate and MIBK. The invention solves the technical problem that the existing process production flexibility of extracting and separating zirconium and hafnium using the MIBK method is low, and the requirements of small-scale customized production cannot be quickly met.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for separating zirconium and hafnium by centrifugal extraction based on a MIBK method. Background Art

[0002] Zirconium and hafnium are important materials in the nuclear industry. Hafnium is mainly used to make control rods of nuclear reactors due to its large thermal neutron cross section. Zirconium is mainly used to make cladding materials and other structural materials for uranium fuel elements in nuclear reactors due to its small thermal neutron cross section. Hafnium does not exist as a separate mineral in nature, and it always coexists in zirconium ores. Due to the lanthanide contraction, the atomic radius and ionic radius of zirconium and hafnium are similar, and their physical and chemical properties are very similar. It is very difficult to separate them from each other, and they are considered to be one of the most difficult pairs of elements to separate.

[0003] There are three main processes for separating zirconium and hafnium by solvent extraction, namely trialkyl (mixed) amine (N235) extraction and separation, tributyl phosphate (TBP) extraction and separation, and methyl isobutyl ketone (MIBK) extraction and separation. Among them, methyl isobutyl ketone (MIBK) extraction and separation is the process with the largest industrial capacity currently used for separating zirconium and hafnium. However, the MIBK method currently uses tower extraction in industry. If process parameters need to be adjusted, it takes a long time (about a week) to rebalance the system and ensure product stability, which cannot meet the market's growing high-end customized production requirements. Summary of the invention

[0004] The present invention aims to provide a method for centrifugal extraction and separation of zirconium and hafnium based on the MIBK method, so as to solve the technical problem that the existing process production flexibility of extracting and separating zirconium and hafnium using the MIBK method is low and cannot quickly meet the requirements of small-scale customized production.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method, comprising the following steps:

[0006] S1 extraction stage: the extractant, feed liquid and auxiliary extractant are put into the centrifugal extraction device for countercurrent extraction. The extracted loaded organic phase formed after extraction enters the next step. The auxiliary extractant is recovered from the residual water phase, and then converted and calcined to form nuclear grade zirconium oxide;

[0007] S2 washing section: the extracted loaded organic phase and the detergent are put into the centrifugal extraction device for countercurrent washing. The washed loaded organic phase formed after washing enters the next step, and the washing water phase returns to the S1 extraction section together with the feed liquid;

[0008] S3 stripping section: the washing loaded organic phase and the stripping agent are put into the centrifugal extraction device for countercurrent stripping. A part of the stripping water phase formed after stripping is circulated into the washing section to participate in the preparation of the detergent, and the other part is firstly used to recover the auxiliary extractant, and then precipitated and calcined to obtain hafnium oxide; a part of the blank organic phase formed after stripping is circulated into the extraction section as the extractant feed, and the other part is neutralized and regenerated to recover thiocyanate and MIBK.

[0009] The principles and advantages of this solution are:

[0010] As described in the background technology, the MIBK method is currently the technology with the largest application capacity in the separation of zirconium and hafnium industry. Compared with the N235 method and the TBP method, the MIBK method preferentially extracts hafnium with a smaller content into the organic phase during extraction, so that hafnium oxide and zirconium oxide with higher purity can be obtained with less extractant (the extractant is expensive).

[0011] The inventors of this application have found in long-term production that when the MIBK method is used in industry to separate zirconium and hafnium, most of the tower extraction separation technology is used, that is, extraction, washing and stripping are performed using an extraction tower. Although this technology is relatively mature, due to the large size of the extraction tower, if the production parameters need to be adjusted during the production process to produce products of different specifications, it will take about a week for the system to rebalance and stably produce qualified products, which results in a significant increase in production costs. Currently, most orders for zirconium oxide and hafnium oxide on the market are small-scale customized orders, and the characteristics of tower extraction separation technology are gradually unable to meet the needs of the current market.

[0012] Based on the above reasons, the inventors of the present application introduced centrifugal extraction technology into the MIBK method, and used a cascade extraction process to ensure the full separation of zirconium and hafnium, and to prepare zirconium oxide and hafnium oxide with higher purity. Compared with the current tower extraction technology, the centrifugal extraction machine used in the centrifugal extraction technology has a small liquid storage volume, a short residence time, a wide range of adaptable flow ratios, a fast mass transfer equilibrium speed, high mass transfer stage efficiency, easy start and stop, and can quickly reach steady-state operation after starting. When it is necessary to change production parameters or start production, it only takes 3-4 hours to achieve balanced and stable production, which greatly shortens the production time and reduces production losses, and can promptly meet customers' small-batch and different-purity zirconium and hafnium production needs.

[0013] At the same time, the inventors of the present application have found that, unlike other MIBK processes, the centrifugal extraction MIBK technology has high efficiency, high separation factor, high production intensity and strong reliability. At the same time, the centrifugal extraction technology based on the MIBK method can still ensure the purity of zirconium and hafnium obtained under a process with a lower extraction level, wherein the maximum purity of zirconium can reach less than 20ppm or even several ppm of hafnium in zirconium, and the maximum purity of hafnium can reach less than 1000ppm or even tens of ppm of zirconium in hafnium, which is much higher than the existing technology.

[0014] Preferably, as an improvement, the extractant in S1 is a MIBK solution for extracting saturated thiocyanate, wherein the thiocyanate concentration is 1.0-3.0 mol / L; the feed liquid is a mixed solution of zirconium oxychloride and hydrochloric acid, wherein the zirconium oxychloride concentration is 100-250 g / L, and the feed liquid acidity is 3.0-5.0 mol / L; and the auxiliary extraction liquid is a 3.0-9.0 mol / L ammonium thiocyanate solution.

[0015] In the present application, MIBK is used as an extractant to generate complexes with different stability with zirconium and hafnium in thiocyanate, wherein the thiocyanate complexing ability of hafnium is greater than that of zirconium, so hafnium is preferentially extracted into the organic phase. Since the content of hafnium in the feed solution is much less than that of zirconium, the preferential extraction of hafnium can significantly improve the purity level of hafnium. Ensuring the concentration of thiocyanate in the solution can improve the separation coefficient of zirconium and hafnium.

[0016] Preferably, as an improvement, the O / A (organic phase / aqueous phase) volume ratio in S1 is 0.5-5.0, wherein the organic phase is a MIBK solution saturated with thiocyanate, and the aqueous phase is a feed solution plus ammonium thiocyanate solution and a detergent.

[0017] In the present application, the O / A ratio can significantly affect the effect of centrifugal extraction separation. If the O / A ratio is too large, it will cause too much organic load phase to be extracted, making subsequent processing difficult and too much zirconium will be extracted, reducing the purity of the product. If the O / A ratio is too small, the extraction capacity will decrease, and the complete separation of zirconium and hafnium cannot be guaranteed.

[0018] Preferably, as an improvement, the total concentration of thiocyanate in the equilibrium aqueous phase in the S1 centrifugal extraction device is 1.0 to 5.0 mol / L.

[0019] In the present application, ensuring the total concentration of thiocyanate can improve the distribution coefficient of zirconium and hafnium, and can also improve the separation coefficient of zirconium and hafnium.

[0020] Preferably, as an improvement, the total acidity of the equilibrium aqueous phase in the S1 centrifugal extraction device is 0.5-4.0 mol / L.

[0021] In the present application, the acidity of the equilibrium aqueous phase is ensured so that the centrifugal extraction separation can be carried out at a suitable acidity. Because the reaction of MIBK extraction and separation of zirconium and hafnium is related to acidity, the hafnium separated at different acidities exists in different forms. In the present application, it is necessary to ensure that the reaction is carried out at a higher acidity so that the hafnium exists in the form of thiocyanate.

[0022] Preferably, as an improvement, the detergent in S2 is formed by compounding hydrochloric acid and the stripping water phase in S3, the concentration of hydrochloric acid is 1.0-6.0 mol / L, and the concentration of sulfate ions in the detergent is 50-200 g / L.

[0023] In the present application, some zirconium remains in the stripping aqueous phase in S3, so it can be used as a detergent to improve the separation and recovery effect. Hydrochloric acid can be used as a detergent to wash zirconium out of the extraction-loaded organic phase, further improving the separation effect of zirconium and hafnium.

[0024] Preferably, as an improvement, the O / A volume ratio in S2 is 0.5 to 5.0, wherein the organic phase is the extraction-loaded organic phase, and the aqueous phase is the detergent solution.

[0025] In this application, the O / A volume ratio in S2 plays a key role in effective washing. If the O / A ratio is too small, it will cause waste of washing liquid, and if the O / A ratio is too large, it will lead to unsafe washing.

[0026] Preferably, as an improvement, the stripping agent in S3 is a sulfuric acid solution, the concentration of the sulfuric acid solution is 1.0-6.0 mol / L, the O / A volume ratio in S3 is 0.5-5.0, the organic phase is the washing load organic phase, and the aqueous phase is the stripping agent solution.

[0027] In the present application, sulfuric acid as a stripping agent can strip hafnium from the organic phase into the aqueous phase, ensuring the subsequent production and preparation of hafnium oxide. The O / A volume ratio in S3 needs to be maintained in an appropriate range to ensure that the hafnium in the loaded organic phase can be fully stripped.

[0028] Preferably, as an improvement, the reaction temperature of the centrifugal extraction device is 15-25°C.

[0029] In the present application, it is necessary to ensure that the temperature of the centrifugal extraction device is low, reduce the decomposition and polymerization of the auxiliary extraction agent ammonium thiocyanate, and avoid the generation of precipitates adhering to the device.

[0030] Preferably, as an improvement, the reaction order of the extraction section is 10 to 15, the reaction order of the washing section is 5 to 10, and the reaction order of the stripping section is 3 to 5.

[0031] In the present application, the reaction technologies of the extraction section, the washing section and the stripping section are lower than those of the prior art, but the separation effect produced is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a schematic diagram of the extraction reaction of the method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method of the present invention. DETAILED DESCRIPTION

[0033] The following is further described in detail through specific implementation methods:

[0034] The present invention provides a method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method. First, a relevant solution is prepared:

[0035] Feed liquid: Take zirconium oxychloride solid, add deionized water to dissolve, then add hydrochloric acid solution to mix. After mixing, the acidity of the feed liquid is 1.0-5.0 mol / l, and the ZrOCl2 concentration is 100-250 g / l.

[0036] Extraction agent: Take MIBK solution, add thiocyanate solution to it until saturated to prepare extraction agent, the concentration of MIBK in the extraction agent is 1.0-3.0 mol / L.

[0037] Extraction aid: prepare ammonium thiocyanate solution with a concentration of 3.0-9.0 mol / l.

[0038] Detergent: Prepare a hydrochloric acid solution with a concentration of 1.0-6.0 mol / l, add an appropriate amount of stripping water phase to make SO4 2- The concentration is 50-200g / l.

[0039] Stripping solution: prepare a sulfuric acid solution with a concentration of 1.0 to 6.0 mol / l.

[0040] Extraction separation includes the following steps:

[0041] S1 extraction stage: the extractant, feed liquid and auxiliary extractant are put into the centrifugal extraction device for countercurrent extraction. The extracted loaded organic phase formed after extraction enters the next step. After the auxiliary extractant is recovered from the residual water phase, it is precipitated, converted and calcined to form nuclear grade zirconium oxide;

[0042] Specifically, the prepared extractant is added from the organic phase feed port of the centrifugal extraction device, and the feed liquid and the auxiliary extractant are added from the corresponding feed ports of the feed stage of the centrifugal extraction device, respectively. The volume ratio of the organic phase (extractant) added to the extraction device and the volume of the water phase (feed liquid, ammonium thiocyanate solution and washing water phase from the washing section) is controlled to be 0.5-5.0, the temperature of the extraction device needs to be maintained at 15-25°C, and the number of extraction stages is 10-15. When the centrifugal extraction step is completed, most of the hafnium and a small part of the zirconium in the feed liquid are extracted into the extraction load organic phase, and the extraction load organic phase enters the washing section from the water phase feed stage of the centrifugal extraction device. Most of the zirconium remains in the raffinate water phase, which is discharged from the organic phase feed stage of the centrifugal extraction device, and the ammonium thiocyanate therein is recovered and used as an auxiliary extractant. The remaining raffinate water phase is precipitated and converted to obtain basic zirconium sulfate, and finally calcined to obtain high-purity zirconium oxide.

[0043] S2 washing section: the extracted loaded organic phase and the detergent are put into the centrifugal extraction device for countercurrent washing. The washed loaded organic phase formed after washing enters the next step, and the washing water phase, the feed liquid and the auxiliary extraction agent enter the S1 extraction section;

[0044] Specifically, the extracted loaded organic phase discharged from S1 is discharged into the centrifugal extraction device of the washing section, and then the prepared detergent is added, the volume ratio of the extracted loaded organic phase to the detergent is controlled to be 0.5-5.0, the washing temperature is maintained at 15-25° C., and the washing stages are 5-10. The zirconium contained in the extracted loaded organic phase is washed into the washing water phase, and the washed loaded organic phase formed after washing enters the S3 stripping section. Since the washing water phase contains zirconium elements, it is recycled into the S1 extraction section for re-extraction.

[0045] S3 stripping section: the washing loaded organic phase and the stripping agent are put into the centrifugal extraction device for countercurrent stripping. A part of the stripping water phase formed after stripping is circulated into the washing section to participate in the preparation of the detergent, and the other part is first used to recover the auxiliary extractant, and then precipitate and calcine to obtain hafnium oxide; a part of the blank organic phase formed after stripping is circulated into the extraction section as the extractant feed, and the other part is neutralized and regenerated to recover thiocyanate and MIBK.

[0046] Specifically, the washing load organic phase generated in S2 is discharged into the centrifugal extraction device of the stripping section, and then the prepared stripping agent is added to the centrifugal extraction device, the volume ratio of the washing load organic phase to the stripping agent is controlled to be 0.5-5.0, the stripping temperature is maintained at 15-25°C, and the stripping level is 3-5. After stripping, hafnium is stripped into the stripping water phase, a small part of the stripping water phase is used to prepare the detergent, and most of the stripping water phase is recovered after ammonium thiocyanate is recovered, and then ammonia water is added to it to precipitate hafnium hydroxide, and finally high-purity hafnium oxide is obtained by calcination. The blank organic phase formed after stripping is saturated with a certain concentration of thiocyanic acid, a part of which is recycled into the extraction section and used directly as an extractant, and another part is neutralized and regenerated by adding ammonia water to recover thiocyanate and MIBK. The regenerated and recovered thiocyanate is circulated into the extraction section as an auxiliary extractant feed, and the regenerated and recovered MIBK can be used as an organic feed for the residual water phase and the stripping water phase to recover the auxiliary extractant.

[0047] The data of the embodiments and comparative examples of the present application are recorded in the table below. The embodiments and comparative examples set in the present application are only adjusted in the relevant technologies as comparative experiments, and the operations in other steps remain the same.

[0048]

[0049] From the comparative experimental results, it can be seen that the difference between Comparative Example 1 and the embodiment is that the acidity of the feed solution is reduced, resulting in a significant decrease in the purity of the separated hafnium oxide. The reason is that the acidity of the feed solution reduces the separation coefficient and distribution coefficient of zirconium and hafnium, resulting in incomplete separation of zirconium and hafnium in the extraction separation stage.

[0050] The difference between Comparative Example 3 and the Example is that the reaction order is reduced. Although the separation purity of zirconium oxide can be guaranteed, the separation coefficient of hafnium oxide is significantly reduced.

[0051] The difference between Comparative Example 4 and the embodiment is that the O / A ratio in each stage is changed, which leads to a decrease in the purity of both hafnium oxide and zirconium oxide.

[0052] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method, characterized in that: The following steps are involved: S1 extraction stage: the extractant, feed liquid and auxiliary extractant are put into the centrifugal extraction device for countercurrent extraction. The extracted loaded organic phase formed after extraction enters the next step. The auxiliary extractant is recovered from the residual water phase, and then converted and calcined to form nuclear grade zirconium oxide; S2 washing section: the extracted loaded organic phase and the detergent are put into the centrifugal extraction device for countercurrent washing. The washed loaded organic phase formed after washing enters the next step, and the washing water phase returns to the S1 extraction section; S3 stripping section: the washing loaded organic phase and the stripping agent are put into the centrifugal extraction device for countercurrent stripping. A part of the stripping water phase formed after stripping is circulated into the washing section to participate in the preparation of the detergent, and the other part is firstly used to recover the auxiliary extractant, and then precipitated and calcined to obtain hafnium oxide; a part of the blank organic phase formed after stripping is circulated into the extraction section as the extractant feed, and the other part is neutralized and regenerated to recover thiocyanate and MIBK; The extractant in S1 is a MIBK solution for extracting saturated thiocyanate, wherein the concentration of thiocyanate is 1.0-3.0 mol / L; the feed liquid is a mixed solution of zirconium oxychloride and hydrochloric acid, wherein the concentration of zirconium oxychloride is 100-250 g / L, and the acidity of the feed liquid is 3.0-5.0 mol / L; the auxiliary extraction liquid is a 3.0-9.0 mol / L ammonium thiocyanate solution; the detergent in S2 is formed by compounding hydrochloric acid and the stripping water phase in S3, wherein the concentration of hydrochloric acid is 1.0-6.0 mol / L, and the concentration of sulfate ions in the detergent is 50-200 g / L; the stripping agent in S3 is a sulfuric acid solution, wherein the concentration of the sulfuric acid solution is 1.0-6.0 mol / L; The reaction order of the extraction section is 10 to 15, the reaction order of the washing section is 5 to 10, and the reaction order of the stripping section is 3 to 5.

2. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 1, characterized in that: The O / A (organic phase / aqueous phase) volume ratio in S1 is 0.5-5.0, wherein the organic phase is a MIBK solution saturated with thiocyanate, and the aqueous phase is a feed solution plus an ammonium thiocyanate solution and a washing aqueous phase.

3. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 2, characterized in that: The total concentration of thiocyanate in the equilibrium aqueous phase of the S1 centrifugal extraction device is 1.0-5.0 mol / L.

4. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 1, characterized in that: The total acidity of the equilibrium aqueous phase in the S1 centrifugal extraction device is 0.5-4.0 mol / L.

5. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 1, characterized in that: The O / A volume ratio in the S2 is 0.5-5.0, wherein the organic phase is the extraction loading organic phase, and the aqueous phase is the detergent solution.

6. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 1, characterized in that: The O / A volume ratio in S3 is 0.5-5.0, wherein the organic phase is the washing load organic phase, and the aqueous phase is the stripping agent solution.

7. The method for separating zirconium and hafnium by centrifugal extraction based on the MIBK method according to claim 1, characterized in that: The reaction temperature of the centrifugal extraction device is 15-25°C.

Images