RU2521561C2 - Extraction separation of zirconium and hafnium - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to hydrometallurgy of zirconium and hafnium. Proposed method comprises total extraction of zirconium and hafnium from initial solution nitrate using the tribytilphosphate solution in hydrocarbon diluent. Then, they are separated at decrease in acidity with extraction of zirconium from hafnium re-extract by return extragent with combination of both extracts in the flow and weak-acid zirconium re-extraction with subsequent recovery of extragent. After total extraction, combined extract is flushed with nitric acid solution with concentration equal to nitric acid content in initial solution. Then, hafnium re-extraction is performed. Now, a portion of hafnium re-extract flow is returned back to cycle start for it to be fed along with initial solution at preset acidity while other portion is directed to additional extraction of zirconium.

EFFECT: high-purity concentrated hafnium, decreased amount of reagents for further processing.

7 cl, 2 dwg, 2 tbl, 2 ex

Description

The present invention relates to the field of hydrometallurgy of zirconium and hafnium and can be used to obtain pure compounds of zirconium and hafnium extraction method.

Various methods are known for the extraction of zirconium and hafnium from nitric acid solutions using tributyl phosphate (TBP) with a concentration of 50-70% by volume in various hydrocarbon diluents and their separation; moreover, the extraction process is carried out at a concentration of nitric acid of 360-530 g / l, depending on the concentration of TBP. These methods differ mainly in the methods of separation of zirconium and hafnium.

Thus, according to the method (JS El-Jamani, FA Abd El-Aleim "Refining of zirconium by tributyl phosphate in pulsed packed columns", Hydrometallurgy, 13 (1984), p.213-220), both components are first removed from the solution with 60% tributyl phosphate (TBP) in sulfonated kerosene from a solution containing 56 g / l Zr, 0.765 g / l Hf [1.2% of Σ (Zr + Hf)], 8.39 mol / l HNO ₃ - in the ratio of organic and aqueous phases 1: 1 in the pulsation column. After that, hafnium is subsequently reextracted with a solution of 315 g / l HNO ₃ and zirconium with water, and the hafnium reextract is washed additionally from zirconium with the same extractant. Get a commodity hafnium re-extract with a concentration of 0.35 g / l Zr and 0.77 g / l Hf [68.8% to Σ (Zr + Hf)] and a zirconium re-extract with a concentration of Zr - 48.9 g / l, Hf - 0.15 g / l [0.03% to Σ (Zr + Hf)], 2.65 mol / l HNO ₃ . The yield of zirconium in the product is only 90%. The main disadvantages of this method are its low productivity, low yield of zirconium and its insufficient hafnium purity, low absolute and relative content of hafnium in the hafnium product.

In another method (RF Patent No. 2190677, Bull. 29, 2002), zirconium is selectively extracted, and hafnium residues are washed from the extract into the raffinate by acid washing of the extract, the washing solution being added to the initial solution in the extractor duct, and to displace hafnium in this operation part of the zirconium reextract after acidification of this fraction is used in the aqueous phase as a washing solution. The raffinate is evaporated, after which hafnium is recovered from the bottom residue in a separate cycle. The method is rather cumbersome, and the yield of hafnium in it does not exceed 80% due to the formation of hafnium and zirconium on the residue with decomposition products of TBP formed during evaporation of the raffinate.

Closest to the claimed invention is the method used in production for the extraction of zirconium and hafnium using a pre-acidified organic solution of 70% TBP in saturated hydrocarbons and their primary selective separation with the removal of hafnium into a separate product before zirconium is re-extracted by adjusting the acidity of the stripping agent in the range of 180-220 g / l HNO ₃ and the relative consumption of stripping agent in the range of O: B = 5 ÷ 7: 1, followed by extraction washing of the hafnium re-extract from zirconium at O: B = 0.5 ÷ 1: 1 and adding by draining this extract in the duct to a joint extract of these elements, followed by reextraction of zirconium; the final operation of the process is the regeneration of the circulating extractant (Shtutsa MG, Filippov VB, Koparulina ES and others. Extraction scheme for producing zirconium of nuclear purity // Chemical technology, 2005, No. 4. p.22-25) . The process is carried out in centrifugal extractors. This method is taken by us as a prototype. The main operations of this method are patented by the same authors (RF Patent No. 2278820, Bull. 18, 2006).

The final concentration and purification of hafnium in production can be achieved by crystallization of its oxynitrate during the evaporation of the corresponding reextract (RF Patent No. 2225841, Bull. 8, 2004).

The disadvantage of the prototype method is the low concentration of hafnium (actually 10-12 g / l with a solubility limit of up to 90 g / l), as well as insufficient purification of hafnium from zirconium and other associated impurities that are completely washed from the extract to hafnium re-extract, and cleaning them requires the organization of an additional cycle of extraction refining of hafnium and / or evaporation of the final hafnium product with crystallization and separation of solid hafnium oxynitrate. Thus, the method does not provide high-purity content of impurity elements of concentrated solutions of hafnium. There is no information on the regeneration mode of the circulating extractant.

The present invention solves the problem of developing a scheme for producing a high-purity concentrated product of hafnium directly in the framework of one cycle of extraction separation of zirconium and hafnium, as well as conditions are provided for reducing the number of reagents for its further processing.

To achieve these goals, we propose a method of extraction separation of zirconium and hafnium, including the total extraction of zirconium and hafnium from a nitric acid solution using a solution of tributyl phosphate in a hydrocarbon diluent, their separation with a decrease in acidity with the extraction of zirconium from a hafnium reextract with a reverse extractant with the combination of both extracts in a weak and a duct re-extraction of zirconium followed by regeneration of the extractant, in which, after total extraction, acid washing the co-extract with a solution of nitric acid with a concentration equal to the content of nitric acid in the initial solution, then hafnium is reextracted, after which part of the hafnium reextract stream is returned to the beginning of the cycle to be fed along with the initial solution while maintaining the combined acidity, and the rest is directed to additional extraction of zirconium.

This method differs from the prototype in two technological methods. The first of these consists in applying the return of a part of the hafnium reextract, which was not subjected to additional extraction of zirconium, into the cycle, that is, the return of a part of the reextract to earlier stages of the process without violating its stability.

Best results are achieved when up to 90% of hafnium re-extract is returned.

It is optimal that the combined stock solution fed to the extraction contains 400-430 g / l HNO ₃ at a concentration in the TBP extractant of at least 70% vol.

The maximum concentration of hafnium in the stream returned to the cycle is controlled by the flow rate of a stripping agent containing 180-220 g / l HNO ₃ within the solubility of its oxynitrate.

The second method consists in the fact that the combined zirconium and hafnium extract obtained by extraction from the initial solution is subjected to washing with an acid with a concentration approximately equal to that in the initial solution.

In this case, it is optimal that the flow rate of an aqueous solution of nitric acid be with a ratio of organic and aqueous phases (O: B): O: B≤10: 1, but not lower than O: B = 4: 1. To carry out this operation, an additional 3-6 extraction steps are installed. This allows you to significantly increase the cleaning of noticeably extracted impurities, such as titanium or iron, as well as other corrosion products, ore contaminants (niobium) and / or introduced with water (calcium), but does not increase the cleaning of zirconium. In this case, the total flow of hafnium reextract is approximately half that of the prototype.

Part of the hafnium reextract is subjected to extraction extraction of zirconium, however, due to the rupture of the flow of the organic phase, the relative consumption of extractant for this operation is three times lower than the flow of the aqueous phase, and in relation to the prototype is 5-6 times lower. This makes it possible to increase the concentration of hafnium in 6-8 times in comparison with the prototype.

Reextraction of zirconium after re-extraction of hafnium is carried out with a lower consumption of stripping agent.

Then, the extractant is regenerated in an alkaline medium with a complexing agent to remove TBP decomposition products and a certain amount of zirconium held by them. It is enough to regenerate 10-35% vol. working extractant. To do this, use a solution of 0.25-0.5 mol / L Na ₂ CO ₃ , however, it is more effective to use a solution of 0.1-1 mol / L NaOH in a mixture with 0.1-0.6 mol / L H ₂ O ₂ , moreover, a solution of 1-4 mol / L NaOH is additionally introduced into the first step along the extractant to neutralize the nitric acid brought with the circulating extractant after zirconium reextraction. To wash additional extraction of zirconium from hafnium re-extract, a regenerated extractant should be used after acidification of the regenerated fraction, carried out separately.

In general, the implementation of the claimed technological methods allows to reduce the content of impurities in the hafnium reextract from 1.5% to less than 0.1% while increasing its concentration to 75-80 g / l, which is close to the solubility of hafnium oxy nitrate of 90 g / l.

The invention is illustrated by figures, which depict:

Figure 1 - Scheme illustrating the method of extraction concentration of hafnium with separation from zirconium in accordance with the prototype. In the diagram, the numbers indicate the flow codes and italic numbers of the extraction steps. The decoding of the codes indicating the characteristics and composition of the flows is presented in table 1, while the flow of the initial solution is taken as 100% flow rate. In bold, codes of operations carried out sequentially along the extractant and described in example 1 are given.

Figure 2 - Scheme illustrating the method of extraction separation of zirconium and hafnium in accordance with the invention. In the diagram, numbers indicate the numbers of steps and codes of flows. The decoding of the codes indicating the characteristics and composition of the flows is presented in table 2, while the flow of the initial solution is taken as 100% flow rate. The designations of the operations are the same as in figure 1. Additional operations are highlighted in the text in Example 2 ..

The foregoing can be illustrated by the following examples:

Example 1

As a basis for comparison, the prototype method is adopted. The scheme of the extraction cascade is presented in figure 1, and the characteristics of the flows in table 1.

As a starting point, a solution obtained by dissolving zirconium hydroxide in nitric acid with a content of 50 g / l Zr, 5.5 g / l Hf, 360-380 g / l HNO ₃ ; other impurities <3 g / l.

The process consists of the following operations in the course of a circulating extractant:

100 - acidification of the circulating extractant (a mixture of regenerated extractant and extractant after zirconium reextraction) with a solution of nitric acid to obtain an acidified raffinate and an acidified circulating extractant (with a high residual content of zirconium and hafnium);

110 - the total extraction of zirconium and hafnium from the initial solution with an acidified reverse extractant, with obtaining the total extraction raffinate and total extract;

130 - primary re-extraction of hafnium from the total extract and the extract of the extraction with a reextracting solution, to obtain an intermediate re-extract of hafnium and an extract of zirconium;

140 - additional extraction of zirconium from an intermediate hafnium reextract with an acidified circulating extractant to obtain a commodity hafnium reextract and an extra extract combined in the duct with a total zirconium and hafnium extract;

150 - re-extraction of zirconium from the zirconium extract with a reextracting solution, to obtain a re-extract of zirconium and an extractant solution;

160 - regeneration of the circulating extractant;

210 - evaporation of the hafnium reextract to obtain hafnium oxynitrate.

Example 2

The inventive method. The diagram is presented in figure 2, and the characteristics of the flows in table 2.

Operations 100, 110, 130, 140, 150, 160 are similar to those described in example 1.

A solution obtained by dissolving zirconium hydroxide in nitric acid with the addition of a part of hafnium reextract is added to the circuit as a starting solution to obtain a solution containing 37.6 g / l of zirconium, 18 g / l of hafnium, 415 g / l of nitric acid.

In contrast to the prototype, operation 120 was introduced into the scheme — washing the extract into which nitric acid with a concentration of 415 g / l was supplied at a relative flow of O: B = 9–10: 1.

For the preparation of washing and stripping solutions, distilled water / condensate of the secondary rectification vapor of the regenerated nitric acid and pure nitric acid are used.

After the initial re-extraction of hafnium, 75-80% of the intermediate re-extract stream, in contrast to Example 1, is returned to mixing with the initial solution.

The commodity part of hafnium re-extract is directed to the operation of additional extraction of zirconium with a part of the regenerated fraction of the circulating extractant at O: B = 0.25 ÷ 0.5: 1. The obtained commercial product hafnium contains 70-80 g / l Hf, 0.05 g / l Zr, the sum of the remaining impurities <0.01 g / l, i.e. the hafnium content is ~ 99.9%.

Then, partial regeneration (10-35% vol.) Of the extractant solution is carried out. Regeneration is carried out at 4-7 steps with alkaline and alkaline peroxide solutions, using a solution of 0.1-1.0 mol / L NaOH in a mixture with 0.1-0.6 mol / L H ₂ O ₂ , and in the first step, in the course of the extractant, a solution of 1-4 mol / L NaOH is additionally introduced into the duct to neutralize the nitric acid brought with the circulating extractant after zirconium re-extraction. The regenerated extractant is acidified. As a result of the regeneration of the extractant, a spent alkaline peroxide solution and an acidified regenerated extractant are obtained, which is used mainly to extract zirconium from hafnium reextract, while its excess is attached to the extractant after zirconium reextraction, forming a reverse extractant.

The obtained commercial hafnium re-extract is transferred directly to the alkaline precipitation of hafnium hydroxide and then to the finished product.

Table 1. Process flows of the extraction unit and the primary separation of zirconium and hafnium (according to the prototype). Stream code Characteristic Relative consumption,% The concentration of components, g / l HNO ₃ Zr Hf Ti Ca Fe 102 Circulating extractant 227 30-50 0.5 103 Raffinate Acidification 56 110-150 - 105 Nitric acid solution 59 400-450 - 106 Acidified extractant 232 105-125 0.5 111 Stock solution one hundred 360-380 fifty 5.5 0.08 0.08 0,07 112 Acidified extractant for total extraction of Zr + Hf 186 105-125 0.5 113 Total extraction raffinate 98 350-370 0.1 0.05 0.05 0.05 0.06 114 Total Zr + Hf Extract 189 110-130 27 2.9 0.01 0.01 0.006 134 Zr extract 234 90-110 22 0.002 0.001 0.001 0,0005 135 Stripping Agent Hf 45 170-190 - 142 Acidified Extractant for Zr Recovery 46 105-125 0.5 149 Commodity re-extract Hf 43 280-300 0.2 12.6 0,03 0,03 0.002 155 Reextractor Zr 86 3-15 - 156 The extractant after stripping Zr 227 30-50 0.8 159 Reextract Zr 84 170-190 56 0.004 0.001 0.002 0.001 161 Alkaline peroxide solution (30 g / l NaOH + 15 g / l H ₂ O ₂ ) 16 - 162 Regeneration Extractant 45 30-50 0.8 163 Spent alkaline peroxide solution 27 - 1.3 166 Regenerated Extractant 45 0-20 0 167 Alkaline solution (70 g / l NaOH) eleven -

Table 2. Process flows node extraction and deep separation of zirconium and hafnium (according to the present method) Stream code Flow characteristic Relative consumption,% The concentration of components, g / l HNO ₃ Zr Hf Ti Ca Fe 101 Zirconium-hafnium hydroxide * - 300 3.3 0.48 0.48 0.42 102 Circulating extractant 178 30-50 0.2 103 Raffinate Acidification 57 150-200 0.5 0.01 105 Nitric acid solution 59 400-430 106 Acidified recycle extractant 182 110-130 0.2 107 Nitric acid * fourteen 750 111 Stock solution 140 400-420 37,4 16.5 0.06 0.06 0.05 112 Acidified extractant for total extraction of Zr + Hf 182 110-130 0.2 113 Total extraction raffinate 159 350-370 0.1 0.05 0.05 0.05 0.04 124 Total Zr + Hf Extract 183 110-130 28 12.6 125 Wash solution 23 410-420 134 Zr extract 184 80-100 27 0.001 135 Stripping Agent Hf 27 180-220 137 Hf Return Reextract 21 350-370 6.8 81 139 Hf Intermediate Reextract 28 350-370 6.8 81 142 Acidified Regenerated Extractant for Zr Extraction 2,5 110-130 0.2 146 Intermediate Zr Extract 2,5 110-130 twenty 19.5 147 Re-extract of Hf for additional extraction of Zr 7.5 350-370 6.8 81 149 Commodity re-extract Hf 7.5 330-340 0.01 73.3 0.001 0.001 0.001 155 Reextractor Zr 73 3-15 156 The extractant after stripping Zr 180 25-45 0.8 159 Reextract Zr 75 140-150 66.5 0.004 0.001 0.001 0.001 161 Alkaline peroxide solution 16 - 162 Regeneration Extractant 45 25-45 0.8 163 Spent alkaline peroxide solution 27 - 1.3 164 Acid Tail Solution fourteen 90-100 165 Acid for washing the regenerated extractant 16 400-460 166 Regenerated Acid Extractant 45 110-130 167 Alkaline solution eleven - 172 Excess regenerated extractant 43 110-130 * - are taken in the ratio required to obtain the initial solution 111.

Claims (7)

1. The method of extraction separation of zirconium and hafnium, including the total extraction of zirconium and hafnium from a nitric acid stock solution using a solution of tributyl phosphate in a hydrocarbon diluent, their separation with a decrease in acidity with the extraction of zirconium from a hafnium reextract with a reverse extractant with the combination of both extracts in a duct and weak acid reduct followed by regeneration of the extractant, characterized in that after the total extraction, acid washing of the joint ext act with a solution of nitric acid with a concentration equal to the content of nitric acid in the initial solution, then hafnium is reextracted, after which part of the hafnium reextract stream is returned to the beginning of the cycle to supply it together with the initial solution while maintaining the specified acidity of the combined stream, and the rest is directed to additional extraction zirconium. 2. The method according to claim 1, characterized in that up to 90% of the hafnium re-extract is returned to the cycle. 3. The method according to claim 1, characterized in that the acid washing of the joint extract is carried out with the flow rate of an aqueous solution of nitric acid at a ratio of organic and aqueous phases (O: B): O: B <10: 1, but not lower than O: B = 4: 1, with the acidity of this solution not lower than in the initial solution. 4. The method according to claim 1, characterized in that the combined stock solution fed to the extraction contains 400-430 g / l HNO ₃ at a concentration of tributyl phosphate in the extractant of not less than 70% vol. 5. The method of claim 1, characterized in that the maximum concentration of hafnium in the stream returned to the cycle is controlled by the flow rate of a stripping agent containing 180-220 g / l HNO ₃ within the solubility of its oxynitrate. 6. The method according to claim 1, characterized in that for the extraction of zirconium from the hafnium reextract, a part of the circulating extractant is used immediately after its regeneration and acidification, it is supplied in relation to the hafnium reextract O: B = 0.25 ÷ 0.5: 1. 7. The method according to claim 1, characterized in that the regeneration carried out in an alkaline medium in the presence of a complexing agent is subjected to 10-35% of the extractant stream, followed by separate acidification of this fraction.

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