RU2274486C2 - Metal extraction process - Google Patents

Abstract

FIELD: metal recovery processes.

SUBSTANCE: process comprises keeping metal-containing matrix in high-pressure chamber within solvent medium in presence of water and fluorine-containing organic acid followed by accumulation of extracted metal in solution. Organic acid utilized is selected from di(octafluoroformyl)phosphoric acid, di(dodecafluoroheptyl)phosphoric acid, and mixture of acid with trialkyl phosphate. Solvent is used in its liquid state.

EFFECT: enabled recovery of radionuclides from solid phase.

2 cl, 4 tbl, 4 ex

Description

The invention relates to the field of extraction of metals from a solid phase using solutions of extractants in low boiling liquids or liquefied gases at elevated pressure (in particular liquid carbon dioxide) and can be used for analytical purposes or for the decontamination of radioactive waste.

Known methods for supercritical extraction of various metals (Wai, CM; Smart NG; Phelps, C. US Patent 5606724 A. Publ. Feb 25, 1997; Beckman, EJ; Russel AJ US Patent 5641887 A. Publ. June 24, 1997; Wai, CM Patent PCT International; WO 9533541 A1. Publ. December 14, 1995), allowing the extraction of various metals, such as uranium, rare earth elements. According to the proposed methods, a matrix containing metals (sand, paper, stainless steel surface, etc.) is treated with a complexon dissolved in supercritical carbon dioxide. Various organic compounds were used as complexones; the best results were observed for fluorinated β-diketones.

There is also a known method (Murzin A.A., Starchenko V.A., Shadrin A.Yu. et al. Report "Decontamination of Real World Contaminated Stainless Steel Using Supercritical CO ₂ "Spectrum'98, Denver, Colorado, USA, September 13 -18, 1998, Proceedings, American Nuclear Society Inc, USA, 1998, p. 94-98). In this method, a cesium containing matrix (sand, paper, stainless steel surface, etc.) is treated with a mixture of crown ether and di-2-ethylhexylphosphoric acid dissolved in supercritical carbon dioxide. The method allows to extract cesium and transuranic elements (TUE) from various matrices.

A known method of supercritical fluid extraction of cesium (C.M. Wai, Y.M. Kulyako, B.F. Myasoedov // Mendeleev Communications. (1999) 5, N9, pp. 180-181) using fluorinated carboxylic acids and crown ethers.

A known method of supercritical fluid extraction of metals, comprising holding the matrix containing the metal in a high pressure chamber in a supercritical solvent in the presence of water, polyfluorocarboxylic acids and polyethylene glycols (Babain V.A., Kiseleva R.N., Murzin A.A., and other RF Patent 2168779 "Method for supercritical fluid extraction of metals". BI No. 16. 06/10/2001. IPC G 21 F 9/28) - prototype.

A common drawback of all previously proposed methods, as well as the prototype method, is that with their help it is possible to extract metals such as cesium and strontium only in supercritical carbon dioxide at high pressures (100-400 atm) and using additional complexones - crown esters or polyethylene glycols. The extraction of these metals is very important, because their isotopes - cesium-137 and strontium-90 make the main contribution to the radioactivity of spent nuclear fuel. The use of crown ethers or polyethylene glycols leads to difficulties in the re-extraction of metals, which makes it difficult and in some cases makes regeneration of the extractant practically impossible.

The use of high pressures - 100-400 atm creates difficulties, especially in relation to radiochemical processes. Safety requirements for the operation of high-pressure installations (more than 100 atm) are much stricter and greatly increase the cost of the process. Depressurization during an accident at such pressures will lead to the release of radionuclides into the environment. Ways to prevent such an outbreak are complex and greatly increase the cost of work.

The task of the invention is the provision of extraction from the solid phase of various radionuclides, including cesium and strontium at a pressure of not higher than 70 atm.

The proposed method consists in treating a matrix (for example, a solid salt, a stainless steel surface or a fabric contaminated with radionuclides) with a liquid at a moderately elevated pressure (30-70 atm), a solvent containing an organic acid, such as di-polyfluoroalkylphosphoric acid, or its mixture with octanol or TBP, followed by passing a liquid solvent through a high-pressure chamber to ensure complete extraction, collecting the extract in an evaporator and evaporating the liquid solvent from the extract.

The following are the formulas of the acids used.

When using the proposed method, the degree of extraction is achieved the same, and sometimes higher than in the prototype method, while crown ethers or polyethylene glycols are not used and the process takes place at a pressure of less than 100 atm. Therefore, the regeneration of the extractant is reduced to a simple washing of the metal from the organic phase using acid. An additional advantage of the proposed method is the ability to simultaneously extract cesium and strontium. When extraction with carboxylic acids or dialkylphosphoric acids, the extraction of strontium together with cesium is impossible.

Carbon dioxide can be used as a liquid solvent. However, you can use other carriers, such as, for example, freons. There was an opinion that the extraction efficiency in liquid carbon dioxide is ten times lower than under supercritical conditions, which turned out to be incorrect in this case - the extraction efficiency is almost the same as under supercritical conditions.

As acids, it is possible to use di- (polyfluoroalkyl) phosphoric acids, while the highest degrees of extraction are observed for di- (polyfluoroalkyl) phosphoric acids with a C ₅ -C ₇ alkyl radical length.

The following examples illustrate the scope and application of the method. The experiments were performed as follows: a) a radionuclide was previously applied to the surface of the sample; b) acid and (or) octanol were applied to the same sample, placed in a 50 ml extraction chamber and carbon dioxide containing 0.02% vol. was injected. water, the chamber was left under these conditions for 20 minutes, after which 200 ml of pure liquid solvent was passed through the cell, the extract was collected, and the liquid solvent was evaporated at a temperature of 60 ° C. The pressure was 50-70 atm.

Example 1

The surface of the cotton sample containing 100 μg of cesium nitrate per 10 cm ² was treated as described above. Carbon dioxide was used as a liquid solvent. Extraction of cesium by the prototype method and the proposed method are given in table 1

Table 1
Extraction of cesium nitrate from the surface of cotton with solutions of acids in carbon dioxide (60 atm., 25 ° C, 100 μg CsNO ₃ ) Acid H ₂ O, μ1 OctOH, μ1 Recovery% Perfluorovaleric acid, 10 μ1 10 --- 25 _{± 5} 10 10 35 _{± 9} Di-2-ethylhexylphosphoric acid, 10 μ1 10 --- 11 _{± 5} 10 10 12 _{± 4} Dioctafluoroamylphosphoric acid, 10 μ1 10 --- 25 _{± 3} 10 10 38 _{± 8}

The data in Table 1 show that solutions of both perfluorovaleric and dioctafluoroamylphosphoric acids in liquid carbon dioxide can be used to remove cesium from the surface of cotton.

Example 2

A cotton surface containing 3.5 μg of strontium nitrate per 10 cm ² was treated as described above. Carbon dioxide was used as a liquid solvent. Extraction of cesium by the prototype method and the proposed method are shown in table 2

Table 2
Extraction of strontium nitrate from the surface of cotton with solutions of acids in carbon dioxide (60 atm., 25 ° C, 3.5 μg Sr (NO ₃ ) ₂ ) Acid H ₂ O μ1 OctOH, μ1 Recovery% Perfluorovaleric Acid, PFVA 10 μ1 10 --- 8 _{± 5} 10 10 8 _{± 3} Di-2-ethylhexylphosphoric acid, D2EHPA 10 μ1 10 --- 15 _{± 7} 10 10 12 _{± 4} Dioctafluoroamylphosphoric acid, DOFAPA 10 μ1 10 --- 77 _{± 11} 10 10 68 _{± 8}

It is obvious that only solutions of dioctafluoroamylphosphoric acid can effectively remove both cesium and strontium from the surface of the cotton.

Example 3

Acid and (or) octanol were deposited on a stainless steel surface containing 3.5 μg of strontium nitrate, placed in a 5 ml extraction cell, where carbon dioxide was injected at a pressure of 150 atm (in a supercritical state), containing 0.02% vol. water, the cell was left under these conditions for 20 minutes, after which 200 ml of pure carbon dioxide were pumped through the cell and the extract was collected in water at a temperature of 25 ° C. The extraction of strontium by the proposed method are given in table.3

Table 3
Extraction of strontium nitrate from the surface of cotton with solutions of acids in carbon dioxide (150 atm., 25 ° C, 3.5 μg Sr (NO ₃ ) ₂ ) Acid H ₂ O, μ1 OctOH, μ1 Recovery% Dioctafluoroamylphosphoric acid, DOFAPA 10 μ1 10 --- 80 _{± 12} 10 10 79 _{± 9}

Example 4

On the surface of the lavsan containing 3.5 μg of strontium nitrate, 4 μg of cesium nitrate per 10 cm ² and indicator amounts of americium were treated as described above, adding tributyl phosphate in addition to acid and octanol. Extraction of metals by the proposed method are given in table 4

Table 4
Extraction of metals from the surface of the lavsan by solutions of di (dodecafluoroheptyl) -phosphoric acid in carbon dioxide (60 atm., 25 ° C) Acid H ₂ O, μ1 OctOH, μ1 TBP, μ1 Recovery% Cs Sr Am Di (dodecafluoroheptyl) -phosphoric acid, 10 μ1 10 40 75 10 10 70 60 60 10 10 10 40 fifty 80

Thus, di-polyfluoroalkylphosphoric acids, for example, di (dodecafluoroheptyl) or dioctafluoroamylphosphoric acid, unlike perfluorocarboxylic acids or dialkylphosphoric acids, effectively remove cesium and strontium simultaneously from surfaces of various materials in the form of solutions in a subcritical (liquid) solvent. A mixture of di-polyfluoroalkylphosphoric acids and TBP in a liquid (subcritical) solvent can simultaneously extract cesium, strontium and americium. Such a process is significantly (5-10 times) cheaper than the supercritical option (prototype) and safer, which is especially important during decontamination.

Claims (2)

1. The method of metal extraction, comprising exposing the matrix containing the metal in a high pressure chamber in a solvent in the presence of water and a fluorinated organic acid, followed by collecting the extracted metal in a solution, characterized in that di- (octafluoroamyl) phosphoric acid is used as an organic acid acid, or di- (dodecafluoroheptyl) phosphoric acid, or a mixture of acid and trialkyl phosphate, and the solvent is in a liquid state. 2. The method according to claim 1, characterized in that the solvent used is carbon dioxide or freon.