Method of preparing technetium solutions

IPC classes for russian patent Method of preparing technetium solutions (RU 2513724):

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/ 2253161

/ 2256965

/ 2267176

/ 2281573

/ 2286612

/ 2291504

/ 2295787

/ 2301465

/ 2302677

FIELD: chemistry.

SUBSTANCE: invention relates to processing liquid radioactive wastes formed when processing spent nuclear fuel. Described is a method of processing technetium solutions, which involves precipitation of technetium from nitrate solutions with concentration of nitric acid or the nitrate ion of not more than 3 mol/l, with concentrated aqueous solutions of o-phenanthroline or α-bipyridyl complexes of divalent transition metals, or mixed complexes of said organic compounds or mixed complexes containing o-phenanthroline or α-bipyridyl with dibasic amines. The obtained precipitates of organometallic pertechnetates are calcined in a hydrogen current at temperature of 600-1200°C with or without a low-melting metal or oxide thereof with melting point of 200-800°C to obtain stable matrices that are suitable for further storage and processing.

EFFECT: obtaining technetium in the final form which is suitable for further storage and processing.

5 cl, 2 tbl, 6 ex

The invention relates to the field of processing of liquid radioactive waste and can be used for localization of technetium from nitrate solutions followed by obtaining as a final form of solid metalloceramic matrix.

Known methods of coprecipitation and deposition of reduced forms of technetium on the hydroxides of metals [E. lamb, Sigrun X., E. Beauchamp in the book. "Proceedings of the Second international conference on peaceful uses of atomic energy (Geneva, 1958) 10. M: Atomizdat. S-126]. In these works we are talking mainly about the amounts of technetium during its extraction from irradiated blocks.

There are also known methods of coprecipitation of macroscopic quantities of technetium in the interaction in alkali (ammonia) environment with hydrazine and its derivatives, as well as with other reductants [Antoshkin, Slicom / study of the sorption of technetium on the precipitation of hydroxides of iron and aluminum in terms of conditions of lake Karachay. / Issues of radiation safety, 1999, No.1, p.12-17], [Swichkow and Wppirate "Behavior of technetium (IV)-(VII) in alkaline solutions in the presence of reducing agents, oxidizing agents, complexing agents and under the action of γ-irradiation". / Abstracts of the Second Russian conference on radiochemistry, Dmitrovgrad. 1997, s]. The disadvantages of the methods described here should be attributed to the instability of the effect of deposition due to oxide the Oia formed hydroxides of iron by oxygen or other oxidants, and the need to perform the deposition process in strongly alkaline (0.5 to 15 mol/l) and, therefore, strongly saline environment, which complicates the subsequent disposal of radioactive stock solution.

There is also known a method of deposition of technetium in the form of TCO₂[patent RU 2201896, 10.04.2003]. Despite a fairly high rate deposition of technetium to 50-99,9% of the initial content in the solution, the main drawback of this method is the necessity of preliminary neutralization of oxidative air reductants such as U(IV) or Ti (III), the effect of which leads to the formation in solution of technetium dioxide and its coprecipitation with hydroxides mentioned tetravalent metals.

There are also other ways of curing solutions of technetium. As a matrix for technetium is used granular silica gel and rich metal sorbent further subjected to annealing [patent RU 2132094, 20.06.1999]. The main disadvantage of this invention consists in the necessity of processing technologo solution by complexing agents, which increases its adsorption on silica gel and then processing the saturated technetium sorbent reducers to obtain technetium dioxide, which leads to increased salinity mother liquor and complicates it further is pererabotka.

Also known is a method of obtaining metal technecally matrix recovery salt pertechnitat ammonium to metal [patent RU 2103403, 27.01.1998]. The main disadvantage of this invention is the extensive preparatory work to obtain salt pertechnitat ammonium, including sorption on cation exchange resin and neutralizing the resulting solution with ammonia, resulting in increased volumes of both liquid and solid radioactive wastes.

The prototype of the present invention is a method for the deposition of technetium from solution with a concentration of nitric acid and 1.5 mol/l and below with a solution of hydrazine or with a solution of iron (II) [patent RU 2199163, 20.02.2003].

Despite the good results of the deposition of the Cu: 95-99% of technetium in sediments of the original quantity in the solution, the main disadvantages of the prototype are the need for preliminary neutralization of the nitric acid solution with a concentration of nitric acid and 1.5 mol/l and lower solutions of salts of carboxylic acids or alkali to a pH of 5-11 and the lack of options for further processing of the received precipitation. Pre-treatment solution again leads to a significant salinization source solution that causes difficulties in subsequent processing.

The objective of the invention is to develop a method of localization of technetium deposition from ASOT the acidic solutions and then get on the basis of the precipitate formed solid suitable for further storage of the matrix.

The deposition is carried out on the initial concentrations of nitric acid or nitrate ion, not more than 3 mol/L.

For the deposition of technetium from nitrate solutions were used on-phenanthroline or α-bipyridine complexes of divalent transition metals such as Zn, Ni, Co, Cu, etc. mixed complexes of these organic compounds or mixed complexes containing o-phenanthrolin or α-bipyridyl with dibasic amines. The molar ratio of transition metal:organic ligand in the precipitator was 1:(1-12). The deposition is carried out at a molar ratio of metal precipitator:Cu = 1:(1÷2). The result is precipitation ORGANOMETALLIC pertechnetate that, after annealing in hydrogen flow at a temperature of 600-1200°C for 40 min in the presence of low-melting metal, such as Sn, Al, Zn, etc., or its oxide with a melting temperature of 200-800°With or without it allow to obtain metal-containing matrix.

Thus, the proposed method allows to besiege the technetium from the neutral and acid solutions of complexes of divalent transition metals with dibasic amines with getting technologo ORGANOMETALLIC sediment, subsequent annealing which allows to derive a metal matrix.

The localization of technetium method "direct wasp is Denia" using on-phenantroline transition metal complexes in solution remains in the middle of 2-20% of the technetium from the initial amount depending on the precipitator. When using the "reverse deposition" 98-100% TC goes into the sediment. BaselCement matrices obtained after precipitation annealing in hydrogen flow meets the standards for CAO.

Example 1

Direct deposition"

Neutral or nitrate technetium solution with a concentration of technetium 1 g/l and the concentration of nitrate-ion 0,5, 1, 1,5, 2, 3 mol/l at room temperature, add a solution of precipitator, representing nitrate o-phenantroline complex of copper (II) with a ratio of transition metal:organic ligand is 1:9. The deposition is carried out at a molar ratio of metal precipitator:technetium, which is 1:1,1.

Table 1 provides data on the deposition of technetium concentrated solutions of organic complexes of divalent transition metals from neutral and acid solutions.

Table 1
A solution of precipitator	The concentration of nitric acid in the original solution, mol/l	The metal content in the sediment after deposition of the initial content in the solution, %
Metal precipitant	TC
	0	91	98
Cu(phen)₉(NO₃)₂,
	0,5	93	98
Fe(bipy)₃(NO₃)₂,
	1	95	98
Fe(bipy)₂(phen)(NO₃)₂,
	1,5	95	95
Co(phen)₂(en)(NO₃)₂,
	2	94	93
Co(bipy)₂(en)(NO₃)₂,
3	88	91
where
phen - o-phenanthrolin,	4	the precipitate is not formed	the precipitate is not formed
bipy-bipyridyl,
en-ethyldiamine

The residual concentration of technetium in solution after precipitation was 0.02-0.1 mg/l

Example 2

Direct deposition"

Neutral or nitrate technetium solution with a concentration of technetium 1 g/l and the concentration of nitrate-ion 0,5, 1, 1,5, 2 mol/l at room temperature, add a solution of precipitator, representing nitrate o-phenantroline complex of iron (II) with a ratio of transition metal:organic ligand is 1:3. The deposition is carried out at a molar ratio of metal precipitator:technetium equal to 1:1,7.

Table 2 shows data on the deposition of technetium concentrated aqueous solutions of an organic complex of iron (II) from neutral and acid solutions.

Table 2
A solution of precipitator	The concentration of nitric acid in the original solution, mol/l	The metal content in the sediment after deposition of the initial content in the solution, %
Fe	TC
Fe(phen)₃(NO₃)₂,	0	48	90
where	0,5	52	86
phen - o-phenanthrolin	1	61	85
	1,5	64	80
	2	68	80
	3	70	80
	4	The precipitate is not formed	The precipitate is not formed

The residual concentration of technetium in solution after precipitation amounted to 0.1-0.2 mg/l

Example 3

"Reverse deposition"

To the concentrated solution of precipitator poured original neutral or nitrate technicaly solution with a concentration on metal 1 g/l and the concentration of nitrate-ion up to 3 mol/l depending on the precipitator. When used as a precipitator of concentrated solution of an organic complex of iron up to 95% of the technetium is tons of original content in the solution passes into the sediment.

Example 4

Localization of technetium carried out by the method of "reverse" deposition, i.e. the gradual addition of an initial solution to the precipitant solution with constant stirring. The deposition is conducted as in neutral solutions and acid solutions with concentrations of nitric acid 0,5, 1, 1,5, 2 and 3 mol/l and the concentration of technetium 1 g/l at room temperature.

The residual concentration of technetium in solution after precipitation when using a concentrated solution of an organic complex of copper was 20 mg/L.

Example 5

The obtained precipitation ORGANOMETALLIC pertechnetate dried for 20 minutes at a temperature of 200-250°C., and then calcined from 20 minutes to 1 hour in a stream of hydrogen at a temperature of 600-1200°C.

Example 6

To the obtained precipitation ORGANOMETALLIC pertechnetate to reduce the porosity of the samples generated during the calcination, add a low-melting metal such as Al, Sn, Zn, etc. with a melting temperature of 200-800°C or its oxide. The samples are dried for 20 minutes at a temperature of 200-250°C., and then calcined from 20 minutes to 1 hour in a stream of hydrogen at a temperature of 600-1200°C.

These examples show that the proposed solution has the following advantages: no need for pre-oxidation-reduction processing is similar solution, and its neutralization; the method is extremely simple in its execution and is either adding a concentrated solution of precipitator directly in the source solution, or Vice versa, you can also get technetium in final form, suitable for further storage and processing.

1. A method of processing technicaly solutions, including deposition of technetium from nitric acid solutions of a compound containing divalent transition metal, wherein the precipitation is carried out on the initial concentrations of nitric acid or nitrate ion, not more than 3 mol/l, concentrated aqueous solutions of o-phenantroline or α-bipyridinium complexes of divalent transition metals, or mixed complexes of these organic compounds, or mixed complexes containing o-phenanthrolin or α-bipyridyl with dibasic amines, and the resulting precipitation ORGANOMETALLIC pertechnetate translated into a form suitable for long term storage.

2. The method according to claim 1, characterized in that the ratio of the transition metal organic ligand in solution precipitator is 1:(1-12), and the deposition is carried out at a molar ratio of metal precipitator:TC equal to 1:(1÷2).

3. The method according to claim 1, characterized in that the process of deposition of technetium exercise as a method of "direct the th deposition", the addition of the precipitant solution in the original solution and the method of "reverse deposition", gradual addition of the starting solution in the solution precipitator.

4. The method according to claim 1, characterized in that the precipitation is calcined in a stream of hydrogen at a temperature of 600-1200°C.

5. The method according to claim 1, characterized in that the calcination of the obtained precipitation is carried out in the presence of low-melting metal, such as Sn, Al, Zn, etc. or its oxide with a melting temperature of 200-800°C in a stream of hydrogen at a temperature of 600-1200°C.