FR2826354A1 - PROCESS FOR DECOMPOSING HYDRAZINE CONTAINED IN AQUEOUS LIQUID - Google Patents

Abstract

The invention relates to a method for decomposing hydrazine contained in an aqueous liquid such as water, arising from a nuclear or thermal boiler or other type of industrial unit producing aqueous effluents containing hydrazine. According to the inventive method, hydrazine contained in the aqueous liquid is reacted with at least one peroxide in the presence of a catalyst comprising at least one metal alloy. The invention also relates to a device for carrying out said method.

Description

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METHOD OF DECOMPOSING HYDRAZINE
CONTAINED IN AQUEOUS LIQUID
The present invention relates to a process for decomposing hydrazine contained in an aqueous liquid such as water from a nuclear or thermal boiler, or any other industrial unit producing aqueous effluents containing hydrazine.

 It is known to decompose by catalytic oxidation the hydrazine contained in water.

 The German patent application published under the number DE 36 44 080 proposes to use hydrogen peroxide to purify industrial wastewater containing in particular hydrazine, operating at a pH greater than 7 and in the presence of a sodium salt. a heavy metal, such as copper sulfate, and / or a catalyst which may be potassium permanganate or a salt of nickel, chromium or cobalt.

 The Japanese patent application published under the number JP 09234473 relates to a wastewater treatment process containing hydrazine, which essentially consists in adding to the water to be treated hydrogen peroxide, as an oxidant, and a copper-based compound as a catalyst, and subjecting the hydrazine to oxidative decomposition by exposing it to air for 0.5 to 12 hours, the pH being maintained at 10-11, 5.

 More recently, Japanese Patent Application Publication No. JP 2000301171, which is directed to improving the process of the aforementioned Japanese Patent Application, has proposed a method of subjecting the hydrazine contained in waste water to oxidative decomposition at the same time. double presence of a metal percarbonate such as sodium or potassium

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 and at least one catalyst selected from compounds based on copper, manganese, cobalt or nickel.

Examples of such compounds are sulphates and chlorides.

 All the processes which have just been mentioned have the major drawbacks of forming by-products (chlorides, sulphates, etc.) and of introducing metals into the treated water.

 The object of the invention is to propose a process for decomposing hydrazine contained in water that does not have these disadvantages.

 According to this process, the hydrazine contained in an aqueous liquid is reacted with at least one peroxide in the presence of a catalyst comprising at least one metal alloy.

 Such a process offers the following advantages: it can be easily operated at neutral pH or close to neutrality, ambient temperature, without exposure to the air or external oxygen supply; - It does not give rise to an uncontrollable exotherm, - It does not alter the catalyst, and it retains its effectiveness over long periods.

 The invention also relates to a device capable of implementing this method.

donné en référence aux dessins dans lesquels : - la Figure 1 est un schéma représentant un dispositif selon l'invention, apte à mettre en oeuvre le procédé selon l'invention ; - la Figure 2 est une représentation graphique des courbes d'évolution des teneurs en hydrazine et Other features and advantages of the invention will appear on reading the following description, which is

given with reference to the drawings in which: - Figure 1 is a diagram showing a device according to the invention, adapted to implement the method according to the invention; FIG. 2 is a graphical representation of the evolution curves of hydrazine contents and

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 in hydrogen peroxide as a function of time, during the implementation of the process according to the invention and a method of the prior art; FIG. 3 is a graphical representation of the evolution curves, as a function of time, of the hydrazine contents of a demineralised water, during three similar trials of implementation of the process according to the invention; FIG. 4 is a graphical representation of the evolution curves, as a function of time, of the hydrazine contents of a demineralized water and a Seine-type water, during the implementation of the process according to the invention and a process of the prior art; FIG. 5 is a graphical representation of the evolution of the hydrazine and hydrogen peroxide contents as a function of time, during the implementation of the process according to the invention according to two successive phases; FIG. 6 is a graphical representation showing the evolution of the oxidant contents, namely hydrogen peroxide or sodium hypochlorite, during the implementation of the process according to the invention and of three processes of the art prior.

DETAILED PRESENTATION OF THE INVENTION
According to the invention, hydrazine, generally in the form of hydrazine hydrate, contained in any aqueous liquid, for example, waste water, water from nuclear or thermal boilers leaving the die, or water from Waste or accidental spills of hydrazine, can be destroyed rapidly, using a peroxide as oxidant, following a reaction catalysed by a solid catalyst that includes a metal alloy.

 As a metal alloy, a transition metal alloy is advantageously used.

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 Catalysts comprising such an alloy have the particular feature of self-regenerating during the process of decomposition of hydrazine.

 In addition, they have the advantage of not forming a passivating protective layer on their surface, a layer that would prevent the passage of electrons and reduce their activity. In addition, these catalysts, because they do not contain precious metals, have a relatively low Nernst potential, which is to say that they easily transmit the electrons to the environment. Finally, the surface of these catalysts corresponds to a metal-oxygen bronze. This type of structure is a very favorable condition for the reversibility of electron migration: the electrons are thus transmitted and recovered without generating metal cations in solution. As a result, the catalyst remains stable throughout the decomposition process of hydrazine.

 The alloy of at least one transition metal, a nickel-based alloy, is preferably used.

 Among the nickel-based alloys, mention may be made of nickel and copper alloys, in particular those comprising 25 to 35% nickel and 75 to 65% copper, these percentages being expressed by weight relative to the total weight of the alloy.

 Mention may also be made of nickel, cobalt and chromium alloys, in particular those comprising from 5 to 15% of nickel, from 80 to 60% of cobalt and from 15 to 25% of chromium, these percentages being expressed by weight by weight. relative to the total weight of the alloy.

 The catalyst may be in the form of a metal grid or a mesh of wire mesh.

 The catalysis is therefore of the heterogeneous type and, consequently, easy to implement.

 On the surface of the catalyst, the peroxide is activated and generates OH 'radicals, the oxidizing effect is very effective. Indeed, the oxidation potential

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 electrochemical of an OH-radical is 2.8 V, against 1.78 V for hydrogen peroxide and 1.36 V for chlorine.

 The peroxide used can be organic or mineral.

Preferably, hydrogen peroxide is used.

The decomposition of hydrazine by hydrogen peroxide can then be illustrated by the following simplified equation:
N2H4 + 2H2O2-N2 + 4H20
Hydrogen peroxide is thus activated without external energy (UV rays, etc.) or external oxygen and without forming by-products.

 Hydrogen peroxide is generally introduced as an aqueous solution. The stability of the aqueous solution of hydrogen peroxide is not affected by the catalyst as such.

 In addition, the reaction does not release metals into the water during treatment. This has the great advantage of not causing induced pollution.

 The molar ratio hydrazine / hydrogen peroxide is generally between 1 and 4, preferably between 1.6 and 2.2.

 The duration of the reaction between hydrazine and hydrogen peroxide can be between 1 minute and 8 hours. Preferably, it is between 30 minutes and 3 hours.

 Another advantage of the process according to the invention is that it is not necessary to use it at a particular pH. It can therefore be used at a neutral pH or close to neutrality and it is also not necessary to maintain this pH at a particular value. However, it is desirable that the pH be not too low, as this may result in dissolution of the catalyst metals.

 In addition, the process according to the invention can be carried out in a very wide range of temperatures.

Generally, it is carried out at a temperature of between 15 and 60 ° C., and preferably between 20 and 60 ° C.

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 25OC, so that it is not necessary to heat the reaction medium.

 The process according to the invention, because of the automatic regeneration of the catalyst, has a high reproducibility of the decomposition reaction of hydrazine without loss of efficiency over time.

 It can therefore operate in a discontinuous or continuous mode.

 It can be used to detoxify the water from nuclear or thermal boilers leaving the die, to decontaminate containers containing hydrazine or to safely decompose waste or accidental spills of hydrazine.

Device according to the invention
The method according to the invention can be implemented by means of a device essentially comprising: a container containing the aqueous liquid to be treated; a catalyst comprising at least one metal alloy, this catalyst being in a container; means for introducing the peroxide into the aqueous liquid to be treated; means for passing the aqueous peroxide-containing liquid into the container through the catalyst; and optionally means for returning the aqueous liquid exiting the container into the container.

 Such a device is shown schematically in FIG.

 The liquid to be treated loaded with hydrazine is placed in a tank 1 to which is connected by a pipe 2 a pump 3 whose output is connected by a pipe 4 to the inlet of a column 5 containing the catalyst 6.

 The peroxide is introduced into the aqueous liquid to be treated by means of a metering pump (not shown) and

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 a pipe 7 preferably connecting to the pipe 4 upstream of the column 5.

 The operation of the pump 3 passes the aqueous liquid containing hydrazine and peroxide in the column 5, through the catalyst 6.

 According to a preferred embodiment of the device according to the invention, the decontaminated aqueous liquid coming out of the column 5 is brought back via a line 8 into the tank 1. Thus, the device according to the invention constitutes a system of rotation in a circle allowing maintain some agitation of the liquid in contact with the catalyst.

 In order to avoid excessive temperature rises, preferably relatively low reactant concentrations are used (eg hydrogen peroxide at 10% by weight hydrogen peroxide).

 If necessary, an exchanger can be added to the recirculation loop to regulate the exotherm. If the proportions of reactants and catalyst are appropriately selected, the decomposition of hydrazine can be maintained at room temperature with satisfactory kinetics.

Examples
The following examples illustrate the present invention without, however, limiting its scope.

 The analytical means used in the examples are the following: - determination of hydrazine: by visible absorption at 455 nm on the HACH DR 2010 spectrometer (method 8141); p-dimethylaminobenzaldehyde method; determination of hydrogen peroxide: by titanium chloride in a sulfuric acid medium; visible absorption at 410 nm on the HACH DR 2010 spectrometer;

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- copper dosage: by visible absorption at
560 nm on HACH DR spectrometer 2010 (method
8506); bicinchoninate method; - redox probe (ORION 9778BN combined electrode).

Example 1
With the aid of the device of FIG. 1, the hydrazine contained in demineralized water solutions (pH about 7.2) is removed.

 Each time, the container is filled with 1 liter of demineralised water containing 463 mg of hydrazine (molar mass: 32 g).

 9.2484 g of oxygenated water containing 10% of hydrogen peroxide (molar mass: 34 g) are then added.

 The molar ratio hydrazine / hydrogen peroxide is therefore 0.534.

 The procedure is carried out first according to the prior art, that is to say in the absence of a catalyst.

 Then, it proceeds according to the invention, that is to say is introduced into the container 2.0058 g of a catalyst which is an alloy of 32% nickel and 68% copper (% by weight).

 The evolution of hydrazine and hydrogen peroxide concentrations is monitored as a function of time.

 The following table groups the results obtained.

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<Tb>
<Tb>

Art <SEP> Invention
<tb> previous
<tb> Time <SEP> Hydrazine <SEP> Hydrazine <SEP> Peroxide <SEP> Temperature <SEP> pH
<ss><SEP> (in SEP><SEP> mg / l) <SEP> (in SEP> mg / l) <SEP> of hydrogen <SEP> (in <SEP> C)
<tb> (in <SEP> mg / 1)
<tb> 0 <SEP> 463 <SEP> 463 <SEP> 920 <SEP> 18, <SEP> 9 <SEP> 9.2
<tb> 15 <SEP> 457 <SEP> 32.3 <SEP> 202 <SEP> 20.9 <SEP> 7.9
<tb> 30-4, <SEP> 3 <SEP> 152 <SEP> 20, <SEP> 9 <SEP> -
<tb> 45 <SEP> 3, <SEP> 2 <SEP> 14220, <SEP> 9
<tb> 60 <SEP> 459 <SEP> 2,3 <SEP> 141 <SEP> 20.9 <SEP> 5.9
<tb> 75-1, <SEP> 5 <SEP> 132 <SEP> 20.9 <SEP> 5, <SEP> 9
<tb> 90 <SEP> 458 <SEP> 0.5 <SEP> 118.6 <SEP> 21.0 <SEP> 6.0
<tb> 105 <SEP> 0, <SEP> 45 <SEP> 118.9 <SEP> 21.0 <SEP> 6.0
<tb> 120-0, <SEP> 4 <SEP> 117.4 <SEP> 21.1 <SEP> 6, <SEP> 1
<tb> 240 <SEQ> 444 <SEP> - <SEP> - <SEP> - <SEP> -
<tb> 1380 <SEP> 428 <SEP> - <SEP> - <SEP> - <SEP> -
<Tb>

On constate immédiatement que l'utilisation du catalyseur permet de décomposer plus rapidement l'hydrazine contenue dans l'eau déminéralisée.

It is immediately apparent that the use of the catalyst makes it possible to decompose the hydrazine contained in the demineralised water more rapidly.

The temperature remains substantially stable.

The reaction is complete in about 2 hours.

The pH gradually changes from 9 to 6. It is ensured that it does not fall below 6, possibly adding soda.

No trace of metal is found in the solution at the end of the reaction.

The yield of the removal of hydrazine is therefore 99.9% and 87.2% of the hydrogen peroxide has been consumed.

The curves in Figure 2 represent changes in hydrazine and hydrogen peroxide as a function of time.

EXAMPLE 2 In order to verify the repetitiveness of the hydrazine elimination reaction, two new

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 successive tests, as in Example 1, with the catalyst which has already been used in Example 1 and without changing or in any way treat this catalyst during these two tests.

 The results are represented by the curves in Figure 3.

 It is observed that the repetition of the reaction is perfect, the activity of the catalyst remaining identical in all three cases.

Example 3
In this example, synthetic water of the Seine type (pH approximately 8-8.5, TAC 200F, THCa 200F) was used [Na2SO4 = 74 mg / l; NaHCO 3 = 336 mg / l; CaCl2 = 0.002 mol / l; MgCl2 = 0.0005 mol / l).

 2 successive tests are carried out with the nickel / copper catalyst of Example 1 under conditions which are similar to those of Example 1.

 The water initially contains 400 ppm hydrazine.

 The amount of hydrogen peroxide (in solution in water at 10%) added is 9 ml.

 The amount of catalyst used is 2.0065 g / l. The catalyst is washed with demineralised water between the two tests.

 The molar ratio hydrazine / hydrogen peroxide is 0.49.

 The results are collated in the following table.

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<Tb>
<Tb>

Time <SEP> Hydrazine <SEP> Hydrazine <SEP> Peroxide <SEP> Temperature <SEP> pH
SEP (mg / l) <SEP> (SEQ) <SEP> (SEQ) <SEP>(SEP> hydrogen)
<tb> Assay <SEP> 1 <SEP> Assay <SEP> 2 <SEP> Assay <SEP> 1 <SEP> Assay <SEP> 1
<tb> 0 <SEP> 421 <SEP> 414 <SEP> 920 <SEP> 18, <SEP> 0 <SEP> 9, <SEP> 3
<tb> 30 <SEP> 125 <SEP> 102 <SEP> 271 <SEP> 19, <SEP> 4 <SEP> 8, <SEP> 8
<tb> 60 <SEP> 41 <SEP> 26111 <SEP> 19, <SEP> 5 <SEP> 8, <SEP> 1
<tb> 90 <SEP> 5, <SEP> 7 <SEP> 0, <SEP> 96 <SEP> 66, <SEP> 8 <SEP> 19.3 <SEP> 7.6
<tb> 120 <SEP> 0, <SEP> 3 <SEP> 0, <SEP> 09 <SEP> 48, <SEP> 2 <SEP> 19.2 <SEP> 7, <SEP> 5
<tb> 150 <SEP> 0.043 <SEP> 0, <SEP> 02 <SEP> 45, <SEP> 5 <SEP> 19, <SEP> 0 <SEP> 7, <SEP> 7
<tb> 180 <SEP> 0.015 <SEP> 0.01 <SEP> 43.6 <SEP> 18, <SEP> 9 <SEP> 7, <SEP> 9
<tb> 210 <SEP> 0, <SEP> 012 <SEP> 0, <SEP> 009 <SEP> 40, <SEP> 9 <SEP> 18, <SEP> 9 <SEP> 8.0
<tb> 240 <SEP> 0, <SEP> 01 <SEP> 0, <SEP> 0083818, <SEP> 9 <SEP> 8, <SEP> 1
<Tb>

The curves in FIG. 4 represent the variations of the hydrazine and hydrogen peroxide contents as a function of time, for the tests 1 and 2 of this example.

 Since, in the absence of catalyst, no difference in the kinetics of hydrazine decomposition by hydrogen peroxide has been observed between the demineralized water and the Seine-type synthetic water, the curve obtained in Example 1 (see FIG. 2) was added in FIG. 4.

 In addition, for comparison purposes, the curve obtained in Example 1 was also added in FIG. 4 using a catalyst and deionized water.

 It is therefore found that, as before, the use of the catalyst makes it possible to neutralize the hydrazine contained in the synthesis water more rapidly.

 We also note that the neutralization is slower than in the case of demineralised water, but still fast enough to allow the disappearance of hydrazine in about 2 hours.

 The yield of the hydrazine decomposition is 100% and the amount of hydrogen peroxide consumed is 95.9%.

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Example 4
This example aims to show the maintenance of the efficiency of the method according to the invention in operation in continuous mode.

 In a first phase, the demineralized water containing 400 ppm of hydrazine is treated with a 10% aqueous solution of hydrogen peroxide, in the presence of the catalyst of Example 1.

 At the end of the reaction, 400 ppm of hydrazine and 920 ppm of hydrogen peroxide are reinjected to carry out a second phase of decomposition of the hydrazine, in the same medium and without washing the catalyst.

 The amount of catalyst used is 2.0065 g / l.

 During the first phase, the hydrazine / hydrogen peroxide molar ratio is 0.47. The yield of the hydrazine decomposition is 100%. The amount of hydrogen peroxide consumed is 93%. The reaction time is 2 hours.

 During the second phase, the hydrazine / hydrogen peroxide molar ratio is 0.444. The yield of the hydrazine decomposition is 100%. The amount of hydrogen peroxide consumed is 85.2%. The reaction time is 30 minutes.

 The results are collated in the following table.

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<Tb>
<Tb>

Time <SEP> Hydrazine <SEP> Peroxide <SEP> Temperature <SEP> pH
<ss><SEP> (mg / l) <SEP> hydrogen <SEP> (C)
<tb> First <SEP> phase
<tb> 0 <SEP> 408 <SEP> 920 <SEP> 20.2 <SEP> 9.1
<tb> 30 <SEP> 34.8 <SEP> 203 <SEP> 22, <SEP> 1 <SEP> 7.9
<tb> 60 <SEP> 2.7 <SEP> 145 <SEP> 22.1 <SEP> 7.4
<tb> 90 <SEP> 0.07 <SEP> 126 <SEP> 22, <SEP> 0 <SEP> 7.5
<tb> 120 <SEP> 0, <SEP> 0111622, <SEP> 0 .. <SEP> 7.7
<tb> 210 <SEP> 0, <SEP> 007 <SEP> 74 <SEP> 21, <SEP> 7 <SEP> 8.3
<tb> 240 <SEP> 0, <SEP> 005 <SEP> 65 <SEP> 21, <SEP> 7 <SEP> 8.4
<tb> Second <SEP> phase <SEP>: <SEP> after <SEP> reinjection <SEP> of hydrazine <SEP> and <SEP> of
<tb> hydrogen peroxide <SEP>
<tb> 241 <SEP> 412 <SEP> 985 <SEP> 21, <SEP> 7 <SEP> 9.0
<tb> 270 <SEP> 0.014 <SEP> 195.4 <SEP> 23.3 <SEP> 8.3
<tb> 300 <SEP> 0.011 <SEP> 117.4 <SEP> 22.8 <SEP> 8.4
<tb> 330 <SEP> 0, <SEP> 01 <SEP> 170.9 <SEP> 22.6 <SEP> 8.4
<tb> 480 <SEP> 0.008 <SEP> 145 <SEP> 22, <SEP> 3 <SEP> 8, <SEP> 4
<Tb>

It is observed that there is no loss of efficiency of the system after continuous reinjection of the reagents. Moreover, the second phase seems to be realized more quickly.

 The curves representing the variations of hydrazine and hydrogen peroxide as a function of time for the first and second phases are visible in FIG. 5.

Example 5
In this example, the process according to the invention is compared with the following processes of the prior art: a process A in which the catalyst is non-existent; a process B implementing a homogeneous catalysis by means of an aqueous solution of copper sulphate; and

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 a process C where the catalyst is non-existent and the oxidant is no longer hydrogen peroxide but sodium hypochlorite.

 The aqueous starting solution is demineralized water containing 400 ppm of hydrazine.

 Hydrogen peroxide is used in 10% aqueous solution.

 In Method B, the copper sulfate is used as a 5 ppm aqueous solution of Cu.

 In process C, sodium hypochlorite is in the form of a 13.5% (wt / wt%) aqueous solution or 42 Cl.

 In process D according to the invention, the catalyst of example 1 is used at a rate of 2 g / l.

The results are recorded in the following table.

<Tb>
<Tb>

Process <SEP> Process <SEP> Process <SEP> Process <SEP> D
<tb> A <SEP> B <SEP> C <SEP> (Invention)
<tb> Ratio <SEP> molar <SEP> 1/2, <SEP> 06 <SEP> 1/2, <SEP> 18 <SEP> 1/1, <SEP> 96 <SEP> 1/1, <SEP > 87
<tb> hydrazine / oxidant
<tb> Time <SEP> of <SEP> reaction <SEP> 4 <SEP> h <SEP> 1 <SEP> h <SEP> 10 <SEP> 2 <SEP> h
<tb> minutes
<tb> Consumption <SEP> of <SEP> 9% <SEP> 82.6% <SEP> 32.7% <SEP> 87.2%
<tb> the oxidant
<tb>% <SEP> Hydrazine <SEP> 4.5% <SEP> 100% <SEP> 100% <SEP> 99.9%
<tb> destroyed
<tb> Temperature <SEP> (OC) <SEP> Ambient <SEP> Ambient <SEP> Ambient <SEP> Ambient
<Tb>

It is observed that the presence of a catalyst makes it possible to significantly accelerate the decomposition of hydrazine by hydrogen peroxide.

 Homogeneous catalysis by addition of copper sulfate in aqueous solution is faster than the process according to the invention. However, it has the disadvantage of introducing copper into the solution.

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 The use of sodium hypochlorite leads to an instantaneous elimination of hydrazine, but it has the drawback of requiring a high mass of oxidant, ie 149 g of sodium hypochlorite per 32 g of hydrazine and introducing sodium chloride in the solution as hydrazine reacts with sodium hypochlorite to give sodium chloride, nitrogen and water.

 The curves representing the variations of the contents of hydrazine, hydrogen peroxide and sodium hypochlorite as a function of time are visible in FIG. 6.

Claims (12)

 1. A method of decomposing hydrazine contained in an aqueous liquid, wherein the hydrazine is reacted with at least one peroxide, in the presence of a catalyst, characterized in that the catalyst comprises at least one metal alloy. 2. Method according to claim 1, characterized in that the metal alloy is an alloy based on at least one transition metal. 3. Method according to claim 2, characterized in that the alloy based on at least one transition metal is a nickel-based alloy. 4. Method according to claim 3, characterized in that the nickel-based alloy is an alloy of nickel and copper. 5. Method according to claim 4, characterized in that the alloy comprises, by weight, 25 to 35% nickel and 75 to 65% copper. 6. Method according to claim 3, characterized in that the nickel-based alloy is an alloy of nickel, cobalt and chromium. 7. Process according to claim 6, characterized in that the alloy comprises, by weight, from 5 to 15% of nickel, from 80 to 60% of cobalt and from 15 to 25% of chromium. 8. Method according to one of claims 1 to 7, characterized in that the peroxide is hydrogen peroxide. <Desc / Clms Page number 17> 9. Method according to claim 8, characterized in that the molar ratio hydrazine / hydrogen peroxide is between 1 and 4, preferably between 1.6 and 2.2. 10. Process according to claim 8 or claim 9, characterized in that the hydrazine and the hydrogen peroxide are reacted together for a period of time between 1 minute and 8 hours, preferably between 30 minutes and 3 hours.  11. Apparatus suitable for carrying out the method according to one of claims 1 to 10, comprising: - a container (1) containing the aqueous liquid loaded with hydrazine to be treated; a catalyst (6) comprising at least one metal alloy, this catalyst being in a container (5); means (7) for introducing the peroxide into the aqueous liquid to be treated; means (2,3,4) for passing the aqueous liquid containing the peroxide into the container (5) through the catalyst (6); and optionally, means (8) for returning the aqueous liquid leaving the container (5) in the container (1). 12. Use of a metal alloy as defined in claims 1 to 7 for the catalytic oxidation of hydrazine contained in an aqueous liquid.