EP0266272B1 - Process for the recovery of acid organo-phosphorous compounds and/or organo-phosphorous ions from an aqueous solution, and its use in treating aqueous effluents - Google Patents

Description

The subject of the invention is a process for recovering acidic organophosphorus compounds and / or organophosphate ions present in an aqueous solution.

More specifically, it relates to the treatment of aqueous effluents containing such organophosphorus compounds with a view to recovering these organophosphorus compounds which constitute products which are harmful to the environment and can in certain cases be reused for the separation of metals by liquid extraction. liquid.

In recent years, it has been used more and more in the industry of acid organophosphorus compounds to carry out the separation of metals by liquid-liquid extraction. These compounds generally consist of mono or dialkylphosphoric acids such as di-2-ethylhexylphosphoric acid, which have advantageous properties for the purification of many metals such as nickel, copper, zinc, rare earths, uranium and plutonium.

These acid organophosphorus compounds or their salts with mineral cations being very slightly soluble in water, the aqueous solutions leaving these extraction installations therefore contain small amounts of acid organophosphorus compounds which it is desirable to recover before discharge of effluents, on the one hand to avoid polluting the environment and, on the other hand to recover these extractants and recycle them in the liquid-liquid extraction installation.

Acid organophosphorus compounds which cannot be used for extraction may also be found in effluents from liquid-liquid metal extraction installations. This is the case, for example, of extraction facilities for uranium and / or plutonium which use tributyl phosphate as an extractant, because the degradation by hydrolysis, photolysis and / or radiolysis of tributyl phosphate leads to the formation of mono and di-butylphosphoric acids; the presence of these acids in the organic extraction phase may disturb the extraction process, they are generally extracted from this organic phase by washing in a basic aqueous solution, which leads to the production of basic effluents containing salts organophosphorus acids. In this case, it is also desirable to extract these organophosphorus compounds before discharging the aqueous effluents.

This recovery of acidic organophosphorus compounds and / or organophosphate ions poses certain problems because the pH of the aqueous solutions which contain them can vary within a wide range.

Indeed, these solutions can come from extractions carried out in an acid medium as is the case for example of dilute sulfuric solutions from which various metals have been extracted. They can also consist of basic solutions, as is the case, for example, for solutions for washing solvents from irradiated fuel treatment plants using tributyl phosphate.

Among the processes making it possible to treat aqueous effluents of this type, there is known a process for extracting mono and di-butylphosphoric acids present in basic carbonate solutions, which consists in first acidifying the carbonated solution by adding acid nitric to bring its acidity to a value of 3-4N and then to extract the phosphoric acids by 2-ethyl 1-hexanol, as described by EH HORWITZ et al, "Actinides Separations", Honolulu, Hawai, April 3- 5, 1979, p. 475, ACS Symposium, Series 117.

This method has the disadvantage that it can only be used in a limited range of acidity, which can cause certain problems, since this acidification can lead to precipitation or troublesome chemical reactions in the effluent to be treated.

The present invention specifically relates to a process for recovering acidic organophosphorus compounds and / or organophosphate ions present in an aqueous solution which overcomes this drawback.

The process according to the invention for recovering acidic organophosphorus compounds and / or organophosphate ions present in an aqueous solution is characterized in that the aqueous solution is brought into contact with at least one poorly soluble amino organic compound. in water, chosen from the compounds comprising at least one amine function, the salts of these amino compounds with an acid and the quaternary ammonium salts, and in that the complex formed by reaction is separated from the aqueous solution acid organophosphorus compounds and / or organophosphate ions with the amino organic compound (s).

According to the invention, the amino compounds used must be sparingly soluble in water so as not to pollute the aqueous solution with which they are brought into contact. Generally, an amino compound is chosen whose solubility in water does not exceed approximately 1 mg / l.

By way of example, the amino organic compound used can be a primary, secondary or tertiary amine or else a quaternary ammonium salt. It can also be constituted by a salt obtained by reaction of a primary, secondary or tertiary amine with an inorganic acid such as hydrochloric acid, or an organic acid such as formic acid or acetic acid. It is also possible to use an amine partially salified by an acid.

The amines which can be used are preferably alkylamines, in particular trialkylamines such as triisooctylamine. However, cyclic amines can also be used, for example dibenzylamine and tribenzylamine.

dans lesquels RN peut représenter une amine primaire RNH₂, une amine secondaire RR′NH ou une amine tertiaire RR′R˝N.In the process of the invention, the acid organophosphorus compound AH or the organophosphate ions A ^_ react with the organic compound with amine function RN or with its salt RN ⁺ H ... B ^_ according to the following reaction schemes:

in which RN can represent a primary amine RNH₂, a secondary amine RR′NH or a tertiary amine RR′R˝N.

A complex is thus obtained which can then be separated from the aqueous solution.

qui constituent un mécanisme d'échange d'anions. Les anions B^_ (minéraux comme NO $\genfrac{}{}{0ex}{}{\text{\_}}{\text{3}}$

, Cl^_ , etc...) seront déplacés par les ions organophospate A^_ , permettant ainsi de séparer les composés organophosphorés acides ou les ions organophosphate de solutions aqueuses.In the case where a quaternary ammonium salt of formula RR′R˝R ‴ N ⁺ ... B ^_ is used as the amino organic compound, which is symbolized by R₄ N ⁺ ... B ^_ , the acid organophosphorus compound AH or the organophosphate ions A ^_ react with this quaternary ammonium salt according to the following reaction schemes:

which constitute an anion exchange mechanism. The anions B ^_ (minerals like NO $\genfrac{}{}{0ex}{}{\text{\_}}{\text{3}}$

, Cl ^_ , etc ...) will be displaced by the organophosphate ions A ^_ , thus making it possible to separate the acid organophosphorus compounds or the organophosphate ions from aqueous solutions.

The process of the invention can be used to treat a wide variety of aqueous solutions, with pH ranging over a wide range which can range, for example, from 0.3 to very basic pH, greater than 12.5, while retaining very good efficiency at these very basic pHs.

To promote the separation of the complex formed, an organic amino compound can be used in an organic phase immiscible with water so as to extract the complex in the organic phase. In this case, the process can be carried out in a solvent extraction installation in which the co-current or counter-current contact the aqueous solution to be treated with the organic phase containing at least one of the amino compounds mentioned above. Generally the amino organic compound is dissolved or diluted in an organic solvent which can consist of a paraffinic or aromatic hydrocarbon, a chlorinated compound such as CHCl₃ or CCl₄, an ether, an ester, an alcohol, a ketone, alone or as a mixture. Preferably, in the invention an organic solvent is used which consists of a mixture of a hydrocarbon and an alcohol, for example a mixture of n-dodecane and octanol-1.

The extraction devices that can be used are conventional equipment such as mixer-settler batteries, liquid-liquid extraction columns (pulsed, agitated, packed, etc.), liquid-liquid chromatography columns . In these devices, the flow rates of aqueous solution and of organic solution are chosen so as to obtain the desired contact time between the two solutions. Likewise, the concentration of amino compound in the organic solution is chosen as a function of its solubility in the solvent so as to obtain a good extraction of the acid organophosphorus compounds or of the organophosphate ions while having good physico-chemical characteristics linked to the hydrodynamics of systems.

Generally, the extraction is carried out at room temperature, but it can be carried out at higher temperatures, ranging for example from 20 to 50 ° C., or at temperatures below room temperature if this proves necessary.

According to a variant of the invention, it is also possible to facilitate the separation of the complex formed during the reaction by bringing the aqueous solution containing the acid organophosphorus compounds or the organophosphate ions into contact with a solid support on which the organic compound is fixed, optionally dissolved or diluted in the organic solvents described above. In this case, liquid-liquid chromatography techniques can be used to highlight performs the reaction and separation steps.

The process of the invention applies to many acidic organophosphorus and / or organophosphate compounds. However, it is most often used to recover acidic organophosphorus compounds consisting of mono or di-alkylphosphoric acids or the corresponding organophosphate ions.

Other characteristics and advantages of the invention will appear better on reading the following examples given, of course, without limitation, to illustrate the process of the invention.

EXAMPLE 1 Use of a primary amine.

In this example, treating aqueous solutions containing 4,4.10 ^-3 mol.l ^-1 of dibutyl phosphoric acid (DBP) and 0.1 mol.l ^-1 of NaNO₃, having pH from 4.5 to 7, using as organic phase the product Primene JMT which is a mixture of primary amines having 18 to 22 carbon atoms, in nitrate form at a concentration of 0.38 mol.l ^_1 in the mixture octanol-1-n-dodecane at 18% d 'octanol-1 and 82% n-dodecane. The contacting is carried out for 5 min at room temperature using equal volumes of aqueous solution and of organic solution. After settling of the phases, the DBP concentrations of the aqueous phase and of the organic phase are determined. This gives the value of the partition coefficient D of dibutylphosphoric acid DBP which is equal to the ratio of the concentration of DBP in the organic phase to the concentration of DBP in the aqueous phase.

Under the conditions described above, the partition coefficient D of the DBP is always greater than 40.

EXAMPLE 2 Use of a secondary amine.

In this example, aqueous solutions containing 0.1 mol.l ^_1 of NaNO₃ and 5.3.10 ^_3 mol.l ^_1 of DBP, having a pH ranging from 3 to 7.1, are brought into contact with an organic phase consisting of Genamine CS200 nitrate (Hoechst) in solution in an octanol n-dodecane mixture containing 18% octanol and 82% dodecane. Genamine is a mixture of secondary amines containing 51% of amine with 12 carbon atoms, 22% of amine with 14 carbon atoms, 11% of amine with 16 carbon atoms and 14% of amine with 18 carbon atoms. The extraction is carried out as in Example 1 but operating at a temperature of 50 ° C.

The DBP sharing coefficients are always greater than 50 for these solutions.

EXAMPLE 3 Use of a quaternary ammonium salt.

Aqueous solutions having a pH ranging from 2.5 to 12.5, containing 0.1 mol.l ^_1 of NaNO₃ and 4.8.10 ^_3 mol.l ^_1 of DBP are brought into contact with an organic phase consisting of tetraheptylammonium chloride at a concentration of 0.4 mol.l ^_1 in the mixture 18% octanol and 82% n-dodecane.

The contacting is carried out for 5 min at a temperature of 20 ° C. using equal volumes of aqueous phase and of organic phase.

The partition coefficient of the DBP is always greater than 40.

EXAMPLE 4 Use of a tertiary amine.

In this example, an aqueous solution is treated containing 5.10 ^_3 mol.l ^_1 of dibutylphosphoric acid (DBP) and 0.5 mol.l ^_1 of sodium chloride using as organic phase triisooctylamine diluted to 0.44 mol. l ^_1 in a mixture of dodecane-octanol-1 at 16% by volume of octanol-1.

A volume of the aqueous solution is brought into contact with a volume of the organic phase for 5 minutes with stirring, then the phases are allowed to settle and the concentrations of dibutylphosphoric acid in the aqueous phase and the organic phase are determined. This gives the value of the partition coefficient D of the dibutylphosphoric acid between the aqueous phase and the organic phase, the latter being equal to the ratio of the concentration of dibutylphosphoric acid in the organic phase to the concentration of dibutylphosphoric acid in the phase aqueous.

Under the conditions described above, the partition coefficient D of dibutylphosphoric acid is 35.

EXAMPLE 5

The same procedure is repeated as in Example 4, but the starting aqueous solution contains 0.5 mol.l ^_1 of sodium nitrate instead of sodium chloride.

Under these conditions, the partition coefficient D of dibutylphosphoric acid is 30.

EXAMPLE 6

The same procedure is repeated as in Example 4, but the starting aqueous solution contains 0.5 mol.l ^_1 of sodium perchlorate instead of sodium chloride. Under these conditions, the partition coefficient D is 15.

EXAMPLE 7

The same procedure is repeated as in Example 4, but the starting aqueous solution contains 0.5 mol.l ^_1 of sodium sulfate instead of sodium chloride. Under these conditions, the partition coefficient D of dibutylphosphoric acid is 59.

In view of these examples, it can be seen that the use of triisooctylamine makes it possible to purify more than 93% all the solutions treated in examples 4 to 7, the majority being purified to more than 95%.

EXAMPLE 8

The procedure of Example 4 is repeated, the aqueous solution this time being a solution containing 0.45 mol.l ^_1 of nitric acid, 5.3 gl ^_1 of trivalent plutonium, 0.1 mol.l ^_1 of nitrate of hydrazinium and 5.10 ^_3 mol.l ^_1 of DBP. An organic phase is used consisting of triisooctylamine at 0.44 mol.l ^_1 in a mixture of octanol and n-dodecane containing 16% by volume of octanol.

Under these conditions, the distribution coefficient of DBP is equal to 50 and that of plutonium is equal to 0.06.

EXAMPLE 9

In this example, an aqueous solution is treated obtained during the washing of tributylphosphate (TBP) used in a plutonium and uranium purification cycle. Washing of the TBP is carried out with an aqueous carbonic solution obtained by partial neutralization of the hydrazine base with CO₂. The aqueous solution leaving the washing installation contains 4,78.10 ^_3 mol.l ^-1 of dibutyl phosphate and its pH is adjusted to a value of 6.8 by adding nitric acid, then treated according to the method of invention, in a counter-current liquid-liquid extraction installation comprising two stages, using an organic phase comprising as solvent a mixture of n-dodecane and octanol-1 at 16% by volume of octanol-1 , containing 0.32 mol.l ^-1 of triisooctylamine and 0.12 mol.l ^-1 of triisooctylammonium nitrate.

In this installation, a ratio: aqueous flow / organic flow of 0.46 is used and an aqueous phase is collected at the outlet of the installation, the dibutylphosphate content is 0.08.10 ^_3 mol.l ^_1 , this which corresponds to a purification rate of 98.4%.

It is noted further that the plutonium IV is present in the aqueous phase, does not substantially extract is in the organic phase, the plutonium of the partition coefficient is less than 1.2.10 ^_2. Also, the purified aqueous solution can be recycled for subsequent treatments for the recovery of fissile material.

Claims (11)

1. Process for the recovery of acid organophosphorus compounds and/or organophosphate ions present in an aqueous solution, characterized in that the aqueous solution is contacted with at least one organic amino compound which is not very soluble in water, chosen from among compounds having at least one amine function, the salts of these amine compounds with an acid and quaternary ammonium salts and in that the complex formed is separated from the aqueous solution by the reaction of the acid organophosphorus compounds and/or organophosphate ions with the organic amino compound or compounds.

2. Process according to claim 1, characterized in that the organic amino compound is a primary, secondary or tertiary amine, or a quaternary ammonium salt.

3. Process according to claim 2, characterized in that the organic amino compound is a trialkylamine.

4. Process according to claim 3, characterized in that the amine is partly or totally salified by an acid.

5. Process according to claim 3, characterized in that the trialkylamine is triisooctylamine.

6. Process according to any one of the claims 1 to 5, characterized in that the organic amino compound is dissolved or diluted in an organic solvent.

7. Process according to claim 6, characterized in that the organic solvent is a mixture of a hydrocarbon and an alcohol.
8. Process according to claim 7, characterized in that the organic solvent is a mixture of n-dodecane and 1-octanol.

9. Process according to any one of the claims 1 to 8, characterized in that the organic amino compound is fixed to a solid support.

10. Process according to any one of the claims 1 to 9, characterized in that the acid organophosphorus compounds are monoalkylphosphoric or dialkylphosphoric acids.

11. Process for the treatment of aqueous effluents containing acid organophosphorus compounds and/or organophosphate ions characterized in that it consists of extracting from these effluents the acid organophosphorus compounds and /or the organophosphate ions by realizing the process according to any one of the claims 1 to 10.