AU595248B2 - Process for the separation of metals from aqueous solutions using dialkyl substituted amides - Google Patents

Description

i FORM 10 SPTUSON FERGUSON COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: o673186 5952 4 8 Class Int. Class Complete Specification Lodged: Accepted: Published: 9 o•0 9 0 0 O O ooooo Priority: Related Art: Name of Applicant: Address of Applicant: Actual Inventor(s): Address for Service: Comitato Nazionale per La Ricerca e per Lo Sviluppo dell'Energia Nucleare e delle Energie Alternative 125 Viale Regina Margherita, 1-00198 Roma RM, Italy GIULIO MARIA GASPARINI and GIUSEPPE GROSSI Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia 9 9 Complete Specification for the invention entitled: "PROCESS FOR THE SEPARATION OF METALS FROM AQUEOUS SOLUTIONS USING DIALKYL SUBSTITUTED AMIDES" The following statement is a full description of this invention, including the best method of performing it known to us SBR:ALB:L1OM

ABSTRACT

The present invention relates to a process for the selective separation of actinides and/or Au, Pt, Ir and Pd metals from aqueous solutions using techniques of liquid- liquid extraction in the presence of an organic phase or techniques of chromatography in the presence of a solid phase, comprising the operations of: adjusting the acidity of said aqueous solution to obtain a value of the distribution coefficient such as to enable said actinides and/or metals to be transferred to said organic phase or solid phase; subjecting said acidified aqueous solution to extraction or chromatography by said organic or solid phase, respectively, containing as extracting agents dialkylsubstituted amides of formula (I)

R'

R C N (I) II S* 0 R" in which R is a straight or branched aliphatic chain with 8 or less carbon S 20 atoms, and R' and R" are straight or branched aliphatic chains in which the sum of the carbon atoms in R' R" is less than or equal to 8; and contacting said organic or solid phase containing said actinides and/or metals with a fresh aqueous solution to re-extract said actinides and/or metals from said organic or solid phase and transfer them to said fresh aqueous solution for further processing.

The process according to the invention may be used both in the Sseparation of nuclear materials (Pu, U, Th) and in the separation and recovery of more directly commercial materials (Au, Pt, Ir, Pd).

0^ JLH/637. .3 13 ~iinrr~hc 1A The present invention relates to a process for the selective separation of actinides and/or Au, Pt, Ir and Pd metals from aqueous solutions using techniques of liquid-liquid extraction in the presence of an organic phase or techniques of chromatography in the presence of a solid phase, comprising the operations of: adjusting the acidity of said aqueous solution to obtain a value of the distribution coefficient such as to enable said actinides and/or metals to be transferred to said organic phase or solid phase; subjecting said acidified aqueous solution to extraction or chromatography by said organic or solid phase, respectively, containing as extracting agents dialkylsubstituted amides of formula (I)

/R'

R C -N (I) 011 R" in which R is a straight or branched aliphatic chain with 8 or less carbon 15 atoms, and o and R" are straight or branched aliphatic chains in which the sum of the carbon atoms in R' R" is less than or equal to 8; and contacting said organic or solid phase containing said actinides and/or metals with a fresh aqueous solution to re-extract said actinides and/or metals from said organic or solid phase and transfer them to said fresh aqueous solution for further processing.

Although these amides are known in the literature, they have been used mainly as plastifying agents.

•The process according to the invention may he applied in a range of applications, including conventional nuclear technologies for the recovery, separation and purification of metals in solutions, in particular for the separation of natural and/or enriched uranium and/or plutonium and thorium 1 from JLH/637y i

I

2 0 4, *r 0 0 0 0600 00 0000 *i 4 0000 solutions of dissolved spent nuclear fuel.

Currently uranium and plutonium are separated using liquid-liquid extraction, but with tributylphosphate (TBP) as selective extracting agent.

Known as the PUREX process, it offers the disadvantage, especially with highly active fuels, of producing breakdown products of tributylphosphate which can interfere with the process because they are not soluble in water or they form slightly soluble complexes with some metals which are difficult to remove. These complexes distribute themselves in a semisolid phase between the two phases, progressively blocking the extraction process and necessitating the replacement of the organic phase.

15 The process according to the invention prevents the problems cited above since breakdown of the disubstituted amides gives rise mainly to secondary amines and carboxylic acids, accordinq to the following general formula: 20 RCO-NR'R" RCOOH 4 HNR'R" These compounds are not as strong eomplexinq agents as the 'breakdown products of tributylphosphato.

Furthermore, as a function of the length of the aliphatic chains on the carbon and nitrogen, the pr, let carboxylic acid and secondary aminp may be soluble in water and so eliminated automatically from the -3 organic phase during the extraction.

It should also be considered that while re-extraction of the uranium in aqueous phase with tributylphosphate offers some difficulties, with the amides said extraction is simple and quantitative.

Therefore an object of this invention is a process for the separation of uranium and plutonium comprising: a first step for separation of uranium and plutonium from the solution of dissolved spent nuclear fuel; 10 a second step for -reatment with a reducing agent to convert the Pu (IV) to Pu (ITT); and a third step of liquid-liquid extraction to extract the uranium into the organic phase, wherein the extracting agents used are dialkylsubstituted amides of formula (I) as or

S

a.

*t 0

S.

.S S a a 4* $too a.

a a 54r a *0* a~r R C- N 0 R" where R, R' and R" are as defined above.

NN'-di-n-butyloctanamide has been found particularly suitable for separation of uranium from plutonium.

This new process has hben called AMDEX.

It has also been found that the disubstituted amides used in the process for separation of uranium from plutonium show a high selectivity in the separation of hexavalent actinides with respect to tetra- ORG.PHASE ALK. WASHING ASHING SQL.

OBOA 1A NA 2C0 3 0.5n it 2 I 1 'n 1K MrSIIILft 1. 1 4 valent. actinides, particularly as a function of the acidity of the solution.

Therefore a further object of the present invention is a process for the separation using liquid-liquid extraction techniques, or hexavalent ac'tinides from tetravalent actinides, wherein amides of formula are used as extract inq aqents in the o.ganic phase: 7

RI

R C N

(T)

0R where R, RPI andi P r as, dlef ined aoe The advantage of this process, applied in particular to the separation of ITiVT) from Th(TV) (called the TAMDEX process) and to thc- separation of U(VT) from *Pu(TV) (called the PAMIPEX process) lies in the fact that rno previous reduction of plutonium to valence 3 is required and in Fhe hiqh sol,,etivity of the process itself.

0:0 20 For the separation of uranium and -hcrium, N,N'l" di-n-butyl-2-ethylhe-xanamidC has beon found advan- tacjeous (is tho cEalkylqubstitutod ami do; for that of uranium and plut-onium, NN riu J ,'-irehl hut yramido is preferred.

T t has also been f ound tha t The disubstituted am id(-s show intOrest inq proporties also for tHif soparn- UO/ 21,L U~4 13,39/ 11 o shj 5 tion of non-nuclear elements of high commercial or strategic interest, such as gold, platinum, iridium, palladium.

Therefore another object of this invention is a process for the liquid-liquid extraction and/or for the separation or quantitative recovery of one of the metals cited above (Au, Pt, Tr, Pd) from aqueous solutions prepared by dissolving the metals or from industrial waste solutions at low concentration, where'n amides of formula are used as selective extracting agents: 0

R

R-C N" (I) O R" where R, R' and R" are as described above.

This process has been called AUMIDEX.

In this process as well the acidity plays an im- 0• 'portant role in determining selectivity.

As mentioned above, the amides of formula (I) S 20

/R'

R C N

(I)

U

0 R" where R, R' and R" are as described above, used in the process for separation of metals from aqueous solution according to the invention were previously used mainly ns plastifying agents.

_i 6 Therefore another object of the present invention is the use of amides of formula as sequestrants or extracting agents in separation chromatography or in liquid-liquid extraction of all the metals cited above from acqueous solution.

The dialkylsubstituted amides used according to the invention have a different structure as a function of their use. Amides with completely straight chains, such as N,N'-dibutyloctanamide or N,N'-dibutylhexan- 10 amide are particularly suitable as alternatives to .e o.

tributylphosphate in a PUREX type process with partition of plutonium by means of reduction (AMDEX process). They are also suitable for extraction of gold (AUMIDEX process).

Dialkylsubstituted amides with a branch in the alpha position with respect to the carbonyl, for example N,N'-dibutyl-2-ethylhexanamide, are particularly suitable for the separation of hexavalent actinides from tetravalent actinides (TAMIDEX).

20 Dialkyl amides with other types of branching, for example N,N'-dibutyl-3,3'-dimethylbutyramide, are particularly suitable for the separation of hexavalent uranium from tetravalent plutonium with iio reduction of the plutonium to valence three (PAMIDEX process).

Extraction of these metals is more rapid and phase I -7 separation is quicker than in analogous tests with tributylphosphate.

The possibility of saturation of the metal in the organic phase is highly dependent not only on the experimental conditions but also on the degree of branching of the aliphatic or aromatic chain.

The concentration of the amides, generally dissolved in an aromatic solvent, depends on the quantity of metal to be extracted.

0 Table 1 reports the principle properties of the amides used.

Table 1 Properties of the amides

C

S.

S.

C C

C

0

CCC.

C.

C

CC..

r 15 Amide N,N'-di-nbutyloctanamide N,N'-di-nbutyl-2ethyl- 20 butyramide N,N'-di-nbutyl-3,3'methylhutyramide N,N'-disec-butylhexanamide

B.P.

100-112 (760) 111-112 (1) 145-150 (28) nD 2 0 solubility d H20 dode- mesicane thylene 1.452 0.861 <0.01 >1000 1.451 0.861 <0.001 >1000 1.449 0.833 <0.001 >1000 >1000 >1000 >1000 >1000 130-150 1.490 0.856 <0.01 >1000 Tables 2 and 3 below report several distribution coefficients D for the liquid-liquid separation process u -8in which the amides according to the invention are used.

Table 2 Distribution coefficients organic plase: di-n-butyloctanamide or di-n-butyl-hexanamide (UM in mesith: 1 ene) Aqueous phase: 4M HN03 4M HC1 (1:3) metal D(o/a) Au 1.0000 Fe Sn I.

5Hg, Zn, Ag 0.

Cu, Pb 0.01 *Table 3 woo$ Distribution coeficients for U(VT), Pu(IV) and PU(IIT) *and some fission products (M amide in mesithylene; phase ratio =1) Nitric acid in aqueous phase *goo* 3M 6M o o 20 Di-n-butyl-actanamide D tJ(VI) 33 18 D Pu(TV) 310 D Pu(ITI) 0,1 D Zr 0.1-0.01 D Ru 0. 0001 Di-sec-butyl-hexanami do D U(VI) 10 14 r i~ 9 D Pu(IV) Di-3,3'-di-methyl-butyl-butyramide D U(VI) D Pu(IV) Di--butyl-2-ethyl-octanamide D U(VI) D Pu(IV) 0* *e 0 000 @0 0 0 0*00 @0 9 .R 000 The liquid-liquid extraction processes for which the dialkylsubstituted amides according to the invention are proposed consist essentially in placing the aqueous solution containing many metals, including those to be separated, in intimate contact with an organic solution immiscible with water, containing a substance (in this 15 case an amide) capable of 'binding' and so extracting selectively and qulntitatively from the aqueous phase to the organic phase the metal or metals of interest, separating them from the others.

The organic phase containing the metal(s) is then placed in contact in the sane way with a suitable aqueous solution to re-extract all or some of the metals in the organic phase and return them to an aqueous phase.

Slightly acidic or reducing solutions are normally used which, by changing the valence of the metal, make it less extractable. This is the case for the separation of uranium from plutonium in the PUREX process, whero 10 .I I eo 9 9 9 the tetravalent plutonitum extracted with tributylphosphate into the organic phase is reduced to trivalent plutonium, which is not soluble and so returns to the aqueous phase.

In other cases competitive water-soluble extracting agents are used.

The apparatus used for these extraction operations consists of multistep contac-ors of various types, such as: banks of mixer settlers, pulsed columns and centrifugal contactors.

The amides proposed may also be used in columns (pure or dissolved in solvent) dispersed on a finely divided inert support. In this case the aqueous solution containing the metals of interest is passed through the column and the metals remain 'bound' to the material in the column. They are then recovered by passing a suitable aqueous solution through the column. This process is no longer liquid-liquid extraction, but rather extractive chromatography.

EXAMPLES

The invention will be illustrated with reference to the attached drawings, in which; figure 1 shows an example of the AMDEX prower"s figure 2 shows and example of the TAMIDEX nrover figure 3 shows an example of the \4M' and figure 4 shows an fxample of the AtMIMDEX proco c 11 The following examples are exemplificative only and do not in any way limit the scope of the invention.

Example 1 (AMDEX process) With reference to figure 1, a 1M solution of N,N'di-n-butylactanamide (DBOA) in mesithylene is passed at a flow rate of 6.5 liters/hour through a multistep contactor in the opposite direction to an aqueous solution containing 250 q/liter of uranium and 2.5 q/liter of plutonium, which flows at a rate of 2.2 liters/hour.

1 0 This 2M acid solution contains fission products as well.

After the extraction step, the fission products are found in the extract in the same quantity, while the Concentration of uranium has fallen to 5.9 x 10- 2 g/liter and that of plutonium to 8.7 x 10- 6 g/liter.

The organic solution is then treated with a reducing agent to separate the Pu(III) from the uranium according to the classic PUREX process, from which the AMDEX process differs in its use of N,N'-di-n-butyloctanamide instead of tributylphosphate.

20 Example 2 (TAMDEX process) Figure 2 shows an example of a process for the separation of U(VI) from Th(TV) using a 1M solution of NN'- -di-.-butyl-2-ethylhexanaride in mesithylene.

A solution containing 13.75 q/liter of uranium and 236.7 g/liter of thorium is separated chromatographically to give an aqueous solution containing approximately 12 120 g/liter of thorium and 4 0.015 g/liter of uranium and an organic phase enriched in uranium. The final extract contains more than 3.4 g/liter of uranium and no detectable thorium.

Example 3 (PAMIDEX process) Figure 3 shows a process for the separation of U(VI) from Ph(IV). In this case N,N'-dibutyl-3,3'-dimethylbutyramide is used.

Example 4 (AUMIDEX process) Figure 4 shows the broad outline of a process for the separation and recovery of gold from solutions for working and cleaning the metal or its minerals. Starting from a solution containing 1000ppm of gold and 2 g/liter of iron, after varying the phase ratio and acidity, a final solution is obtained with 37.4 mg/liter of gold *and only 0.02 mg/liter of iron. The amide used in this process is N,N'-di-n-butyloctanamide. In this case it should be noted that fav. urable distribution coefficient of gold (see table 2) (in general dissolved 20 in HC1/HN0 3 mixtures) and the low concentration of the metal allow the use of very low concentrations of extracting agent.

I .1.

Claims (9)

1. A process for the selective separation of actinides and/or Au, Pt, Ir and Pd metals from aqueous solutions using techniques of liquid- liquid extraction in the presence of an organic phase or techniques of chromatography in the presence of a solid phase, comprising the operations of: adjusting the acidity of said aqueous solution to obtain a value of the distribution coefficient such as to enable said actinides and/or metals to be transferred to said organic phase or solid phase; subjecting said acidified aqueous solution to extraction or chromatography by said organic or solid phase, respectively, containing as extracting agents dialkylsubstituted amides of formula (I) /R' R C N (I) 0R" in which R is a straight or branched aliphatic chain with 8 or less carbon atoms, and R' and R" are straight or branched aliphatic chains in which the sum of the carbon atoms in R' R" is less than or equal to 8; and contacting said organic or solid phase containing said actinides and/or metals with a fresh aqueous solution to re-extract said actinides and/or metals from said organic or solid phase and transfer them to said fresh aqueous solution for further processing.

2. Process as claimed in claim 1, applied to the separation of uranium and plutonium, in which said separation is effected after reducing the plutonium to Pu(III) with a suitable reducing agent and using N,N'-di-n-butyloctanamide as extracting agent.

3. Process as claimed in claim 1, for the separation of uranium (VI) from an aqueous solution containing thorium in which N,N'-di-n- butyl-2-ethylhexanamide is used as extracting agent.

4. Fiocess as claimed in claim 1, for the selective extraction of uranium (VI) from plutonium in which N,N'-dlbutyl-3,3'-dimethyl- butyramide is used as extracting agent.

JLH/637y ,d 1 n 14 Process as claimed in claim 1, for che selective extraction of gold from aqueous solutions containing other metal ions in which N,N'-di-n- butyloctanamide is used as extracting agent.

6. Process as claimed in claim 1 or 5, for selective extraction of platinum and/or iridium and/or palladium from their aqueous solutions.

7. A process for the selective separation of actinides and/or Au, Pt, Ir and Pd metals from aqueous solutions using techniques of liquid- liquid extraction in the presence of an organic phase or techniques of chromatography in the presence of a solid phase, substantially as hereinbefore described with reference to Example 1 and Figure 1, Example 2 and Figure 2, Example 3 and Figure 3 or Example 4 and Figure 4.

8. Actinides and/or Au, Pt, Ir and Pd metals, whenever separated by the process according to any one of claims 1 to 7. 9* 9 9 .9 9

9. 99 99 r. DATED this Comitato Nazionale per Nucleare SIXTEENTH day of JANUARY 1990 la Ricerca e per lo Sviluppo dell'Energia e delle Energie Alternative Patent Attorneys for the Applicant SPRUSON FERGUSON 9 9. .9 4 A JLH/637y