US3896045A

US3896045A - Decontamination process for radio-active liquids

Info

Publication number: US3896045A
Application number: US317224A
Authority: US
Inventors: Karel J A Peeters; De Voorde Norbert L C Van
Original assignee: Belgonucleaire SA
Current assignee: Belgonucleaire SA
Priority date: 1971-08-24
Filing date: 1972-12-21
Publication date: 1975-07-22
Anticipated expiration: 1992-07-22

Abstract

Radio-active liquids and the products thereof are decontaminated by contacting the radio-active liquid with a sorbent in a sulfate-containing medium selected from the group consisting of a barium salt and a barium salt mixed with up to 50 percent of a metal ferrocyanide.

Description

Elite States Patent 1191 Peeters et a1.

1 1 DECONTAMINATION PROCESS FOR RADIO-ACTIVE LIQUIDS [75] Inventors: Karel J. A. Peeters, Geel; Norbert L.

C. Van De Voorde, Mol, both of Belgium [73] Assignee: Belgonucleaire S.A., Brussels,

Belgium [22] Filed: Dec. 21,1972

[21] Appl. N0.: 317,224

Related US. Application Data 163] Continuation-impart of Ser. No. 174,504, Aug. 24,

1971, abandoned.

[30] Foreign Application Priority Data Augv 29, 1972 Germany 2242412 152] US. Cl..... 252/30l.1 W; 210/53; 252/301.l R; 423/2; 423/6; 423/11; 423/12 [51] Int. Cl. G2lc 19/46 [58] Field of Search 252/30l.l R, 301.1 W; 210/53; 423/2, 6,11,12

[4 1 July 22,1975

Primary ExaminerLeland A. Sebastian Assistant Examiner-R. E. Schafer Attorney, Agent, or FirmOstrolenk Faber Gerb & Soffen [57] ABSTRACT Radio-active liquids and the products thereof are decontaminated by contacting the radio-active liquid with a sorbent in a sulfate-containing medium selected from the group consisting of a barium salt and a barium salt mixed with up to 50 percent of a metal ferrocyanide.

13 Claims, No Drawings DECONTAMINATION PROCESS FOR RADIO-ACTIVE LIQUIDS This is a continuation-in-part of application Ser. No. 174,504, filed Aug. 24, 1971, now abandoned.

Heretofore it has been proposed to purify radioactive liquids with the help of ion exchangers, however, ion exchangers are expensive so that they have to be regenerated, which regeneration gives rise to further radioactive liquids (regeneration liquids).

Another known process for the treatment of radioactive liquids involves the chemical co-precipitation of the radio-active ions. The precipitate obtained is then filtered and homogeneously mixed with hot bitumen, during which step the water present evaporates, and the mass thus obtained is then stored in steel drums. As the precipitates cannot easily be filtered, large filtering installations are needed, or otherwise the precipitate must be dehydrated according to the frost-thaw method in order to make it more filterable.

All these methods furthermore have the disadvantage that they are not specific for radio-active ions, so that the ion exchangers tend to become largely saturated by ions which it is not desired to extract (such as Na, Ca or Mg), or that the precipitate consists largely of ions which it is not desired to extract, such ions being always present in the water to be purified.

The object of this invention is to provide a new method that is specific for radio-active ions, and at the same time allows the disadvantages of the methods already known to be at least partly avoided.

The present invention pertains to a method for extracting radio-active ions present in tracer quantities in a contaminated liquid, in which the liquid is contacted with a sorbent in a sulfate-containing medium selected from the group consisting of a barium salt, and a barium salt mixed with a metal ferrocyanide.

lons such as Na, Ca, Mg, Fe, Al, thus are not extracted, while the radio-active ions are extracted from the liquids to be purified.

As a matter of fact, experiments have shown that different inorganic substances have specific sorption characteristics when they are brought into contact with solutions containing radio-active ions and more particularly ions in tracer quantities.

The term sorption as used in this specification includes any and every means by which an ion can be transferred from a solution to a solid mineral substance in contact with the solution.

The sorption may be achieved by, for example, one or more of isotopic exchanging, formation of mixed crystals, and more particularly precipitation, coprecipitation and post-precipitation.

The problem of the purifying of radio-active liquids lies particularly in the extraction of the following ions: strontium, cesium, cerium, cobalt, ruthenium, radium and antimony.

DESCRlPTION OF THE PREFERRED EMBODIMENTS The invention will be hereafter described with the help of a number of tests and various examples. Barium sulfate BaSO, is prepared by mixing, at room temperature, equal volumes BaCl and Na SO the precipitate thereby formed is filtered and, without being washed, dried at 100C. The powder thus formed is used for determining the sorption characteristics, expressed by the distribution coefficient Kd, which is defined as the ratio of the concentration of the ion on the sorbent (per gram) to the concentration of the ion in the solution (per ml). The experiments were carried out with demineralized water to which the radio-active ions to be determined, and 40 ppm Ca, were added. The Kds obtained are for Sr 7, for Ra 27 and for Ce 284.

After addition of H to the test water, for instance to lower the pH to 2, the Kd values increase to the following values for Sr l950, for Ra 3000 and *for Ce 6600.

The sorption mechanism may be deduced from these facts. If pure BaSO, itself had sorption properties, there would be no difference in the Kd values before and after the addition of H 80 However, this addition is necessary to achieve good sorption. On the other hand, as can easily be proved with the help of a reference solution, the sulfate ions in the solution, originating from the added H 80 are insufficient to reduce the solubility product of Sr and Ra, in order to precipitate them as tracers.

The reason why Sr and Ra are more effectively sorbed after the addition of H 80 is probably due to the co-precipitation phenomenon on newly formed BaSO Indeed, barium ions still present in the prepared BaSO (not washed out during the preparation) form, together with the sulfate ions in the solution, a supplementary BaSO, precipitate on the already existing solid BaSO During this formation, strontium, radium and cerium are co-precipitated.

The Kd values can be considerably increased by preparing BaSO as above, but with a surplus of barium ions. The Kd values thus obtained are summarized in Table 1. Furthermore, it is possible to increase the sorption properties of BaSO by activating it, for instance by adding NaNO during preparation of the BaSO The concentration of NaNO to be used will be such that there is the range from 1 Na ion for l Ba ion to 1 Na ion for 24 Ba ions.

Other concentrations ofNaNO do not favorably influence the sorption capacity of BaSO TABLE 1 Sorption of Sr, R21 and Ce on BaSO,

Test water demineralized water containing Sr, Ra and Ce and 40 ppm Ca to I which H 80 is added till a pH 2 is obtained Composition B2180 Kd Y Sr Ra Ce 5 Ca *Ba/SO, 1/ l 7 27 284 0 Bra/S0 1/1 1.950 3.000 6.600: l20 Ba/SO 2/1 14.000 28.000 45.000 l60 Ba/SO 3/l 27.400 39.000 70.000 I60 Ba/SO, 3/1 45.300 73.000 194.000

Test water without addition of H 50. "*BaSO, activated by addition of l volume NaNO to 3 volumes BaCl during the preparation of BaSO,

water, to which sodium and magnesium ions were added, show that these ions are not co-precipitated.

From the above considerations it appears that the coprecipitation takes place during the formation of freshly formed BaSO It is to be noted that fresh BaSO could also be formed starting from any soluble barium salt by the addition of SO, ions. Good results have been obtained with BaCO in a sulfate medium. Thus, fresh BaSO, is formed and the coprecipitation of strontium. radium, cerium is achieved. With the same test water, the sorption on BaCO has been carried out in the same acid conditions (pH 2 H SO as for BaSO and then in a Na SO, medium. The Kds obtained are summarized in Table 2.

itate is then allowed to form for l or 2 hours before being filtered. Without being washed, the precipitate is then dried at 100C. The cake thus obtained is then ground into grains of the required size (larger than 80 mesh in this example). The theoretical composition of said grains is 97.7 BaSO with a molar ratio Ba/SO of 3/1, and 2.3 (Cu Fe(CN) with a molar ratio Cu Fe(CN) of 1/1. Said grains are then placed in a column, through which test water is poured.

The Kd values obtained are given in Table 3.

The same example is repeated, but NaNO is added in a ratio of 3 Ba ions for 1 Na ion.

The same example is repeated but NaNO is replaced by CaCl in a ratio of 3 Ba ions for 1 Ca ion.

TABLE 3 Sorption of Sr. Ce and Cs on mixed sorbent BaSO /Cu -Fe(CN).

Tcst water deminerulized water containing Sr. Ra, Ce and Cs. 100 ppm Na and ppm Cu. to which H. ,SO is added till a pH 2 is obtained CuCl Ca/Bu V3 9150 H.500 63.750

Kd for Ru has not been determined TABLE 2 Sorption of Sr, Ra and Ce on BaCO Test water demineralized water containing Sr, Ra and Ce and 40 ppm Ca by pH 2 obtained in a medium as given in column 2. BaCO commercially available This table shows that in a medium of 0.1 N Na SO the results of sorption on BaCO are comparable with those of BaSO in a molar ratio of Ba/SO. equal to 3/1.

As it is not always economical to handle large volumes of effluents in a medium of 0. l N Na SO it is proposed according to the invention to handle said volumes in an ion exchanger and to treat the regeneration liquids subsequently obtained from said ion exchanger with BaCO It should be noted that ruthenium and antimony will also be sorbed on BaCO To facilitate industrial use of these products, however, they should preferably have a structure which facilitates their use in industrial apparatus, for example columns, or mixer settlers. Barium sulfate and barium carbonate however are obtained as a fine powder and as such are unsuitable for use in industrial columns.

According to another feature of the invention, a suitable structure can be imparted to BaSO, by preparing it as a mixed salt with a metal ferrocyanide. For instance, BaSO; and Cu Fe(CN) prepared as a mixed substance has a good granular structure and can be These examples clearly show the importance of the activation of the sorbents.

Another sorbent which could be used according to the present invention is BaCO- and Cu Fe(CN) Contrary to the above-mentioned mixed product containing BaSO.,, this mixed salt based on BaCO is still a fine powder so that the contact between the mixed product and the effluents to be treated will have to be carried out in batches. The sorbent can, for example, be prepared as follows.

On the one hand, one volume 1 molar BaCl is added to one volume 1 molar Na CO and allowed to precipitate homogeneously. On the other hand, one volume 0.1 molar K.,Fe(CN) is added to two volumes 0.1 molar CuSO, and allowed to precipitate homogeneously. Both precipitates are mixed, stirred and dried without being washed. This preparation results in a mixed sorbent comprising 91 BaCO with a molar ratio Ba/CO of 1/1 and 9 Cu Fe(CN) with a molar ratio Cu /Fe(CN) of 1/1. The Kds on this sorbent are determined with the same test water as used in Table 3 and given hereafter in Table 4.

The pH 2 was obtained in a medium as given in column 2. (5 g sorbent was mixed with 1 liter solution for 15 mins. and then centrifuged).

TABLE 4 Composition Medium Kd sorbent Sr Ce Cs 91 7r BaCO and H 50 1.120 17.720 12.500 9 '7! Cu Fe(CN)., 0.0lN Na SO, 8.630 56.200 30.700 0.1N Na SO, 20.460 59.600 77.000

quently obtained from the ion exchangers with this sorbent.

As the sorbent is effective in a concentrated salt solution, it will present an answer to the problem for decontamination of regeneration liquids of ion exchangers.

It is to be noted that ion exchangers have been proposed several times for decontaminating radio active liquids. However, up to now they have not been practical because of the problems raised by the decontamination of their regeneration liquids, which in fact are effluents with radio-active ions in a concentrated salt solution. With the help of mixed BaCO Cu Fe(CN) sorbent, these regeneration waters can be simply and effectively treated without further problems.

The sorbent is used in a sulfate medium if strontium is present in the effluents to be treated. As a matter of fact, it has been found that the sulfate concentration influences the sorption of the different radio-active ions. Table 5 shows the influence of the sulfate concentration while using the above described BaCO Cu Fe(CN),,- sorbent. The test water contained a concentration of 2 molar NaCl and 0.05 molar CaCl, and traces of Cs, Sr, Ce, Ra, Co, Ru and Sb. 3 g. sorbent were added to 1 liter test water and mixed for one hour before filtration.

Ce and Ra, on the other hand, are sorbed mainly by BaCO The proportion of the mixed sorbent should especially be considered for the sorption of Sr and Co. It has been found that for a good sorption of Sr at least 90 of BaCO should be present in the mixed sorbent.

As far as Co is concerned, the same proportion gives good results, but could still be' increased to a proportion of 85 BaCO .and 15 CuF e(CN) However, in view of the radiological toxicity of Sr, a mixed sorbent comprising at least 90 BaCO is preferred to ensure sorption of the maximum amount of Sr.

It is clear that the proportion of these salts will be adapted by the man skilled in theart in function of the liquids to be decontaminated. If onlyCs, Ru and Sb are to be extracted, the mixed sorbent may containlarge proportions of metal ferrocyanide. However, the mixed sorbent will contain generally at least 50 percent of the barium salt and preferably at least 85 percent.

Further examples of the sorption of radio-active ions present in the regeneration liquids of ion exchangers used for decontaminating radioactive effluents are described hereafter.

An effluent containing the following metal ions 13 2 ppm, Mn 0.16 ppm, Fe 0.2 ppm, Mg 1.15 ppm, Si 2.55 ppm, Ca 41 ppm, Na 112 ppm, Sr 0.06 ppm, and K 6.4 ppm, in addition to following isotopes Ce, Ru

TABLE 5 Ions present Percentage of sorption with a sulfate concentration in regeneration liquid in 0.01 N 0.025 N 0.05 N 0.1 N 0.125 N 0.15 N

trace amounts cesium 99.0 72 99.3 7r 99.5 7r 995 7r 99.2 7: 99.5 7! strontium 36.5 7? 80.0 7: 94.1 7: 97.0 7( 97.7 7( 98.0 7: cerium 98.5 '7: 98.9 99.3 7! 99.5 7c 99.2 99.3 '7: radium 97.0 71 97.2 71 97.6 7: 97.4 7! 97.6 97.3 7r cohult 94.2 '7! 93.4 7! 93.1 71 95.3 7c 95.1 7r 94.7 7r ruthenium 96.4 71 97.1 7r 97.5 7: 97.0 7( 97.1 7( 96.8 7: untimon 97.2 71 97.9 7( 97.8 7: 97.9 7( 978 7c 98.0 7:

This table shows clearly that the sorption of Sr especially is a function of the sulfate concentration. A concentration of 0.1N Na SO is preferred because higher concentrations could give rise to the formation of CaSO Furthermore, it should be noted that carbonates are generally soluble in an acid medium, so that a pH higher than 3.5 is indicated. Although the above described experiments have been carried out with a mixed sorbent comprising 91 BaCO and 9 Cu Fe(CN) other proportions of these salts could be used. Table 6 shows the sorption of radio-active ions on Cu Fe(CN) on one side, BaCO on the other side and a mixture of 91 BaCO and 9 Cu Fe(CN) The test water comprised 2 molar NaCl and 0.2 molar CaCl in addition to Cs, Sr, Ce, Ra, Co, Ru and Sb. N32. 50., was added up to 0.1 N and the sorbent was added Cs Zr Nb C0 C0 Mn, and Sr was poured at a pH 3 through a column containing a synthetic ion exchanger in the sodium form (amberlite 1R-120). After having passed 350 volumes of said effluent, the water was decontaminated to the following extent.

Co 100 %.and Co 98.3 Ce 100 The ion exchanger was then regenerated withseven volumes of 4 molar NaCl. The pH of the regeneration liquid is raised to 3.5 and Na SO is added up to 0.1N.

10 g. of the mixed sorbent 91 BaCO 9 Cu in a proportion of 7 g. sorbent per litre of water. 55

TABLE 6 Traced Percentage Decontamination lsotope Cu Fe(CN),, BaCO 91 BaCO & 9 Cu Fe(CN) Cesium 96.07 71 26.11 7c 99.77 Strontium 12.00 7: 86.79 7c 95.05 7c Cerium 63.10 7: 99.42 7: 99.76 Radium 75.30 97.57 99.64 Cobalt 2320 9? 47.49 7: 94.60 7r Ruthenium 98.08 71 96.81 7: 98.90 Antimony 98.33 7c 98.69 98.90 70 This table shows that Ru and Sb are sorbed by both components, while Cs is sorbed mainly by Cu Fe(CN) Fe(CN) are added to 1.5 liters of this effluent, stirred for 1 hour and centrifuged for 10 minutes. The water was tested and found to be decontaminated for 95.1 gamma decontamination, 98.7 beta decontamination, and as far as Sr is concerned, 98.6 was decontaminated.

A further effluent containing following metal ions B 1 ppm, Mn 0.09 ppm, Fe 1.3 ppm, Mg 0.9 ppm, Si 2 ppm, Al 1.95 ppm, Ca 61.5 ppm, Na 38 ppm, Sr 0.1

ppm and K 6.5 ppm, in addition to following isotopes Ce', Ru Cs Zr Nb C C0 Mn and Sr was poured through a column containing the same ion exchanger as in the preceding example. After having passed 625 volumes of said effluent, the water was decontaminated for 94.8 gamma-betadecontamination and for 97.8 Sr decontamination.

The ion exchanger was then regenerated with 12.5 volumes of 2 molar NaCl. The pH of the regeneration liquids was raised to 6.5 with the addition of NaOl-l, and Na SO was added up to 0.1 N. g. of the mixed sorbent 91 BaCO 9 Cu Fe(Cl l) were added to 2 liters of this effluent, stirred for one hour and filtered. The water was tested and found to be decontaminated for 97.7 gamma-beta-decontamination, and for 99.8 Sr decontamination. This last example shows that the Sr decontamination was more effective with a pH Other ions for example U, Pu, l, Zr, Nb and Mn can also be sorbed by the method of the invention.

The method according to the invention is particularly effective when the mixed salt is a mixture of a barium salt and a metal ferrocyanide. BaSO, or BaCO are preferably used as barium salts.

As metal ferrocyanides, especially copper ferrocyanide, manganese ferrocyanide, cobalt ferrocyanide, nickel ferrocyanide and zinc ferrocyanide are to be considered A ferrocyanide with different metal ions can also be used.

Different experiments have been made, in which the test water to be purified contained a concentration of 2 molar NaCl and 0.05 molar CaCl as well as traces of Cs, Sr, Ce, Ra, Co, Ru and Sb. 3 g sorbent were added to 1 liter test water and mixed for an hour before filtration. The values obtained are shown in Table 7, the mixed salts mentioned herein are composed as follows:

Cu: Fe (CN)8 91 BaCO Mn: Fe (CN)6 91 BaCO Ni Fe (CN)6 91 BaCO CO2 Fe (CNN; 91 BaCO; e 9 Zn Fe (CNh, 91 BaCO The sorbents are all prepared in the same way from metal sulfates, BaCl Na CO and K Fe (CN) The sorbent is used in a sulfate medium with a concentration of 0.1 N Na SO radioactive ions sorbed The experiments show that a mixed salt with copper ferrocyanide gives good results, and that good results can also be obtained with a mixed salt containing manganese ferrocyanide. The starting substance for the preparation of manganese ferrocyanide is MnSO which, like CuSO is a very cheap product. A mixed barium salt containing manganese ferrocyanide can thus advantageously be used as sorbent for radio-active ions generally contained in contaminated water.

The mixed salt with zinc ferrocyanide does not give as good results as with copper ferrocyanide for the sorption of cesium and cobalt, but it can be used for the sorption of strontium, ruthenium and antimony.

Cobalt and nickel salts also give good results, but since they are expensive, their value is more theoretical than practical.

It is evident that this invention may be used in many different ways and for many different applications by a man skilled in the art.

We claim:

1. A method for extracting radioactive ions present in tracer quantities from a contaminated liquid which comprises contacting said liquid with a mixed sorbent of an insoluble barium salt selected from the group consisting of barium sulfate and barium carbonate, mixed with up to 50 percent of a metal ferrocyanide in a sulfate-containing medium.

2. The method of claim 1 wherein the barium salt is barium sulfate and has a ratio of 3 barium ions to l sulfate ion.

3. The method of claim 1 wherein sodium nitrate is added to the barium sulfate in an amount such that the resulting mixture has 1 sodium ion for from 1 to 24 barium ions.

4. The method of claim 1 wherein said mixed sorbent contains at least 2 percent metal ferrocyanide.

5. The method of claim 4 wherein the metal ferrocyanide is copper ferrocyanide, manganese ferrocyanide, cobalt ferrocyanide, nickel ferrocyanide or zinc ferrocyanide.

6. The method of claim 5 wherein the sorbent is from 98 percent barium salt which has an excess of barium cations and from 15-2 percent of a metal ferrocyanide in a sulfate-containing medium.

7. The method of claim 5 wherein said barium salt is barium sulfate having a ratio of 3 barium ions to l sulfate ion, and wherein said metal ferrocyanide is copper ferrocyanide having a ratio of 1 copper ion to 1 ferrocyanide ion in a sulfate-containing medium.

8. The method of claim 6 wherein said mixed sorbent is barium carbonate and copper ferrocyanide in a sulfate-containing medium.

9. The method of claim 4 wherein said mixed sorbent additionally contains sodium nitrate in an amount such that there is one sodium ion for from 1 to 24 barium ions.

10. The method of claim 4 wherein said mixed sorbent additionally contains calcium chloride in an amount such that there is 1 calcium ion for from 1 to 20 barium ions.

11. The method of claim 4 wherein at least of the mixed sorbent is barium carbonate.

12. The method of claim 1 wherein the contaminated liquids are the regeneration liquids from an ion exchanger previously used for decontaminating radioactive effluents.

13. The method of claim 4 wherein the contaminated liquids are the regeneration liquids from an ion exchanger previously used for decontaminating radioactive effluents.

Claims

2. The method of claim 1 wherein the barium salt is barium sulfate and has a ratio of 3 barium ions to 1 sulfate ion.

6. The method of claim 5 wherein the sorbent is from 85-98 percent barium salt which has an excess of barium cations And from 15-2 percent of a metal ferrocyanide in a sulfate-containing medium.

7. The method of claim 5 wherein said barium salt is barium sulfate having a ratio of 3 barium ions to 1 sulfate ion, and wherein said metal ferrocyanide is copper ferrocyanide having a ratio of 1 copper ion to 1 ferrocyanide ion in a sulfate-containing medium.

11. The method of claim 4 wherein at least 90% of the mixed sorbent is barium carbonate.