Decontamination process for radio-active liquids
United States Patent 3896045
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.
US Patent References:
Method for decontamination of radioactively contaminated aqueous solution
Lowe - October 1956 - 2766204
Precipitation process
Clifford et al. - November 1956 - 2769780
Cesium recovery from aqueous solutions
Goodall - September 1960 - 2952640
Removal of fission products from water
Rosinski - December 1961 - 3013978
Ion exchange
Cohen et al. - April 1964 - 3128247
Method for decontamination of radioactively contaminated aqueous solution
Lowe - October 1956 - 2766204
Precipitation process
Clifford et al. - November 1956 - 2769780
Cesium recovery from aqueous solutions
Goodall - September 1960 - 2952640
Removal of fission products from water
Rosinski - December 1961 - 3013978
Ion exchange
Cohen et al. - April 1964 - 3128247
Inventors:
Peeters, Karel J. A. (Geel, BE)
Van De, Voorde Norbert L. C. (Mol, BE)
Van De, Voorde Norbert L. C. (Mol, BE)
Application Number:
05/317224
Publication Date:
07/22/1975
Filing Date:
12/21/1972
View Patent Images:
Export Citation:
Assignee:
Belgonucleaire S.A. (Brussels, BE)
Primary Class:
Other Classes:
588/20, 423/11, 423/6, 423/2, 423/12, 210/724, 976/DIG.383
International Classes:
G21F9/12; G21C19/46
Field of Search:
252/31.1R,31.1W 210/53 423/2,6,11,12
US Patent References:
| 3449065 | METHOD OF SEPARATION OF RADIUM | June 1969 | Kremer |
Primary Examiner:
Sebastian, Leland A.
Assistant Examiner:
Schafer R. E.
Attorney, Agent or Firm:
Ostrolenk Faber Gerb & Soffen
Parent Case Data:
This is a continuation-in-part of application Ser. No. 174,504, filed Aug. 24, 1971, now abandoned.
Claims:
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 1 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 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.
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 90% 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.
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 1 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 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.
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 90% 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.
Description:
Heretofore it has been proposed to purify radio-active 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 radio-active 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.
Ions 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, co-precipitation 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be hereafter described with the help of a number of tests and various examples.
Barium sulfate
BaSO 4 is prepared by mixing, at room temperature, equal volumes BaCl 2 and Na 2 SO 4 ; the precipitate thereby formed is filtered and, without being washed, dried at 100°C. 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 Kd's obtained are for Sr = 7, for Ra = 27 and for Ce = 284.
After addition of H 2 SO 4 to the test water, for instance to lower the pH to 2, the Kd values increase to the following values for Sr = 1950, for Ra = 3000 and for Ce = 6600.
The sorption mechanism may be deduced from these facts. If pure BaSO 4 itself had sorption properties, there would be no difference in the Kd values before and after the addition of H 2 SO 4 . 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 2 SO 4 , 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 2 SO 4 is probably due to the co-precipitation phenomenon on newly formed BaSO 4 . Indeed, barium ions still present in the prepared BaSO 4 (not washed out during the preparation) form, together with the sulfate ions in the solution, a supplementary BaSO 4 precipitate on the already existing solid BaSO 4 . During this formation, strontium, radium and cerium are co-precipitated.
The Kd values can be considerably increased by preparing BaSO 4 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 4 by activating it, for instance by adding NaNO 3 during preparation of the BaSO 4 . The concentration of NaNO 3 to be used will be such that there is the range from 1 Na ion for 1 Ba ion to 1 Na ion for 24 Ba ions.
Other concentrations of NaNO 3 do not favorably influence the sorption capacity of BaSO 4 .
TABLE 1 ______________________________________ Sorption of Sr, Ra and Ce on BaSO 4 Test water = demineralized water containing Sr, Ra and Ce and 40 ppm Ca to which H 2 SO 4 is added till a pH = 2 is obtained Composition BaSO 4 Kd Sr Ra Ce Ca ______________________________________ *Ba/SO 4 1/1 7 27 284 0 Ba/SO 4 1/1 1.950 3.000 6.600 120 Ba/SO 4 2/1 14.000 28.000 45.000 160 Ba/SO 4 3/1 27.400 39.000 70.000 160 **Ba/SO 4 3/1 45.300 73.000 194.000 180 ______________________________________ *Test water without addition of H 2 SO 4 **BaSO 4 activated by addition of 1 volume NaNO 3 to 3 volumes BaCl 2 during the preparation of BaSO 4
As shown before a surplus of Ba ions in the BaSO 4 sorbent is necessary for good sorption properties. While a ratio of 3 Ba ions to 1 SO 4 ion gives good sorption, it must be noted that still higher proportions of Ba ions no longer improve the sorption properties.
Furthermore, it should be said that this co-precipitation is very selective and for instance practically no precipitate of calcium is obtained, as shown in Table 1. Analogous experiments with demineralized 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 co-precipitation takes place during the formation of freshly formed BaSO 4 . It is to be noted that fresh BaSO 4 could also be formed starting from any soluble barium salt by the addition of SO 4 ions. Good results have been obtained with BaCO 3 in a sulfate medium. Thus, fresh BaSO 4 is formed and the co-precipitation of strontium, radium, cerium is achieved. With the same test water, the sorption on BaCO 3 has been carried out in the same acid conditions (pH = 2 - H 2 SO 4 ) as for BaSO 4 . and then in a Na 2 SO 4 medium. The Kd's obtained are summarized in Table 2.
TABLE 2 ______________________________________ Sorption of Sr, Ra and Ce on BaCO 3 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 3 = commercially available Compo- sition Kd sorbent Medium Sr Ra Ce Ca ______________________________________ BaCO 3 H 2 SO 4 300 9.800 8.200 40 BaCO 3 0.01N Na 2 SO 4 3.500 11.050 52.000 100 BaCO 3 0.01N Na 2 SO 4 30.300 38.700 70.000 230 ______________________________________
This table shows that in a medium of 0.1 N Na 2 SO 4 the results of sorption on BaCO 3 are comparable with those of BaSO 4 in a molar ratio of Ba/SO 4 equal to 3/1.
As it is not always economical to handle large volumes of effluents in a medium of 0.1 N Na 2 SO 4 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 3 .
It should be noted that ruthenium and antimony will also be sorbed on BaCO 3 .
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 4 by preparing it as a mixed salt with a metal ferrocyanide. For instance, BaSO 4 and Cu 2 Fe(CN) 6 prepared as a mixed substance has a good granular structure and can be used to extract at the same time strontium, radium and cerium as well as cesium, ruthenium and antimony.
The following example gives a preferred method of preparation of this mixed substance : 300 volumes 1 molar Na 2 SO 4 are added to 150 volumes 0.1 molar CuSO 4 . While stirring, 945 volumes 1 molar BaCl 2 are added to this mixture. 75 volumes 0.1 molar K 4 Fe (CN) 6 are then added to the obtained precipitate of BaSO 4 and vigorously stirred for 2 minutes. The precipitate is then allowed to form for 1 or 2 hours before being filtered. Without being washed, the precipitate is then dried at 100°C. 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 4 with a molar ratio Ba/SO 4 of 3/1, and 2.3 % (Cu 2 Fe(CN) 6 with a molar ratio Cu 2 /Fe(CN) 6 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 3 is added in a ratio of 3 Ba ions for 1 Na ion.
The same example is repeated but NaNO 3 is replaced by CaCl 2 in a ratio of 3 Ba ions for 1 Ca ion.
TABLE 3 ____________________________________________________________ ______________ Sorption of Sr, Ce and Cs on mixed sorbent BaSO 4 /Cu 2 Fe(CN).sub .6 Test water = demineralized water containing Sr, Ra, Ce and Cs, 100 ppm Na and 30 ppm Ca, to which H 2 SO 4 is added till a pH = 2 is obtained Mixed sorbent Activation Kd Sr Ce Cs ____________________________________________________________ ______________ Nil 2.560 7.850 32.100 97.7 % BaSO 4 / NaNO 3 : Na/Ba = 1/3 15.800 45.000 55.000 2.3% Cu 2 Fe(CN) 6 CaCl 2 : Ca/Ba = 1/3 9.150 31.500 63.750 ____________________________________________________________ ______________ Kd for Ra has not been determined
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 3 and Cu 2 Fe(CN) 6 . Contrary to the above-mentioned mixed product containing BaSO 4 , this mixed salt based on BaCO 3 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 2 is added to one volume 1 molar Na 2 CO 3 and allowed to precipitate homogeneously. On the other hand, one volume 0.1 molar K 4 Fe(CN) 6 is added to two volumes 0.1 molar CuSO 4 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 3 with a molar ratio Ba/CO 3 of 1/1 and 9 % Cu 2 Fe(CN) 6 with a molar ratio Cu 2 /Fe(CN) 6 of 1/1. The Kd's 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 % BaCO 3 and H 2 SO 4 1.120 17.720 12.500 9 % Cu 2 Fe(CN) 6 0.01N Na 2 SO 4 8.630 56.200 30.700 0.1N Na 2 SO 4 20.460 59.600 77.000 ____________________________________________________________ ______________
It should be noted that ruthenium, antimony and cobalt will also be sorbed on this sorbent. Further examples will illustrate the results obtained. This table shows the excellent results obtained in a medium of 0.1 N Na 2 SO 4 . As already stated in the specification, it is not always economical to handle large volumes of effluents in a medium of 0.1 N Na 2 SO 4 . It is therefore proposed according to the invention to treat the effluents with ion exchangers and to treat regeneration liquids subsequently 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 3 - Cu 2 Fe(CN) 6 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 3 - Cu 2 Fe(CN) 6 sorbent. The test water contained a concentration of 2 molar NaCl and 0.05 molar CaCl 2 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.
TABLE 5 ____________________________________________________________ ______________ Ions present Percentage of sorption with a sulfate concentration in regenerat- ion 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 % 99.3 % 99.5 % 99.5 % 99.2 % 99.5 % strontium 36.5 % 80.0 % 94.1 % 97.0 % 97.7 % 98.0 % cerium 98.5 % 98.9 % 99.3 % 99.5 % 99.2 % 99.3 % radium 97.0 % 97.2 % 97.6 % 97.4 % 97.6 % 97.3 % cobalt 94.2 % 93.4 % 93.1 % 95.3 % 95.1 % 94.7 % ruthenium 96.4 % 97.1 % 97.5 % 97.0 % 97.1 % 96.8 % antimony 97.2 % 97.9 % 97.8 % 97.9 % 97.8 % 98.0 % ____________________________________________________________ ______________
This table shows clearly that the sorption of Sr especially is a function of the sulfate concentration. A concentration of 0.1N Na 2 SO 4 is preferred because higher concentrations could give rise to the formation of CaSO 4 . 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 3 and 9 % Cu 2 Fe(CN) 6 , other proportions of these salts could be used. Table 6 shows the sorption of radio-active ions on Cu 2 Fe(CN) 6 on one side, BaCO 3 on the other side and a mixture of 91 % BaCO 3 and 9 % Cu 2 Fe(CN) 6 . The test water comprised 2 molar NaCl and 0.2 molar CaCl 2 in addition to Cs, Sr, Ce, Ra, Co, Ru and Sb. Na 2 SO 4 was added up to 0.1 N and the sorbent was added in a proportion of 7 g. sorbent per litre of water.
TABLE 6 ____________________________________________________________ ______________ Traced Percentage Decontamination Isotope Cu 2 Fe(CN) 6 BaCO 3 91 % BaCO 3 & 9 % Cu 2 Fe(CN) 6 ____________________________________________________________ ______________ Cesium 96.07 % 26.11 % 99.77 % Strontium 12.00 % 86.79 % 95.05 % Cerium 63.10 % 99.42 % 99.76 % Radium 75.30 % 97.57 % 99.64 % Cobalt 23.20 % 47.49 % 94.60 % Ruthenium 98.08 % 96.81 % 98.90 % Antimony 98.33 % 98.69 % 98.90 % ____________________________________________________________ ______________
This table shows that Ru and Sb are sorbed by both components, while Cs is sorbed mainly by Cu 2 Fe(CN) 6 . Ce and Ra, on the other hand, are sorbed mainly by BaCO 3 . 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 3 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 3 and 15 % Cu 2 Fe(CN) 6 . However, in view of the radiological toxicity of Sr, a mixed sorbent comprising at least 90 % BaCO 3 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 the art in function of the liquids to be decontaminated. If only Cs, Ru and Sb are to be extracted, the mixed sorbent may contain large 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 B 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 144 , Ru 106 , Cs 137 , Zr 95 , Nb 95 , Co 58 , Co 60 , Mn 54 , and Sr 90 , was poured at a pH = 3 through a column containing a synthetic ion exchanger in the sodium form (amberlite IR-120). After having passed 350 volumes of said effluent, the water was decontaminated to the following extent.
______________________________________ Sr 90 = 99.7 % Ru 106 = 95.6 % Cs 137 = 94.1 % Co 58 = 100 % and Co 60 = 98.3 % Ce 144 = 100 % Zr 95 + Nb 95 = 100 % Mn 54 = 100% ______________________________________
The ion exchanger was then regenerated with seven volumes of 4 molar NaCl. The pH of the regeneration liquid is raised to 3.5 and Na 2 SO 4 is added up to 0.1N.
10 g. of the mixed sorbent 91 % BaCO 3 - 9 % Cu 2 Fe(CN) 6 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 90 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 144 , Ru 106 , Cs 137 , Zr 95 , Nb 95 , Co 58 , Co 60 , Mn 54 and Sr 90 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-beta-decontamination and for 97.8 % Sr 90 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 NaOH, and Na 2 SO 4 was added up to 0.1 N. 10 g. of the mixed sorbent 91 % BaCO 3 - 9 % Cu 2 Fe(CN) 6 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 90 decontamination. This last example shows that the Sr 90 decontamination was more effective with a pH = 6.5.
Other ions for example U, Pu, I, 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 4 or BaCO 3 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 2 , 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:
a = 9 % Cu 2 Fe (CN) 6 / 91 % BaCO 3 b = 9 % Mn 2 Fe (CN) 6 / 91 % BaCO 3 c = 9 % Ni 2 Fe (CN) 6 / 91 % BaCO 3 d = 9 % CO 2 Fe (CN) 6 / 91 % BaCO 3 e = 9 % Zn 2 Fe (CN) 6 / 91 % BaCO 3 .
The sorbents are all prepared in the same way from metal sulfates, BaCl 2 , Na 2 CO 3 and K 4 Fe (CN) 6 .
The sorbent is used in a sulfate medium with a concentration of 0.1 N Na 2 SO 4 .
TABLE 7 ______________________________________ Radio- Sorbent active ions a b c d e ______________________________________ cesium 99.6 % 99.8 % 99.5 % 99.7 % 53.0 % strontium 96.7 % 96.4 % 96.3 % 97.5 % 96.2 % cobalt 95.3 % 99.1 % 91.2 % 82.7 % 72.0 % ruthenium 96.0 % 92.8 % 97.5 % 96.7 % 97.0 % antimony 99.4 % 99.4 % 99.4 % 99.3 % 99.6 % ______________________________________ radio-active 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 4 , which, like CuSO 4 , 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.
Another known process for the treatment of radio-active 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.
Ions 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, co-precipitation 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be hereafter described with the help of a number of tests and various examples.
Barium sulfate
BaSO 4 is prepared by mixing, at room temperature, equal volumes BaCl 2 and Na 2 SO 4 ; the precipitate thereby formed is filtered and, without being washed, dried at 100°C. 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 Kd's obtained are for Sr = 7, for Ra = 27 and for Ce = 284.
After addition of H 2 SO 4 to the test water, for instance to lower the pH to 2, the Kd values increase to the following values for Sr = 1950, for Ra = 3000 and for Ce = 6600.
The sorption mechanism may be deduced from these facts. If pure BaSO 4 itself had sorption properties, there would be no difference in the Kd values before and after the addition of H 2 SO 4 . 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 2 SO 4 , 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 2 SO 4 is probably due to the co-precipitation phenomenon on newly formed BaSO 4 . Indeed, barium ions still present in the prepared BaSO 4 (not washed out during the preparation) form, together with the sulfate ions in the solution, a supplementary BaSO 4 precipitate on the already existing solid BaSO 4 . During this formation, strontium, radium and cerium are co-precipitated.
The Kd values can be considerably increased by preparing BaSO 4 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 4 by activating it, for instance by adding NaNO 3 during preparation of the BaSO 4 . The concentration of NaNO 3 to be used will be such that there is the range from 1 Na ion for 1 Ba ion to 1 Na ion for 24 Ba ions.
Other concentrations of NaNO 3 do not favorably influence the sorption capacity of BaSO 4 .
TABLE 1 ______________________________________ Sorption of Sr, Ra and Ce on BaSO 4 Test water = demineralized water containing Sr, Ra and Ce and 40 ppm Ca to which H 2 SO 4 is added till a pH = 2 is obtained Composition BaSO 4 Kd Sr Ra Ce Ca ______________________________________ *Ba/SO 4 1/1 7 27 284 0 Ba/SO 4 1/1 1.950 3.000 6.600 120 Ba/SO 4 2/1 14.000 28.000 45.000 160 Ba/SO 4 3/1 27.400 39.000 70.000 160 **Ba/SO 4 3/1 45.300 73.000 194.000 180 ______________________________________ *Test water without addition of H 2 SO 4 **BaSO 4 activated by addition of 1 volume NaNO 3 to 3 volumes BaCl 2 during the preparation of BaSO 4
As shown before a surplus of Ba ions in the BaSO 4 sorbent is necessary for good sorption properties. While a ratio of 3 Ba ions to 1 SO 4 ion gives good sorption, it must be noted that still higher proportions of Ba ions no longer improve the sorption properties.
Furthermore, it should be said that this co-precipitation is very selective and for instance practically no precipitate of calcium is obtained, as shown in Table 1. Analogous experiments with demineralized 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 co-precipitation takes place during the formation of freshly formed BaSO 4 . It is to be noted that fresh BaSO 4 could also be formed starting from any soluble barium salt by the addition of SO 4 ions. Good results have been obtained with BaCO 3 in a sulfate medium. Thus, fresh BaSO 4 is formed and the co-precipitation of strontium, radium, cerium is achieved. With the same test water, the sorption on BaCO 3 has been carried out in the same acid conditions (pH = 2 - H 2 SO 4 ) as for BaSO 4 . and then in a Na 2 SO 4 medium. The Kd's obtained are summarized in Table 2.
TABLE 2 ______________________________________ Sorption of Sr, Ra and Ce on BaCO 3 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 3 = commercially available Compo- sition Kd sorbent Medium Sr Ra Ce Ca ______________________________________ BaCO 3 H 2 SO 4 300 9.800 8.200 40 BaCO 3 0.01N Na 2 SO 4 3.500 11.050 52.000 100 BaCO 3 0.01N Na 2 SO 4 30.300 38.700 70.000 230 ______________________________________
This table shows that in a medium of 0.1 N Na 2 SO 4 the results of sorption on BaCO 3 are comparable with those of BaSO 4 in a molar ratio of Ba/SO 4 equal to 3/1.
As it is not always economical to handle large volumes of effluents in a medium of 0.1 N Na 2 SO 4 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 3 .
It should be noted that ruthenium and antimony will also be sorbed on BaCO 3 .
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 4 by preparing it as a mixed salt with a metal ferrocyanide. For instance, BaSO 4 and Cu 2 Fe(CN) 6 prepared as a mixed substance has a good granular structure and can be used to extract at the same time strontium, radium and cerium as well as cesium, ruthenium and antimony.
The following example gives a preferred method of preparation of this mixed substance : 300 volumes 1 molar Na 2 SO 4 are added to 150 volumes 0.1 molar CuSO 4 . While stirring, 945 volumes 1 molar BaCl 2 are added to this mixture. 75 volumes 0.1 molar K 4 Fe (CN) 6 are then added to the obtained precipitate of BaSO 4 and vigorously stirred for 2 minutes. The precipitate is then allowed to form for 1 or 2 hours before being filtered. Without being washed, the precipitate is then dried at 100°C. 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 4 with a molar ratio Ba/SO 4 of 3/1, and 2.3 % (Cu 2 Fe(CN) 6 with a molar ratio Cu 2 /Fe(CN) 6 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 3 is added in a ratio of 3 Ba ions for 1 Na ion.
The same example is repeated but NaNO 3 is replaced by CaCl 2 in a ratio of 3 Ba ions for 1 Ca ion.
TABLE 3 ____________________________________________________________ ______________ Sorption of Sr, Ce and Cs on mixed sorbent BaSO 4 /Cu 2 Fe(CN).sub .6 Test water = demineralized water containing Sr, Ra, Ce and Cs, 100 ppm Na and 30 ppm Ca, to which H 2 SO 4 is added till a pH = 2 is obtained Mixed sorbent Activation Kd Sr Ce Cs ____________________________________________________________ ______________ Nil 2.560 7.850 32.100 97.7 % BaSO 4 / NaNO 3 : Na/Ba = 1/3 15.800 45.000 55.000 2.3% Cu 2 Fe(CN) 6 CaCl 2 : Ca/Ba = 1/3 9.150 31.500 63.750 ____________________________________________________________ ______________ Kd for Ra has not been determined
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 3 and Cu 2 Fe(CN) 6 . Contrary to the above-mentioned mixed product containing BaSO 4 , this mixed salt based on BaCO 3 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 2 is added to one volume 1 molar Na 2 CO 3 and allowed to precipitate homogeneously. On the other hand, one volume 0.1 molar K 4 Fe(CN) 6 is added to two volumes 0.1 molar CuSO 4 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 3 with a molar ratio Ba/CO 3 of 1/1 and 9 % Cu 2 Fe(CN) 6 with a molar ratio Cu 2 /Fe(CN) 6 of 1/1. The Kd's 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 % BaCO 3 and H 2 SO 4 1.120 17.720 12.500 9 % Cu 2 Fe(CN) 6 0.01N Na 2 SO 4 8.630 56.200 30.700 0.1N Na 2 SO 4 20.460 59.600 77.000 ____________________________________________________________ ______________
It should be noted that ruthenium, antimony and cobalt will also be sorbed on this sorbent. Further examples will illustrate the results obtained. This table shows the excellent results obtained in a medium of 0.1 N Na 2 SO 4 . As already stated in the specification, it is not always economical to handle large volumes of effluents in a medium of 0.1 N Na 2 SO 4 . It is therefore proposed according to the invention to treat the effluents with ion exchangers and to treat regeneration liquids subsequently 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 3 - Cu 2 Fe(CN) 6 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 3 - Cu 2 Fe(CN) 6 sorbent. The test water contained a concentration of 2 molar NaCl and 0.05 molar CaCl 2 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.
TABLE 5 ____________________________________________________________ ______________ Ions present Percentage of sorption with a sulfate concentration in regenerat- ion 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 % 99.3 % 99.5 % 99.5 % 99.2 % 99.5 % strontium 36.5 % 80.0 % 94.1 % 97.0 % 97.7 % 98.0 % cerium 98.5 % 98.9 % 99.3 % 99.5 % 99.2 % 99.3 % radium 97.0 % 97.2 % 97.6 % 97.4 % 97.6 % 97.3 % cobalt 94.2 % 93.4 % 93.1 % 95.3 % 95.1 % 94.7 % ruthenium 96.4 % 97.1 % 97.5 % 97.0 % 97.1 % 96.8 % antimony 97.2 % 97.9 % 97.8 % 97.9 % 97.8 % 98.0 % ____________________________________________________________ ______________
This table shows clearly that the sorption of Sr especially is a function of the sulfate concentration. A concentration of 0.1N Na 2 SO 4 is preferred because higher concentrations could give rise to the formation of CaSO 4 . 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 3 and 9 % Cu 2 Fe(CN) 6 , other proportions of these salts could be used. Table 6 shows the sorption of radio-active ions on Cu 2 Fe(CN) 6 on one side, BaCO 3 on the other side and a mixture of 91 % BaCO 3 and 9 % Cu 2 Fe(CN) 6 . The test water comprised 2 molar NaCl and 0.2 molar CaCl 2 in addition to Cs, Sr, Ce, Ra, Co, Ru and Sb. Na 2 SO 4 was added up to 0.1 N and the sorbent was added in a proportion of 7 g. sorbent per litre of water.
TABLE 6 ____________________________________________________________ ______________ Traced Percentage Decontamination Isotope Cu 2 Fe(CN) 6 BaCO 3 91 % BaCO 3 & 9 % Cu 2 Fe(CN) 6 ____________________________________________________________ ______________ Cesium 96.07 % 26.11 % 99.77 % Strontium 12.00 % 86.79 % 95.05 % Cerium 63.10 % 99.42 % 99.76 % Radium 75.30 % 97.57 % 99.64 % Cobalt 23.20 % 47.49 % 94.60 % Ruthenium 98.08 % 96.81 % 98.90 % Antimony 98.33 % 98.69 % 98.90 % ____________________________________________________________ ______________
This table shows that Ru and Sb are sorbed by both components, while Cs is sorbed mainly by Cu 2 Fe(CN) 6 . Ce and Ra, on the other hand, are sorbed mainly by BaCO 3 . 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 3 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 3 and 15 % Cu 2 Fe(CN) 6 . However, in view of the radiological toxicity of Sr, a mixed sorbent comprising at least 90 % BaCO 3 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 the art in function of the liquids to be decontaminated. If only Cs, Ru and Sb are to be extracted, the mixed sorbent may contain large 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 B 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 144 , Ru 106 , Cs 137 , Zr 95 , Nb 95 , Co 58 , Co 60 , Mn 54 , and Sr 90 , was poured at a pH = 3 through a column containing a synthetic ion exchanger in the sodium form (amberlite IR-120). After having passed 350 volumes of said effluent, the water was decontaminated to the following extent.
______________________________________ Sr 90 = 99.7 % Ru 106 = 95.6 % Cs 137 = 94.1 % Co 58 = 100 % and Co 60 = 98.3 % Ce 144 = 100 % Zr 95 + Nb 95 = 100 % Mn 54 = 100% ______________________________________
The ion exchanger was then regenerated with seven volumes of 4 molar NaCl. The pH of the regeneration liquid is raised to 3.5 and Na 2 SO 4 is added up to 0.1N.
10 g. of the mixed sorbent 91 % BaCO 3 - 9 % Cu 2 Fe(CN) 6 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 90 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 144 , Ru 106 , Cs 137 , Zr 95 , Nb 95 , Co 58 , Co 60 , Mn 54 and Sr 90 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-beta-decontamination and for 97.8 % Sr 90 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 NaOH, and Na 2 SO 4 was added up to 0.1 N. 10 g. of the mixed sorbent 91 % BaCO 3 - 9 % Cu 2 Fe(CN) 6 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 90 decontamination. This last example shows that the Sr 90 decontamination was more effective with a pH = 6.5.
Other ions for example U, Pu, I, 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 4 or BaCO 3 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 2 , 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:
a = 9 % Cu 2 Fe (CN) 6 / 91 % BaCO 3 b = 9 % Mn 2 Fe (CN) 6 / 91 % BaCO 3 c = 9 % Ni 2 Fe (CN) 6 / 91 % BaCO 3 d = 9 % CO 2 Fe (CN) 6 / 91 % BaCO 3 e = 9 % Zn 2 Fe (CN) 6 / 91 % BaCO 3 .
The sorbents are all prepared in the same way from metal sulfates, BaCl 2 , Na 2 CO 3 and K 4 Fe (CN) 6 .
The sorbent is used in a sulfate medium with a concentration of 0.1 N Na 2 SO 4 .
TABLE 7 ______________________________________ Radio- Sorbent active ions a b c d e ______________________________________ cesium 99.6 % 99.8 % 99.5 % 99.7 % 53.0 % strontium 96.7 % 96.4 % 96.3 % 97.5 % 96.2 % cobalt 95.3 % 99.1 % 91.2 % 82.7 % 72.0 % ruthenium 96.0 % 92.8 % 97.5 % 96.7 % 97.0 % antimony 99.4 % 99.4 % 99.4 % 99.3 % 99.6 % ______________________________________ radio-active 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 4 , which, like CuSO 4 , 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.