Patent Number: 047909609
Section: description

DETAILED DESCRIPTION OF THE INVENTION It has been found in accordance with the present invention that the acid stability of the precipitation agent molecule and of the resulting precipitate which has low solubility is increased by the introduction of electron-attracting substituents in the phenyl rings of the molecule which prevents to a large extent that positive charges stabilize on the phenyl rings and thus initiate the decomposition of the molecule. The electron-attracting substituents protect the phenyl rings from electrophilic attacks. The synthesis for the precipitation agents, usable for the process according to the present invention can occur, e.g., according to the following scheme: Preparation of Sodium Tetrakis(2,4-difluorophenyl)borate: ##STR1## In the above process, 2,4-difluorobromobenzole (a) in a di-ethyl-ether solution is transformed at -78.degree. C. into a phenyllithium derivative (B) with n-butyllithium (n-BuLi). Into the thus obtained phenyllithium derivative (B) solution, a BCl.sub.3 solution in hexane is dripped. After warming up to room temperature, hydrolization is done, the ether pulled off over water, the aqueous phase (now containing derivative (c)) mixed with some active carbon, filtered and mixed with an aqueous trimethylamine solution. The resulting trimethylammonium salt (D) is recrystallised from methanol/water and dried. With sodium hydride it is transformed into the corresponding alkaline salt (E), which, as needed, can then be recrystallized from chloroform/acetone. The compound lithiumtetrakis(2,3,5,6-tetrafluorophenyl)borate was produced in the same manner by employing lithium hydride instead of sodium hydride. The lithiumtetrakis(pentafluorophenyl)borate production has been taken from A. G. Massey, A. J. Park: J. Organometal. Chem., 2 (1964), pages 245 to 250. The products were analyzed with the aid of IR, NMR and elementary analysis. In order to present the salts in pure form, the "detour" through trimethylammonium salts is needed. However, for precipitation reactions, the aqueous solution of the precipitation reagents (containing derivatives according to derivatives "C" respectively) is already sufficient, the concentrations of which can be simply determined by quantitative precipitation with trimethylamine. The solubilities of the corresponding Cs salts in pure water (298.degree. K.) are given below: Sodium tetrakis(2,4-difluorophenyl)borate: 2.0.10.sup.-4 mol/l PA1 Lithium tetrakis(2,3,5,6-tetrafluorophenyl)borate: 3.7.10.sup.-4 mol/l PA1 Lithium tetrakis(pentafluorophenyl)borate: 2.4.10.sup.-4 mol/l PA1 (1) Sodiumtetrakis(2,4-difluorophenyl)borate PA1 (2) Lithiumtetrakis(2,3,5,6-tetrafluorophenyl)borate PA1 (3) Lithiumtetrakis(pentafluorophenyl)borate The solubilities were determined by means of radiometry. All reagents from precipitates with Cs.sup.+ which have a low solubility, but not with potassium. Coprecipitation of potassium appears in lithium tetrakis(2,3,5,6-tetrafluorophenyl)borate but only with a K.sup.+ to Cs.sup.+ ratio of .gtoreq.100, and appears with sodiumtetrakis(2,4-difluorophenyl)borate and lithiumtetrakis(pentafluorophenyl)borate only at K.sup.+ to Cs.sup.+ ratio of &gt;100. Cs.sup.+ precipitates which have a low solubility also form with sodium tetrakis(4-fluorophenyl)borate, sodium tetrakis(3,4-difluorophenyl)borate, and with lithiumtetrakis(2,4,6-trifluorophenyl)borate, with the precipitate of the first two compounds being formed in neutral and in alkaline media in a very good selectivity, and the precipitate of the third compound also being formed in acid media up to 3 molar acid, but for this compound coprecipitation with K.sup.+ occurs from the ratio of K.sup.+ :Cs.sup.+ as 1 up to higher K.sup.+ /Cs.sup.+ ratios. The following examples are given by way of illustration to further explain the principles of the invention. These examples are merely illustrative and are not to be understood as limiting the scope and underlying principles of the invention in any way. All percentages referred to herein are by weight unless otherwise indicated. EXAMPLE 1 (Cs.sup.+ Precipitation from a Simulated MAW) A simulated MAW solution was prepared having the composition shown in Table 1. TABLE 1 ______________________________________ Sample Composition of the Simulated MAW Solution Element Used as Concentration (Mol/l) ______________________________________ Na NaNO.sub.3 3.53 Al Al(NO.sub.3).sub.3 9H.sub.2 O 8.52 .multidot. 10.sup.-3 Ca Ca(NO.sub.3).sub.2 4H.sub.2 O 3.68 .multidot. 10.sup.-2 Cr Cr(NO.sub.3).sub.3 9H.sub.2 O 1.54 .multidot. 10.sup.-3 Cu Cu(NO.sub.3).sub.3 3H.sub.2 O 2.36 .multidot. 10.sup.-3 Fe Fe(NO.sub.3).sub.3 9H.sub.2 O 6.80 .multidot. 10.sup.-3 K KNO.sub.3 2.50 .multidot. 10.sup.-3 Mg Mg(NO.sub.3).sub.2 6H.sub.2 O 3.09 .multidot. 10.sup.-2 Mn Mn(NO.sub.3).sub.2 4H.sub.2 O 1.46 .multidot. 10.sup.-3 Mo Na.sub.2 MoO.sub.4 2H.sub.2 O 3.96 .multidot. 10.sup.-3 Ni Ni(NO.sub.3).sub.2 6H.sub.2 O 1.36 .multidot. 10.sup.-3 Ru Ru(NO.sub.3).sub.3 (NO)8.8% ig 7.50 .multidot. 10.sup.-4 Zn Zn(NO.sub.3).sub.2 4H.sub.2 O 2.29 .multidot. 10.sup.-3 TBP 7.51 .multidot. 10.sup.- 4 DBP 9.51 .multidot. 10.sup.-4 HNO.sub.3 1.0 ______________________________________ The simulated MAW was mixed with inactive Cs.sup.+. Two different solutions were prepared, one with a Cs.sup.+ concentration 1.0.multidot.10.sup.-3 and the second with a Cs.sup.+ concentration of 1.0.multidot.10.sup.-2 mol/l. The solutions were doped with Cs-137, and this doping was independent of the inactive Cs.sup.+ concentration, to provide an activity of 1 .mu.Ci/ml. In each case, the precipitation agent was added in a threefold amount of the stoichiometric amount with respect to the Cs.sup.+ concentration, whereby it was of no importance if it was added as solution or solid matter. Samples were taken after about 24 hours, they were filtered, the activity of the filtrate measured and the Cs.sup.+ concentration then calculated through calibration. The results are shown in Tables 2 to 4. The following compounds were used as precipitation agents: TABLE 2 ______________________________________ Cs.sup.+ Precipitation with Compound (1) Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 1.0 .multidot. 10.sup.-3 293 6.0 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-3 277 3.7 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-3 260 1.6 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 293 5.6 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 277 3.5 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 260 1.3 .multidot. 10.sup.-5 ______________________________________ TABLE 3 ______________________________________ Cs.sup.+ Precipitation with Compound (2) Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 1.0 .multidot. 10.sup.-3 293 3.0 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-3 277 1.9 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-2 293 3.0 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-2 277 1.8 .multidot. 10.sup.-4 ______________________________________ TABLE 4 ______________________________________ Cs.sup.+ Precipitation with Compound (3) Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 1.0 .multidot. 10.sup.-3 293 1.8 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-3 277 6.8 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 293 1.6 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-2 277 5.4 .multidot. 10.sup.-5 ______________________________________ EXAMPLE 2 (Cs.sup.+ Precipitation from 5M-Nitric Acid) The same procedure was employed as described in Example 1, except that only Compounds (1) and (3) were tested as precipitation agents, and the acid molarity of the aqueous solution used was chosen in such a manner that in this context it simulated a HAW concentrate (HAW=high radioactive aqueous waste). To prepare the aqueous solution, 5 molar HNO.sub.3 was mixed with inactive Cs.sup.+ to provide a Cs.sup.+ concentration of 1.0.multidot.10.sup.-2 mol/l. The solution was doped with Cs-137 to provide an activity of 1 .mu. Ci/ml. The precipitation agent was added in a threefold amount of the stoichiometric amount with respect to the Cs.sup.+ concentration. After 24 hours, samples were taken, they were filtered, the activity of the filtrate measured and the Cs.sup.+ concentration calculated via calibration. The results are shown in Tables 5 and 6. TABLE 5 ______________________________________ Cs.sup.+ Precipitation with Compound (1): Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 1.0 .multidot. 10.sup.-2 293 2.6 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 273 1.8 .multidot. 10.sup.-5 1.0 .multidot. 10.sup.-2 260 1.5 .multidot. 10.sup.-5 ______________________________________ TABLE 6 ______________________________________ Cs.sup.+ Precipitation with Compound (3): Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 1.0 .multidot. 10.sup.-2 313 1.6 .multidot. 10.sup.-3 1.0 .multidot. 10.sup.-2 298 8.4 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-2 273 6.9 .multidot. 10.sup.-4 1.0 .multidot. 10.sup.-2 260 6.4 .multidot. 10.sup.-4 ______________________________________ Sodium tetrakis(2,4-difluorophenyl)borate (Compound 1) is acid stable to 6M-HNO.sub.3 and at temperatures up to 293.degree. K. Under conditions as they are prevalent in radioactive waste solutions, the Cs salt has the lowest solubility of the compounds examined. The remaining Cs.sup.+ concentration in MAW-simulate or in 5M nitric acid, depending on temperature (239.degree. to 293.degree. K.), are between 1.0.multidot.10.sup.-5 and 8.0.multidot.10.sup.-5 mol/l. (With Kalignost such a solubility determination cannot be done, as the decomposition of the compound occurs too fast under the test conditions). The lowest Cs.sup.+ concentration to be reached by precipitation is determined by the solubility of the corresponding Cs.sup.+ salts. EXAMPLE 3 (Cs.sup.+ Precipitation from Simulated HAW) A simulated HAW solution was prepared having the composition shown in Table 7. The simulated solution was 5 molar in HNO.sub.3 and contained the largest amount of elements in the form of nitrate salts. TABLE 7 ______________________________________ Concentration in the Simulated Element Aqueous solution (g/l) ______________________________________ Ag 0.03 Ba 2.65 Cd 0.14 Ce 3.70 Cr 0.57 Cs 3.54 Eu 0.28 Fe 2.19 Gd 0.25 La 1.90 Mn 0.06 Mo 5.24 Nd 6.16 Pd 2.01 Pr 1.78 Rb 0.49 Rh 0.57 Ru 2.13 Sb 0.009 Se 0.08 Si 0.04 Sm 1.35 Sn 0.06 Sr 1.15 Tc 2.26 Te 0.74 Y 0.66 Zr 5.27 Rest 0.03 Active Compound 4.55 (Am, Cm, Np, Pu, U) Impurities 0.63 ______________________________________ The solution was doped with Cs-137 to provide an activity of 1 .mu.Ci/ml. The precipitation was done as described in Example 2, but only with Compound (3). The result is shown in Table 8: TABLE 8 ______________________________________ Precipitation with Compound (3) Remaining Cs.sup.+ Concentration in the Initial Inactive Solution After Cs.sup.+ Concentration Temperature Stripping of Precipitate [mol/l] [.degree.K.] [mol/l] ______________________________________ 2.68 .multidot. 10.sup.-2 298 7.2 .multidot. 10.sup.-4 2.68 .multidot. 10.sup.-2 283 6.2 .multidot. 10.sup.-4 2.68 .multidot. 10.sup.-2 273 5.9 .multidot. 10.sup.-4 ______________________________________ EXAMPLE 4 (Effectiveness) It is now possible to obtain by precipitation, for example with Compound (1), high decontamination for Cs-137 in various ways and manners as follows: (1) Adjusting the MAW solution to an inactive Cs.sup.+ concentration of 1.0.multidot.10.sup.-3 mol/l. Precipitation at a temperature of 293.degree. K. with Compound (1) in a threefold amount of the stoichiometric amount with respect to the Cs.sup.+ concentration and stripping the precipitate (by filtration or centrifugation) supplies a decontamination factor (DF) of 17. The resulting Cs+ concentration of about 6.0.multidot.10.sup.-5 mol/l is again adjusted to 1.0.multidot.10.sup.-3 mol/l, again precipitated and the whole process repeated as often as desired. With four cycles it is thus possible to attain, without much material investment, a DF for the active Cs of about 80,000 (precipitation temperature 293.degree. K. in each case). (2) Adjusting the MAW solution to an inactive Cs.sup.+ concentration of 1.0.multidot.10.sup.-2 mol/l, and then following the same procedure as in (1) above. The first precipitation results in a DF of 170, after the next cycle, a DF of 29,000 etc. (Precipitation temperature in each case 293.degree. K.). (3) The same procedure is employed as in (1), except that the precipitation temperature is 277.degree. K. The first precipitation produces a DF of 26, after the fourth precipitation the DF is higher than 400,000. (4) The same procedure is employed as in (2), except that the precipitation temperature is 277.degree. K. The first precipitation supplies a DF of 280, the second precipitation already a DF of more than 78,000. (5) The same procedure is employed as in (1), except that the precipitation temperature is 260.degree. K. The first precipitation supplies a DF of 62, after the third precipitation the DF is &gt;230,000. (6) The same procedure is employed as in (2), except that the precipitation temperature is 260.degree. K. The first precipitation supplies a DF of 770, the second precipitation already a DF of &gt;590,000. (7) Adjusting a 5M HNO.sub.3 to an inactive Cs.sup.+ concentration of 10.sup.-2 mol/l. The process otherwise is the same as in (1). The first precipitation supplies a DF of 384, the second precipitation already a DF of 148,000. The precipitation temperature in each case was 293.degree. K. (8) The same procedure is employed as in (7), except that the precipitation temperature is 260.degree. K. The first precipitation supplies a DF of 667, the second precipitation already a DF of 444,000. EXAMPLE 5 (Separation of the Cs precipitate from Compound (3) by Liquid Extraction from an Aqueous Solution) Water was mixed with inactive Cs.sup.+ to provide a Cs.sup.+ concentration of 1.0.multidot.10.sup.-3 mol/l. The solution was doped with Cs-137, as in the previous examples. The precipitating agent was added in a double amount of the stoichiometric amount with respect to the Cs.sup.+ concentration. After 24 hours, samples were taken and subjected to different precipitation separation methods, namely, filtration on the one hand, and extraction on the other, in order to compare the effectiveness of the different precipitation separation methods. In the filtration separation method, the precipitates were filtered off and the residual Cs.sup.+ concentration in the filtrate solution of the samples determined. This Cs.sup.+ concentration in the filtrate solutions amounted to 6.5.multidot.10.sup.-5 mol/l. In the extraction separation method, the solutions containing the precipitates were extracted using various organic solvents, and the residual Cs.sup.+ concentrations in the aqueous phases were measured. The results are shown in Table 9. TABLE 9 ______________________________________ Extraction from the Aqueous Solution Residual Cs.sup.+ Concentration in the Solution Extraction Agent after Extraction (mol/l) ______________________________________ Chloroform 6.2 .multidot. 10.sup.-5 Diethyl ether/ligroine 6.6 .multidot. 10.sup.-5 (b.p. 40-60.degree. C.) 2:1 (vol./vol/) 4-methyl-2-pentanone 6.6 .multidot. 10.sup.-6 (5% by volume in chloroform) 4-methyl-2-pentanone 6.9 .multidot. 10.sup.-6 (5% by volume in toluol) ______________________________________ EXAMPLE 6 (Separation of the Cs.sup.+ precipitates from Compound (3) by means of Liquid Extraction from a Simulated HAW.) Execution of the experiments and the comparison of the separation methods occurred as described in Example 5, except that the precipitant was in this case added in a threefold amount of the stoichiometric amount with respct to the Cs.sup.+ concentration. The residual Cs.sup.+ after filtration of the samples amounted to 7.2.multidot.10.sup.-4 Mol/l. The result of the extractions are shown in Table 10. TABLE 10 ______________________________________ Extraction from Simulated HAW Simulate: Residual Cs.sup.+ Concentration in the Solution Extraction Agent after Extraction (mol/l) ______________________________________ Chloroform 7.1 .multidot. 10.sup.-4 Diethyl ether/ligroine 6.3 .multidot. 10.sup.-4 (b.p. 40-60.degree. C.) 2:1 (vol./vol/) 4-methyl-2-pentanone 6.2 .multidot. 10.sup.-5 (5% by volume in chloroform) 4-methyl-2-pentanone 6.4 .multidot. 10.sup.-5 (5% by volume in toluol) ______________________________________ Other organic solvents may also be used as extraction agents, however, they were not investigated for effectiveness. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.