c 2006 Institute of Chemistry, Slovak Academy of Sciences DOI: 10.2478/s11696-006-0023-y
Determination of Technetium-99 in Soils and Radioactive Wastes Using ICP-MS a
a Department
A. BARTOŠOVÁ, a P. RAJEC, and b A. KLIMEKOVÁ
of Nuclear Chemistry, Faculty of Natural Sciences, Comenius University, SK-842 15 Bratislava e-mail:
[email protected] b Slovak
Hydrometeorological Institute, SK-852 82 Bratislava
Received 8 January 2005; Revised 12 September 2005; Accepted 20 September 2005
Three methods have been used for the determination of 99 Tc in soils and solid radioactive wastes using 99m Tc as a yield monitor. In the method one and three the samples were leached in low concentrated nitric and sulphuric acid. Many contaminants were then co-precipitated with Fe(OH)3 in alkali media and Tc in the supernatant was separated using anion-exchange extraction chromatography. There were made also some studies how to improve the chemical recovery of 99m Tc in the process of chromatography. In the method two the sample was ashed and then leached in 8 mol dm−3 HNO3 and after iron precipitation, technetium was separated on chromatographic column. The chemical recovery of 99m Tc was optimized in the process of chromatography and leaching. Typical recoveries of technetium determined with 99m Tc tracer for all these methods were in the range 39 %—87 %. The 99 Tc activity was measured using proportional low-background beta detector after one week of staying to allow decay of 99m Tc activity. 99 Tc was also determined by the non-radiometric method using inductively coupled plasma mass spectrometer.
INTRODUCTION Technetium-99 is an artificial long-lived pure beta isotope (τ 1/2 = 2.17 × 105 years). 99 Tc is produced with high yield during nuclear fission of 235 U (≈ 6 %) and has a radiological implication and environmental risk [1]. In aqueous solutions, where no reducing agents are present, 99 Tc exists as a pertechnetate ion, TcO− 4. Technetium in this form is very mobile in soils, ground, and surface waters [2]. Technetium behaves as a nutrient analogue and may be concentrated by plants and deposited on their outer membrane. In humans and animals the pertechnate ion localizes in the gastrointestinal tract and thyroid gland [3]. Several methods have been used to determine 99 Tc in the environment [4—12]. The most common measurement techniques are based on radiometric counting methods, for example low-background gas-flow proportional and liquid scintillation counters, which often require time-consuming separation process and long measurement time. 99 Tc in radioactive wastes is also usually determined by radiometric methods, which requires a chemical separation to remove interfering radionuclides often with much higher radioactivities than 99 Tc contained. Radioactivity of 99 Tc is usually less than that of contaminants.
Chem. Pap. 60 (2) 125—131 (2006) c 2006 Institute of Chemistry, Slovak Academy of Sciences
ICP-MS [5, 6, 9] has been successfully used to determine various radioactive elements in different matrices and radioactive wastes. ICP-MS technique requires elimination of interfering elements with the same position of m/z peak as the detected nuclide in the mass spectrum. ICP-MS has been proposed as an alternative technique for 99 Tc measurement in environmental samples and other radionuclides due to its ultra-low detection limit [6]. ICP-MS technique serves as an aid to improve the detection limits and overcomes the disadvantages in radiometric counting having lower MDA. ICP-MS technique, as well as the radiometric counting was used for determination of 99 Tc in this study. 99 Tc was separated using extraction chromatography column filled with prepared sorbent [7] based on Aliquat-336/hydrophobised silica gel, which has properties similar to the TEVA Spec sorbent produced by EICHROM Technologies. EXPERIMENTAL Samples of soils 1 and 2 and solid radioactive wastes – Debris No. 7/665, Debris No. 8/666, Debris No. 13/668 from nuclear power plant Jaslovské Bohunice (Slovakia) were used for technetium-99 separation. Analytical reagents and deionised water were used
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throughout this study. Nitric acid, ammonium hydroxide, hydrogen peroxide, hydrofluoric acid, and ammonium persulphate were supplied by Slavus (Slovakia) and pure sulphuric acid by Merck (Germany). Sodium chloride, ferric chloride, benzene, Silicagel L 5/40 “250 mesh” were supplied by Lachema, Brno (Czech Republic). An Amertec II generator (Amersham, England) was used as a 99m Tc source – activity 15 GBq. The 99m TcO− 4 was eluted from the generator usually by 5 cm3 of physiological solution. All measurements of 99m Tc activities were performed on well-type NaI(Tl) gamma-ray detector NP420 (Hungary). 99 Tc was determined using a lowbackground proportional Counter TESLA NRR 610 (Czech Republic). Non-radiometric measurement of 99 Tc was made on inductively coupled plasma mass spectrometer (ICP-MS) – Perkin—Elmer Sciex, Elan DRC II with argon plasma. HPGe detector ORTEC and Multi-Channel Analyser ORTEC (USA) were used for gamma measuring of soils samples. Procedure for Separation of
99
Tc
Method 1 (with HNO3 ) 10 g of the soil sample was weighed up on an analytical balance, 50 cm3 of 1 mol dm−3 HNO3 and 50 mm3 of 99m TcO− 4 was added to the beaker and then heated to 80 ◦C for 4 h on a hot plate. The solution was transferred to a centrifuge tube and centrifuged for 10 min at 2000 min−1 . 10 cm3 of 30 % H2 O2 was added to the supernatant and heated at 80 ◦C until the effervescence and the yellow colour disappeared. After cooling the sample to a room temperature, precipitation with NH4 OH solution followed, at the pH = 8—9 forming of reddish-brown precipitate of iron was observed. The solution was transferred to a centrifuge tube and centrifuged for 10 min at 2000 min−1 . The supernatant was evaporated to dryness on a hot plate and then dissolved in 20 cm3 of 0.1 mol dm−3 HNO3 and in this form the sample was loaded on the column. The extraction chromatography column filled with prepared sorbent on Aliquat-336/silica gel basis [7] was washed with 20 cm3 of deionised water and conditioned to the nitrate form with 20 cm3 of 0.1 mol dm−3 HNO3 and after this treatment the sample was loaded. To desorb technetium from the column 25 cm3 of 8 mol dm−3 HNO3 was used for elution. The chemical recovery of 99m Tc was optimized according to this method in the process of chromatography and leaching. There were tested some variants for improvement of the separation recovery of 99m Tc after extraction chromatography: – desorption of technetium-99m with 8 mol dm−3 HNO3 from the extraction column without washing the sorbent after sorption of 99m Tc; 126
– desorption of technetium-99m with 8 mol dm−3 HNO3 with washing the column with 25 cm3 of 0.5 mol dm−3 HF/0.02 mol dm−3 HNO3 after sorption of 99m Tc; – precipitation of Fe3+ with adding of NH4 OH solution before loading the sample on the column; – washing the column with 15 cm3 of 0.1 mol dm−3 HNO3 after sorption of 99m Tc for removal of impurities. There was taken 10 g of soils and two samples were analysed parallel according to the described method. 1 cm3 of eluted solution was taken and the activity 99m of Tc measured on NaI(Tl) detector to determine chemical recovery. After decay of technetium-99m (5 d) beta activity was measured on low-background proportional detector. Method 2 (with H2 SO4 ) 10 g of the soil sample was weighed up on an analytical balance, 45 cm3 of 1.5 mol dm−3 H2 SO4 , 450 mg of (NH4 )2 S2 O8 , and 50 mm3 of 99m TcO− 4 as a tracer were added to the beaker and then heated for 2 h under infra-lamp. The solution was left to stand for 24 h at room temperature, then it was transferred to a centrifuge tube and centrifuged for 10 min at 2000 min−1 . 10 cm3 of H2 O2 was added to the supernatant and heated at 80 ◦C until the effervescence and the yellow colour disappeared. After cooling the sample to a room temperature, precipitation with NH4 OH solution followed. The mixture was transferred to a centrifuge tube and centrifuged for approximately 10 min at 2000 min−1 . The supernatant was evaporated to dryness on a hot plate and then dissolved in 20 cm3 of 0.1 mol dm−3 HNO3 or in 20 cm3 of 1 mol dm−3 H2 SO4 , respectively. The sample was then loaded on chromatography column that was washed with 20 cm3 of deionised water and then with 20 cm3 of 1 mol dm−3 H2 SO4 or 0.1 mol dm−3 HNO3 . The column was washed with 15 cm3 of 1 mol dm−3 H2 SO4 or 0.1 mol dm−3 HNO3 . To desorb technetium from the column, 25 cm3 of 8 mol dm−3 HNO3 was used for elution. 1 cm3 of this eluted solution was taken and the activity of 99m Tc was measured using NaI(Tl) detector. Beta activity was measured on low-background counter after decaying of technetium-99m. Method 3 (according to Wigley) A method for separation and purification of technetium in soils [3] and radioactive wastes was tested. A schematic summary for this method is shown in Scheme 1. The analysis was done according to Method 3 which included ashing, leaching, precipitation with Fe3+ and purification of 99m Tc on extraction chromatography column filled with prepared sorbent. Samples of solid radioactive wastes from nuclear power plant Jaslovské Bohunice (Slovakia) were treated and measured in the same time after separa-
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Chem. Pap. 60 (2) 125—131 (2006)
TECHNETIUM-99 IN SOILS
10 g of soil or radioactive waste ↓ add approx. 35 kBq 99m Tc and 2.5 Bq 99 Tc as a yield monitor ↓ wet sample with 30 cm3 of NH4 OH and evaporate to dryness ↓ ash sample at 250 ◦C for 1 h. Increase temperature, 50 ◦C h−1 , until 550 ◦C, ash for a further hour ↓ leach in 50 cm3 of 8 mol dm−3 HNO3 on a hot plate at 125 ◦C for 2 h ↓ centrifuge and filter the sample ↓ neutralise with 25 cm3 of NH4 OH until a reddish-brown precipitate is formed ↓ centrifuge, discard the precipitate and evaporate to dryness ↓ dissolve the sample in 20 cm3 of 0.1 mol dm−3 HNO3 ↓ wash the column with prepared sorbent with deionised water and then with 20 cm3 of 0.1 mol dm−3 HNO3 ↓ load the solution onto a prepared sorbent and wash with 20 cm3 of 0.1 mol dm−3 HNO3 ↓ eluate Tc with 25 cm3 of 8 mol dm−3 HNO3 ↓ take 1 cm3 from the eluate for determination of the chemical recovery for gamma measurement of 99m Tc ↓ evaporate to dryness on a hot plate and dissolve the sample in 5 cm3 of 0.1 mol dm−3 HNO3 ↓ determine 99 Tc concentration by ICP-MS Scheme 1. Determination of
99 Tc
in soils and radioactive wastes by Method 3.
tion of technetium with NaI(Tl) gamma counter for determination of separation yield. After decaying of 99m Tc, five days after separation, the 99 Tc was measured on low-background counter. At the determination of activity of 99 Tc in soils using low-background proportional detector eluted solutions obtained by all separation processes described above after decay of short-living 99m Tc were evaporated to dryness on a hot plate and then dissolved in 20 cm3 of 0.1 mol dm−3 HNO3 . 10 cm3 of this solution was transferred to the nickel planchet, evaporated to dryness under infra-lamp. The planchet was then measured on low-background proportional counter. The activity of 99 Tc was calculated using the following equation Ni − Nb A= tER
(1) 3
where Ni represents counts measured in 1 cm of the initial solution, Nb count rate of the background, t the same registration time for counts Nb , Ni , E efficiency of the low-background detector for 99 Tc (30 %), R yield of 99m Tc separation. At the determination of 99 Tc the samples of soils and debris after measurements on low-background proportional counter were dissolved in 20 cm3 of 1 % HNO3 , put in 50 cm3 of polyethylene container and
Chem. Pap. 60 (2) 125—131 (2006)
analysed on ICP-MS spectrometer with pure argon plasma. ICP-MS detector was calibrated with diluted 99 Tc solutions in 1 % HNO3 from standard 99 Tc solution. The contents of 99 Tc were in the range 0.25—25 ppt (each standard solution consists of 25 cm3 of 1 % HNO3 ). Blank samples were also prepared from the soil without adding technetium-99. Chemical recoveries of technetium to determine the sorption and desorption recovery in the process of extraction chromatography were calculated using the following equations N 1 − nb t Rsorp = 1 − · 100 % N 0 − nb t Rdesorp =
(N2 − nb t) Vdesorp · 100 % (N0 − nb t) Vsorp
(2)
(3)
where N0 represents measured counts of 1 cm3 of the initial solution, N1 counts in 1 cm3 of solution after the sorption, measured at the same time as N0 , N2 counts in 1 cm3 of solution after the desorption of 99m TcO− 4, nb count rate of the background (s−1 ), t registration time for counts N0 , N1 , and N2 (s), Vsorp volume of solution used for the sorption (cm3 ), Vdesorp volume of solution used for the desorption (cm3 ). Chemical recoveries of technetium after used separation steps were calculated using the following equa-
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Table 1. Beta Counting Rates of Samples Prepared with Different Procedure of Blank Soil-Leaching Solution Measured with Proportional Detector Counting rate/s−1
Column treatment without washing the sorbent 0.19 ± 0.009 washing the sorbent with 15 cm3 of 0.1 mol dm−3 HNO∗3 precipitation of Fe3+ /washing with 15 cm3 of 0.1 mol dm−3 HNO∗3 washing the sorbent with 15 cm3 of 0.2 mol dm−3 HF/0.02 mol dm−3 HNO3 ∗
0.073 ± 0.007 0.042 ± 0.006
Parallel samples, n = 2.
Table 2. Chemical Recoveries of
99m Tc
in the Separation Process with HNO3 Soil 1∗
Procedure Chem. recovery Chem. recovery Chem. recovery Chem. recovery Chem. recovery Total yield/% ∗
0.069 ± 0.007 0.049 ± 0.007 0.043 ± 0.004
after after after after after
86.9 ± 110.2 ± — 88.3 ± 89.1 ± 68.3 ±
leaching and centrifugation/% adding H2 O2 and heating/% precipitation and centrifugation/% dissolving and filtration/% extraction chromatography/%
6.4 8.1 6.4 6.3 13.2
Soil 2∗ 90.6 105.2 68.7 95.4 90.8 56.7
± ± ± ± ± ±
6.7 7.7 5.1 5.9 6.8 13.3
Parallel samples, n = 4.
tion R=
V1 (N1 − nb t) · 100 % V0 (N0 − nb t)
(4)
where N0 represents measured counts of 1 cm3 of the initial solution, N1 counts in 1 cm3 of solution after used separation procedure, measured at the same time as N0 , nb count rate of the background (s−1 ), t registration time for counts N0 and N1 (s), V0 volume of the initial solution (cm3 ), V1 volume of solution used for the separation procedure (cm3 ). RESULTS AND DISCUSSION Many radionuclides can interfere during radiometric detection of technetium-99 and by ICP-MS detection. 450 g of soils were measured in Marinelli vessel using HPGe detector and MCA for determination of radionuclides, which can interfere by radiometric or ICP-MS detection of technetium-99. Some peak positions of isobaric nuclides with 99 Tc, 99 Ru, and 98 Mo (creates compounds with hydrogen – 99 MoH) can interfere by mass spectrometry. 137 Cs, decay products of thorium and uranium and 40 K belong to the main contaminants and it is necessary to remove all these radionuclides before radiometric detection of 99 Tc. The whole process of separation of 99 Tc by Method 1 was done by different ways of column treatment: the sorbent based on Aliquat-336 anchored on hydrophobised silica gel support was washed using several methods and the recovery of technetium-99m was studied. Counting rates of samples prepared with different procedures are shown in Table 1. It can be seen that the lowest counting rate of the background beta activity was obtained by wash128
ing the sorbent with 15 cm3 of 0.1 mol dm−3 HNO3 after loading of 99m TcO− 4 in the column in extraction chromatography step (including Fe3+ precipitation in alkali media). When the sorbent was washed with 0.1 mol dm−3 HNO3 after technetium sorption, interfering nuclides were removed – alkali metals and divalent transition metals passed through without their interception on the column. Separations of technetium-99 from 60 Co, 63 Ni, 90 Sr, 137 Cs, and also 99 Ru and 98 Mo were successfully carried out in the process of column extraction chromatography. When the column was washed with 25 cm3 of 0.5 mol dm−3 HF/0.02 mol dm−3 HNO3 , the prepared sorbent bubbled and was chemically unstable because of F− with silica interaction, which destroyed the silica support of the sorbent. 99m TcO− 4 tracer was added to the initial soils solution and separation was made with and without precipitation of iron. The chemical recoveries of technetium-99m for sample with iron precipitation were about 42 %—46.6 % and without precipitations of iron the chemical recoveries of 99m TcO− 4 were about 76.6 %—80.6 %. Chemical recoveries of 99m TcO− 4 were higher without iron precipitations but this step was necessary to include to the technetium separation because of decontamination and removal of interfering radionuclides. Chemical recoveries of 99m TcO− 4 after each separation are presented in Table 2. Average chemical recovery of 99m Tc obtained with this method was about 70 %. The results of technetium separation by Method 2 using sulphuric acid are shown in Table 3. Chemical recoveries of 99m Tc were about 15 % lower in the process with H2 SO4 than those reached
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Chem. Pap. 60 (2) 125—131 (2006)
TECHNETIUM-99 IN SOILS
Table 3. Chemical Recoveries of
99m Tc
in the Separation Process with H2 SO4 Soil 1∗
Procedure Chem. recovery Chem. recovery Chem. recovery Chem. recovery Total yield/% ∗
after after after after
87.7 ± 77.3 ± 92.4 ± — 58.6 ±
leaching and centrifugation/% precipitation and centrifugation/% extraction chromatography with HNO3 /% extraction chromatography with H2 SO4 /%
Soil 2∗ 81.1 ± 55.8 ± — 85.5 ± 45.4 ±
6.4 5.1 5.9 10.3
6.0 4.2 6.5 9.8
Parallel samples, n = 4.
Table 4. Chemical Recoveries of
99m Tc
and Activity of
99 Tc
for the Individual Samples
Procedure
Debris No. 7/665
Chem. recovery after ashing and leaching/% Chem. recovery after precipitation and centrifugation/% Chem. recovery after extraction chromatography/% Total recovery of 99m Tc/% Activity of 99 Tc/(Bq g−1 )
99 73.3 89.9 65.2 0.06
± ± ± ± ±
Debris No. 8/666
7.7 6.1 6.2 11.6 0.06
99.6 90.5 97.1 87.5 0.13
± ± ± ± ±
Debris No. 13/668
8.1 7.9 8.1 13.9 0.04
99.5 73.3 98.2 71.2 0.42
± ± ± ± ±
7.9 6.9 8.4 13.4 0.05
n = 4. Table 5. Comparison of Chemical Recoveries for
99m Tc
for Soils according to Method 1 and Method 3
Procedure
Method 1
Chem. recovery after ashing and leaching/% Chem. recovery after precipitation and centrifugation/% Chem. recovery after extraction chromatography/% Total recovery of 99m Tc/%
96.7 74.9 78.5 68.6
± ± ± ±
6.9 5.7 5.5 10.5
n=4
in the process with HNO3 . Beta activities of samples were measured on low-background counter for 3000 s after extraction chromatography with HNO3 or H2 SO4 after decaying of 99m Tc. Samples of soils and radioactive wastes were elaborated according to Method 3. Prepared sorbent based on Aliquat-336/hydrophobised silica gel was successfully used in the method instead TEVA sorbent. The results of technetium separation in samples of solid radioactive wastes are shown in Table 4. The chemical recoveries of 99m Tc for soil were nearly the same as for the debris samples, typical technetium-99m yields were in the range 65.2 %— 87.5 %. The organic matrix was effectively removed by ashing. The losses of technetium by the heating can be explained by releasing of Tc2 O7 – the product of dehydration of HTcO4 by heating. The acid HTcO4 was made by oxidation of technetium in the presence of organic acids. The addition of ammonia before ashing neutralised free chemical bonds on organic acids surface and inhibited the HTcO4 production. After leaching the sample with 50 cm3 of 8 mol dm−3 HNO3 it was necessary to evaporate the acid solution to approximately 10 cm3 . When a large volume of the nitric acid was precipitated with ammonium hydroxide, great amount of NH4 OH was needed to adjust pH for precipitation of iron. Iron precipitation was
Chem. Pap. 60 (2) 125—131 (2006)
Method 3 71.2 87.9 91.7 77.1
± ± ± ±
5.8 6.8 6.7 5.6
n=6
used for removal of transition metals, actinides, and lanthanides. Alkali metals, rare-earth metals (137 Cs, 90 Sr), Re(VII), Ru(VIII), and Tc(VII) were in the solution. The sample containing high concentration of salts complicated the process of extraction chromatography, the column was obstructed and the flow rate decreased rapidly. Pertechnetate was strongly retained to sorbent based on hydrophobised 30 % Aliquat-336/silica gel in low acid concentration due to the high selectivity of quaternary ammonia salt (Aliquat-336) to the 99 TcO− 4 anion in column extraction chromatography. This is why the pertechnetate was sorbed on the sorbent and actinides and transition metals were eluted from the column. When the interfering radionuclides were successfully removed, the column was washed with 25 cm3 of 0.1 mol dm−3 HNO3 for removal of impurities. 99 Tc was eluted with 20 cm3 of 8 mol dm−3 HNO3 . Chemical recoveries of 99m Tc for Methods 1 and 3 are shown in Table 5. Chemical recoveries of 99m Tc obtained using Method 3 were about 10 % higher than for Method 1. Chemical recoveries of pertechnetate were about 66.5 %—75.1 % for samples of soils and debris in separation process with nitric acid. Counting rates measured on proportional counter for debris samples No. 7 and No. 8 treated with Method 1 were two times
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Table 6. Content of 99 Tc in Samples of Soils and Solid Radioactive Wastes Determined on ICP-MS and Low-Proportional Detector Sample m (sample)/g m of 99 Tc (ng/sample) ICP-MS Recovery of 99m Tc R/% A of 99 Tc/Bq sample m(ng/sample)∗ ICP-MS m(ng/sample)∗∗ ∗
Soil 2
Debris No. 7/665
Debris No. 8/666
Debris No. 13/668
10.023 0.233 57.13 ± 5.6 1.8 ± 0.4 0.82 2.8 ± 1.4
10.097 0.18 65.2 ± 4.7 1.17 ± 0.5 0.55 1.85 ± 0.6
10.12 0.64 87.5 ± 6.5 2.58 ± 0.6 1.47 4.07 ± 1.3
10.054 0.97 71.2 ± 5.9 5.27 ± 0.8 2.71 8.32 ± 1.2
Recalculated from the ICP-MS measurements on chemical recovery; calculated from the measurements using the proportional detector.
∗∗
hihger than the counting rates for the same samples treated with Method 3. Method 3 – separation according to Wigley ensured better purification and higher decontamination factor because of more separation steps. All organic materials were removed by ashing the sample. Debris No. 7/665 and No. 8/666 determined according to Method 1 contained 137 Cs, which obstructed the radiometric determination on low-background proportional detector. The soils samples and radioactive wastes (10 g sample) after separation procedure (Method 3) were analysed on ICP-MS. Each solution after separation was splitted and one part was used for ICP-MS determination and the second part for radiometric determination. A set of solutions in 0.1 mol dm−3 HNO3 were prepared with different concentration of 99 Tc for the calibration of the ICP-MS spectrometer. The results of 99 Tc determination using ICP-MS and proportional detector in samples of soils and solid radioactive wastes are in Table 6. Relationship between activity of 99 Tc and technetium-99 content was calculated from ICP-MS measurements: 1 Bq 99 Tc. . . . . . . .1.579 ng 99 Tc The difference in technetium-99 content between ICP-MS and proportional counter results in samples of radioactive wastes and soils was caused by the sensitivity of detection equipment. ICP-MS detector is more sensitive and at the determination of technetium-99 there were no interferences from contaminants with the position of m/z peak 99. 99 Tc contents in samples of soils and debris measured on proportional counter are higher than the results obtained from ICP-MS measurements. It was caused by the occurrence of Cs-137 in samples of debris No. 13 and No. 8. Cs-137 interfered by radiometric detection in samples of radioctive wastes. Caesium-137 can be partially removed using column extraction chromatography, for full remotion of 137 Cs and for purification of the samples it was necessary to integrate liquid extraction system with tetraphenylarsonium chloride to the separation process. Ruthenium and molybdenum interferences were successfully removed by column extraction chromatography using the prepared sorbent based on 30 % Aliquat-336/hydrophobised silica gel. 130
Proportional counter is not as suitable for measurement of 99 Tc activity as ICP-MS because of lack of contaminants discrimination with higher beta energy. A better separation factor for the detection using proportional counter is necessary. From the experimentally obtained results ICP-MS technique seems to be the most suitable choice for technetium-99 determination, namely for radioactive wastes due to its insensitivity to the radioactivity contamination and detection limit to 10−12 g. Compared to the radiometric method, the analysis time on ICPMS was shortened by about 25 times. CONCLUSION Three methods of 99 Tc determination in soil and solid radioactive wastes were studied. Chemical recoveries of Tc separation were determined using NaI(Tl) detector by gamma-activity measuring of 99m Tc. The analytical procedures were studied and the separation conditions were optimized. For Method 1 (HNO3 procedure) typical chemical recoveries of 99m Tc were about 66.5 %—75.1 % for soils and radioactive wastes samples. Typical chemical recoveries of 99m Tc for Method 2 (H2 SO4 procedure) were in the range 44.9 %—58.6 % for soils samples. Typical chemical recoveries of 99m Tc for Method 3 were in the range 62.3 %—86.1 % for solid radioactive wastes and about 78 % for soils. This method – separation according to Wigley ensured better purification because of more separation steps and higher decontamination factor. 99 Tc was radiometrically determined by measuring beta activity using the low-background proportional counter after decay of technetium-99m. Technetium99 was also determined by ICP-MS in soils and radioactive wastes samples. Interfering elements, Ru, Mo, lanthanides, and actinides were removed using puirification steps: extraction chromatography and precipitation with iron in alkali media. By the detection of 99 Tc the main difference between ICP-MS and radiometric measurements was shown. The main contaminant 137 Cs occurring in samples of radioactive wastes was shown by radiometric detection of technetium-99 compared to the results from ICP-MS.
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Chem. Pap. 60 (2) 125—131 (2006)
TECHNETIUM-99 IN SOILS
By radiometric detection of technetium-99 interfering caesium-137 can be partially removed using the extraction chromatography column. For the full removal of 137 Cs, tetraphenylarsonium chloride extraction system is necessary to be used. By ICP-MS measurement column extraction chromatography was sufficient as the last decontamination step with samples of radioactive wastes. ICP-MS technique seems to be the most suitable choice for technetium-99 determination, namely for radioactive wastes. Acknowledgements. This work was supported by the Grant No. 86/2003, Comenius University.
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