Purification of actinide containing water with Gaiasafe filter papers

Rainer Haas¹, Fritz Pfeiffer¹, Olga Tsivunchyk²

1: gaiasafe Ltd., Stadtwaldstrasse 45a, D-35037 Marburg, Germany

2: Yanka Kupala Grodno State University, Ozheshko str.´ 22, Grodno, 230023, Republic of Belarus

Abstract

gaiasafe Ltd. has developed ironoxide-impregnated filter papers for heavy metals and metalloides sorption. For arsenic(III) a sorption capacity is 9% of the paper weight, the weight of ironoxide is 9% from the paper weight, it means 50 mg Fe in 1 g paper.

Experiments were done to investigate the sorption capacity of gaiasafe filter papers for actinides. 80 ml aqueous solution of Uranium nitrate (c = 62.5 mg/ml), Uranyl acetate (c = 18.8 mg/ml) and Thorium nitrate (c = 62.5 mg/ml) were prepared, 1 ml acetic acid (30 %) was added. 1 g gaiasafe filter paper (as filter wool) was put to each of these solutions. After 1 h, 2 h, 4 h, 8 h, 24 h and 48 h the filter wool was recovered from the solution. The gamma activity of the solutions and paper were measured with a gamma counter.

The results of the experiments showed, that after 24 h the reduction rates in the solutions were determined as 85% for Uranium nitrate, 76% for Uranyl acetate and 82% for Thorium nitrate. The weight of the dry filter papers was 2.42 g for Uranium nitrate, 1.62 g for Uranyl acetate and 2.08 g for Thorium nitrate. It means that one iron atom bounds 6.7 Uran atoms (from Uranium nitrate), 7.6 Uranium atoms (from Uranyl acetate) and 5.2 Thorium atoms (from Thorium nitrate).

Gaiasafe filter paper is a high effective sorbing material for actinides, as experiments showed. It can be used for filtration and purification of aqueous solutions. Because of the high sorption capacity gaiasafe filter papers are good matrix for the fixing actinide wastes for storage.

Key Words: analyses, filtration, sorption, thorium, uranium

1 Introduction

gaiasafe Ltd. has developed ironoxide-impregnated filter papers for heavy metals and metalloides sorption. E.g. for arsenic(III) a sorption capacity is 9% of the paper weight, the weight of ironoxide is 9% of paper weight, it means 50 mg Fe in 1 g paper. Other heavy metals like copper, lead, cadmium, mercury etc. can be sorbed on this papers too (1).

The idea was to determine the sorption capacity of gaiasafe filter papers with two actinides, Thorium and Uranium.

Three experiments were done to determine the sorption capacity of the gaiasafe filter papers and to determine the kinetics of the reduction of actinides from aqueous solutions with radiation spectroscopy of the test solution and the adsorber matrix.

2 Experimental

2.1 Material and equipment

Chemicals

As actinide compounds Thorium nitrate, Uranium nitrate and Uranyl acetate were used. Destilled water with acetic acid 30% as a co-solvent was used for the test solutions.

For the experiments each: 5.0 g Uranium nitrate, 5.0 g Thorium nitrate and 1.5 g Uranyl acetate were soluted in 80 ml dest. water, 1 ml acetic acid (30%) was added.

Materials

1 g gaiasafe filter wool gs 988. was used for each experiment. This filter wool contains 9% ironoxide and before was tested for the sorption of heavy metals from aqueous solutions (1). All used vessels, filters and pipetts were from borosilicate glas from Schott/Mainz, RFA.

Equipment

For radiation detection a Siemens Counter fitted with a proportional detector set to lim10000 cts/sec was used. For each measurement ten readings at 30 sec intervals in a timeframe of 100 sec each were done.

The working voltage was 1600 V, with a 1.5 mm borosilicate glass filter. Time rise was set up to 0.1 µsec, attenuator factor 1 with a baseline of 7.00 V.

The measuring distance was shutter length i.e. 15 mm.

Gravimetry was done with a Sartorius Weight.

2.2 Experimental Set-up

The gaiasafe filter wool (gaiasafe filter paper, cutted in 1 mm stripes) were put into beakers filled with the test solutions, three each and set up with a dust cover.

For the experiments 5.0 g Uranium nitrate, 5.0 g Thorium nitrate and 1.5 g Uranyl acetate were soluted each in 80 ml dest. water, 1 ml acetic acid (30%) was added.

To set up reproducable working procedures, a test scheme was established to keep measuring short due to radiation and contamination avoidance.

At the first, the actual zero effect of the gamma spectrometer was determined. Then the gamma counts of the dry filter paper and the three test solutions were made to determine the initial count setting.

Then, in progressive time intervals after 0, 1, 2, 4, 8, 24 and 48 hours the filter papers were taken from the solutions and their gamma activity was determined. Then the gamma activity of the solutions without the filter papers were measured.

After 48 hours the filter papers were dried at 25 °C for 12 hours. Then their weight was determined.

3 Results and discussion

In the first approach, reaction kinetics in all three experiments were similar and therefore found to be comparable. The activity of gamma radiation spectroscopy after 24 hours, for the counts of the solution in percentage of the original test solution [C _soln.% ] and the counts of the filter wool in percentage of the original test solution [C _FW% ] are shown. The coincidence is the sum of the both. This results are shown in table 1.

Table 1: Sorption of actinides on gaiasafe filter wool after 24 hours

The major changes in the process are mostly finished after 24 hours. The coincidence was between 90-93% and indicated that the mistake of measurement was less than 10%. The remaining concentration of actinides in aqueous solutions was between 15% and 24% from the initial concentration. All results of the kinetical studies are shown in table 2. The total yield, means recovered amount of acitinides from aqueous solution to gaiasafe filter wool, after 48 hours was for- Soln. 1 1.42 g Uranium, i.e. 47% of total amount in the original test solution

- Soln. 2 0.62 g Uranium, i.e. 73% of total amount in the original test solution

- Soln. 3 1.08 g Thorium, i.e. 45% of total amount in the original test solution.

Therefore we have found gravimetrically a sorption capacity from

- Soln. 1 with 6.7 U-atoms for 1 Fe atom

- Soln. 2 with 7.6 U-atoms for 1 Fe atom

- Soln. 3 with 5.2 Th-atoms for 1 Fe atom

on the used gaiasafe filter wool.

In table 2 the results of the kinetical studies of the sorption of actinides on gaiasafe filter wool are shown. In picture 1 the desorption of actinides from the solution, in picture 2 the sorption of actinides on gaiasafe filter wool are shown. After 8 hours most of the components are sorbed on the gaiasafe filter wool. The decay function of the kinetics of all three experiments is similar and follows a logarithmic function. Similar results were obtained by sorption experiments of Uranium salts at ferrihydrite (2).

The experiments showed that gaiasafe filter paper was a high effective sorbing material for actinides. It can be used for filtration and purification of aqueous solutions. Because of the high sorption capacity gaiasafe filter papers are good matrix for the fixing of actinide wastes for storage.

The gaiasafe filter paper can be used as passive collector for water investigation (3). Because of this fact it is possible to investigate contaminations with actinides in ground and surface water very easily.

Table 2: Kinetical studies of sortion and desorption of actinides from aqueous solutions on gaiasafe filter wool

C_{soln (cts)} gamma activity of solution (counts per second)

C_{FW (cts)} gamma activity of filter wool (counts per second)

C_{soln (%)} normed concentration in solution (native concentration = 100%)

C_FW(%) normed concentration on filter wool (native concentration = 100%)

Picture 1: Desorption of actinides from aqueous solutions; (1): Thorium nitrate; (2): Uranyl acetate; (3): Uranium nitrate

Picture 2: Adsorption of actinides on gaiasafe filter wool; (1): Thorium nitrate; (2): Uranyl acetate; (3): Uranium nitrate

References:

[1] R. Haas, F.D. Oeste: Imprägnierte Filterpapiere für die Wasserreinigung. UWSF-Z. Umweltchem. Ökotox. 11 (1999), 20

[2] K. Schmeide, V. Brendler, S. Pompe, M. Bubner, K.H. Heise, G. Bernhard: Sorption Kinetics in the System Uranium/Sulfate/Humic Acid/Ferrihydrite. in: eds.: F.H. Frimmel, G. Abbt-Braun: Symposium on refractory organic substances in the environment - Rose II. Karlsruhe 2000.

[3] R. Haas, F.D. Oeste: Passivsammler zur Wasseruntersuchung. UWSF-Z. Umweltchem. Ökotox. 13 (2001), 2-4

Back zu start page