Radiochimica ActayutsrponmlihedcbaWVSIFDCBA 44/45, 147-151 (1988) © R. Oldenbourg Verlag, München 1988 - 0033-8230/88 $ 3.00+0.00 Sorption of Cesium and Strontium on Montmorillonite and Kaolinite* By H. N. ERTEN^ S. AKSOYOGLU 2 , S. HATI POGLU 2 and H. GÖKTÜRK 2 , 1 Department of Chemistry, Bilkent University Ankara-Turkey 2 Department of Chemistry, Middle East Technical University, Ankara-Turkey (Received September 12, 1987; revised January 11, 1988) Clays ¡Sorption IFission products/Batch method / Distribution ratios Summary Sorption characteristics of Cs + and Sr ++ on montmorillonite and kaolinite type clays and soil fractions from various regions of Turkey were studied using the batch method. 137 Cs and ,0 Sr were used as tracers. Concentrations of Cs + and Sr ++ ions ranged from 10"' to 10" 2 mol/1; natural groundwater was used and the grain size of the solid particles was < 20 /am. Equilibrium was reached in 4 - 7 days for Cs + and 7 - 1 1 days for Sr ++ . The distri- bution coefficient, R D , increased with decreasing grain size, sug- gesting mainly a surface phenomenon. The sorption isotherms were non-linear suggesting at least two different sorption proces- ses. The sorption was found to be predominantly reversible. Cs + was sorbed much stronger than Sr TT in all samples. Introduction Storage of radioactive wastes in underground repositories necessitates information on the mobility and chemical behaviour of the individual radionuclides in geologic en- vironments. The fission products 137 Cs (f 1/2 = 30.2y) and 90 Sr (t 1 i2 =28.8y), are the principle sources of radioactivity during the first 1000 years, due to their long half-lives and high fission yields. They may be discharged into the environment from nuclear power plants, nuclear weapon tests and accidents occuring at reprocessing plants. The interaction of Cs + and Sr 2 + ions with various soil fractions plays an important role in their dispersal to the environment and thus in the extent of contamination of underground waters. Of the various soil fractions, clays are the most important components in such interactions. The sorption properties of several radionuclides on various sorbents has been the subject of many recent in- vestigations [1—9]. In this work, the sorption characteristics of Cs + and Sr 2+ on two types of clays and one soil fraction from Turkey were studied, in line with plans to establish a radioactive waste treatment and storage facility. Experimental Kaolinite and montmorillonite type clays from two re- gions of Turkey (Mihaliccik and Resadiye) and soil frac- tions from Sarayköy were used. Neutron activation ana- lysis, Fourier Transform Infrared (FTIR) and X-Ray Dif- fraction Spectrometry were used to elucidate the struc- ture of the clay and soil fractions. Particles were separated into various size fractions by a combination of wet sieving followed by sedimentation using an Andreasen pipette. The sorption experiments were carried out using groundwater from the Middle East Technical University (METU) and Sarayköy Ground Water (SGW). The water samples were filtered through 0.22 μ τη zyxwvutsrqponmlkihgfedcbaTSRF Seitz bacteriologi- cal filters before use. For the composition see Table 1. Since 90 Sr and 137 Cs constitute the principle radio- contaminants from relatively fresh spent uranium fuels, Sr 2+ and Cs + were first chosen for sorption studies. The initial concentrations ranged from 10" 8 to 10" 2 mol/1. 137 Cs and 90 Sr were obtained from the Radiochemical Center, Amersham. The sorption and desorption experiments were carried out using the batch method. About 100 mg of clay or soil samples were kept in contact with 10 ml of groundwater in closed centrifuge tubes. They were shaken for four days in the pretreatment step in order to equilibrate the clay samples with the groundwater prior to the sorption experiments. The phases were separated by centrifuging at 6000 rpm for 30 minutes. After addition of 10ml Cs or Sr solution the samples were shaken again and centri- fuged. The change of the adsórbate concentration in the solution was determined radiochemically. The distribution coefficient, R D , was calculated from: = í£li = V-A°-A(V+AV) D [C], AW s where, [C^ = Concentration of the cation in the solid phase after sorption (mmol/g). [C] ; = Concentration of the cation in the solution after sorption (mmol/ml). A o = Initial activity of the solution (cpm). A = Activity of the solution after sorption (cpm). V = Volume of solution added (ml). AV = Volume of liquid remaining after pretreatment and décantation (ml). W = Mass of solid material (g). For desorption studies 10 ml of groundwater was added to the sample tube following the adsorption step, shaken for seven days, centrifuged and decanted. The activity of the liquid phase was then determined. Similar expressions as above were used for the calcu- lation of R D values for desorption studies. Correction for the remaining activity from the adsorption step was * Supported in part by the International Atomic Energy Agency Vienna, and by the Turkish Atomic Energy Authority, Ankara. Brought to you by | Bilkent University Authenticated Download Date | 12/7/18 8:06 PM