title: Diffusion of Na(I), Cs(I), Sr(II) and Eu(III) in smectite rich natural clay.
abstract: Diffusion of Na(I), Cs(I), Sr(II) and Eu(III) in smectite rich natural clay, proposed as a backfill material in the Indian geological repository, was studied using the out-diffusion method. Radiotracers (22)Na, (137)Cs, (85)Sr and (154)Eu were used; the first three are carrier-free enabling experimental work at sub-micromolar metal ion concentration, and Eu(III) tracer (154)Eu was used at sub millimolar concentration. An out-diffusion methodology, wherein a thin planar source of radioactivity placed between two clay columns diffuses out, was used to obtain the apparent diffusion coefficient (Da) values. This methodology enabled determination of diffusion coefficient even for strongly sorbing (154)Eu. Da values for (22)Na, (137)Cs, (85)Sr and (154)Eu were 2.35 (±0.14) × 10(-11), 2.65 (±0.09) × 10(-12), 3.32 (±0.15) × 10(-11) and 1.23 (±0.15) × 10(-13) m(2) s(-1), respectively. Da values were found to be in fair agreement with literature data reported for similar mineralogical sediments. Sorption of radionuclides on the clay was also determined in the present study and differences in Da values were rationalized on the basis of sorption data. Distribution ratios (Kd) for Cs(I) and Eu(III) were higher than that for Sr(II), which in turn was higher than that for Na(I).
authors.affiliation: Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Sharayu
authors.initials: S
authors.lastname: Kasar
authors.affiliation: Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Sumit
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Technology Development Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: R K
authors.initials: RK
authors.lastname: Bajpai
authors.affiliation: Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India. Electronic address: bstomar@barc.gov.in.
authors.forename: B S
authors.initials: BS
authors.lastname: Tomar
mesh_terms: D000538:Aluminum Silicates / Q000032:analysis; D002588:Cesium Radioisotopes / Q000032:analysis; D000077215:Clay; D004058:Diffusion; D005063:Europium / Q000032:analysis*; D007194:India; D011834:Radiation Monitoring; D011868:Radioisotopes / Q000032:analysis*; D017640:Silicates / Q000032:analysis; D012979:Sodium Radioisotopes / Q000032:analysis; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013326:Strontium Radioisotopes / Q000032:analysis
chemical_list: D000538:Aluminum Silicates; D002588:Cesium Radioisotopes; D011868:Radioisotopes; D017640:Silicates; D012979:Sodium Radioisotopes; D012990:Soil Pollutants, Radioactive; D013326:Strontium Radioisotopes; D005063:Europium; C033214:Smectite; D000077215:Clay
keywords: (137)Cs; (154)Eu; (22)Na; (85)Sr; Diffusion; Smectite rich clay