TY - JOUR

T1 - Retention of radionuclides by organophilic bentonite

AU - Bors, J.

AU - Dultz, St

AU - Riebe, B.

N1 - Funding information: This work was supported by the European Commission ‘Nuclear Fission Safety’ programme (1994–1998) under Contract No. FI4WCT950012. The skilful experimental work by Gabriele Erb-Bunnenberg and Karl-Heinz Iwannek is gratefully acknowledged.

PY - 1999/9

Y1 - 1999/9

N2 - Distribution ratios (R(d)-values), and isotherms for sorption of iodide (125I), technetium ((95m)Tc), cesium (134Cs) and strontium (85Sr) were measured on MX-80-bentonite, which had been modified with hexadecylpyridinium (HDPy+). Synthetic ground water was used as the equilibrium solution (ionic strength: 0.037 mol 1-1). Additionally, the mineralogical characteristics, like regular and in situ powder X-ray diffraction (XRD), thermogravimetric (TG), calorimetric (DTA) measurements, IR spectral analysis of the organo-bentonite samples, and the exchange behaviour of HDPy+ (chemical analysis) were investigated. With HDPy+-modified MX-80-bentonite, iodide and pertechnetate ions exhibited increasing adsorption (R(d)), while cesium and strontium showed decreasing adsorption with increasing organophilicity. Sorption of technetium was found to be almost completely reversible with samples of relatively high (>100% of the cation exchange capacity, CEC) HDPy+ loading. Generally, sorption and desorption were linear over a wide concentration range of the elements investigated (up to ~10-1 mmol g-1 organo-bentonite) suggesting ion exchange as the principal sorption mechanism. Sorption capacities for the anions investigated were estimated to be ~5 x 10-1 mol kg-1. Concerning the cationic radionuclides, higher distribution coefficients were found for the Cs+ compared to the Sr2+ ions in the untreated and modified samples. On the basis of mineralogical and chemical analysis it was concluded that the alkylammonium ions are adsorbed as: 1, HDPy+ cations; 2, HDPyCl molecules; and 3, micelles with decreasing binding intensities in this order. The observed uptake of the organic cations in excess of the CEC leads to the formation of modified microstructures different from samples with relatively low HDPy+ saturation. As the organo-bentonites showed a fairly sufficient thermal stability, their use in nuclear waste isolation should be taken into consideration.

AB - Distribution ratios (R(d)-values), and isotherms for sorption of iodide (125I), technetium ((95m)Tc), cesium (134Cs) and strontium (85Sr) were measured on MX-80-bentonite, which had been modified with hexadecylpyridinium (HDPy+). Synthetic ground water was used as the equilibrium solution (ionic strength: 0.037 mol 1-1). Additionally, the mineralogical characteristics, like regular and in situ powder X-ray diffraction (XRD), thermogravimetric (TG), calorimetric (DTA) measurements, IR spectral analysis of the organo-bentonite samples, and the exchange behaviour of HDPy+ (chemical analysis) were investigated. With HDPy+-modified MX-80-bentonite, iodide and pertechnetate ions exhibited increasing adsorption (R(d)), while cesium and strontium showed decreasing adsorption with increasing organophilicity. Sorption of technetium was found to be almost completely reversible with samples of relatively high (>100% of the cation exchange capacity, CEC) HDPy+ loading. Generally, sorption and desorption were linear over a wide concentration range of the elements investigated (up to ~10-1 mmol g-1 organo-bentonite) suggesting ion exchange as the principal sorption mechanism. Sorption capacities for the anions investigated were estimated to be ~5 x 10-1 mol kg-1. Concerning the cationic radionuclides, higher distribution coefficients were found for the Cs+ compared to the Sr2+ ions in the untreated and modified samples. On the basis of mineralogical and chemical analysis it was concluded that the alkylammonium ions are adsorbed as: 1, HDPy+ cations; 2, HDPyCl molecules; and 3, micelles with decreasing binding intensities in this order. The observed uptake of the organic cations in excess of the CEC leads to the formation of modified microstructures different from samples with relatively low HDPy+ saturation. As the organo-bentonites showed a fairly sufficient thermal stability, their use in nuclear waste isolation should be taken into consideration.

KW - Adsorption

KW - Anions and cations

KW - Organo-bentonite

KW - Radionuclides

KW - Reversibility

UR - http://www.scopus.com/inward/record.url?scp=0345062322&partnerID=8YFLogxK

U2 - 10.1016/S0013-7952(99)00074-5

DO - 10.1016/S0013-7952(99)00074-5

M3 - Conference article

AN - SCOPUS:0345062322

VL - 54

SP - 195

EP - 206

JO - Engineering geology

JF - Engineering geology

SN - 0013-7952

IS - 1-2

T2 - 1998 Symposium on Microstructural Modelling of Natural and Artificially Prepared Clay Soils with Special Emphasis on the Use of Clays for Waste Isolation

Y2 - 12 October 1998 through 14 October 1998

ER -