TY - JOUR
T1 - Modelling the diffusive transport and remobilisation of 137Cs in sediments
T2 - the effects of sorption kinetics and reversibility
AU - Smith, J. T.
AU - Comans, R. N. J.
N1 - Funding Information:
Acknowledgments-J.T.S. would like to thank Dr. P. G. Appleby (University of Liverpool) and Dr. J. Hilton (Institute of Freshwater Ecology), his Ph. D. supervisors during much of this work, and acknowledge the financial support of a UK Natural Environmental Research Council CASE award. R.N.J.C. acknowledges partial funding by The European Commission Nuclear Fission Safety Programme, contract no. FI3P-CT92-0029. We would both like to thank Mrs. P. A. Geelhoed-Bonouvrie for assistance with the laboratory analyses. Helpful comments were received from L. K. Benninger, B. P. Boudreau, J. A. Robbins, X. Wang, and one anonymous referee.
PY - 1996/3/1
Y1 - 1996/3/1
N2 - In determining the mobility of ions in sediments it is important to take account of the solid phase sorption and speciation. Measurements were made of activity depth profiles of 137Cs from fallout from Nuclear Weapons Testing and from the Chernobyl accident in two lake sediments. The fraction of 137Cs in the aqueous, exchangeably sorbed and "fixed" phases was determined at each depth interval. A model was developed to simulate the transport of 137Cs in these sediments, taking account of changes in sorption properties as the concentration of the competing ammonium ion changes with depth, as well as transfers of activity to less-exchangeable sites on the solids. The model simulations give reasonable agreement with experimental data, and the fitted rate constant for slow transfers to less-exchangeable sites (T1/2 = 50-125 d) is in agreement with independent measurements. The modelling gave evidence for a reverse reaction from less-exchangeable to exchangeable sites with a half-life of order 10 y. Model results were compared with those generated by a physical mixing model and the standard molecular diffusion model assuming equilibrium sorption to the solid phase. Estimates were made of the remobilisation of Chernobyl 137Cs from these sediments to the water column: predicted rates vary from around 3% of the inventory per year 2 years after the fallout event to 0.04% per year 30 years after the fallout.
AB - In determining the mobility of ions in sediments it is important to take account of the solid phase sorption and speciation. Measurements were made of activity depth profiles of 137Cs from fallout from Nuclear Weapons Testing and from the Chernobyl accident in two lake sediments. The fraction of 137Cs in the aqueous, exchangeably sorbed and "fixed" phases was determined at each depth interval. A model was developed to simulate the transport of 137Cs in these sediments, taking account of changes in sorption properties as the concentration of the competing ammonium ion changes with depth, as well as transfers of activity to less-exchangeable sites on the solids. The model simulations give reasonable agreement with experimental data, and the fitted rate constant for slow transfers to less-exchangeable sites (T1/2 = 50-125 d) is in agreement with independent measurements. The modelling gave evidence for a reverse reaction from less-exchangeable to exchangeable sites with a half-life of order 10 y. Model results were compared with those generated by a physical mixing model and the standard molecular diffusion model assuming equilibrium sorption to the solid phase. Estimates were made of the remobilisation of Chernobyl 137Cs from these sediments to the water column: predicted rates vary from around 3% of the inventory per year 2 years after the fallout event to 0.04% per year 30 years after the fallout.
UR - http://www.scopus.com/inward/record.url?scp=0029753658&partnerID=8YFLogxK
U2 - 10.1016/0016-7037(96)00030-0
DO - 10.1016/0016-7037(96)00030-0
M3 - Article
AN - SCOPUS:0029753658
SN - 0016-7037
VL - 60
SP - 995
EP - 1004
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 6
ER -