Coprecipitation of 14C and Sr with carbonate precipitates: The importance of reaction kinetics and recrystallization pathways

This study investigated the simultaneous removal of Sr2+ and (CO32-)-C-14 from pH > 12 Ca(OH)(2) solution by the precipitation of calcium carbonate. Initial Ca2+:CO32- ratios ranged from 10:1 to 10:100 (mM:mM). Maximum removal of C-14 and Sr2+ both occurred in the system containing 10 mM Ca2+ and 1 mM CO32- (99.7% and 98.6% removal respectively). A kinetic model is provided that describes C-14 and Sr removal in terms of mineral dissolution and precipitation reactions. The removal of C-14 was achieved during the depletion of the initial TIC in solution, and was subsequently significantly affected by recrystallization of the calcite precipitate from an elongate to isotropic morphology. This liberated >46% of the C-14 back to solution. Sr2+ removal occurred as Ca2+ became depleted in solution and was not significantly affected by the recrystallization process. The proposed reaction could form the basis for low cost remediation scheme for Sr-90 and C-14 in radioactively contaminated waters (<$0.25 reagent cost per m(3) treated). (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).