The Kinetics of Reversible Th Reactions with Marine Particles

Abstract Experiments on the reversibility of Th adsorption on natural marine particles utilized the short-lived isotope 234 Th as a tracer. The adsorption of Th from seawater onto mineral particles is a reversible process. The extent to which Th can desorb from the particles decreases as the particles age. The kinetics of adsorption-desorption reactions have been modelled as a three-stage equilibrium; values of the six rate constants have been evaluated. Attempts to determine a single rate constant for the adsorption of Th from seawater from a single parent-daughter disequilibrium, or to determine a forward and a back rate constant using two such disequilibria will yield rate constants that depend on the time for which the marine particles have been reacting with Th in seawater.