The hydrolytic scavenging of metal ions by marine particulate matter

A simple chemical model of hydrolytic scavenging by marine particulate matter is developed, incorporating adsorption of free metal ions and hydrolysis complexes and taking into account competitive complexation by major seawater anions. The model is applied to laboratory adsorption data and successfully predicts the trend in adsorption for a range of metals on different natural particles, but fails where adsorptive behaviour is dominated by oxide or mineral phases. Experimentally determined distribution coefficients and adsorption rate constants for strongly adsorbed metals such as Th, Pu and Sn appear to be consistent with those derived for Th from ocean data, at the same suspended particle concentration. Using Th as a model, the hydrolytic scavenging behaviour of metals (except oxyanions) in the ocean can be estimated from thermodynamic data for hydrolysis and complex formation with the major anions of seawater. An index of scavenging for over fifty metals is presented.