Partition of Elements Between Solid and Liquid Phases in Aquatic Environments

Abstract The average composition of natural waters such as rivers, lakes, ocean, and hydrothermal vents and corresponding solids in equilibrium (e.g., river-suspended particles or shale; lake sediments; oceanic pelagic clay, organisms, and manganese nodules; and the mid-ocean ridge basalts) do not change randomly. The observed positive correlation between the electron binding energy (Iz [*Iz]) and logarithms of bulk distribution coefficient (log Kd) for cations with charge of 1–4, and the negative correlation between Iz [*Iz] and log Kd for anions in various aquatic systems are consistent with the prediction from the surface complexation model. In other words, the bond strength between the adsorbed cation and the surface oxygen of hydrated metal oxides, and between the oxygen of adsorbed oxyanion and the surface metal of hydrated metal oxides control the partition of elements between solid and associated liquid in natural aquatic systems. For Mn, Co, Ce, Pb, and Tl, the oxidative uptake at the solid–water interface in the ocean is an additional important process. For alkali and alkaline-earth cations with large ionic radius (such as Cs, Rb, K, and Ba), their relatively small secondary solvation energy further enhances their adsorption onto solid particles. For living and non-living organic matter, the adsorbed B-type cations form extra strong bindings with hydrophilic functional groups such as –SH and –NH2 on organic matter surface.