Rare earth elements in vivianite from Lake Åstrum

The rare carth elements are determined in vivianite concretions and surrounding clay sediments. Approximately 3/4 of the rare earth elements in the clay is present in adsorbed state. The concentration of REE in the pore water is calculated from the composition of the vivianite, assuming a diffusion model for the formation of the concretions and lower solubility of the rare earth elements above the concretions than in the pore water at some distance from the concretions. The concentrations thus calculated are similar to published values for ocean water.