Partitioning of Rare Earth Elements between Dissolved and Colloidal Phases

To utilize rare earth elements (REEs) as tracers in the weathering environment, an understanding of how these elements partition between aqueous and solid phases is essential. This study evaluates the partitioning between REEs and colloidal material over a range in pH (3.6-8.0) and solid and aqueous compositions. This paper presents results of filtration studies for REEs in 4 different conditions. Sample aliquots include an unfiltered fraction, a 0.45 μ m filtrate, and an ultrafiltrate (∼<0.005 μ m). Results show that the REEs behave conservatively in waters with pH below ∼5.0. REEs tend to partition onto solid phases in circumneutral waters that have colloidal material, but the nature of the fractionation can vary from light REE enriched, heavy REE enriched, or no fractionation.