Rare Earth Element Uptake by the Marine Diatom

Rare earth distribution coefficients, D T = (moles cm ^-3 , cells)/(moles cm ^-3 , solution), obtained using seawater ( S = 36.4, t = 25°C, pH ∼ 8.2, p CO ₂ ∼ 345 μatm) and the marine diatom, Skeletonema costatum, exhibited a strong tendency toward the order Ce > Gd > Yb. Observations of rapid initial uptake, with subsequent gradual uptake over time, are suggestive of initial adsorption onto cell surfaces followed by slow transport to interior cell sites. The average volume concentration factors ( D T) obtained in our study are: D TCe = (3.33 ± 0.9) × 10 ⁵ ; D TGd = (2.41 ± 0.7) × 10 ⁵ ; D TYb = (1.64 ± 0.3) × 10 ⁵ . Distribution coefficient results, expressed as a competition between solution and solid-state complexation terms, indicate that rare earth element complexation, both in solution and on surfaces, strongly increases with atomic number. Relatively small differences in rare earth element distribution coefficients ( D T) with atomic number are the result of small differences between large solution and solid-state complexation terms.