Marine Science Faculty Publications

Rare Earth Element Complexation by Carbonate and Oxalate Ions

Document Type


Publication Date


Digital Object Identifier (DOI)


Rare earth carbonate and oxalate complexation constants have been determined through ex-amination of distribution equilibria between tributyl phosphate and an aqueous perchlorate phase. Carbonate complexation constants appropriate to the REE in seawater (25°C, 35%., 1 atm) can be described in terms of atomic number, Z. nlog swβ1 = 4.853 + 0.1135(Z − 57) − 0.003643(Z − 57)2log swβ2 = 80.197 + 0.1730(Z − 57) − 0.002714(Z −57)2 where swβ1=[MCO+3][M3+][CO2−3]T">swβ1=[MCO+3][M3+][CO2−3]T , swβ2=[M(CO3)−3][M3+][CO2−3]2'T">swβ2=[M(CO3)−3][M3+][CO2−3]2'T [M3+] is an uncomplexed rare earth concentration in seawater, [MCO+3] and [M(CO3)2] are carbonate complex concentrations, and [CO2−3]T is the total (free plus ion paired) carbonate ion concentration in seawater (molal scale). Our analyses indicate that in seawater with a total carbonate ion concentration of 1.39 × 10−4 moles/Kg H2O, carbonate complexes for the lightest rare earth, La, constitute 86% of the total metal, 7% is free La3+ and the remaining 7% exists as hydroxide, sulfate, chloride and fluoride complexes. For Lu, the heaviest rare earth, carbonate complexes are 98% of the total metal, 0.3% is uncomplexed and 1.5% is complexed with hydroxide, sulfate, chloride and fluoride. Oxalate and carbonate constants are linearly correlated. This correlation appears to be quite useful for estimating trivalent metal-arbonate stability constants from their respective oxalate stability constants.

Was this content written or created while at USF?


Citation / Publisher Attribution

Geochimica et Cosmochimica Acta, v. 51, issue 3, p. 597-605