A Comparative Study of the Dynamic Fractionation of Rare-Earth Elements in Soils Using a Rotating Coiled Column and a Microcolumn

Rare earth elements (REEs) are currently used in fertilizers, but their behavior in the soil–plant system remains poorly studied. The assessment of the binding of REEs to various organomineral phases of soils remains an important task. Using soddy-podzolic soil and typical chernozem as examples, we performed a comparative study of the dynamic fractionation of REEs in a rotating coiled column (RCC) and a microcolumn (MC). We isolated the exchangeable fraction, specifically adsorbed fraction, and fractions bound to manganese oxides, bound to organic matter, and bound to amorphous and weakly crystallized iron and aluminum oxides using, 0.05 M Ca(NO3)2, 0.43 M CH3COOH, and a 0.1 M NH2OH·HCl solution (pH 3.6), a 0.1 M K4P2O7 solution (pH 11.0), and a 0.1 M (NH4)2C2O4 solution (pH 3.2), respectively. Concentrations of elements in the initial samples and eluate fractions were determined by atomic emission spectrometry and inductively coupled plasma mass spectrometry. The results suggest that the main extractable REE form (up to 40% of the total content) is provided by organometallic complexes extracted with a 0.1 M K4P2O7 solution. For chernozem (soils with a high content of organic matter), fractionation in the RCC and MC yielded comparable results. For soddy-podzolic soil, some differences were observed in the isolation of the first three fractions: exchangeable, specifically adsorbed, and bound to manganese oxides. Both RCC and MC can be successfully used for the dynamic fractionation of REE in soils; however, it is preferable to use an MC in analyzing many samples as a simpler and more affordable device.