Rare Earth Elements in Iron Oxyhydroxides from Biofilms Containing the Fe-Oxidizing Bacteria

Iron oxyhydroxides extracted from present-day biofilms with the Fe-oxidizing bacteria Arthrobacter spp., Gallionella spp., and Leptothrix ochracea in the northwest of the East European Platform display a significant content of rare earth elements (up to 1100 ppm). The REE concentration in oxyhydroxides produced by active bacterial communities increases by one order of magnitude during 1 yr, suggesting a high sorption capacity of the newly formed iron mineral phases. Values of (La/Yb)_N, Ce, and Y anomalies in the iron oxyhydroxides are consistent with the REE distribution in surface waters accommodating the bacterial communities. The Nd isotope composition of the studied bacterial iron oxyhydroxides inherits the isotopic composition in the ambient water; ¹⁴³Nd/¹⁴⁴Nd values in the bacterial iron minerals vary from 0.511570 to 0.512220; and ε_Nd(0) from –21.8 to –9.2. The maximum proportion of radiogenic Nd is typical for the samples taken from areas marked by the presence of Paleozoic carbonate rocks in Quaternary glaciolacustrine sediments.