Geochemical fractionation of lanthanides in soils and rocks: A review of publications

In recent years, lanthanides (Ln) have become an object of active studies by soil scientists and geologists, which is favored by the development of instrumental equipment. It has become possible to obtain reliable soil clarkes of lanthanides. The study of lanthanides in soils is important not only from the theoretical and pedogenetic viewpoints but also because of its applied value, as Ln-containing substances and wastes are used as microfertilizers. The established fact of the geochemical fractionation of lanthanides in soils and rocks appears to be one of the latest significant achievements. The tetrad-effect in lanthanides was revealed and theoretically substantiated. Strong positive anomalies of the Ce content and weak anomalies of the Eu content were found in soils (unlike many rocks). Ferromanganese soil concretions are depleted in Y as compared with light-weight lanthanides. The type of lanthanide fractionation in the course of soil formation in different zones depends on the content of Ln-minerals in the parent rock. In the zone of supergenesis, Mn oxides are among the most important Ln-bearing phases, many of which (Ce, in particular) are classified as manganophilic. In calcite, Ca 2+ may be replaced by lanthanides, including Y. Humus acids stabilize Ce 3+ and prevent positive cerium anomalies in the newly formed bodies. Microorganisms favor Ln accumulation in biogenic bodies, such as Fe-Mn nodules and Fe-ocher.