Abstract
Rare earths and yttrium (REY) distribution patterns of the hydrosphere reveal systematic correlations of Gd and Y anomalies besides the non-correlated redox-dependent Ce and Eu anomalies. Eu anomalies are inherited by dissolution of feldspars in igneous rocks, whereas Ce, Gd and Y anomalies develop in aqueous systems in contact with minerals and amorphous matter. Natural, positive Gd and Y anomalies in REY patterns characterize high-salinity fluids from the Dead Sea, Israel/Jordan, the Great Salt Lake, USA, the Aral Sea, Kazakhstan/Uzbekistan, ground- and surface water worldwide. Extreme Gd anomalies mostly originate from anthropogenic sources. The correlation of Gd and Y anomalies at low temperature in water bodies differ from geothermal ones. In nature, dynamic systems prevail in which either solids settle in water columns or water moves through permeable sediments or sedimentary rocks. In both cases, the anomalies in water develop due to repeated equilibration with solid matter. Thus, these anomalies provide information about the hydrological history of seawater, fresh groundwater and continental brines. When migrating, the interaction of aqueous phases with mineral surfaces leads to increasing anomalies because the more hydrophillic Gd and Y preferentially remain in the aqueous phase compared to their nearest neighbors. The correlation coefficients between Gd and Y anomalies in groundwater is 0.5–0.9. In lakes and oceans, it is about 0.1–0.8, under anomalous conditions it can increase to 1.
Highlights
The fourteen stable rare earth elements, REE, are unique because of the coherence of their chemical properties
The anoxic deep Mediterranean brine at 3400 m from the Tyro Basin, which is not involved in yearly overturning of the local water column, shows the highest Rare earths and yttrium (REY) abundance with positive Ce anomaly (Figure 4c)
Weathering of igneous rocks leads to isomorphous replacement of Ca2+ by REY3+ during precipitation of mainly carbonates or scavenging by Fe-Mn oxihydroxides
Summary
The fourteen stable rare earth elements, REE, are unique because of the coherence of their chemical properties. Y is not a member of the REE suite, it behaves to Ho in minerals crystallizing from siliceous melts due to the same ionic charge and nearly identical crystallographic ionic radii [1,2]. The fractionation of Gd(III) and Y(III) in phase separation processes such as either liquid–liquid extraction [3] or incorporation in mainly Ca minerals is caused by non-linear variation of physical parameters such as partial molal volumes [4] and formation constants of dissolved species. Chemical complexations of REY with chloride [14], fluoride [15,16] and sulfate [17] do not show deviations of formation constants of Gd and Y with respect to their nearest neighbors. MCO3+ and M(CO3)2− are the most abundant species in seawater (Figure 1b)
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