TY - JOUR

T1 - Equilibrium ree fractionation between minerals and waters in the north Kazakhstan Salt Lakes

AU - Gaskova, Olga

AU - Shironosova, Galina

PY - 2017/1/1

Y1 - 2017/1/1

N2 - REE determinations were conducted for two mineralized lakes of the Ishim steppe, situated between the Irtysh and Tobol rivers in the southern part of Western Siberia, by means of atomic absorption spectrometry (AAS). They are of Cl-Na-type but differ in salinity and pH. It was shown that REE distribution patterns for the Zhamantuz and Kishikaroy lake waters were identical. Nevertheless, coherent fractionation from LREE to HREE is disrupted after the equilibrium calculations. Thermodynamic modeling was performed with the “HCh” computer code and the UNITHERM database using a Gibbs free energy minimization algorithm at 25°C and 1 bar total pressure. The 255 dissolved species and solid-phase thermodynamic data were incorporated into the UNITHERM database from the literature elsewhere. In addition to the 53 solid-phases of constant composition, the formation of ideal solid solutions (ss) is expected: of monazite (La,Ce,Pr,Nd,Sm,Eu,Gd)PO4xenotime (Y,Dy,Er,Yb)PO4REE-fluorite, REE-F-apatite and REE-calcite. Activity coefficients were calculated with the third approximation of the Debye-Hückel equation. Both lake waters are supersaturated with respect to Goethite, K-Montmorilonite and REE-F-apatite. Microcline or AlOOH are presented in Zhamantuz and Kishikaroy lakes respectively. In addition, REE-bearing solid solution precipitated in Zhamantuz lake is REE-calcite (pH 8.5), but in Kishikaroy lake it is REE-fluorite. Important cause of the REE fractionation is differential solubility of REE-bearing Ca-minerals: apatite << fluorite < calcite. Different minerals tend to concentrate the light and heavy REE. According to model calculations, F-apatite contains more light REE, fluorite contains more heavy REE, calcite contain pronounced concentration of Y2(CO3)3Fractionation may occur due to the variable stability of REE complexes in chloride lake waters. Our model presents recognition that rare earth fractionation could occur with time (when equilibrium will be reached) in different ways due to the various chemical composition of salt waters in spite of their coherent distribution in sampled solutions.

AB - REE determinations were conducted for two mineralized lakes of the Ishim steppe, situated between the Irtysh and Tobol rivers in the southern part of Western Siberia, by means of atomic absorption spectrometry (AAS). They are of Cl-Na-type but differ in salinity and pH. It was shown that REE distribution patterns for the Zhamantuz and Kishikaroy lake waters were identical. Nevertheless, coherent fractionation from LREE to HREE is disrupted after the equilibrium calculations. Thermodynamic modeling was performed with the “HCh” computer code and the UNITHERM database using a Gibbs free energy minimization algorithm at 25°C and 1 bar total pressure. The 255 dissolved species and solid-phase thermodynamic data were incorporated into the UNITHERM database from the literature elsewhere. In addition to the 53 solid-phases of constant composition, the formation of ideal solid solutions (ss) is expected: of monazite (La,Ce,Pr,Nd,Sm,Eu,Gd)PO4xenotime (Y,Dy,Er,Yb)PO4REE-fluorite, REE-F-apatite and REE-calcite. Activity coefficients were calculated with the third approximation of the Debye-Hückel equation. Both lake waters are supersaturated with respect to Goethite, K-Montmorilonite and REE-F-apatite. Microcline or AlOOH are presented in Zhamantuz and Kishikaroy lakes respectively. In addition, REE-bearing solid solution precipitated in Zhamantuz lake is REE-calcite (pH 8.5), but in Kishikaroy lake it is REE-fluorite. Important cause of the REE fractionation is differential solubility of REE-bearing Ca-minerals: apatite << fluorite < calcite. Different minerals tend to concentrate the light and heavy REE. According to model calculations, F-apatite contains more light REE, fluorite contains more heavy REE, calcite contain pronounced concentration of Y2(CO3)3Fractionation may occur due to the variable stability of REE complexes in chloride lake waters. Our model presents recognition that rare earth fractionation could occur with time (when equilibrium will be reached) in different ways due to the various chemical composition of salt waters in spite of their coherent distribution in sampled solutions.

KW - REE fractionation

KW - Salt lakes

KW - Thermodynamic calculations

UR - http://www.scopus.com/inward/record.url?scp=85032333507&partnerID=8YFLogxK

U2 - 10.5593/sgem2017/31/S15.108

DO - 10.5593/sgem2017/31/S15.108

M3 - Conference article

AN - SCOPUS:85032333507

VL - 17

SP - 855

EP - 862

JO - International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM

JF - International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM

SN - 1314-2704

IS - 31

ER -