Thermodynamic properties of CaTh(PO4)2 synthetic cheralite

Karin Popa; Tatiana Shvareva; Lena Mazeina; Eric Colineau; Franck Wastin; Rudy J.M. Konings; Alexandra Navrotsky

doi:10.2138/am.2008.2794

Thermodynamic properties of CaTh(PO₄)₂ synthetic cheralite

Karin Popa, Tatiana Shvareva, Lena Mazeina, Eric Colineau, Franck Wastin, Rudy J.M. Konings, Alexandra Navrotsky

Research output: Contribution to journal › Article › peer-review

24 Scopus citations

Abstract

The mineral cheralite [CaTh(PO₄)₂] allows for the incorporation of tetravalent actinides in monazite-based crystalline phases. Experimental determination of its thermodynamic properties is crucial for defining its stability and subsequent long-term ability to immobilize radionuclides. Low-temperature heat capacity from 0.5 to 300 K, enthalpy increments from 485 to 1565 K, and the enthalpy of formation of cheralite from the oxides were measured and reported on for the first time. At 298.15 K, S° = (201.6 ± 2.6) J/(K·mol), which includes the configurational entropy of Ca and Th mixing, ΔH_f^ox = -(506.4 ± 9.5) kJ/mol, ΔH_f^e1 = -(3872.8 ± 10.2) kJ/mol, ΔG_f^ox = -(501.6 ± 9.6) kJ/mol, and ΔG_f^e1 = -(3635.5 ± 10.2) kJ/mol. In aqueous environments, cheralite is able to form from whitlockite or apatite and thorianite. Under anhydrous conditions, cheralite can form by solid-state reaction only if the resultant product includes very stable Ca salts instead of CaO.

Original language	English (US)
Pages (from-to)	1356-1362
Number of pages	7
Journal	American Mineralogist
Volume	93
Issue number	8-9
DOIs	https://doi.org/10.2138/am.2008.2794
State	Published - 2008
Externally published	Yes

Keywords

Actinide phosphates
Cheralite
Nuclear waste
Thermodynamic properties

ASJC Scopus subject areas

Geophysics
Geochemistry and Petrology

Access to Document

10.2138/am.2008.2794

Cite this

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title = "Thermodynamic properties of CaTh(PO4)2 synthetic cheralite",

abstract = "The mineral cheralite [CaTh(PO4)2] allows for the incorporation of tetravalent actinides in monazite-based crystalline phases. Experimental determination of its thermodynamic properties is crucial for defining its stability and subsequent long-term ability to immobilize radionuclides. Low-temperature heat capacity from 0.5 to 300 K, enthalpy increments from 485 to 1565 K, and the enthalpy of formation of cheralite from the oxides were measured and reported on for the first time. At 298.15 K, S° = (201.6 ± 2.6) J/(K·mol), which includes the configurational entropy of Ca and Th mixing, ΔHfox = -(506.4 ± 9.5) kJ/mol, ΔHfe1 = -(3872.8 ± 10.2) kJ/mol, ΔGfox = -(501.6 ± 9.6) kJ/mol, and ΔGfe1 = -(3635.5 ± 10.2) kJ/mol. In aqueous environments, cheralite is able to form from whitlockite or apatite and thorianite. Under anhydrous conditions, cheralite can form by solid-state reaction only if the resultant product includes very stable Ca salts instead of CaO.",

keywords = "Actinide phosphates, Cheralite, Nuclear waste, Thermodynamic properties",

author = "Karin Popa and Tatiana Shvareva and Lena Mazeina and Eric Colineau and Franck Wastin and Konings, {Rudy J.M.} and Alexandra Navrotsky",

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AU - Popa, Karin

AU - Shvareva, Tatiana

AU - Mazeina, Lena

AU - Colineau, Eric

AU - Wastin, Franck

AU - Konings, Rudy J.M.

AU - Navrotsky, Alexandra

PY - 2008

Y1 - 2008

N2 - The mineral cheralite [CaTh(PO4)2] allows for the incorporation of tetravalent actinides in monazite-based crystalline phases. Experimental determination of its thermodynamic properties is crucial for defining its stability and subsequent long-term ability to immobilize radionuclides. Low-temperature heat capacity from 0.5 to 300 K, enthalpy increments from 485 to 1565 K, and the enthalpy of formation of cheralite from the oxides were measured and reported on for the first time. At 298.15 K, S° = (201.6 ± 2.6) J/(K·mol), which includes the configurational entropy of Ca and Th mixing, ΔHfox = -(506.4 ± 9.5) kJ/mol, ΔHfe1 = -(3872.8 ± 10.2) kJ/mol, ΔGfox = -(501.6 ± 9.6) kJ/mol, and ΔGfe1 = -(3635.5 ± 10.2) kJ/mol. In aqueous environments, cheralite is able to form from whitlockite or apatite and thorianite. Under anhydrous conditions, cheralite can form by solid-state reaction only if the resultant product includes very stable Ca salts instead of CaO.

AB - The mineral cheralite [CaTh(PO4)2] allows for the incorporation of tetravalent actinides in monazite-based crystalline phases. Experimental determination of its thermodynamic properties is crucial for defining its stability and subsequent long-term ability to immobilize radionuclides. Low-temperature heat capacity from 0.5 to 300 K, enthalpy increments from 485 to 1565 K, and the enthalpy of formation of cheralite from the oxides were measured and reported on for the first time. At 298.15 K, S° = (201.6 ± 2.6) J/(K·mol), which includes the configurational entropy of Ca and Th mixing, ΔHfox = -(506.4 ± 9.5) kJ/mol, ΔHfe1 = -(3872.8 ± 10.2) kJ/mol, ΔGfox = -(501.6 ± 9.6) kJ/mol, and ΔGfe1 = -(3635.5 ± 10.2) kJ/mol. In aqueous environments, cheralite is able to form from whitlockite or apatite and thorianite. Under anhydrous conditions, cheralite can form by solid-state reaction only if the resultant product includes very stable Ca salts instead of CaO.

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