TY - JOUR
T1 - Thermodynamic properties of CaTh(PO4)2 synthetic cheralite
AU - Popa, Karin
AU - Shvareva, Tatiana
AU - Mazeina, Lena
AU - Colineau, Eric
AU - Wastin, Franck
AU - Konings, Rudy J.M.
AU - Navrotsky, Alexandra
N1 - Copyright:
Copyright 2019 Elsevier B.V., All rights reserved.
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, ΔHf ox = -(506.4 ± 9.5) kJ/mol, ΔHf e1 = -(3872.8 ± 10.2) kJ/mol, ΔGf ox = -(501.6 ± 9.6) kJ/mol, and ΔGf 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.
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, ΔHf ox = -(506.4 ± 9.5) kJ/mol, ΔHf e1 = -(3872.8 ± 10.2) kJ/mol, ΔGf ox = -(501.6 ± 9.6) kJ/mol, and ΔGf 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.
KW - Actinide phosphates
KW - Cheralite
KW - Nuclear waste
KW - Thermodynamic properties
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U2 - 10.2138/am.2008.2794
DO - 10.2138/am.2008.2794
M3 - Article
AN - SCOPUS:50849092900
VL - 93
SP - 1356
EP - 1362
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 8-9
ER -