Formation of CeSiO₄ from cerium(iii) silicate precursors

Abstract

Pure CeSiO4 (zircon type) was prepared by hydrothermal conversion of Ce(iii) silicate based solid precursors A-Ce2Si2O7 or Ce4.67(SiO4)3O.

High-Temperature Thermodynamics of Cerium Silicates, A-Ce2Si2O7, and Ce4.67(SiO4)3O

“…Particularly, hematite was found to be associated with the mineral deposit where stetindite was discovered,36 creating a localized oxidizing environment, allowing for Ce 4+ to form through the oxidation of Ce 3+ -fluoride complex or other Ce 3+ silicates such as percleveite 36,98. This does bare a similarity to the procedure described by Estevenon et al for the hydrothermal synthesis of CeSiO 4 from both aqueous and solid precursors 37,99. Furthermore, the enthalpy of reaction of A-Ce 2 Si 2 O 7 Ce 3+ silicates could serve as potential solid precursors if the local redox of the deposit conditions became oxidizing, such as what was observed at the deposit where stetindite was discovered 36,98.…”

“…Mineral redox buffer assemblages are often used in the geochemical system to fix the oxygen fugacity (ƒ O₂ ). 97 14,16,21,27,37 While the above offers both a formational mechanism for CeSiO 4 in nature and its overall rarity, it does not offer a direct explanation to why A-Ce 2 Si 2 O 7 is so rare in nature. As the mineral assemblages to form a reducing environment are possible to occur across the entire spectrum of the igneous classification, from mafic to felsic, 44,97 and as Ce concentrations are also relatively conserved across the igneous classification, 100,101 one would expect percleveite to be observed at more than just one mineral deposit.…”

“…A more detailed description of the synthesis procedure and characterization techniques is described in the previously published work. 37…”

“…15,21 Furthermore, in the pursuit of pure cerium orthosilicate (CeSiO 4 ; space group I4 1 /amd), a rare mineral, 36 which is isostructural to coffinite (USiO 4 ), thorite (ThSiO 4 ), and PuSiO 4 , both A-Ce 2 Si 2 O 7 and Ce 4.67 (SiO 4 ) 3 O were used as solid precursors during hydrothermal synthesis. 37 Such observations imply that the three Ce silicate phases could be close in energetics. A recent work published by Estevenon et al 38 in 2020 also showed that impure PuSiO 4 was synthesized hydrothermally from a plutonium disilicate (Pu 2 Si 2 O 7 ) precursor, again suggesting the equilibrium between these silicate phases.…”

The formation of PuSiO4under hydrothermal conditions

“…2 However, even if these two mechanisms could be complementary, the apparent absence of Ce(III) silicate dissolution was also observed in alkaline conditions (pH > 8) which would promote the solubility of silica. 77 Therefore, it might be supposed that the same behavior occurred for the Pu(III) silicate analogs. (Figure 2).…”