Structural characterization of amorphous hydrous Zr(IV) oxide and the transformation occurring under hydrothermal conditions

IF 3.1 3区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Applied Geochemistry Pub Date : 2025-02-16 DOI:10.1016/j.apgeochem.2025.106302

Christian Kiefer , Xavier Gaona , Tomo Suzuki-Muresan , Dieter Schild , Krassimir Garbev , Taishi Kobayashi , Kathy Dardenne , Oliver Dieste Blanco , Marcus Altmaier , Bernd Grambow , Horst Geckeis

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引用次数: 0

Abstract

The impact of temperature on the transformation of ZrO₂(am, hyd) in aqueous systems was systematically investigated using a multi-method approach for solid phase characterization. Ageing at T = 80 °C in NaOH and alkaline CaCl₂–Ca(OH)₂ solutions triggered the conversion of ZrO₂(am, hyd) to more crystalline, thermodynamically stable anhydrous oxides. Compared to the fresh amorphous solid and solids aged at T = 22 °C, an increase in crystallinity and particle size accompanied by a significant decrease in the amount of hydration water or hydroxide was observed. After equilibration for 4 or 10 months at T = 80 °C, XRD measurements confirmed the predominance of monoclinic ZrO₂ with a particle size of 23–27 nm in NaOH systems, whereas tetragonal/cubic ZrO₂ with a particle size of 11–14 nm formed in CaCl₂–Ca(OH)₂ solutions. All solids aged at T = 22 °C remained X-ray amorphous within the timeframe of this study. Rietveld refinement of the XRD patterns, EDX and EXAFS supported that the stabilization of a different crystal structure in CaCl₂–Ca(OH)₂ systems is caused by the incorporation of Ca²⁺ in the ZrO₂ structure. The weight loss observed with TG-DTA was attributed to a decreasing amount of hydration water during the ageing at T = 80 °C. Assuming a stoichiometry of ZrO₂·nH₂O, the fresh solid showed a weight loss corresponding to n = 2.1, which remained constant during the ageing at T = 22 °C. The solids aged at T = 80 °C showed a smaller weight loss corresponding to n = 0.2–0.6. This behavior was qualitatively confirmed by IR-ATR. XPS analysis of the O1s line also showed a decrease of H₂O/OH⁻ contributions and an increase of O²⁻ contributions in the solid phases aged at T = 80 °C.

This study provides new insights for the understanding of the transformation of M(IV) amorphous, hydrous oxides into the thermodynamically stable anhydrous crystalline oxide phases. The process involves particle growth, increased ordering and loss of H₂O/OH⁻ groups. In aqueous systems, the presence of other metal ions like Ca²⁺ may promote the stabilization of different crystal structures, even if they are found at low concentrations.

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来源期刊

Applied Geochemistry 地学-地球化学与地球物理

CiteScore

6.10

自引率

8.80%

发文量

272

审稿时长

65 days

期刊介绍： Applied Geochemistry is an international journal devoted to publication of original research papers, rapid research communications and selected review papers in geochemistry and urban geochemistry which have some practical application to an aspect of human endeavour, such as the preservation of the environment, health, waste disposal and the search for resources. Papers on applications of inorganic, organic and isotope geochemistry and geochemical processes are therefore welcome provided they meet the main criterion. Spatial and temporal monitoring case studies are only of interest to our international readership if they present new ideas of broad application. Topics covered include: (1) Environmental geochemistry (including natural and anthropogenic aspects, and protection and remediation strategies); (2) Hydrogeochemistry (surface and groundwater); (3) Medical (urban) geochemistry; (4) The search for energy resources (in particular unconventional oil and gas or emerging metal resources); (5) Energy exploitation (in particular geothermal energy and CCS); (6) Upgrading of energy and mineral resources where there is a direct geochemical application; and (7) Waste disposal, including nuclear waste disposal.