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Filimonova ON, Snigireva II, Thompson P, Wermeille D. Incorporation of palladium into pyrite: Insights from X-ray absorption spectroscopy analysis and modelling. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 920:170927. [PMID: 38369156 DOI: 10.1016/j.scitotenv.2024.170927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 02/09/2024] [Accepted: 02/10/2024] [Indexed: 02/20/2024]
Abstract
Pyrite (FeS2) often accommodates elevated concentrations of platinum-group elements in ores of magmatic and hydrothermal origin. In order to elucidate the role of pyrite in concentrating Pd, Pd-doped synthetic crystals were studied via X-ray absorption spectroscopy (XAS). Crystals were obtained by salt-flux method in the system saturated with respect to Pd at the temperature of 580 °C and sulphur fugacity of log f (S2) = -0.4. Scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry studies demonstrated a uniform distribution of Pd within the pyrite crystals. The median and average values of Pd content of ∼0.7 ± 0.1 wt% were measured. Comparison of the Pd K-edge X-ray absorption near edge structure (XANES) spectra with the spectra of standards revealed that the formal oxidation state of Pd was close to +2. Fitting of the extended X-ray absorption fine structure (EXAFS) and Finite Difference Method for Near-Edge Structure (FDMNES) theoretical simulations of XANES spectra showed that Pd substituted for Fe in the crystal structure of pyrite. The isomorphous Pd in pyrite was octahedrally coordinated by S atoms at ∼2.385 Å. The PdS interatomic distance was 5.6 % larger than that of FeS due to the difference in their covalent radii of ∼5.3 %. The expansion caused by the incorporation of Pd into the pyrite structure disappeared at the distance of R > 3 Å. The information on the state of Pd in pyrite, including the local atomic environment and formal oxidation state, is essential for scientific and industrial purposes, e.g. physical-chemical modelling and improvement of leaching and extraction processing respectively.
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Affiliation(s)
- Olga N Filimonova
- The XMaS Beamline CRG c/o European Synchrotron Radiation Facility (ESRF), 71 avenue des Martyrs, 38000 Grenoble, France; Department of Physics, University of Liverpool, Oliver Lodge Laboratory, Liverpool L69 7ZE, UK.
| | | | - Paul Thompson
- The XMaS Beamline CRG c/o European Synchrotron Radiation Facility (ESRF), 71 avenue des Martyrs, 38000 Grenoble, France; Department of Physics, University of Liverpool, Oliver Lodge Laboratory, Liverpool L69 7ZE, UK
| | - Didier Wermeille
- The XMaS Beamline CRG c/o European Synchrotron Radiation Facility (ESRF), 71 avenue des Martyrs, 38000 Grenoble, France; Department of Physics, University of Liverpool, Oliver Lodge Laboratory, Liverpool L69 7ZE, UK
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Blackburn LR, Townsend LT, Lawson SM, Mason AR, Stennett MC, Sun SK, Gardner LJ, Maddrell ER, Corkhill CL, Hyatt NC. Phase Evolution in the CaZrTi 2O 7-Dy 2Ti 2O 7 System: A Potential Host Phase for Minor Actinide Immobilization. Inorg Chem 2022; 61:5744-5756. [PMID: 35377149 PMCID: PMC9019813 DOI: 10.1021/acs.inorgchem.1c03816] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Zirconolite
is considered to be a suitable wasteform material for
the immobilization of Pu and other minor actinide species produced
through advanced nuclear separations. Here, we present a comprehensive
investigation of Dy3+ incorporation within the self-charge
balancing zirconolite Ca1–xZr1–xDy2xTi2O7 solid solution, with the view to simulate
trivalent minor actinide immobilization. Compositions in the substitution
range 0.10 ≤ x ≤ 1.00 (Δx = 0.10) were fabricated by a conventional mixed oxide
synthesis, with a two-step sintering regime at 1400 °C in air
for 48 h. Three distinct coexisting phase fields were identified,
with single-phase zirconolite-2M identified only for x = 0.10. A structural transformation from zirconolite-2M to zirconolite-4M
occurred in the range 0.20 ≤ x ≤ 0.30,
while a mixed-phase assemblage of zirconolite-4M and cubic pyrochlore
was evident at Dy concentrations 0.40 ≤ x ≤
0.50. Compositions for which x ≥ 0.60 were
consistent with single-phase pyrochlore. The formation of zirconolite-4M
and pyrochlore polytype phases, with increasing Dy content, was confirmed
by high-resolution transmission electron microscopy, coupled with
selected area electron diffraction. Analysis of the Dy L3-edge XANES region confirmed that Dy was present uniformly as Dy3+, remaining analogous to Am3+. Fitting of the
EXAFS region was consistent with Dy3+ cations distributed
across both Ca2+ and Zr4+ sites in both zirconolite-2M
and 4M, in agreement with the targeted self-compensating substitution
scheme, whereas Dy3+ was 8-fold coordinated in the pyrochlore
structure. The observed phase fields were contextualized within the
existing literature, demonstrating that phase transitions in CaZrTi2O7–REE3+Ti2O7 binary solid solutions are fundamentally controlled by the ratio
of ionic radius of REE3+ cations. Zirconolite (CaZrTi2O7) ceramics are
candidate wasteform materials for Pu and other minor actinides. Herein,
the Ca1−xZr1−xDy2xTi2O7 solid solution was fabricated by a conventional mixed oxide
synthesis, with Dy3+ included as a structural simulant
for Am3+. A phase transformation from zirconolite-2M to
zirconolite-4M was observed at low Dy concentrations (0.20 ≤ x ≤ 0.30) after which cubic pyrochlore was stabilized
as the dominant phase. Observations and interpretations were supported
by electron diffraction and X-ray absorption spectroscopic methods.
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Affiliation(s)
- Lewis R Blackburn
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Luke T Townsend
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Sebastian M Lawson
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K.,GeoRoc International (GRI) Ltd, Whitehaven, Cumbria CA28 8PF, U.K
| | - Amber R Mason
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Martin C Stennett
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Shi-Kuan Sun
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K.,School of Materials Science and Energy Engineering, Foshan University, Foshan 528000, China
| | - Laura J Gardner
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Ewan R Maddrell
- National Nuclear Laboratory, Workington, Cumbria CA20 1PJ, U.K
| | - Claire L Corkhill
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
| | - Neil C Hyatt
- Department of Materials Science and Engineering, Immobilisation Science Laboratory, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, U.K
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