Coupling X-ray absorption spectroscopy and chemical extractions to investigate phosphorus phase partitioning in Ningxiang iron deposits
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Raw data for the manuscript to be published by Geochimica et Cosmochimica Acta as “Coupling X-ray absorption spectroscopy and chemical extractions to investigate phosphorus phase partitioning in Ningxiang iron deposits”
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Summary of Analytical Methods To comprehensively characterize the samples, a multi-scale analytical approach was employed, progressing from bulk composition and mineralogy to specific elemental speciation. 1. Mineralogical and Microstructural Characterization Polarizing Microscopy & XRD: Sample morphology was observed using polarizing microscopy. Bulk mineralogy was identified by X-ray Diffraction (XRD) on a Bruker D2 Phaser diffractometer (Cu Kα radiation, 10-80° 2θ), with phase matching performed using the PDF database in MDI Jade 6.0 software. SEM-EDS: Microstructures and the distribution of key elements (P, Fe) were analyzed using a Sigma 500 Scanning Electron Microscope coupled with an Oxford Inca Energy 400 Energy Dispersive Spectrometer (EDS). 2. Bulk Elemental and Organic Carbon Analysis Sample Preparation: Samples were ground to <200 mesh. For major elements, powders were ashed and dissolved with a mixture of HF-HNO₃-HClO₄. ICP-OES: Concentrations of major elements (Ca, Al, P, Fe) were determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES; ThermoFisher iCAP 7400). TOC: Total Organic Carbon was measured on a Costech ECS 4024 analyzer after removing carbonates with 1 M HCl pretreatment. 3. Phosphorus Speciation via Sequential Extraction Extraction Protocol: Chemically distinct P pools (e.g., Pauth, Pcryst, Porg, PFe) were separated using a sequential extraction procedure. Quantification: Extracts were analyzed either by the molybdate-blue spectrophotometric method (for Pauth, Pcryst, Porg; RSD <5%) or by ICP-OES (for PFe phases due to color interference; RSD <2%). 4. Molecular-Scale Speciation Analysis ³¹P Solid-State NMR: Phosphorus speciation was investigated using ³¹P Solid-State NMR on a 400 MHz Bruker AVANCE III spectrometer with a 4.0 mm HX probe. Samples were spun at 14 kHz, and spectra were acquired using a single-pulse sequence (3 µs 90° pulse, 120 s relaxation delay). Chemical shifts were referenced to 85% H₃PO₄. Between 300 and 30,000 scans were accumulated per sample to achieve adequate signal-to-noise. P K-edge XANES: Spectra were collected in fluorescence mode at beamlines X15B (NSLS) and SXRMB (Canadian Light Source). Data from 25-40 scans were averaged, and energy was calibrated against standards (e.g., AlPO₄, fluorapatite). Fe K-edge EXAFS: Data were acquired in transmission mode at the Beijing Synchrotron Radiation Facility (BSRF), with energy calibrated using an Fe foil. S K-edge XANES: Spectra were collected in fluorescence mode at beamline 4B7A (BSRF). Data Processing for XAS: All XAS data were processed and analyzed using the ATHENA software package. Linear Combination Fitting (LCF) was performed on normalized spectra to quantify the contribution of standard compounds to the sample spectra.
Institutions
- University of Science and Technology of China
- Nanjing University
- University of Leeds
- University of Wyoming
- Chang'an University