Results for “Powder Diffraction” — Page 4

USGS2020

Evaluating the utility of principal component analysis on EDS x-ray maps to determine bulk mineralogy

Due to advances in EDS technology, electron microscopy techniques have become an important tool to determine the relative abundance of mineral phases. However, few studies have directly compared EDS X‐ray mineralogy with traditional techniques for assessing bulk mineralogy and elemental composition. We show that analysing a limited area (~ 0.5–3.2 mm 2 ) of fine‐grained metal extraction samples using EDS X‐ray principal component analysis phase mapping yields results that agree within 10% with more traditional techniques for mineral phases present at greater than 5% m / m . Electron beam sensitive minerals, such as the carbonates, have poor correlations between EDS and X‐ray Diffraction (XRD) and/or WD‐XRF. Likewise, poor correlations between methods can be expected for particles that are smaller than the interaction volume of the electron beam (~ 1.5 µm); this strongly affected the phyllosilicates. One strength of EDS phase mapping is that it can identify phases present below the detection limit of powder XRD (< 1%). Our results demonstrate that EDS phase mapping is sufficient to estimate bulk sample mineralogy. If polished thin sections have been prepared, this approach may save time and/or money relative to the more traditional approaches of preparing separate subsamples for XRD and/or WD‐XRF.

Geostandards and Geoanalytical Research↗

USGS2001

Chemical analysis and modes of occurrence of selected trace elements in a Powder River basin coal and its corresponding simulated cleaned coal

This report provides semi-quantitative data on modes of occurrence of 19 elements in as-mined Powder River Basin coal and its corresponding simulated cleaned coal. The data are in support of the project "Prediction of Trace Element Removal from Coal" --a Cooperative Research and Development Agreement (CRADA) with CQ Inc. The purpose of this CRADA is to apply modes of occurrence information to coal cleaning procedures. Techniques used in this study include sequential selective leaching procedures, scanning electron microscopy, X-ray diffraction analysis, and electron microprobe analysis. Selective leaching results indicate that greater than 40 percent of the elements Co, U, Be, Ca, Fe, Mn, Ba, Zn, Cd, Pb are associated with HCIsoluble carbonates, iron oxides, or monosulfides, greater than 40 percent of the Al, Cr and Mo are associated with HF-soluble silicates, greater than 40 percent of the Ni, Cu, As and Sb are associated with acid-insoluble phases and/or organic matter, and greater than 50 percent of the Hg is associated with HMDs-soluble pyrite. Thirty percent of the Th was leached by HCI and 30 percent of this element was leached by HF. Scanning electron microscopy indicates that quartz, kaolinite, illite and iron oxide, possibly hematite, are the major minerals present. X-ray diffraction analysis confirmed that quartz, kaolinite and hematite are present, but did not determine illite, indicating that illite in these coals is of low abundance or is poorly crystalline. Electron microprobe data indicate that concentrations of the chalcophile elements As, Se, Cu, Ni, Zn, and Cd in most pyrite grains are at or below the detection limit of about 100-200 ppm in both the as-mined coal and its corresponding simulated cleaned coal product. The results of this project should aid in the development of models for predicting the response of potentially toxic trace elements in commercial coal cleaning procedures.

Open-File Report↗