X-ray diffraction (XRD) is used to identify the minerals or phases that are present in a sample, based on their crystalline structural properties. Minerals are naturally occurring compounds, whereas phases are man-made.
Using XRD, the Mineralogy Division provides a service to a large variety of customers, whether it’s metallurgists in Mintek’s other divisions, or external customers in the minerals industry, from exploration, to mining and beneficiation.
X-ray powder diffraction is utilised in the Mineralogy Division, as this is sufficient for routine identification of minerals or phases in samples. Sample preparation involves pulverisation of the samples prior to analysis.
To obtain more accurate data, particularly for quantification, the sample should be ground much finer than by conventional means. For this, we use a microniser to obtain particle sizes usually less than 10 µm.
The powdered sample is carefully mounted in the appropriate holder, and then inserted into the X-ray diffractometer.
The instrument utilised is a Bruker D8 diffractometer, which takes up to 90 samples for automated analysis. The instrument is equipped with a Linxeye detector and variable divergence- and fixed receiving slits, with Ni filtered Cu-K? or Fe filtered Co-K? radiation as options. The X-rays generated in the source tube are directed onto the flat surface of the sample, and the minerals at that surface then diffract the X-ray beam at appropriate angles. Thus, the instrument scans the sample over an angular range.
The resulting output is in the form of an X-ray diffractogram, which is a plot of angle vs X-ray intensity obtained from the sample. The mineralogist will then interpret this diffractogram with the aid of DIFFRAC.EVA© software and a database for mineral or phase identification..
After analysis, the mineralogist can then report to the customer what minerals or phases are present in his sample, with an estimate of their abundance, enabling him to take appropriate steps in his process, for example.
We also conduct research into quantitative XRD, using the DIFFRACplus TOPAS© software package, along with the Inorganic Crystal Structure database. Mineral abundance in samples is quantified using the Rietveld method and a fundamental parameters approach. The data obtained are checked against bulk chemical compositions using mineral compositions where available. In this respect we are able to conduct electron microprobe analyses where appropriate.
Additionally the DIFFRACplus PolySNAP© software is available. It is designed to match and analyse powder diffraction patterns for cluster analyses. This is a very useful tool for variability studies.
The XRD method is efficient, and can be used on its own to answer a specific problem. In the Mineralogy Division this technique is very often integrated with our other services to provide a holistic solution to our customer’s needs.