How to analyse elemental distribution in rocks with XRF. In this case study, we examine columbite-tantalite (coltan) in rocks from Canada using the Bruker S8 TIGER Series 2 WDXRF spectrometer.
Columbite-Tantalite (Coltan)
Columbite-tantalite, also known as Coltan, is a key material in the semiconductor industry. Tantalum capacitors are used in virtually all electronic products. However, coltan mining is a volatile market, so there’s a constant search for new sources. These need to be evaluated for quality, and XRF is an ideal technique for characterising element distribution in geological samples to refine and enhance mineral beneficiation.
Bruker S8 TIGER
The S8 TIGER Series 2 is a high-power wavelength dispersive X-ray fluorescence spectrometer (WD-XRF). It detects all elements from Be to Am, with up to 100% coverage of the trace region.
- Excitation of elements with a voltage from 20 kV (light elements) to 60 kV (heavier elements).
- Adjust the current instantly from 5 – 170 mA:
- Detect trace elements
- Maintain a count rate in the linear range of the detector for major elements.
- Up to 4 collimators and up to 8 analyser crystals – optimise for resolution and/or intensity for analysing fluorescence lines.
- Detect the intensity of element lines with Bruker’s new HighSense detector technology:
- Flow counter for light elements
- Scintillation counter for heavy elements
XRF2 Small Spot Mapping
With XRF2 small spot mapping, you can analyse element distribution and very small sample amounts, even down to a single particle. This provides detailed maps of elemental distribution in materials, with the highest resolution available in WDXRF (300µm spot size).
Major, minor and trace elements can be mapped with extremely high sensitivity. The surface is scanned with a step size of 100 µm. WDXRF delivers much higher intensities than EDXRF for both light and heavy elements, with high spectral resolution. This is key for detecting rare elements (which can be measured even in the trace region) and for avoiding line overlays from major elements.
Setting Scanning Parameters
The S8 TIGER automatically captures an image of the sample when it’s loaded, as shown in the example below. Using this image you can visually select spots, lines, areas or the entire sample surface. Next, set the spot size, step size and measurement parameters, and the sample is scanned for you.
Element Maps
These examples, from a Bruker application note, are scans of Coltan taken to examine the elemental distribution of valuable elements of interest to geologists and metallurgists. This demonstrates the S8 TIGER’s sensitivity, which is significantly higher than that of other WDXRF instruments while still providing high resolution.
Two boxes were selected on the surface for element mapping. Clear, brownish and purple grains are visible on the rock. The brown areas have a high concentration of calcium from the host rock carbonatite.
The purple granules indicate typical base-metal elements at high concentration; they are linked to each other. The two main rock phases in Coltan are (Fe, M n)Nb2O6 and (Fe, Mn)Ta2O6. In both phases, iron and manganese are linked – the only difference is the third metal, Nb or Ta. There is also a spotty distribution of lanthanum in the rock at a trace level. Very small local spots of lanthanum were found, mainly on the host rock.
The very high 300 µm resolution and 100 µm step size enable you to analyse fine-grained rock. Even small differences in element concentration are visible, with the sensitive HighSense beam path. Specific rock types can be identified, including traces of lanthanum.
Mn and Fe can be used as tracers for fast rock screening, highlighting valuable minerals for geological classification and valuation. The S8 TIGER can be used in the production lab for process control, as well as for process optimisation and classification tasks.
Further Information
For more information about the S8 TIGER or our other geology and geoscience instruments, please get in touch. Blue Scientific is the official distributor for Bruker XRF in the Nordic region – we’re available to provide quotes and to answer all your questions.
Contact us on +44 (0)1223 422 269 or info@blue-scientific.com
