Use of Portable XRF In Coltan Exploration
Portable Analytical Solutions
Is Factory Calibration of Portable XRF In Coltan Exploration Accurate and Reliable, or is user calibration required?
A paper published by the Department of Geology at Brandon University in Canada answers this question.
The Purpose of the Paper
While FPXRF is known as a technique that can produce fast and accurate results (depending on the concentration, sample type and operational conditions) with little or no sample preparation, there were still some questions around the reliability of the factory calibration.
Field-Portable X-Ray Fluorescence (FPXRF) has many applications in the earth and environmental sciences, including Coltan (Columbite-Tantalite) exploration, mining and trading. Common elements of interest including Ta, Nb, Sn, W and Fe can be easily identified and quantified using FPXRF, which can simultaneously analyze a wide range of elements from Mg to U, with detection limits down to a few ppm for some elements.
The paper discusses the analysis of 21 dry powder specimens using a ThermoFisher Niton XL3t-950 with x-ray excitation at 50 kV, 200 µA, using Ag anode, compared to lab data of the same samples.
It explains in detail the application of this analytical technique on Coltan and associated metals (Ta, Nb, Sn, W and Fe), as well as suitability of the factory calibration on these metals and benefits of a user calibration.
As the paper states, it is proven that this technique is very beneficial to any project; however, the users need to be familiar with limits of the instrument and adjust their expectations accordingly. The comprehensive Camiro study (Hall et al., 2014) showed that in many cases, in order to use FPXRF as a quantitative tool a user calibration is required.
This research is also an example of how the accuracy of raw FPXRF data can be improved applying the user calibration. It shows that for coltan samples, the threshold for the acceptable results (based on the factory calibration) varies depending on the element of interest and the concentrations. This adjustment, or user calibration, is done using certified standards or known samples which have been analyzed by laboratory techniques.
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