Most natural ore deposits do not possess high concentrations of minerals or metals, meaning that ore grading and mineral concentration analysis are required before the final product (for example, metal) can be created from the original raw material.
Handheld X-ray fluorescence (XRF) analysis instruments allow the straightforward determination of elemental constituents in most low-concentration natural samples, but there are challenges associated with this technology’s application in concentrated ore samples.
Handheld XRF Analyzers in Mining
Handheld XRF offers rapid, accurate elemental analysis results with little or no sample preparation required. This versatile tool is applicable in numerous stages of mining activity, ranging from grass root exploration, exploitation, and ore grade control through to environmental investigations.
The Thermo ScientificTM NitonTM range of handheld XRF analyzers is extensively used throughout the international mining industry. These instruments are used to measure a wide range of elements, from magnesium (Mg) to uranium (U).
Niton XRF analyzers have enabled transformative improvements in terms of data acquisition time while continuing to deliver excellent limits of detection and accurate results over a wide range of samples.
Application
Once identified and extracted, ore minerals are typically concentrated using various techniques. These techniques leverage the ore’s physical and chemical properties, such as chemical separation techniques, including floatation and acid leaching, and mechanical separation methods, including screening.
This processing results in a homogeneous and uniform mineral concentrate with a relatively simple composition and mineralogy.
Niton XRF analyzers feature a UserMethod function (sometimes referred to as User Mode) that employs empirical calibration. This method is partfor analyzing concentrated samples of heavy metals. However, the sample’s composition must be homogeneous for this functionality to be effective.
The instruments’ Fundamental Parameter (FP) factory mode is a general-purpose mode suitable for use with a wide range of sample types. FP mode is also “standardless,” meaning it does not need known samples to acquire quantitative results.
In high-concentration processed samples, the concentration of the metal of interest may be reported as less than the true value when the regular FP mode is used. It is, therefore, advisable to employ the UserMethod in order to obtain accurate quantitative results for these samples.
This method involves analyzing samples and reporting signals as intensity (counts per second per microampere). Calibration curves are then plotted based on known concentrations (acquired via laboratory values) and intensity (acquired via HHXXRF results).
The equation derived from the trend line shown in Figure 1’s graphs is then employed to convert HHXRF readings (in unknown samples) from intensity to elemental concentrations, either in weight percents or parts per million.
Figure 1. Example of generation of calibration curve. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection
Method
This example study presented here was performed using UserMethod on a Thermo ScientificTM NitonTM XL3t GOLDD analyzer to investigate molybdenite (MoS2) concentrate samples.
The ore grade in concentrates like this can range from 25 % to 65 % Mo. Figure 2 displays the concentrations of molybdenum (Mo), iron (Fe), and copper (Cu) in these concentrates, as well as their correlation with lab assay data.
Results
The coefficient of determination, or R2 value, represents how closely data sets correlate with one another. A perfect correlation would possess an R2 value of 1.
Correlations for Mo, Cu, and Fe were determined to be 0.97, 0.99, and 0.97, respectively (Figure 2). The value of the slope beside X in the trendline equation would indicate systematic errors if this was found to be significantly different from 1. These errors are also referred to as ‘biases.’
All three elements show values between 0.95 and 1.05, confirming that the measurements are accurate and biases are low.
Figure 2. Correlation of Mo, Cu and Fe data between portable XRF and lab in molybdenite (MoS₂) concentrate samples. Image Credit: Thermo Fisher Scientific – Handheld Elemental & Radiation Detection
Conclusions
HHXRF represents an effective and reliable tool suitable for analyzing any type of mining or metal ore sample, whether encountered in the exploration stage (low grade) or the ore grading stage (high grade).
The UserMethod offers a useful alternative to the standardless fundamental parameter calibration approach when working with concentrated mineral samples of heavy metals. This approach can offer more accurate results in some cases, such as when investigating molybdenum or lead concentrates.
Results are displayed directly on the analyzer after a UserMethod has been uploaded, affording users on the production line the instant insight required to maintain the correct grade control.
Acknowledgments
Produced from materials originally authored by Thermo Scientific. Freeport–McMoRan Copper & Gold, Inc. provided the analyzed samples in this study.
This information has been sourced, reviewed, and adapted from materials provided by Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.
For more information on this source, please visit Thermo Fisher Scientific – Handheld Elemental & Radiation Detection.