Optimization of X-ray Fluorescence Calibration through the Introduction of Synthetic Standards for the Determination of Mineral Sands Oxides

An XRF spectrometer traditionally requires its methods to be calibrated using certified reference materials (CRMs). This means choosing from a limited selection of CRMs, which are costly and not widely available. This article examines the application of synthetic oxide standards made from commercially available high purity compounds for the calibration of an XRF spectrometer. Enabling it to analyze for major, minor and trace elements (Mg, Al, Si, P, Hf, Ca, Ti, Zr, Fe, Th, U) in heavy mineral sands processing. Calibration standards were synthesized by mixing pure compounds and mineral sands reference materials, to mimic matrices similar to that of the routine samples and cover the required analytical range. The aliquots were mixed in % fractions and fused with a 1:9 sample/borate dilution to make glass beads. The optimized calibration was validated as per SANAS TR 26-02 criteria for linearity, working range, limit of detection (LOD) and quantification (LOQ), precision and accuracy. The correlation coefficients (r) of the resulting calibration curves were >0.999, showing excellent linearity. The working range for all the calibration lines was satisfactory. The LOD and LOQ values for all the lines were low enough to prevent extrapolation below the lowest calibration point. The precision of the calibration was sufficiently high, and the accuracy was of adequate quality with z(MAD) <2. These observations support the successful synthesis and use of a well-selected set of synthetic standards. Additionally, it has been successfully utilized to analyze a variety of heavy mineral sands samples.