The CSIRO Mineral Resources X-ray Technologies Group is leading the development of industrial X-ray analysis instruments capable of real-time elemental and mineralogical measurement. This study examines the challenges of measuring light elements: silicon, aluminium and sulphur, when performing X-ray Fluorescence (XRF) analysis on mineral slurries, and the engineering and analytical approaches developed to overcome them.
Light-element measurement is valuable because these elements frequently define ore grade, gangue content and processing performance, yet they are the most difficult elements to measure by XRF. Their characteristic K-line fluorescence is low in energy [Al: 1.5, Si: 1.7, S: 2.3 keV], making it both inefficiently excited by conventional hard X-ray sources and strongly absorbed by any material in the measurement path. In a slurry system this is compounded by the window required to retain the sample, which absorbs low-energy fluorescence, and by the surrounding air path and detector window, each of which further attenuates the already weak signal.
Overcoming this requires optimising every stage of the signal chain including variables such as tube target and voltage, filter choice and detector choice. These configurations were guided by Monte-Carlo simulations to optimise the XRF response of light elements while saving time and costs associated with experimental testing.
The effect of this optimisation is demonstrated in the measurement of sulphur across the tailings, feed and concentrate streams of a stibnite slurry. Under a poorly optimised configuration the sulphur signal was recoverable only in the high-grade concentrate (Figure 1); with the optimised configuration described in this study. These results show that, despite the inherent difficulty of light-element XRF in slurries, reliable online measurement of S is achievable through purpose-built instrumentation and physics-based optimisation.
Figure 1: Sulphur measured across tailings, feed and concentrate of a stibnite slurry under a sub-optimal configuration; the S signal is recoverable only in the high-grade concentrate, motivating the optimisation described here.