Analysis of Sulphur in Gypsum

Applied Rigaku Technologies (Japan) recently announced a new empirical method for the analysis of sulphur in gypsum. Gypsum is a soft sulphate mineral added to Portland cement to prevent flash setting of concrete. Application Note #1255 demonstrates the performance of the Rigaku NEX QC energy dispersive X-ray fluorescence (EDXRF) spectrometer in the monitoring of gypsum for quality control during the cement production process.

X-ray fluorescence (XRF) spectroscopy is integral to control of the production process in modern cement plants, enabling a cement maker to produce a consistent product. Energy dispersive X-ray fluorescence spectrometry is routinely employed for screening and quality control, providing rapid compositional data at various stages of production. Whether at the quarry, cement plant or industrial manufacturing site, the sulphur content of the gypsum as it is processed needs to be closely monitored to ensure the quality and proper formulations of the final products. EDXRF analysers are typically implemented to monitor the addition of gypsum throughout the manufacturing process.

For this method, each gypsum sample is prepared by grinding the material to dry, homogeneous powder <200 mesh (<75um particle size). Approximately 8 grams of powder is then placed in a 32mm sample cup and packed to an even and consistent sample. Empirical calibration was developed using a set of six assayed standards with sulphur content ranging between 12-17%. Analytical results and precision data are shown from the measurement of the low and high sulphur content calibration standards. Detection limits were in part determined by the calibration range and analysis time.

The data confirm that the NEX QC analyser yields excellent results for the measurement of sulphur in gypsum, without the need for helium purge. Other elements in the gypsum, including calcium, can also be measured. The method shows how the Rigaku NEX QC analyser, with its simple, modern touch screen interface, enables reliable and efficient measurement to meet analytical needs at the quarry or cement plant when testing gypsum and finished cement, as well as during the manufacturing of other gypsum products.