An accurate determination of cryolite ratio in industrial aluminum baths by wavelength-dispersive X-ray fluorescence spectrometry

Abstract

The efficiency of aluminum smelting cells relies on control in maintaining different cell's parameters, including bath chemistry. In industry, X-ray diffraction analysis is normally used to control the primary characteristic of bath chemistry, namely cryolite ratio. However, from 2 to 3% of all the results contain over-normative errors, and this declines the efficiency of the process control and the overall smelting efficiency. Present paper provides a wavelength-dispersive X-ray fluorescence spectrometric methodology for measuring cryolite ratio of aluminum bath in detail. It guarantees measuring cryolite ratio with the accuracy of 0.04, which is required by the smelting technology. The methodology includes the calibration of a wavelength X-ray fluorescence spectrometer with reference materials, the measurement of concentrations of F, Na, Al, Ca and Mg, and the calculation of cryolite ratio from the measured concentrations. We evaluated two possible strategies of measuring cryolite ratio by X-ray fluorescence. The one that does not involve oxygen quantification provides the technologically required accuracy of cryolite ratio measurements. Also, new results of implementing the methodology in the process control at Krasnoyarsk aluminum smelter are provided. The combined process control of cryolite ratio by X-ray diffraction and X-ray fluorescence ensures accurate and reliable results, eliminates gross analytical errors and stabilizes overall performance of a smelter's process control system. Thus, use of X-ray fluorescence analysis for measuring CR contributes in stable current yield of aluminum.