No abstract

A combination of the methods of X-ray phase and X-ray spectral analyzes is used at domestic aluminum plants for operational technological control of the composition of cooled electrolytes. In this case, standard samples of chemical and phase composition are used to calibrate measuring instruments. The synthesis of standard samples from simple components is impossible due to the inadequacy of their microcrystalline structure to real electrolyte samples. Therefore, it is necessary to develop standard samples directly from the material of real electrolytes with a reliably established quantitative chemical and mineralogical phase composition. We managed to develop a set of 30 standard samples of aluminum-produced electrolyte using electrolytes taken from the electrolysis baths of various plants; some of the samples were doped with so­dium, aluminum, calcium, and magnesium fluorides to expand the range of compositions. A metrological certification of the set with the status of "Industry standard samples" was performed based on the data of interlaboratory analysis according to the methods of X-ray control used at the plants and according to the well-known Rietveld X-ray phase method for determining the quantitative phase composition. The set has been successfully implemented at seven RUSAL plants.

The present paper provides a combined application of X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods in process control for the analysis of aluminum baths of different compositions. Developed approaches to the combined calibration XRD and XRF methods, independent calibration XRF techniques and to the full-profile automated Rietveld analysis of a bath composition are described.We established that combined XRD-XRF calibration techniques provide an accurate stable analysis of technological parameters in a wide range of traditional and low-melting compositions due to an accurate quantification of CaF 2 , MgF 2 and KF additives. The developed XRF techniques provide quantitative analysis of both cryolite ratio and alumina with the accuracy of 0.03 and 0.25% wt. respectively, which is comparable with the technologically required accuracy.The evolutionary approach that automates full profile quantitative XRD analysis of bath composition and uses XRF data on Ca and Mg provides a better accuracy of measuring cryolite ratio compared to an accuracy of non-automated analysis by Rietveld method.Combined application of the two X-ray methods eliminates gross analytical errors and stabilizes overall performance of a smelter's process control system.