An analytical method to determine the composition of cryolitic melts involved in the Hall-Heroult process by Raman spectroscopy

The Hall-Héroult process involves the metallic aluminium production from electroreduction of aluminium oxide in cryolitic melt (mostly composed of cryolite and aluminium fluoride) around 1000°C. In order to reduce the energy loss during this process, controlling the melt composition turns out to be critical. Unfortunately, no in situ analytical method allows measuring the melt composition yet. Since the Raman spectrum of the melt depends on both the cryolitic ratio (molar NaF/AlF3 ratio, CR) and the aluminium oxide content, our laboratory proposed in the past to apply Raman spectroscopy for direct melt composition determination by recording the spectrum from the top. However, experimental problems made the practical application difficult. Nowadays, the method is becoming more feasible because of new instrumental developments such as new sensitive CCD, fiber optics and new optical filters.