Fluoride Desorption of Secondary Alumina at High Temperatures

Abstract

Primary alumina is used as the raw material as well as the sorbent for fluoride in aluminum electrolysis. Secondary alumina is the product of primary alumina after absorbing fluoride in exhaust pot gas. The fluorine and mass loss during heating secondary alumina was measured to study the fluoride desorption process of alumina. It was found that during the heating of secondary alumina, HF emission was always combined with H 2 O escape at approximately 740°C or below. 47% fluorine in secondary alumina desorbed in the form of HF at 30-740°C, while the rest 53% desorbed in the form of chiolite at 740-1100°C.

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“…The characteristic peaks of γ-alumina are shown in Figure 6 and they are in good agreement with previous reports [62,63]. Therefore, XRD results confirm the observations from EDS characterization that primary alumina loses its fluorine content in this temperature range [64].…”

“…The third stage is rather an artefact from the measuring device presenting a small drift in the mass loss associated to the temperature increase. Although weight losses were directly related to transformations of the alumina substrate leading to the evolution of water, fluoride desorption should also occur in this temperature range although producing smaller weight losses as described by Yang et al [64].…”