Sammendrag
A major contributor to HF gas evolution during aluminium electrolysis is the hydrolysis of alumina water. The objectives of this work were to investigate the kinetics of HF generation, and how water residence time in the atmosphere above the bath influences the HF formation. The HF concentration in the off-gas was measured during additions of alumina to a NaF-AlF3 melt (r = 2.2). The alumina water release rate upon rapid heating was also measured separately when alumina was added to a hot empty quartz cell. In the melt experiments, the residence time of the alumina water was varied by changing the nitrogen gas flow rate through the experimental reactor. The HF formation occurred instantly and the rate determining step is the alumina water release rate. For the range in this study, there was no effect of residence time of the gas in the reaction chamber on the amount of HF formed.