| Low temperature electrolyse is a great trend in the industry of aluminium electrolyse. However, the solubility and dissolution rate of alumina in electrolytic process stops its development. So the alumina easy to be dissolved in cryolite melts needs to be studied. Based on related references home and abroad, this paper mainly took up consideration on the alumina easy to be dissolved in cryolite melt through the calcination of Al(OH)3.First the effects of AlF3 on the dehydration process kinetics of Al(OH)3 were studied. The results indicate that, due to AlF3, the dehydration process of Al(OH)3 is mainly effected in the high temperature range of 560～1100℃where the dehydration mechanism is converted from nucleation and growth to phase boundary reaction and three-dimensional diffusion. Based on it, the effect regulations of AlF3 on LOI (Loss on ignition) of alumina were investigated through experiments and the following results are learned:the calcination temperature can be reduced greatly as the result of addition of AlF3; provided the alumina with LOI lower than 0.8% is preferred, with 1%, 2% and 3% addition of AlF3, respectively, the calcination temperature of Al(OH)3 can be reduced to 900℃,850℃and 800℃, respectively; with 3% addition of AlF3, when the calcination temperature is 800℃, LOI of alumina can be reduced to as low as 0.39%. Finally the solubility property of alumina in cryolite melt was analyzed by IR. The results show that if the dissolution time is less than 8 minutes, the alumina calcined by industrial seed aluminum hydroxide at 1000℃for 1h can be dissolved more; with the dissolution time continuing to extend, the alumina calcinated by Al(OH)3 with 3% addition of AlF3 at 800℃for 1h dissolved faster and more in cryolite melt. |
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