The Effectiveness of Cooled-Finger and Vacuum Distillation Processes in View of the Removal of Fe, Si and Zn from Aluminium

Abstract

The increasing demand for ultra-high purity aluminum for technological applications has led to the improvement of refining methods in recent decades. To achieve ultra-purity levels (>5N), the common industrial way is to firstly purify aluminum from 2N8 up to 4N8 via three-layer electrolysis, followed by fractional crystallization (usually zone melting). Since both of these methods are very cost- and time-intensive, this paper aims at providing other alternatives of purification. For this purpose, here, the purification of some selected impurities through cooled-finger fractional crystallization method and vacuum distillation have been the focus of this investigation. Both processes are more environmentally friendly than three-layer electrolysis and require less time than zone melting. In this paper, both methods were explored for the aluminum purification. Moreover, the effect of process parameters on the purification efficiency of iron, zinc, and silicon has been investigated. At the end, the effectiveness of the two processes was compared and advantages and disadvantages were summarized. The results showed that the cooling finger process effectively removed iron and silicon impurities, but the removal efficiency of zinc was low. The vacuum distillation process successfully removes zinc in the first stage of distillation. Iron and silicon removal requires additional distillation stages to achieve lower impurity levels.