Abstract
Zone refining is a well-known technique, usually using pure initial materials to produce high purity metals. However, the effectiveness of zone refining in the purification of different purity levels of metals as well as its feasibility for use as a recycling technique for low quality metals are rarely investigated. In this work, conducted at IME/RWTH Aachen University, three kinds of Al with different purities, i.e., three-layer electrolysis (4N), commercial pure (2N8) and recycled Al (1N7), were put on focus to address the above-mentioned issue. The experiments were conducted with an optimized zone length combination at the moving rate of 1.2 mm/min for five zone passes. The results showed that the 4N pure initial Al was improved to 5N5 after five passes, much higher than the results for commercial pure- or recycled Al, where less than 50% reduction of total impurities was achieved.
Highlights
Efficiency of Aluminum via ZoneZone refining is an effective methodology to produce high purity metals, which enables the distribution of impurities based on the principle of crystallization
Zone refining has been applied for the production of highly pure metals such as from gallium [3], aluminum [4], up to tellurium [5], cadmium [6] and germanium [7] since the early 1950s [8]
It shows that a purity of 5N5 could be achieved after five passes, manifesting the effectiveness of zone refining deployed to purify the 4N pure Al
Summary
Zone refining is an effective methodology to produce high purity metals, which enables the distribution of impurities based on the principle of crystallization. Similar to other crystallization technologies, this process can be applied to refine any metals in which the distribution coefficients (k, the ratio of the concentration of an impurity in the solid phase to that in the liquid phase) of the impurities are smaller or bigger than unity. The bigger the difference from the unity k is, the higher the tendency of the impurities is to separate from the base metal. A rule is that a high initial purity of the materials is already demanded
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