5N (99.999%) Aluminum and higher purities use 4N Aluminum as the starting raw material and separates the lower grade aluminum from the pure metal. The same two methods – Three-Layer and Crystallization - are used for both 4N and 5N purities, but for 4N production, the waste generated is minimal since the difference from 99.9 to 99.99% is not so great.
Crystallization is the preferred method for 5N production since Three-Layer method adds Copper contamination. To produce 5N and better purities, energy and processing represent the majority of the cost, and the aluminum raw material is much less portion of the cost since so much of the aluminum raw material is discarded in the process. Higher purities require even more processing, and it is significantly more expensive to go up each purity step.
Another difference is that 4N production can be made in larger quantities with batches in 1 to 2 metric ton (MT) quantities, but 5N production is in much smaller batches – typically 100 to 200 kg per batch.
With 5N production requiring minimal contaminants, cleanliness is so important and this adds more cost to the production process.
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