11. Alumina Quality, HF Removal, Dissolution and Aluminum Purity

This chapter is intended to serve as a useful reference for those at alumina refineries and aluminum smelters who have interest in technical matters involving usage of Smelter Grade Alumina, or SGA. Accordingly, information on many physical and chemical properties has been categorized into various sections of this chapter that make it straightforward for readers to reference. Clearly the primary purpose of SGA is to serve as feedstock for the production of aluminum metal. However there are a number of additional technical requirements that may vary in degrees of importance for each end user. This chapter will discuss these specific requirements in detail. Much may be expected of this granular, synthetic material that is never fully communicated back to the process engineers on the “red” sides and “white” sides of alumina refineries. In the past it was often possible for suppliers of alumina to meet with their smelting counter-parts at co-located facilities. Factors of importance to the end users were then a part of everyday conversations about process control. With some exceptions those days are now long-gone for most of the western world. Smelters and refineries are now quite often separated by oceans. Tight connections in communications between refineries and smelters have for a large part been lost. Accordingly, in a world in which persons in smelting locations may not know, and may have never visited, a single person at an alumina refinery and vice-versa it becomes useful to know what is important and what is needed by smelting customers, not only what might be “nice to have” in the way of alumina properties. Providing this information to the readers is the primary purpose of this chapter. Let’s begin.