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The use of aluminium scrap to produce different alloys has increased considerably at the start of the current century because of the low amount of energy required for its melting, in comparison to the energy required to produce aluminium from bauxite. However, contamination problems can arise if the different kinds of scrap with several chemical compositions are not separated using appropriate methods. In this way, contamination with elements such as Fe, Sb, Mg, Na, K, Pb, and Sn is quite common, so melt treatment practices have been recommended. Of these contaminants, antimony is considered to be among the most harmful because of its high potential toxicity, which is of special concern for products intended for handling of food and drink. Also, modification with sodium and/or strontium is not effective because of the formation of intermetallic compounds that remove these elements from solution, preventing any effect of this modification on the eutectic silicon phase. The negative effects of antimony on the rate of modification of the silicon eutectic with sodium and/or strontium in casting Al-Si alloys have been broadly studied by (Wang & Gruzleski, 1990), (Wang & Gruzleski, 1992), (Garant et al., 1992), and (Tuttle et al., 1991). The general problem in mixing antimony with sodium and/or strontium is the formation of high melting temperature compounds that are difficult to remove. Moreover, it is possible to generate phases with harmful morphologies that affect the mechanical properties of this type of alloy. These compounds eliminate sodium and/or strontium from the solution, preventing the effect of sodium/strontium modification on the silicon eutectic phase. On the other hand, antimony has been shown to possess a great chemical affinity for calcium, forming stable compounds that can be removed through dross. However, to study the mechanism of reaction, it is first necessary to define the stoichiometry of the reaction. Different techniques have been proposed to hinder the effects of antimony, including dilution with pure aluminium, separation of polluted scrap, addition of an excess of the modifier agent, or removal by means of chemical agents, as described by (Castrejon, 1995). However, no effective method has yet been developed at the cast shop facility level. Antimony, among other elements, possesses great affinity for calcium, as demonstrated long ago by (Hardy, 1941), who established that Ca3Sb2 or AlSb phases could form when these elements are present in molten aluminium. Nevertheless, the mechanism of reaction outside of molten aluminium scrap has not been determined.

New Approaches to Reaction Kinetics during Molten Aluminum Refining Using Electron Backscatter Diffraction (EBSD)