Removal of Magnesium from Aluminum Scrap by Compound-Separation Method Using Shirasu as an Additive

Abstract

The removal of magnesium from the molten aluminum scrap containing magnesium was examined by compound-separation method. As an additive, three types of Shirasu (a natural resource in South Kyushu, Japan) with different particle sizes were used. The addition of Shirasu to the molten aluminum scrap at 1023 K resulted in the formation of MgAl 2 O 4 and MgO by the reactions among SiO 2 and Al 2 O 3 in Shirasu and magnesium in the molten scrap. It was feasible to remove magnesium by separating these reaction products as dross. Assuming that all the Shirasu reacted with magnesium in the molten scrap, the amount of removed magnesium, which was calculated from these reactions, was in agreement with the measured one. In the addition of flaky Shirasu with a small particle size, the amount of removed magnesium increased linearly with agitation time after Shirasu addition. This is because the over-all reaction is mainly controlled by a surface-controlled reaction. In the addition of granular Shirasu with a large particle size, the increase in magnesium removal was parabolic. This is because the over-all reaction is mainly by a diffusion-controlled reaction.