Impurity iron separation from molten secondary aluminum by pulsed electric current

Abstract

Secondary aluminum has received extensive attention due to its low energy consumption, low emissions, and good recyclability; however, the high impurity iron content in secondary aluminum limits its development. Traditional iron removal methods generally have the problems of high cost and low efficiency. Therefore, exploring an efficient, economical, and environmentally friendly iron removal method is of great significance for achieving sustainable development and adhering to a circular economy. The effect of pulsed electric current on the distribution of impurity element iron in secondary aluminum melt was investigated. Compared to the non-pulsed sample, iron impurity accumulates near the cathode and at the bottom in the pulsed sample, while the content in the middle region is greatly reduced, that is, the impurity iron in the secondary aluminum melt is effectively driven and separated. Based on the difference in the effective charge number between Al and Fe, the iron atoms are forced to diffuse and move directionally toward the cathode under the action of electromigration, resulting in a gradual increase in the concentration of iron atoms near the cathode. According to the Al-Fe phase diagram, the increase of iron content makes the solidification point of the alloy to the right, and the solidification temperature of the alloy increases. In other words, at the same temperature, the Fe-rich phase is preferentially precipitated near the cathode. Due to the different electrical conductivity from the matrix, the Fe-rich phase migrates to the bottom of the melt driven by electrical free energy.