Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment

Takehito Hiraki, Osamu Takeda, Kenichi Nakajima, Kazuyo Matsubae, Shinichiro Nakamura, Tetsuya Nagasaka

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    Abstract

    In this paper, the possibility of removing impurities during magnesium recycling with pyrometallurgical techniques has been evaluated by using a thermodynamic analysis. For 25 different elements that are likely to be contained in industrial magnesium alloys, the equilibrium distribution ratios between the metal, slag and gas phases in the magnesium remelting process were calculated assuming binary systems of magnesium and an impurity element. It was found that calcium, gadolinium, lithium, ytterbium and yttrium can be removed from the remelted end-of-life (EoL) magnesium products by oxidization. Calcium, cerium, gadolinium, lanthanum, lithium, plutonium, sodium, strontium and yttrium can be removed by chlorination with a salt flux. However, the other elements contained in magnesium alloy scrap are scarcely removed and this may contribute toward future contamination problems. The third technological option for the recycling of EoL magnesium products is magnesium recovery by a distillation process. Based on thermodynamic considerations, it is predicted that high-purity magnesium can be recovered through distillation because of its high vapor pressure, yet there is a limit on recoverability that depends on the equilibrium vapor pressure of the alloying elements and the large energy consumption. Therefore, the sustainable recycling of EoL magnesium products should be an important consideration in the design of advanced magnesium alloys or the development of new refining processes.

    Original languageEnglish
    Article number035003
    JournalScience and Technology of Advanced Materials
    Volume12
    Issue number3
    DOIs
    Publication statusPublished - 2011 Jun

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    Keywords

    • distribution ratio
    • end-of-life products
    • impurity removal
    • Recycling of magnesium
    • thermodynamic analysis

    ASJC Scopus subject areas

    • Materials Science(all)

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