title: Thermodynamic criteria for the removal of impurities from end-of-life magnesium alloys by evaporation and flux treatment.
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.
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Takehito
authors.initials: T
authors.lastname: Hiraki
authors.affiliation: Graduate School of Engineering, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Takeda
authors.affiliation: Research Center for Material Cycles and Waste Management, National Institute for Environmental Studies, Tsukuba 305-8506, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Nakajima
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Matsubae
authors.affiliation: Graduate School of Economics, Waseda University, Tokyo 169-8050, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Sendai 980-8578, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Nagasaka
keywords: distribution ratio; end-of-life products; impurity removal; recycling of magnesium; thermodynamic analysis