Use of Thermodynamic Modeling for Selection of Electrolyte for Electrorefining of Magnesium from Aluminum Alloy Melts
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I.
INTRODUCTION
A
recently published paper[1] describes the process details, experimental results and product marketability, and economic analysis of the process for extracting a desired amount of magnesium from secondary aluminum scrap melts using an electrorefining technology. The project was funded by the United States Department of Energy Advanced Research Project Agency.[4] North America produces only ~70,000 tonnes of primary Mg annually. The only practical recycling of postconsumer Mg is as alloying content in the Al alloy recycling system. However, in that system, over 30,000 tonnes of Mg content is chlorinated or fluxed out of Al to end up as Mg chloride contamination of dross.[1] An economical, environmentally friendly, and chlorine-free Mg recovery process could be disruptive and transformational for the Mg production industry by enabling the recycling of 30,000 tonnes of primary quality Mg annually. An experimental proof-of-concept was demonstrated for a patent-pending[2] and trademark-pending[3] RE12TM process for extracting a desired amount of Mg from recycled scrap secondary Al melts. Mg was extracted by electrorefining producing Mg product suitable as Mg alloying hardener additive to primary grade Al alloys. This efficient electrorefining process operates at high current efficiency, high Mg recovery, and low-energy consumption. Mg electrorefining
ADAM J. GESING, formerly Technical Director with Phinix, LLC, Lexington, KY, is now President, Gesing Consultants Inc., Toronto, Canada. SUBODH K. DAS, CEO, is with Phinix, LLC. Contact e-mail: [email protected] Manuscript submitted December 30, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
product can meet all the impurity specifications with subsequent melt treatment for removing alkali contaminants. All technical results obtained in the RE12TM project indicate that the electrorefining process for extraction of Mg from Al melt is technically feasible. A techno-economic analysis indicates high potential profitability for applications in Al foundry alloys as well as beverage can and automotive sheet alloys. The combination of technical feasibility and potential market profitability completes a successful proof-ofconcept. The compositions of the electrolytes for the electrorefining cell were explored. The preferred composition was selected using the best available information and tools. These included the molten salt literature and the commercially available FactSage software program for thermodynamic and phase diagram calculations.[6–25] FactSage[5] includes the thermodynamic and material property databases, and computational models. FactSage is a fully integrated thermochemical database that couples proven FactSage software with self-consistent critically assessed FACT thermodynamic data. The research team prepared and characterized the electrolyte composition required for the electrorefiner, and demonstrated that the electrolyte composition can be maintained and cleaned of oxide contamination.
II.
PROCESS CONCEPT
The process concept for extraction of Mg from Al
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