Electrochemical Separation and Recovery of Metals from Liquid Alloys

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

The research made possible by this award will explore faster, safer, and more sustainable methods of precious metal recycling. This will guide researchers toward understanding the science behind the processing of materials. By virtue of its higher productivity, this new method can be utilized to the benefit of the US manufacturing economy. Precious metals have seen an increased prevalence in electronics; unfortunately, these devices have short lifetimes as they are quickly discarded for newer models. This grant supports investigation of a new method for metal recycling, called electrometallurgy, which makes use of electric fields to separate and recycle metals from scrap. This approach provides substantial benefits over existing methods for metal separation, which involve combustion or harsh acid dissolution. This fundamental research will investigate how electricity can be used to selectively recycle and purify the many different metals contained in electronic waste, targeting the precious metals (gold and silver). Bringing together the fields of processing science, thermodynamics, chemical engineering, and electrochemistry, this cross-disciplinary work will bring new knowledge of benefit to engineers in multiple fields. The basic principles developed can be extended to the sustainable production of metals for aerospace and defense, construction, and technology, presenting a large benefit to the US economy as well as public health. Furthermore, the computational tools developed in this work will be made widely available as free teaching tools for thermodynamics. This online tool will reach a broad and diverse audience, empowering students to pursue science and engineering. When compared to other recycling methods, electrometallurgy has the potential to reduce the energy use by 80x and the time needed for recycling by a factor of 10. In order to realize these benefits, however, the electrochemistry of liquid alloy electrodes must be better understood in order to be able to control which metal, among the many present in electronic waste (e-waste), is recycled. Furthermore, a high-temperature solvent, the first of its kind able to accommodate molten gold, copper, and silver simultaneously, will be investigated. This research aims to understand the underlying kinetic, transport, and thermodynamic factors that determine which species is reduced at the cathode and oxidized at the anode made of melted e-waste. A new model predicting which metals are stable and in what proportions will be developed. In addition, the rate-limiting step in the process will be verified with experimental electrochemical measurements. Advanced electrochemical characterization techniques, such as alternating current cyclic voltammetry, alongside traditional chronoamperometry and electromotive force measurements, will be employed experimentally. Mutiphysics modeling, thermodynamic calculations, and phase diagram predictions will be used to iterate and optimize process conditions on the computational side. Together, both experimental and modeling techniques will inform the underlying fundamentals of electrochemical behavior of molten precious metals. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.