Concentrated Ionic Fluids: Is There a Difference Between Chloride-Based Brines and Deep Eutectic Solvents?

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Deep Eutectic Solvents (DESs) are novel solvents with tunable properties.
• Concentrated aqueous brines also offer adjustable water and chloride ion activity.
• Understanding the continuum of properties between these fluids is crucial for applications like metal processing.

Purpose of the Study:

• To investigate the relationship between Deep Eutectic Solvents (DESs) and concentrated brines.
• To demonstrate a continuum of properties across concentrated ionic fluids.
• To explore the use of these fluids in selective metal etching.

Main Methods:

• Investigated charge transport, molar conductivity, and fluidity in various concentrated ionic fluids.
• Measured diffusion coefficients of iron(III) and copper(II) chloride.
• Performed etching experiments on copper, silver, and nickel using these fluids.

Main Results:

• Charge transport is governed by fluidity, showing no discontinuity across different ionic fluids.
• Diffusion coefficients of metal chlorides linearly correlate with fluidity.
• Selective etching of metals depends on chloride and water activity, with passivation occurring at higher water activity.

Conclusions:

• Concentrated brines offer high chloride content and lower viscosity than DESs.
• DESs are more effective at preventing passivation due to lower water content.
• Tuning chloride and water activity allows for selective etching of mixed metal waste streams.