(347r) Microfluidic Ionic Separations Using Selective Electrodes

Separation of highly soluble ionic constituents is a useful tool in the treatment of industrial wastewaters. In this study, a microfluidic electrochemical deionization cell has been employed for the treatment of ionic mixtures representative of certain wastewaters. Symmetric silver/silver chloride electrodes, in combination with microscale flow, separate Cl^- and SO₄^2- ions present in an input stream, enriching them in alternate streams. This electrode system exhibits a few useful characteristics including excellent reversibility and stability which allow rapid cycling.

Concentration gradients created in the cell during operation are maintained against diffusion by design of the advective flow field. During separation, the silver anode is oxidized and absorbs Cl^- ions from solution, while the silver cathode releases Cl^- ions. Electrode polarity reverses, and electrode function switches, when the oxidized electrode becomes saturated.

Ion chromatography is used for characterization of separation. The system shows increases, from input to enriched streams, of Cl^- and SO₄^2- ions of 42.8% and 21.8%, respectively. We implement an electrochemical transport model including the effect of ionic properties and flow and electrical parameters to elucidate factors influencing system performance characteristics including separation and charge efficiency. Modeling suggests potential changes to cell design and operational regimes for enhanced performance. The method considered offers useful alternative separation approaches for ionic mixtures containing Cl^-.