Selective ion separation by supported liquid membranes under electrodialysis conditions

Abstract

Electrodialysis (ED) is a membrane-based process in which ions are transported under the influence of an externally applied electrical potential. Ion-exchange membranes (IEMs) are key components in ED processes. There are two types of IEMs: (1) cation-exchange membranes (CEMs), which contain fixed, negatively charged groups, and (2) anion-exchange membranes (AEMs), which contain fixed, positively charged groups. ED processes have been widely applied for water desalination. This thesis investigates the application of ED in the treatment of drainage water of greenhouses. A key objective in sustainable greenhouse horticulture is the recirculation of drainage water, thereby minimizing the water volume used, which would otherwise be disposed into the environment.[1] The drainage water of greenhouses contains both K+ and Na+. Whereas K+ is a valuable nutrient, Na+ is detrimental for plant growth. Because of its toxicity, the Na+ level should be controlled below the crop-specific threshold.[2-4] Because Na+ is not taken up by plants, it accumulates and the excess needs to be removed. The main challenge here is to selectively separate and remove Na+ without removing K+ and other key nutrients like Ca2+ and Mg2+. Na+ and K+ are two competitive cations ion separations as they have the same valence (+1), quite similar crystal and hydrated radii and a rather similar transport behavior (i.e. electrophoretic mobility), causing that separation by charge, size, and/or mobility is challenging. This thesis focusses on the development and characterization of a membrane-based process for the selective removal of Na+....