Advanced materials for selective nitrate/chloride separation (Anchor)

The selective removal or recovery of elements from a multicomponent stream plays a key role in many industrial and agricultural applications. For instance, nitrate needs to be removed from industrial brines. In closed horticulture systems, however, the aim is to retain the nitrate in the recirculating water but to selectively remove the chloride, a requirement also mandatory in the production process of fertilizers. Currently used electrochemical and biological methods deal with safety issues, season-dependent environmental factors, time-consuming process steps and/or high capital costs. For all these reasons, alternative approaches have to be explored. The technological challenge of the nitrate/chloride separation is related to the slight difference between these two equally charged ions in terms of their size and hydration energy. Epsztein et al. [1] explored ion permeation in ion-exchange membranes. Ions were shown to have an activation behavior of transport – attributed to ion dehydration – according to an Arrhenius-type equation, and smaller and more strongly hydrated ions showed a higher energy barrier for transport. Sata et al. [2] showed how the presence of a longer alkyl chain bonded to the quaternary ammonium functional group in the polymeric structure of the membrane increases the nitrate’s permeation. Building further on these previous contributions, we studied the selective separation of nitrate and chloride by increasing the hydrophobicity of anion-exchange membranes (AEMs) manufactured by casting, blending different kinds of polymers, resins and additives such as quaternary ammonium salts. Each membrane will be then characterized in order to study the electrical resistance, permselectivity, and selectivity for a multicomponent solution of nitrate and chloride. The goal is to make a membrane that shows an increased selectivity for nitrate over chloride. [1] Epsztein et al. Journal of Membrane Science, 580, (2019), 316–326 [2] Sata et al. Journal of Membrane Science, 167, (2000), 1–31