Selective removal of sodium from alkali-metal solutions with tetraoctylammonium monensin

Abstract

Accumulation of sodium ions in fresh water limits its use for drinking water. In the greenhouse industry reuse of irrigation water, which still contains valuable nutrients is limited due to an increasing sodium concentration, and next to this high concentrations of sodium also result in corrosion problems. Existing technologies are not yet able to selectively remove sodium to solve above mentioned problems. Therefore, it was tried to develop a novel sodium selective ionic liquid based on the monensin anion combined with the tetraoctylammonium cation. Ionic crystals were obtained instead of an ionic liquid. Nevertheless, it was proven that these crystals could selectively remove sodium. Metal extraction experiments of an aqueous solution containing Li, Na, K, Mg and Ca with the monensin ionic crystals dissolved in toluene showed a selective single stage extraction efficiency of 41wt% for sodium, while the extraction of the other salts was negligible. Regeneration is possible by applying an acidic solution, however this also prevents its reuse.