To produce high purity sodium used in the sodium-sulfur secondary batteries and as flux for crystal growth of gallium nitride, behavior of the exchange reaction between Ca or K in the Na and Na ions in the hydrophobic ionic liquids was investigated. Na containing Ca and K was floated on the NaTFSI or NaFSI and TEATFSI mixed at a molar ratio of 1:4. At a reaction time of 720 min and temperature of 160 degrees C, the purity of Na calculated from the concentrations of Ca and K in the Na increased to the 99.998% and 99.999% in NaTFSI-TEATFSI and NaFSI-TEATFSI ionic liquid, respectively. It was confirmed that Ca and K dissolved by the exchange reaction form a precipitate with little accumulation in the ionic liquid. (C) 2018 The Electrochemical Society.