Apparatus and system for refining sodium

A method for refining sodium, in which impurities contained in sodium are removed by a solid electrolyte having sodium ion conductivity, the method comprising the steps of:

• applying a DC voltage to an impurity-containing sodium;
• measuring oxygen concentration of the impurity-containing sodium;
• containing the impurity-containing sodium or a lesser amount of highly pure sodium in a bottom-closed casing made of a solid electrolyte;
• accommodating said bottom-closed casing in an outer casing and containing, outside said bottom-closed casing, a highly pure sodium when said bottom-closed casing contains impurity-containing sodium, or impurity-containing sodium when said bottom-closed casing contains highly pure sodium, wherein the amount of highly pure sodium contained outside said bottom-closed casing when the bottom-closed casing contains impurity-containing sodium is smaller than the amount of impurity-containing sodium contained outside said bottom-closed casing when the bottom-closed casing contains highly pure sodium;
• inserting a first electrode in the impurity-containing sodium or in the highly pure sodium;
• inserting a second electrode in the highly pure sodium when the first electrode is inserted in the impurity-containing sodium, or in the impurity-containing sodium when the first electrode is inserted in the highly pure sodium;
• applying DC voltage to the electrodes;
• and
• adjusting the liquid-surface level of the bottom-closed casing formed of solid electrolyte and that of the outer casing to be approximately equal to each other;
• wherein
• the impurity-containing sodium and the highly pure sodium are in electrical contact with each other via the solid electrolyte;
• and when the DC voltage is applied, the impurity-containing sodium is positively charged and the highly pure sodium is negatively charged, to thereby ionize sodium contained in the impurity-containing sodium;
• and
• the thus-formed sodium cations are caused to pass through the solid electrolyte and, subsequently, are combined with electrons at the surface of the solid electrolyte, to thereby yield refined sodium.