Process for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides

An electrolytic cell for oxidizing an alkali metal monosulfide or alkali metal polysulfides comprising:

• an anolyte compartment configured with an anode and containing an anolyte solution comprising an alkali metal monosulfide, an alkali metal polysulfide, or a mixture thereof and an anolyte solvent that partially dissolves elemental sulfur, the anolyte compartment further comprising an anolyte solution inlet and an anolyte solution outlet;
• a catholyte compartment configured with a cathode and containing a catholyte, wherein the catholyte comprises a molten alkali metal, the catholyte compartment further comprising a catholyte outlet;
• an alkali ion conductive membrane configured to selectively transport alkali ions, wherein the alkali ion conductive membrane is substantially impermeable to anions, the anolyte solvent, and dissolved sulfur;
• a source of electric potential electrically coupled to the anode and the cathode and configured to:
• oxidize the alkali metal monosulfide or polysulfide in the anolyte compartment to form liquid elemental sulfur and alkali metal ions;
• cause the alkali metal ions to pass through the alkali ion conductive membrane from the anolyte compartment to the catholyte compartment;
• and
• reduce the alkali metal ions in the catholyte compartment to form liquid elemental alkali metal;
• an elemental sulfur settling zone where the liquid elemental sulfur forms a second liquid phase and separates from the anolyte solution;
• and
• a sulfur outlet for removal of the liquid elemental sulfur from the electrolytic cell disposed at a location lower than the anolyte solution outlet.