Recycling kraft pulping chemicals with molten salt electrolysis

Molten salt mixtures containing sodium carbonate, sodium sulfide and sodium sulfate have been electrolyzed to generate sodium oxide and sodium sulfide while removing carbon from the system in the form of gas and maintaining a sulfur balance in the melt. These molten salts are presently found in the chemical recovery process of kraft wood pulping. Electrolysis was performed in a divided melt/undivided atmosphere and divided melt/divided atmosphere to avoid consumption of the oxide and sulfide products. The anodic reaction is carbonate oxidation to carbon dioxide and oxygen while sulfide oxidation to polysulfides occurs to a lesser extent at less positive potentials; sulfate oxidation is not observed to occur. The cathodic reaction is sulfate reduction to Sulfide and oxide, the desired molten precursors for recycled pulping liquors.