Recycling kraft pulping chemicals: cyclic voltammetry of molten salt mixtures containing Na2CO3, Na2SO4, Na2S/Na2S x and Na2O/Na2O2

Cyclic voltammetry (CV) has been used to investigate molten salt mixtures in the temperature range of 820–840 °C between the initial and anticipated final compositions for the proposed electrolytic recausticizing process of inorganic pulping chemicals. A mixture simulating the initial conditions for the proposed process (sodium carbonate, sodium sulfide/polysulfide and sodium sulfate) exhibited carbonate oxidation and sulfate reduction at the limits of the potential window. Additional oxidation of sulfide to sulfur occurs at potentials inside the positive limit of the potential window with subsequent chemical reaction to form polysulfide. To simulate the final composition sodium oxide and peroxide were added to the mixtures; the resulting CVs had an additional oxidation peak attributed to oxide and peroxide oxidation. We conclude the electrolytic recycle process is feasible, producing sulfide and oxide from carbonate and sulfate of sodium in the molten state, yet separation is necessary between the anolyte and catholyte so the reduction products are not consumed by oxidation.