ELECTROCHEMICAL PRODUCTION OF POLYSULFIDES AND SODIUM-HYDROXIDE FROM WHILE LIQUOR .2. ELECTROLYSIS IN A LABORATORY-SCALE FLOW CELL

Electrochemical production of polysulfide-containing white liquor and pure sodium hydroxide solution was investigated at 90 degrees C in a l aboratory scale flow cell. A mixed iridium-tantalum oxide coated titan ium electrode was used as the anode and the two electrolyte compartmen ts were separated by a cation-exchange membrane. The process was demon strated at current densities up to 5 kA m(-2), resulting in high curre nt efficiencies for both products. The previously reported autocatalyt ic effect of polysulfide ions was confirmed, and its technical implica tions on the use of three-dimensional electrodes were demonstrated and discussed. The current efficiency was found to depend strongly on the degree of conversion of sulfur(-II) to sulfur(0). The anode material showed favourable properties, with respect to activity and selectivity , but suffered from limited durability.