ELECTRODE PROCESSES OF SULPHUR SPECIES IN MOLTEN SALTS

摘要

The effect on the cathode and anode reactions when adding sodium sulphate to molten chlorides and fluorides was investigated by chronopotentiometry and cyclic voltammetry in the temperature range 820 deg C -1000 deg C. The cathode process was explained under the assumption that Na_2SO_4 thermally dissociates into Na_2O and SO_3, which is the electroactive species. The formation of sulphide was observed. The influence of sulphide on aluminium electrolysis will be discussed. The anode reaction of sulphate depends on the electrode material. On gold electrodes, no electrochemical activity of sulphate was observed. However, when a platinum anode was used, sulphate was oxidized to oxygen and SO_3 that decomposed thermally. When a normal carbon anode was used, the presence of COS and SO_2 in the anode gas leaving the laboratory aluminium cell was observed.