Influence of the Sulfur Species on the Current Efficiency and Carbon Consumption in the Aluminum Electrolysis Process

The influence of sulfur species on the current efficiency and carbon consumption in the aluminum electrolysis was investigated. Prebaked and graphite anodes with varying levels of sulfur were used. It was found that increasing the sulfur content in the anodes decreases the current efficiency and increases the carbon consumption of both types of anodes. The current efficiency decreased by 1.3 pct and the carbon consumption rose by 6.1 pct per 1 wt pct S in the prebaked anodes. The addition of sodium sulfate to the electrolyte during electrolysis with graphite anodes led to a decrease in current efficiency from 0.9 to 1.0 pct per 1 wt pct S, and to an increase in carbon consumption from 3.1 to 7.0 pct per 1 wt pct S. Electrolyte analysis showed the presence of sulfates, sulfides and polysulfides. Some link between sulfur content in the anodes and sulfur content in the electrolyte and outgoing gases was found. A comparison of the polarized and non-polarized conditions showed that the electrolysis increases the sulfur depletion from the cell and promotes the formation of soluble sulfides. Reactions of sulfur participation in redox processes have also been proposed.