Sulfur removal with active carbon supplementation in digestion process

This paper proposes a novel approach to sulfur removal with active carbon supplementation in alkali digestion process. The effects of active carbon dosage on the concentrations of different valence sulfur in sodium aluminate solution were investigated. The results demonstrated that along with increases of active carbon dosage high-valence sulfur (S2O32−, SO32−, SO42−) concentration decreased, but the concentration of the S2− increased. This suggests that active carbon reacts with high-valence sulfur to generate low-valence sulfur at digestion temperature, which is consistent with our thermodynamic calculation results. As active carbon dosage increases, sulfur digestion rate decreases while sulfur content in red mud markedly increases; the alumina digestion rate, conversely, remains fairly stable. This suggests that high-valence sulfur in the sodium aluminate solution can be converted to S2− and then enter red mud by adding active carbon during the digestion process.