Study on the vertical release characteristics of alkali and fluoride in red mud with different compaction degrees

Abstract In this study, the vertical migration and release characteristics of alkali and fluoride in Bayer red mud with different compaction degrees were investigated by conducting constant head vertical leaching tests. The experimental results showed that the breakthrough time of leaching liquid across the red mud column increased with the increase of compaction degree, the alkali and fluoride concentrations of the leaching outflow decreased fast as the compaction degree of red mud column increased, as well as the time required to reach the leaching equilibrium. Moreover, for all the leaching red mud columns, the cumulative release of alkali and fluorine from the increased with the increase of leaching durations. However, the total release of major pollutants decreased with the increase of red mud compactness. After leaching, the soluble alkali and water-soluble fluorine (Ws-F) residual in the red mud gradually increased from top to bottom along the leaching column, and at the identical depth, the higher the compactness of the leaching column, the greater the soluble alkali and water-soluble fluorine (Ws-F) remaining in the column after leaching. These phenomena indicated that improving the compactness can effectively slow down the release of main pollutants in the red mud. The results were expected to provide a scientific basis for the prevention and control of alkali and fluoride pollutants in red mud yard.