Reclamation of fine fraction bauxite processing residue (red mud) amended with coarse fraction residue and gypsum

Establishment of vegetation on residues produced from the bauxite refining process is a beneficial part of their environmental management. Of the two fractions produced in the refining, the coarse fraction has greater efficiency in the leaching of excess salts and alkalinity. However, these same properties can result in increased loss of nutrients and low water-holding capacity. The current study investigated the use of mixing coarse fraction residue with fine fraction residue, at two different application rates (10% and 25%), with and without the use of gypsum as an ameliorant, for re-vegetation of the residue with Trifolium pratense. Optimum plant growth was observed in treatments that had also received gypsum amendment, with higher plant biomass, Mn nutrition and lower Al and Fe concentration. However, use of process sand at the higher application rate (25%) promoted lower levels of soluble Al and Fe and exchangeable Na in the substrate and, consequently, lower plant uptake of Na. Results indicate that co-disposal of the coarse fraction sand at 25% w/w with fine fraction residue can improve the substrate and, therefore, plant uptake and growth. Further monitoring is recommended to determine the effect of the absence of gypsum and other nutrient sources on plant growth.