Use of waste gypsum in the revegetation on red mud deposits: A greenhouse study

The disposal of fine bauxite refining residue (red mud) has occupied huge areas of land which remain derelict and subject to wind and water erosion. The major constraints in rehabilitation are the high alkalinity, salinity and sodicity of red mud. This paper describes a greenhouse study to evaluate the use of waste gypsum as ameliorants for red mud. Red mud was amended with gypsum at 0, 2, 5 and 8% (w/w) and its effect on the growth of two grass species, Agropyron elongatum (Tall wheat grass) and Cynodon dactylon (Bermuda grass), was evaluated. Gypsum amendment significantly reduced the pH, electrical conductivity (EC), and Na and Al content of red mud and provided a continuous supply of Ca ²⁺, which resulted in a lower soil exchangeable sodium percentage (ESP). The improved soil conditions at ≥ 5% gypsum amendment significantly increased seedling emergence and dry weight yields. The enhanced plant growth and seedling emergence show significant negative correlations with pH, Al and ESP of soil. Tissue analyses indicated that the availability of P, K, Mg and Ca also increased for ≥ 5% gypsum amended red mud, while Na and Fe were less available. Results from the present study indicated that waste gypsum is an effective ameliorant for red mud revegetation and no topsoil amendment is required.