SEWAGE-SLUDGE AS ORGANIC AMELIORANT FOR REVEGETATION OF FINE BAUXITE REFINING RESIDUE

The rise in aluminium demand in the world has signficantly increased t he generation of bauxite residue which occupies huge areas of land wor ldwide. Direct revegetation of residue storage areas has been unsucces sful because of the high alkalinity and salinity, and poor nutrient co ntents of the fine residue (red mud). This paper describes glasshouse and field experiments evaluating the potential use of sewage sludge as an organic ameliorant for gypsum amended red mud. The growth of Agrop yron elongatum in red mud receiving gypsum (0 and 38.5 t ha-1) and sew age sludge (0, 38.5 and 77 t ha-1) amendment was assessed in a glassho use study. Leachate and soil analyses revealed that gypsum was effecti ve in reducing the pH, EC and ESP of red mud, while sewage sludge gave additional reductions in EC, Na and ESP. No evidence of any significa nt increases in heavy metal contents were observed in the leachates fo llowing sewage sludge amendment. However, soil Al contents were more a vailable in red mud receiving only sewage sludge treatment. Sewage slu dge amendment significantly increased dry weight yield and provided su fficient nutrients for plant growth except K which was marginal. No he avy metal accumulation was observed in Agropyron. Following that, a fi eld experiment was performed having red mud amended with sewage sludge (38.5, 77 and 154 t ha-1) and gypsum (38.5 and 77 t ha-1) to evaluate their effects on soil physical properties of red mud. Sewage sludge s ignificantly reduced soil bulk density (25%) and particle density (9%) and increased the total porosity of red mud (8%). Hydraulic conductiv ity also increased from 1.5 to 23 X 10(-5) m s-1. Plant cover percenta ge and dry weight yield of Agropyron increased with an increase in gyp sum and sewage sludge amendment. The results confirm that sewage sludg e is effective in improving both soil structure and nutrient status of gypsum amended red mud. The use of sewage sludge for red mud revegeta tion provides not just an option for sludge disposal, but also a cost effective revegetation strategy for bauxite refining industry.