Growth of Trifolium pratense in Red Mud amended with process sand, Gypsum and thermally dried sewage sludge

Aughinish Alumina Ltd. annually produces approximately 1.5 M tonnes of alumina, 1.05 M tonnes red mud and 0.15 M tonnes of process sand residue. The residues which are stored in a mudstack are susceptible to wind erosion in a plant closure scenario. Establishment of vegetation on the residues is an attractive desirable method of suppressing dust generation. However, there are constraints in achieving vegetation growth on the residues due to the inherent high pH and sodium levels. The present study examined the use of gypsum and thermally dried sewage sludge as amendments for establishing the clover species Trifolium pratense on a red mud/process sand mix. Gypsum was applied to plots at rates of 0 and 3% (w/w) with both treatments receiving thermally dried sludge at 35 t/ha. Gypsum amendment improved chemical conditions of the substrate and increased plant yield. Plant tissue analysis indicated adequate levels for Ca and Mg but a deficiency of Mn. High Fe and Na levels were also recorded. Results demonstrate that growth of clover on red mud is possible with the addition of dried sludge and without the addition of gypsum. However, future monitoring is recommended to determine if the absence of gypsum will have a deleterious effect.