Life cycle assessment of seawater neutralised red mud for treatment of acid mine drainage

One feature that has not been analysed in the re-use of bauxite residue (or “red mud”) is the comparison of its environmental benefits with competing products. The life cycle assessment (LCA) described in this article compares the use of seawater neutralised red mud to treat acid mine drainage (AMD) at Mount Morgan in Queensland, Australia with that of lime. The aim of the LCA is to evaluate the environmental merits of each neutralant by comparing the carbon dioxide emissions and the net energy use over their respective life cycles. Both life cycles involve the collection and processing of raw materials from Gladstone in Central Queensland, their transportation to Mount Morgan (about 150km away) and finally their application in a wastewater treatment plant. This plant, which currently uses lime as its treatment media, increases the pH of the acidic open cut pit water to acceptable levels for discharge. The results of the analysis revealed that seawater neutralised red mud would, over the entire life cycle, generate 20% of the carbon dioxide emissions and use 44% of the electricity compared with that of lime. This amounts to a saving of about 3500kg of carbon dioxide for every 1000m3 of pit water treated. However, as red mud is a much weaker neutralant compared with lime on a weight basis, significantly more red mud is required to perform the same duty; as a result the fuel usage in the red mud scenario is 12 times that compared with lime, which is primarily due to increased transportation requirements for red mud. The results of a sensitivity analysis demonstrated that even if the seawater neutralised red mud neutralisation capability was half the expected value, seawater neutralised red mud would still generate only 35% of the carbon dioxide and use 44% of the electricity compared with that of lime. The fuel usage for seawater neutralised red mud would, however, be nearly 24 times greater than that for lime.