A Study on Evaluating the Usefulness and Applicability of Additives for Neutralizing Extremely Alkaline Red Mud Waste

The chemico-mineralogical compositions of red mud lead to its abnormal pH (>11), rendering it unusable as a resource material for civil engineering applications. Such extreme alkalinity accentuates the dearth of contriving a solution to ensure the acceptability and reutilization of the waste. Curing period has considerable significance in the context that the previous studies reported reversal of pH of the red mud after neutralization. Thus, efforts are made in the present study to evaluate the usefulness and applicability of a variety of additives for neutralizing the red mud waste. Additives such as lime, ground granulated blast furnace slag, fly ash, gypsum in different proportions, and acids such as nitric acid and hydrochloric acid of varying strengths were employed, aiming at investigating the alkalinity mitigation capacity in the red mud. The results demonstrated a substantial reduction in the alkalinity levels of the red mud immediately after treatment, but the post-neutralization pH results exhibited noteworthy reversal with time. It has also been found that the type of neutralizing additives has considerable influence on the chemistry which in turn might have affected alkalinity levels in the red mud.