Performance of Lime Stabilization on Extremely Alkaline Red Mud Waste under Acidic Environment

Abstract

Excessive pH (>11) and inconsistent engineering properties because of the chemicomineralogical composition of red mud warrant devising an alternate approach to render it more environmentally benign. In this study, the performance of lime stabilization coupled with oxalic acid, which acts as a neutralizing agent, was explored systematically to improve the long-term strength and to reduce the alkalinity of red mud. The mechanisms governing the behavior of additives along with their effects were investigated by examining the mineralogical, elemental, and morphological characteristics. The results suggest an effect of sodalite and alumina on the inconsistency in dry unit weight and claylike behavior of red mud. A reduction in pH was found to be instrumental during early phases of lime stabilization and in precipitation of cementitious hydration products, leading to strength gain in the long term in red mud. Moreover, the addition of lime and oxalic acid was found to yield more encouraging results than lime treatment alone, and hence this is recommended to be used for red mud stabilization. The obtained results were substantiated by comparison with code provisions.