Neutralization of Red Mud with Organic Acids and Assessment of Their Usefulness in Abating pH Rebound

This study provides a practical and efficient alternative to neutralize the exorbitant pH of red mud (>11.5) followed by long-term sustenance of the neutralization. The usefulness of organic acids (oxalic acid and citric acid) as standalone additives and admixed with lime in mitigating red mud alkalinity was investigated. The efficiency of these acids in terms of posttreatment pH rebound for curing period up to 180 days was monitored. The neutralization treatment produced pH reduction with simultaneous accentuation of coagulation and precipitation of hydrates, which was determined from scanning electron microscope (SEM) analysis. The uniqueness of the study lies in proposing the rebound rate of pH (RRP) and rebound termination period (trt). The observed results offer distinctive insight into the factors affecting red mud chemistry including the role of lime as an additive. It is recommended to use 2.0 M oxalic acid or 2.5 M citric acid for neutralizing red mud. For improved microstructure, it is warranted to resort to a combination of 5% lime and 2.0 M oxalic acid.