Abstract: A method of treating alkaline industrial by-products, such as red mud generated by Bayer process bauxite refining, is described. Embodiments of the method comprise treating the alkaline industrial by-products with salts of divalent and/or polyvalent cations, thereby lowering pH of the alkaline industrial by-products. The method involves replacement reactions in which relatively insoluble hydroxide salts form precipitates, thereby removing hydroxide ions from solution.

Abstract: Disclosed is a method for processing waste to render it fit for ultimate disposal. The method comprises first contacting together in a reaction mixture the waste stream, an ammonia source capable of evolving ammonia for treating the waste, Ca(OH).sub.2, pozzolanic chemicals SiO.sub.2, Fe.sub.2 O.sub.3, and Al.sub.2 O.sub.3, and at least one pozzolanic accelerator selected from the group consisting of anionic metal silicates, anionic carbon compounds, anionic boron compounds (borate family), anionic phosphorous compounds (phosphate family), and gelling enhancers, in a manner suitable to cause pozzolanic stabilization reactions to occur thereby increasing the solids percentage of the reaction mixture. Next, the reaction mixture is allowed to reach a target temperature of at least about 90.degree. C., to reach a pH of at least about 11.5, and to evolve ammonia gas, thereby forming a heated mixture.