Beneficial reuse of refinery spent caustic solution in alkaliactivated infrastructure materials
Over the past half-century, societal awareness of the detrimental effects of environmental pollution resulting from human activity has increased, and this newfound awakening has given an impetus to research on sustainable construction materials. In particular, research efforts are aimed at developing greener alternatives to portland cement, production of which accounts for 5-10% of global anthropogenic carbon dioxide emissions. Alkali-activated materials, which can be produced almost entirely from industrial by-products, have received considerable interest in this regard. Previous studies on waste-based alkali-activated materials have focused almost exclusively on reuse of solid waste (e.g., fly ash, slag); however, these materials require a highly-concentrated solution of alkali-hydroxides and/or alkali-silicates (typically 8-14M) to catalyze geopolymerization. Although the environmental and economic impact associated with consumption of excessive amounts of virgin alkalis and safety concerns associated with handling highly-alkaline solutions could substantially threaten the scalability of these materials, little work has been aimed at addressing these issues. In the current study, aqueous alkaline waste from industrial caustic washing of hydrocarbons (deemed unsuitable for regeneration or purification processes due to the presence of contaminants) was used as an activating solution for alkaliactivated concrete in place of a conventional virgin alkali solution. The impact of impurities in the waste activator, particularly organics and heavy metals, on mechanical properties, temporal reactivity, mineralogy, and thermal stability of the materials was assessed. Results suggested that this toxic waste stream, for which there are currently few options available for beneficial reuse, could be used to produce alkali-activated materials in place of virgin alkalis without compromising performance.