Sequestration of CO2 in Mixtures of Bauxite Residue and Saline Wastewater

Experiments were conducted to explore the concept of beneficially utilizing mixtures of caustic bauxite residue slurry (pH 13) and produced oil-field brine to sequester carbon dioxide from flue gas generated from industrial point sources. Data presented herein provide a preliminary assessment of the overall feasibility of this treatment concept. The Carbonation capacity of bauxite residue/brine mixtures was considered over the full range of reactant mixture combinations in 10% increments by volume. A bauxite residue/brine mixture of 90/10 by volume exhibited a CO2 sequestration capacity of greater than 9.5 g/L when exposed to pure CO2 at 20 °C and 0.689 MPa (100 psig). Dawsonite and calcite formation were predicted to be the dominant products of bauxite/brine mixture carbonation. It is demonstrated that CO2 sequestration is augmented by adding bauxite residue as a caustic agent to acidic brine solutions and that trapping is accomplished through both mineralization and solubilization. The product mixture solution was, in nearly all mixtures, neutralized following carbonation. However, in samples (bauxite residue/brine mixture of 90/10 by volume) containing bauxite residue solids, the pH was observed to gradually increase to as high as 9.7 after aging for 33 days, suggesting that the CO2 sequestration capacity of the samples increases with aging. Our geochemical models generally predicted the experimental results of carbon sequestration capacities and solution pH.