(156e) CO2 Sequestration Via Brine/bauxite Residue Mixture

In recent years, a great deal of concern has been expressed with regard to global climate change and its link to growing atmospheric concentrations of carbon dioxide. In order to decrease the impact of anthropogenic CO2 on global climate, several strategies are under development that will potentially remove CO2 from the atmosphere or decrease CO2 emission. One such strategy involves the capture of CO2 from large point sources (such as fossil fuel-fired power plants) and the long-term storage of CO2 underground. Carbon dioxide may be sequestered in various geological formations, including depleted oil and gas reservoirs, unmineable coal seams, basalt formations, and deep saline aquifers. However, there are additional options for CO2 sequestration that should be considered including the use of industrial waste products. One of the proposed strategies under investigation by the National Energy Technology Laboratory (NETL) is sequestration of CO2 from the atmosphere through promotion of solubility and mineral trapping in Ca, Mg, and Fe-bearing caustic waste streams.

Currently 20-30 billion barrels of saline wastewater are produced annually with the production of oil and gas in the USA. About 35% of this acidic wastewater (pH 3 to 5) is treated and discharged as surface water. Many of the gas/oil-field brines have high concentrations of dissolved Ca, Mg, and Fe ions. Carbonate minerals could be formed in the presence of CO2 under certain conditions. This suggests the possibility of using Ca, Mg, and Fe ions from saline wastewater for CO2 sequestration via the formation of carbonate minerals.

Over 70 million tons of bauxite residues are generated annually when aluminum is extracted from the principal ore, bauxite. The residue is mostly comprised of iron and titanium oxides, silica, calcium carbonate, and unrecoverable alumina and soda. The pH of the liquid is as high as 13.5, and the solids and solid surfaces also contain high alkalinity. The caustic nature of the residue causes concerns associated with long-term environmental liability. Worldwide, there are about 200 million tons of bauxite residues that are mostly stored in tailings ponds. For decades, the aluminum industry has been investigating options for treating, disposing, and using bauxite residue. However, environmentally and economically sound methods and processes are still elusive. Addition of CO2 to this caustic material will not only result in carbonate mineral formation but will also serve to decrease the pH of the residue, making disposal more environmentally sound. Moreover, bauxite residue (pH 13.5) can serve as an effective source of caustic material to treat oil and gas field wastewater brines (pH 3 to 5) for mineral carbonation. The use of bauxite residue/brine to capture and store CO2 will serve to not only help mitigate the impact of anthropogenic CO2 on global warming but will also help neutralize caustic industrial waste for safe storage and reuse.

NETL have explored a novel concept that achieves full neutralization of bauxite residue through reaction with acidic oil and gas field wastewater brines with subsequent carbonation. Experiments are conducted to determine the ability of bauxite residue brine reactant mixtures to absorb and sequester CO2 both from a concentrated stream and as a component of a mixed flue gas. The use of bauxite residue/brine mixtures to capture and store CO2 can serve to not only help mitigate the impact of anthropogenic CO2 on global warming but also serve to achieve complete neutralization of the caustic industrial waste for safe storage and potential reuse.