American chemists investigate sequestering CO2 in natural gas brines.

[NNadir]

As we all know by now, nobody knows what to do with fossil fuel waste, the result being that it is simply dumped into the air and water with fatal consequences through the agency of global climate change and toxicity. One of the most important constituents of this waste is represented by carbon dioxide, followed by in importance by acidic species such as nitrogen oxides, and sulfur oxides. Heavy metals from ash, notably mercury, uranium, thorium and the elements of the radiaoctive decay series including radon, and radium are also of some importance.

Rather than stop the production of these dangerous wastes, many schemes have been proposed for dumping them, including the injection of the gaseous forms into rock formations.

In the ASAP section of the journal Energy and Fuels a study has been published examining the carbon dioxide properties of natural gas brines.

In 2001, United States CO2 emissions accounted for 1.57 GtC, which was 24% of the total global carbon releases from CO2.1 Of that 1.57 GtC, 36% was from energy- and industry-related coal combustion. It is also projected that by the year 2025 coal consumption by U.S. electricity generators will increase by 48% from the 2001 level.1 Carbon sequestration, along with increases in efficiency and the advancement of clean-coal technologies, may serve to minimize the environmental impact of coal. With the proximity of U.S. electricity generators to deep saline aquifers of large estimated capacity, geologic sequestration is proposed as a suitable method to reduce CO2 emissions. Capability exists in the technologies currently being explored by energy industries regarding concentrating and transporting CO2 from flue gas, fluid injection into subsurface media, and the characterization of geologic formations. U.S. deep saline aquifers are estimated to provide storage for approximately 130 GtC equivalent, which is approximately 80 times the United States’ total carbon emissions in 2001.1,2 Geologic sequestration in saline aquifers is a complex process with multiple mechanisms for carbon storage. Saline aquifers are deep porous rock formations that are saturated with brine, which is typically rich in various metals. Following the injection of CO2 into the subsurface below a typical depth of 800 m, the mechanism for CO2 storage is initially hydrodynamic as the CO2 is stored as a dense supercritical fluid...

...Conclusions
Calcite formation was induced at temperatures of 150 °C and pressures ranging from 600 to 1500 psi by reacting CO2 with a natural gas well brine of low iron content. The most favorable initial brine pH for calcite formation was approximately 9.0, as opposed to the lower values investigated. During the reactions, the system pH immediately dropped following the introduction of high-pressure CO2 due to the formation of carbonic acid. An experimental reaction time of 18 h revealed little change in system pH following the initial decrease. At the start of the reactions, the liquid-phase composition of various metals, such as Na, Ca, Mg, and Sr, was inversely related to the adjusted pH as minerals have a lower solubility at a high pH. Throughout the course of the reactions, compositional trends in the metals most important for mineral carbonate formation were not identified. Large fluctuations indicate that the system did not reach steady state. ICP-AES data cannot be used to correlate changes in brine composition with pH changes and the precipitation of carbonates using a reaction time of 18 h. XRD has verified that calcite was most abundantly present in the solid products for the reactions with an initial pH of approximately 9.0. No other carbonate minerals, such as magnesite or dolomite, were detected despite the significant brine concentrations of magnesium...

Not surprisingly, the ability of these brines to absorb CO2 and precipitate is carbonates is pH dependent. None of this will of course have any insight into the long term stability of these systems and their possible consequences for future generations.

The most important conclusion is this sentence from the "too little too late heading:"

...Feasibility for an industrial-scale operation to sequester carbon in natural gas well brine is currently limited by the extent that pH needs to be raised and maintained to promote the rapid formation of carbonates...

People may or may not be aware that the raising of pH under these circumstances will involve the input of energy.


The abstract is found here: http://pubs.acs.org/cgi-bin/abstract.cgi/enfuem/asap/abs/ef050115u.html

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