0. Recovery of Carbon Dioxide
Carbon dioxide is a product of complete combustion of carbonaceous material, such as many fuels, and hence is a component of their combustion flue gases. Carbon dioxide is frequently a component of fermentation and other biological process off-gases. Carbon dioxide is also a component of many naturally occuring gases, including air.

We believe that Austherm has available the physical and chemical property information needed to evaluate and design many of the various options that may be used to recover carbon dioxide from natural and artificial gas mixtures. We are aware of much of the technology that may be used to recover carbon dioxide. Austherm also has available the information needed to calculate other effects associated with particular options for carbon dioxide recovery.

Austherm believes that urgent action is required to mitigate the carbon dioxide emissions from fossil fuel powered utilities. Most studies currently underway have lead times that would not have a significant effect in the necessary time frame.

Austherm believes that practical technology already exists to produce concentrated carbon dioxide product gas from utilities. The main diluent of carbon dioxide in flue gases is the nitrogen (plus argon) from the air used for combustion. Commercial technology exists to produce gas containing 90%vol to 95%vol oxygen from air (e.g. Pressure Swing Adsorption, PSA). Existing utilities are not designed to use oxygen enriched gas in the combustion process. However if flue gas (containing carbon dioxide) was recycled and used to dilute an oxygen-rich combustion gas then existing power station combustion infrastructure would not have to be significantly modified. Austherm believes that this concept would result in product gas containing 90%vol to 95%vol carbon dioxide (dry basis) for direct disposal. This concept would also improve air quality by minimising nitrogen oxide production in utilities during combustion.

1. Temporary Ocean Disposal of Carbon Dioxide
Because the oceans are a natural sink for about half of the atmospheric carbon dioxide emissions, but the rate of transfer from atmosphere to ocean is relatively slow, it is believed that temporary direct ocean disposal of carbon dioxide would reduce the maximum or peak concentration that carbon dioxide might attain in the atmosphere and hence reduce the extent of climatic changes. As the residence time of carbon dioxide in the oceans is finite, possibly as short as 100 years, the oceans cannot be considered to be a permanent sink for carbon dioxide.

The solubility of carbon dioxide in aqueous solutions decreases with increasing temperature. Consequently global warming would reduce the capacity of the oceans to act as a reservoir for carbon dioxide.

A general ocean circulation pattern is downward at the poles and upward at the equator. Degassing of rising ocean water at the equator would create a "gas-lift" effect due to the average lower density and would increase this circulation pattern. This would increase the risk of rapid release of any carbon dioxide held in deep ocean waters.

Papers from Austherm principals describing ocean disposal of carbon dioxide are listed below. We have considered disolution of carbon dioxide in sea water, the formation of a separate liquid carbon dioxide phase and the formation of solid carbon dioxide hydrate. We have also considered the possible chemical changes in the surrounding sea water and interaction sea water made acidic by carbon dioxide with various sediment minerals.

M.W.Wadsley, "Thermodynamics of Multi-Phase Equilibria in the CO2-Seawater System" pp.195-216 in Handa,N. and Ohsumi,T. Eds, "Direct Ocean Disposal of Carbon Dioxide" Terrapub, Tokyo, 1995.

M.W.Wadsley, "Thermodynamics of Multi-Phase Equilibria in the CO2-Seawater System" ICO-2 Second International Symposium on Interaction between CO2 and Ocean, Tsukuba, Japan, 1-2 June, 1993.

T.R.A. Davey and M.W.Wadsley "Sea Water Dissolution - An Interim Solution to Industrial Carbon Dioxide Emissions" pp.33-38 in "Mineral Fuels and the Greenhouse Effect Seminar" 25-27 July, 1989, Aus.I.M.M., Melbourne

2. Sequestration and Geosequestration of Carbon Dioxide
Carbon dioxide may react with particular natural minerals to form stable solid products, a process known as non-reductive sequestration. Carbon dioxide may react with other natural minerals to form reduced products, a process known as reductive sequestration. Both processes are described as mineral sequestration.

Austherm Pty Ltd has available the physical and chemical property information needed to evaluate and design the various sequestration and geosequestration process options, including calculation of the mineral volume changes that will be involved and calculation of the chemical interaction of aqueous solutions of carbon dioxide with natural minerals. The latter calculation is of interest in predicting the stability of potential reservoirs. Austherm personnel have studied geosequetration chemical equilibria.

Austherm has performed calculations with respect to mineral sequestration of carbon dioxide with calcium- and magnesium-containing minerals. Austherm predicts that calcium-containing minerals or calcium-rich minerals will be superior to magnesium-containing minerals or magnesium-rich minerals for long term mineral sequestration of carbon dioxide. Austherm believes that some proposed mineral sequestration schemes involving magnesium silicates might result in the eventual release of carbon dioxide back into the environment.

Austherm believes that direct mineral sequestration of carbon dioxide with calcium silicate minerals represents one of the cheapest and most readily implemented means of removing carbon dioxide from the atmosphere.

Austherm has considered technology that might be used to seal carbon dioxide geosequestration reservoirs that are leaking into the environment.

Austherm is one of the few organisations to have software and thermochemical data able to predict and validate equilibria over a range of pressures and temperatures from ambient to elevated values between a gas phase containing carbon dioxide, an aqueous phase containing significant concentrations of ionic and molecular solutes, and solid phases such as natural minerals, possible precipitates and gas-hydrates. Many available codes lack at least one of these essential capabilities. The Austherm code can indicate the potential for chemical breakout or pore plugging in sequestration reservoirs.

3. Sustainable Recycling of Carbon Dioxide
A sustainable energy cycle could involve the use of solar- derived energy to convert carbon dioxide into fuels and petrochemicals. Austherm Pty Ltd principals have investigated the conversion of carbon dioxide into formic acid which may be considered to be an energy-rich intermediate to be used in the production of fuels and chemicals. This concept was described in the paper given below.

Go to AUSTHERM Pty Ltd Formfuel Page

M.W. Wadsley, "The FORMFUEL Process" preprint of a paper presented at the 1980 ANZAAS Congress, University of Queensland, 1980

Sustainable Methane from Atmospheric Carbon Dioxide
Some metal carbonates react chemically with hydrogen gas to form methane plus the metal oxide or the metal hydroxide.

MCO₃ + H₂ = MO + CH₄ + H₂O
MCO₃ + H₂ = M(OH)₂ + CH₄ + H₂O

Some metal oxides and/or metal hydroxides react with carbon dioxide in the Earth's atmosphere to form metal carbonates thus providing a means of carbon capture.

MO + CO₂ = MCO₃
M(OH)₂ + CO₂ = MCO₃ + H₂O

Combination of this chemistry with the electrolysis of water using solar-derived electricity to obtain hydrogen gas leads to a sustainable process for the production of methane, that is, synthetic natural gas.

The water for electrolysis could be absorbed from the Earth's atmosphere and from the product methane using concentrated aqueous solutions of lithium chloride, lithium bromide or zinc chloride.

Sulfuric acid or phosphoric acid could be used as the water electrolysis medium.

A process based on the above chemistry and engineering could be located in dry, sunny regions and would not compete with land or resources used for food production or human habitation. Some such regions also have existing methane reticulation pipelines and infrastructure.

Bibliography

Yoshida N.1; Hattori T.1; Komai E.1; Wada T.1.
"Methane formation by metal-catalyzed hydrogenation of solid calcium carbonate"
Catalysis Letters, Volume 58, Numbers 2-3, 1999 , pp. 119-122(4)

John Emsley
"Let them burn limestone . . ."
New Scientist Print Edition 05 September 1992

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Recovery of Water from Air

The recovery of water from air is now a commercial reality albeit on a small scall best suited, for example, to military and emergency uses.

Aqua Sciences™ Inc atmospheric water extraction machines can be furnished and installed in disaster sites, urban, rural and isolated communities to capture, purify and dispense water of superior quality on demand. Machines can provide between 350-1,200 USgallons of water per day with a target price of approximately $US0.25 per gallon dependent upon actual conditions and costs. Machines may be powered by electricity or a self-contained diesel generator and are environmentally friendly due to lower energy requirements and no harmful or toxic by-products

The existence and commercial availability of this technology is hopefully a fore-runner of the eventual commercial availability of technology to provide large scale quantities of water from air and also a fore-runner of cheaper technology that would be accessible to disadvantaged peoples.

The theoretical amount of energy needed to recover liquid water from air is not large. What is required in the ingenuity to achieve it by appropriate technology. Austherm has access to computer software that calculates the theoretical energy requirements of such processes.

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Salinity

L.A.Chambers, M.W.Wadsley and G.J.Brereton "Modelling Halite Formation and Brine Densities - A Comparison of Non- Marine and Seawater Brines", pp.533-538 in "Seventh Symposium on Salt", Vol.1, Elsevier, Amsterdam, 1993. (6-9 April, 1992 Kyoto, Japan)

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Metals

M.W.Wadsley "Prediction of Equilibrium Mercury Partial Pressures over Aqueous Halide Solutions" pp. 17-22 in Proceedings 6th AusIMM Extractive Metallurgy Conference 3-6 July, 1994, Brisbane, Australia, The AusIMM, Melbourne

M.W.Wadsley and F.Lawson "Complementary Hydro- and Bio-Metallurgical Processes in the Pyrometallurgical Processing of Complex Materials and Wastes" pp.303-317 in Nilmani,M., Lehner,T. and Rankin,W.J. Eds "Pyrometallurgy for Complex Materials and Wastes" TMS-AIME, Warrendale, 1994

M. Wadsley, "Metals and Energy Options", in M. Diesendorf (Ed.), Energy and People: Social Implications of Different Energy Futures, proceedings of the National Conference on Energy and People, Canberra, 7-9 Sept. 1978 (Society for Social Responsibility in Science, Canberra, 1979), pp. 167-169.

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Radioactivity in Extractive Metallurgy

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