October 2008 Issue - Volume 4, Number 5

Carbon Dioxide Sequestration

David R. Cole and Eric H. Oelkers – Guest Editors

Overview

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Overview

The geoscientific and economic significance of the PGE is immense. Due to their extreme siderophile and chalcophile behaviour, the PGE are highly sensitive tracers of geological processses involving metal and sulfide phases. Furthermore, there are two radioactive decay series involving PGE, which combine both lithophile and chalcophile characteristics in various parent or daughter elements. PGE con- sequently offer insight into a wide range of geo- logical processes that no other group of ele- ments can provide. The PGE are also very important economically, primarily due to their “noble” character in common applications such as jewelry, electrodes, catalysts, and fuel cell technology. Unfortunately, the PGE are also bioavailable as potential toxins to organisms in the natural environment. Their widespread use, particularly in automotive catalytic converters, makes their environmental behavior a matter of increasing concern. This issue of Elements will provide an overview of our current understanding of the distribution of PGE and their isotopes in the Earth and solar system, and what this knowledge tells us about the workings of our planet, about extraction of PGE resources, and about the environmental risks attendant on their use.

Carbon Dioxide Sequestration A Solution to a Global Problem
CO2 Capture and Transport
Ocean Storage of CO2
CO2 Sequestration in Deep Sedimentary Formations
Mineral Carbonation of CO2

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Thematic Articles

Carbon Dioxide Sequestration A Solution to a Global Problem

Human and industrial development over the past hundred years has led to a huge increase in fossil fuel consumption and CO2 emissions, causing a dramatic increase in atmospheric CO2 concentration. This increased CO2 is believed to be responsible for a significant rise in global temperature over the past several decades. Global-scale climate modeling suggests that the temperature increase will continue, at least over the next few hundred years, leading to glacial melting and rising sea levels. Increased atmospheric CO2 also leads to ocean acidification, which will have drastic consequences for marine ecosystems. In an attempt to solve these problems, many have proposed the large-scale sequestration of CO2 from our atmosphere. This introductory article presents a summary of some of the evidence linking increasing atmospheric CO2 concentration to global warming and ocean acidification and our efforts to stem this rise though CO2 sequestration.

CO2 Capture and Transport

By Edward S. Rubin

International interest in CO2 capture and storage (CCS), as a method of reducing carbon dioxide emissions linked to global climate change, has been growing in recent years. CCS is particularly attractive for large industrial facilities, especially electric power plants, which contribute a large share of global CO2 emissions from combustion of coal and other fossil fuels. This paper describes the current status of technologies to capture CO2 and transport it to a storage site. The performance and cost of capture technologies are discussed, along with related environmental issues and the outlook for improved, lowercost strategies. The key need now is financing of full-scale demonstrations of CCS at the various types of large coal-based power plants.

Ocean Storage of CO2

By E. Eric Adams, Ken Caldeira

One method for minimizing climate change is to capture CO2 from power plants and inject it into the deep ocean, thus reducing the magnitude and rate of change of CO2 concentration in the atmosphere and the surface ocean. Many discharge options are possible, with varied mixing and retention characteristics. The ocean’s capacity is vast, and mathematical models suggest that injected CO2 could remain sequestered for several hundred years. While theoretical and laboratory studies support the viability of ocean storage, field experiments are necessary to realistically evaluate the environmental impact.

CO2 Sequestration in Deep Sedimentary Formations

By Sally M. Benson, David R. Cole

Carbon dioxide capture and sequestration (CCS) in deep geological formations has recently emerged as an important option for reducing greenhouse emissions. If CCS is implemented on the scale needed to make noticeable reductions in atmospheric CO2, a billion metric tons or more must be sequestered annually—a 250 fold increase over the amount sequestered today. Securing such a large volume will require a solid scientific foundation defining the coupled hydrologic–geochemical–geomechanical processes that govern the long-term fate of CO2 in the subsurface. Also needed are methods to characterize and select sequestration sites, subsurface engineering to optimize performance and cost, approaches to ensure safe operation, monitoring technology, remediation methods, regulatory overview, and an institutional approach for managing long-term liability.

Mineral Carbonation of CO2

By Eric H. Oelkers, Sigurdur R. Gislason, Juerg Matter

Asurvey of the global carbon reservoirs suggests that the most stable, long-term storage mechanism for atmospheric CO2 is the formation of carbonate minerals such as calcite, dolomite and magnesite. The feasibility is demonstrated by the proportion of terrestrial carbon bound in these minerals: at least 40,000 times more carbon is present in carbonate rocks than in the atmosphere. Atmospheric carbon can be transformed into carbonate minerals either ex situ, as part of an industrial process, or in situ, by injection into geological formations where the elements required for carbonate-mineral formation are present. Many challenges in mineral carbonation remain to be resolved. They include overcoming the slow kinetics of mineral–fluid reactions, dealing with the large volume of source material required and reducing the energy needed to hasten the carbonation process. To address these challenges, several pilot studies have been launched, including the CarbFix program in Iceland. The aim of CarbFix is to inject CO2 into permeable basaltic rocks in an attempt to form carbonate minerals directly through a coupled dissolution– precipitation process.