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The potential of enhanced weathering in the UK

Author(s): Renforth P

Published: July, 2012

Publisher: International Journal of Greenhouse Gas Control

DOI: 10.1016/j.ijggc.2012.06.011

Tags: Enhanced Weathering

URL: http://www.sciencedirect.com/science/article/pii/S1750583612001466

Abstract: Enhanced weathering is the process by which carbon dioxide is sequestered from the atmosphere through the dissolution of silicate minerals on the land surface. The carbon capture potential of enhanced weathering is large, yet there are few data on the effectiveness or engineering feasibility of such a scheme. Here, an energy/carbon balance is presented together with the associated operational costs for the United Kingdom as a case study. The silicate resources are large and could theoretically capture 430 billion tonnes (Gt) of CO2. The majority of this resource is contained in basic rocks (with a carbon capture potential of -0.3 tCO2 t-1 rock) There are a limited number of ultrabasic formations (0.8 tCO2 t-1 rock)with a total carbon capture potential of 25.4 GtCO2. It is shown that the energy costs of enhanced weathering may be 656–3501 kWh tCO2−1 (net CO2 draw-down, which accounts for emissions during production) for basic rocks and 224–748 kWh tCO2−1 for ultrabasic rocks. Comminution and material transport are the most energy intensive processes accounting for 77–94% of the energy requirements collectively. The operational costs of enhanced weathering could be £44–361 tCO2−1 ($70–578 tCO2−1) and £15–77 tCO2−1 ($24–123 tCO2−1) for basic and ultrabasic rocks respectively. Providing sufficient weathering rates full exploitation of this resource is not possible given the environmental and amenity value of some of the rock formations. Furthermore, the weathering rate and environmental impact of silicate mineral application to the land surface is not fully understood, and further investigation in this area is required to reduce the uncertainty in the estimated costs presented here.


Passive Sequestration of Atmospheric CO2 through Coupled Plant-Mineral Reactions in Urban soils

Author(s): Manning DAC, Renforth P

Published: May, 2012

Publisher: Environmental Science and Technology

DOI: 10.1021/es301250j

Tags: Carbon Cycle

URL: http://pubs.acs.org/doi/abs/10.1021/es301250j

Abstract: Photosynthetic removal of CO2 from the atmosphere is an important planetary carbon dioxide removal mechanism. Naturally, an amount equivalent to all atmospheric carbon passes through the coupled plant–soil system within 7 years. Plants cycle up to 40% of photosynthesized carbon through their roots, providing a flux of C at depth into the soil system. Root-exuded carboxylic acids have the potential to supply 4–5 micromoles C hr–1g–1 fresh weight to the soil solution, and enhance silicate mineral weathering. Ultimately, the final product of these root-driven processes is CO2, present in solution as bicarbonate. This combines with Ca liberated by corrosion associated with silicate mineral weathering to enter the soil–water system and to produce pedogenic calcium carbonate precipitates. Combining understanding of photosynthesis and plant root physiology with knowledge of mineral weathering provides an opportunity to design artificial soils or to plan land use in ways that maximize removal and sequestration of atmospheric CO2 through artificially enhanced pedogenic carbonate precipitation. This process requires relatively low energy and infrastructure inputs. It offers a sustainable carbon dioxide removal mechanism analogous to the use of constructed wetlands for the passive remediation of contaminated waters, and is likely to achieve wide public acceptance.


Laboratory carbonation of artificial silicate gels enhanced by citrate: Implications for engineered pedogenic carbonate formation

Author(s): Renforth P, Manning DAC

Published: September, 2011

Publisher: International Journal of Greenhouse Gas Control

DOI: 10.1016/j.ijggc.2011.09.001

Tags: Enhanced Weathering, Carbon Cycle

URL: http://www.sciencedirect.com/science/article/pii/S175058361100171X

Abstract: Carbon dioxide sequestration through carbonation of calcium or magnesium-rich silicate materials is a geoengineering technology that could mitigate a substantial proportion of anthropogenic emissions. Contemporary mineral carbonation research considers optimising this process to overcome energy requirements for mineral pre-treatment and reactor operation. This paper compliments previous studies in this area by demonstrating enhanced weathering through the action of organic acids including those exuded by plant roots. Batch weathering experiments, conducted as part of this study, with hydrated cement gels have shown that up to 80-85% of calcium is leached from the material in 5h when exposed to solutions containing citrate anions, at an approximate log weathering rate between -8.26 and -6.86molCacm-2s-1, which is much more rapid than observed carbonate precipitation rates in previous studies for urban soils that contain cement-derived minerals. Thus Ca availability is not rate limiting. Coupled silicate-dissolution/carbonate precipitation reactions provide a carbon sequestration function that can be designed into soils specifically engineered to facilitate carbon capture.


Designing a carbon capture function into urban soils

Author(s): Renforth P, Edmondson J, Leake JR, Gaston KJ, Manning DAC

Published: June, 2011

Publisher: Proceedings of the Institution of Civil Engineers: Urban Design and Planning

DOI: 10.1680/udap.2011.164.2.121

Tags: Terrestrial Carbon Storage, Carbon Cycle

URL: http://www.icevirtuallibrary.com/content/article/10.1680/udap.2011.164.2.121

Abstract: Soils, if designed and managed correctly, can retain carbon from the atmosphere as accumulated organic matter, refractory forms of carbon (e.g. biochar) or stable, inorganic, carbonate minerals. This soil 'carbon capture function' is highly applicable to the constructed environment in urban areas and should be considered when planning for new or existing developments. The total carbon capture potential of soils in cities may be as high as 7 Mt/year within the UK using biochar and accumulated carbonate minerals, which is equivalent in significance to other forms of geoengineering. Furthermore, soil and vegetation management practices may be implemented to accumulate plant-derived organic carbon in urban soils. The potential for substantial soil-based carbon sequestration in urban environments has yet to be realised, and the varied praxis of soil carbon capture presents accreditation and regulatory challenges to the planning system which need to be resolved.


Silicate production and availability for mineral carbonation

Author(s): Renforth P, Washbourne CL, Taylder J, Manning DAC

Published: February, 2011

Publisher: Environmental science & technology

DOI: 10.1021/es103241w

Tags: Enhanced Weathering

URL: http://pubs.acs.org/doi/abs/10.1021/es103241w

Abstract: Atmospheric carbon dioxide sequestered as carbonates through the accelerated weathering of silicate minerals is proposed as a climate change mitigation technology with the potential to capture billions of tonnes of carbon per year. Although these materials can be mined expressly for carbonation, they are also produced by human activities (cement, iron and steel making, coal combustion, etc.). Despite their potential, there is poor global accounting of silicates produced in this way. This paper presents production estimates (by proxy) of various silicate materials including aggregate and mine waste, cement kiln dust, construction and demolition waste, iron and steel slag, and fuel ash. Approximately 7−17 billion tonnes are produced globally each year with an approximate annual sequestration potential of 190−332 million tonnes C. These estimates provide justification for additional research to accurately quantify the contemporary production of silicate minerals and to determine the location and carbon capture potential of historic material accumulations.


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