Negative emissions technologies will play an important role in preventing 2 °C warming by 2100. The next decade is critical for technological innovation and deployment to meet mid-century carbon removal goals of 10−20 GtCO 2 /yr. Direct air capture (DAC) is positioned to play a critical role in carbon removal, yet remains under paced in deployment efforts, mainly because of high costs. This study outlines a roadmap for DAC cost reductions through the exploitation of low-temperature heat, recent U.S. policy drivers, and logical, regional end-use opportunities in the United States. Specifically, two scenarios are identified that allow for the production of compressed high-purity CO 2 for costs ≤$300/tCO 2 , net delivered with an opportunity to scale to 19 MtCO 2 /yr. These scenarios use thermal energy from geothermal and nuclear power plants to produce steam and transport the purified CO 2 via trucks to the nearest opportunity for direct use or subsurface permanent storage. Although some utilization pathways result in the re-emission of CO 2 and cannot be considered true carbon removal, they would provide economic incentive to deploying DAC plants at scale by mid-century. In addition, the federal tax credit 45Q was applied for qualifying facilities (i.e., producing ≥100 ktCO 2 /yr).
Mineral carbonation (MC) is a form of carbon capture and storage that reacts CO2 with alkaline feedstock to securely store CO2 as solid carbonate minerals. To improve process economics and accelerate commercial deployment, research has increased around product utilization, where markets exist primarily in the construction industry. This review assesses the potential for advancing MC product utilization to decrease CO2 emissions toward neutral, or even negative, values. First, the literature surrounding the current state and challenges for indirect MC processes is reviewed, indicating that process intensification and scale‐up are important areas for further research. Alkalinity sources available for MC are examined, differentiating between those sourced from industrial processes and mining operations. Investigation of possible end uses of carbonate products reveals that further CO2 avoidance can be achieved by replacing conventional carbon‐intensive products. Companies that are currently commercializing MC processes are categorized based on the feed used and materials produced. An analysis of company process types indicates that up to 3 GtCO2 year–1 could be avoided globally. It is suggested that upcoming commercial efforts should focus on the carbonation of industrial wastes located near CO2 sources to produce precast concrete blocks. Carbonation of conventional concrete shows the highest potential for CO2 avoidance, but may face some market resistance. Carbonation of Mg silicates lacks sufficient market demand and requires the development of new high‐value products to overcome the expense of mining and feed preparation. It is suggested that research focus on enhanced understanding of magnesia cement chemistry and the development of flame‐retardant mineral fillers. © 2019 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons, Ltd.
The iron and steel industry has played a large part in global industrialization and now accounts for about 7% of global anthropogenic CO2 emissions. As thorough progress has already been made in minimizing the carbon footprint through process optimization efficiency increases, further emissions reductions could be achieved through carbon capture and sequestration (CCS). In an analysis of existing production capacity around the globe, most production facilities will likely continue to run in the coming decades, presenting an opportunity to install retrofit CCS technologies onto existing plants, like absorption and oxyfuel top gas recycling. More advanced CCS technologies such as hydrogen direct reduction and smelting reduction should be installed within the upcoming production plants being constructed. Current international initiatives like ULCOS and HYBRIT, evolving government policies and incentives, and pilot projects are helping to improve process economics and shedding light on industrial viability.
Global efforts to combat climate change call for methods to capture and store CO2. Meanwhile, the global transition away from fossil energy will result in increased production of tailings (i.e., wastes) from the mining of nickel and platinum group metals (PGMs). Through carbon mineralization, CO2 can be permanently stored in calcium- and magnesium-bearing mine tailings. The Stillwater mine in Nye, Montana produces copper, nickel, and PGMs, along with 1 Mt of tailings each year. Stillwater tailings samples have been characterized, revealing that they contain a variety of mineral phases, most notably Ca-bearing plagioclase feldspar. Increases in inorganic carbon in the tailings and ion concentration in the tailings storage facilities suggest carbonation has taken place at ambient conditions over time within the tailings storage facilities. Two experiments were performed to simulate carbon mineralization at ambient temperature and pressure with elevated CO2 concentration (10% with N2), revealing that less than 1% of the silicate-bound calcium within the tailings is labile, or easily released from silicate structures at low-cost ambient conditions. The Stillwater tailings could be useful for developing strategies of waste management as production of nickel and PGM minerals increases during the global transition away from fossil energy, but further work is needed to develop a process that can realize their full carbon storage potential.
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