Using CaO- and MgO-rich industrial waste streams for carbon sequestration

To prevent rapid climate change, it will be necessary to reduce net anthropogenic CO 2 emissions drastically. This likely will require imposition of a tax or tradable permit scheme that creates a subsidy for negative emissions. Here, we examine possible niche markets in the cement and steel industries where it is possible to generate a limited supply of negative emissions (carbon storage or sequestration) cost-effectively. Ca(OH) 2 and CaO from steel slag or concrete waste can be dissolved in water and reacted with CO 2 in ambient air to capture and store carbon safely and permanently in the form of stable carbonate minerals (CaCO 3). The kinetics of Ca dissolution for various particle size fractions of ground steel slag and concrete were measured in batch experiments. The majority of available Ca was found to dissolve on a time scale of hours, which was taken to be sufficiently fast for use in an industrial process. An overview of the management options for steel slag and concrete waste is presented, which indicates how their use for carbon sequestration might be integrated into existing industrial processes. Use of the materials in a carbon sequestration scheme does not preclude subsequent use and is likely to add value by removing the undesirable qualities of water absorption and expansion from the products. Finally, an example scheme is presented which could be built and operated with current technology to sequester CO 2 with steel slag or concrete waste. Numerical models and simple calculations are used to establish the feasibility and estimate the operating parameters of the scheme. The operating cost is estimated to be US$8/t-CO 2 sequestered. The scheme would be important as an early application of technology for capturing CO 2 directly from ambient air.