Mineral Carbonation of CO2 with Steel Slags and Waste Concrete

The use of fossil fuels faces challenge due to the vast amounts of Carbon Dioxide (CO2) released into the atmosphere. The CO2 concentration has increased by 30% since the industrial revolution. (Olajire 2013)

Therefore, it is important to adapt new technologies within industries in order to reduce the emissions.  Carbon Capture and Storage (CCS) technology become an important research topic for CO2 reduction and carbon capture utilization and storage (CCUS) is increasingly investigated in research.

Among the various routes proposed, mineral carbonation represents a thermodynamically favorable and safe alternative route to the sequestration of CO2. It can be described as the reaction of CO2 with alkaline earth metals occurring in silicate minerals. It forms stable carbonate minerals.

Potential feedstock materials for mineral carbonation could be mineral rocks and alkaline residues. The investigations indicated that industrial wastes required less degree of ore-treatment and has less energy-intensive carbonation conditions, in comparison to mineral rocks. (Costa, Baciocchi et al. 2007)

Construction and demolition processes generate a lot of waste (inert, inorganic and organic material: clay, stone, gravel, tiles, concrete, cementitious material, aggregates, sand and steel). It is estimated that about 146 million tons and 11 million tons waste are generated annually in the United States and Canada respectively. (Venta and Nisbet 2001)

Approximately 42% of the total quantity of waste is typically reused or recycled and the rest is transferred to the landfill (Venta and Nisbet 2001). Concrete represents more than 50% of construction and demolition wastes. (Nisbet, Venta et al. 2012) This considerable quantity should be re-used in the proper way, especially in CO2 sequestration.

In fact, construction and demolition waste concrete have the potential to absorb CO2. Naturally, concrete is carbonated by atmospheric CO2. It is due to the presence of reactive elements, essentially calcium. It is s a slow and continual process beginning from the outer surface of the concrete.

On the other hand, steel industry plants produce large amounts of by-product. The main solid by-products generated during steel manufacturing are slags. The annual world production of slags from iron and steel industries reaches almost 50 million tons. (Proctor, Fehling et al. 2000) Those materials contain high concentrations of calcium which imparts their alkaline properties for mineral carbonation.

In the United States, it is estimated that industrial alkaline by-products have the potential to mitigate approximately 7.6 Mt CO2/yr, of which 7.0 Mt CO2/yr are CO2 sequestered through mineral carbonation and 0.6 Mt CO2/yr are CO2 emissions avoided through reuse as synthetic aggregate. (Kirchofer, Becker et al. 2013)

The main advantages by using alkaline residues are: material availability, reactivity and low-energy pre-treatment. It represents feedstock material for niche application of mineral carbonation process. The cost of mining and material transportation could be also avoided.
In term of economic, the current processes using ex-situ mineral carbonation are limited according to its high costs, which range from $50 to $300 per ton CO2 sequestered. (Sanna, Uibu et al. 2014) It is due to the high energy intensity, the low reaction conversion, and the slow reaction kinetics.

In this project, the main objective is to develop economical mineral carbonation process. In that way, we choose to work at mild conditions without using chemical products, in order to limit energy and chemical consumption. Valorization of products is considered. Waste concrete and steel slags are used as raw material.
The waste concrete is sampled from the “eco-center” of Quebec-city. Steel slags are recovered from steel industry. It corresponds to secondary waste produced during the production of steel in electric arc furnaces (EAF).
Tests in direct aqueous route have been carried out in batch reactor. Process parameters are studied and optimized by using Box-Benkhen design technique (Response Surface Methodology).
The tests are conducted at moderate pressure and ambient temperature. Gas stream used simulates industrial flue gas composition.
The reuse of solid residue in successive gas batches is studied to improve the CO2 sequestration capacity of the material.
The continuous mode will be tested in our next experiments. The economic feasibility will be evaluated and compared with current process costs.

References

Costa, G., R. Baciocchi, et al. (2007). "Current status and perspectives of accelerated carbonation processes on municipal waste combustion residues." Environmental Monitoring and Assessment 135(1-3): 55-75.
Kirchofer, A., A. Becker, et al. (2013). "CO2 Mitigation Potential of Mineral Carbonation with Industrial Alkalinity Sources in the United States." Environmental Science & Technology 47(13): 7548-7554.
Nisbet, M., G. Venta, et al. (2012). "Demolition and deconstruction: Review of the current status of reuse and recycling of building materials." Retrieved April 3, 2012, from ftp://ftp.tech-env.com/pub/Retrofit/AWMA%20paper_wm1b.pdf.
Olajire, A. A. (2013). "A review of mineral carbonation technology in sequestration of CO2." Journal of Petroleum Science and Engineering 109(0): 364-392.
Proctor, D. M., K. A. Fehling, et al. (2000). "Physical and Chemical Characterisctics of Blast Furance, Basic Oxygem Furnace, and Electric Arc Furnace Steel Industry Slags." Environ. Sci. Technol. 34: 1576-1582.
Sanna, A., M. Uibu, et al. (2014). "A review of mineral carbonation technologies to sequester CO2." Chemical Society Reviews.
Venta, G. J. and M. Nisbet (2001). Waste Streams from Building Construction and Demolition with a Specific Focus on Concrete. Canada. Ottawa.