Assessing the Potential of Mineral Carbonation with Industrial Alkalinity Sources in the U.S

Abby Kirchofer, Adam Brandt, Sam Krevor, Valentina Prigiobbe, Austin Becker, Jennifer Wilcox
2013 Energy Procedia  
The availability of industrial alkalinity sources is investigated to determine their potential for the mineral carbonation of CO 2 from point-source emissions in the United States. The available aggregate markets are investigated as potential sinks for the mineralized CO 2 products. Additionally, a life-cycle assessment of aqueous mineral carbonation suggests that a variety of alkalinity sources and process configurations are capable of net CO 2 reductions. The CO 2 storage potential of mineral
more » ... carbonation was estimated using the life-cycle assessment results and alkalinity source availability. et al. / Energy Procedia 37 ( 2013 ) 5858 -5869 5859 conditions. Both natural and industrial alkalinity sources exist and have been investigated for mineral carbonation. While naturally available alkalinity sources are abundant, their use as alkalinity resources is associated with high-energy costs due to the mining and pre-processing (e.g., grinding) required. [5] Renforth et al. investigated industrial alkalinity source (e.g., aggregate and mine waste, construction and demolition waste, iron and steel slag, and fuel ash) availability for mineral carbonation, and estimate global production and sequestration potential are 7 17 Gt/yr and 67 1217 Mt-CO 2 /yr, respectively; however, the sequestration potential results are based on the assumption that the divalent cation content of the material is completely converted to carbonate. [6] Despite the promise of mineral carbonation technologies, to date accounting of alkalinity source production and sequestration potential is limited due to lack of accurate alkalinity source availability/production data, variation in chemical and mineralogical content of alkalinity sources, and inconsistent methods of estimating potential. The present work focuses on industrial alkalinity sources, due to their availability and reactivity, and assesses the feasibility of using industrial alkalinity sources based upon availability, geography, and a life-cycle assessment of their carbonation via aqueous processes. Common industrial-sourced alkaline byproducts include coal fly ash (FA)[5], electric arc furnace (EAF) dust and steel-making slag [7] [8] [9] [10] [11] , waste concrete[7, 12] and cement kiln dust (CKD) [12] [13] [14] , municipal waste incinerator (MSWI) ash [15] [16] [17], asbestos mine tailings [5, 18] and bauxite residue [19] . In addition to the potential CO 2 mitigation associated with the mineral carbonation of industrial alkalinity sources, this process adds significant environmental benefit in the handling of industrial byproducts that may otherwise be considered as waste (or hazardous waste) materials. For instance, mineral carbonation has been shown to immobilize trace metals in alkaline waste byproducts [20, 21] . Due to the abundance of the alkaline byproduct sources from coal-fired power, cement manufacturing, and steel production industries, the focus of the current study is the potential mitigation of CO 2 via mineralization using CKD, FA, and SS. Cement kiln dust is an alkali-rich dust produced during cement manufacturing at a ratio of approximately 0.15 0.20 tons CKD per ton cement. [22] Approximately 5.2 million metric tons (Mt) of CKD are produced annually in the U.S. The typical weight percent ranges of calcium oxide (CaO) and magnesium oxide (MgO) in CKD are 38 50 and 0 2, respectively.[23] Cement kiln dust is a finegrained solid, with particle size on the order of micrometers ( m) [14] , and is an ideal source of alkalinity for mineral carbonation due to its composition and small particle size. [24] Huntzinger et al. investigated carbonation of CKD at conditions of approximately 98% relative humidit pressure of CO 2 of 0.8 atm, and found that the degree of carbonation correlates directly with the mass fraction of calcium oxide and hydroxide content of the CKD.[14] The degree of carbonation at a given time, t, is defined as the mass of CO 2 taken up by the sample, M CO2 (t), divided by the maximum theoretical carbonation of the sample. The average degree of carbonation was found to be approximately 77% over 8 days, with 90% of the carbonation occurring in less than 2 days. [14] Fly ash is a residue generated from the combustion of coal, and is typically captured after coal combustion by air pollution control devices such as fabric filters or electrostatic precipitators. Fly ash comprises approximately 60% of all coal combustion waste, and in the U.S. alone coal-fired power plants produce approximately 42.4 Mt of FA annually. [25] Fly ash is a complex, amorphous, and chemically heterogeneous material, and its physicochemical properties depend on the composition of the feed coal and the operating conditions of the coal-fired power plant. In the U.S., coal is ranked as one of four broad categories, listed in order of increasing rank (purity): lignite, subbituminous, bituminous, and anthracite. While FA is often classified based on these ranks, it is important to note that FA composition even within these categories varies greatly due to coal heterogeneity. In general, inorganic minerals comprise approximately 90-99% of fly ash, while organic compounds makeup up approximately 1-9%. [26] The inorganic minerals consist primarily of silicon dioxide (SiO 2 ) and CaO, along with other metal oxides
doi:10.1016/j.egypro.2013.06.510 fatcat:crqh6w3ilfbslbrozna6bvd42q