Carbon dioxide sequestration on steel slag

Carbon dioxide sequestration on steel slag

8

Liwu Mo Nanjing Tech University, Jiangsu, China

8.1

Introduction

Mineral carbonation is a promising and safe approach for permanent sequestration of CO2 via the transformation of CO2 into various carbonates. There are several elements that can be carbonated, but alkaline earth metals in terms of calcium and magnesium are the most suitable for carbonation due to their abundance and insolubility in nature (Sipil€a et al., 2008). Natural minerals rich in calcium or magnesium, for example, olivine (Mg2SiO4), serpentine (Mg3Si2O5(OH)4), and wollastonite (CaSiO3), are used as the feedstock for providing the Mg and Ca for the formation of carbonates. However, it could be very energy intensive for the processes of mining, mineral pretreatment (i.e., crashing, grinding, and milling, etc.), kinetic enhancement on the carbonation via temperature elevation, or acid dissolution of the natural minerals. Iron could also be employed for carbonation, but considering it is a valuable mineral resource for other industrial applications, it is less suitable for large-scale carbonation. In addition to the natural minerals rich in Mg and Ca, there are also some industrial solid wastes containing large amounts of Mg, Ca, and even Fe. The industrial wastes include fly ash, various types of iron and steelmaking slags, carbide slag, cement dust, etc. In comparison to the natural feedstock of Mg- and Ca-containing minerals, the industrial wastes are more suitable for economical CO2 sequestration. This is because the industrial wastes are more kinetically unstable and hence are more reactive to carbonation, and therefore require less pretreatment and less energy-intensive carbonation conditions. In addition, the industrial wastes are always near the CO2 intensive point, providing a possible way for in-situ sequestration, which in turn cuts the transportation cost. Iron and steelmaking slags are byproducts produced during the manufacturing processes of iron and steel respectively. Blast furnace slag (BFS) is a product of iron production, which has been widely investigated and utilized, particularly as a supplementary cementitious material for cement or alkali-activated material, owing to its high hydraulic property or alkali activation reactivity. Steelmaking slag is a byproduct produced in the process of refining the iron to steel in various furnaces (Shi, 2004). For a ton of steel, around 0.13e0.2 ton of slag is produced (Yu and Wang, 2011). According to the US Geological Survey, the global production of steelmaking slag is estimated to be on the order of 170 million to 250 million tons (USGS, 2018). Unlike the iron slag, the steel slag exhibits much lower hydration reactivity and poorer hydraulic properties. Furthermore, it usually contains high content of free-CaO Carbon Dioxide Sequestration in Cementitious Construction Materials https://doi.org/10.1016/B978-0-08-102444-7.00008-3 Copyright © 2018 Elsevier Ltd. All rights reserved.

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Carbon Dioxide Sequestration in Cementitious Construction Materials

and periclase, which can produce excessive volume expansion as a result of hydration and therefore induce volume instability. In addition, the grinding of steel slag is energy intensive due to its poor grindability. In general, the utilization of steel slag is quite limited or of less economic value; for instance, in China only approximately 10% of steel slag has been used. Nonetheless, more approaches for the use of steel slag are still under seeking. It is found that under CO2 rich environment, the steel slag is very carbonation reactive, and hence has a big potential to be used as the feedstock for CO2 sequestration. This has attracted increasing attention from researchers and abundant work has been focused on this. As reported, up to 13 and 21.5 wt% of CO2 (by weight of steel slags) could be sequestrated into stainless steel slag and basic oxygen furnace slag (BOFS) respectively (Baciocchi et al., 2009; Chen et al., 2016). To further reduce the energy consumption and cut the relevant cost for the CO2 sequestration in steel slag, more researches are conducted to integrate CO2 sequestration with valueadded products development, for example, development of construction materials. This provides a novel and promising way for the economic CO2 sequestration and valorization treatment of steel slag.

8.2 8.2.1

Composition, properties, and conventional use of steel slag Type, composition, and basic properties of steel slag

From the process of crude iron production to the following refining of crude iron into steel, various types of slags are produced at different stages of the steel manufacturing with different furnace processes. BFS is produced during the manufacturing of crude steel in blast furnace. BOFS and electric arc furnace slag (EAFS) are produced in basic oxygen furnace and electric arc furnace respectively, which are the most widely used processes for the steel manufacturing. In the electric arc furnace process, the electric arc furnace oxidizing slag is firstly produced when the iron scrap is melted and refined into steel, and then the electric arc furnace reducing slag is produced in the ladle refining furnace. Further refining of the stainless steel in the ladle furnace generates argon oxygen decarburization slag and desulfurization slag. Generally, the main chemical compositions of steel slag include CaO, FeO (Fe2O3), MgO, SiO2, Al2O3, Na2O, K2O, and small amounts of heavy metals, for example, Pb, Cr, V, Mn, etc. However, the quantities of different chemical compositions vary with the type of steel slag. Fig. 8.1 shows the normalized CaO(MgO)-SiO2(Na2O, K2O)Al2O3(Fe2O3) composition diagram of various types of steel slags drawn by Pan et al. (2016) on the basis of a series of data from literature. Apparently the steel slag has a wide range of chemical compositions depending on the raw materials and furnace process for the steel refining. For BFS, the compositions are primarily silica and alumina from the original iron ore, with some calcium and magnesium oxides from the added flux (mainly lime), while for the BOFS and EAFS more quantity of FeO and little quantity of Al2O3 are contained. The chemical components of the steel slag exist in different mineral forms and exhibit various physico-chemical properties.

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20

80

40 (% )

SiO

60

+M

BFS

80

) (%

EAFOS

a 2O

40 EAFRS

+N

O

O

2

Ca

+K

gO

2

PS

60

20 AODS LFS BOFS

100 0

0 20

40

60

80

Fe2O3 + Al2O3 (%)

Figure 8.1 Normalized CaO(MgO)-SiO2(Na2O, K2O)-Al2O3(Fe2O3) composition diagram of various types of steel slags drawn by Pan et al. (2016) on the basis of data from literature. AODS, argon oxygen decarburization slag; BFS, blast furnace slag; EAFOS, electric arc furnace oxidizing slag; EAFRS, electric arc furnace reducing slag; LFS, ladle furnace slag; PS, phosphorus slag.

As a main component, Ca presents in many mineral forms, for instance, free-CaO, Portlandite (hydration products of free-CaO), various calcium silicates (e.g., larnite (Ca2SiO4) g
C2S, b
C2S, C3S), complicated Ca-containing silicates (e.g., bredigite/merwinite(Ca14Mg2(SiO4)8), gehlenite(Ca2Al(Al, Si)2O7), etc.), and other solid solutions containing Mg, Fe, Al, etc. Free-CaO is very hydration and carbonation reactive; the hydration of free-CaO (when the contents are high) in steel slag may cause excessive volume expansion and hence induce unsoundness. Small party of calcium silicate presents in the forms of b
C2S, C3S, C4AF, and C2F, exhibiting cementitious performance when mixed with water. Therefore, steel slag can act as raw material for cement clinker production and as a potential mineral admixture for concrete at a proper replacement level (Wang and Yan, 2010; Li et al., 2011; Wang et al., 2011). Most part of the calcium silicate, in particular, in the form of the solid solution of Ca, Mg, Fe, and O, presents very low hydraulic property. Nonetheless, under the concentrated CO2 environment, most of the Ca containing phases in steel slag are carbonation reactive. Iron mainly exists in the mineral forms of wustite (FeO), hematite (Fe2O3), magnetite (Fe3O4), magnesioferrite (MgFe2O4), etc. Fe influences the grindability of steel slag. With the increasing Fe content in the slag, the hardness of steel slag increases and thus decreases its grindability. This makes the grinding of steel slag very energy

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intensive and inefficient. For example, in comparison to the reductive EAFS, the oxidizing EAFS normally contains 24e38 wt% of iron oxide, and exhibits higher hardness and grinding resistance. The Mg content presents in two main forms of periclase and Mg containing solid solution (i.e., wustite in the formula of Fe(Mn, Mg, Ca, O)) (Wang et al., 2010). The presence of periclase contained in steel slag could also hydrate to form Mg(OH)2, giving rise to volume expansion and may cause unsoundness when the periclase content is excessive. These Mg phases exhibit relatively low hydration reactivity (Wang and Yan, 2010; Wang et al., 2011). However, magnesium can also be carbonated and therefore has an impact on the capacity of CO2 sequestration. Heavy metals in terms of Ba, Cr, V, Mn, As, Cd, Hg, etc., are contained in the steel slag, which may leach out from the steel slag and hence induce potential pollution of the environment or detrimental effects on human health (Proctor et al., 2000; Das et al., 2007). Therefore the potential leaching of heavy metals is also an obstacle for its application.

8.2.2

Conventional use of steel slag

The utilization of steel slag depends on its compositions and properties. Conventionally, the steel slag is mainly used in civil engineering in various ways, for example, using as a feedstock for the manufacture of cement clinker, coarse aggregate in road, pavement, or fine aggregate in concrete, supplementary cementing material in cement, etc. (Kriskova et al., 2012; Manso et al., 2006; Pellegrino et al., 2013; Bessa et al., 2014; Yi et al., 2012). The steel slag was used as raw material for producing cement clinker with comparable properties to the ordinary Portland cement (Tsakiridis et al., 2008; Monshi and Asgarani, 1999). As some hydraulic components might be contained in steel slags, such as C3S, C2S, and C4AF, and the quantities of which depend on the type of slags, the steel slags are usually ground into fine powders and used as supplementary cementitious materials in cement (Wang et al., 2017; Zhang et al., 2011; Li et al., 1997). The incorporation of steel slag as the mineral admixtures into concrete improves the properties of concrete, for instance, reduction in water demand, improvement of workability (Kourounis et al., 2007), improved resistance to carbonation and chloride penetration (Wang et al., 2013), low hydration heat (Zhang et al., 2012; Liu and Li, 2014), and prolonged setting time (Eylu and Filyos Refractories, 2002; Rai et al., 2002). However, the increasing incorporation of steel slag decreases the strength of cement. As reported by Kourounis et al. (2007), cement containing 15 or 30 wt% steel slag met the strength requirements of class 42.5 of EN 197-1, while cement containing 45 wt% steel slag only reached the strength requirements of class 32.5 of EN 197-1. This is due to low content of hydraulic components in steel slag, leading to poor hydraulic property of steel slag under hydration condition. To improve the hydraulic property, steel slag is usually ground into fine powders; however, this could be an intensive energy-consuming process due to the poor grindability of steel slag and is not very effective for the hydraulic property promotion. Moreover, due to the presence of expansive components of free-CaO and periclase in steel slag, excessive volume expansion may be generated as a result of the transformation of CaO

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and MgO into Ca(OH)2 and Mg(OH)2, respectively, during hydration, leading to the durability reduction and mechanical strength loss of concrete (Sheen et al., 2015b; Adegoloye et al., 2015). According to a previous study, the maximum contents of free-CaO and MgO contained in steel slag without causing soundness problems in concrete, even under the strict autoclave test, were 2.09 and 7.68 wt%, respectively (Wang et al., 2017). It may cause poor soundness when the quantity of MgO exceeds 70 wt% of the MgO-bearing solid solution phase in steel slag (Wang et al., 2017). Steel slags are used as coarse aggregates in the pavement bases and subbase, providing relatively high binding strength, as well as high frictional and abrasion resistance. In addition, steel slags are used as coarse or fine aggregates for preparation of concrete as replacements of natural sands and aggregates (Sheen et al., 2015a,b). Some improved properties of concrete are reported. For instance, excellent fire resistance, anti-chloride ion penetration, high compressive strength are gained by using these fine steel slag aggregates to produce high-strength and refractory concrete. However, the total volume of steel slag aggregates used in concrete is limited considering the volume instability due to the excessive contents of free-CaO and periclase in the steel slag (Adegoloye et al., 2015; Le et al., 2017). Sheen et al. (Sheen et al., 2016; Sheen et al., 2015a,b) have conducted a series of researches on the utilization of stainless steel slag as aggregate or binding material in self-compacting concrete production and gained some positive results. In Germany, the steel slags are used as aggregates for some hydraulic structures, for example, dams, dikes, stabilization of river bottoms and banks, and the refilling of erosion area on river bottom, and it is found that the long-term resistance to dynamic force coming from waves and river flow is improved owing to the high strength, good resistance to abrasion, and rough texture of the steel slags (Motz and Geiseler, 2001). In addition, the steel slag is also used in asphalt pavement along with the bituminous mixes, cold-mix, and hot-mix asphalt.

8.3 8.3.1

Carbonation of steel slag Carbonation mechanism of steel slag

Although the hydration reactivity of steel slag is quite low, under the CO2-rich environment, the Ca component in various forms contained in steel slag exhibits high carbonation reactivity. Therefore the steel slag has a potential to be used as a feedstock for CO2 sequestration and even used to produce carbonated products. In addition, via the accelerated carbonation, the contents of free-CaO and free-MgO could be largely consumed, providing a new approach for improving the volume stability of steel slags. The carbonation reactive components in the steel slag include free-CaO, periclase, hydraulic calcium silicate (C3S, b-C2S), non-hydraulic calcium silicate (e.g., g-C2S, CS), Portlandite (hydration products of free-CaO or calcium silicate), akermanite (Ca2Mg-Si2O7), merwinite (Ca3Mg(SiO4)2), cuspidine, as well as a number of Ca-Al oxides and Ca-Mg-Al-silicates (Baciocchi et al., 2015a; Chang et al., 2013; Johnson et al., 2003; Salman et al., 2014; Uibu et al., 2011; Mo et al., 2016).

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The carbonation of CaO and Ca(OH)2 could be described as following equations: CaO þ CO2 / CaCO3

(8.1)

Ca(OH)2 (hydrated free-CaO) þ CO2 / CaCO3

(8.2)

The carbonation of calcium/magnesium silicate phases in the steel slag could be described with a general equation (Pan et al., 2013): ðCaO; MgOÞx ðSiO2 ÞyðsÞ þ xCO2 ðgÞ/xðCa; MgÞCO3 ðsÞ þ ySiO2 ðsÞ

(8.3)

Water is a prerequisite medium for the above carbonation reactions taking place as the carbonation of steel slag proceeds via a dissolution and precipitation process. To accelerate the carbonation, there are two typical routines employed, namely direct carbonation and indirect carbonation, both of which are under rich CO2 environment. In the former approach, the carbonation of steel slag takes place in a single route step. This process can be divided into two types: (1) dry gas-solid carbonation, typically with a liquid-to-solid (L/S) ratio lower than 0.2, and (2) aqueous carbonation with a high L/S ratio, being higher than 5. For the indirect carbonation it usually requires an acid as the extractant to dissolve the Ca2þ and Mg2þ from the steel slag first, and then the Ca2þ and Mg2þ precipitate together with the carbonate ions to form calcium carbonate (CaCO3) or magnesium carbonate. The acids mainly include hydrochloric acid (HCl), acetic acid (Mun et al., 2017), oxalic acid, citric acid, and ethylenediaminetetraacetic acid (Mikkelsen et al., 2010). Basically the carbonation of steel slag via aqueous carbonation takes place by the following main steps: 1. Leaching of Ca or Mg ions form the Ca/Mg-containing minerals in the steel slag with or without assistance of effective solvent, which includes a process of diffusion of Ca and Mg ions toward the surface of the solid steel slag particles; 2. Separation of Ca and Mg from other elements leached out from the slag (optional for purifying the carbonates); 3. The dissolution of gaseous CO2 into a liquid phase, transforming carbonic acid to carbonate and/or bicarbonate ions; 4. Formation of supersaturated solution, and the subsequent nucleation and precipitation of Ca/Mg carbonates with varying degree of purity (Doucet, 2010).

Among the above reaction steps, the processes of Ca leaching from the steel slag and the following precipitation as carbonates are the two pivotal steps. In particular, the diffusion of calcium through the solid matrix toward the surface appears to be the rate-determining reaction step (Huijgen, 2005). After the leaching of Ca, amorphous SiO2 is formed. According to the 29Si MAS NMR, prior to carbonation the silicon species in the steel slag exist as Q0 with no bridging oxygen, and it becomes Q4 with four bridging oxygen after the Ca-leaching (Guan et al., 2016; Liu et al., 2017). Fig. 8.2 shows the microstructure of carbonated steel slag particles via aqueous carbonation with a high L/S ratio of 10 and in steel slag paste with a low L/S ratio of 0.4. With the high L/S ratio, CaCO3 is agglomerated loosely (Fig. 8.2(a)) while

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Figure 8.2 Microstructures of the carbonated steel slag with high and low L/S ratios: (a) SEM images of the carbonated steel slag, PCO2 ¼ 20 bar, T ¼ 150, t ¼ 30 min, d < 106 mm, L/S ¼ 10 (Huijgen, 2005). (b) BSE image of carbonated steel slag, PCO2 ¼ 20 bar, T ¼ 150, t ¼ 30 min, d < 106 mm, L/S ¼ 10 (Huijgen, 2005). (c) SEM image of the calcium carbonate formed due to the carbonation of steel slag, PCO2 ¼ 0.1 MPa, T ¼ 23, t ¼ 1 d, L/S ¼ 0.4 (Mo et al., 2016). (d) BSE image of the carbonated steel slag, PCO2 ¼ 0.1 MPa, T ¼ 23, t ¼ 1 d, L/S ¼ 0.4. C, CaCO3; CS, calcium silicate (Mo et al., 2016).

under the low L/S ratio the CaCO3 is aggregated very densely (Fig. 8.2(c)). Fig. 8.2(b) shows the BSE image of a carbonated steel slag particle, which shows clearly four main phases: (1) The porous CaCO3 coating on the surface of carbonated particles, (2) the Ca-depleted area consisting of SiO2 which is formed due to the leaching out of Ca, (3) uncarbonated calcium silicate, and (4) uncarbonated Ca-Fe-O minerals, and most of the calcium silicate is dissolved to form the CaCO3. This implies that the calcium silicate exhibits higher carbonation reactivity than that of the Ca-Fe-O phase. Similar microstructure is observed in steel slag paste with much lower L/S ratio (Fig. 8.2(d)), which shows clearly that the SiO2 rim is formed around the uncarbonated inner core part of steel slag particle while the Ca diffuses toward the surface of the steel particle to form a CaCO3 coating layer. It should be noted that for the high L/S ratio in

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aqueous carbonation, the CaCO3 layer would be easily detached from the particles via stirring, but for the low L/S ratio, the formation of CaCO3 constructs a denser microstructure and eventually produces a mechanical strength of 44.1 MPa. The newly precipitated rim of CaCO3 and SiO2 layer around the reacting steel slag particles forms a barrier preventing the following diffusion of Ca from the internal part into the surface of the solid steel slag particle (Dri et al., 2014; Santos et al., 2013b; Uibu et al., 2011; Polettini et al., 2016). Under natural weathering, the free-CaO or hydrated free-CaO (namely Ca(OH)2) could react with the atmospheric CO2 in the presence of moisture, whereas the carbonation of periclase is much slower and even does not take place since it is much less reactive in comparison to the free-CaO. Similarly, the calcium silicates or calcium containing solid solution may not be carbonated under the natural condition with atmospheric CO2 concentration. Various types of calcium or magnesium containing minerals exhibit different carbonation reactivities. For example, g-C2S is reported to have the highest carbonation reactivity among these types of calcium silicates. Theoretically steel slag containing more Ca and Mg content exhibits greater capacity of CO2 sequestration. Steel slag normally contains over 40 wt% CaO; it has great potential for being used in the CO2 sequestration.

8.3.2

Factors influencing the carbonation rate of steel slag

In addition to the theoretical CO2 uptake capacity of the steel slag, the carbonation rate and relevant efficiency are the vital factors for the CO2 sequestration. Many variables influence the carbonation rate of steel slag, which include the mineralogical composition of steel slag with specific carbonation reactivity, and the carbonation routine with given operation parameters in terms of temperature, CO2 pressure, L/S ratio, time, particle size of steel slag, etc. (Polettini et al., 2016). The mineralogical composition of steel slag strongly influences the CO2 uptake capacity and efficiency. Steel slag containing more content of carbonation reactive components would carbonate more rapidly. Calcium and magnesium in the forms of free-CaO, MgO, Ca(OH)2, and Mg(OH)2 show relatively high carbonation degree, whereas the calcium/magnesium silicates and aluminosilicates are less susceptible to carbonation and therefore exhibit lower carbonation degree. By studying the pure minerals that are typically present in steel slag, it is found that bredigite (Ca7Mg(SiO4)4) is the most reactive phase during carbonation, followed by dicalcium silicate polymorphs (b- and g-C2S) and cuspidine (Ca4Si2O7F2), or by srebrodolskite (Ca2Fe2O5) and calcium monoferrite (CaFe2O4) (Bodor et al., 2013). However, other investigators reported some low reactivity of srebrodolskite upon carbonation (Berryman et al., 2015). Some researches indicate that the g-C2S contained in the steel slag is more carbonation reactive than b-C2S (Ghouleh et al., 2015). The particle size of steel slag has a strong influence on the carbonation rate as it is related to its specific surface area, which directly affects the carbonation reaction area. Particles in smaller size possess higher specific surface area and more rapid Ca leaching would take place. It is reported that the reduction of particle size from <2 mm to <38 mm increases the carbonation degree from 24% to 74% (Huijgen, 2005).

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The reaction temperature has two opposite effects on the carbonation rate. At higher temperatures, the leaching of Ca from the matrix is likely to proceed faster as the increasing temperature facilitates the diffusion of Ca, but on the other hand, the solubility of CO2 in the solution decreases (Huijgen, 2005). In addition, the temperature also affects the physical characteristics of the reaction system, for example, the liquid viscosity and CO2 diffusion rate, or indirectly through the evaporation of the liquid phase (Bauer et al., 2011). The nature of carbonates formed is also influenced by temperature. For instance, higher temperature has been reported to favor the formation of metastable phases or polymorphs (Bertos et al., 2004), or to promote the formation of carbonate forms which would be unfavorable at lower temperatures (Back et al., 2011) Therefore, a moderate temperature would be optimum for the carbonation, for example, 50 C (Ukwattage et al., 2017). Increase of CO2 pressure facilitates the dissolving of CO2 into water to form the carbonate and/or bicarbonate ions for the generation of supersaturated solution. According to the Henry’s law, increased pressure enhances the CO2 solubility in the liquid: the molar fraction of CO2 increases at 25 C from 6.22 3 10L4 to 3.01 3 10L3 at 101 C and 500 kPa CO2 partial pressures respectively (Carroll et al., 1991). From this point, the increase of CO2 pressure has a positive influence on the carbonation rate of steel slag in both the direct and indirect carbonation routines. For the direct carbonation with low L/S ratio, the increase of CO2 pressure enhances the penetration of CO2 into the inner part of the aggregated steel slag particles or the steel slag compacts. However, higher CO2 dissolution into the liquid phase also implies lower pH, which may in turn impair carbonate precipitation (Back et al., 2008). It is reported that high CO2 pressures may inhibit the formation and growth of carbonate crystals (Chang et al., 2011b). The insignificant effect of the CO2 pressure shows it is the leaching of Ca rather than CO2 mass transfer controlling the reaction rate The leaching of Ca consists of two steps: (1) diffusion of Ca toward the surface of a particle; (2) dissolution of Ca from the particle surface into the solution. The former is likely the key step controlling the overall carbonation rate (Huijgen, 2005). L/S ratio has a significant influence on the carbonation rate since water is a prerequisite media for the reaction. For the aqueous carbonation, increase of L/S ratio enhances significantly the carbonation rate and the ultimate sequestration quantity of CO2. This is attributed to the increased Ca extraction efficiency in the presence of ample water with the continuous stirring provided in the aqueous carbonation system (Ukwattage et al., 2017). With a wide range of L/S ratio, 0.25e3, Ranjith (Ukwattage et al., 2017) reported that the CO2 sequestered in the steel slag was increased with the L/S ratio. At low L/S ratio, the formation of Ca-depleted silicate rim around the particles and precipitation of CaCO3 on the surface of particle hindered the further diffusion of Ca2þ from the particle interior and the transportation of CO2 and carbonate ions. However, the researches indicated that too much water had a negative impact on the carbonation rate as the water interfered with the diffusion of CO2 gas into solid due to the blockage of pores in the solid (Ukwattage et al., 2017). Therefore in the aqueous carbonation, the operation of continuous stirring is usually taken to enhance the CO2 diffusion (Ukwattage et al., 2017). For a given carbonation operation, there

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may be an optimum L/S ratio. Other operation parameters, for example, the stirring speed for the aqueous carbonation and relative humidity control also influence the carbonation rate. Among the above mentioned variables, the key variables controlling the carbonation depend on the specific carbonation routine, as well as the carbonation conditions. For the aqueous carbonation in suspension solution, the particle size of steel slag and the reaction temperatures are the two most important factors influencing the carbonation rate (Huijgen, 2005).

8.3.3

Strategies for the acceleration of carbonation of steel slag

Based on carbonation mechanism of steel slag and the influences of relevant variables on the carbonation rate, some strategies have been developed for accelerating the carbonation of steel slag. This includes not only the operation parameters (Ukwattage et al., 2017), for example, optimal temperature, increase of CO2 pressure, control of L/S ratio, and reduction in steel particle size, but also the use of suitable dissolving agent and development of carbonation apparatus with high efficiency. To enhance the dissolving of Ca from the steel slag, different types of solvent are usually used to extract Ca, such as NH4NO3, NH4Cl (Kodama et al., 2008; Lee et al., 2016; Hosseini et al., 2016), CH3COONH4, (NH4)2SO4. The types of solvent, as well as the operation conditions (reaction temperature, reaction time, solvent concentration, and L/S ratio), influence the calcium extraction efficiency, which is found to be proportional to the above mentioned variables (Lee et al., 2016). In addition, some acid-based solvents are used, for example, HCl (Jo et al., 2017) and acetic acid (Teir et al., 2007; Bao et al., 2010). In acetic acid with a given concentration, for example, 33.3 wt%, almost all the Ca and other metals (e.g., Mg, Al, Fe) from the steel slags could be dissolved. In the meantime, the silicon from the steel slag also dissolves and forms a gel when the reaction temperature exceeds 70 C. By using HCl and sodium hydroxide, high purity nano-CaCO3 from steel slag is produced. It was reported that NH4Cl could be used as an extracting agent to dissolve Ca ions efficiently and selectively from the steel slag (Kodama et al., 2008). The ammonium chloride generated ammonium ions (NHþ 4 ) to remain within a range of constant pH (11.10e10.52) with higher value than other acids (Mun et al., 2017). This is believed to be beneficial for the precipitation of carbonates. During the dissolving process by the use of extractant, the Ca ions have higher dissolution rates than the Mg ions, and the metal ion dissolution efficiencies follow the order of Ca > Mg > K > Fe > Al (Jo et al., 2017). Optimum of the operation process is also a mean to accelerate the carbonation of steel slag and improve the carbonation efficiency. Therefore different carbonation equipments and relevant operation processes have been developed. Aqueous carbonation in an autoclave reactor with elevated temperature and pressure is a typically used process (Chang et al., 2011b). To minimize the negative effect of water on the diffusion and transfer of CO2, thin-film technology, to make a very thin water film around steel slag particle to enhance the transfer of CO2, is used (Baciocchi et al., 2015a). Rotating packed bed (PRB) reactor with a high-gravity carbonation process is reported to be more efficient than the slurry reactor and autoclave reactor

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(Chang et al., 2011a, 2012a,b). By using the PRB, a thin liquid film and tiny liquid droplets via high centrifugal acceleration can be formed, enhancing the micromixing abilities and gas-liquid mass transfer (Tan and Chen, 2006; Chang et al., 2012a; Pan et al., 2013). More recently a two-stage reactor consisting of a high and a low fluidflux chamber is proposed for CO2 sequestration by steel slag carbonation, allowing dissolution of the slag and precipitation of calcium carbonate to occur within a single flow-through system (Berryman et al., 2015).

8.3.4

Heavy metal leaching from carbonated steel slag

Owing to the leaching of Ca during the carbonation, the initial mineral microstructure is broken and may influence the leaching of other ions, especially the heavy metals including Ba, Cr, Pb, and V from BOFS, and Cr, Ba, and V from EAFS. On the other hand the carbonation may also reduce the pH value which also plays a role in the leaching of metals (Baciocchi et al., 2015a). The carbonation of steel slag results in the reduction of basicity by up to one unit, and contributes to reducing the leaching of several heavy metals and metalloids (Salman et al., 2014). In addition, the denser microstructures are formed due to the formation of carbonates; this would physically hinder the leaching out of heavy metals. The influence of carbonation on the leaching behavior of the heavy metals in steel slags depends on the type of heavy metal, as well as the type of steel slag. At natural pH, Cr and V are more leachable from the carbonated slag, while the opposite occurred for Mo. For the Cr, its leachability in AOD slag is higher than that in EAFS, and is affected more significantly by carbonation. However, for Cr the leachability as a function of pH appeared not to be significantly affected by carbonation, whereas Mo showed a certain reduction in leaching after carbonation in the entire pH range was investigated. The release of Zn and Mo upon the EN 12457 test decreases upon carbonation; Cr and V display an opposite trend (Baciocchi et al., 2015b). The decreases in the leaching of Zn and Ba are observed for carbonated steel slags (Santos et al., 2013a; Suer et al., 2009; Salman et al., 2014).

8.4 8.4.1

Applications of steel slag via accelerated carbonation Precipitated calcium carbonate products

Calcium and magnesium carbonates are high value-added products which can be used as coating pigments and as fillers in the pulp, rubber, plastic, paper, and paint industries to provide opacity, high brightness, and improved printability. However, this relates closely to its purity and the crystal structures. An indirect carbonation process is widely employed to obtain precipitated CaCO3 with relatively high purity, in the form of calcite (rhombohedral or scalenohedral shape) and aragonite (orthorhombic acicular shape) (Eloneva et al., 2008). For specific industrial applications, it is necessary to control the morphology and particle size of synthesized CaCO3, which are

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strongly influenced by the type of extractant employed for the dissolving of Ca and the temperature and alkali concentration used for the precipitation process after the Ca leaching (Mun et al., 2017; Eloneva et al., 2008). Fig. 8.3 shows the typical morphology of CaCO3 precipitated via carbonation of steel slag under various dissolving and precipitating processes. In the presence of ammonium chloride extractant, the increase of reaction temperature favors the formation of plate-shaped or needle-shaped particles of aragonite and decreases the formation of rhombohedral calcite. When acetic acid is used as an extractant, spherical calcite crystals with particle size of 10e20 mm can be formed by the indirect carbonation of granulated BFS with <500 mm in size.

Figure 8.3 Typical morphology of CaCO3 synthesized via the carbonation of steel slag. (a) rhombohedral CaCO3 crystals, acetic acid solvent, 1 L/min CO2 flow, 30 C, 61 g/L NaOH added for the precipitation, (b) acicular CaCO3 crystals (aragonite), acetic acid solvent, 14 L/ min CO2 flow, 70 C, (c) CaCO3 with more complex shapes, 1 L/min CO2 flow, and 15 g NaOH/L solution,70 C, and (d) rhombohedral nano-CaCO3 crystals, 0.5 M HCl solvent, 30 C, 1M NaOH, pH ¼ 11(Jo et al., 2017). From Eloneva, S., Sebastian Teir, Justin Salminen, Carl-johan Fogelholm, Ron Zevenhoven, 2008. Steel converter slag as a raw material for precipitation of pure calcium carbonate. Industrial & Engineering Chemistry Research 2 (1), 7104e7111.

Carbon dioxide sequestration on steel slag

8.4.2

187

Carbonated steel slag aggregates

The volume instability of steel slag, which may be caused due to the presence of excessive free-CaO and periclase, is one of the main barriers to its application as the aggregates in concrete materials. Fig. 8.4 shows a typical BSE image of a cracked steel slag aggregate in concrete. Cracks arise from the internal part of steel slag aggregate due to the hydration of free-CaO. Applicable steel slag must have the free-CaO content lower than 2e3 wt% or even up to 4 wt% in asphaltic layer. Otherwise, slag must be further treated before being used as construction material (Frías et al., 2010). To avoid the volume instability, the steel slag must be stabilized, controlled, or treated with appropriate methods. Exposure of steel slag in outdoor environment for several months as a treatment (depending on particle size) is beneficial to apply but needs more land for disposal (Svanera et al., 2012; Le et al., 2017). On pretreatment by exposing to outdoor environment, the free-CaO content decreased from 1.20% to 0.61% (Le et al., 2017), and reduced the expansion under heating catalysis and autoclave test (as shown in Fig. 8.5). To shorten the treatment time, temperature catalytic, hot-water or steam aging, autoclave techniques are normally taken, which also sufficiently enhance the stabilized process (Wang, 2014; Yunxia et al., 2008). Carbonation treatment is employed to carbonate the free-CaO to improve the stability of steel slag aggregates. Steel slag can be carbonated to make aggregates for concrete (Ghouleh et al., 2017). Via carbonation, not only the carbonated steel slag shows stable volume but also exhibits good mechanical properties.Mo et al. (2017) prepared concrete with steel slag as the aggregate and binding material under the CO2 curing, indicating the CO2 curing has improved the volume stability of the concrete containing steel slag.

8.4.3

Alternative binders or construction products prepared via carbonation of steel slag

Carbonate binder, on the base of Ca or Mg-bearing carbonates, is a kind of novel alternative binding material which has advantages of utilizing high volume of industrial wastes, CO2 sequestration, and rapidly developed,high mechanical strength. It has attracted increasing attention in recent years in the context of CO2 emission cut and resources recycling. The Ca/Mg carbonate binders are typically produced via the carbonation of Ca and/or Mg-bearing sources. The calcium carbonate binders can be prepared via the direct accelerated carbonation of steel slag (Zhao et al., 2010; Chang and Wu, 2010). Through the carbonation of steel slag compacts, desirable mechanical properties are gained, which meet the requirement of strength of the construction material. Ghouleh et al. (2015) prepared a compacted steel slag paste with a high compressive strength of 80 MPa and a CO2 uptake of 13 wt% after 2 h exposure to CO2 with a concentration of 99.5% and a pressure of 0.15 MPa. Carbonation under high temperature and high CO2 pressure was reported to improve the strength gain of stainless steel slag (Boone et al., 2014). For instance, under the condition with a CO2 pressure of 2 MPa and

188

Carbon Dioxide Sequestration in Cementitious Construction Materials

1200 Mg

1000 O Fe

800 600 400

Fe

200

Fe Ca

C

0 0

2

4 keV

Fe

6

8

Elements of point 1 (EDX) 1500

Ca

1000 500

O C

0

Mg

0

Fe

2

4 6 keV Elements of point 2 (EDX)

1200

8

Ca

1000 O

800 600 400 200

C

Mg Al

Fe

0 0

2

4 keV

6

8

Elements of point 3 (EDX)

Figure 8.4 BSE image of a cracked steel slag aggregate in concrete cured under moist condition. L, free-CaO; P, periclase; Po, Portlandite (Mo et al., 2017).

Carbon dioxide sequestration on steel slag

189

(a) 0.20 Break (72-h heating) Break (autoclave) Break (96-h heating)

Expansion (%)

0.15

0.10 Autoclave 24h 48h 72h 96h

0.05

0.00 0

25

50

75

100

%SSOS replacement

(b) 0.20 Break (autoclave) Break (72-h heating) Break (96-h heating)

Expansion (%)

0.15

0.10 Autoclave 24h 48h 72h 96h

0.05

0.00 0

25

50

75

100

%SSOS replacement

Figure 8.5 Comparison of expansion between the heating catalysis and autoclave test on specimens prepared with (a) 5 months treated stainless steel oxidizing slag (SSOS), and (b) 8 months treated SSOS. Autoclave (steam pressure of 2.10 MPa for 3 h) and heating catalytic (100 C) curing (Le et al., 2017).

temperature of 80 C, the compressive strength of stainless steel slag compact is found to reach 50 MPa after 2 h of carbonation (Boone et al., 2014). For the valorization of CO2 sequestration in steel slag, the carbonation of steel slag is usually integrated with developing construction materials that have required mechanical properties. Steel slag bricks, porous blocks, etc., are produced via the accelerated carbonation of steel slag (Zhang, 2009). Numerous factors, for example, steel slag particle size, compact pressure, CO2 pressure, carbonation time, relative humidity, etc., may influence the carbonation rate, carbonation degree, and the ultimate strength obtained. For the carbonation of steel slag compact, the effects of variables on the carbonation are in the declining sequence of particle size > CO2 pressure > compact

190

Carbon Dioxide Sequestration in Cementitious Construction Materials

pressure > carbonation time. Incorporation of lime or Ca(OH)2 facilitates the compressive strength of steel slag bricks, reaching at 20 MPa (Zhang, 2009). For the enhancements of CO2 transfer and carbonation, besides the increase of CO2 pressure and control of the relative humidity, creation of a porous structure in the steel slag compact is an effective way. By creating a porous structure, the CO2 can diffuse through the whole depth of a cubic steel slag block with a size of 1 m (Isoo et al., 2000). After carbonation for a period of 12 days, approximately 6 wt% CO2 was absorbed, and the compressive strengths of the slag blocks are 18.4  3.3 MPa and a density of 2.4 g/cm3. Appropriate water content is vital for the carbonation reaction. Too high water content in concrete may hinder the transfer of CO2, while too low amount of water is insufficient for the complete carbonation of steel slag. As reported by Isoo (Isoo et al., 2000), the maximum compressive strength was obtained when the amount of water is 5.3e6.3 wt%. Nonetheless, when the water content was less than 5.3 wt%, the amount of water in the capillaries between the particles was insufficient to produce enough carbonate products to bind the slag particles together. As reported by Mo et al. (2017), via CO2 curing, the concrete cast with steel slag as aggregates or binding materials exhibited excellent mechanical strengths and stable volume without causing soundness problem. Concrete cast with 60 wt% of steel slag powders as the binding materials but only 20 wt% of Portland cement and steel slag aggregates as replacement of natural river sands and coarse limestone aggregates gained compressive strengths of 38.6 and 61.3 MPa respectively after 1 and 14 days of CO2 curing, being higher than the 11.5 MPa at 28 days under normal moist curing. Moreover, the volume of carbonated steel slag concrete shows very stable volume under the followed 80 C steam curing, whereas the conventional moist cured steel slag concrete deteriorated due to the excessive expansion caused by the hydration of freeCaO in the steel slag. The mechanical performance of carbonate binders produced via carbonation of steel slag is mainly attributed to the structure densification, as well as the high mechanical performance of the aggregated CaCO3 crystal itself (Mo et al., 2016). Due to the formation of CaCO3, the total pore volume of steel slag products was reduced and the pore diameter was decreased (Mo et al., 2016; Boone et al., 2014). As reported by Mo et al. (2016), after 1 and 14 days of carbonation, the total porosity of steel slag paste decreased from 33.6% prior to carbonation to 27.5% and 15.7% respectively. The pore diameter in the steel slag paste shifted from the range of 0.2e3 mm to 0.1e1 mm, and further to less than 0.1 mm respectively when the carbonation age increased from 1 to 3 days and 14 days. This is beneficial for the strength improvement of carbonated steel slag. Boone et al. (2014) reported the pores with maximum opening size between 50 and 18 mm were diminished. Jang et al. (Jang and Lee, 2016) indicated that the microstructural densification of pores with a diameter range of 50 nm to 10 mm in the carbonated belite-rich cement contributed to the compressive strength. Moreover, the dense pore structure as a result of carbonation contributes to improved transport properties and durability, and better resistance to ingress and leaching (Ghouleh et al., 2017). Via Vickers microhardness test on the carbonated steel slag compact, Ghouleh et al. (2015) reported that the mechanical strength of the steel slag compact was associated

Carbon dioxide sequestration on steel slag

191

(a)

(b)

182.0 172.0 160.0 148.0 136.0 124.0 112.0 100.0 88.0 76.0 64.0 52.0 40.0 28.0 16.0 4.0 Er /GPa

(c)

14.1 13.1 12.1 11.1 10.1 9.1 8.1 7.0 6.0 5.0 4.0 3.0 2.0 1.1 0.1 Hardness /GPa

Figure 8.6 The micro-mechanical properties of carbonated slag: (a) BSE image coupled with indentation grid, (b) nano-indentation modulus map, and (c) nano-indentation hardness map with a compressive strength of 44.1 MPa. C, calcium carbonate; HF, high Fe content phase; S, Si-rich and Ca-depleted phase (Mo et al., 2016).

with microhardness, and the microhardness of carbonated steel slag was higher than that of the hydrated steel slag. Mo et al. (2016) investigated further the mechanical properties of the carbonated steel slag by using the nano-indentation, and the results are shown in Fig. 8.6. Accordingly the indentation grid covers three main phases, namely the CaCO3, Ca-depleted phase, and the uncarbonated mineral phase, containing high content of Fe/Al. The nano-indentation modulus and hardness of CaCO3 are 38.9  12.1 GPa and 1.79  0.63 GPa, respectively, which are higher than that of the cement hydration products C-S-H (Table 8.1). As reported, the indentation modulus

The nano-indentation modulus and hardness of different mineral phases in carbonated steel slag paste (Mo et al., 2016)

Table 8.1

Phases

Calcium carbonate

Calcium silicate after Ca-leaching

Uncarbonated mineral phases containing high Fe/Al

Modulus/GPa

38.9  12.1

11.1  1.1

148.1  48.1

Hardness/GPa

1.79  0.63

0.49  0.32

10.56  3.35

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Carbon Dioxide Sequestration in Cementitious Construction Materials

and hardness of low density C-S-H were 18.2  4.2 GPa and 0.45  0.14 GPa, while they were 29.1  4.0 GPa and 0.83  0.18 GPa for high density C-S-H respectively (Constantinides Georgios and Ulm, 2007). Some studies claimed that the high polymerized amorphous SiO2 in the form of gel formed after the Ca leaching also contributes to binding performance (Guan et al., 2016; Liu et al., 2017). However, according to the BSE, the SiO2-rich zone is formed in a core surrounded by the carbonate products. In addition, the modulus is very low, being 11.1 GPa. It is reported that the formation of a hardened composite paste matrix consisting of C-S-H and CaCO3 crystal precipitates in the carbonated steel slag system yields a hybrid reinforcing effect, which also contributes to the superior binding properties (Ghouleh et al., 2017).

8.5

Future trends

Accelerated carbonation of steel slag provides a promising way for the economical utilization of steel slag and CO2 sequestration. Integration of the use of steel slag and CO2 sequestration brings new future for the reclamation of steel slag and development of alternative construction materials with low CO2 emission. Herein further work is still needed to expand the application of technology, which mainly covers the following four fields: the improvement of carbonation efficiency, decrease in the cost and energy intensive processes, increase in the value added for products, and the scaling up of the technology in industry. In addition, the close collaboration among the researcher, policy maker (government), and industry is also very vital for the implementation of such accelerated carbonation technology at a large industrial scale.

References Adegoloye, G., Beaucour, A.L., Ortola, S., Noumowé, A., 2015. Concretes made of EAF slag and AOD slag aggregates from stainless steel process: mechanical properties and durability. Construction and Building Materials 76, 313e321. Baciocchi, R., Giulia, C., Alessandra, P., Raffaella, P., 2009. Influence of particle size on the carbonation of stainless steel slag for CO2 storage. Energy Procedia 1 (1), 4859e4866. Baciocchi, R., Costa, G., Di Gianfilippo, M., Polettini, A., Pomi, R., Stramazzo, A., 2015a. Thinfilm versus slurry-phase carbonation of steel slag: CO2 uptake and effects on mineralogy. Journal of Hazardous Materials 283, 302e313. Baciocchi, R., Costa, G., Polettini, A., Pomi, R., 2015b. Effects of thin-film accelerated carbonation on steel slag leaching. Journal of Hazardous Materials 286, 369e378. Back, M., Kuehn, M., Stanjek, H., Peiffer, S., 2008. Reactivity of alkaline Lignite fly ashes towards CO2 in water. Environmental Science & Technology 42, 4520e4526. Back, M., Markus, B., Helge, S., Stefan, P., 2011. Applied geochemistry sequestration of CO2 after reaction with alkaline earth metal oxides CaO and MgO. Applied Geochemistry 26 (7), 1097e1107. Bao, W., Li, H., Zhang, Y., 2010. Selective leaching of steelmaking slag for indirect CO2 mineral sequestration. Industrial & Engineering Chemistry Research 49, 2055e2063.

Carbon dioxide sequestration on steel slag

193

Bauer, M., Gassen, N., Stanjek, H., Peiffer, S., 2011. Carbonation of lignite fly ash at ambient T and P in a semi-dry reaction system for CO2 sequestration. Applied Geochemistry 26, 1502e1512. Berryman, E.J., Williams-Jones, A.E., Migdisov, A.A., 2015. Steel slag carbonation in a flowthrough reactor system: the role of fluid-flux. Journal of Environmental Sciences 27 (C), 266e275. Bertos, M.F., Simons, S.J.R., Hills, C.D., Carey, P.J., 2004. A review of accelerated carbonation technology in the treatment of cement-based materials and sequestration of CO2. Journal of Hazardous Materials 112, 193e205. Bessa, I.S., Castelo Branco, V.T.F., Soares, J.B., 2014. Evaluation of polishing and degradation resistance of natural aggregates and steel slag using the aggregate image measurement system. Road Materials and Pavement Design 15, 385e405. Bodor, M., Santos, R.M., Kriskova, L., Elsen, J., Vlad, M., Van Gerven, T., 2013. Susceptibility of mineral phases of steel slags towards carbonation: mineralogical, morphological and chemical assessment. European Journal of Mineralogy 25, 533e549. Boone, M.A., Peter Nielsen, Tim De Kock, Matthieu N Boone, Mieke Quaghebeur, 2014. Monitoring of stainless-steel slag carbonation using X - ray computed microtomography. Environmental science & Technology 48, 674e680. Carroll, J.J., Slupsky, J.D., Mather, A.E., 1991. The solubility of carbon dioxide in water at low pressure. Journal of Physical and Chemical Reference Data 20, 1201e1209. Chang, J., Wu, H., 2010. Study on carbonation mechanism of steel slag. The Journal of the Chinese Ceramic Society 38, 1185e1190 (in Chinese). Chang, E.E., Chen, C.H., Chen, Y.H., Pan, S.Y., Chiang, P.C., 2011a. Performance evaluation for carbonation of steel-making slags in a slurry reactor. Journal of Hazardous Materials 186, 558e564. Chang, E.E., Shu Yuan Pan, Yi Hung Chen, Hsiao Wen Chu, Chu Fang Wang, Pen Chi Chiang, 2011b. CO2 sequestration by carbonation of steelmaking slags in an autoclave reactor. Journal of Hazardous Materials 195, 107e114. Chang, E.E., Pan, S.Y., Chen, Y.H., Tan, C.S., Chiang, P.C., 2012a. Accelerated carbonation of steelmaking slags in a high-gravity rotating. Journal of Hazardous Materials 227e228, 97e106. Chang, E.E., Wang, Y.C., Pan, S.Y., Chen, Y.H., Chiang, P.C., 2012b. CO2 capture by using blended hydraulic slag cement via a slurry reactor. Aerosol and Air Quality Research 12, 1433e1443. Chang, E.-E., Chen, T.-L., Pan, S.-Y., Chen, Y.-H., Chiang, P.-C., 2013. Kinetic modeling on CO2 capture using basic oxygen furnace slag coupled with cold-rolling wastewater in a rotating packed bed. Journal of Hazardous Materials 260, 937e946. Chen, K.W., Shu Yuan Pan, Chun Tao Chen, Yi Hung Chen, Pen Chi Chiang, 2016. Highgravity carbonation of basic oxygen furnace slag for CO2 fixation and utilization in blended cement. Journal of Cleaner Production 124, 350e360. Constantinides Georgios, Ulm, F-josef, 2007. The nanogranular nature of C e S e H. Journal of the Mechanics and Physics of Solids 55, 64e90. Das, B., Prakash, S., Reddy, P.S.R., Misra, V.N., 2007. An overview of utilization of slag and sludge from steel industries. Resources, Conservation and Recycling 50, 40e57. Doucet, F.J., 2010. Effective CO2 -specific sequestration capacity of steel slags and variability in their leaching behaviour in view of industrial mineral carbonation. Minerals Engineering 23 (3), 262e269. Dri, M., Sanna, A., Maroto-Valer, M.M., 2014. Mineral carbonation from metal wastes: effect of solid to liquid ratio on the efficiency and characterization of carbonated products. Applied Energy 113, 515e523.

194

Carbon Dioxide Sequestration in Cementitious Construction Materials

Eloneva, S., Sebastian Teir, Justin Salminen, Carl-johan Fogelholm, Ron Zevenhoven, 2008. Steel converter slag as a raw material for precipitation of pure calcium carbonate. Industrial & Engineering Chemistry Research 2 (1), 7104e7111. Eylu, D., Filyos Refractories, 2002. Study on steel furnace slags with high MgO as additive in Portland cement. Cement and Concrete Research 32, 1247e1249. Frías, M., San-José, J.T., Vegas, I., 2010. Steel slag aggregate in concrete: the effect of ageing on potentially expansive compounds. Materiales de Construcci on 60 (297), 60. Ghouleh, Z., Rodrick I.L. Guthrie, Yixin Shao, 2015. High-strength KOBM steel slag binder activated by carbonation. Construction and Building Materials 99, 175e183. Ghouleh, Z., Roderick I L Guthrie, Yixin Shao, 2017. Production of carbonate aggregates using steel slag and carbon dioxide for carbon-negative concrete. Journal of CO2 utilization 18, 125e138. Guan, X., Liu, S., Feng, C., Qiu, M., 2016. The hardening behavior of g-C2S binder using accelerated carbonation. Construction and Building Materials 114, 204e207. Hosseini, T., Haque, N., Selomulya, C., Zhang, L., 2016. Mineral carbonation of Victorian brown coal fly ash using regenerative ammonium chloride e process simulation and technoeconomic analysis. Applied Energy 175, 54e68. Huijgen, W.J.J., 2005. Mineral CO2 sequestration by steel slag carbonation. Environmental Science and Technology 39 (24), 9676e9682. Isoo, T., Takahashi, T., Okamoto, N., Fukuhara, M., 2000. Development of large steelmaking slag blocks using a new carbonation process. Advances in Cement Research 12 (3), 97e101. Jang, J.G., Lee, H.K., 2016. Microstructural densification and CO2 uptake promoted by the carbonation curing of belite-rich Portland cement. Cement and Concrete Research 82, 50e57. Jo, H., Lee, M.-G., Park, J., Jung, K.-D., 2017. Preparation of high-purity nano-CaCO3 from steel slag. Energy 120, 884e894. Johnson, D.C., Macleod, C.L., Carey, P.J., Hills, C.D., 2003. Solidification of stainless steel slag by accelerated carbonation. Environmental Technology 24 (6), 671e678. Kodama, S., Nishimoto, T., Yamamoto, N., Yogo, K., Yamada, K., 2008. Development of a new pH-swing CO2 mineralization process with a recyclable reaction solution. Energy 33, 776e784. Kourounis, S., Tsivilis, S., Tsakiridis, P.E., Papadimitriou, G.D., Tsibouki, Z., 2007. Properties and hydration of blended cements with steelmaking slag. Cement and Concrete Research 37 (6), 815e822. € Mertens, G., Veulemans, W., Geysen, D., 2012. Effect of Kriskova, L., Pontikes, Y., Cizer, O., mechanical activation on the hydraulic properties of stainless steel slags. Cement and Concrete Research 42, 778e788. Le, D-hien, Yeong-nain Sheen, Quoc-bao Bui, 2017. An assessment on volume stabilization of mortar with stainless steel slag sand. Construction and Building Materials 155, 200e208. Lee, S., Kim, J.W., Chae, S., Bang, J.H., Lee, S.W., 2016. CO2 sequestration technology through mineral carbonation: an extraction and carbonation of blast slag. Journal of CO2 Utilization 16, 336e345. Li, D.X., Fu, X.H., Wu, X.Q., Tang, M.S., 1997. Durability study of steel slag cement. Cement and Concrete Research 27, 983e987. Li, J.X., Yu, Q., Jiangxiong Wei, Tongsheng Zhang, 2011. Structural characteristics and hydration kinetics of modified steel slag. Cement and Concrete Research 41, 324e329. Liu, S.H., Li, L.H., 2014. Influence of fineness on the cementitious properties of steel slag. Journal of Thermal Analysis and Calorimetry 117, 629e634.

Carbon dioxide sequestration on steel slag

195

Liu, S., Xuemao Guan, Saisai Zhang, Chi Xu, Haiyan Li, Jianwu Zhang, 2017. Sintering red mud based imitative ceramic bricks with CO2 emissions below zero. Materials Letters 191, 222e224. Manso, J.M., Polanco, J.A., Losa~nez, M., Gonzalez, J.J., 2006. Durability of concrete made with EAF slag as aggregate. Cement and Concrete Composites 28, 528e534. Mikkelsen, M., Jørgensen, M., Krebs, F.C., 2010. The teraton challenge. A review of fixation and transformation of carbon dioxide. Energy & Environmental Science 3, 43e81. Mo, L., Feng Zhang, Min Deng, 2016. Mechanical performance and microstructure of the calcium carbonate binders produced by carbonating steel slag paste under CO2 curing. Cement and Concrete Research 88, 217e226. Mo, L., Feng Zhang, Min Deng, Fei Jin, Abir Al-tabbaa, Aiguo Wang, 2017. Accelerated carbonation and performance of concrete made with steel slag as binding materials and aggregates. Cement and Concrete Composites 83, 138e145. Monshi, A., Asgarani, M.K., 1999. Producing Portland cement from iron and steel slags and limestone. Cement and Concrete Research 29, 1373e1377. Motz, H., Geiseler, J., 2001. Products of steel slags an opportunity to save natural resources. Waste Management 21, 285e293. Mun, M., Heechan Cho, Jihoe Kwon, 2017. Study on characteristics of various extractants for mineral carbonation of industrial wastes. Journal of Environmental Chemical Engineering 5 (4), 3803e3821. Pan, S.Y., Chiang, P.C., Chen, Y.H., Tan, C.S., Chang, E.E., 2013. Ex Situ CO2 Capture by Carbonation of Steelmaking Slag Coupled with Metalworking Wastewater in a Rotating Packed Bed. Environmental Science and Technology 47, 3308e3315. Pan, S.Y., Rahul Adhikari, Yi Hung Chen, Ping Li, Pen Chi Chiang, July 2016. Integrated and innovative steel slag utilization for iron reclamation, green material production and CO2 fixation via accelerated carbonation. Journal of Cleaner Production 137, 617e631. Pellegrino, C., Paolo Cavagnis, Flora Faleschini, Katya Brunelli, 2013. Properties of concretes with black/oxidizing electric arc furnace slag aggregate. Cement and Concrete Composites 37 (1), 232e240. Polettini, A., Raffaella Pomi, Alessio Stramazzo, 2016. CO2 sequestration through aqueous accelerated carbonation of BOF slag: a factorial study of parameters effects. Journal of Environmental Management 167, 185e195. Proctor, D.M., Hart, M., Two North, North Star Steel, Centennial Lake, Office Park, Structural Metals, et al., 2000. Physical and chemical characteristics of blast furnace, basic oxygen furnace, and electric arc furnace steel industry slags. Environmental Science & Technology 34 (8), 1576e1582. Rai, A., Prabakar, J., Raju, C.B., Morchalle, R.K., 2002. Metallurgical slag as a component in blended cement. Construction and Building Materials 16, 489e494. € Salman, M., Ozlem Cizer, Yiannis Pontikes, Rafael M. Santos, Ruben Snellings, Lucie Vandewalle, Bart Blanpain, Koen Van Balen, 2014. Effect of accelerated carbonation on AOD stainless steel slag for its valorisation as a CO2-sequestering construction material. Chemical Engineering Journal 246, 39e52. Santos, R.M., Van Bouwel, J., Vandevelde, E., Mertens, G., Elsen, J., Van Gerven, T., 2013a. Accelerated mineral carbonation of stainless steel slags for CO2 storage and waste valorization: effect of process parameters on geochemical properties. International Journal of Greenhouse Gas Control 17, 32e45. Santos, R.M., François, D., Mertens, G., Elsen, J., Van Gerven, T., 2013b. Ultrasound intensified mineral carbonation. Applied Thermal Engineering 57, 154e163.

196

Carbon Dioxide Sequestration in Cementitious Construction Materials

Sheen, Y.-N., Le, D.-H., Sun, T.-H., 2015a. Greener self compacting concrete using stainless steel reducing slag. Construction and Building Materials 82, 341e350. Sheen, Y.-N., Le, D.-H., Sun, T.-H., 2015b. Innovative usages of stainless steel slags in developing self-compacting concrete. Construction and Building Materials 101, 268e276. Sheen, Y.-N., Huang, L.-J., Sun, T.-H., Le, D.-H., 2016. Engineering properties of selfcompacting concrete containing stainless steel slags. Procedia Engineering 142, 79e86. Shi, C., 2004. Steel slag-its production, processing, characteristics, and cementitious properties. Journal of Materials in Civil Engineering 16, 230e236. Sipil€a, J., Sebastian Teir, Ron Zevenhoven, Johan Sipil€a, 2008. Carbon Dioxide Sequestration by Mineral Carbonation Literature Review Update 2005e2007. Suer, P., Lindqvist, J.-E., Arm, M., Frogner-Kockum, P., 2009. Reproducing ten years of road ageingdaccelerated carbonation and leaching of EAF steel slag. The Science of the Total Environment 407, 5110e5118. Svanera, M., Panza, S., Uberto, F., Roberti, R., 2012. An innovative system for the re-use of slag from the electric arc furnace. Metallurgia Italiana 104, 37e43. Tan, C., Chen, J., 2006. Absorption of carbon dioxide with piperazine and its mixtures in a rotating packed bed. Separation and Purification Technology 49, 174e180. Teir, S., Sanni Eloneva, Carl Johan Fogelholm, Ron Zevenhoven, 2007. Dissolution of steelmaking slags in acetic acid for precipitated calcium carbonate production. Energy 32 (4), 528e539. Tsakiridis, P.E., Papadimitriou, G.D., Tsivilis, S., Koroneos, C., 2008. Utilization of steel slag for Portland cement clinker production. Journal of Hazardous Materials 152, 805e811. Uibu, M., Kuusik, R., Andreas, L., KirsimVae, K., 2011. The CO2-binding by Ca-Mg-silicates in direct aqueous carbonation of oil shale ash and steel slag. Energy Procedia 4, 925e932. Ukwattage, N.L., Ranjith, P.G., Li, X., 2017. Steel-making slag for mineral sequestration of carbon dioxide by accelerated carbonation. Measurement: Journal of the International Measurement Confederation 97, 15e22. U.S. Geological Survey, Mineral Commodity Summaries, January, 2018. https://minerals.usgs. gov/minerals/pubs/commodity/iron_&_steel_slag/. Wang, W.C., 2014. Feasibility of stabilizing expanding property of furnace slag by autoclave method. Construction and Building Materials 68, 552e557. Wang, Q., Yan, P., 2010. Hydration properties of basic oxygen furnace steel slag. Construction and Building Materials 24, 1134e1140. Wang, G., Wang, Y.H., Gao, Z.L., 2010. Use of steel slag as a granular material: volume expansion prediction and usability criteria. Journal of Hazardous Materials 555e560. Wang, Q., Yan, P.Y., Feng, J.W., 2011. A discussion on improving hydration activity of steel slag by altering its mineral compositions. Journal of Hazardous Materials 186, 1070e1075. Wang, Q., Yan, P.Y., Yang, J.W., Zhang, B., 2013. Influence of steel slag on mechanical properties and durability of concrete. Construction and Building Materials 47, 1414e1420. Wang, Q., Dengquan Wang, Shiyu Zhuang, 2017. The soundness of steel slag with different free CaO and MgO contents. Construction and Building Materials 151, 138e146. Yi, H., Xu, G., Cheng, H., Wang, J., Wan, Y., Chen, H., 2012. An overview of utilization of slag and sludge from steel industries. Procedia Environmental Sciences 16, 791e801. Yu, J., Wang, K., 2011. Study on characteristics of steel slag for CO2 capture. Energy & Fuels 25, 5483e5492. Yunxia, L.U.N., Zhou Mingkai, C A I Xiao, X U Fang, 2008. Methods for improving volume stability of steel slag as fine aggregate. Journal of Wuhan University of TechnologyMaterials Science Edition 23, 737e742.

Carbon dioxide sequestration on steel slag

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Zhang, L., 2009. Construction Materials Prepared by Steel Slag with Carbonation Curing. Jinan University. Zhang, T.S., Yu, Q.J., Wei, J.X., Li, J.X., Zhang, P.P., 2011. Preparation of high performance blended cements and reclamation of iron concentrate from basic oxygen furnace steel slag. Resources, Conservation and Recycling 56, 48e55. Zhang, T.S., Yu, Q.J., Wei, J.X., Li, J.X., 2012. Investigation on mechanical properties, durability and micro-structural development of steel slag blended cements. Journal of Thermal Analysis and Calorimetry 110, 633e639. Zhao, H., Chang, J., Cheng, X., 2010. Manufacturing of Building Materials with Carbonated Steel Slag and Cement, vol. 24. J. Univer Jinan, pp. 111e114 (in Chinese).