CO2 sequestration exploration utilizing converter slag and cold-rolling waste water: The effect of carbonation parameters

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Abstract

The exploration of carbonation routine utilizing BOFs, CRW and CO2 has a significant effect on terminated treatment of metallurgical wastes resourceful disposal at a low cost. This paper investigated the collaborative effect of CRW composition on slag carbonation degree and CRW decalcification rate in CO2 sequestration system, furthermore, the effect of reaction time etc. on both were also discussed under optimal composition. Moreover, the carbonation process was simulated by Aspen software for comparing with the experimental results. The results showed that slag carbonation degree and CRW decalcification rate increased as CRW hardness increased, and kept stable. The optimal calcium conversion was 50.4 %, corresponding to 15.9g CO2/100g slag, and the decalcification rate was 87.1 %, respectively, at 80 °C and 10 L/kg for 60 min. The Aspen simulation results showed the correlation degrees were 0.94 for calcium conversion and 0.98 for decalcification rate.

Introduction

Accelerated carbonation, referring to carbonize with alkaline materials, is proved to be a feasible and appropriate technology for carbon capture, utilization and storage (CCUS) (Chang et al., 2012; Zhang et al., 2018; Pan et al., 2015). Because it can accelerate the natural weathering of metallic oxide and silicate to react with CO2, and form carbonates with stable chemical properties. Otherwise, accelerated carbonation had advantages of longer storage time and economical (Lackner, 2003). For accelerated carbonation, the sequestration carrier was significant. There are many natural minerals and industrial residues containing metallic oxide and silicate. The former was rarely considered due to its cost for grounding, the latter such as slag (EAF and BOF) (Kinoshita et al., 2014; Meddah et al., 2014) was utilized for mineral carbonation due to its large output (about 130 million tons) (van Zomeren et al., 2011), fine particle size and high alkalinity (36−60 wt% CaO (Waligora et al., 2010)), which was produced from the process of steel production. In addition, the carbonated slag is more stable and can be used as construction building materials and roadbed materials. Thus, it can not only cut CO2 emission but also dispose of slag resources reasonably by utilizing slag to sequestrate CO2.

Slag sequestration CO2 research aims at accelerating the carbonation. Therefore, many process routes have been discussed for mineral CO2 sequestration (Comans and Huijgen, 2003), of which the aqueous carbonation route (O’connor et al., 2005) was selected due to technological and economical consideration. In aqueous carbonation, the reaction was found to occur in three steps: (1) dissolution of CO2 in solutions; (2) leaching of calcium from slag; (3) precipitation of CaCO3 on the surface of slag. The limited step was proved to be the reaction kinetics of calcium leaching (Huijgen and Comans, 2005). To promote the kinetics of calcium leaching, researchers have done a lot of work. The results showed that longer duration time (about 120 min), higher temperature (around 80 °C), lower liquid to solid ratio (20 L/Kg) and finer particle size (<200 μm) can accelerate calcium leaching and enhance carbonation efficiency obviously (Huijgen and Comans, 2005; Chang et al., 2011a; Librandi et al., 2017; Polettini et al., 2016a; Chang et al., 2011b). Otherwise, the reactor can also affect the calcium leaching kinetics through the principle of operation. For example, the rotating packed bed (RPB) enhanced the calcium leaching kinetics via destroying the dense CaCO3 layer on the surface of slag, carbonation degree could reach from 70 % to 93.5 % at about 60 °C, 120 min, 20 L/Kg and 1 atm (Chang et al., 2012; Li et al., 2018). The column can promote the calcium leaching by aeration stirring, the carbonation degree reached 32.7 %–44 % at 50 ± 10 °C, 120 min, 10 L/Kg and 1 atm (Chang et al., 2011a; Pan et al., 2016). The autoclave was also used to accelerate carbonation due to the dissolution kinetics of calcium-silicon phase was better as temperature increased and the CO2 solubility was promoted at high pressure, the results could reach 52.43 %–56.18 % at 100 ± 10 °C, 80 ± 10 min, 10 ± 5 L/Kg and 15 ± 5 atm (Huijgen and Comans, 2005; Polettini et al., 2016b; Santos et al., 2012). In our work, we choose autoclave to perform aqueous carbonation, comprehensively because of carbonation degree, cost and operation energy.

Otherwise, leaching agent also had a significant effect on calcium leaching kinetics, in the later, distilled water and specific salts system were extensively investigated in detail. The carbonation process in distilled water required a large amount of water and the carbonation degree was 15 %–40 % (Comans and Huijgen, 2003; Polettini et al., 2016a, b; Baciocchi et al., 2009). In terms of low carbonation degree, some researchers had proposed to add certain salts into water to promote calcium leaching. For example, a bicarbonate/salt mixture (NaHCO3/NaCl) was used to accelerate carbonation reaction by O'Connor et al. (O’Connor et al., 2000), and Katsunori Yogo et al. used ammonium salts (NH4Cl, NH4NO3) in carbonation process to promote the calcium leaching in aqueous and the ammonium salts can be recycled (Katsunori Yogo et al., 2005). The calcium leaching could reach 60 %–94.9 % at 50 ± 10 °C, 40 ± 10 min, 15 ± 5 L/Kg and 1 atm. Similar to them, Eloneva et al. also tried some agents (HCl, acetic acid and NH4Cl) to promote the carbonation efficiency. The results showed that carbonation degree could reach 60 %–70 % at similar condition (Teir et al., 2007; Eloneva et al., 2008, 2010; Eloneva et al., 2012). Other ions such as SO42−, Mg2+, COOH- and Na+ were also added into water to facilitate carbonation (Sun et al., 2011; Lee et al., 2016; Teir et al., 2016; Chiang et al., 2014). Compared with Danielle et al. (Bonenfant et al., 2008) used distilled water to carbonize and carbonation degree reached 13.2 %–25.55 % at 20 °C, 80 ± 30 min, 5 L/Kg and 1 atm, the results were better. The reason was that the existing ion in water can increase the mass transfer rate of CO2, although the solubility of CO2 was reduced (Gilbert et al., 2016). On the other hand, some ions (NH4+, Cl-) can enhance calcium leaching kinetics through reacting with calcium-silicon phase to release Ca2+ from slag. However, the collaborative effect of ions superposition on carbonation degree was not discussed at all. Thus, a kind of economical leaching medium binding with ions superposition effect is need to be explored.

Cold-rolling waste water (CRW), producing in the steelmaking process, mainly contains a large number of calcium ion, chloride ion, sulfate ion and sodium ion, etc. The traditional CRW treatment methods are acid-base neutralization and softening desalinization. Compared with the methods, carbonation treatment strategy is suitable for purifying some ions such as calcium ion due to its lowering energy consumption. In carbonation route, the collaborative effect of ions on reaction kinetics of calcium leaching will be well and carbonation efficiency will be promoted. CRW also had a high alkalinity (pH value), which increased the CO32− content in solutions (Comans and Huijgen, 2003; Chang et al., 2013). Additionally, the ions in CRW increased the mass transfer rate of CO2 (Nyambura et al., 2011). Researchers had done some work to accelerate carbonation utilizing CRW, especially terminal CRW (Chang et al. and Pan et al.) at 65 ± 10 °C, 40 ± 10 min, 15 ± 5 L/Kg and 1 atm, and the results showed that carbonation efficiency was 70 %–95.3 % (Chang et al., 2013; Pan et al., 2013a). However, there were many kinds of CRW in multiple stages depending on steelmaking process, and their composition was fluctuating, which may dominate the carbonation efficiency. There was rare discussion on the effect of CRW composition on carbonation degree. Thus, we decided to focus on the effect of CRW composition changes on carbonation efficiency.

In this paper, a route utilizing slag-CRW−CO2 to carbonize in an autoclave was investigated. The effect of CRW composition on carbonation degree was systematically discussed, and at the same time, a new parameter was introduced, decalcification rate, which meant the change of calcium content before and after carbonation in waste water. The main purpose in this study was to obtain the optimal CRW composition using slag and CRW to carbonize. Additionally, different reaction temperature, duration time and liquid to solid ratio were explored under optimal CRW composition. Finally, another analyzing method such as Aspen was used to simulate the carbonation process. The results were compared with the experimental results.

Section snippets

Materials

The BOF slag used in this study was provided by Wuhan iron and steel group corporation (Wuhan, China). The chemical composition of the fresh BOF slag was determined with ASTM method C114 using XRF (Axios max, PANalytical). The main composition of the slag is 48.5 wt%CaO, 16.3 wt%SiO2, 1.7 wt%Al2O3, 2.0 wt%MnO, 7.7 wt%MgO and 14.1 wt%Fe2O3, respectively. The alkalinity (ratio of Ca/Si) of this study is 2.9, which is lower than those of 3.8 (Chang et al., 2013) and 3.1 (Li et al., 2018). The slag

Properties of feedstock and carbonated product

The results of thermodynamic properties analysis of fresh and carbonated slag are shown in Fig. 2. It can be seen that the TG curve of fresh slag was basically a straight line, which meant that trace amount of CaCO3 in fresh slag was tested. For carbonated slag, there was a mass change in TG curve and a heat change in DTA curve at about 105 °C, due to the evaporation of moisture. Another point of mass change was from 105 °C to 725 °C because of the decomposition of organic. The last paint of

Conclusion and prospect

This paper aims to accelerate carbonation in an autoclave with converter slag and CRW. The effect of parameters on carbonation degree of slag and decalcification rate of CRW were investigated. The conclusions were:

  • 1

    Through the investigation of CRW composition, the results showed that carbonation degree and decalcification rate increased as CRW composition increased, eventually reached 38.4 % and 96.9 % when CRW composition was 300.0 ppm Ca2+, 304.0 ppm Na+, 350.0 ppm Cl, 400.0 ppm SO42- and

Contribution of authors

I really appreciate the contribution of Master Jianping Dong, who arranged the TGA-DSC, SEM/EDS and the XRD analysis. Additional, thank you very much supervisor Huining Zhang, who has reviewed and proposed much more valuable comments for polishing this article. Editorial efforts from journal editors are as well acknowledged. Thank you for the finance support of National Natural Science Foundation of China (52064020),Jiangxi provincial education department project (GJJ170509), Science and

Declaration of Competing Interest

The authors report no declarations of interest.

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