Effects of Ca-ligand stability constant and chelating agent concentration on the CO2 storage using paper sludge ash and chelating agent

doi:10.1016/j.jcou.2020.101202

Journal of CO2 Utilization

Volume 40, September 2020, 101202

https://doi.org/10.1016/j.jcou.2020.101202 Get rights and content

Highlights

•
This study provides how to maximize CO2 storage and produce high purity CaCO3.
•
Ca-ligand stability constant affects the yield, purity, and morphology of CaCO3.
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Chelating agent concentration affects the yield, purity, and morphology of CaCO3.
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Use of citrate with Log K of 4.7 enables the CaCO3 yield maximized.
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Chelating agent with low stability constant produces pure vaterite type CaCO₃.

Abstract

In this paper, we performed an experimental study on how to maximize CO₂ storage, produce high purity CaCO₃, and control the morphology of CaCO₃ in the process of indirect carbonation using paper sludge ash (PSA) and chelating agents as solvents. To this end, the effects of the Ca-Ligand (Ca-L) stability constant and concentration of chelating agents on the Ca extraction efficiency, carbonation efficiency, and the characteristics of CaCO₃ produced were investigated. For the study, a total of seven chelating agents (fumarate, adipate, malonate, IDA, citrate, NTA, and EDTA) in a wide range of Ca-L stability constant (Log K) of 2.0–12.4 were adopted, and the concentrations of each chelating agent were adjusted to 0.1 and 0.5 M. According to the experimental results, it was revealed that the storage of CO₂ and the yield, purity, and morphology of CaCO₃ could be controlled by adjusting the type (or Ca-L stability constant) and concentration of the chelating agent. The higher the Ca-L stability constant and concentration of the chelating agent, the higher the Ca extraction efficiency, but the lower the carbonation efficiency. The highest CO₂ storage and CaCO₃ production were obtained by using citrate with a Log K value of 4.7.

Introduction

Recently, the carbon capture, utilization, and storage (CCUS), which not only stores CO₂ but also utilizes it as an industrial resource, has drawn considerable attention [[1], [2], [3]]. A typical example of such a CCUS technology is indirect carbonation. Indirect carbonation is a technology that extracts Ca and Mg from natural minerals and industrial by-products by using solvents, then stores CO₂ through carbonation reaction and simultaneously produces high purity carbonate solids. High purity CaCO₃ produced through indirect carbonation can be used in paper, plastics, paint, cosmetics, and medical industries [4].

The solvents that have been mainly used for indirect carbonation include acids, ammonium salts, and chelating agents [[5], [6], [7], [8], [9], [10], [11], [12], [13], [14]]. Many researchers have studied Ca extraction reactions and carbonation reactions under a wide variety of physicochemical conditions in order to increase CO₂ storage and CaCO₃ production through indirect carbonation using various solvents and industrial by-products. For example, Jo et al. [6] performed indirect carbonation using waste concrete and ammonium salts (NH₄Cl, CH₃COONH₄, NH₄NO₃, and (NH₄)₂SO₄) as solvents. When CH₃COONH₄ and NH₄NO₃ were used, the Ca elution efficiency and carbonation efficiency were higher than those of the other solvents. Also, Kim et al. [10] eluted Ca from cement kiln dust using 12 solvents, among which five solvents (hydrochloric acid, acetic acid, ammonium chloride, ammonium acetate, and sodium citrate) exhibited high Ca extraction efficiency. In the study, they determined optimal solvent concentration, reaction time, solid to liquid ratio, and reaction temperature for maximizing Ca elution from cement kiln dust. Subsequently, Kim et al. [13] conducted indirect carbonation using paper sludge ash (PSA) and six solvents (acetic acid, hydrochloric acid, ammonium chloride, ammonium acetate, sodium citrate, and water) to maximize CO₂ storage and CaCO₃ production by pH swing and CO₂ dose adjustment.

In this study, we attempted to conduct Ca extraction by using chelating agents as solvents and then proceed carbonation reaction. Until now, there have not been conducted many studies on indirect carbonation using chelating agents. In addition, most of the previous studies have focused only on metal extraction, not on carbonation reactions [[15], [16], [17]]. In literature, the Ca extraction using chelating agents has been studied as follows. Seo et al. examined acetic, gluconic, and citric acids used as solvents for the Ca extraction from blast furnace slag [15]. They found that citric acid exhibited the highest efficiency. The Ca extraction rate could be increased by either decreasing particle size and solid/liquid ratio or increasing solvent concentration and stirring speed. Jadhav et al. used a total of four organic acids, including citric, malic, oxalic, and gluconic acids, to compare the Ca extraction efficiency from incineration bottom ash (IBA) and then found that citric acid was the most effective extracting agent [16]. For example, 1 M citric acid could extract 84 wt% Ca from IBA at 30 °C. Ghoorah et al. evaluated the effects of formic, acetic, and DL-lactic acids on the Ca-leaching process from wollastonite to explain the fact that the chelating agent weakens the Ca-O bond and then releases Ca from the crystal lattice to form complexes [17].

After extracting Ca from natural minerals and industrial by-products using chelating agents, CaCO₃ was mostly produced by injecting CO₂, but in some cases, Ca-L complexes could be precipitated in the process. Santos et al. attempted to extract Ca from steelmaking blast furnace slag using succinic and acetic acids for the CaCO₃ production [18]. While the extraction efficiency by succinic acid was superior, carbonation of the succinic acid leachate did not result in the production of CaCO₃, but rather precipitation of calcium succinate. In contrast, carbonation of the acetic acid leachate produced CaCO₃ after pH swing using sodium hydroxide or bicarbonate. In another study, Zhao et al. extracted Ca from wollastonite using a total of eleven chelating agents (acetic, picolinic, gluconic, phthalic, citric, ascorbic, glutamic, and oxalic acids, IDA, NTA, and EDTA) [5]. They attained about 15 % Ca extraction by improving the dissolution rate of wollastonite with a dilute chelating agent of 0.006 M. Here, both calcite and vaterite types of CaCO₃ were produced by injecting CO₂ into the Ca leachates. Baldyga et al. conducted indirect carbonation with wollastonite as raw material by using succinic and acetic acids as solvents [19]. The Ca extraction from wollastonite was facilitated at higher temperature, and the carbonation to produce CaCO₃ was also promoted at higher temperature and pressure.

When chelating agents are used as solvents in indirect carbonation, their Ca-L stability constants may affect not only the Ca extraction efficiency, but also the carbonation efficiency. However, few studies have been conducted to scrutinize the effects of the stability constant using various chelating agents. To the best of the authors’ knowledge, no attempt has been made in the literature up to now to find optimal chelating agents with Ca-L stability constants suitable for maximizing CO₂ storage and producing high purity CaCO₃ through indirect carbonation.

Paper sludge ash (PSA), an alkali industrial by-product produced in paper mills, is not only high in the Ca content, but also tiny in the particle size, indicating that it is excellent raw material that can be used in indirect carbonation without pre-treatment such as grinding. CO₂, emitted in large quantities from the paper production process, can be stored in the form of CaCO₃ through indirect carbonation, and further the produced CaCO₃ can be reused in paper mills. Nevertheless, so far, PSA has not been used so much as raw material in indirect carbonation [13,20]. In Korea, average annual paper production is about 12 million tons, and paper sludge is about 7–17 % of the paper production [[21], [22], [23]]. Currently, most of the PSA is landfilled, and only a small part of them are recycled. Research has been conducted to recycle the PSA mainly into solidifying agents, light-weight aggregates, and recycled bricks.

In this study, we extracted Ca from PSA by using a total of seven chelating agents (fumarate, adipate, malonate, IDA, citrate, NTA, and EDTA) with Ca-L stability constants (Log K) of 2.0–12.4 and then injected CO₂ into the Ca leachates for carbonation (Fig. 1). We compared the CO₂ storage and the yield, morphology, purity, and particle size of CaCO₃ obtained using the seven different chelating agents of two concentrations (0.1 M and 0.5 M). After investigating the effects of the Ca-L stability constant on the Ca extraction and carbonation, we determined optimal chelating agents for maximizing the CO₂ storage and producing the high purity CaCO₃. We also examined the effects of the chelating agent concentration on Ca extraction and carbonation.

Section snippets

Experimental materials and analysis

PSA, supplied from a ‘G’ paper manufacturing company in Korea, was dried at 105 °C for 24 h and then sieved to 425 μm. The seven solvents that extract Ca from PSA include fumarate, adipate, malonate, iminodiacetate (IDA), citrate, nitrilotriacetate (NTA), and ethylenediaminetetraacetate (EDTA) ligands (Table 1). For convenience, throughout this manuscript, they have named ligands: fumarate, adipate, malonate, IDA, citrate, NTA, and EDTA. Their Ca-L stability constants (Log K) ranged from

Characteristics of PSA

The major components of PSA were Ca (67.2 %), followed by Si (15.0 %), Al (6.6 %), Mg (4.4 %), S (2.7 %), Fe (1.8 %), P (0.5 %), and others. According to the XRD and TGA analyses, Ca was present in PSA mainly in the form of CaCO₃, CaO, and Ca(OH)₂, and the CaCO₃ content was as high as 30.2 % (Fig. 2). The average particle size of PSA was 17.5 μm (Fig. 3).

Ca extraction from PSA using chelating agents

Fig. 4 shows the results of Ca extraction from PSA using the seven chelating agents with concentrations of 0.01 M–1.0 M and water. For all

Conclusions

In this study, we found that the stability constant and concentration of the chelating agents had significant effects on the yield, purity, and morphology of CaCO₃ produced. The use of citrate with Log K of 4.7 enabled the CaCO₃ yield maximized, and the chelating agents (fumarate, adipate, malonate, and IDA) with low stability constants (Log K = 2.0–3.5) produced high purity CaCO₃ with a relatively high content of vaterite. The maximum CO₂ sequestered using PSA was 142 kg−CO₂/ton-PSA when 0.1 M

CRediT authorship contribution statement

Myoung-Jin Kim: Conceptualization, Methodology, Writing - original draft, Writing - review & editing. Junhyeok Jeon: Investigation, Visualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was a part of the project titled ‘Production of highly functional calcium-magnesium composites based on CCUS using seawater and shell and raw material standardization’, funded by the Ministry of Oceans and Fisheries, Korea. This work was also supported by the research fund of the Busan Green Environment Center (19-3-50-54).

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View full text

Effects of Ca-ligand stability constant and chelating agent concentration on the CO2 storage using paper sludge ash and chelating agent

Highlights

Abstract

Introduction

Section snippets

Experimental materials and analysis

Characteristics of PSA

Ca extraction from PSA using chelating agents

Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

Chem. Eng. J.

Energy

Chem. Eng. J.

Chem. Eng. J.

Appl. Energy

Chem. Eng. J.

Chem. Eng. J.

Qual. Assur. Util. Rev.

Qual. Assur. Util. Rev.

Fuel.

Hydrometallurgy.

Chem. Eng. Res. Des.

Chem. Geol.

Worldwide innovations in the development of carbon capture technologies and the utilization of CO2

Energy Environ. Sci.

A review of mineral carbonation technologies to sequester CO2

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