Determination of Free MgO in Steelmaking Slags by Solvent Extraction Using 2,2,2-trichloroethanol Combined with Atomic Absorption Spectrometry

Abstract

Magnesium oxide (MgO) contained in steelmaking slags in its liberated form, referred to as free MgO, expands when hydrated. The expansion of free MgO sometimes causes the deterioration of steelmaking slags used as construction materials for roads. Therefore, a method that determines the free MgO content in steelmaking slags is required. Solvent extraction is a promising preparation method for determining free MgO in steelmaking slags. Herein, organic solvents were explored for their extraction capabilities, and MgO was successfully extracted with 2,2,2-trichloroethanol (TCE) at 140°C over 3 h. TCE could not be used to extract any other magnesium compounds in blast furnace slags or merwinite, which contain no free MgO, indicating that free MgO was selectively extracted with TCE. The MgO content determined by TCE extraction and atomic absorption spectrometry was found to be reasonably consistent with that determined by other methods, which implies that this method is suitable for measuring the MgO content in steelmaking slags. The mechanism for the extraction of MgO by TCE was also investigated, and it was found that TCE extraction occurred via an acid-base reaction and an oligomerization crosslinking reaction.

1. Introduction

Most steelmaking slags produced in steel manufacturing are reused as materials in the construction of roads and other civil engineering projects. Magnesium oxide (MgO) derived from dolomite, which is added during steel manufacturing, sometimes remains in the steelmaking slags in its liberated form. MgO may also crystallize during the solidification step of the manufacturing process.¹⁾ MgO liberated from the crystal phase in the slags is called free MgO. When MgO is converted to Mg(OH)₂ by a hydration reaction, its volume increases by approximately 2.2 times, resulting in expansion. Similar reactions are known to occur for calcium oxide (CaO), which is also contained in steelmaking slags.²⁾ The expansion of steelmaking slags may sometimes lead to the deterioration of roads when the slags are used as road-construction materials. Therefore, accurate methods to determine the free CaO and free MgO content in steelmaking slags are required for the recycling of steelmaking slags. For the determination of the free CaO content in steelmaking slags, a method for extraction using ethylene glycol followed by atomic spectrometric analysis was developed and recommended by the research group of the Iron and Steel Institute of Japan in 2013.^3,4) This method is based on the extraction of CaO in ethylene glycol via the chelation of calcium ions with ethylene glycol.⁵⁾ However, ethylene glycol does not effectively dissolve MgO, as the smaller magnesium ions do not form stable chelating rings with oxyethylene units. Consequently, it is difficult to determine free MgO in steelmaking slags by extraction with ethylene glycol.

While standard analytical methods for free CaO in steelmaking slags have been established as described above,^3,4) there are no reliable methods to determine the contents of free MgO in steelmaking slags, despite several attempts by researchers.^{6,7,8,9,10,11,12)} X-ray diffraction (XRD),^{6) 29}Mg nuclear magnetic resonance (NMR),⁷⁾ and thermogravimetric (TG) analysis,⁸⁾ as well as extraction methods using aqueous ammonium nitrate,⁹⁾ an ethanolic iodine solution,¹⁰⁾ ethylene glycol containing iodine,¹¹⁾ and a mixture of ethanol and ethylene glycol containing iodine¹²⁾ have been reported as potential methods to determine the free MgO content in steelmaking slags. Among these analytical methods,²⁹Mg NMR is believed to be the most accurate because the chemical shifts of MgO differ significantly from those of other Mg compounds.⁷⁾ However, as ²⁹Mg NMR requires a long analysis time to acquire reliable data, it is not considered practical. Compared to physical methods, such as NMR, XRD, and TG, chemical methods that combine solvent extraction with atomic spectrometry are considered more practical to determine the MgO content in steelmaking slags, because these techniques are commonly used for steel analyses and are easy to perform. However, because the solvents used in the extraction methods lack selectivity for MgO, they also extract some other unwanted magnesium compounds from steelmaking slags.^9,10,11,12)

In this study, we explored a variety of solvents for the selective extraction of free MgO from steelmaking slags to develop a selective determination method for free MgO. Throughout the investigation, we considered the high basicity of MgO compared to other magnesium compounds. The study focused predominantly on chlorinated alcohols because their hydroxyl groups possess an acidic proton that reacts with MgO. The chemical mechanisms associated with the dissolution of MgO in 2,2,2-trichloroethanol (TCE) were also investigated in this study.

2. Experimental

2.1. Apparatus

Free MgO was extracted from steelmaking slags under heating and stirring conditions in an oil bath filled with silicone oil placed on a magnetic stirrer. Disposable syringes equipped with hydrophilic PTFE membrane filters with a pore size of 0.45 μm were used to filter the mixture. A HORIBA F53 pH meter was used to measure the pH. A high-resolution continuous light source atomic absorption spectrometer (ContraAA800D, Analytik Jena) was used to determine the Mg extracted from steelmaking slags. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (TOF-MS, Autoflex II, Bruker-Daltonics, Bremen, Germany) and gas chromatography/mass spectrometry (GC-MS, GC-17A-QP5050A, Shimadzu) with an HP-1MS column were conducted to obtain the mass spectra of the extracted MgO.

2.2. Reagents

Reagent-grade halogenated alcohols, TCE, 2,2,2-trifluoroethanol, and 2,2,3,3,3-pentafluoropropanol were purchased from Tokyo Chemical Industry. Table 1 shows the structural formulas, acid dissociation constants,¹³⁾ and boiling points of these alcohols. MgO (99.99%) was obtained from Wako Pure Chemical Industries. All other reagents were of special grade. Tap water was purified with a Millipore Elix Advantage 5 pure water production device, followed by further purification with an ORGANO PURELAB ultrapure water production system to achieve a specific resistance of 18.2 MΩ·cm. Ultrapure water was used in all experiments.

Table 1. List of alcohols investigated.

Alcohol	Chemical formula	boiling point/°C	pKa13)
Ethanol	CH3CH2OH	78.37	16
2,2,2-trichloroethanol	CCl3CH2OH	152–154	12.24
2,2,2-trifluoroethanol	CF3CH2OH	77–80	12.4
2,2,3,3,3-pentafluoropropanol	CF3CF2CH2OH	80–81	not available

Steelmaking slags, blast furnace slags, and merwinite were donated by the “Development and Standardization of Free MgO Analysis Method in Steel Slag” research group of the Iron and Steel Institute of Japan; they were crushed and sieved to achieve a particle size of 75 μm or smaller. The samples were then stored in a desiccator. Prior to use, the samples were heated to 400°C and subsequently cooled at 20–25°C under vacuum for 4 h.

2.3. Dissolution of MgO in Alcohols

Alcohol (20 g) and MgO (0.0404 g, 1.00 × 10⁻³ mol) were added to a 100 mL Erlenmeyer flask with a stopper, and the mixture was heated and stirred in an oil bath at a prescribed temperature for a prescribed time. When a gel was formed during heating with TCE, 20 g of methanol was added to the reaction mixture to collapse the gel to form a homogeneous solution. Subsequently, the Erlenmeyer flask was transferred to a water bath and cooled for 10 min. The resulting mixture was transferred to a centrifuge tube and centrifuged at 3000 rpm for 10 min. The supernatant was filtered using a 0.45 μm membrane filter. The filtered solutions (4.0 g) were added to a 200 mL conical beaker with 50 mL of water, 1 mL of ammonia buffer (pH 10.0), and a few drops of Eriochrome Black T indicator solution. The resulting solution was subjected to chelating titration using 5 × 10⁻³ mol/L EDTA.

2.4. Extraction and Quantification of Free MgO from Steelmaking Slag

TCE (20 g) and steelmaking slag (0.100 g) were added to a 100 mL Erlenmeyer flask with a stopper. The mixture was heated and stirred at 140°C for 3 h in an oil bath. After the extraction of free MgO, the solution was filtered using a membrane filter with a pore size of 0.45 μm. Ten grams of the filtrate were transferred to a 50 mL beaker and heated on a hot plate to volatilize the solvent. After adding 5 mL of concentrated nitric acid to dissolve the residue, the mixture was heated to dryness. After cooling the beaker, 5 mL of 2 mol/L hydrochloric acid was added to completely dissolve the residue. The final volume of the resulting solution was adjusted to 100 mL using water. The concentration of Mg in the solution was measured by atomic absorption spectrometry. The free MgO content was calculated from the measured concentration, as the magnesium species extracted from the steelmaking slag was known to be free MgO.

3. Results and Discussion

3.1. Exploration of Extraction Solvents

As metal oxides are typically inorganic compounds, they have poor solubility in organic solvents. The solubilization of CaO in ethylene glycol is a rare exception, which is facilitated by the chelation of calcium ions with ethylene glycol.^4,5) However, as ethylene glycol does not dissolve MgO, we had to explore other solvents in this study.¹⁴⁾

The acid-base reaction is another reaction that can potentially dissolve metal oxides in organic solvents. Protonic solvents are promising candidates for the dissolution of basic metal oxides. Hence, halogenated alcohols were examined for their ability to dissolve MgO, because the electronegative halogen atoms attract the lone pairs of electrons on the oxygen atom of the halogenated alcohols, which increases the acidity of the hydroxyl group. The halogenated alcohols studied here exhibited weak acidity in water (Table 1).¹³⁾ In addition to the three halogenated alcohols, ethanol was also tested for comparison. Table 2 presents the solubility of MgO in alcohols at 78°C and 120°C. While low solubility was observed at 78°C for MgO in every halogenated alcohol, the solubility in TCE increased above 120°C. Ethanol did not dissolve MgO under the studied heating conditions. In addition, ethylene glycol did not dissolve MgO at 120°C (data not shown). Thus, the acidity of the solvent is more important for dissolving MgO than complexation, suggesting that the acid-base reaction between MgO and the halogenated alcohols plays an important role in the dissolution of MgO. Note that calcium ions did not interfere with the determination of Mg by atomic absorption spectrometry, although TCE also dissolved CaO and MgO. Therefore, the dissolution of CaO from steelmaking slag is not discussed here.

Table 2. Solubility of magnesium oxide in halogenated alcohols under heating condition.

Alcohol	at 78°C	Solubility g-MgO/ g-solvent at 120°C
Ethanol	insoluble	Not examined
2,2,2-trichloroethanol	9.8×10−6	1.7×10−3
2,2,2-trifluoroetanol	1.6×10−6	Not examined
2,2,3,3,3-pentafluoroethanol	7.8×10−6	Not examined

3.2. Effect of Heating on Dissolution of MgO in TCE

As discussed in the previous section, heating is an important factor for dissolving MgO in TCE. In this section, the effects of temperature and heating time on the dissolution of MgO in TCE are investigated. Increasing temperature increased the solubility of MgO (Fig. 1(a)). Note that heating at 150°C should be avoided for the sake of the safe operation because of the boiling point of TCE, 152–154°C. As shown in Fig. 1, entire dissolution of 1.00 × 10⁻³ mol of MgO could not be attained at 140°C for 3 hours. However, 5.00 × 10⁻⁴ mol of MgO was completely dissolved in TCE under the conditions. Note that the solubility of MgO increased remarkably above 120°C along with gel formation, indicating that chemical reactions involving dissolved Mg species other than the acid-base reaction would increase the solubility of MgO. No gels were formed in the absence of MgO, even when TCE was heated. At 140°C, the solubility of MgO increased with increasing heating time (Fig. 1(b)). Gel formation became significant after 1 h at 140°C. Considering the above results, 140°C and 3 h were selected as the temperature and time for the subsequent experiments.

Fig. 1.

Effects of a) temperature and b) heating time on dissolution of 1.00 × 10⁻³ mol of MgO into 20 g of 2,2,2-trichloroethanol (TCE). When the temperature was varied, the heating time was set to 3 h. When the heating time was varied, the temperature was set to 140°C. (Online version in color.)

To confirm the involvement of MgO in gel formation, the formed gels were isolated from a TCE solution by filtration and heated to dryness. The obtained white residue was weighed and dissolved in water to quantify the Mg content. The dried gels contained 11.8% g/g magnesium, indicating that the MgO that dissolved in TCE participated in the formation of the gel skeleton. The content of magnesium in dried gels were not influenced by the amount of MgO added into TCE. Considering the content of magnesium of 11.8% in dried gels, it was estimated that almost 77% of magnesium participated in linkages in the gel networks.

3.3. Dissolution of other Mg Compounds in TCE

The selective extraction of MgO is also an important issue for the development of a reliable method to determine MgO in steelmaking slags, because other Mg compounds extracted in TCE could interfere with the atomic spectrometric determination of MgO. Figure 2 shows the results for the dissolution of commercially available Mg compounds. Note that the dissolution of Mg is governed by the quantities of Mg compounds added. We added 1.00 × 10⁻³ mol of each Mg compound to 20 g of TCE to evaluate their solubility. Under these conditions, only MgO was dissolved by almost 50%. Note that Mg(OH)₂ was slightly dissolved in TCE under these conditions, although Mg(OH)₂ is a hydration product of MgO. Presumably, Mg(OH)₂ is an ionic salt, whereas MgO is a metal oxide, in which the Mg–O bonds exhibit somewhat covalent features. This difference would result in different solubilities for both Mg compounds. An investigation of the different solubilities of MgO and Mg(OH)₂ is ongoing in our laboratory. The other examined Mg salts such as magnesium acetate, magnesium nitrate and magnesium chloride exhibited low solubility, which might interfere the selective quantification of MgO by TCE extraction. However, these magnesium salts are usually not contained in steel making slags due to the high temperature of steel making furnaces. Although the slight solubility of magnesium silicate might also cause another potential interference, any magnesium salts contained in blast furnace slags and merwinite, which had similar compositions to steel making slags, were not extracted into TCE. These results suggest that every magnesium salt studied here does not interfere the selective determination of MgO practically, which will be discussed in Section 3.5.

Fig. 2.

Solubility of magnesium compounds in TCE. 1.0 × 10⁻³ mol of magnesium compounds were dissolved in 20 g of TCE at 140°C for 3 h.

3.4. Examination of the Conditions for Extracting Free MgO from Steelmaking Slags

To apply the extraction method using TCE to actual slag samples, the optimized heating conditions discussed in Section 3.2 were reexamined using slag samples. The No. 3 slag was used as it is expected to contain a relatively large quantity of free MgO. Figures 3(a) and 3(b) show the effects of temperature and time on the extraction of Mg species from this slag. High-temperature extraction enhanced the extraction of the Mg species, which is consistent with the results from the heating investigation in Section 3.2 (Fig. 1(a)). Heating at 140°C resulted in the highest solubility. We did not examine temperatures higher than 140°C to avoid unintended accidents, as the boiling point of TCE is 150°C. The effect of the extraction time on the extractability was examined with the extraction temperature set to 140°C. The extraction of Mg species increased as the extraction time increased, and the extraction percentage became almost constant after 3 h (Fig. 3(b)), which is also consistent with the results from the heating study from Section 3.2 (Fig. 1(a)). Thus, we consider these heating conditions to be suitable for extracting free MgO from steelmaking slag.

Fig. 3.

Effects of a) temperature and b) heating time on extraction of magnesium in 0.1 g of No. 3 steelmaking slag in 20 g of TCE. Experimental conditions are the same as those in Fig. 1.

3.5. Extraction and Determination of Free MgO in Steelmaking Slag Using TCE

The free MgO content in steelmaking slag was determined by extraction with TCE followed by analysis via atomic absorption spectrometry and other analytical methods. Table 3 summarizes the results for free MgO in steelmaking slag obtained by the iodine-ethanol ethylene glycol method,^11,12) iodine-ethanol method,¹⁰⁾ TG analysis method,⁸⁾ and TCE extraction method. Magnesium compounds were extracted from all steelmaking slags containing free MgO. In contrast, no magnesium compounds were extracted from the merwinite and blast furnace slags, as they did not contain free MgO. Note that the MgO in merwinite (chemical composition: 3CaO·MgO₂·SiO₂) and in blast furnace slags, which contain a melilite phase consisting of gerenite (Ca₂Al₂Si₂O₇), and acermanite, is chemically bonded with neighboring atoms. Considering the results of extraction of magnesium salts mentioned in Section 3.3, TCE practically extracts only free-MgO in steel making slags, suggesting that TCE extraction has a high selectivity for free MgO. On the other hand, iodine solutions of ethanol,¹⁰⁾ ethylene glycol,¹¹⁾ and a mixture of ethanol and ethylene glycol¹²⁾ extracted a certain amount of magnesium salts other than free MgO, so that the combination of atomic absorption spectrometry and these iodine solutions may overestimate the content of free MgO in steel making slags.

Table 3. Analytical results of the content (wt%) of free-MgO in steelmaking slag.

Steelmaking slags	TCE	RSD (n=4)	I2/EtOH/EG	I2/EtOH	I2/EtOH/EG*	XRD*	TG*
	(Present method)
No. 1	5.04	0.20	1.20	1.09	2.38	0.2	1.78
No. 2	2.77	0.11	4.23	4.23	5.43	2.3	5.1
No. 3	5.81	0.80	7.00	4.50	5.8	6.6	4.58
No. 4	2.70	0.40	6.40	3.10	4.3	3.5	1.03
No. 5	1.78	0.22	1.87	0.51	2.97	1.9	0.95
BF-slag	0.00	0	–	–	–	–	–
Merwinaite	0.00	0	–	–	–	–	–

*  Data were obtained from the research group of Development and Standardization of Free MgO Analysis Method in Steel Slag” in ISIJ.

A critical challenge to developing analytical methods for free MgO in steelmaking slags is the lack of certified reference materials for steelmaking slags that contain precise known quantities of free MgO. Although the ²⁹MNR method is considered as one of the most reliable method to determine free MgO in steel making slags,⁷⁾ the NMR method could not be applied to the slag samples listed in Table 3 due to the serious interference from iron in the slags. Therefore, to evaluate the reliability of the developed extraction method, we compared the obtained results with those obtained from the use of other reported methods that measured free MgO in steelmaking slags. Significant deviations between the values from different analytical methods were observed for all steelmaking slags, indicating the difficulties of developing accurate analytical methods for this type of analysis. Considering these difficulties, the TCE extraction method yielded acceptable results, except in the case of the No. 1 slag. It is presumed that the No. 1 slag may contain unidentified Mg compounds that dissolve in TCE but are not present in other slags. We speculate that the unidentified magnesium species in the No. 1 slag might be a kind of magnesium silicate containing oxides of transitional metals as impurities. Considering that metal impurities can enhance acidity of silanol in silica gels,^15,16) the oxides of transitional metals in magnesium silicate could also enhance the acidity of neighboring silicates to increase ionic interaction between magnesium cations and silicates, which would facilitate the dissolution of magnesium into TCE. The results in Table 3 suggest that the present method is useful for determining the content of free MgO in steelmaking slags.

3.6. Mechanism of Dissolution of MgO in TCE

Elucidating the mechanism by which MgO dissolves in TCE is important not only for optimizing the extraction system, but also because it allows for the exploration of new extraction systems. As TCE is a protonic solvent and MgO is a basic substance, a neutralization reaction between TCE and MgO is expected to cause the dissolution of MgO, as shown in Eq. (1)   

$$2\mathrm{R}\text{-}\mathrm{O}\mathrm{H}+\mathrm{M}\mathrm{g}\mathrm{O}\to \mathrm{M}\mathrm{g}{\left(\mathrm{O}\mathrm{R}\right)}_2+{\mathrm{H}}_2\mathrm{O}$$(1)

where R-OH denotes TCE.

Equation (1) indicates that the same quantity of water is produced via the reaction with MgO. In practice, however, the addition of 5.0 × 10⁻⁴ mol of MgO to TCE produced 7.2 × 10⁻⁴ mol of water after the reaction. The 2.2 × 10⁻⁴ mol difference may represent water that is generated by other unrelated reactions.

To elucidate the production of excess water, we investigated the reaction of TCE alone when heated without MgO. Figure 4 shows moles of hydrogen ions and chloride ions produced in the heated TCE as a function of the heating time at 140°C. Notably, heating the TCE produced almost the same number of hydrogen ions as chloride ions, indicating that hydrogen chloride is desorbed from TCE by heating. The resulting hydrogen chloride facilitated the dissolution of MgO. The number of hydrogen ions produced after 24 h of heating is erroneous because of an unintended mistake (Fig. 4).

Fig. 4.

Production of hydrogen and chloride ions from TCE as a function of heating time. The temperature was set to 140°C. ●, hydrogen ions; ■, chloride ions.

A possible reaction for the generation of HCl from TCE is expressed in Eq. (2).   

$$\mathrm{C}\mathrm{C}{\mathrm{l}}_3\text{-}\mathrm{C}{\mathrm{H}}_2\text{-}\mathrm{O}\mathrm{H}\to \mathrm{C}{\mathrm{l}}_2\mathrm{C}=\mathrm{C}\mathrm{H}\text{-}\mathrm{O}\mathrm{H}+\mathrm{H}\mathrm{C}\mathrm{l}$$(2)

The resulting vinyl alcohol is converted to dichloroacetaldehyde (DAA) through keto-enol tautomerization, as expressed in Eq. (3).   

$$\mathrm{C}{\mathrm{l}}_2\mathrm{C}=\mathrm{C}\mathrm{H}\text{-}\mathrm{O}\mathrm{H}\to \mathrm{C}\mathrm{H}\mathrm{C}{\mathrm{l}}_2\text{-}\mathrm{C}\mathrm{H}\mathrm{O}$$(3)

These reactions were confirmed by GC-MS measurements. Figure 5(a) shows the total ion chromatogram of TCE heated at 140°C for 48 h, in which an intense peak occurred at 17 min. The peak at 4 min was assigned to TCE and a weak peak was detected at 21.5 min (see Fig. 5(b) for the mass spectrum). The mass spectrum of the peak at 21.5 min is very similar to that of the peak at 21.3 min (Fig. 6(b)) in the total ion chromatogram of DAA (Fig. 6(a)). Comparisons between the mass spectra and total ion chromatograms for the heated TCE and DAA confirmed that DAA was produced by heating TCE.

Fig. 5.

a) Total ion chromatogram of heated TCE and b) mass spectrum of peak at 20.7 min. TCE was heated at 140°C for 48 h.

Fig. 6.

a) Total ion chromatogram of heated dichloroacetaldehyde and b) mass spectrum of the peak at 21.3 min.

Further heating caused another reaction. When TCE was heated at 140°C for 168 h, white crystals precipitated in the resulting TCE solution. The white crystals were identified through X-ray structural analysis as 1,1,1,7,7,7-hexyachliro-4-dichloromethyl-3,5-dioxaheptane, which is a dehydration product composed of TCE and hydrated DAA. The structure of the resulting compound and proposed chemical reaction are shown in Fig. 7. When this reaction proceeds, a water molecule is produced for every molecule of product produced. Therefore, we surmise that the excess water may have been produced by a dehydration reaction.

Fig. 7.

Scheme of reactions occurring upon further heating of TCE.

Gel formation is another possible mechanism by which MgO dissolves in TCE. As stated in Section 3.2, the dissolved magnesium in TCE participates in the formation of gels. Further studies on gel formation were performed using TOF-MS. Prior to the mass analyses, the gels were collapsed by the addition of methanol. The mass spectrum of the resulting mixture produced intense peaks at approximately 676.8 m/Z that correspond to an oligomer composed of six DAA molecules. The peaks with the highest m/Z ratio occur at approximately 798.9 m/Z and correspond to oligomers composed of seven DAA molecules (Fig. 8). The oligomerization resulted from the aldol condensation of DAA, considering the oligomerization of ethylene glycol with CaO.⁵⁾ The resulting oligomers of DAA were crosslinked with magnesium ions that dissolved in the TCE to form gels. Thus, the dissolution of MgO in TCE is characterized by several chemical reactions, including an acid-base reaction, oligomerization, and crosslinkage formation.

Fig. 8.

Mass spectrum of heated TCE. TCE was heated at 140°C for 168 h. (Online version in color.)

4. Conclusion

We investigated the determination of free MgO in steelmaking slags using quantitative TCE extraction followed by atomic absorption spectrometry. Free MgO in steelmaking slag was extracted with TCE at 140°C for 3 h. However, TCE did not extract Mg compounds in merwinite and blast furnace slags, which do not contain MgO, indicating that TCE extracted selectively. When the free MgO in the steelmaking slags was determined by atomic absorption spectrometry combined with TCE extraction, the obtained analytical values were reasonably similar to those obtained using other methods for measuring the MgO content in steelmaking slags, considering that the overall agreement between results from different methods is not high.

The extraction of MgO by TCE involved not only an acid-base reaction, but also a reaction between the magnesium ions with the oligomers of DAA that formed from TCE under heating, leading to the formation of crosslinks between oligomers to form gels.

Acknowledgement

This research was supported by the 28th ISIJ Research Promotion Grant (2018). N.U. thanks Dr. Takafumi Sato, professor at Utsunomiya University, for his support with the GC-MS measurements. N.U. also thanks Dr. Tetsuo Okada and Dr. Harada at the Tokyo Institute of Technology, for their assistance with water analysis by Karl-Fischer titration.

References

• 1)   H.  Wang,  R.  Caballero and  D.  Sichen: J. Eur. Ceram. Soc., 38 (2018), 789. https://doi.org/10.1016/j.jeurceramsoc.2017.09.030
• 2)   L. F.  Amaral,  I. R.  Oliveira,  P.  Bonadia,  R.  Salomão and  V. C.  Pandolfelli: Ceram. Int., 37 (2011), 1537. https://doi.org/10.1016/j.ceramint.2011.01.030
• 3)   M.  Inui,  M.  Oda and  T.  Tanaka: Bull. Iron Steel Inst. Jpn., 19 (2014), 569.
• 4)   M.  Kato,  T.  Hari,  S.  Saito and  M.  Shibukawa: Tetsu-to-Hagané, 100 (2014), 340 (in Japanese). https://doi.org/10.2355/tetsutohagane.100.340
• 5)   N.  Uehara and  A.  Tanaka: Tetsu-to-Hagané, 100 (2014), 911 (in Japanese). https://doi.org/10.2355/tetsutohagane.100.911
• 6)   N. K.  Katyal,  S. C.  Ahluwalia,  R.  Parkash and  R. N.  Sharma: Cem. Concr. Res., 28 (1998), 481.
• 7)   K.  Kanehashi and  M.  Aimoto: Tetsu-to-Hagané, 99 (2013), 543 (in Japanese). https://doi.org/10.2355/tetsutohagane.99.543
• 8)   M.  Kato,  K.  Tsukagoshi,  M.  Aimoto,  S.  Saito and  M.  Shibukawa: ISIJ Int., 58 (2018), 1834. https://doi.org/10.2355/isijinternational.ISIJINT-2018-192
• 9)   P.  Arjunan and  A.  Kumar: Cem. Concr. Res., 24 (1994), 343.
• 10)   N.  Uehara and  M.  Takita: ISIJ Int., 58 (2018), 1474. https://doi.org/10.2355/isijinternational.ISIJINT-2018-166
• 11)   J. H.  Yu and  X.  Wu: Chin. J. Anal. Chem., 26 (1998), 1075.
• 12)   K.  Hanada,  M.  Inose,  S.  Sato,  K.  Watanabe and  K.  Fujimoto: Tetsu-to-Hagané, 102 (2016), 24 (in Japanese). https://doi.org/10.2355/tetsutohagane.TETSU-2015-064
• 13)  SciFinder, American Chemical Society, Washington, D.C., (2021).
• 14)   A. E.  Martell and  R. D.  Hancock: Metal Complexes in Aqueous Solutions, Modern Inorganic Chemistry, ed. by J. P. Fackler, Jr., Plenum Press, New York, (1996), 123.
• 15)   R. Ł.  Gwarda,  W.  Szwerc,  M.  Aletańska-Kozak,  A.  Klimek-Turek,  A.  Torbicz,  A.  Chomicki,  R.  Kocjan,  D.  Matosiuk and  T. H.  Dzido: J. Planar Chromatogr. -Mod. TLC, 30 (2017), 375. https://doi.org/10.1556/1006.2017.30.5.6
• 16)   J.  Nawrocki,  D. L.  Moir and  W.  Szczepaniak: Chromatographia, 28 (1989), 143.