Early Strength and Microscopic Mechanisms of Alkali-Metal Hydroxide-Activated Tungsten Tailings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

·       The subject is suitable for the journal and is relevant to current interests.

·       Table 2 – It is not clear whether the content of alkalis and water refers to molar or mass %.

·       What was the consistency of the mixture? As it was compressed to molds, the consistency must have been rather dry. In that case, please specify the consistency and the mixing process that was applied.

·       The authors should provide detailed information about the testing methods and devides. For instance, the FTIR technique – transmission mode in KBr or ATR or other different method.

·       Chapter 3 should be indicated just as Experimental results. Duscussion is provided in the next chapter.

·       How many specimens were used to determine the mechanical properties? Can you add error bars to Figure 4?

·       Line 270 – these vibrations refer to the asymmetric stretching mode of carbonate group. Symmetric band is prohibited in IR and can be observed only in Raman spectra.

·       Line 283 -  A sharp bands at 875 cm-1 and 720 cm-1 are associated with bending mode of carbonate group and do not correlate with Al-O vibrations.

·       Line 285 – I really doubt about the decrease in peak intensity of O-H vibration band with increased curing time because there is overall difference in the intensity of the spectra.  You should normalize the spectra to a certain band which does not change its intensity or at least the intensity of which does not change much, e.g. band at 1090 or 1000 cm-1. It would provide more accurate information about the changes in intensities of other bands and/or species, respectively. Maybe you will come to a slightly different conclusion.

·       Discussion must be improved because some of the conclusions are not justified by experimental data. I strongly doubt about the crystallinity of (C,N)-A-S-H and (C,K)-A-S-H phases. Some pseudocrystalline structure of these phases is usually recognized as a diffuse hump around 30 degrees (2theta) but there is no evidence of it in the XRD pattern. Moreover, the peaks assigned to this structure are very weak and can be found even in raw tailings. Neither SEM shows any evidence of enhanced crystallinity. Therefore, I assume these phases are highly amorphous. The other point is that crystallization of alkali-activated products leads to a reduction in the mechanical properties (e.g. when geopolymers are transformed to crystalline zeolite phases). I also recommend to provide some porosimetry measurement. It may give some explanation to the differences in the mechanical properties.

·       References [1], [3], [6], [7], [8], [10], [15], [16], [18], [19], [21], [24], [26], [27], and [30] are written in Chinese, so they have no relevance for the international reader. Please, replace them!

Comments on the Quality of English Language

English should be improved by using proofreading services.

Author Response

1.Table 2 – It is not clear whether the content of alkalis and water refers to molar or mass %.

Thank you very much for your comments; they are very insightful. In this experiment, the content of alkali and water is expressed as a percentage by mass, that is to say, 5% NaOH means 5% of the mass of 652 g of slag.

2.What was the consistency of the mixture? As it was compressed to molds, the consistencymust have been rather dry. In that case, please specify the consistency and the mixing process that was applied.

Thank you very much for your comments; they are very insightful. After multiple preliminary experiments, we finalized three concentrations of alkali activator: 5%, 8%, and 11%. After being poured into dry slag and stirred, all three mixtures resulted in a relatively dry powder. To ensure thorough mixing, the stirring time was set to 10 minutes. The mixing process is as follows: after pouring the slag powder into the JJ-5 cement mortar mixer, the prepared alkali solution is added, and the mixture is stirred thoroughly for 10 minutes. After stirring, the mixture is layered and filled into a steel mold measuring 70 mm × 70 mm × 120 mm. Using the UTM5305 electronic universal testing machine, the sample is compressed axially at a rate of 0.1 kN/s until the height is reduced to 70 mm, forming a cube with dimensions of 70 mm × 70 mm × 70 mm.

3.The authors should provide detailed information about the testing methods and devides. For instance, the FTIR technique – transmission mode in KBr or ATR or other different method.

Thank you very much for your comments. The FTIR equipment used in this experiment is the Thermo Nicolet NEXUS 670 Fourier Transform Infrared Raman Spectrometer for mineral composition testing. The scanning angle ranges from 5° to 80° (2θ), and the scanning speed is set at 2°/min.

4.Chapter 3 should be indicated just as Experimental results. Duscussion is provided in the next chapter.

Thank you very much for your comments。“Experimental Results and Discussion” has been changed to“Experimental Results”

5.How many specimens were used to determine the mechanical properties? Can you add error bars to Figure 4?

Thank you very much for your comments; they are very insightful. In this experiment, we created one piece for each type of sample. To reduce errors, we conducted an additional set of parallel experiments for each sample type and used the average of the two sets of results as the final data.

6.Line 270 – these vibrations refer to the asymmetric stretching mode of carbonate group. Symmetric band is prohibited in IR and can be observed only in Raman spectra.

Thank you very much for your comments; they are very insightful. Change "asymmetric stretching vibrations of C-O bonds" to "symmetric stretching vibrations of C-O bonds" in line 270.

7.Line 283 - A sharp bands at 875 cm-1 and 720 cm-1 are associated with bending mode of carbonate group and do not correlate with Al-O vibrations.

Thank you very much for your comments. We have made some modifications to the content in the text by replacing (SiAl-O) with (T(Si/Al)-O) in line 278-283. And remove “the sharpening of the Al-O bands at 720 cm^-1 and 875 cm^-1 further corroborates gel formation”.

8.Line 285 – I really doubt about the decrease in peak intensity of O-H vibration band with increased curing time because there is overall difference in the intensity of the spectra. You should normalize the spectra to a certain band which does not change its intensity or at least the intensity of which does not change much, e.g. band at 1090 or 1000 cm-1. It would provide more accurate information about the changes in intensities of other bands and/or species, respectively. Maybe you will come to a slightly different conclusion.

Thank you very much for your insightful comments. they are very insightful. We have changed the text in “The O-H bond signals spanning 3200 cm^-1 to 3600 cm^-1 ^[33] show a decrease in peak intensity and a shift… …”to“he O-H bond signals spanning 3200 cm^-1 to 3600 cm^-1 ^[32] show a shift from 3450 cm^-1 to 3420 cm^-1 with increased curing time… …”in the line 285-288.

In data processing, we normalized the intensity of the characteristic peak near 1000 cm⁻¹, but no clear pattern was observed; therefore, it was not described in the text. We speculate that the variations in peak intensity may be due to the significant influence of different activation conditions (such as type and concentration of alkali, reaction time, etc.) on the transformation of the slag and the structure of the resulting gelled material. This could lead to fluctuations in the intensity of the characteristic peaks. The network structures of Si-O and Si-Al bonds may form different coordination states, affecting the intensity of the infrared absorption peaks.

9.Discussion must be improved because some of the conclusions are not justified by experimental data. I strongly doubt about the crystallinity of (C,N)-A-S-H and (C,K)-A-S-H phases. Some pseudocrystalline structure of these phases is usually recognized as a diffuse hump around 30 degrees (2theta) but there is no evidence of it in the XRD pattern. Moreover, the peaks assigned to this structure are very weak and can be found even in raw tailings. Neither SEM shows any evidence of enhanced crystallinity. Therefore, I assume these phases are highly amorphous. The other point is that crystallization of alkali-activated products leads to a reduction in the mechanical properties (e.g. when geopolymers are transformed to crystalline zeolite phases). I also recommend to provide some porosimetry measurement. It may give some explanation to the differences in the mechanical properties.

Thank you very much for your insightful comments. We have added to the discussion section in line 316-323. As the curing time and alkali content increase, the number of formed colloids increases, and theoretically, the crystallinity of these colloids should also improve. However, no significant diffraction peaks were observed around 30 degrees (2θ) in the XRD patterns (as shown in Fig. 5), and similar peaks can even be found in the original tailings. Additionally, different morphologies of gels were observed in the scanning electron microscope (SEM) analysis (as shown in Fig. 6(a3)), however, there was no clear evidence of enhanced crystallinity. Therefore, this suggests that the (C, N)-A-S-H and (C, K)-A-S-H phases exhibit a high degree of amorphousness.

10.References [1], [3], [6], [7], [8], [10], [15], [16], [18], [19], [21], [24], [26], [27], and [30] are written in Chinese, so they have no relevance for the international reader. Please, replace them!

Thank you very much for your comments; they are very insightful. References [1], [3], [6], [7], [8], [10], [15], [16], [18], [19], [21], [24], [26], [27], and [30] have been replaced with English literature.

[1] A.O.Purdon. The action of alkalis on blast-furnace slag[J]. Journal of the society of chemical industry, 1940, 59:191-202.

[3] F.Pacheco-torgal, J.Castro-gomes, S.Jalali. Alkali-activated binders: A review Part 1. Historical background, terminology, reaction mechanisms and hydration products[J]. Construction and Building Materials,2008,22(7):1305-1314.https://doi.org/10.1016/j.conbuildmat.2007.10.015.

[6] I.Garcia Lodeiro, N.Cristelo, A.Palomo, et al. Use of industrial by-products as alkaline cement activators[J]. Construction and Building Materials,2020,253(Aug.30):119000.1-119000.11. https://doi.org/10.1016/j.conbuildmat.2020.119000.

[7] S.França, M.V.De Moura Solar Silva, P.H.Ribeiro Borges, et al. A review on some properties of alkali-activated materials[J]. Innov. Infrastruct. Solut. 7, 179 (2022). https://doi.org/10.1007/s41062-022-00789-w.

[8] V.Zivica. Effects of type and dosage of alkaline activator and temperature on the properties of alkali-activated slag mixtures[J].Construction & Building Materials, 2007, 21(7):1463-1469. https://doi.org/10.1016/j.conbuildmat.2006.07.002.

[10] S.Aydin, B.Baradan. Effect of activator type and content on properties of alkali-activated slag mortars[J]. Composites, Part B. Engineering,2014,57B(Feb.):166-172. https://doi.org/10.1016/j.compositesb.2013.10.001.

[15] H.Juan, B.Wenbin, Z.Weihao, et al. Influence of hydrated lime on mechanical and shrinkage properties of alkali-activated slag cement[J]. Construction and Building Materials,2021,289(Jun.28):123201.1-123201.11. https://doi.org/10.1016/j.conbuildmat.2021.123201.

[16] J.Davidovits. Geopolymer technology : the current state of the art[J]. Journal of Materials Science,2007,42(9):2917-2933.https://doi.org/10.1007/s10853-006-0637-z.

[18] P.Duxson, A.Fernández-Jiménez, J.L.Provis, et al. Geopolymer technology: the current state of the art[J]. Journal of Materials Science,2007,42(9):2917-2933. https://doi.org/10.1007/s10853-006-0637-z.

[19] F.Puertas, B.Gonzalez-Fonteboa, I.Gonzalez-Taboada, et al. Alkali-activated slag concrete: Fresh and hardened behaviour[J]. Cement & concrete composites,2018,8522-31. https://doi.org/10.1016/j.cemconcomp.2017.10.003.

[21] G.S.Ryu, Y.B.Lee, K.T.Koh, et al. The mechanical properties of fly ash-based geopolymer concrete with alkaline activators[J]. Construction and Building Materials,2013,47(Oct.):409-418. https://doi.org/10.1016/j.conbuildmat.2013.05.069

[24] E.Kapeluszna, L.Kotwica, A.Rozycka, et al. Incorporation of Al in C-A-S-H gels with various Ca/Si and Al/Si ratio: Microstructural and structural characteristics with DTA/TG, XRD, FTIR and TEM analysis[J]. Construction and Building Materials,2017,155(Nov.30):643-653. DOI:10.1016/j.conbuildmat.2017.08.091.

[26] C.K.Yip, G.C.Lukey, J.L.Provis. Effect of calcium silicate sources on geopolymerisation[J]. Cement and Concrete Research,2008,38(4):554-564. https://doi.org/10.1016/j.cemconres.2007.11.001

[27] I. Garcia-Lodeiro, A. Fernandez-Jimenez, P. Pena. Alkaline activation of synthetic aluminosilicate glass[J]. CERAMICS INTERNATIONAL,2014,40(4):5547-5558.http://dx.doi.org/10.1016/j.ceramint.2013.10.146

[30] A.Fernández-Jiménez, A.Palomo. Mid-infrared spectroscopic studies of alkali-activated fly ash structure[J].Microporous & Mesoporous Materials, 2005, 86(1-3):207-214. https://doi.org/10.1016/j.micromeso.2005.05.057.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript covers a topical issue concerning the expansion of the raw material base for obtaining promising types of materials - alkali-activated materials. The manuscript contains a wide range of analytical studies for the Tungsten tailings used, as well as many characteristics of alkali-activated composites based on them. Interesting patterns that explain the scientific significance of the work have been established. The presented conclusions fully correspond to the stated objective of the study. The results obtained in the study allow us to evaluate the effectiveness of using tungsten tailings in AAM, which explains the practical significance of the manuscript.

However, to improve the quality of the manuscript, as well as for a deeper understanding of the idea of the study, the authors should pay attention to the following comments:  

Line 35. Keyword «Alkali-activated» should be replaced by «Alkali activation». Also, this keyword is better to use without bold format;

Line 102. Figure 2. Replace «SiO2» by «SiO2»or use «Quartz»;

Line 122. Explain why the alkali solution used was cooled to room temperature, 25℃ before its use?

Line 175. In chemical formula «(CaNa2(CO3)2(H2O)2)», please use sub-index as following «(CaNa2(CO3)2(H2O)2)»;

Line 194. Figure 5. Replace «diffract grams» by «diffractograms»;

Line 228. Figure 6. Perhaps the phrase «(a3) 8% NaOH, Cured for 7 Days» should be replaced with «(a3) 5% NaOH, Cured for 7 Days»;

Lines 260-261. Figure 7. In the sentence «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al2O3-Na2O System and b) the Ternary CaO-Al2O3-K2O System, Excluding SiO2 Content...»

in chemical formulas, please use sub-index as following «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al2O3-Na2O System and b) the Ternary CaO-Al2O3-K2O System, Excluding SiO2 Content...».

Author Response

1.Line 35. Keyword «Alkali-activated» should be replaced by «Alkali activation». Also, this keyword is better to use without bold format;

Thank you very much for your comments. The keyword "Alkali-activated" has been changed to "Alkali activation." in line 35.

2.Line 102. Figure 2. Replace «SiO2» by «SiO2»or use «Quartz»;

Thank you very much for your comments. The «SiO2» has been changed to«SiO₂» in line 102.figure2.

3.Line 122. Explain why the alkali solution used was cooled to room temperature, 25℃ before its use?

Thank you very much for your comments. The main reason for cooling the prepared alkaline solution to room temperature before conducting the experiment is that operations at room temperature usually yield more uniform and controllable results. The high-temperature alkaline solutions may generate bubbles, which can affect the mixing uniformity and the final density of the material.

4.Line 175. In chemical formula «(CaNa2(CO3)2(H2O)2)», please use sub-index as following «(CaNa2(CO3)2(H2O)2)»;

Thank you very much for your comments. The "(CaNa2(CO3)2(H2O)2)" has been changed to "(CaNa₂(CO₃)₂(H₂O)₂)." in line 175.

5.Line 194. Figure 5. Replace «diffract grams» by «diffractograms»;

Thank you very much for your comments. The «diffract grams» has been changed to «diffractograms» in line 194.

6.Line 228. Figure 6. Perhaps the phrase «(a3) 8% NaOH, Cured for 7 Days» should be replaced with «(a3) 5% NaOH, Cured for 7 Days»;

Thank you very much for your comments. In this experiment, the micro-morphology of 5% NaOH, cured for 7 days, is almost identical to that of 5% NaOH, cured for 3 days; therefore, the 7-day condition was not utilized.

7.Lines 260-261. Figure 7. In the sentence «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al2O3-Na2O System and b) the Ternary CaO-Al2O3-K2O System, Excluding SiO2 Content.in chemical formulas, please use sub-index as following «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al2O3-Na2O System and b) the Ternary CaO-Al2O3-K2O System, Excluding SiO2 Content...».

Thank you very much for your comments. Lines 260-261. «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al2O3-Na2O System and b) the Ternary CaO-Al2O3-K2O System, Excluding SiO2 Content...» has been changed to «Projection of Alkali-Activated Material (Gels) Chemistry onto a) the Ternary CaO-Al₂O₃-Na₂O System and b) the Ternary CaO-Al₂O₃-K₂O System, Excluding SiO₂ Content

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Some of the previous comments were answered but the response was not included in the text. Please, impove appropriatly thejtext according to following comments and your responses bacuase it is important for readers.

1.Table 2 – It is not clear whether the content of alkalis and water refers to molar or mass %.

Thank you very much for your comments; they are very insightful. In this experiment, the content of alkali and water is expressed as a percentage by mass, that is to say, 5% NaOH means 5% of the mass of 652 g of slag.

2.What was the consistency of the mixture? As it was compressed to molds, the consistencymust have been rather dry. In that case, please specify the consistency and the mixing process that was applied.

Thank you very much for your comments; they are very insightful. After multiple preliminary experiments, we finalized three concentrations of alkali activator: 5%, 8%, and 11%. After being poured into dry slag and stirred, all three mixtures resulted in a relatively dry powder. To ensure thorough mixing, the stirring time was set to 10 minutes. The mixing process is as follows: after pouring the slag powder into the JJ-5 cement mortar mixer, the prepared alkali solution is added, and the mixture is stirred thoroughly for 10 minutes. After stirring, the mixture is layered and filled into a steel mold measuring 70 mm × 70 mm × 120 mm. Using the UTM5305 electronic universal testing machine, the sample is compressed axially at a rate of 0.1 kN/s until the height is reduced to 70 mm, forming a cube with dimensions of 70 mm × 70 mm × 70 mm.

3.The authors should provide detailed information about the testing methods and devides. For instance, the FTIR technique – transmission mode in KBr or ATR or other different method.

Thank you very much for your comments. The FTIR equipment used in this experiment is the Thermo Nicolet NEXUS 670 Fourier Transform Infrared Raman Spectrometer for mineral composition testing. The scanning angle ranges from 5° to 80° (2θ), and the scanning speed is set at 2°/min.

Comments on the Quality of English Language

I recommend checking the quality of English by the editorial service.

Author Response

Comments 1: Table 2 – It is not clear whether the content of alkalis and water refers to molar or mass %.

Response 1:Thank you very much for your comments We would like to clarify that the content of alkalis and water is expressed in mass percentage. We have molded in table 2 in the revised manuscript.

Comments 2: What was the consistency of the mixture? As it was compressed to molds, the consistencymust have been rather dry. In that case, please specify the consistency and the mixing process that was applied.

Response 2: Thank you very much for your comments. The moisture content of the sodium hydroxide-excited sample is 19%, whereas the moisture content of the potassium hydroxide-excited sample is 16%, please see the lines 116 and 117. Please refer to lines 122 to 134 for sample preparation and testing procedures.

Comments 2:The authors should provide detailed information about the testing methods and devides. For instance, the FTIR technique – transmission mode in KBr or ATR or other different method.

Response 3: Thank you very much for your comments. The relevant content has been added in lines 137 to 145 of the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript can be accepted in present form

Author Response

Comments: Manuscript can be accepted in present form.

Response: Thank you very much for your comments.