Stabilization/Solidification of Strontium Using Magnesium Silicate Hydrate Cement
Round 1
Reviewer 1 Report
(General) In order to more clearly understand the novelty of this study, please clarify the following. What are the clear merits of the proposed MSH cement as a solidification agent for stabilizing Sr2+ present in radioactive waste, compared to other cementitious materials such as Portland cement and other recently proposed solidification agent?
(p.1 Line 16-17) The authors described that "The MgO-SiO2-H2O is highly effective at 16 stabilizing/solidifying Sr radionuclides". However, no specific comparative assessments on the effectiveness of the MSH cement with other conventional solidification agents can be found in this study. Please revise the manuscript appropriately.
(p.1, Line 27) The authors described that "...strontium and cesium are the two most harmful nuclides". It is true that those two radionuclides are radiologically harmful, however, they cannot be called as "two most harmful nuclides" in terms of dose coefficients for ingestion, inhalation, and direct radiation. Please check the description and revise it appropriately.
(p.3, Line 79) Is the mentioned water-to-binder ratio (0.6-0.8) for mass, volume or molar basis?
(p.3, Line 100-101) Please specify the reference(s) for Equations (1) and (2).
(p.3, Line 104) The dimension of F (cm^2) is missed.
(p.12, Line 1) Reference 1 (IAEA Safety Series No. 111-G-1.1) has been revised and superseded with IAEA GSG-1 in 2009. Please revise the manuscript appropriately.
(p.4, Line 115) The authors mentioned that "...ionic strength should be 0.71 mol/kg". Is the mass unit "kg" for "Solution" or "Solvent/water"?
(p.6, Line 166; p.8, Line 175) The authors described "a petal-like substance" where SrCO3 is mainly concentrated as per Figure 3(b). It is not clear whether B or "B and C" is a so-called petal-like substance. Furthermore, Table 3 shows that strontium is comparatively concentrated on substance B and C than A. In addition, please clarify that similar surface structures like Figure 3(b) after 28 d have been observed in the other part/location of the sample.
(p.9, Line 212) Legends for seawater plots should be rewritten for temperatures 25 and 40 degrees Celsius in Figure 5.
(p.9, Line 218) Write the full name of MIP in an appropriate part of the manuscript.
(p.11, Line 275-276) Please deliberate more on the scientific basis of the analysis that "dissolution and diffusion are main leaching forms of the radionuclide strontium in the cement solidified body".
(p.11, Line 277-286) The descriptions seem to be just a series of assumptions rather than observations. Please deliberate more on the scientific basis of the analysis.
(p.11, Line 293) "The effect of Cs+" should be replaced with "The effect of Sr2+".
(Chinese Standards) Cited Chinese Standards are not listed in the reference. Please add the Standards referred to in the reference. GB/T17671-2011 (p.3, Line 90-91) and GB/T7023-2011 (p.4, Line 129) : These two standards are not listed in the following website: https://www.chinesestandard.net/List/GBT.aspx/Page1. Please check it and ensure that the standards are officially effective and applicable at this moment. GB-7023 (p.8, Line 198): It seems to be mistakenly named from GB/T7023-2011.
(Miscellaneous errors, typos, and inconsistency, etc.) "Light-burned" and "Light-burnt" are mixedly used in the manuscript.
END.
Author Response
Response to Reviewer 1 Comments
Thanks for your comments. We have revised all the problems appropriately.
Point 1: In order to more clearly understand the novelty of this study, please clarify the following. What are the clear merits of the proposed MSH cement as a solidification agent for stabilizing Sr2+ present in radioactive waste, compared to other cementitious materials such as Portland cement and other recently proposed solidification agent?
Response 1: Some nuclear wastes are significant quantities of mixed wastes (the main nuclides: Sr and Cs) containing both Mg and Al alloys. Whilst the high pH in Portland cement based binders passivates the corrosion of Mg alloys, Al alloys corrode under high pH conditions with evolution of H2 gas. The pH of water in equilibrium with the MSH system will tend to the range from 9.5 to 10.5, so MSH system is suitable for stabilizing this special unclear waste. We want to have research on the effect of the low alkalinity solution of MSH system on the solidification of Sr2+. (The new manuscript: Line 62-67)
Point 2: p.1 Line 16-17) The authors described that "The MgO-SiO2-H2O is highly effective at 16 stabilizing/solidifying Sr radionuclides". However, no specific comparative assessments on the effectiveness of the MSH cement with other conventional solidification agents can be found in this study. Please revise the manuscript appropriately..
Response 2: We are sorry for the omission in our expression. We have made corresponding revision in the manuscript. (The new manuscript: Line 16-17)
“The microstructure of the samples has also been characterized. The stabilizing/solidifying process of Sr radionuclide in the MgO-SiO2-H2O had been shown in the study.”
Point 3: (p.1, Line 27)The authors described that "...strontium and cesium are the two most harmful nuclides". It is true that those two radionuclides are radiologically harmful, however, they cannot be called as "two most harmful nuclides" in terms of dose coefficients for ingestion, inhalation, and direct radiation. Please check the description and revise it appropriately.
Response 3: We are sorry for the omission in our expression. We have made corresponding revision in the manuscript. (The new manuscript: Line 26-28)
Point 4: (p.3, Line 79) Is the mentioned water-to-binder ratio (0.6-0.8) for mass, volume or molar basis?
Response 4: Thanks for your comments. The mentioned water-to-binder ratio (0.6-0.8) is for mass. We have made corresponding revision in this paper. (The new manuscript: Line 86-87)
Point 5: (p.3, Line 100-101) Please specify the reference(s) for Equations (1) and (2).
Response 5: We are sorry that there is an omission in our expression. We have added corresponding revision in this point. (The new manuscript: Line 107)
Point 6: (p.3, Line 104) The dimension of F (cm2) is missed.
Response 6: Thanks for your comments. We have made corresponding revision in this paper. (The new manuscript: Line 111-112)
Point 7: (p.12, Line 1) Reference 1 (IAEA Safety Series No. 111-G-1.1) has been revised and superseded with IAEA GSG-1 in 2009. Please revise the manuscript appropriately.
Response 7: We are sorry that there is a deviation in our paper. We have checked the IAEA GSG-1(2009) for the classification of radioactive waste and made corresponding revision in this paper. (The new manuscript: Line 311)
Point 8: (p.4, Line 115) The authors mentioned that "...ionic strength should be 0.71 mol/kg". Is the mass unit "kg" for "Solution" or "Solvent/water"?
Response 8: Ionic strength is a measure of the electric field strength produced by the presence of ions in a solution. Its value is equal to half of the sum of the terms obtained by multiplying the molar concentration of each ion in the solution by the square of the valence number of the ion. So, the mass unit "kg" is for "Solvent ". (The new manuscript: Line 123)
Point 9: (p.6, Line 166; p.8, Line 175) The authors described "a petal-like substance" where SrCO3 is mainly concentrated as per Figure 3(b). It is not clear whether B or "B and C" is a so-called petal-like substance. Furthermore, Table 3 shows that strontium is comparatively concentrated on substance B and C than A. In addition, please clarify that similar surface structures like Figure 3(b) after 28 d have been observed in the other part/location of the sample.
Response 9: B is the well-developed petal-like substance. We have repeatedly tested different test samples under the same conditions, and found many petal-like substances only in the samples with 3.2 wt.% Sr2+ cured for 28 days, and made EDS energy spectrum analysis, where the element distribution shows that it is strontium carbonate. This is a representative picture we selected from all the SEM images. (The new manuscript: Line 171-172)
Point 10: (p.9, Line 212) Legends for seawater plots should be rewritten for temperatures 25 and 40 degrees Celsius in Figure 5.
Response 10: We are sorry that there is a mistake in the picture. We have made corresponding revision in this point. (The new manuscript: Line 218)
Point 11: (p.9, Line 218) Write the full name of MIP in an appropriate part of the manuscript.
Response 11: Thanks for your reminder. We have made corresponding supplement lines. (The new manuscript: Line 232)
Point 12: (p.11, Line 275-276) Please deliberate more on the scientific basis of the analysis that "dissolution and diffusion are main leaching forms of the radionuclide strontium in the cement solidified body".
Response 12: We can’t conclude the stabilization/solidification form of Sr from the Figure 4 and 5, so we have deleted the corresponding statements. (The new manuscript: Line 250-252)
Point 13: (p.11, Line 277-286) The descriptions seem to be just a series of assumptions rather than observations. Please deliberate more on the scientific basis of the analysis.
Response 13: We don’t make the statement clearly. In this part, we want to represent that the reasons for the poor solidification effect at the beginning of the reaction. The molding process becomes more difficult resulted in the decrease of density of the solidified body, so the system does not have obvious advantages for physically inclusion of the nuclide. (The new manuscript: Line 253-260)
Point 14: (p.11, Line 293) "The effect of Cs+" should be replaced with "The effect of Sr2+".
Response 14: Sorry for that mistake. We have made corresponding revision. (The new manuscript: Line 286)
Point 15: (Chinese Standards) Cited Chinese Standards are not listed in the reference. Please add the Standards referred to in the reference. GB/T17671-2011 (p.3, Line 90-91) and GB/T7023-2011
Response 15: Thanks for your reminder. We have made corresponding supplement in references [35] and [36]. (The new manuscript: Line 98-100)
Point 16: (p.4, Line 129) : These two standards are not listed in the following website: https://www.chinesestandard.net/List/GBT.aspx/Page1. Please check it and ensure that the standards are officially effective and applicable at this moment. GB-7023 (p.8, Line 198): It seems to be mistakenly named from GB/T7023-2011.
Response 16: We are sorry for the mixed use of the standard edition in written. We confused the edition, but the content was correct. We have checked these in this website: http://www.chinesestandard.net/China/Home.aspx and revised the right ones: GB/T 17671-1999, GB/T 7023-2011, GB 14569.1-2011 in Line 91-94, 129, 197.
Point 17: (Miscellaneous errors, typos, and inconsistency, etc.) "Light-burned" and "Light-burnt" are mixedly used in the manuscript.
Response 17: Sorry for the mixed uses of the words, we have thoroughly checked the paper. (The new manuscript: Line 85)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Summary
This paper had good investigation of reference researches, it is useful to other researchers or readers.
Abstract
Please more make new concept or advantage in this paper.
Line 20
If authors mention mechanisms, should be demonstrate with phenomena.
Line from 32 to line 60
Authors had good works on introducing knowledge’s or research potential at present. However, reviewer afraid that between results in literatures and purpose of this study is not enough. Please would you like to establish clear subjection with engineering practices using literatures.
Line 95
Why did you focused seawater for this study ?
Table 3
Three difference samples were prepared. Please would you like to mention concept to preparing.
Figure 1
Authors indicated results of compressive strength. If you have related results in literature, please show it and add the results into Figure 1.
Figure 4
Are there the influence of water-cement value on cumulation leaching fraction ?
Reviewer though that there were no affect in all immersion time.
Figure 5
Please would you explain reduction of cumulation leaching fraction due to 40 degrees.
Also, if you have related results in literature, please describe it.
Discussion
Authors provide as follows:
Dense structure, pore structure, molecular structure. They are not correct term, because authors not mention previous portion (i.e. before discussion). Please would you like to more explain them.
Conclusion
All sentence had a limited tendency without quantity.
Author Response
Response to Reviewer 2 Comments
Thanks for your comments. We have revised all the problems appropriately.
This paper had good investigation of reference researches, it is useful to other researchers or readers.
Point 1: Abstract: Please more make new concept or advantage in this paper.
Response 1: Thanks for your comment. We have defined the abstract.
“The microstructure of the samples has also been characterized. The stabilizing/solidifying process of Sr radionuclide in the MgO-SiO2-H2O system with low alkalinity had been shown in the study.” (The new manuscript: Line 16-18)
Point 2: Line 20: If authors mention mechanisms, should be demonstrate with phenomena.
Response 2: Thanks for your comment. We have defined the abstract.
“Sr2+ was effectively incorporated into M-S-H hydration products and new phase formation resulting in the low Sr leaching observed.” (The new manuscript: Line 19-21)
Point 3: Line from 32 to line 60: Authors had good works on introducing knowledge’s or research potential at present. However, reviewer afraid that between results in literatures and purpose of this study is not enough. Please would you like to establish clear subjection with engineering practices using literatures.
Response 3:
We have adjusted the introduction. We emphasize the clear merits of the proposed MSH cement as a solidification agent for stabilizing Sr2+ present in radioactive waste, compared to other high alkalinity cementitious materials such as Portland cement and other recently proposed solidification agent? (The new manuscript: Line 62-67)
“Some nuclear wastes are significant quantities of mixed wastes (the main nuclides: Sr and Cs) containing both Mg and Al alloys. Whilst the high pH in Portland cement based binders passivates the corrosion of Mg alloys, Al alloys corrode under high pH conditions with evolution of H2 gas [26]. The pH of water in equilibrium with the M-S-H system will tend to the range from 9.5 to 10.5, so M-S-H system is suitable for stabilizing this special unclear waste [34].”
Point 4: Line 95: Why did you focused seawater for this study ?
Response 4: We refer to the practices in the national standards GB/T 7023-2011. Of course, it is also mentioned in the standard that the underground water of the buried site can be used as the leachant to test the leaching effect of the solidified body, but it is difficult to find the data in this regard to simulate the underground water conditions in China, so we choose the more complex environment of sea water to characterize the anti leaching performance of the solidified body. (The new manuscript: Line 97-100)
Point 5: Table 3: Three difference samples were prepared. Please would you like to mention concept to preparing.
Response 5: Thank you for your reminder. The data shown in Table 3 came from the same sample. We found the petal –like substance existed in the sample with 3.2 wt.% strontium after cured for 28 days only when we took SEM images, so we did EDS in there different regions in this sample to judge this special substance. The specimen tested by electron microscope is the central thin section taken out after crushing the solidified body, with the scale of 3-5mm. We have made corresponding supplement in Line 115.
Point 6: Figure 1: Authors indicated results of compressive strength. If you have related results in literature, please show it and add the results into Figure 1.
Response 6: We have added references in this part. (The new manuscript: Line 136)
Point 7: Figure 4: Are there the influence of water-cement value on cumulation leaching fraction ? Reviewer though that there were no affect in all immersion time.
Response 7: According to the measured data, the influence of water cement ratio on leaching rate and cumulative leaching fraction is not obvious. On the one hand, the two kinds of values are very small in themselves, and the difference is not significant. On the other hand, after adding strontium, the formation of solidified body is difficult, and the viscosity of slurry is large, so the effect of a small amount of water on the performance of solidified body is not very different.
Point 8: Figure 5: Please would you explain reduction of cumulation leaching fraction due to 40 degrees. Also, if you have related results in literature, please describe it.
Response 8: The temperature increase is beneficial to accelerate the reaction process of MSH system and improve the density of matrix. We will make a research on the mechanism in the future.
Point 9: Discussion: Authors provide as follows:
Dense structure, pore structure, molecular structure. They are not correct term, because authors not mention previous portion (i.e. before discussion). Please would you like to more explain them.
Response 9: we have modified the correct term. “Dense structure” changed into “density ”; “pore structure” changed into “pore size distribution”
“the molecular structure of the final hydration reaction product M-S-H gel of the MgO-SiO2-H2O system is close to the molecular structure of sepiolite, with specific surface area of ~ 200m2/g, which is unique for adsorbing heavy metal ions[40].”
(The new manuscript: Line 246,253,254)
Point 10: Conclusion: All sentence had a limited tendency without quantity.
Response 10: We have added the quantity. (The new manuscript: Line 301)
Author Response File: Author Response.pdf
