Review Reports

Round 1

Reviewer 1 Report

The authors have re-submitted a manuscript with barely any changes from the version I rejected previously. The XRD and TGA data that I had concerns about are still exactly the same, and therefore remain of low value. The TGA is particularly bad, with huge wegiht losses unexplained and marginal weigh loss of interest. More significantly, I have now realized that the XRD peaks attributed to siderite cannot be siderite. I have searched the literature, and in all cases, the main peaks of siderite occur at 32.05, 52.75, and 24.78 degrees. See here (http://rruff.info/Siderite/R050349) and here (http://webmineral.com/data/Siderite.shtml#.XXJxxmZ7lO8), as well as many journal articles. The present manuscript is assigning the main peaks as siderite at approx. 11, 15 and 23 degrees; this cannot be siderite. Hence, there is no way I can accept this manuscript for publication.

Author Response

Dear Professor

It is a pleasure to communicate with you directly. In first place, authors appreciate all of your corrections, comments and suggestions about our manuscript. We are sure that they have helped us so much for improve it.

About your last comments we can say:

XRD patterns were processed for identify products after carbonation, calcination and to calculate the CO₂ capture capacity. Hence, these calculations are very important to identify the capture process. This information was added in the manuscript.

It was necessary to include water in carbonation reaction to improve kinetics, since water acts a catalyst. TGA plots show a huge loss due to this condition, which affects calcination temperature, as you commented. Besides, it was remarkable to understand the behavior of decomposition temperature due to impurities through these plots.

We employed powder X-ray diffraction patterns which were collected using Bruker GADDS/D8 diffractometer equipped with Apex Smart CCD Detector and molybdenum rotating anode. Moreover, collected 2D diffraction patterns were integrated using Fit2D software. According this equipment, the peaks attributed to siderite correspond to the ones that appear in the XRD plots presented in the manuscript. This information can be corroborated in:

Kumar, S.; Drozd, V.; Durygin, A.; Saxena, S. Capturing CO₂ Emissions in the iron industries using a magnetite–iron mixture. Energy technology. 2016, 10.1002/ente.201500451, 1-5.

Mora, E.; Sarmiento, A.; Lopez, E.; Drozd, V.; Durigyn, A.; Saxena, S.; Chen, J. Iron oxides as efficient sorbents for CO₂ capture. Journal of Materials Research and Technology. 2019, 8, 3, 2944-2956.

We think that the peaks you speak correspond to X-ray beam from Cu radiation.

Best Regards

Eduin Yesid Mora Mendoza

Corresponding autor

Reviewer 2 Report

The manuscript ‘siderite formation by mechanochemical and high pressure high temperature processes for CO2 capture using iron ore as initial  sorbent’ presents an approach for CO2 capture using iron ores. The work presents important concerns that should be evaluated in detail. Please check the following comments:

The authors propose a process to capture CO2. This is a hot topic in the literature due to the worldwide impacts. However, we need to be careful with the emissions related to the proposed process, which may be even higher than the captured CO2. In this work, the authors propose a high temperature and high pressure process for the capture, and a thermal process for the regeneration of the metal oxide. And what are the emissions related to the extraction of the metal ore? Thus, what is the CO2 capture/CO2 emitted ratio of the overall process? The authors should present clear calculations of this ratio so that their research has a justified interest and value.

A second comment is the possibility of scaling up the technology. How much metal oxide would be needed to face the emissions of a typical power plant? And the extrapolation to all the global emissions from flue gases? What is the main target emissions of the authors?

Figure 2: why is the simulation done at 32°C if the reactor is operated at more than 100°C (see Figure 3)?

Table 2: which are the conclusions from this table? The authors should elaborate a deep discussion on the effect of pressure, revolution speed and time of reaction on the adsorption capacity.

Same comment about results shown in Table 3.

Section ‘Discussion’ should be better integrated with the results. The reader would appreciate receiving the discussion as soon as the results are shown so that the flow of ideas is kept in a better way.

Figure 9: please remove the lines since it is not a model.

Figure 10: remove the points if there are not experimental points involved.

Author Response

Dear Professor

It is a pleasure to communicate with you directly. In first place, authors appreciate all of your corrections, comments and suggestions about our manuscript. We are sure that they have helped us so much for improve it.

About your last comments we can say:

The process includes carbonation and calcination in several cycles. The CO₂ gas for carbonation can be taken from flue gases mixed with others. In the calcination process, pure CO₂ is obtained. This pure gas can be used in valuable industrial applications as recover oil, food industry etc. This information was up dated in the manuscript. Iron ore would be extracted from the mines in the same that is done currently because this will be processed for CO₂ capture or for iron steel process. According to this there won´t be extra-emissions of CO₂. In case that material losses its capture features, it can be send to iron steel process.

Moreover, according to carbonation reactions, it was possible to establish a projection of the amount of raw material that would be used in large-scale CO₂ emissions, which is shown in table 6. Besides the energy needed in HTHP and mechano chemical process was calculated, in order to see the projection in a real process taking account this important factor.

Operation temperatures are 32°C in mechano chemical and over 100° C in HTHP. Hence, the simulations were performed at those conditions, as you can see in Fig 2 and Fig 3. The behavior and conclusions about CO₂ capture capacity using HTHP and mechano chemical are explained is the sections 3.3, 3.4 y 3.7.

Fig 9 and Fig 10 were corrected according your suggestions

Best Regards

Eduin Yesid Mora Mendoza

Corresponding author

Reviewer 3 Report

The work studies the absorption of CO2 by iron ore in order to produce iron carbonate siderite and the inverse process to recover the ore. The use a milling methins under high pressure of CO2 and a High T high P method.  The proposal is interesting and this metyhod is scarcely studied, but the paper is poorly written and need major changes

The abstract phrase  beingning "The higest CO2 capacity achieved were..." It is not clear what results correspond to each method. Please rewrite.

Also in the abstract it is saluid reachs, the correct is reaches

in line 34 it must be achieve, not achiev. In general please revise the language and the spelling.

In line 76. How is calculated the material ratio os the ore. Only with the amount of iron oxide? Please explain further.

How is defined activity in fig 2 and 3?

In  lines 266-272 it is not clear. They mention  "adding water siderite yield was acomplished by just by mechanical method" But in other tables it is shown siderite wield by HTHP methids as well. It is mean in the resuing? Please be more clear. In general is difficult to undertand what results refer to what. Maybe dividing the paper in subsections clearly defined?

How is defined siderite yield? With respect to what?

for me it is not clear what represents x in eq. 6. Mass fraction of waht?

Energy units used are w-h, if w means Watts must be capital.

Author Response

Dear Professor

It is a pleasure to communicate with you directly. In first place, authors appreciate all of your corrections, comments and suggestions about our manuscript. We are sure that they have helped us so much for improve it.

About your last comments we can say:

Abstract was rewritten according your corrections. Line 34 was corrected.

XRF analysis gives us just elemental information such as the weight percentage of iron and the impurities. These percentages are obtained directly from the equipment. The real proportion of iron oxides inside iron ore is obtained in XRD pattern through Rietveld refinement.  This information is explained in 3.1 section.

Activity is a measurement of effective concentration of a chemical species. This has no units. It is just molar fraction in order to check the stability.  

Lines 266-272 were rewritten in order to divide the results in recarbonation  in both methods.

Siderite yield is related to formation of siderite. In the manuscript is used just to identify the presence of siderite. The amount of siderite (FeCO₃) with relation to amount of initial sorbent is associated to the CO₂ capture capacity measured as mmol CO₂/gsorbent.

In 3.7 section, was corrected the symbol of mass fractional conversion    to have correspondence with eq. 6. This value was calculated from the data shown in Fig 9, as a percentage of conversion.

Energy units were corrected

Best Regards

Eduin Yesid Mora Mendoza

Corresponding author

Round 2

Reviewer 2 Report

Some effort has been done by the authors to justify the interest of their research. The real applicability of the proposed process is very limited considering the large volume of CO2 emissions and the relatively low adsorption capacity of the proposed materials. Still, it may be of interest as alternative method to capture the emissions of the steel industry. Since this industry produces around 2 ton CO2 per ton of steel, the authors should focus on this and present a case of study in which the real applicability is shown. If the authors make this small effort, the manuscript will attract the attention of more readers that are looking for realistic solutions in specific sectors.

Author Response

Dear professor

We agree with you. In 3.7 section was included a case study for the amount of needed materials in carbonation and calcination reactions taking account the blast furnace emissions.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

In this manuscript, the authors studied the CO2 capture by mechanochemical and high pressure high temperature methods with iron ore as absorbents. The effects of processing conditions on CO2 capture capacities were investigated. I have the following questions as listed below:

1. What was the highest temperature during the ball milling process?

2. How to compare the two iron ore compositions obtained from XRF and XRD?

3. The quality of Fig 2 and 3 should be improved. It is hard to recognize the legends and axis titles.

4. Change format of line 154.

5. How did you calculate the yield of siderite? Did you consider the amount of Fe2O3, FeOOH, and perhaps Fe?

6. How did you calculate the “conversion” in line 162?

7. The sentence in line 177 and 178 was confusing.

8. In line 216, it was claimed that “However, siderite decomposition begins at lower temperatures for the sample produced by ball milling.” What was the evidence for this conclusion. It was very hard to identify the differences between the TGA curves in Fig 6 (a) and (b).

9. Based on reaction (3), magnetite and carbon were generated during calcination. What was the effect of the presence of these two newly formed chemicals on the carbonation reaction, i.e. on the carbonation-calcination recycles?

10. In table 4, why did the CO2 capture capacity increased as the increase of cycle times, while in table 5, it was decreased as the increase of cycle times? Similarly, in line 304, why was it concluded that “The release of CO2 starts at lower temperatures in mechanochemical process compares with HTHP”?

11. Please also add the initial CO2 capture capacity in table 4 and 5, for easy comparison.

12. Why did HTHP exhibit higher CO2 capture capacity than that of mechanochemical process?

13. Some crammer mistakes: line 122 “accomplish” should be “accomplishing”; line 175 “faster of” should be “faster than”; line 177 and line 239Du “by mean of” should be “by means of”; line 278 “a” should be “an”; in many places “accord” should be “according to”; line 283 “depends strongly of” should be “depends strongly on”; line 284 “lower than” should be “lower than”.

Reviewer 2 Report

The authors present experimental results on the carbonation of iron ore, using two equipment, for the purpose of CO2 sequestration/capture as siderite. The experimental methodology is not well executed, which results in poor results that have little to no value. I will explain why:

1-) Iron in siderite is Fe(II), while iron in iron ore is Fe(III). So the only way to make siderite from iron ore is to first, or at the same time, reduce the iron from Fe(III) to Fe(II). Carbonation is not a redox reaction, so is not capable of reducing iron.

2-) The CO2 absorption was determined by Rietveld analysis of XRD data. The XRD diffractograms shown are of poor quality (insufficient steps to obtain sharp peaks), and the authors have shown no evidence of the quality of their Rietveld refinement (e.g. by quantifying a standard material or showing the modeled diffractograms generated during the Rietveld analysis). This poor XRD analysis might explain why values in Table 3 have almost random order (i.e. cannot be justified by process conditions).

3-) The TGA plots shown have very poor data. Most of the mass loss occurs before the decomposition temperature of siderite, in fact much mass loss happens are low temperatures, so the samples might have been wet during analysis. Siderite decomposition, according to literature, occurs at temperatures higher than 450C, and yet no mass loss is seen after this temperature. So the TGA data does not agree at all with XRD results.

4-) Table 6 says that metallic Fe is needed to converted hematite into siderite, which then is a redox reaction, but the iron ore used was not shown to contain any significant quantity of metallic Fe. In fact, using metallic Fe for CO2 sequestration would not be a feasible process given the cost and emissions generated to make metallic Fe metallurgically.

5-) In summary, the methods and results of this manuscript are of poor quality and reflects on the authors' lack of knowledge about carbonation reactions.

Reviewer 3 Report

I recommend that this paper be accepted if the authors can rewrite their paper and pay attention to the issues raised below:

a. "adsorbent" for solids, NOT "absorbent"

b. Proofreading by a native English speaker is highly recommended as there are several grammatical errors.

c. I recommend you rewrite the abstract, your current abstract is not very logical and that makes it difficult to follow. For instance, you wrote,  

"Kinetics of carbonation 16 reactions were studied as a function of CO2 pressure, and parameters like planetary mill rotation 17 speed in the mechanochemical process, while in the HTHP process the carbonation reactions were studied 18 as a function of CO2 pressure and temperature"

This sentence is followed by "In order to overcome the kinetics limitations..." but your initial sentence didn't highlight any limitations. 

d. Instead of "[1] [2] [3]" do [1,2,3]?

e. Reference: [37] have a mix of capital and small letters. Update. Also in some of your references on the list, you used capital letters for the name of the journal and in some, you did not. Must be consistent

e. This "..100.000 million..." in your introduction is confusing. You must be talking about "100 billion". The agreement to invest 100 billion was not reached at the COP-21 in Paris, it was only reaffirmed. Update with the correct info on the Paris agreement. 

f. Instead of "Ref. [13]" in your introduction, you should have Kumar et al [13]

g. The literature review is not comprehensive. Have you cited related papers on this journal? How is this paper relevant to this journal?

h. You have not stated the novel contribution of this work. This must arise from clearly stating what has been done in the literature and highlighting in what ways your work is different from existing studies. 

i. What is the need for Fig. 2 since they are basically a straight line. What insight are readers supposed to derive from this figure?