CO2 Capture by Alkaline Carbonation as an Alternative to a Circular Economy
, Mirella Gutiérrez-Arzaluz 2 and Miguel Torres-Rodríguez 2,*
Round 1
Reviewer 1 Report
1) The authors need to say that the system used in continuous for the gas phase and batch for the liquid/solid phases. In the paper they called semi-contonious ehich may be confusing
2) Please give detailed information on how the gas phase is dispersed in the liquid solution
3) What is the solubility of the feed CO2 on the liquid solutions?
4) The discussion of results is qualitative. I would like to see the linetics of carbonation reaction discussed in more depth.
Author Response
R
Review 1.
Review 1. The authors need to say that the system used in continuous for the gas phase and batch for the liquid/solid phases. In the paper they called semi-contonious ehich may be confusing.
Response: Thank you for the observation, wherein, the gas phase is fed continuously and the batch is the liquid phase.
Review 1. Please give detailed information on how the gas phase is dispersed in the liquid solution.
Response: Following the reviewer's request, the gas phase is dispersed in the liquid phase by a porous glass diffuser, coupled to the end of the feed tube.
Review 1. What is the solubility of the feed CO2 on the liquid solutions?
Response: The solubility of CO2 at 298 K was estimated applying Henry's constant, at the feed pressure of CO2, using the reported data in the paper, R. Sander, Compilation of Henry’s law constants (version 4.0) for water as solvent, Atmos. Chem. Phys., 2015, 15, 4399–4981, “2.4.2 The dimensionless Henry solubility Hcc”. pag, 4401-4404, 4488.
Solubility CO2 = 26 mol m-3
Review 1. The discussion of results is qualitative. I would like to see the cinetics of carbonation reaction discussed in more depth.
Response: Thank you for the observation, but at this time for obtaining a carbonation kinetics we do not have enough data for a rigorous determination, nevertheless, the behavior of the system was reviewed and analyzed in greater depth and the wording updated, in discussion section.
The capture of CO2 in aqueous solutions for carbonate formation is a complex gas-liquid reaction system, presenting several series stages of mass transfer and reaction. The analysis of the pH behavior during the first 10 minutes of reaction, shows that the pH of the solution presented a slight decrease, which suggests that at the beginning of the reaction is controlled by CO2 mass transfer from the gas phase to the liquid phase, by solubilization, then CO2 gradually reaches the semi-stationary state followed by the formation of dissociated carbonic acid in aqueous solution, generating two protons and the carbonate ion that reacts with the cation Ba+2 or Sr+2 to form the corresponding carbonate; that reaction generates a rapid decrease in the solution pH that is observed in a change in the slope of the pH where carbonate formation exists, thereafter, the transformation of carbonates to bicarbonates occurs at pH values lower than 8, this behavior is consistent with the stability of chemical species at different pH values according to the carbonate system [16].
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper deals with an interesting issue, which is relevant with the scope of the journal. It has high quality data. Also, the results are interesting and quite relevant to answer the questions posed in the article. The structure of the paper is excellent and they are not serious grammar and spelling problems.
However, it needs some changes prior to being acceptable for publication. Some parts have to move from the results to the discussion. Additionally, the authors have to elaborate more on the discussion chapter, concentering their geochemical, mineralogical and mineral-chemistry findings.
My comments for the authors are:
Line 51 change paragraph (it will be useful for the readers to find easy the aim of the paper)
Lines 134-6, 234-236 they belong to the discussion chapter and please elaborate
Lines 141-143 they belong to the methods chapter
Lines 149, 171, 186, 195, 220, 229 please don’t start the paragraph with “Figure …”, rephrase.
Line 254 “metallic carbonate” what do you mean?
Discussion: please use paragraphs
Lines 260-270 maybe it will be better to start the discussion chapter with that paragraph
Author Response
Review 2.
Review 2. Line 51 change paragraph (it will be useful for the readers to find easy the aim of the paper).
Response: the suggestion was answered and the wording of lines 51 and 52 were reviewed, for clarify.
This work aims to explore a CO2 capture alternative oriented to small and micro industries, trough CO2 capture as carbonates using Sr and Ba solutions in a semicontinuous reactor. In addition, this work addresses morphological characterization, evaluation of the recovered solids purity, and reaction time effect at ambient temperature and atmospheric pressure conditions were performed. This alternative can be considered as a process readily implementable, devoid of scaling problems for small industries.
Review 2. Lines 134-6, 234-236 they belong to the discussion chapter and please elaborate
Response: In response to the reviewer's suggestion, we agree to relocate lines 134-136 and 234-236 to the discussion section.
Review 2. Lines 141-143 they belong to the methods chapter.
Response: We agree with the reviewer and we have change those sentences to methodology section.
Review 2. Lines 149, 171, 186, 195, 220, 229 please don’t start the paragraph with “Figure …”, rephrase.
Response: Following the reviewer's suggestion, we change the beginning of the paragraphs that were suggested.
Review 2. Line 254 “metallic carbonate” what do you mean?.
Response: We refer generically to synthesized carbonates, the Ba carbonate formed during the reaction between CO2 and Ba hydroxide.
For clarification we change, metallic carbonate for Ba carbonate.
Review 2. Discussion: please use paragraphs
Lines 260-270 maybe it will be better to start the discussion chapter with that paragraph.
Response: We prefer to keep those lines at the end of the discussion section.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The revised version is acceptable.
Reviewer 2 Report
My suggestion is to publish the paper.
