Experimental Investigation on the Combination of Enzyme-Induced Calcium Carbonate Precipitation and Organic Materials for Underground Backfilling Preparation

Round 1

Reviewer 1 Report

This paper presents an experimental study aiming to examine the preparation of underground backfilling materials through the combination of EICP and organic materials. The research presented in this paper is interesting, and minor revisions are required to improve the paper before accepted. Some comments are as follows.

1、Some grammatical and English errors can be seen. Please carefully correct the writing throughout paper.

2、The abstract should be revised to be much more concise.

3、The introduction should be re-organized and improved. It is more reasonable to introduce the EICP technology after the engineering background. In addition, the author did not focus on the on the research status and achievements of EICP technology in underground backfilling.

4、The horizontal coordinate in Figure 2 should be supplemented.

5、The number of samples tested for each group was not given in the UCS test.

6、The results of SEM and XRD analysis are not in-depth.

7、In the discussion, the findings of this study should be summarized more than other studies. It is suggested that the discussion should be combined with the experimental results.

Minor editing of English language is required.

Author Response

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Reviewer 2 Report

The article is devoted to solving one of the most important problems associated with increasing the efficiency of mining coal resources, while facilitating the rapid filling of mineralized materials.

Considering nature-like technologies as borrowing and adapting the principles of natural processes in the conditions of the technological realities of the building materials industry with the production of environmentally friendly materials, one of the knowledge-intensive promising areas is biotechnology, which fully corresponds to the ideology of the adaptation principle of environmental strategy. It is advisable to implement the self-healing function of building composite materials at the initial stages of their destruction, in particular under the influence of mechanical loads. When cracks are restored under the influence of microorganisms, physicochemical processes occur, leading to the formation of calcite bridges, which seal the cracks.

The focus should be on the biogeochemical process that causes calcium carbonate precipitation in the soil matrix (microbiologically induced calcium carbonate precipitation). Calcium carbonate can be precipitated in three polymorphic forms, which in order of their usual stability are calcite, aragonite and vaterite. The main groups of microorganisms that can cause carbonate precipitation are photosynthetic microorganisms such as cyanobacteria and microalgae; sulfate-reducing bacteria; and some types of microorganisms involved in the nitrogen cycle.

Calcium carbonate heals concrete by hardening onto the cracked concrete surface, mimicking the healing process of bone fractures in the human body by osteoblast cells that mineralize and reform the bone. Two methods currently being studied are the introduction of bacteria that precipitate calcium carbonate. and by applying bacteria and nutrients as surface treatments.

The results obtained in this work will be of interest to readers in the field under consideration.

However, a number of comments about the article should be clarified:

1. Has there been a comparative analysis of the coal mining bases in question in northwest China (Figure 1) with similar regions in other regions of the world?

2. In sections “2.1 Test materials”, “3.3. SEM/XRD" should go into more detail on how the X-ray diffraction analysis was carried out. This method is quite promising when conducting various studies using differential equations (transformations and Fourier transformants) and constructing the Ewald sphere, mathematical analysis, mathematical logic, and mathematical modeling. In particular, the following works could be analyzed: https://doi.org/10.3390/cryst13030528, https://doi.org/10.1016/j.cemconres.2007.02.008.

3. Are there any future plans to consider a wider range of sand parameters than those presented in Table 1?

4. In section “2.2 Test schemes” a generalized method of conducting experimental research should be presented, for which a patent may possibly be obtained.

5. It should be explained what software was used to process the experimental results (section “3. Results”).

6. According to the data presented in Figure 4, a regression analysis should be carried out with the use of mathematical models that allow the calculation and prediction of the considered output values and the corresponding coefficients of determination.

7. It is necessary to dwell in more detail on the research methods used to assess the uniformity of distribution of calcium carbonate in the sand column, presented in Figure 6.

8. The analysis of Figure 8 is not complete enough. The results presented in the figure represent the most important research part of the presented work.

9. In the conclusions it is necessary to present numerical practical results obtained from the work, so that they can be used by other authors when conducting similar studies.

10. The article should provide further prospects for continuing the work.

Author Response

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Reviewer 3 Report

This article assesses the EICP technology as a means to tackle the escalating ecological security concerns associated with coal mining. The paper is well-crafted, and the results are adequately presented.

I recommend omitting section 4 (Mineralized material underground backfilling method) as it does not align with the objectives of this paper.

Author Response

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Round 2

Reviewer 2 Report

The authors have corrected my comments and the article can be accepted in my opinion.