Copper and Zinc Recovery from Sulfide Concentrate by Novel Artificial Microbial Community

Round 1

Reviewer 1 Report

The article does not have much innovation and a lot of work has been done in this field It is necessary to summarize in a table a review of past articles (who did what and in what year and what was the result) The results need to be validated The results need to be discussed

Author Response

We gratefully appreciated for your suggestion. Your suggestion is of great guiding significance to our research work. According to your suggestion, we have not only summarized the previous studies and results, but also added three latest research results. The summary was displayed in Table 1. Moreover, it was also displayed in manuscript with Table 1. Thank you again for your valuable advice.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript “Biodesulfurization of sulfide concentrate for efficient recovery of copper and zinc by novel artificial bacterial community” by Liu and coworkers presents an interesting approach for Cu and Zn recovery using an artificial bacterial community.

The manuscript is well written and presented. However some comments need to be addressed before publications.

• Authors claim that this is the first time where artificial bacterial community is used as bioleaching method. It is a strong claim and I don’t think that need to be here. Could be “to our knowledge ….” Because there are several articles using the same technique. So the major differences between this study and previous studies need to be discussed more in the introduction.
• To make this discussion is more valuable to the readers in the field and help new researcher, I suggest to summarize all up-to date bioleaching Zn and cu recovery researches in a table including the bacterial communities used and the recovery efficiency in each study.
• Study about the stability of the used artificial bacterial community in the study environment, pH and temperatures to be discussed.
• Method used for measuring the particle size distribution need to discuss. Is there any correlation between the particle size and the metal recovery efficiency? Is this in all cases? This point has been discussed but need more discussion and need to be added to the conclusion.

 

The manuscript can be published in Metals after addressing the previous points.

Author Response

Thank you very much for your approval for our research. We listened to your suggestions carefully and revised our paper according to your suggestions. We have revised the content as attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

In the manuscript with the title “Biodesulfurization of sulfide concentrate for efficient recovery of copper and zinc by novel artificial bacterial community”, the authors are reporting a novel artificial bacterial community which is promised as an environmentally friendly and high –efficiency bioleaching technology. This is a very interesting paper and gives a clear exposition of the work and results which have been found. A couple of comments:

1. Delete the space before the dot in Figure 3
2. Are the authors able to comment on the repeatability in the number of bacteria in the culture of the artificial bacterial community?

The article is well-written, easy to comprehend and can be valuable for readers.

 

I believe that this paper can be considered for publication.

Author Response

We gratefully thanks for your approval of our research work and your valuable suggestions. We have carefully modified our paper according to your suggestions. 

Author Response File: Author Response.pdf

Reviewer 4 Report

The article needs major revisions as some experimental procedures are not clearly described and the article requires extensive editing.

 

In general, the manuscript requires extensive editing of English language and style as some sentences are not clear.

 

Specific comments:

1. Title. The term bacterial community is usually used for natural or artificial microbial populations, in which microorganisms interact and which have been formed under the influence of different factors. In the case of the present work, you have deal with the mixture obtained from three pure cultures. Thus, use the term “mixed culture” instead “community”. Also, replace “bacterial” with “microbial”, as you used both bacterial and archaeal strains.
2. The abstract should be rearranged as in the present form, it does not show the main results and does not describe goals and experimental procedures.
3. Abstract “Therefore, this new-type artificial bacterial community is promised as an environmentally-friendly and high-efficiency bioleaching technologies scheme with potential large-field applications of engineering in the future”. The community (or culture) is not a method or a technology. It can be used in technological scheme. Rewrite the sentence.
4. The paragraph “In the bioleaching technology, microorganisms, such….” is not clear.

4.1. It includes the examples of different microorganisms application for metal leaching including neutrophilic bacteria and fungi. In practice, bioleaching is performed using acidophilic bacteria and archaea as in your experiments. Therefore, focus this paragraph on the data on acidophilic microorganisms and their application in bioleaching.

4.2. Also, you postulate that “Above all, the majority of bioleaching experiments employed the single wild microorganisms, which make an impact to result of leaching efficiency was relatively limited.” In the same time, mixed microbial populations are usually used in bioleaching. Therefore, check relevant reviews on this topic published in last decades and cite in the Introduction.

5. Aim of the work. ”In our study, with the aim for developing new environmentally-friendly and high-efficiency bioleaching technologies…” Bioleaching technologies are well-known and in your article, you have used well-known processes. Thus, the aim of the work should be reformulated. For example, the aim of the was to evaluate the influence of different factors on the bioleaching Cu and Zn from the concentrate……
6. Lerroplasma acidiphilum YT? Ferroplasma acidiphilum YT?
7. Materials and methods.

7.1 Leaching procedures should be described in detail in the separate sub-section.

7.2 “2.2. Culture for the artificial community.”

The subsection should include brief description of the strains used. The data on the source of isolation, media and culture conditions should be described. If the  trains were obtained from the collections, relevant information should be presented (collection, accession numbers, references). If you isolated the strains used, you should include information on the isolation or provide relevant references.  

7.3 Nikon ECL IPSE 50I is light microscope (not electron!).

8. Subsection 3.1 and Table 2 – sulfide concentrate (not sulfur).
9. Figure 3a. Did you control the pH during the experiment? The pH is changed du to sulfide concentrate biooxidation.
10. Figure 3 b. Separate figure 3b into 2 different diagrams (for temperature and rpm effect).
11. Figure 5. Separate Fig. 5 into 2 different diagrams (for inoculation quantity and pulp density).
12. What was the control? Leaching under aseptic conditions?

Author Response

We gratefully thanks for your valuable suggestions. We have carefully modified our paper according to your suggestions. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks for sending the reply, in the sent reply, only a part of the items announced by me have been corrected and the rest can be done as before

Author Response

We gratefully appreciated for your suggestion. Your suggestion is of great guiding significance to our research work. According to your suggestion, we have not only summarized the previous studies and results, but also revised Abstract, Materials and Methods. All of them are in red text. Thank you again for your advice.

Reviewer 4 Report

Review 2

1. Abstract.

“Therefore, this new-type artificial microbial community is promised as an environmentally-friendly and high-efficiency bioleaching technologies scheme with potential large-field applications of engineering in the future”. See the comments to the aim of the work.

 

2. Table 1. The following references are not directly related to the aim of the study and may be excluded:

 Nitric acid-sulfuric acid mixture (chemical method) - Selenium (99.23%) - Xuejiao Li et al., 2017 [32]

Reduction roasting-leaching-magnetic separation - Cu (82.18%); Fe (65.58%) - Hanquan Zhang et al., 2021 [34]

 

3. “In our study, with the aim for building new microbial composition and developing environmentally-friendly and high-efficiency bioleaching technologies scheme, and further explore the factors of temperature, pH value and rotation speed to influence the bioleaching process.”

In fact, the effect of different conditions on the bioleaching was studied. In the same time, novel technological schemes were not proposed in the study. Thus, I suggest to correct the aim. For example, “The aim of the work was to develop novel microbial culture to extract Cu and Zn from the sulfide concentrate and study the effect of different conditions( temperature, pH value and rotation speed) on metal recovery, which can be used in further investigations to develop environmentally-friendly and high-efficiency bioleaching technology”.  

4. Materials and Methods

4.1 Bacteria of the genus Sulfobacillus [What about other microorganisms used in the sudy?] are successfully used in biotechnologies of treatment of sulfide ore materials [reference(s)?].

4.2 The artificial microbial community was constituted by Sulfobacillus thermotolerans 6Y-1(CCTCC No. M2010279), Leptosirillum ferriphilum MJ-CL (CCTCC No. M2011019) and Lerroplasma acidiphilum YT (CCTCC No. M2010356) (with a concentration ratio for 1: 1: 1).

Is CCTCC a China Center for Type Culture Collection? Please include this information in the methods. For example, “Cultures deposited in China Center for Type Culture Collection (CCTCC) were used in the study”.

I cannot find any information on Lerroplasma acidiphilum YT (CCTCC No. M2010356) (both in published papers and in the collection catalogue using accession number). Did you write the species name correctly? It seems to be Ferroplasma acidiphilum YT (type strain). Could you clarify the information on this strain.

Also, include short characteristic of each strain (growth temperature, ferrous iron/sulfur oxidation, autotrophic CO₂ fixation, etc.) to understand its functional role in the community.

4.3 “…we have described the leaching procedures in detail in the separate subsection…” Revised manuscript does not contain additional section with the description of the leaching procedure. Please, check the manuscript. This section should include the information on the equipment used, temperature, pH values, inoculation, duration of the experiments, etc.

4.4 In the first version of the manuscript it was pointed that you have used Nikon ECL IPSE 50I (light microscope) to count the cell number. In the revised version you have deleted this information. In the same time, in the section “3.3. Artificial Microbial community Growth Characteristic Analysis”, it is shown that cell number was determined during the experiment. How did you determine cell number?

5. 3.3. Artificial Microbial community Growth Characteristic Analysis

5.1 Did you determine optimal growth conditions in the presence of the concentrate or using liquid nutrient medium with ferrous sulfate? It is not obvious.

5.2 Data on cell number are shown as CFU/mL. CFU technique requires culturing the microbes and counts only viable cells in serial dilutions. Did you use CFU technique or did you count the cell nimber using the microscope? If you used microscope, cell number should be expressed as cell/mL (not CFU).   

5.3 “According to your suggestion, we have separated figure 3b into 2 different diagrams. However, the visual effect is not good, so we made corresponding marks in figure 3b to make the information expression more intuitive” There are not any reasons to bad visual effect when separating the diagrams. Please, use two separate figures for different experiments

6. “Based on above results, we conclude that the artificial bacterial community preferred value of pH, temperature and cultural revolving speed was 1.8, 30℃ and 160 r/min respectively.” and “Based on the artificial bacterial community growth characteristic analysis results, the leaching efficiency of Cu and Zn were studied under different pH (pH=1.0, 1.2, 1.5, 1.8) and different temperature (35℃, 45℃, 55℃) conditions.” Optimal temperature was 30°C. Why did not you use this temperature in the further experiments?
7. Iinclude ±SE bars in the diagrams in the section “3.4. Reaction Condition Exploration for Biodesulfurization Process” demonstrating leaching rates for Cu and Zn.
8. Optimal conditions for the growth and metal recovery did not coincide. Could you discuss this result?
9. The title of the revised version is “Biodesulfurization of sulfide concentrate for efficient recovery of copper and zinc by novel artificial microbial community”. Desulfurization was not studied. Change the title. For example, “Copper and zinc recovery from the sulfide concentrate by novel artificial microbial community”

Author Response

We gratefully appreciated for your suggestion. Your suggestion is of great guiding significance to our research work.We have  revised and all of them are in red text. Thank you again for your advice.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

no

Author Response

We gratefully appreciated for your suggestion. 

Reviewer 4 Report

The article requires further improvement. 

 

1. Unfortunately, the authors did not understand comment regarding the title:

“The title of the revised version is “Biodesulfurization of sulfide concentrate for efficient recovery of copper and zinc by novel artificial microbial community”. Desulfurization was not studied. Change the title. For example, “Copper and zinc recovery from the sulfide concentrate by novel artificial microbial community”

Reply: we gratefully thanks for your suggestion. According to your suggestion, we have modified title as “Biodesulfurization of sulfide concentrate for copper and zinc recovery by novel artificial microbial community”, and red marked in the manuscript. Thank you again for your suggestion”

The term biodesulfurization means the decrease of sulfur content in the concentrate by means of bioleaching. In the present work, you did not study the decrease in sulfur content (you determined sulfur content in the concentrate but did not determine in the bioleaching residues) Thus, “Biodesulfurization” should be excluded from the title and the title should be changed. As you have study Cu and Zn extraction, the variant of the title may be “Copper and zinc recovery from the sulfide concentrate by novel artificial microbial community”.

 

2. “According to your suggestion, we have described the conditions related to the leaching process (time, speed, equipment) in section 2.3 of Materials and Methods.”

Text of the section “2.3. Chemical analysis procedure of leached elements

During each leaching process experiment, 50 mL samples of suspension were asepti-cally removed at 24 h intervals. Then, distilled water was added to replenish the evapo-rated solution before sampling. After the leaching finished, the residual ore concentrate was separated into solids. The supernatant immediately by centrifugation (Eppendorf Centrifuge 5804 R) with 11,000 r/min for 10 min to obtain the supernatant and sediment. The quantitative analysis of the main elements was carried out by ICP-OES (Inductively coupled plasma emission Spectrometer, Agilent 725-ES).”

The section does not contain any information regarding leaching process. Please, include this information!

3. “The bacteria concentration was estimated using a colony-forming unit (CFU) assay. Each dilution was plated in triplicate onto agar plates and incubated at 45 °C for 5 days. Then, the number of the colonies on each plate was counted”

The bacteria used in the study require specific solid media to be cultivated, which are differ each other. Which media did you use? Used acidophiles could not be grown used MPA or similar media.

4. You did not understand the question 5.2 “Did you determine optimal growth conditions in the presence of the concentrate or using liquid nutrient medium with ferrous sulfate? It is not obvious.” Did you use liquid medium with ferrous iron in the section 3.3?

Author Response

We feel great thanks for your professional review work on our article. We have corrected the problems point by point.

Author Response File: Author Response.pdf

Round 4

Reviewer 1 Report

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Author Response

Thank you again for your valuable suggestion.Also thank you for your recognition of our research work and approval of acceptance and publication. We will continue our efforts.

Reviewer 4 Report

The manuscript has been improved and may be accepted.

Author Response

Thank you again for your valuable suggestion.Also thank you for your recognition of our research work and approval of acceptance and publication. We will continue our efforts.