Liberation of Gold Using Microwave-Nitric Acid Leaching and Separation-Recovery of Native Gold by Hydro-Separation

Round 1

Reviewer 1 Report

1. The abstract needs a through revision. There are grammatical and typo errors.
2. Change "experiment " to "process" in line 12
3. You wrote "The native gold in 1-4M was  insoluble residue, yet in the discussion it was 1-3M 
4. Add observations/results from characterisation of hydro-separation products in the abstract.
5. First sentence of the introduction is a little careless. You need citations if you believe in this statement.
6. Line 67. Note clear what the authors mean by oxidation zone.
7. No reference was done to to Fig 1a in the discussion
8. Delete line 192
9. Change Su to Au: line 206
10. Data in Table 4 can be presented better as a figure (Graph)
11. Line 224 must be revised. Is it 1M or 2M
12. Line 259 contradicts line 224. Did pyrite completely dissolved at 2 or 3M?
13. Caption for Figure 7 is wrong.
14. Line 314. Reference properly
15. You need to rewrite the conclusion. Here the authors simply repeated the results.

Author Response

Dear Reviewer

We greatly appreciate your thoughtful comments that helped improve the manuscript. We trust that all of your comments have been addressed accordingly in a revised manuscript. Thank you very much for your effort.

Point 1: The abstract and conclusion needs a through revision.

Response 1: All over the abstract was revised again. Your comment helped our manuscript substantially improved. We appreciate your precise evaluation.

Point 2: Some data mistakes should be revised. Improve better the manuscript.

Response 2: Thanks for the reviewer's comment. We checked all of the mistakes throughout the manuscript. I have changed the manuscript and grammar improved clarity.

Author Response File: Author Response.pdf

Reviewer 2 Report

You find here enclosed some comments and suggestions about your paper

English should be improved.

What is the main purpose of this study? A possible industrial application of this process?. If so, it should be explained and justified in the work, including the high consumption of nitric acid to dissolve almost all sulphides, and what would be done with nitrous vapors generated during leaching, etc. In any case, the specific objective of this work should be justified in more detail

Abstract, line 12: In observing the SEM-BSE image of... Here and in all the work

Lines 13-15: This expression is not understood. I think it should be written again for clarity. Perhaps all the abstract should be rewritten

Abstract, line 16: ...residue...

Page 2, lines 69 and 78: ...by SEM-EDS analysis... Here and in all the paper.

Page 2: The experiments were developed over the concentrate? Any experiment by using the original material?

Page 2: How were determined the experimental conditions employed? In a previous work, in a reference of other authors? If so, it should be indicated in the text.

Page 3, lines 118-127: A scheme of the Hydro-separator would be appreciated.

Page 5, Figure 1: Figure caption is very long; part of the information contained should be included in the text.

Page 5, Figure 1: Only three significant digits. I.e. 61.3 / 34.8 / 2.11 / 1.91 / 58.1 / 28.2 / and so on. This comment is valid for this table and for all the work. The totals of 100.00 in this table must be removed.

Pages 4-7: In relation to the chemical analysis (page 7): you includes in the paper is SEM-EDS, XRD, granulometric analysis and finally the chemical analysis. In my opinion, the order of presentation is: 1) Previously to the mineralogical analysis you need to know the chemical composition of the samples; Then the mineralogical analysis starting with XRD, then SEM-EDS and finally, the granulometric analysis.

Page 6, Table 2: 100.00 must be removed. Only three significant digits.

Page 7, Figure 2, Figure caption: SEM-SE image (a) and SEM-BSE image (b) ...

Page 6, Line 180: ... 1715.20 ... Six significant digits? Maximum three: 1.72 kg Au/t.

Page 6, lines 182-183: you indicate “middling ore and tailing” What are these solids? They has not been presented in this work. It must be clarified.

Page 7, Table 3: 11.9 / 0.800 / 0.280 / 0.200 / 103 g Ag/t / 1,72 kg Au/t.

Page 7, Figure 5: the bar of image, 0.5 mm; remove this data in the figure caption.

Page 8, line 206: .... Therefore, the undissolved Su will be ... It can be Sn?

Page 8, line 208: Table 4 is not presented in the text (not appears there). In table 4 the gold extraction line can be eliminated, because dissolved gold is not detected and it is already indicated in the text itself

Page 9: All the information included on page 9 is very difficult to follow. I think it would be necessary to rewrite this information to reach your understanding.

Figure 8, Figure captions: it is not necessary to indicate: The scale bar is 50 ㎛(c), 100 ㎛(a) 270 and 200 ㎛(b, d, e and f) in length. 271. It appears in each image. In the same figure: you indicate “Red dot square is a EDS analysis area(Fig. 8a)”. But this red dot square not appears in Figure 8 a).

Page 10, Figure 7: you should indicate the same in figure captions as was included in Figure 3.

Page 13, Figure 10, Lines 277-290: The results obtained in Figure 10 are not understood. In heavy minerals obtained after leaching with acid 1M (weight loss of the solids of 16%), gold appears in significant amount. After 2M, there is practically no gold when the solid has decreased by 40%, in the 3M that does not appear (47% decrease in solid). And then suddenly with 4M the gold appears again in small quantity and with 5 and 6M the gold reappears with great quantity. It's not understood. The results must be reanalyzed to be interpreted again.

Figure 10 is not presented in the text.

Page 14, Figure 10: Quartz not appears at 1M, small peaks appears at 2-3M, high peaks at 5M but quartz not appears at 6M. Why these differences in the peaks intensity of quartz, when it would appear approximately at the same intensity, at least in the interval 2M-6M?

Page 14, line 296: point analysis, red dot??

Page 15: In Figure 11, ... SEM-BSE image... The same figure, remove the scale bar, it appears in the image.

Page 16: Figure 12. SEM-SE image (a,c) and SEM-BSE image (b,d)... The same figure: red dots? Remove the scale bar in the figure caption

Page 16, line 318: ...of 1.72 kg Au/t Page 16, line 322: SEM-BSE image here and in all the work

Author Response

Dear Reviewer,

Thank you for taking the time to review our paper.

The manuscript was revised in the aim to improve the overall quality of the writing in accordance with the recommendations of the reviewer. Thank you very much for your effort.

Point 1: “What is the main purpose of this study? A possible industrial application of this process? If so, it should be explained and justified in the work, including the high consumption of nitric acid to dissolve almost all sulphides, and what would be done with nitrous vapors generated during leaching, etc. In any case, the specific objective of this work should be justified in more detail”

Response 1: I understand your concerns and agreed your comments. I have made improved to the purpose of this study.

 “This study will contribute to alternative treatment for a complex or refractory gold concentrate, which improves the process performance of the fine and invisible gold recovery. It is focused on the development of simply microwave-nitric acid leaching process.”

Point 2: The abstract and conclusion needs a through revision.

Response 2: All over the abstract was revised again. Your comment helped our manuscript substantially improved. We appreciate your precise evaluation.

Point 3: The unit change

Response 3: We corrected the Unit as you recommended.

Point 4: Figure caption is very long and remove the scale bar

Response 4: As you point out, the previous expression was awkward. Thank you for your recommendation. We corrected the Figure caption as you recommended.

Point 5: Some data mistakes should be revised. Improve better the figure.

Response 5: We checked all of the mistakes throughout the figure. I have changed the figure.

Point 6: Justification of experimental conditions and methods should be clearly mentioned

Response 6: We changed it as your comment

Point 7: what do you want to say? Unclear sentence……

Response 7:  All over the manuscript was revised again. Your comment helped our manuscript substantially improved. We appreciate your precise evaluation. We trust that all of your comments have been addressed accordingly in a revised manuscript.

Point 8: etc.

Response 8-1: We changed it as your comment.

Figure 3. Schematic diagram of hydro-separation process.

Response 8-2: We changed it as your comment.

Figure 6. Effect of the HNO₃ concentration on the leaching efficiencies of Cu, Pb, Zn, Ag and Fe and weight loss rate from the gold concentrate. Leaching conditions: (a) HNO₃ Concentration; 1.0 to 6.0M, reaction time; 15 min.

Response 8-3: We changed it as your comment.

Figure 7. Comparative XRD patterns of raw and solid-residue after microwave-nitric acid leaching as a function of nitric acid concentration. A; adularia, C; calcite, F; fluorite, M; muscovite, P; pyrite, Q; quartz and Gy; gypsum.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

1. Revise sentences line 17-19, 26,  and line 28 is not complete
2. You do not use pronouns when writing scientific work, lines 71, 93, 207, 258, 462, 477
3. Line 150 -151. How do you assay solids using AAS?
4. The conclusion still needs some improvement. Its not a mere summary of your results but you conclude on your results. It must state clearly the contribution of the article based on your own findings.

Author Response

Dear Reviewer

Thank you for taking the time to review our paper.

The manuscript was revised in the aim to improve the overall quality of the writing in accordance with the recommendations of the reviewer. Thank you very much for your effort.

Point 1: Revise sentences line 17-19, 26 and line 28 is not complete

Response 1: We corrected the sentence as your recommendation

Point 2: You do not use pronouns when writing scientific work, lines 71, 93, 207, 258, 462, 477

Response 2: Before change manuscript line ~256.

Point 3: Line 150 -151. How do you assay solids using AAS?

Response 3:  The solution was analyzed by AAS. The amounts of metal ion leached was calculated via the following equation:

Where L is the leaching percentage of metal ion; M₀ and M₁ correspond to metal ion contents of sample before and after leaching.

Point 4: The conclusion still needs some improvement. It’s not a mere summary of your results but you conclude on your results. It must state clearly the contribution of the article based on your own findings.

Response 4: We corrected the sentence as your recommendation.

Author Response File: Author Response.pdf

Reviewer 2 Report

The work has been substantially improved. However, there are some points that could be improved, most of them already indicated in the first review.

• Point 1 of the previous review: I think a comment is missing from the paper on the subject of nitric acid consumption, if it is high, if it is adequate in relation to the amount of gold contained in the concentrate?
• Point 2: I think that when you are talking about BSE, SEM-BSE should be indicated and when you are talking about EDS, it should be indicated: SEM-EDS, in all the work.
• Point 3, In relation to Table 1: 11.9 / 0.800 / 0.280 / 0.200 / 103 / 1.72
• Point 3: I think that the results of chemical analysis should always be presented before those of X-ray diffraction.

Author Response

Dear Reviewer

We greatly appreciate your thoughtful comments that helped improve the manuscript. We trust that all of your comments have been addressed accordingly in a revised manuscript. Thank you very much for your effort.

Point 1: I think a comment is missing from the paper on the subject of nitric acid consumption, if it is high, if it is adequate in relation to the amount of gold contained in the concentrate?

Response 1:

1. According to the results of chemical analysis, it is differ in the contents (Fe, Cu, Pb etc.,) of sulfide; therefore, the study considered leaching rate of concentrate. In particularly, iron leaching rate was considered as the main component indicating the degree of sulphide oxidation, as it is included in pyrite. XRD analyse was conducted, and the results of these analyses are presented in Fig. 7. It can be concluded that pyrite in the sulfide minerals is not decomposed by nitric acid at < 1.0M. Therefore, we investigated to increased nitric acid concentration to enhance the recovery of gold.
2. Refractory gold-containing ores refer to materials, the extraction of gold from which by acid solution (e.g., cyanidation, thiourea etc.) is low or requires significant amounts of energy and reagents [1]. Currently, it is considered proven that the refractory characteristics of gold associated with sulphides is not only due to the presence of nanoparticles of native gold but also due to the existence of solid solution, colloidal particles, surface gold.
3. One of the possible methods of hydrometallurgical processing of refractory sulfide concentrate is the use of HNO₃ to oxidize the materials without the use of high pressure or fine grinding [2, 3], as nitric acid is one of the most effective oxidizing and leaching agents [4, 5].

※ Reference

1. Invisible and microscopic gold in pyrite: Methods and new data for massive sulfide ores of the Urals. Geol. Ore Deposits 2015, 57, 237–265.
2. Refractory leaching solutions. Aust. Min. 2009, 101, 20.
3. Hydrometallurgical process development for complex ores and concentrates. J. South. Afr. Inst. Min. Metall. 2009, 109, 253–271.
4. Leaching Kinetics of Sulfides from Refractory Gold Concentrates by Nitric Acid. Metals. 2019. 9(4)

→ Experimental conditions: nitric acid concentration (10~40%),

5. Hydrometallurgical Processing of a Nigerian Galena Ore in Nitric Acid: Characterization and Dissolution Kinetics. J. Mmce. 2018, 6, 271-293

→ Experimental conditions: nitric acid concentration (2.0 ~ 12.0M)

Point 2: I think that when you are talking about BSE, SEM-BSE should be indicated and when you are talking about EDS, it should be indicated: SEM-EDS, in all the work.

Response 2: We corrected the sentence as your recommendation

Point 3: In relation to Table 1: 11.9 / 0.800 / 0.280 / 0.200 / 103 / 1.72 I think that the results of chemical analysis should always be presented before those of X-ray diffraction.

Response 3: We changed the sentence as your recommendation.

Author Response File: Author Response.pdf