Review Reports

Round 1

Reviewer 1 Report

This study has conducted batch and continuous mode experiments to elucidate the kinetics and mechanisms on biooxidation process for recovery of gold. The mechanisms section needs to be improved. Moreover, the reviewer has the following additional comments on the manuscript.

Give chemical formula of pyrite and arsenopyrite in the text.

Figs 4 (c) and (d): Could you explain the potential reasons for the positive correlation between gold recovery and S removal rate.

Eq, (1) – (4): Bacteria is too generic. Could you be more specific, i.e., provide the specific name of bacteria that drive the biotransformation.

Among the pure and mixed culture system, which would work better.

What are the potential key parameters that impact the bio-oxidation process?

What is the purity of the recovered gold? Give a comparison with pure gold.

Would the process be economically feasible?

What are the possible key challenges to scale-up the bioprocess?

In microbial analysis, this study has analysed only the bacterial population. There may be some interesting archaea which could co-exist with bacteria and co-contribute to the bioprocess. Are there any studies related to archaea in literature? Authors should improve the discussion in the context of archaea.

What are the practical implications of this study and what additional future works are needed to better understand the bioprocess, mechanisms, enhancement of Au recovery, etc.

The reviewer is suggesting doing some statistical treatment of the data to verify where the differences in performance of biooxidation with various agents (S, Fe and As) are statistically significant.

The quality of most of the figures should be considerably improved.

Author Response

Dear reviewer，

    Please see the attachment.

    Regards,

Author Response File: Author Response.docx

Reviewer 2 Report

Comparative Study on Refractory Gold Concentrate Kinetics and Mechanisms by Pilot Scale Batch and Continuous Bio-Oxidation

The study shows information of interest related to the recovery of gold by biohydrometallurgy and the results shown are adequate.

However I think work can be improven taking into account some observations and comments:

1. Authors pointed that gold and silver are as Electrum enclosed in different kind of minerals such as sulfate, sulfide, and silicate. Principally sulfur from hydrometallurgical point of view is not considered as refractory ore. Why authors say that pyrite and aresenopyrite are refractory?
2. According the point 1, how authors determined the presence of such kind of minerals in the concentratte, please expain it.
3. I suggest that could be described the particle size distribution and how could be the influence of this parameter and the morphology during batch and continous bio-oxidation.
4. I would like to see a model describing the bio-oxidation process according the particle area and morphology of particles. What happens with the Au and Ag enclosed in quartz?
5. The bio leaching process is adequate in ores having low valuable metals contents and can be used in wastes or residual ores. Why is studied in concentrates?
6. Please compare with other type of process for the recovery of Au and Ag, like cyaniding, use of thiosulfate, thiourea and dithionite.
7. Please pointed adequatle the innovation of this work with respect to other similar works.

Author Response

Dear reviewer,

    Please see the attachment.

     Best regards,

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

No more comments.

Reviewer 2 Report

Authors have correctly answered the questions and paper now has been improved.