Combined Sulfidation and Vacuum Distillation for the Directional Removal of Hazardous Mercury from Crude Selenium

Round 1

Reviewer 1 Report

It is indeed a very impressive manuscript, which deals with a removal of Hg from crude Se. The manuscript will be of interest of experts and the general public and it is recommended to be published.

Some recommendations for improving the manuscript are as follows:

1. Make the text concise and remove unnecessary and well known facts, for examples:

   - the first two sentences in abstract can be removed.

    - l. 34,35, 38 are not related to the topic of the research. 

    - l. 49,50,51: modify the sentences to make clear that there are two precipitates, one of Hg and one of Se.

    - l. 63 : it is better to emphasize that sulphur is added to from new phase with Hg rather than "modify the phase of Hg"

   - l. 133 -136: not necessary.

2. Move all experiments to experimental procedures, for examples l. 191-203.

3. Specify the variables in formula 1 and 2.

4. Check for the "change" of the Gibbls free energy. Sometimes it is missing, eg. l. 148, 151, 155 etc.

5. Modify the conclusion "0.32% of mercury in the crude selenium was sulfurized".  It sounds like the rate is very low but it represents all Hg in Se. 

Author Response

Comment 1： Make the text concise and remove unnecessary and well known facts, for examples:

   - the first two sentences in abstract can be removed.

    - l. 34,35, 38 are not related to the topic of the research.

    - l. 49,50,51: modify the sentences to make clear that there are two precipitates, one of Hg and one of Se.

    - l. 63 : it is better to emphasize that sulphur is added to from new phase with Hg rather than "modify the phase of Hg"

   - l. 133 -136: not necessary.

Response: Thank you for the recognition. I have deleted this text unnecessary and well-known facts.

Comment 2: Move all experiments to experimental procedures, for examples l. 191-203.

Response: Thank you very much. Line191-203 shown the results of experiments, I think then cannot be move to experimental procedures.

Comment 3: Specify the variables in formula 1 and 2.

Response: Thank you for your comment about formula 1 and 2. In fact, , , , ,  in formula 1 and 2 are all variables obtained based on experimental results.

Comment 4: Check for the "change" of the Gibbls free energy. Sometimes it is missing, eg. l. 148, 151, 155 etc.

Response: Thank you for noting this point. I have checked and corrected the expression of Gibbs free energy changes in the entire text. See Line122-136, Line 153, Line159.

Comment 5: Modify the conclusion "0.32% of mercury in the crude selenium was sulfurized".  It sounds like the rate is very low but it represents all Hg in Se.

Response: Thank you for this note. In the revised manuscript, we have modified the conclusion.

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Thank you very much. The comments were all valuable and very helpful for revising and improving our paper. have added these two references to the revised manuscript.

He et al., Removing of Fe, Pb and Hg from Crude Selenium by Fractional Crystallization
Metals 2023, 13(4), 739; https://doi.org/10.3390/met13040739
2. Luo et al., Removal of impurity Pb during crude selenium purification by controlling
potential oxidation and vacuum distillation, Vacuum, Volume 195, 2022, 110674

Reviewer 3 Report

Combined Sulfidation and Vacuum Distillation for the  Directional Removal of Hazardous Mercury from Crude Selenium is very intersting paper! Some improvent is required.

Line 61: a selective sulfurization-vacuum distillation method (Title: Combined Sulfidation and Vacuum Distillation) what is correct; sulfurization (*S) or sulfidation (formation of MeS)

Line 63, 64: then mercury  can be selectively mineralized (at which temperature?)

Line 94: in internally heated vacuum distillation furnaces (Producer, Typ, Country)

Line 118: Please to use one word or to explain same difference: Sulfuration, or sulfurization or sulfidation

Line 16O: After being heated, the metal will melt and vaporize to form metal gas (which metal? Hg?, Se?

Line 162: The saturated vapor pressure of pure metal changes with temperature (which metal?)

Line 229: How is added the elemental S as the sulfurizing agent? (Please to explain it?)

Line 297: The above discussion demonstrates that it is reasonable to combine sulfidation with vacuum distillation for the removal of mercury from crude selenium to purify selenium. What is important to obtain one continuous process?

Author Response

Thank you for your valuable comments. We have studied the comments carefully and have made corrections that we hope will be met with approval. Our point-to-point responses to the reviewers’ comments are listed below:

Comment 1: Line 61: a selective sulfurization-vacuum distillation method (Title: Combined Sulfidation and Vacuum Distillation) what is correct; sulfurization (*S) or sulfidation (formation of MeS)

Response: The two expressions of "selective sulfurization-vacuum distillation method" and “Combined Sulfidation and Vacuum Distillation” are consistent. The two expressions of "sulfurization" and “sulfidation” are consistent. 

Comment 2: Line 63, 64: then mercury  can be selectively mineralized (at which temperature?)

Response: Figure 4 showes the mineralized temperature of mercury.

Comment 3: Line 94: in internally heated vacuum distillation furnaces (Producer, Typ, Country)

Response: The internally heated vacuum distillation furnaces  is self-made in our laboratory. 

Comment 4:  Line 118: Please to use one word or to explain same difference: Sulfuration, or sulfurization or sulfidation.

Response: The two expressions of "sulfurization" and “sulfidation” are consistent. 

Comment 5:  Line 160: After being heated, the metal will melt and vaporize to form metal gas (which metal? Hg?, Se?

Response: After being heated, the metal will melt and vaporize to form Se gas.

Comment 6:  Line 162: The saturated vapor pressure of pure metal changes with temperature (which metal?)

Response: This is a universal expression that refers to the specific metal being studied.

Comment 7:  Line 229: How is added the elemental S as the sulfurizing agent? (Please to explain it?)

Response: Mix crude selenium powder with sulfur powder and react at a certain temperature to achieve selective sulfurization of impurity mercury.

Comment 8: Line 297: The above discussion demonstrates that it is reasonable to combine sulfidation with vacuum distillation for the removal of mercury from crude selenium to purify selenium. What is important to obtain one continuous process?

Response: I think the most crucial thing is that the mercury in crude selenium should exist in the form of mercury selenide, and the removal of mercury can be achieved by combining sulfurization and vacuum distillation.

Round 2

Reviewer 2 Report

The authors have taken all my comments into account, and I do not object if the editor decides to accept it for publication.