Phase and Morphology Transformations in Sulfur-Fixing and Reduction Roasting of Antimony Sulfide
Round 1
Reviewer 1 Report
The topic of the paper is interesting and match the scopes of the journal.
Please indicate the temperature values as °C or K, according to the guidelines of Metals.
The English language needs to be improved... some grammatical errors throughout the manuscript as well as some incorrect sentences like, for instance, "In O2-enriched smelting, O2-enriched to oxidise Sb2S3 concentrate was used to obtain high-concentration SO2" (page 1, line 40) or "Therefore, our team proposed a combined process of metallurgy and beneficiation to extract Sb from Sb2S3. Firstly, Sb2S3 was engaged in S-fixing...." (page 2, line 68).
2.2 Methods
Please provide the N2 flow-rate during the trials.
Please provide few words about the titration used for the measurement of the Sb phase in the roasted products.
2.3. Thermodynamic calculations
Table 1. Is the reaction ZnO + C = Zn + CO possible? If so, please add as well as the relevant thermodynamic data in the following Figures. If ZnO is reduced by carbon, there is less carbon available for Sb.
3. Results and discussion
Figure 4b. If the conversion of Sb2S3 increases with temperature, more SO2 is produced, and more SO2 is captured and converted into H2SO4: why didn't the pH decrease in your opinion? Perhaps the majority of S reacts with Zn to give ZnS instead of SO2, considering that the atmosphere is reductive? Can you give an explanation?
Regarding the cost of the new proposed process, please try to provide an estimation of the costs compared to those of the 1-2 established industrial processes.
References
The size of the characters is different from reference to reference. Please align with the Metals guidelines.
The present paper investigated an interesting process for the production of Sb, and, in my opinion, it deserves to be published in Metals. I also recommend to study, in the future, the separation of the metallic Sb from the other solid material at the end of the process.
Author Response
Dear reviewer
We would like to express our sincere appreciation for your careful reading and helpful comments. Those comments are all valuable for improving our paper. We have addressed the points noted in text.
Reviewer #1:
1. The topic of the paper is interesting and match the scopes of the journal.
2. Please indicate the temperature values as °C or K, according to the guidelines of Metals.
[Answer]: All the temperature values are indicated clearly.
3. The English language needs to be improved... some grammatical errors throughout the manuscript as well as some incorrect sentences like, for instance, "In O2-enriched smelting, O2-enriched to oxidise Sb2S3 concentrate was used to obtain high-concentration SO2" (page 1, line 40) or "Therefore, our team proposed a combined process of metallurgy and beneficiation to extract Sb from Sb2S3. Firstly, Sb2S3 was engaged in S-fixing...." (page 2, line 68).
[Answer]: The English languages are carefully checked by a native English speaking colleague.
4. 2.2 Methods
Please provide the N2 flow-rate during the trials.
Please provide few words about the titration used for the measurement of the Sb phase in the roasted products.
[Answer]: The N2 flow-rate during the trails are 2 L/min. The contents of Sb in the products were determined by titrimetric analysis (oxidation method by cerous sulfate).
5. 2.3. Thermodynamic calculations
Table 1. Is the reaction ZnO + C = Zn + CO possible? If so, please add as well as the relevant thermodynamic data in the following Figures. If ZnO is reduced by carbon, there is less carbon available for Sb.
[Answer]: The direct reducing reaction of ZnO was accessorial calculated, and the results indicated that this reaction cannot carry out before 1000 °C (1273 K). This results is also meet the industrial practice.
6. 3. Results and discussion
Figure 4b. If the conversion of Sb2S3 increases with temperature, more SO2 is produced, and more SO2 is captured and converted into H2SO4: why didn't the pH decrease in your opinion? Perhaps the majority of S reacts with Zn to give ZnS instead of SO2, considering that the atmosphere is reductive? Can you give an explanation?
[Answer]: As calculating in figure 3, an increase in temperature can promote the sulfur-fixing and reducing reaction and facilitate the formation of Sb, and sulfur was fixed by ZnO in the form of ZnS rather than SO2 and S. This issues was once proved in reference 14, and the citation was also added to text. So the oxidation and decomposition of Sb2S3 decreased, and the pH of KMnO4 solution didn't decrease.
7. Regarding the cost of the new proposed process, please try to provide an estimation of the costs compared to those of the 1-2 established industrial processes.
[Answer]:The energy consumption between new process and traditional process was compared in part 3.3.6.
References
8. The size of the characters is different from reference to reference. Please align with the Metals guidelines.
[Answer]: The format of the reference was adjusted according to the Metals guidelines.
9. The present paper investigated an interesting process for the production of Sb, and, in my opinion, it deserves to be published in Metals. I also recommend to study, in the future, the separation of the metallic Sb from the other solid material at the end of the process.
Reviewer 2 Report
The method developed in the manuscript is exposed as a clean approach for the production of antimony from Sb2S3.
However, it is difficult to believe in the economic and environmental benefits of the proposed process. The use of ZnO for sulfur fixation (via ZnS formation) followed by physical separation of Sb from ZnS and roasting of ZnS (producing SO2) can be, probably, an expensive process for large scale development.
The authors stated that in the proposed process, ZnO ash with high F and Cl contents will be used. However, the F and Cl bearing compounds can react with Sb2S3 leading to high volatilization antimony halides requiring special operations for their recovery.
…large generation of low-concentration SO2 [6],…
It seems that this Reference is not devoted to the “low-concentration SO2“ gases during Sb extraction by thermal route. The authors are invited to check again the context of this reference and to modify the text (if necessary).
Furthermore, please check all references for correctness.
…600-1000 °C (873-1273 K)…
…800 °C (1073 K)…
…(>1200 °C i.e., >1473 K) and reduction smelting (>1000 °C i.e., >1273 K)…
…
It is not necessary to write everywhere the temperature in "K" beside the temperature in "°C".
R. Padilla et al investigated…
should be: Padilla et al. investigated…
Figure 1. 8-KMnO4; Please write: 8-KMnO4 solution;
The Sb powder can be purified by pyrometallurgical refining.
Please specify: which kind of pyrometallurgical process will be used for Sb purification?
Table 1. Please consider other reactions such as:
C+CO2(g) = CO(g) as well as ZnO+C = Zn (s,l,g)+CO(g), etc.
It seems that at high temperature (around 1000 °C), ZnO is reduced by carbon and part of the obtained zinc is volatilized.
In addition, the authors must take into consideration the temperature of the change of the substance state. For example, the boiling point of zinc is 907 °C which is reflected in the slope change of the curve ΔG° = f(T).
“It can be seen from Fig.4a that the main phase of Sb in the roasted products was Sb2O3 at temperatures lower than 800 °C (1073 K) and little metallic Sb was obtained.”
How do the authors prove that the process products are Sb2O3 and Sb°?
Have the authors the X-ray diffraction results of the product obtained at various temperatures? If yes, please add them to the manuscript. Are there other antimony oxides as an intermediate reaction product?
“…the tube was exposed to air when the furnace door was opened for the reactant mixture to be loaded, and hence the pH of the solution dropped dramatically.”
The reviewer feels that to avoid the reaction of Sb2S3 with air (O2), the reactant mixture can be loaded by the other side of furnace, under nitrogen flow (see Figure 1, near to the 8-KMnO4).
“However, the pH value of the KMnO4 solution increased with temperature, and also achieved equilibration quickly at 1000 °C (1273 K). It can be concluded that the increase in temperature is conducive to the reduction of SO2 emissions”
Usually, at high temperature (1000 °C), the pH value of the solution should be the lowest (as there are more reaction of Sb2S3 with air (O2), hence more SO2), but according to Figure 4 (b), the pH value is higher than that of all processing temperatures. If the author cannot find a more appropriate raison, please delete the sentence: “It can be concluded that the increase in temperature is conducive to the reduction of SO2 emissions.”
Figure 5. Please take care with the indication of photographs (especially for b, c, e and f). E.g. (c) is in second photograph, but its place will be in the third one.
3.3. Effect of ZnO dosage on roasting results
Please use rather “ZnO content” instead of “ZnO dosage”. If necessary, modify also in the text.
In the references list, please add the “doi” (when possible).
The authors are invited to check whole text for spelling and grammar errors.
E.g.: x-axis of Figure 4.
“Tempareture /°C” should be “Temperature /°C”?
Author Response
Dear reviewer
We would like to express our sincere appreciation for your careful reading and helpful comments. Those comments are all valuable for improving our paper. We have addressed the points noted in text.
1. The authors stated that in the proposed process, ZnO ash with high F and Cl contents will be used. However, the F and Cl bearing compounds can react with Sb2S3 leading to high volatilization antimony halides requiring special operations for their recovery.
[Answer]: We just assumed that the F and Cl bearing compounds can volatilize in the roasting process because the current removal process of F and Cl uses the same roasting process. However, the final result is investigating in our laboratory and we will show it in the future work. So the relative words about F and Cl were deleted because a pure ZnO agent was used in this work.
2. …large generation of low-concentration SO2 [6],…It seems that this Reference is not devoted to the “low-concentration SO2“ gases during Sb extraction by thermal route. The authors are invited to check again the context of this reference and to modify the text (if necessary). Furthermore, please check all references for correctness.
[Answer]: All the references were checked carefully, the reference [6] was replaced, and other references were also amended.
3. …600-1000 °C (873-1273 K)…
…800 °C (1073 K)…
…(>1200 °C i.e., >1473 K) and reduction smelting (>1000 °C i.e., >1273 K)…
…
It is not necessary to write everywhere the temperature in "K" beside the temperature in "°C".
[Answer]: The unit "K" was deleted in whole paper.
4. R. Padilla et al investigated…should be: Padilla et al. investigated…
[Answer]: It was revised
5. Figure 1. 8-KMnO4; Please write: 8-KMnO4 solution;
[Answer]: It was revised
6. The Sb powder can be purified by pyrometallurgical refining. Please specify: which kind of pyrometallurgical process will be used for Sb purification?
[Answer]: The Sb powder can be purified by current pyrometallurgical refining process with Na2CO3 addition and O2 blowing
7. Table 1.Please consider other reactions such as:
C+CO2(g) = CO(g) as well as ZnO+C = Zn (s,l,g)+CO(g), etc.
It seems that at high temperature (around 1000 °C), ZnO is reduced by carbon and part of the obtained zinc is volatilized.
In addition, the authors must take into consideration the temperature of the change of the substance state. For example, the boiling point of zinc is 907 °C which is reflected in the slope change of the curve ΔG° = f(T).
[Answer]: The above two reactions were calculated in figure 3, an increase in temperature can promote the sulfur-fixing and reducing reaction and facilitate the formation of Sb, and sulfur was fixed by ZnO in the form of ZnS rather than SO2 and S. For the direct reducing reaction of ZnO showing in (9), the ΔGθ value is also positive below 1000 °C, so the reducing reaction of ZnO cannot carry out before 1000 °C. This results is also meet the industrial practice. Of course, the relationships between ΔGθ and T are not linear, and its slope might change at the transformation temperature, we have considered this change in the calculation yet. The curve are not linear in figure 3 though it was not obviously.
8.“It can be seen from Fig.4a that the main phase of Sb in the roasted products was Sb2O3 at temperatures lower than 800 °C (1073 K) and little metallic Sb was obtained.”
How do the authors prove that the process products are Sb2O3 and Sb°?
Have the authors the X-ray diffraction results of the product obtained at various temperatures? If yes, please add them to the manuscript. Are there other antimony oxides as an intermediate reaction product?
[Answer]: The XRD patterns of the roasted products at different temperature were cited at our previous work, and the corresponding illustrate were added. The X-ray diffraction of the Sb2S3-ZnO-C system indicated that the roasting process was first conducted as a sulfur-fixing reaction to generate antimony oxide (Sb2O3) and ZnS, then Sb2O3 was reduced to metallic antimony after 700 °C largely.
9.“…the tube was exposed to air when the furnace door was opened for the reactant mixture to be loaded, and hence the pH of the solution dropped dramatically.”
The reviewer feels that to avoid the reaction of Sb2S3 with air (O2), the reactant mixture can be loaded by the other side of furnace, under nitrogen flow (see Figure 1, near to the 8-KMnO4).
[Answer]: Yes, this is a very good idea, this method can decrease the air let in and make the pH value more actual. We will compare two methods in the next work.
11.“However, the pH value of the KMnO4 solution increased with temperature, and also achieved equilibration quickly at 1000 °C (1273 K). It can be concluded that the increase in temperature is conducive to the reduction of SO2 emissions”
Usually, at high temperature (1000 °C), the pH value of the solution should be the lowest (as there are more reaction of Sb2S3 with air (O2), hence more SO2), but according to Figure 4 (b), the pH value is higher than that of all processing temperatures. If the author cannot find a more appropriate raison, please delete the sentence: “It can be concluded that the increase in temperature is conducive to the reduction of SO2 emissions.”
[Answer]: Thank you for your logical advice, we deleted this sentence.
12. Figure 5. Please take care with the indication of photographs (especially for b, c, e and f). E.g. (c) is in second photograph, but its place will be in the third one.
[Answer]: It is revised
13. 3.3. Effect of ZnO dosage on roasting results
Please use rather “ZnO content” instead of “ZnO dosage”. If necessary, modify also in the text.
[Answer]: It was revised
14. In the references list, please add the “doi” (when possible).
[Answer]: The “doi” was added after each reference.
15. The authors are invited to check whole text for spelling and grammar errors.
E.g.: x-axis of Figure 4. “Tempareture /°C” should be “Temperature /°C”?
[Answer]: The spelling and grammar are carefully checked by a native English speaking colleague.
Round 2
Reviewer 1 Report
The manuscript is now suitable for the publication in Metals.
Author Response
Thank you for you help and advices.
Reviewer 2 Report
“…energy consumption (>3.6×1010 J/t Sb), large generation of low-concentration SO2 [5], and risk of occupational disease due to volatilisation of As and Sb [7].”
Please check the references’ sequence. Where is Reference [6]? It should be mentioned between [5] and [7].
Author Response
The reference [6] was added
