Volatilization Kinetics of Zinc from the Flotation Products of Low-Grade Lead–Zinc Oxide Ore during Carbothermic Reduction
, Chengyan Wang 1,*, Minting Li 2, Chang Wei 2, Baozhong Ma 1, Xingbin Li 2, Zhigan Deng 2 and Xuchang Wei 2
Round 1
Reviewer 1 Report (Previous Reviewer 1)
Comments and Suggestions for AuthorsDear authors
The comments of the review of the manuscript you will find in the attachment.
Best regards
Comments for author File: 
Comments.pdf
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2860614). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Reviewer #1:
Q1. In line 99, explain, why lead mineral species are not shown in the diffractogram? For example, is Galena not detected by XRD, when the amount of this mineral is very high?
Response: Although the proportion of galena in flotation products is high (68.95%, Table 2), the total lead content is very low (2.54%, Table 1). XRD is difficult to detect the phase with a content of less than 5%.
Q2. How does high calcium content impair flotation? give an explanation.
Response: The research object of this work is a flotation products. Although the calcium oxide content is high (11.10%), flotation is not covered in this work. Previous studies have found that calcium oxide (dolomite), as a slime (including quartz, calcium-bearing gangue and so on), has the following effects on flotation process: (1) Contaminating the surface of useful minerals (such as zinc-bearing minerals), and changing the floating property of its surface; (2) Covering the useful mineral surface to prevent the combination of the target mineral and the collector and the interaction between the collector and the bubble on the target mineral surface; (3) Combining with flotation agents to increase agents consumption. Therefore, the flotation of Lanping low-grade lead-zinc oxide ore generally requires desliming treatment. This is described in lines 47- 50 in this manuscript.
Q3. Explain by which chemical characterization technique the sample was analyzed.
Response: The chemical characterization technique for the Zn and Pb phase distribution (Table 2) was used according to a reference [20] (Liu, Y.Q. Chemical Phase analysis of Ores and Industrial Products, 4th ed.; Metallurgy Industry Press: Beijing, China, 1992.). This method is based on the different chemical properties of compounds, adding specific solvents to selectively dissolve and separate each phase, and then conventional analytical means (complexometric method) is used to determine the composition and content of the phase.
Q4. How was the amount of indium in the sample determined?
Response: The content of indium in the sample was analyzed by inductively coupled plasma emission spectrometry (ICP-MS, ELAN DRC â…¡). The description “and flame atomic absorption spectroscopy (FAAS, PinAAcle 500)” in the lines 140-141 has been deleted.
Q5. A better explanation of how kinetics experiments were performed, should be given.
Response: The carbothermal reduction experiments were performed in a tube furnace (as shown in Fig. 3), which were carried out one by one rather than intermittent sampling in one experiment.
The description “The carbothermal reduction experiments were performed in a tube furnace, as shown in Fig. 3).” in lines 130-131 was revised to “The carbothermal reduction experiments were performed in a tube furnace (as shown in Fig. 3), which were carried out one by one rather than intermittent sampling in one experiment.”.
Q6. In Figure 6, to 1300 °C many light elements are present, it is possible, to revise indexing.
Response: Many light elements (such as Al and Mg) are present in flotation products. But the concentrations of these elements in the flotation products (Table 1) is very low, especially Mg. Assuming that these light metals are all non-volatile, according to the slag rate (the ratio of reduced slag to input raw material, about 45%), then the concentration of these light metals in the reduced slag is about 2 times that of the raw material, about 0.44% (MgO) and 2.6% (Al2O3), which is still very low. Therefore, XRD is difficult to detect the individual phases of these light metals. Moreover, these light metals are mainly combined with Ca, Si and other gangue components, and rarely exist in the form of separate oxides.
Q7. Figure 8 does not show the results of the experiment at 1300 °C, why?
Response: When designing the carbothermal reduction experiments for three minerals (smithsonite, willemite and flotation products), considering that zinc in the flotation products is more difficult to reduce and volatilize, we designed a temperature of 1300 °C for the flotation products. It is found that when the temperature reached 1250 °C, the volatilization of zinc was basically complete. Therefore, in the carbothermal reduction experiment of smithsonite and willemite (Fig. 4), the temperature of 1300 °C is not considered. Hence, Figure 8 does not show the results of the experiment at 1300 °C.
Reviewer 2 Report (Previous Reviewer 3)
Comments and Suggestions for AuthorsDear manuscript authors,
You have correctly corrected the text of your paper.
I would also recommend: Specify the units for the rate constants.
Best Regards
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2860614). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Q1. Specify the units for the rate constants.
Response: The unit of apparent rate constant is s-1. The unit has been specified in line 255.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsREVIEW
Paper title: Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction.
General comments about the manuscript.
The manuscript “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” is written very elaborately, and it is a good work. I consider that the information reported in the present work is enough for a scientific article, however, this paper need a better explanation in the analysis of the results and consider my comments and suggestions for the article to improve in quality and presentation. Please highlight all changes in the revised manuscript.
· The title of the article should not include lead.
· A better explanation about how the chemical composition was obtained should be given
· The sum of the percentages in table 1 is approximately 65.34 %, what elements contains the missing percentage? (we know that the Ag and In are given in g/t)
· The amount of silver and indium in the sample are very high, check whether the values are correct. Table 1
· On table 2, what´s it means Plumbojarosite et al.
· The thermal decomposition of calcium carbonate occurs at 800 °C, why at 900°C do you still have this compound? Line 200.
· Figure 5 is of very poor quality. Authors should improve it.
· Characteristic peaks of metallic lead do not appear at these degrees, check indexation.
· Specify what it means EMPA (Electron microprobe analysis). Line 218
· Why did the authors only use two kinetic models?
· A better explanation of the meaning of each apparent activation energy value should be given.
· What kind of kinetic process is carried out in each process? Give an explanation.
· How does the amount of binder influence the activation energy? give an explanation.
Check the typography of the all manuscrip
The manuscript could be accepted only if all modifications are made.
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2743368). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Q1. The title of the article should not include lead.
Response: The oxide ore used in this work contains both lead and zinc. Hence, it is called lead-zinc oxide ore. In this work, only the volatilization kinetics of zinc is studied, but lead is not involved. The title of the article should not exclude lead.
Q2. A better explanation about how the chemical composition was obtained should be given.
Response: The content of elements in solid samples was analyzed by inductively coupled plasma emission spectrometry and flame atomic absorption spectroscopy and the phase composition of the dried or reduced briquettes was determined by XRD. These are described in section 2.2 in manuscript.
Q3. The sum of the percentages in table 1 is approximately 65.34 %, what elements contains the missing percentage? (we know that the Ag and In are given in g/t)
Response: Take zinc for example, the content of Zn in the material (Table 1) is 26.81% and the proportion of zinc in oxides is 67.51% (Table 2), then the proportion of carbonic acid (CO32-) is about 16.71%. Similarly, the proportion of carbonic acid (CO32-) in cerussite is 0.16%.
The content of CaO is 11.10%. However, the calcium in the material is mainly in the form of CaCO3. Then, the proportion of carbonic acid (CO32-) is about 11.9%.
The sum of the percentages mentioned above is about 93.95%. In addition, some minerals in the material, such as heteromeric ore, contain a certain amount of water (Fig. 1). The sum of all components is close to 100%.
Q4. The amount of silver and indium in the sample are very high, check whether the values are correct. Table 1.
Response: The experimental raw materials have been analyzed in many batches. The indium and silver content data are correct.
Q5. On table 2, what´s it means Plumbojarosite et al.
Response: We modified ‘Plumbojarosite et al.’ to ‘Plumbojarosite’ in Table 2. The ‘et al.’ has been deleted.
Q6. The thermal decomposition of calcium carbonate occurs at 800 °C, why at 900°C do you still have this compound? Line 200.
Response: The initial decomposition temperature of calcium carbonate is about 820-850 °C, but calcium carbonate decomposition is not complete under this temperature. So, there is still a calcium carbonate phase at 900 °C (Section 3.2).
Q7. Figure 5 is of very poor quality. Authors should improve it.
Response: We have modified Figure 5 to improve the resolution and make it clearer.
Q8. Characteristic peaks of metallic lead do not appear at these degrees, check indexation.
Response: We believe that the presence of metallic lead phases at 1050-1150 °C (Fig. 5) is possible due to the lower volatility of metallic lead. However, with the increase of temperature, the volatility of metallic lead increases. At 1250°C, metallic lead is not detected by XRD because of the volatilization of metal lead. On the other hand, the lead content in the raw material is only 2.54%, and the lead content is reduced after volatilization. Hence, the lead phases were not detected by XRD because of the low lead content above 1150 °C.
Q9. Specify what it means EMPA (Electron microprobe analysis). Line 218
Response: We have defined EMPA in Figure 6. Red highlight for additions and green highlight for modification.
Q10. Why did the authors only use two kinetic models?
Response: We believe that for carbothermal reduction, when the temperature is low (less than 1100 °C), the rate of carbon gasification reaction (C+O2=2CO) is low, and the reaction occurring at low temperature is mainly solid-solid reaction (MeO+C=Me+CO). Therefore, the interfacial chemical reaction model was used at low temperature (950-1050 ºC) and the internal diffusion model (Ginstling-Brounshtein 3-D model) was used at higher temperature (1050-1250 ºC). Our investigation also indicated that our assumption about the kinetics model was reasonable. On the other hand, other kinetic models in Table 4 are not suitable for the carbothermal reduction process in this study due to the difference of metal grade and particle shape factor.
Q11. A better explanation of the meaning of each apparent activation energy value should be given.
Response: For the carbothermal reduction of smithsonite, willemite and flotation products, the high apparent activation energy means that the phase transformation and volatilization of zinc need to overcome a high energy barrier, which means that volatilization of zinc is more difficult and requires a higher reaction temperature. This description has been added to Section 3.3.2 (Red part).
Q12. What kind of kinetic process is carried out in each process? Give an explanation.
Response: The explanation about kinetic process in each process has described in Section 3.4. We believed that metal oxide (ZnO) particles and carbon particles contacted each other directly to drive the reaction at the initial stage of the reaction. As the reaction progresses, these reaction products (CaS, FeS and new slag phase) particles grow up and connect continuously, forming a continuous product shell covering the periphery of the core of unreacted ZnO particles, which seriously restrained the diffusion of carbon into the product shell. Meanwhile, the contact area between reducing agent and ZnO particle was reduced, and the solid-solid reaction was difficult to continue. As the temperature rises and the reaction proceeds, the carbon gasification was continuously strengthened. And, CO and CO2 can diffuse into and pass through the porous product layer and continue to react with ZnO in the briquettes.
Therefore, we believed that the volatilization of Zn from the pure minerals (smithsonite and willemite) or flotation products was controlled by the interfacial chemical reaction within 950-1050 °C and the internal diffusion in the range of 1050-1250 °C.
Q13. How does the amount of binder influence the activation energy? give an explanation. Check the typography of the all manuscript
Response: The binder is mainly composed of three elements, carbon, hydrogen and oxygen, which does not inhibit or promote the reduction and volatilization of zinc. After the binder is decomposed at high temperatures, the reducing substances, such as carbon, hydrogen and methane, etc., provide the reducing agent required for the reduction reaction. Moreover, the addition of binder is very little, only 3% (raw material weight). This data has added in Section 2.2 (red part). Therefore, we believed that the addition of binder would not affect influence the activation energy. We have revised the typography of the manuscript.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript presents an analysis of the kinetics of zinc release from oxide ore. The presented content and results are consistent with each other and the authors explain the issue which is confirmed in the results section. The editorial style, uniform font and font size should be improved in the paper.
The methodology section lacks information on the statistical methods used to analyse the influence of factors on the obtained zinc release values from the ore.
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2743368). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Q1. This manuscript presents an analysis of the kinetics of zinc release from oxide ore. The presented content and results are consistent with each other and the authors explain the issue which is confirmed in the results section. The editorial style, uniform font and font size should be improved in the paper.
The methodology section lacks information on the statistical methods used to analyse the influence of factors on the obtained zinc release values from the ore.
Response: We reformatted the manuscript. Based on our previous research (Data not given), we found that temperature is the most important factor affecting zinc volatilization rate apart from the addition of reducing agent. Hence, in order to study zinc volatilization kinetics, we focused on the effect of temperature on the zinc volatilization rate. However, we don’t use statistical methods analyse the influence of factors on the zinc volatilization rate. We believed that the effect of temperature on the zinc volatilization rate can be revealed according to Figure 3.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors,
Your manuscript is very interesting and represents a useful research for a wide scientific and professional public.
I have certain objections, which should be taken into account:
1. Table 1. Content of Ag(g/t) and In (g/t) to be corrected as for other elements
2. Table 2. You cannot list authors this way (Franklinite et all......). Either specify in the title of the table or in the table for lead phase and zinc phase.
3. Lines 138 and 139 where you state the formula for calculating evaporation - it is necessary to state literature data. Of course, if it's your formula then state that you came to that conclusion.
4. In part 3.3.2. Model Evaluation, claim that you have obtained the results of a linear function for a certain temperature interval. However, in the range of 1050-1250 °C, the linear relationship between [1−2/3α− (1−α)2/3] and t was greater than [1−(1− α)1/3] and t (Figure 7(b)). Therefore, stepwise fitting was adopted for the analysis of Zn evaporation during carbothermic reduction. Zn evaporation is controlled by interfacial chemical reaction within 950-1050 °C and internal diffusion within 1050-1250 °C. The value of k(T) was calculated from the slope of the linear regression between [1−(1−α)1/3] and t or [1−2/3α−(1−α)2/3] and t . After that, you specify the values of the apparent evaporation constants. Also, you describe similarly for smithsonite and sphalerite, two phases: interphase chemical reaction and diffusion. You specify the values of constants and activation parameters in the text.
- Please clarify the determination of the apparent constants of evaporation rates as a function of time. Then, the determination of Ea from the obtained models of changes in the mass of the samples. Do this for all samples and list the results in one table. I mean the obtained results of kinetic parameters. This table will make the work clearer and more transparent in terms of comparison of calculated parameters from experimental determinations.
Also, in one sentence, discuss the law of diffusion and the parameters that determine it. Your model is also complex from the aspect of the phenomenon of heat energy transport. State this in one sentence.
Finally, you have a large number of diagrams in the manuscript, and the kinetic indicators should be tabulated.
I wish you luck in your scientific research work.
Best Regards
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2743368). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Q1. Table 1. Content of Ag(g/t) and In (g/t) to be corrected as for other elements
Response: We have modified the content of Ag and In to a weight percent, as shown in Table 1 (green part).
Q2. Table 2. You cannot list authors this way (Franklinite et all......). Either specify in the title of the table or in the table for lead phase and zinc phase.
Response: The franklinite is a mineral containing Zn, O and Fe, etc. We have corrected ‘Franklinite et al.’ to ‘Franklinite’ in Table 2.
Q3. Lines 138 and 139 where you state the formula for calculating evaporation - it is necessary to state literature data. Of course, if it's your formula then state that you came to that conclusion.
Response: We have added a reference in line 139. The explanation of the formula was also modified.
Q4. In part 3.3.2. Model Evaluation, claim that you have obtained the results of a linear function for a certain temperature interval. However, in the range of 1050-1250 °C, the linear relationship between [1−2/3α− (1−α)2/3] and t was greater than [1−(1− α)1/3] and t (Figure 7(b)). Therefore, stepwise fitting was adopted for the analysis of Zn evaporation during carbothermic reduction. Zn evaporation is controlled by interfacial chemical reaction within 950-1050 °C and internal diffusion within 1050-1250 °C. The value of k(T) was calculated from the slope of the linear regression between [1−(1−α)1/3] and t or [1−2/3α−(1−α)2/3] and t. After that, you specify the values of the apparent evaporation constants. Also, you describe similarly for smithsonite and sphalerite, two phases: interphase chemical reaction and diffusion. You specify the values of constants and activation parameters in the text.
Please clarify the determination of the apparent constants of evaporation rates as a function of time. Then, the determination of Ea from the obtained models of changes in the mass of the samples. Do this for all samples and list the results in one table. I mean the obtained results of kinetic parameters. This table will make the work clearer and more transparent in terms of comparison of calculated parameters from experimental determinations.
Also, in one sentence, discuss the law of diffusion and the parameters that determine it. Your model is also complex from the aspect of the phenomenon of heat energy transport. State this in one sentence.
Response: This is a very good idea. We list all the apparent rate constants in a table (Table 5, a newly added table). And then, we state the effect of temperature on the apparent rate constant (Section 3.3.2 Model evaluation, last paragraph, red part).
Q5. Finally, you have a large number of diagrams in the manuscript, and the kinetic indicators should be tabulated.
Response: To better understand kinetics research work, linearly dependent coefficient (R2), apparent rate constants (k) and apparent activation energies (Ea) for smithsonite, willemite and flotation products were listed in Table 5.
Reviewer 4 Report
Comments and Suggestions for AuthorsThank you for submitting your work to Sustainability. Here are some comments.
1) must provide a reference for statements from line 47 to 56.
2) must provide references for lines 60 to 62. In addition, the writing style seems the description of the researcher methodology rather than introduction. Review and write again.
3) lines 73 to 81 provide references for all these statements.
4) section 2 should be materials and methods rather than "experimental"
5) explain how the particle size was defined in line 85.
6) what was the amount of water in the sample before drying?
7) in table 1 must include footer or foot table note explainin the meaning of all acronyms for the species also the meaning of Wt%.
8) what it means Franklinite et al. and Plumbojarosite et al. in table 2? review and fix it, in addition must provide reference number.
9) lines 91 to 100 should be in results section.
10) provide references for XRD analysis in line 98
11) same comment as for table 1
12) explain how was ground in line 110
13) why font style is different in line 116
17) check font size
18) add a workflow of the process
19) add reference for the formula 1 in line 139
20) add footnote in figure 5 to better understand the figure and results
21) must improve visualization of figure 6
22) provide references for all the equations
23) add references in table 4 for all models
24) must include limitations of the actual research and points to improve in future efforts. It is not clear the contribution of this research.
Author Response
Thank you for your letter and the reviewers’ comments concerning our manuscript entitled “Volatilization kinetics of zinc from the flotation products of low-grade Pb-Zn oxide ore by carbothermic reduction” (sustainability-2743368). Those comments are valuable and very helpful. We have read comments carefully and have made corrections.
Q1. must provide a reference for statements from line 47 to 56.
Response: The data from line 47 to 56 has not yet been published in a journal, which are obtained from previous semi-industrial experiments. Hence, we added the statement ‘(data not reported)’ in Section 1, the second paragraph (red part).
Q2. must provide references for lines 60 to 62. In addition, the writing style seems the description of the researcher methodology rather than introduction. Review and write again.
Response: We have provided some references for lines 60 to 62. Such as However, the leaching of ZnS, Zn2SiO4 or ZnFe2O4 was very difficult without oxidation and/or under low acidity [8,17].
The statement ‘Pyrometallurgical processes were used to separate lead and zinc from gangue components to form zinc oxide dust.’ was revised to ‘Pyrometallurgical methods were used to separate lead and zinc from gangue components to form zinc oxide dust.’. We believed that this statement was not required to provide references because it is common knowledge.
The statement ‘However, the leaching of ZnS, Zn2SiO4 or ZnFe2O4 was very difficult without oxidation and/or under low acidity’ indicated the problems with the hydrometallurgical processes.
The statement ‘Pyrometallurgical processes were used to separate lead and zinc from gangue components to form zinc oxide dust.’ showed the purpose of pyrometallurgical processes.
Q3. lines 73 to 81 provide references for all these statements.
Response: The data in the statement ‘lines 73 to 81’ has not yet been published in a journal. Hence, we added the statement ‘(data not reported))’ in line 76.
Q4. section 2 should be materials and methods rather than "experimental"
Response: We have revised ‘experimental’ to ‘Materials and methods’ in Section 2.1 (green part).
Q5. explain how the particle size was defined in line 85.
Response: In order to achieve efficient flotation recovery of valuable metals, the particle size of material is usually ground to very fine during the processing of minerals. The experimental material used in this work is a flotation products obtained from the semi-industrial flotation tests of the Lanping tailings. Its particle size was less than 74 μm.
Q6. what was the amount of water in the sample before drying?
Response: We added the moisture content in the sample to Section 2.1.
The statement ‘and its particle size was less than 74 μm.’ Was revised to ‘and its particle size and moisture content were less than 74 μm and 24.22%, respectively’.
Q7. in table 1 must include footer or foot table note explainin the meaning of all acronyms for the species also the meaning of Wt%.
Response: Wt.% denotes weight percent. We have added to Table 1 in the form of footnote (red part).
Q8. what it means Franklinite et al. and Plumbojarosite et al. in table 2? review and fix it, in addition must provide reference number.
Response: I'm terribly sorry. It was a mistake on our part. The franklinite and plumbojarosite were a mineral respectively. We modified ‘Franklinite et al.’ and ‘Plumbojarosite et al.’ to ‘Franklinite’ and ‘Plumbojarosite’, respectively in Table 2. The ‘et al.’ has been deleted.
Q9. lines 91 to 100 should be in results section.
Response: For the statement in lines 91 to 100, our idea is to characterize the experimental material. In this manuscript, an experimental material is given and then described. From the logical relationship of manuscript, we think this design is more reasonable. Of course, the statement in lines 91 to 100, these descriptions can also be included in the results section (Section 3 Results and discussion). In this case, when the readers read the experimental materials section (Section 2.1), he cannot have a deeper understanding of the materials and must read the results section (Section 3) to learn more information.
Q10. provide references for XRD analysis in line 98
Response: The results of XRD analysis are obtained from Figure 1, which is the result of our own research. Hence, we do not consider it necessary to provide references.
Q11. same comment as for table 1
Response: We have made revised Table 3, revised ‘Content, %’ to ‘Wt.%’ (green part).
Q12. explain how was ground in line 110
Response: We have added the equipment used in ball milling operation. The statement ‘Smithsonite, willemite and thermal coal were ground to less than 74 μm, respectively.’ was revised to ‘Smithsonite, willemite and thermal coal were ground to less than 74 μm, respectively, using a planetary ball mill (QM-2SP12, China)’
Q13. why font style is different in line 116
Response: We have changed to a uniform font size.
Q14. check font size
Response: We have made uniform changes to the font size in this manuscript.
Q14. add a workflow of the process
Response: We have added an experimental process flow, as shown in Fig. 2. The sequence number in the manuscript has been accordingly modified.
Q15. add reference for the formula 1 in line 139
Response: We have added a reference in line 139. The explanation of the formula was also modified (green part in Section 2.3).
Q16. add footnote in figure 5 to better understand the figure and results
Response: We have modified Figure 5 to improve the resolution and make it clearer.
Q17. must improve visualization of figure 6
Response: We have modified Figure 6 to improve the visualization. Image scales, temperatures and elements symbol are not clearly seen in Fig. 6.
Q18. provide references for all the equations
Response: We have added references in Section 3.3.1. But, there is no need to add references for some well-known formulas, such as Arrhenius equation (Eq. (3-4)).
Q19. add references in table 4 for all models
Response: We have added references in Table 4.
Q20. must include limitations of the actual research and points to improve in future efforts. It is not clear the contribution of this research.
Response: We have revised the conclusion section (green part). This study suggests that the presence of calcium oxide and high temperature are necessary for the efficient reduction and volatilization of zinc from low grade lead-zinc oxide ore containing zinc sulfide. The results of this study provide a theoretical basis for the carbothermal reduction treatment of the Lanping flotation products.
