Adsorption Properties of a Polyamine Special Ion Exchange Resin for Removing Molybdenum from Ammonium Tungstate Solutions

Round 1

Reviewer 1 Report

(1) What are "Energy dispersive spectrometer plane scans"?

(2) How to prepare ammonium tungstate sulfide solution?

(3) The mmol/ml, g/mL and mg/mL were used. Adjust to make them be consistent.

(4) Line 160, p4: " Figure 1" should be changed to  “Figure 2”. Meanwhile,  Figure 1 should be cited in the text.

(5) V1 is the volume of polyamine special resin (ml)? In my opinion, the weight of polyamine special resin should be used rather than the volume.

(6) Line 165-166, p5: "the Mo adsorption capacity was stable" should be changed to "the Mo adsorption capacity remained almost unchanged";

(7) What is S2 concentration? Is it S2- concentration?

(8) Error bars should be added for all curves.

(9) The formation of thiomolybdate is an endothermic process? Add the reference.

(10) The research is simple and unoriginal.

(11) The manuscript was not well written.

 

It should be rejected by the journal.

Author Response

Thanks to reviewer for providing valuable feedback on our manuscript. We have accepted the comments and suggestions of reviewers by modifying and adding the missing information. Your suggestions have greatly improved the quality of this article. Thanks again for your positive thoughts and suggestions.

Comment #1:

What are "Energy dispersive spectrometer plane scans"?

Authors’ response to comment #1:

Thank you very much for your suggestions. Energy dispersive spectrometer plane scans was EDS plane scan

 

Comment #2:

How to prepare ammonium tungstate sulfide solution?

Authors’ response to comment #2:

Thank you very much for your suggestions. First, according to the requirements of preparing the target solution, ammonium tungstate solution containing molybdenum was prepared by dissolving solid tungsten oxide (AR) and solid molybdenum oxide (AR) with ammonia water (AR grade). Secondly, according to the detection results of molybdenum in ammonium tungstate solution, add an appropriate amount of ammonium sulfide (AR), stir and mix, and carry out the vulcanization reaction. Finally, sample the sulfurized solution to detect WO₃, Mo, S^2-, pH, etc. for future experiments.

 

Comment #3:

The mmol/ml, g/mL and mg/mL were used. Adjust to make them be consistent.

Authors’ response to comment #3:

Thank you very much for your suggestions. We have carefully examined the full text. The units of data involved in the paper are all standard units. In the paper experiment, the adsorption capacity unit of the resin is mg/ml, and the concentration unit of the substance in the solution is g/L. When introducing the polyamine special resin used in the paper, the total exchange capacity unit is mmol/ml, and the wet true density unit is g/ml.

 

Comment #4:

Line 160, p4: " Figure 1" should be changed to “Figure 2”. Meanwhile, Figure 1 should be cited in the text.

Authors’ response to comment #4:

Thank you very much for your suggestions. We have revised it in the paper.

 

Comment #5:

V1 is the volume of polyamine special resin (ml)? In my opinion, the weight of polyamine special resin should be used rather than the volume.

Authors’ response to comment #5:

Thank you very much for your suggestions. In this paper, V1 refers to the volume of polyamine special resin. We use volume to express the usage of polyamine special resin. The resin used in the experiment is the treated resin (wet resin), which corresponds to the expression of adsorption capacity mentioned in the article. For example, the adsorption capacity of molybdenum refers to the mass of molybdenum adsorbed by the wet resin per unit volume.

 

Comment #6:

Line 165-166, p5: "the Mo adsorption capacity was stable" should be changed to "the Mo adsorption capacity remained almost unchanged";

Authors’ response to comment #6:

Thank you very much for your suggestions. It has been modified in the text.

 

Comment #7:

What is S2 concentration? Is it S2- concentration?

Authors’ response to comment #7:

Thank you for your detailed comments. The concentration of S in the paper refers to the concentration of S^2-, which has been uniformly revised.

 

Comment #8:

Error bars should be added for all curves.

Authors’ response to comment #8:

Thank you very much for your suggestions. We have added error lines to all the figures in the manuscript.

 

Comment #9:

The formation of thiomolybdate is an endothermic process? Add the reference.

Authors’ response to comment #9:

Thank you very much for your suggestions. We have provided references in the revised paper. In the study of the sulfuration process of molybdenum in ammonium tungstate solution, this document found that the higher the sulfuration temperature, the higher the sulfuration degree of molybdenum, and the shorter the sulfuration reaction time. Therefore, we analyzed and inferred that the sulfuration process of molybdenum in ammonium tungstate solution is endothermic.

Reviewer 2 Report

In this manuscript, a polyamine special ion exchange resin was used to adsorb Mo from ammonium tungstate solutions. The effects of adsorption time, S^2- concentration, adsorption temperature, CO3^2- concentration, mass ratio of WO3 to Mo, and Mo concentration on the Mo and WO3 adsorption capacities were investigated. From the dynamic adsorption experiments, the adsorption rates for Mo and WO3 reach 99.05% and 1.81%, respectively. After careful consideration, I think this article needs major revision.

1. The chemical structure of the polyamine shown in Figure 1 is not a polymer’s. What's more, the type of charge on the polyamine is hard to see from this figure. Please provide the general chemical molecular structural formula.

2. What is the source of ammonium tungstate solutions? What is the composition of the solution? What is the difference between the solution prepared by the author and the source solution? Why did the authors prepare the model solution in that way?

3. Actual pH of ammonium tungstate solutions is not invariable. How does the change of pH affect the removal efficiency of Mo?

4. In fact, polyamine resin can remove the Mo in ammonium tungstate solutions fundamentally related to its own chemical structure. In addition, some physical properties of the resin can also affect the adsorption rate, such as porosity or specific surface area. This paper only discusses the influence of adsorption conditions, not from the most fundamental reason (chemical and physical structure of resin). The depth of the study is limited.

Author Response

Thanks to reviewer for providing valuable feedback on our manuscript. We have accepted the comments and suggestions of reviewers by modifying and adding the missing information. Your suggestions have greatly improved the quality of this article. Thanks again for your positive thoughts and suggestions.

Comment #0:

In this manuscript, a polyamine special ion exchange resin was used to adsorb Mo from ammonium tungstate solutions. The effects of adsorption time, S^2- concentration, adsorption temperature, CO₃^2- concentration, mass ratio of WO₃ to Mo, and Mo concentration on the Mo and WO₃ adsorption capacities were investigated. From the dynamic adsorption experiments, the adsorption rates for Mo and WO₃ reach 99.05% and 1.81%, respectively. After careful consideration, I think this article needs major revision.

Authors’ response to comment #0:

We are very grateful to the reviewers for reviewing the manuscript, which is very helpful to promote the improvement of the manuscript. The following is a point-by-point response to each comment.

 

Comment #1:

The chemical structure of the polyamine shown in Figure 1 is not a polymer’s. What's more, the type of charge on the polyamine is hard to see from this figure. Please provide the general chemical molecular structural formula.

Authors’ response to comment #1:

Thank you for your valuable suggestions. We have provided the chemical molecular structure formula of polyamine resin in the manuscript

 

Comment #2:

What is the source of ammonium tungstate solutions? What is the composition of the solution? What is the difference between the solution prepared by the author and the source solution? Why did the authors prepare the model solution in that way?

Authors’ response to comment #2:

Thank you very much for your suggestions. The source of ammonium tungstate solution is prepared in the laboratory, which is mainly prepared by dissolving solid tungsten oxide (AR) and solid molybdenum oxide (AR) with ammonia water (AR grade). The composition of the original ammonium tungstate solution mainly includes WO₄^2-, MoO₄^2-, NH₃-H₂0, NH₄⁺, and ammonium sulfide (AR) for vulcanization. The composition of the sulfurized ammonium tungstate solution mainly includes WO₄^2- , MoO₄^2-, NH₃-H₂0, S^2-, NH₄⁺, and MoO_xS_4-X^2-. The difference between the adopted scheme and the original scheme is that the new scheme has a strong adsorption capacity for molybdenum (high load) and a weak adsorption capacity for tungsten (low tungsten adsorption rate and high recovery rate). The purpose of adopting this new scheme is to achieve efficient separation of tungsten and molybdenum from ammonium tungstate solution containing high molybdenum, improve the recovery rate of tungsten, reduce the cost of the molybdenum removal process, and overcome the defects of traditional adsorption and separation process.

 

Comment #3:

Actual pH of ammonium tungstate solutions is not invariable. How does the change of pH affect the removal efficiency of Mo?

Authors’ response to comment #3:

Thank you very much for your suggestions. The form of molybdenum in the polyamine special resin adsorption solution is mainly MoO_xS_4-X^2-, and the best form of molybdenum adsorption is MoS₄^2-. When the pH value of ammonium tungstate solution is 7-9, the proportion of molybdenum in the form of MoS₄^2- increases with the decrease of pH value, which is more conducive to the adsorption of molybdenum. When the pH value of ammonium tungstate solution is 9-12, the proportion of molybdenum in the form of MoS₄^2- drops sharply with the increase of pH value. When the pH value is 12, the proportion of molybdenum in the form of MoS42 in the solution is almost zero, which is not conducive to the adsorption of molybdenum.

 

Comment #4:

In fact, polyamine resin can remove the Mo in ammonium tungstate solutions fundamentally related to its own chemical structure. In addition, some physical properties of the resin can also affect the adsorption rate, such as porosity or specific surface area. This paper only discusses the influence of adsorption conditions, not from the most fundamental reason (chemical and physical structure of resin). The depth of the study is limited.

Authors’ response to comment #4:

Thank you very much for your valuable suggestions. In the next step, we will study the effect of the structure of polyamine special resin on molybdenum adsorption.

Reviewer 3 Report

Please see attachment.

 

Comments for author File: Comments.pdf

Author Response

Thanks to reviewer for providing valuable feedback on our manuscript. We have accepted the comments and suggestions of reviewers by modifying and adding the missing information. Your suggestions have greatly improved the quality of this article. Thanks again for your positive thoughts and suggestions.

Comment #0:

I recommend this article for publication after considering the following comments.

Authors’ response to comment #0:

We are very grateful to the reviewers for reviewing the manuscript, which is very helpful to promote the improvement of the manuscript. The following is a point-by-point response to each comment.

 

Comment #1:

Please explain types of anion exchange resin.

Authors’ response to comment #1:

Thank you very much for your suggestions. The resin used in this paper is polyamine special resin (macroporous weakly basic anion exchange resin). The chemical molecular structure formula of the resin is as follows:

 

Comment #2:

To attract much attention please do the comparison to a commercially available data.

Authors’ response to comment #2:

Thank you very much for your suggestions. The comparison between process data and commercial process data in the paper is shown in the following table:

Indicator name	Adsorption of molybdenum in ammonium tungstate solution after vulcanization by polyamine special resin	Selective precipitation method-201 × 1 anion exchange resin adsorbs molybdenum in sulfurized ammonium tungstate solution
CuSO4·5H2O consumption/ton	0	≈10
(NH4)2S consumption/ton	≈40.0	≈40.0
NaOH consumption/ton	≈3.5	≈1.0
Mo removal rate/%	≈99.05	≈99.60
WO3 loss/kg	≈50	≈200
Cost excluding Mo/(￥10000 /ton)	≈6.56	≈25.84

 

Comment #3:

This coordination knowledge can be employed to develop an extraction mechanism and derive an isotherm model based on the law of mass action.

Authors’ response to comment #3:

Thank you very much for your suggestions. In the next step, we will study the thermodynamics of the adsorption of molybdenum in ammonium tungstate by polyamine special resin, and establish a thermodynamic isothermal model.

 

Comment #4:

Figure 9 and Figure 10 caption is not well defined. There are so many figures which must be labeled for better understanding.

Authors’ response to comment #4:

Thank you very much for your suggestions. The title of Figure 9 and Figure 10 have been modified in our manuscript to supplement the experimental data.

 

Comment #5:

Can the authors have any explanation about the model used in the analysis of experimental data of adsorption? I mean which type of model they were used like Langmuir model and Freundlich model.

Authors’ response to comment #5:

Thank you very much for your suggestions. We are further studying the thermodynamics (isothermal equation, etc.) of the adsorption of molybdenum in ammonium tungstate solution by polyamine special resin. According to the analysis of the adsorption data obtained in the previous stage, the Langmuir isotherm equation is more suitable for describing the isothermal adsorption process of molybdenum on polyamine special resin in ammonium tungstate solution after vulcanization, which needs further improvement.

 

Comment #6:

The Eq. (1) Eq. (2) reference are missing can it possible for authors to cite these two equations. Similarly, Eq. 3 and Eq. 4.

Authors’ response to comment #6:

Thank you very much for your suggestions. Equations (1), (2), (3) and (4) have been supplemented by references.

 

Comment #7:

In Fig. 2 why there is no adsorption capacity for Mo and WO3 from 0 to 60 minutes? While in literature the adsorption capacity starts from 0mints increase with time. As shown below. Reference of Article https://doi.org/10.1016/S1003-6326(18)64809-5

Authors’ response to comment #7:

Thank you very much for your suggestions. In Figure 2, within 0-60 minutes, polyamine special resin has an adsorption capacity for Mo and WO3. The experiment of adsorption of molybdenum in ammonium tungstate solution after vulcanization by polyamine special resin designed in this paper is to test the sample of the adsorbed solution every 60 minutes, so the starting point of the adsorption experimental data described in Figure 2 is the 60th minute.

 

Comment #8, #9:

The author say that "the WO3 adsorbed on the resin was gradually replaced by MoOxS4- X. Therefore, in the later stages of adsorption, the Mo adsorption capacity gradually increased, and the WO3 adsorption capacity gradually decreased" Is there is any scientific reason for the gradually decrease of WO3.

It will be very good if the author's write a chemical reaction that how the resin adsorbed the Mo and WO3. Is the adsorption depend upon the oxidation state of W and Mo?

Authors’ response to comment #8, #9:

Thank you very much for your suggestions. In the process of adsorption of Mo in the sulfurized ammonium tungstate solution by polyamine special resin, Mo is adsorbed in the form of MoO_xS_4-x^2-, and WO3 is adsorbed in the form of WO_xS_4-x^2- However, the ability of polyamine special resin to adsorb MoO_xS_4-x^2- is stronger than that of WO_xS_4-x^2-. Therefore, in the later stage of dynamic adsorption, MoO_xS_4-x^2- gradually replaces the adsorbed WO_xS_4-x^2-, so that the adsorption capacity of Mo gradually increases and the adsorption capacity of WO₃ gradually decreases. The ability of polyamine special resin to adsorb W and Mo depends on the degree of W and Mo halogenation, not on the oxidation state of W and Mo. For example, the order of Mo adsorption capacity is MoS₄^2-> MoOS₃^2-> MoO₂S₂^2-> MoO₃S^2-.The reaction formula for the adsorption of MoS42 by polyamine special resin is as follows:

 

Comment #10:

Why the adsorption capacity of Mo is constant with increasing temperature (Fig. 4 ) from 25 ℃to 33 ℃ and after 33 ℃ upon increasing the temperature it decrease rapidly while the Wo3 is decreasing very slowly? The Author’s did not declare in all of their results that they matched with previous literature or not which is one of the big deficiencies in the article.

Authors’ response to comment #10:

Thank you very much for your suggestions. In Figure 4, at 25 ℃ to 35 ℃, the adsorption capacity of polyamine special resin for Mo in ammonium tungstate solution after vulcanization actually increased first and then decreased (the adsorption capacity of Mo at 25 ℃ was 97.37 mg/ml, the adsorption capacity of Mo at 30 ℃ was 99.17 mg/ml, and the adsorption capacity of Mo at 35 ℃ was 97.88 mg/ml). From 25 ℃ to 45 ℃, the adsorption capacity of polyamine special resin for WO3 in sulfurized ammonium tungstate solution decreased slowly. The described phenomenon is generally consistent with the previous literature conclusions.

 

Comment #11:

In Fig. 9 EDS image show the W peak is very high but the %concentration of Mo is greater in the table why? In Fig. 10 the Mo peak have same height as compared to the Fig.9 but Mo content is zero in the table as the author have any explanation to that?

Authors’ response to comment #11:

Thank you very much for your suggestions. The problem of W and Mo peaks displayed in EDS images may be related to our preparation of test samples. To better characterize the true distribution of W, Mo, Na, and S elements in the loaded resin and the resin after desorption, we bonded several resins with adhesive, cut the resin from the middle, and then use EDS surface scanning to detect the regional element distribution.

Reviewer 4 Report

This thesis studies the selective adsorption performance and mechanism of ammonium tungstate solution by using polyamine ion-exchange resin, which provides a new idea for providing an efficient molybdenum removal method in ammonium tungstate solution for the separation process of tungsten and molybdenum. The thesis is novel and innovative, and the research content is detailed. It is suggested to publish it after minor revision.

1): Please give the chemical mechanism of polyamine ion exchange resin adsorption

2): Why does the adsorption rate of the resin on molybdenum decrease rapidly after the temperature rise at 35℃ in Figure 4

3): What is the adsorption status of molybdenum-containing leaching solution for molybdenum, please give it in the introduction

4): In this thesis, the influence of molybdenum concentration on the ability of resin to adsorb molybdenum and tungsten is described and explained. The language should be concise and professional

5): The header and table of the chart need to be centered, please check and modify

Author Response

Thanks to reviewer for providing valuable feedback on our manuscript. We have accepted the comments and suggestions of reviewers by modifying and adding the missing information. Your suggestions have greatly improved the quality of this article. Thanks again for your positive thoughts and suggestions.

Comment #0:

This thesis studies the selective adsorption performance and mechanism of ammonium tungstate solution by using polyamine ion-exchange resin, which provides a new idea for providing an efficient molybdenum removal method in ammonium tungstate solution for the separation process of tungsten and molybdenum. The thesis is novel and innovative, and the research content is detailed. It is suggested to publish it after minor revision.

Authors’ response to comment #0:

We are very grateful to the reviewers for reviewing the manuscript, which is very helpful to promote the improvement of the manuscript. The following is a point-by-point response to each comment.

 

Comment #1:

Please give the chemical mechanism of polyamine ion exchange resin adsorption

Authors’ response to comment #1:

Thank you very much for your suggestions. The chemical mechanism of adsorption of MoS42 in sulfurized ammonium tungstate solution by polyamine resin is as follows.

Comment #2:

Why does the adsorption rate of the resin on molybdenum decrease rapidly after the temperature rise at 35℃ in Figure 4

Authors’ response to comment #2:

Thank you very much for your suggestions. After the adsorption temperature is greater than 35 ℃, the expansion coefficient of the resin increases, which destroys the stability of the resin, especially the stability of the adsorption group on the resin that occurs during the adsorption reaction, resulting in the rapid decline of the adsorption capacity of the resin.

 

Comment #3:

What is the adsorption status of molybdenum-containing leaching solution for molybdenum, please give it in the introduction

Authors’ response to comment #3:

Thank you very much for your suggestions. Molybdenum in ammonium tungstate solution is adsorbed by polyamine special resin. The main form of molybdenum is MoO_xS_4-X^2- (X=0,1,2,3), and the best form of molybdenum is MoS₄^2-. (Relevant introduction is supplemented in the 2.1.2 S^2- concentration effect on the adsorption capacity of molybdenum and tungsten in polyamine special resin in the manuscript)

 

Comment #4:

In this thesis, the influence of molybdenum concentration on the ability of resin to adsorb molybdenum and tungsten is described and explained. The language should be concise and professional

Authors’ response to comment #4:

Thank you very much for your suggestions. We have modified the description of this content.

 

Comment #5:

The header and table of the chart need to be centered, please check and modify

Authors’ response to comment #5:

Thank you very much for your suggestions. The title and table in the icon have been modified in the center.

Round 2

Reviewer 1 Report

It can be accepted.

Reviewer 2 Report

The authors have carefully revised the manuscript following the reviewer's comments.