Selective Leaching of Molybdenum from Bulk Concentrate by Electro-Oxidation
Round 1
Reviewer 1 Report
A lot of work has been done on the recovery of molybdenum from Mo/Cu complex rougher concentrates in this paper. However, many papers related to the leaching of molybdenum by electro-oxidation have been published in the international journal. The reported content and results are similar to this paper and it seems little novelty in this paper.
Author Response
Editor
- The title was revised to make the goal of the paper more clear.
. Selective leaching of Molybdenum from rougher concentrate by electro-oxidation
→ Selective leaching of Molybdenum from bulk concentrate by electro-oxidation
. All rougher concentrate was revised to bulk concentrate
- Some mixed expressions was unified
. ClO-/OCl- → OCl-
. Concentrate/concentrates → concentrates
Reviewer 1
Comment 1
A lot of work has been done on the recovery of molybdenum from Mo/Cu complex rougher concentrates in this paper. However, many papers related to the leaching of molybdenum by electro-oxidation have been published in the international journal. The reported content and results are similar to this paper and it seems little novelty in this paper.
Answer
I agree with the comment; many papers related to the leaching of molybdenum by electro-oxidation have been published in the international journal. However, most papers focus on the leaching and recovery of Mo from MoS2 concentrates with minor Cu sulfide or the removal of Mo impurity from CuFeS2 concentrates. In contrast, the present study aimed to leach Mo from bulk concentrate consisting of MoS2 and CuFeS2 obtained at the 1st stage of the flotation process to develop a simple process for recovery of Mo and Cu from Mo/Cu complex ores. This study presented that Mo was be selectively leached while CuFeS2 was unreacted. It indicates that CuFeS2 is possibly obtained by leaching of Mo using the electro-oxidation method. This result suggests that Mo can be recovered as ions, and Cu can be as concentrates. So, no more complex flotation process for the separation of MoS2 and CuFeS2 from bulk concentration. It is expected to simplify the extractive metallurgical processing for MoS2/CuFeS2 complex ore. To make the differentiation of this paper more precise, I revised the title and abstract as below;
- Selective leaching of Molybdenum from rougher concentrate by electro-oxidation
- → Selective leaching of Molybdenum from bulk concentrate by electro-oxidation
- “The reported studies presented that a high leaching yield of Mo was 99%, but molybdenite in residues was still observed in XRD patterns after leaching. This study investigated the leaching behavior of Mo, Cu, and impurity metals at various pHs, currents, and temperatures. In addition, the effect of ultrasonic irradiation was studied.”
- → “Several studies reported the selective leaching of Mo from MoS2 concentrates or CuFeS2 concentrates [22, 23, 25, 29, 30]. However, its application to bulk concentrates comprising MoS2 and CuFeS2 has been little studied. Selective leaching of Mo without oxidation of CuFeS2 from bulk concentrates leads to effective recovery of Mo as ions and Cu as concentrates in addition to the separation of Mo and Cu. Expectedly, it can simplify the flotation process for Cu/Mo complex ores and suppress the loss of Mo and Cu. Therefore, this study presents the selective leaching of Mo from bulk concentrates consisting of MoS2 andCuFeS2 obtained at 1st stage of flotation process, giving rise to CuFeS2 concentrates using the elec-tro-oxidation method. The leaching behaviors of Mo, Cu, and impurity metals at various pHs, currents, and temperatures were investigated. In addition, the effect of ultrasonic ir-radiation was studied.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
this paper indicated Mo leaching recovery from Cu-Mo concentrate and it is important topic to recover Mo from Cu.
this paper need revise as follows:
it needs explanation what kind of reaction occur on each pH. also it did not mentioned about Cu dissolution. it contains large amount of chalcopyrite but is it not reacted or all precipitate? chemical reaction is necessary, not all is ok but it is needed.
is it economically feasible to use electrolysis and what is the advantage? it might possible but please show current process as well.
there are 2 Figure 1.
Figure frame can be seen. it should be removed.
Line 69, IrO2, 2 should be subscript
Figure 1b, anode and cathode seems in same place.
Line101, 4 should be subscript
Figure1 (or 2?), Ph5->pH5
Figure6, which line is before and after?
Reference style need to be consistent.
Author Response
Editor
- The title was revised to make the goal of the paper more clear.
. Selective leaching of Molybdenum from rougher concentrate by electro-oxidation
→ Selective leaching of Molybdenum from bulk concentrate by electro-oxidation
. All rougher concentrate was revised to bulk concentrate
- Some mixed expressions was unified
. ClO-/OCl- → OCl-
. Concentrate/concentrates → concentrates
Reviewer 2
Comment 1
it needs explanation what kind of reaction occur on each pH. also it did not mentioned about Cu dissolution. it contains large amount of chalcopyrite but is it not reacted or all precipitate? chemical reaction is necessary, not all is ok but it is needed.
Answer
The reaction equation related with the leaching of ZnS and CuFeS2 at different pHs and the precipitation of Zn(Cu)MoO4 were presented in equations (4 ~ 11).
It was obtained from XRD analysis that chalcopyrite was not reacted upon the electro-oxidation leaching. To clearfy the results, I revised the results and discussions, and conclusion as below;
- In results and discussion, “In addition, M.-S. Kim reported that CuFeS2 is converted to CuO by OCl- in 0.2M NaOH at 60℃ when the generation rate of OCl- is high [34]. In the present study, CuFeS2 was not oxidized and still existed as a primary phase even after leaching at pH 9, as shown in Fig. 4. The main difference between the two studies is the sample; MoS2 and CuFeS2 mixed bulk and CuFeS2, but CuFeS2 concentrates for the reported studies. A High leaching yield of Mo means that a high amount of OCl- was consumed preferably for the oxidation of MoS2. The rest amount might be insufficient for the fast oxidation of CuFeS2. In addition, the larger size of bulk concentrates than CuFeS2 concentrates by 1.5 times may be another reason for no or minor oxidation of CuFeS2 considering that its oxidation rate was determined by the diffusion of two layers with a layer of solid sulfur produced during leaching and an ash layer remaining after leaching [38]. To summarize, CuFeS2 was un-reacted, unlike MoS2 and ZnS, which indicated that CuFeS2 concentrates are possibly obtained by the electro-oxidation leaching of Mo from Mo/Cu mixed sulfides.”
- In conclusions, “XRD patterns showed that MoS2 disappeared, and CuFeS2 concentrates were obtainable”.
- XRD pattern of residue for conventional leaching at pH 9 was added.
Comment 2
is it economically feasible to use electrolysis and what is the advantage? it might possible but please show current process as well
Answer
Commercially, the leaching of MoS2 is done by oxidation roasting and leaching in ammonia or caustic soda solution. Oxidation roasting requires high temperatures of > 500℃ and exhaust SO2. So, the removal process of SO2 is also needed. To overcome this shortage, several researchers have tried applying the hydrometallurgical method, and it has been reported that MoS2 can be oxidized and leached by hypochlorite. The electro-oxidation method is to oxidize and leach MoS2 using in-situ generated OCl- through electrochemical reaction instead of sodium hypochlorite. So, no storage and transportation of NaOCl are required, which improves safety and eco-friendship. In economic view, the electro-oxidation method is preferred over NaOCl leaching, considering that commercial generation of sodium hypochlorite is done by electrolysis of NaCl.
As for the current process, the study aims to elucidate the feasibility of Mo/Cu separation from bulk concentrates using the electro-oxidation method to develop a simple extractive process for Mo/Cu mixed oxide. The commercial separation of MoS2 and CuFeS2 from Mo/Cu complex ores mainly depends on the flotation process. In general, MoS2 is produced as a by-product in the Cu industry. Thus, the process focuses on the recovery of Cu, so the extensive loss of MoS2 is met. In addition, the flotation process from bulk concentrates on separating Mo and Cu concentrates is much complicated. Unfortunately, hydrometallurgical was is not commercialized. The main reason is that the technical grade of MoO3 with ~ 90% is in sales, while hydrometallurgy is profit to the production of high purity oxide with 99.9% or above. However, the hydrometallurgical method will attract much attention to avoid energy-intensive processes such as high-temperature roasting and the development of high purity related high technology such as Mo-semiconductor. In addition, primary Mo ores containing little Cu are limited to be developed based on the flotation process due to the low recovery yield of Mo. Therefore, this study applied the electro-oxidation method to develop the primary Mo ores containing little Cu of Geumeum mine.
Comment 3
- there are 2 Figure 1.
Figure frame can be seen. it should be removed.
; The frame is not more seen.
- Line 69, IrO2, 2 should be subscript
; 2 was converted to the subscript.
- Figure 1b, anode and cathode seems in same place.
; Figure 1b was corrected.
- Line101, 4 should be subscript
; 4 was converted to the subscript.
- Figure1 (or 2?), Ph5->pH5
; pH was corrected
- Figure6, which line is before and after?
; The label was added to the XRD line
- Reference style need to be consistent.
; All reference style was revised consistently.
Author Response File: Author Response.pdf
Reviewer 3 Report
The standard of English in the manuscript needs to be improved before publication is warranted. After revision there are some other scientific points that require addressing. These are listed below.
1) Please state the specific content of chalcopyrite and molybdenite in the rough concentrate. It would be useful to have along with the chemical composition data. (table 1)
2) Discussions around stability of Cu, Zn and Mo would be aided by the presentation of the Pourbaix diagrams (Eh vs pH) in the manuscript
Author Response
General comment
The standard of English in the manuscript needs to be improved before publication is warranted.
Answer
English was corrected.
Comment 1
Please state the specific content of chalcopyrite and molybdenite in the rough concentrate. It would be useful to have along with the chemical composition data. (table 1)
Answer
The content of Molybdenite, Chalcopyrite and sphalerite was stated according to the comment.
Comment 2
Discussions around stability of Cu, Zn and Mo would be aided by the presentation of the Pourbaix diagrams (Eh vs pH) in the manuscript
Answer
E-pH diagram for Molybdenite, Chalcopyrite and sphalerite was added according to the comment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made a very substantial improvement to their paper and should be congratulated. However, there are a few minor points that they may wish to consider. These are:
- Referring to the latest articles in the journal, Figures 2, 3, 4, 5, 6, 7 and 8 should be drawn more clearly and standard to facilitate the readability of the picture.
- “E-pH diagram revealed in Fig. 5(b) shows that CuFeS2 was oxidatively……”, “Mo is stable as soluble species …… in pH regions of this study (Fig. 5(c))”, the authors should pay attention to the correspondence of the graphs.
Author Response
Answers to reviewers’ comments on Manuscript ID metals-1469070
The authors would like to thank the reviewers for their time. The manuscript has been revised to address the checklist as best as possible. All revised words and sentences were written in blue in the revised manuscript.
Detailed answers to reviewers’ comments were provided on the following pages.
Reviewer 1
Comment 1
Referring to the latest articles in the journal, Figures 2, 3, 4, 5, 6, 7 and 8 should be drawn more clearly and standard to facilitate the readability of the picture.
Answer
Figures of 2 ~ 8 were revised. In Fig. 2, Fe, Pb, and Mg were deleted to make it easier to see; instead, the sentence of “ Mo, Zn, and Mo were observed to be leached at some pH or all pHs studied in this study, while no leach was found for Fe, Pb, and Mg at all pHs.” was added
Comment 2
“E-pH diagram revealed in Fig. 5(b) shows that CuFeS2 was oxidatively……”, “Mo is stable as soluble species …… in pH regions of this study (Fig. 5(c))”, the authors should pay attention to the correspondence of the graphs.
Answer
The Figure numbers were corrected; Fig. 5(b) and Fig, 5(C) → Fig. 4(b) and Fig, 4(C)
- E-pH diagram revealed in Fig. 4(b) shows that CuFeS2 was oxidatively transformed to CuO at high potential region. The oxidation of CuFeS2 to CuO can be presented in equation (11)
- Mo is stable as soluble species as Mo7O242- and MoO42- under oxidative conditions in pH regions of this study (Fig. 4 (c))
Author Response File: Author Response.pdf
Reviewer 2 Report
please correct only this: Mo7O24-2 ->Mo7O242-
then everything has been corrected, it is ok to be published.
Author Response
Answers to reviewers’ comments on Manuscript ID metals-1469070
The authors would like to thank the reviewers for their time. The manuscript has been revised to address the checklist as best as possible. All revised words and sentences were written in blue in the revised manuscript.
Detailed answers to reviewers’ comments were provided on the following pages.
Reviewer 2
Comment 1
please correct only this: Mo7O24-2 -> Mo7O242-
Answer
It was corrected
- Mo is stable as soluble species as Mo7O242- and MoO42- under oxidative conditions in pH regions of this study (Fig. 4 (c))
Author Response File: Author Response.pdf
