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Peer-Review Record

Recoveries of Ru(III) and Co(II) by Solvent Extraction and Ion Exchange from Tungsten Carbide-Cobalt Scrap through a HCl Leaching Solution

Metals 2019, 9(8), 858; https://doi.org/10.3390/met9080858
Reviewer 1: Anonymous
Reviewer 2: Nicholas Pingitore
Reviewer 3: Anonymous
Reviewer 4: Anonymous
Metals 2019, 9(8), 858; https://doi.org/10.3390/met9080858
Received: 1 July 2019 / Revised: 3 August 2019 / Accepted: 4 August 2019 / Published: 6 August 2019
(This article belongs to the Special Issue Solvent Extraction of Transition Metals)

Round 1

Reviewer 1 Report

This manuscript deals with Ru(III) and Co(III) recovery from WC-Co scraps. The importance of this topic has been increasing. Since the authors used commercially available reagents in this study, a more practical point of view is required along with fundamental points.

1. It takes a long time to reach the chemical equilibrium of Ru-Cl solutions (See, Metals, 8, 558 (2018)). Did the authors confirm the equilibrium, especially for lower [HCl] solutions?

2. These amines cannot extract CoCl3- at all? 

3. Fig. 3 shows the effect of Aliquat 336 concentration on Extraction%. How about the effect on distribution ratios of Ru(III)? By slope analysis, the apparent stoichiometry of Ru:Aliquot 331 can be obtained, which could also substantiate the extraction reaction, Eq 2.

4. In Fig. 8, why is the adsorption % saturated at ~80%?

5. How is the Ru(III) recovered from the thiourea solution after the elution?

Author Response

Thank you for the comments to the manuscript. The manuscript has been revised according to the comments.

It takes a long time to reach the chemical equilibrium of Ru-Cl solutions (See, Metals, 8, 558 (2018)). Did the authors confirm the equilibrium, especially for lower [HCl] solutions?

Ans. : Thank you for your comments on the kinetics for the attainment of the equilibrium in Ru(III)-chloride system. As you commented, there should be some aging effect on the solvent extraction and ion exchange behavior of Ru(III) from HCl solution. We previously reported on the solvent extraction of Ru(III) from HCl solution. During this work, we did not find aging effect on the solvent extraction behavior of Ru(III). Therefore, the aging effect was not considered in this work.

Reference: Lee, M.S.; Ahn, J.G. Separation of Palladium(II) and Ruthenium(IV) from Hydrochloric Acid Solution by Solvent Extraction. Korean J. Met. Mater. 2009. 47. 349-355

These amines cannot extract CoCl3- at all?

Ans. :  When only CoCl3- is present in solution, it can be extracted by amines. However, both CoCl42- and CoCl3- is present, CoCl42- is selectively extracted owing to its stronger electrostatic interaction with amine.

Fig. 3 shows the effect of Aliquat 336 concentration on Extraction%. How about the effect on distribution ratios of Ru(III)? By slope analysis, the apparent stoichiometry of Ru:Aliquot 331 can be obtained, which could also substantiate the extraction reaction, Eq 2.

Ans. : Fig. 3 has been revised to draw some information on the stoichiometry of the solvent extraction reaction of Ru(III) and Co(II) by Aliquat 336. The related parts have been revised.

Modified parts : Line 132

Within Aliquat 336 concentration from 0.05 M to 0.7 M, the plot of log [Aliquat 336] vs. log D of Ru(III) and Co(II) results in linear lines whose slope values were close to unity. The slope values of Fig. 3 indicate that one mole of Aliquat 336 takes part in the solvent extraction of one mole of Ru(III) and Co(II) from 3 M HCl solution. Since the distribution coefficient of Co(II) increased linearly with Aliquat 336 concentration,

Figure 3. Plot of log [Aliquat 336] vs. log D of Ru(III) and Co(II) from 3 M HCl solution. ([Ru(III)] = 10 mgL-1 and [Co(II)] =100 mgL-1).

 4. In Fig. 8, why is the adsorption % saturated at ~80%?

Ans. :  We determined the loading capacity of the resins and showed the values of AG 1-X8 and Lewatit MP-64 in Fig. 9. According to the data in Fig. 9, the loading capacity of AG 1-X8 for Ru(III) was determined to be 27.1 mg/g of resin.

Considering this data, most of the Ru(III) should be loaded under the experimental conditions employed in Fig. 8. As is commented by the reviewer, the adsorption percentage of Ru(III) onto Lweit MP-64 and AG 1-X8 was saturated at 80 and 60%, respectively.

The radius of [RuCl4(H2O)] - is much larger than that of chloride ion. Therefore, steric effect might be responsible for the saturation phenomena observed in Fig. 8. Steric effect owing to the difference in the radius might hinder the loading of Ru(III) on the resins. However, further work is necessary to elucidate these data.

 5. How is the Ru(III) recovered from the thiourea solution after the elution?

Ans. : Within our knowledge, the platinum group metals can be recovered from the aqueous solution by adding some reducing agents owing to their positive reduction potentials. In the case of ruthenium, ruthenium metal can be recovered from HCl solution by using hydrogen gas at high temperature.

Reference: Pitchkov. V.N. The discovery of Ruthenium. Platinum Metals Rev. 1996, 40, 181-188.

Reviewer 2 Report

Nice work.

A couple of comments:

Title could be shortened to:

Separation of ......Scrap: Solvent Extraction vs. Ion Exchange

Table 2 - too many significant figures - just round them, no decimal point.

L 69 Since organic phase is not measured, only derived by subtraction, what is possibility of loss of material due to adsorption on containers?

L 57 chemical>Chemical

L 67 40min>40 min

L 127 from Co>of Co

L 190-191 protect the expression so it stays in 1 piece

L 195-199 center justify>left-right justify

L 218 have>has

L 221 of complex>of a complex

L 228 synthetic>a synthetic

L 238 work(>work (

L 252 Cemted>Cemented

L 254 Wc>WC

L 260, 262, 281, 284, 288  elements need to be capitalized

L 269, 276 Incomplete references

L 281 NIU>Niu

Author Response

Thank you for the comments to the manuscript. The manuscript has been revised according to the comments.

 1.Title could be shortened to: Separation of ......Scrap: Solvent Extraction vs. Ion Exchange

Ans. : The title of the manuscript has been changed to “Separation of Ru(III) and Co(II) from Hydrochloric Acid Leaching Solution of WC-Co Scrap: Solvent Extraction vs. Ion Exchange”.

2. Table 2 - too many significant figures - just round them, no decimal point.

Ans. : The significant number of the data in Table 2 has been revised.

Table 2. Elution percentage of Ru(III) from the adsorbed AG 1-X8 and Lewatit MP-64.

Eluants

AG   1-X8 Elution (%)

Lewatit   MP-64 Elution (%)

3 M HCl

37

22

1 M Thiourea

83

80

0.2 M Thiourea + 0.2 M HCl

94

93

Aqua regia (Distilled 10times)

59

39

1 M HCl + 10% acetone

64

32

1 M NaOH

0

0

 

3. 69 Since organic phase is not measured, only derived by subtraction, what is possibility of loss of material due to adsorption on containers?

 Ans. : It may be possible that adsorption of ions onto the surface of the container occurs. We do not think that this adsorption of ions is significant to lead to some error in the extraction/loading percentage. Within our knowledge, this kind of adsorption is not considered in most of the experiments on solvent extraction and ion exchange.

 4. 57 chemical>Chemical

Ans. :  This has been revised.

Modified parts: 57

In synthetic solution, the concentration of Co(II) was fixed at 100 mgL-1, while that of Ru(III) was varied from 10 to 100 mgL-1. 10 v/v% of H2O2 (30%, Daejung Chemical & Metals Co., Ltd.) was added to the synthetic solution.

5. 67 40min>40 min

 Ans. :  This has been revised.

Modified parts: 67

 The extraction and stripping experiments were carried out by contacting equal volume (10 mL) of the aqueous and organic phases at unity phase ratio for 40 min using a wrist action shaker (Burrel, USA) at ambient temperature.

6. 127 from Co>of Co

 Ans. : This has been revised.

Modified parts: 127

Figure 2. Effect of Ru(III) concentration on the separation of Co(II) from 3 M HCl solution. ([Extractant] = 0.1 M and [Co(II)] = 100 mgL-1

7. 190-191 protect the expression so it stays in 1 piece

 Ans. :  Lines 190-191 have been revised as follows.

Modified parts: 193-194

Figure 8 shows the variation in the loading percentage of Ru(III) and Co(II) as the concentration of ion exchange resins increased from 0.5 gL-1 to 10 gL-1.

8. 195-199 center justify>left-right justify

 Ans. : Lines 195-199 have been modified.

Modified parts: 200 – 204

Loading capacity of AG 1-X8 and Lewatit MP-64 for Ru(III) was measured by consecutively contacting fresh aqueous solutions. In these experiments, the concentration of the resins was fixed at 0.5 gL-1. Figure 9 shows the cumulative mass of Ru(III) loaded into the two resins. The loading capacity of AG 1-X8 and Lewatit MP-64 was determined to be 27.1 and 28.7 mg of Ru(III) by 1 g of resin, respectively.

 9. 218 have>has

Ans. :  This has been revised.

Modified parts: 223

 According to the HSAB principle, Ru(III) is a soft acid and thus has a strong tendency to react with thiourea, 

10. 221 of complex>of a complex

 Ans. : This has been revised.

Modified parts: 226

 This can be ascribed to the formation of a complex between the eluted Ru(III) and chloride ion

 11. 228 synthetic>a synthetic

Ans. : This has been revised.

Modified parts: 233

 For this purpose, a synthetic solution containing Ru(III) and Co(II) was employed in the experiments.

12. 238 work(>work (

Ans. : This has been revised.

Modified parts: 243

 this work (AG 1-X8, Amberlite IRA 402, Amberlie XAD 7HP, Bonite BA 304, and Lewatit MP-64).

13. 252 Cemted>Cemented

 Ans. : This has been revised.

Modified parts: 2576

 Lisovskii, A.F. Cemented carbides alloyed with ruthenium, osmium, and rhenuim.

 14. 254 Wc>WC

Ans. : This has been revised.

Modified parts: 259

 2.   Luyckx, S. High temperature hardness of WC-Co-Ru. J. Mater. Sci. Lett. 2002, 21, 1681–1682.

15. 260, 262, 281, 284, 288 elements need to be capitalized

 Ans. : These have been revised.

Modified parts: 265, 286, 289

5.      Potgieter, J.H.; Thanjekwayo, N.; Olubambi, P.; Maledi, N.; Potgieter-Vermaak, S.S. Influence of Ru additions on the corrosion behaviour of WC–Co cemented carbide alloys in sulphuric acid. Int. J. Refract. Met. Hard Mat. 2011, 29, 478–487.

15.   Shen, Y.F.; Xue, W.Y.; Niu, W.Y. Recovery of Co(II) and Ni(II) from hydrochloric acid solution of alloy scrap. Trans. Nonferrous Met. Soc. 2008, 18, 1262–1268.

16.   Goralska, E.; Coll, M.T.; Fortuny, A.; Kedari, C.S.; Sastre, A.M. Studies on the selective separation of Ir(IV), Ru(III) and Rh(III) from chloride solutions using alamine 336 in kerosene. Solvent Extr. Ion Exch. 2007, 25, 65–77.

16. 269, 276 Incomplete references

 Ans. : These have been revised.

Modified parts: 274, 281

9.            Xing, W.D.; Lee, M.S. Recovery of gold(iii) from the stripping solution containing palladium(ii) by ion exchange and synthesis of gold particles. J. Ind. Eng. Chem. 2019. 69, 255-262.

12.         Viljoen, K. The interconversion of the hexachlororuthenate(iii) and aquapentachlororuthenate(iii) species. Degree of Master science. University of Stellenbosch, Stellenbosch, 2003.

 17. 281 NIU>Niu

Ans. : This has been revised.

Modified parts: 286

 15. Shen, Y.F.; Xue, W.Y.; Niu, W.Y. Recovery of Co(II) and Ni(II) from hydrochloric acid solution of alloy scrap. Trans. Nonferrous Met. Soc. 2008, 18, 1262–1268.

Reviewer 3 Report

Title: ““Comparison of the separation of Ru(III) and Co(II) from hydrochloric acid leaching solution of WC-Co scrap between solvent extraction and ion exchange”. It is not representative of the work done. Maybe: “Recoveries of Ru(III) and Co(II) by solvent extraction and ion exchange from Tungsten carbide-Cobalt scrap through a HCl leaching solution”.

Title: Avoid using abbreviations.

The Abstract is not understandable at all. It is very bad structured. Many ideas with no relationship.

Abstract: “The addition of ruthenium to WC-Co hard metals”. What stands for WC-Co?

Abstract: “HCl concentration affected the extraction behavior of Ru(III) and Co(II) by Aliquat 336 and Alamine 300. Highest separation factor between Ru(III) and Co(II) was obtained at 3 M HCl.”. What was the role of HCl? You have to define Aliquat 336 and Alamine 300. MP-64.

Abstract: “The loading of Ru(III) into AG 1-X8 and Lewatit MP-64 followed … ». Define AG 1_X8 and Lewatit MP-64.

 

Introduction:  Why authors decided to use an acidic solution for extraction processes instead of an alkaline solution? Authors need to justify this choice with relevant references or facts.

Introduction: I highly recommend to discuss all related already published work with the current study. These methods are indeed currently very well known. Authors need to explain in a crystal clear way the innovative aspects of this work.

Introduction: “…Ion exchange was found to be more efficient than solvent extraction in separating Co(II) and Ru(III) from hydrochloric acid solutions in terms of separation factor and the ease of operation. Moreover, 3 M HCl concentration was the optimum condition to selectively separate Ru(III) by solvent extraction and ion exchange… ». These are the results obtained in this study. Authors have to present the work here, saying why and how they decided to perform this study after discussing the results found elsewhere.

Materials and methods:  I highly recommend the authors to provide much more details about the performed experiments. This is crucial for readers to reproduce these experiments.

Results: “…Preliminary leaching experiments of WC-Co scrap containing ruthenium were done at the following conditions: 5 M HCl, reaction temperature of 70oC, stirring speed of 200 rpm, pulp density 80 of 3g/L and reaction time of 5h….”.  Why the authors have chosen these experimental conditions? Already published papers? Former findings? If authors have no previous experience on this matter, they will need to perform an “experimental design”, by varying of the parameters within an appropriate range: thus varying simultaneously different HCL concentration, different reaction temperatures, and different stirring speeds. That is the only reasonable way to find representative parameter values.

Author Response

Thank you for the comments to the manuscript. The manuscript has been revised according to the comments.

.Title: ““Comparison of the separation of Ru(III) and Co(II) from hydrochloric acid leaching solution of WC-Co scrap between solvent extraction and ion exchange”. It is not representative of the work done. Maybe: “Recoveries of Ru(III) and Co(II) by solvent extraction and ion exchange from Tungsten carbide-Cobalt scrap through a HCl leaching solution”.

Ans. :  The title of the manuscript has been changed to “Recoveries of Ru(III) and Co(II) by solvent extraction and ion exchange from Tungsten carbide-Cobalt scrap through a HCl leaching solution”.

Modified parts: 2-4

Recoveries of Ru(III) and Co(II) by solvent extraction and ion exchange from Tungsten carbide-Cobalt scrap through a HCl leaching solution

Title: Avoid using abbreviations.

Ans. :  WC-Co has been changed to Tungsten carbide-Cobalt in the title.

“The addition of ruthenium to WC-Co hard metals”. What stands for WC-Co?

Ans. :  “WC-Co” has been changed to “tungsten carbide-cobalt” in the abstract.

Modified parts: 10

The addition of ruthenium to tungsten carbide-cobalt hard metals improves their mechanical properties.

Abstract: “HCl concentration affected the extraction behavior of Ru(III) and Co(II) by Aliquat 336 and Alamine 300. Highest separation factor between Ru(III) and Co(II) was obtained at 3 M HCl.”. What was the role of HCl? You have to define Aliquat 336 and Alamine 300. MP-64.

Ans. :  In this work, HCl was employed as a leaching solution for the dissolution of ruthenium and cobalt from the scrap. Moreover, Ru(III) and Co(II) has a strong tendency to form complexes with chloride ion and the distribution of the complexes of these metal ions depends on the concentration of chloride ion. Therefore, HCl concentration affects greatly the extraction and loading behavior of the two metal ions.

Aliquat 336 and Alamine 300 are commercial extractants which are employed in the solvent extraction of metals. The chemical name of Aliquat 336 and Alamine 300 has been added to the abstract.  Lewatit MP-64 is a kind of anion exchange resins. The physical properties of the resins employed in this work are listed in Table 1.

Modified parts: 16-17

Ru(III) was selectively extracted over Co(II) by Aliquat 336 (trioctyl methylammonium chloride) and Alamine 300(tri-n-octyl amine)

Abstract: “The loading of Ru(III) into AG 1-X8 and Lewatit MP-64 followed … ». Define AG 1_X8 and Lewatit MP-64.

Ans. :  “AG 1-X8 and Lewatit MP-64” have been changed to “anion exchange resins”.

Modified parts: 21-22

The loading of Ru(III) into anion exchange resins followed Freundlich isotherm and the loading capacity of the resins were determined.

Introduction:  Why authors decided to use an acidic solution for extraction processes instead of an alkaline solution? Authors need to justify this choice with relevant references or facts.

Ans. : Compared to acid leaching, alkaline leaching needs either high temperature treatments with molten salts or the supply of oxygen gas to dissolve the metals. In the case of acid leaching, addition of oxidizing agents to the HCl solution is enough to dissolve ruthenium and cobalt.

    The introduction has been revised as follows.

Modified parts: 45-48

Cobalt would be dissolved in the alkaline solution in the presence of ammonia and the supply of oxygen gas. Moreover, it is necessary to employ alkaline molten salts treatment to dissolve ruthenium in the alkaline solution. Therefore, acid leaching is considered to be more efficient than alkaline leaching in recovering valuable metals from the scarp of hard metals containing ruthenium.

Introduction: I highly recommend to discuss all related already published work with the current study. These methods are indeed currently very well known. Authors need to explain in a crystal clear way the innovative aspects of this work.

Ans. :  Lots of works have been reported on the recovery of cobalt from WC-Co scrap. However, few works have been reported on the recovery of ruthenium and cobalt from scarp of hard metals containing ruthenium. That is the reason why we have done this work.

The manuscript has been revised as follows.

Modified parts: 41-43

However, few works have been reported on the recovery of these metals from the scrap of hard metals containing ruthenium. In the hydrometallurgical treatment, the WC-Co hard metals

Introduction: “…Ion exchange was found to be more efficient than solvent extraction in separating Co(II) and Ru(III) from hydrochloric acid solutions in terms of separation factor and the ease of operation. Moreover, 3 M HCl concentration was the optimum condition to selectively separate Ru(III) by solvent extraction and ion exchange… ». These are the results obtained in this study. Authors have to present the work here, saying why and how they decided to perform this study after discussing the results found elsewhere.

Ans. :  As is written in the replies to the above comment (comment 7), few works have been reported on the recovery of ruthenium and cobalt from the scrap. Therefore, few data are available to discuss the reported results in the introduction.

Materials and methods: I highly recommend the authors to provide much more details about the performed experiments. This is crucial for readers to reproduce these experiments.

Ans. :  In the experimental section, the methods to prepare the synthetic solution and to adjust the concentration of extractants have been added. 

Modified parts: 77-79

The synthetic aqueous solution was prepared by dissolving the reagent grade RuCl3 and CoCl2 in dilute HCl solution. The concentration of the extractants was controlled by diluting them with kerosene.

Results: “…Preliminary leaching experiments of WC-Co scrap containing ruthenium were done at the following conditions: 5 M HCl, reaction temperature of 70oC, stirring speed of 200 rpm, pulp density 80 of 3g/L and reaction time of 5h….”.  Why the authors have chosen these experimental conditions? Already published papers? Former findings? If authors have no previous experience on this matter, they will need to perform an “experimental design”, by varying of the parameters within an appropriate range: thus varying simultaneously different HCL concentration, different reaction temperatures, and different stirring speeds. That is the only reasonable way to find representative parameter values.

Ans. :  Few works have been reported on the leaching of WC-Co scrap containing ruthenium. However, some papers and patents have reported the leaching of WC-Co scrap without ruthenium. Therefore, we employed an optimum leaching condition for the WC-Co scrap without ruthenium.

The manuscript has been revised as follows

Modified parts: 92-95

There are some reports on the HCl leaching of WC-Co hard metals without ruthenium. Therefore, the reported optimum condition for the leaching of these WC-Co hard metals was employed to investigate the leaching percentage of WC-Co hard metals containing ruthenium [11-13]. The leaching conditions are as follows :

Reviewer 4 Report

(see attachment)

Comments for author File: Comments.pdf

Author Response

Thank you for the comments to the manuscript. The manuscript has been revised according to the comments.

1.In the experimental conditions followed, authors should explicitly explain why they are sure that Ru(III) does not change its oxidation state to Ru(IV). This issue is because the Ru extraction profile is erratic and sometimes difficult to interpret.

Ans. : According to the standard reduction potentials of Ru(III,IV) and oxygen, oxidation of Ru(III) to Ru(IV) is difficult to occur in the presence of oxygen. The oxidation reaction of Ru(III) by oxygen can be represented as follows.

2Ru3+ + 0.5O2 + H2O = 2Ru4+ + 2OH-    Eo = -0.459 V

    The standard potential of this reaction is negative, indicating that this reaction would not occur. Moreover, we reported the solvent extraction of Ru(III) from HCl solution. During this work, we did not find oxidation effect on the solvent extraction behavior. Therefore, the oxidation of Ru(III) to Ru(IV)  was not considered in this work.

2.The concentration of extractant and stripping solutions should be described in chapter 2.1. Reagents and Chemicals. Which solvents were used?

Ans. : The purity of the reagents has been added to Sec. 2.1. Kerosene was employed as a solvent and this has been added to the manuscript.

Modified parts: 65-71

Thiourea (96%, Daejung ChemiScal & Metals Co., Ltd.), acetone (99.8%, Daejung Chemical & Metals Co., Ltd.), NaOH(97%, Daejung Chemical & Metals Co., Ltd.) and nitric acid(60%, Daejung Chemical & Metals Co., Ltd.) was used for stripping experiments.

Alamine 300 (97%, Samchun Pure Chemical Co.) and Aliquat 336 (99%, BASF Co., USA) were employed in solvent extraction experiments. Kerosene (99.9%, Daejung Chemical & Metals Co., Ltd) was used as a diluent.

3.Lines 111-114: In solutions 2-6 M HCl there are not only the forms [RuCl4(H2O)2]- and [RuCl6]3-, but also [RuCl5(H2O)]2- [E.A. Seddon, K.R. Seddon, The Chemistry of Ruthenium. Elsevier, Amsterdam, Oxford, New York, Tokio 1984], which is also well extractable. The authors should explain that why they considered extraction only one form of Ru(III) chlorocomplex.

Ans. : Ru(III) forms several kinds of complexes with chloride ion and anionic complexes of Ru(III) can be extracted by amines. [RuCl4(H2O)2]- is the predominant species of Ru(III) at 3 M HCl solution. Since the highest separation factor between Ru(III) and Co(II) was obtained at 3 M HCl, we explained the solvent extraction of Ru(III) by amines on the basis of the existence of [RuCl4(H2O)2]- .

The manuscript has been revised as follows

Modified parts: 124-127

In HCl solution, Ru(III) forms several kinds of anionic complexes with chloride ion. These anionic complexes of Ru(III) can be extracted by amines. The fact that the highest extraction percentage of Ru(III) by Aliquat 336 and Alamine 300 occurred at 3 M HCl might be ascribed to the distribution of Ru(III)-chloro complexes with HCl concentration [15].

4.Minor issues:

- line 41: is “ruthenium”, but it should be “Ru(III)”,

Ans. : This has been revised.

Modified parts: 42-49

However, few works have been reported on the recovery of these metals from the scrap of hard metals containing ruthenium. In the hydrometallurgical treatment, the WC-Co hard metals can be dissolved by employing either acid or alkaline solution [7,8]. In acid leaching of WC-Co, tungsten can be separated by precipitation as tungstic acid. Cobalt would be dissolved in the alkaline solution in the presence of ammonia and the supply of oxygen gas. Moreover, it is necessary to employ alkaline molten salts treatment to dissolve ruthenium in the alkaline solution. Therefore, acid leaching is considered to be more efficient than alkaline leaching in recovering valuable metals from the scarp of hard metals containing ruthenium.

- line 72: is “room temperature”, but it should be “ambient temperature”,

Ans. : This has been revised.

Modified parts: 87

In these experiments, incubator (HB-201SF, Hanbaek Scientific Co.) was employed to control the ambient temperature and stirring speed.

- figures: 1-3, 5, 7 and 8 (Y axis): is “%”, but it should be “(%)”,

Ans. : This has been revised.

- figure 7 (X axis): is “HCl concentration”, but it should be “HCl concentration (M)”,

Ans. : This has been revised.

Modified parts: figure 7

- equations 1 and 2, page 5: is “[RuCl4(H2O)]-”, but it should be “[RuCl4(H2O)2]-”,

Ans. : This has been revised.

Modified parts: equations 1 and 2, page 6

R3NH+Cl-(org) + [RuCl4(H2O)2] - = R3NH+[RuCl4(H2O)2]-(org) + Cl-,

(1)

R3NCH3+Cl-(org) + [RuCl4(H2O)2]- = R3NCH3+[RuCl4(H2O)2]- (org) + Cl-,

(2)

 

- line 245: is “W”, but it should be “W(VI)”.

Ans. : This has been revised.

Modified parts: 269-270

A process can be developed to recover Co(II), Ru(III) and W(VI) from the WC-Co hard metals containing ruthenium by leaching with HCl solution followed by ion exchange.

Round 2

Reviewer 3 Report

The manuscript ID: metals-552191 has been revised by authors according to the comments provided by reviewers. The authors have provided answers and modifications to most of the aspects pointed out in the previous review. However, there are still some work to be done such as writing inacuracies and critical discussion:

Line 40-42 “…Ruthenium, tungsten, and cobalt are valuable metals. Therefore, it is necessary to recover these metals from WC-Co scrap and spent WC-Co. However, few works have been reported on the recovery of these metals from the scrap of hard metals containing ruthenium….”.  Why “however”? What are these “few works”? (Provide references). What were the results arising from these “few works”? Discuss these results. This is crucial for readers to understand.

Line 115-118: I suggest to rephrase conveniently this sentence. It is not clear.

Keywords: “Separation” is not representative of the work done.

Finally, before publishing this work I would recommend to look for typos and writing uncertainties. There are many throughout the paper

Author Response

Thank you for the comments to the manuscript. The manuscript has been revised according to the comments.

Line 40-42 “…Ruthenium, tungsten, and cobalt are valuable metals. Therefore, it is necessary to recover these metals from WC-Co scrap and spent WC-Co. However, few works have been reported on the recovery of these metals from the scrap of hard metals containing ruthenium….”.  Why “however”? What are these “few works”? (Provide references). What were the results arising from these “few works”? Discuss these results. This is crucial for readers to understand.Ans. : Many works have been reported on the recovery of cobalt and tungsten from WC-Co scrap without ruthenium. Within our knowledge, no work has been reported on the recovery of ruthenium, cobalt and tungsten from the WC-Co scrap containing ruthenium. These parts have been revised as followsModified parts : Line 41-44                                       Lots of works have been reported on the recovery of cobalt and tungsten from the WC-Co scrap without ruthenium. However, no work has been reported on the recovery of ruthenium and cobalt from the WC-Co scrap containing ruthenium within our knowledge. Line 115-118: I suggest to rephrase conveniently this sentence. It is not clear.                                           Ans. :. That sentence has been revised.              Modified parts : Line 119-120

Since HCl concentration affects the extraction percentage of both metal ions, the separation factor between Ru(III) and Co(II) also depends on HCl concentration.

3. Keywords: “Separation” is not representative of the work done.                                                                             Ans. : This work was on the recovery of ruthenium and cobalt from the WC-Co scrap containing ruthenium. Ru(III) and Co(II) were separated from the synthetic HCl leaching solution of WC-Co scrap by employing solvent extraction and ion exchange.

       We think that separation is one of the most important keywords for this manuscript and thus keep “separation” in the list of keywords.

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