Separation of Gallium(III) and Indium(III) by Solvent Extraction with Ionic Liquids from Hydrochloric Acid Solution

Round 1

Reviewer 1 Report

In this paper, the authors study to develop a new process for the mutual separation of indium(III) and gallium(III) using solvent extraction. It seems that the experiment was done adequately. Using countercurrent three stage extraction, they succeeded in mutually separating indium and gallium using Ali-PC.

However, I cannot understand the advantage of the proposed process in comparison with previously proposed processes. For example, the same author’s group previously published the paper (Lee et al., 2002) as shown in Ref. 6, in which they used D2EHPA. The separation factor presented in that paper is much higher than the present one, and complete separation was achieved using countercurrent three stage extraction from the aqueous solution containing 1 g/L In and 0.5 g/l Ga which were much higher than the present ones. In Lee et al. (2002), considerable amount of alkali would be necessary in order to maintain the pH of the solution against the hydrogen ions released from D2EHPA during the extraction of In3+. In the present process, although such alkali addition is not necessary, acid (HCl in the present case) should be added in order to maintain the pH.

As shown in Fig. 6, stripping of In does not seem to be so efficient. Many stages seem to be necessary in order to obtain aqueous solution with concentrated In, while in the previous process (Lee et al, 2002), the stripping seems to be much easier.

Also, in the present process, after stripping, the organic phase should be converted to IL (R4NA) for reuse, which requires the treatment with NaHCO3 (regeneration of the extractant). This is a serious weak point of the present process.

In my opinion, the papers on solvent extraction published particularly in the present journal “Processes”, the authors should show the relative advantage of the proposed process over the conventional or previously proposed ones considering the whole process including extraction, stripping, and regeneration. Otherwise, the manuscript should be rejected.

In addition, the following points should be reconsidered:

(1) L109-111: The sentence is messy and does not make sense.

(2) L112: The authors should explain the meanings of R and A.

(3) L121-L128: This part is not logical. They should show Table 2 first. Then the readers can understand the basicity order. Otherwise the readers will be confused when they read “observed in our data (L122)”. They will think “which data?”

(4) L132: It seems to be somewhat difficult to use “linearly” as far as I see the increasing trend in Fig. 2.

(5) L148: What does “strength” mean?

(6) Fig.11: In the present case, is the organic phase lower phase? Lower phase should be placed at lower side.

(7) Fig.11 and Table 5 are redundant. Table 5 could be deleted.

Author Response

The replies to the comments are uploded.

                                

Author Response File: Author Response.docx

Reviewer 2 Report

The extraction of indium and gallium are challenging problems, and new technologies would be of significant value.  The paper is a thorough, methodologically-sound study of a novel extraction experiment.  The approach is similar to those taken elsewhere for other metals, and the paper offers little in the way of fundamental insight.  Nevertheless, it is a valuable contribution to the field and merits publication.

Author Response

The extraction of indium and gallium are challenging problems, and new technologies would be of significant value. The paper is a thorough, methodologically-sound study of a novel extraction experiment. The approach is similar to those taken elsewhere for other metals, and the paper offers little in the way of fundamental insight. Nevertheless, it is a valuable contribution to the field and merits publication.

Ans. The authors would like to thank the reviewer for the comments.

Reviewer 3 Report

Dear Editor,

 

The manuscript entitled “Separation of gallium(III) and indium(III) by solvent extraction with ionic liquids from hydrochloric acid solution” described the study of separation by extraction process of mixture of gallium(III) and indium(III) from aqueous solution by ionic liquids containing hydrophobic tetraalkylammonium cation (from ALIQUAT-336) and hydrophobic phosphinate and phosphate anions (conjugated bases of acids here named organophosphorous acids). The parent compounds of these ionic liquids and some other protic-ILs are already used in extraction separation of gallium(III) and Indium (III). However, their separation is pH dependent and the extraction process with ILs influence also pH so the author wanted to study the extraction process from moderate to weak hydrochloric acid solutions as well as to apply cheaper ILs (derived form ALIQUAT-336). The author searched and find the ideal conditions – pH for the selective extraction of In(III) in respect to Ga(III) and applied this conditions for further studies on their separation as well as influence of concentration of two metals in aqueous mixture on extraction. They discover conditions to more selectively extract In(III) in respect to Ga(III) but could not enrich further organic phase in In(III) by stripping of Ga(III) from organic phase by hydrochloric and sulphuric acid due to easier extraction of In(III) into them. Therefore, the scrubbing experiments were done to remove Ga(III) from the loaded IL with enriched indium in scrubbing feed solution, but still could not remove small amount of Ga(III) loaded in the IL.  Finally, as there is much difference in the extraction percentage between In(III) and Ga(III) the authors employment of multistage counter-current extraction and verified that only In(III) was extracted into IL and Ga(III) remained in the raffinate, which enabled the complete separation of both metal.

 The manuscript is interesting and important in the field of metal separation but still a person out of the field cannot easily read it so I would recommend some minor corrections.

 

 

 

Specific comments:

Comment 1: It is very difficult to follow the discussion without chemical formula of the ionic liquids prepared. I would advise the authors to include a scheme containing general chemical structures of the prepared ionic liquids with their abbreviation used in the manuscript and eventually their basicity discussed in this work (i.e. pKa of acid or basicity of the conjugate base). These compounds are used in extraction processes but many of the readers may not be familiar with them, even those who work with ionic liquids in other areas and can be usefull to them.

 

Comment 2: What is the composition of organic phase used for the extraction experiments? Is it a pure ionic liquid or ionic liquid in kerosene and how much diluted? This information is missing and only reviled in the discussion and should be explicitly expressed.

 

Comment 3: The text need overall reediting and correction as it seems that some phrases are not complete. For example:

In line 105 there is a missing word for the phrase to be complete: “When equilibrium pH was less than 4.2, the extraction percentage of In(III) was higher than that of Ga(III) and both metal ions were almost (completely?) extracted after this equilibrium pH.”

Line 110-111 – the phrase is not finished: “The difference 110 in the equilibrium pH at which most of the metal ions(…?)”

 

Comment 3: line 147-149: “According to Janssen et al [15]., when ion exchange reaction is responsible for the extraction of metal ions by an ionic liquid, the strength of the ionic liquid is reduced and thus the ionic liquid is partially dissolved in the aqueous phase.” Please define “strength of ionic liquid” or cite appropriate reference. I could not find this terminology in ref. 15.

 

Thank you for your collaboration.

Author Response

The replies to the comments are uploaded.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors revised the MS according to my former review. Although I am not convinced completely, I will not insist on my opinion any longer. The proposed process has some problems, but I understand that the process is in developing stage. I think that the MS can be accepted after minor revision as written below.

(1) L56: “In this works” should be “In this work”.

(2) L104: “ionic liquids” should be “ILs”.

(3) Fig. 11: In the batch simulation experiment, the feed Ga concentration was 100 mg/L, while the aqueous outlet concentration was 111 mg/L (the organic one was zero). At steady state, these values should be the same. Is this within the experimental error or because the system did not reach steady state?

Author Response

The authors revised the MS according to my former review. Although I am not convinced completely, I will not insist on my opinion any longer. The proposed process has some problems, but I understand that the process is in developing stage. I think that the MS can be accepted after minor revision as written below.

Ans. The authors would like to thank the reviewer for the valuable comments to our manuscript. The manuscript has been revised according to the comments.

 

1. L56: "In this works" should be "In this work".

Ans. “In this works” has been revised.

Modification

Page 2, line 55:

In this work, the ILs synthesized by Cyanex 272, PC88A and D2EHPA with Aliquat 336 were employed to separate Ga(III) and In(III) from HCl solution with moderate to weak acidity.

 

2. L104: “ionic liquids” should be “ILs”.

Ans. “ionic liquids” has been revised.

Modification

Page 3, line 103:

Owing to the ionic properties of the ILs, some ions may be dissolved in the aqueous phase, and the solubility of the ILs is reduced by adding NaCl to the aqueous phase [15].

 

3. Fig. 11: In the batch simulation experiment, the feed Ga concentration was 100 mg/L, while the aqueous outlet concentration was 111 mg/L (the organic one was zero). At steady state, these values should be the same. Is this within the experimental error or because the system did not reach steady state?

Ans. In batch simulation experiments, the two phases were shaken at the same volume ratio for the same time as in other experiments. Therefore, we think that the shaking time was enough to attain equilibrium in both phases. There might be some concentration effect. We think that the concentration of Ga(III) in the aqueous outlet was within the experimental error in batch simulation experiments.

Modification

Page 11, line 281:

In the batch simulation experiment, there was a slight difference in the concentration of Ga(III) between the feed and the aqueous outlet. It might be thought that the concentrations of Ga(III) in the outlet were within the experimental error range.