Column Separation of Am(III) and Eu(III) by α-Zirconium Phosphate Ion Exchanger in Nitric Acid

Round 1

Reviewer 1 Report

Paragraphs 1 and 2 of Introduction need more citations to back up the description. The English is not sound and needs to be corrected by a native speaker. Numerous minor faults and mistakes are present. Just name a few as follows.

Line number	Original expression	Correct format
109, 110	0.5 minutes	0.5 minute
115	microwave plasma optical emission spectroscope	Spectrometer or spectroscope? Instrument model
120	with	plus
121	with	plus
121	eluting pH	Eluate pH
121	Load	loading
159	Second, in our conditions, only the species M3+ and M(NO3)2+ are present for M = Eu, Am	Reference needed
161	the narrow structure acts as an ion sieve and prefers the smaller Eu with the higher charge density	Reference needed
	Fig. 2 Fig. 3 Time	Agitation time
	Fig. 6 E, A	Eu, Am

Author Response

Dear reviewers

Thank you for your numerous corrections, suggestions and for the further discussion they have provoked. All the notes have been considered and replied to, while 95% have resulted in changes to the manuscript. Sincere apologies for slow reply, but the quality of this manuscript has improved greatly based on your critical notes. Both the introduction and discussion/conclusion were reworked based on your proposals. Please see the response for point-by-point changes.

 

Paragraphs 1 and 2 of Introduction need more citations to back up the description. The English is not sound and needs to be corrected by a native speaker. Numerous minor faults and mistakes are present. Just name a few as follows.  

The intro (and conclusions) has been reworked on past and future studies. The examples given below were corrected, among numerous other language changes during the language revision.

 

Line number    Original expression     Correct format

109, 110          0.5 minutes      0.5 minute

This paragraph was overhauled for clarity, and mistakes were corrected.

 

115      microwave plasma optical emission spectroscope     Spectrometer or spectroscope?

Instrument model

Thankfully this was commented on, as the instrument was erroneously(!) reported as OES, which we have used for other purposes. Reworked the sentence to “The eluate was collected in fractions from which Eu concentrations were quantitatively determined by microwave plasma atomic emission spectrometer (Agilent 4200 MP-AES) with lanthanum as the internal standard.”

 

120      with     plus

121      with     plus

121      eluting pH       Eluate pH

121      Load    loading

During the language revision all of these points, among numerous others, were corrected.

 

159      Second, in our conditions, only the species M3+ and M(NO3)2+ are present for M = Eu, Am            Reference needed

This refers to our previous work, were equal conditions were used, and the species that are present were touched on. The citation to the reference 17 was missing from this sentence, although it should have been there. Added.

 

161      the narrow structure acts as an ion sieve and

prefers the smaller Eu with the higher charge density           Reference needed

This is discussion/hypothetical, although it did seem like a factual claim when it was written in such way. The sentence has now been improved to reflect the case.

This discussion is an indirect result from Abraham Clearfield’s writings on various zirconium phosphates compiled in his book from 1982, where cation size is briefly touched on in discussion, but not quantitatively or in a systematic manner. Thus we cannot say for certain how much of an effect does a 10% increase in the effective ionic radius have, for example. The zirconium phosphate family is from time to time referred to as zeolite-like rigid structures with molecular / ion sieve functionality, but to our knowledge, a good reference with solid study on the ion size effect remains absent.

 

 Fig. 2 Fig. 3 Time      Agitation time

 Fig. 6 E, A     Eu, Am

Figures were corrected, and their format will likely change during the final steps.

Reviewer 2 Report

Dear authors,

The separation of actinides and lanthanides, especially for used fuel reprocessing is a very interesting subject and many studies have been done in the last decades. Your paper presents the separation of Eu/Am in dilute nitric media using Zr phosphate ion exchanger. Your methodology is well described and relevant with your objectives. The results obtained are interesting but your separation method may be improved to increase the overall efficiency (capacity and concentration factors) and need to be validated using non-synthetic solution. Here are some suggestion to improve the quality of your manuscript.

Introduction

Revise your introduction by adding more references on An/Ln separations studies (recent and not only focused on Zr phosphate). Better describe in your introduction what is the works that was done before (references to your past studies) and in this study. Provide specific objectives and parameters that were investigated in this study with rationale (salt concentration, metals concentration).

M&M

Describe the Zr phosphate synthesis and characterization. Provide the concentration of nitric media and the formula of commercial salt used used during the experiments. Give rationale for selecting low concentrations of chloride salt and high concentrations of nitrate salt for your study. Provide the quantification limits of your analytical method (MP-OES).

R&D

In the Binary batch uptake experiment, you should improve your discussion by adding the potential formation of other Eu/Am complexes with more than one nitrate ion in concentrated nitric media. In the Effect of salt on Eu uptake, you may discuss the potential formation of chloride Eu complexes. In the Effect of Eu/Am cc on uptake, you should add more emphasis on the speciation of both metals in PWR used nuclear fuel. The presence of others An and FPs may affect significantly your separation method. In the kinetic experiment, you have proven the physical stability but more testing / discussion are needed to assess chemical stability. In the Breakthrough experiment, you reported low experimental capacity that should be compared to other technologies (SX & IX). In the load elution experiment, very good separation factors are reported but the use of high bed volume for elution may led to very low concentration factors for your method and need to be estimate. In the constant feed experiment, how the feed trace concentration compared to what is expect in the treatment of real used nuclear fuel?

Please revise your conclusion, which should be a short summary of the results obtained against your objectives and a short discussion of your findings in regards to future development of your separation method.

Author Response

Dear reviewers

Thank you for your numerous corrections, suggestions and for the further discussion they have provoked. All the notes have been considered and replied to, while 95% have resulted in changes to the manuscript. Sincere apologies for slow reply, but the quality of this manuscript has improved greatly based on your critical notes. Please see the response for point-by-point changes.

The separation of actinides and lanthanides, especially for used fuel reprocessing is a very interesting subject and many studies have been done in the last decades. Your paper presents the separation of Eu/Am in dilute nitric media using Zr phosphate ion exchanger. Your methodology is well described and relevant with your objectives. The results obtained are interesting but your separation method may be improved to increase the overall efficiency (capacity and concentration factors) and need to be validated using non-synthetic solution. Here are some suggestion to improve the quality of your manuscript.

The separation should indeed be validated and although this was a final manuscript during one thesis, much work remains to be done including the use of a better simulated solution and finally non-synthetic one.

 

Introduction

Revise your introduction by adding more references on An/Ln separations studies (recent and not only focused on Zr phosphate). Better describe in your introduction what is the works that was done before (references to your past studies) and in this study. Provide specific objectives and parameters that were investigated in this study with rationale (salt concentration, metals concentration).

The end of the introduction has been overhauled.

 

M&M

Describe the Zr phosphate synthesis and characterization. Provide the concentration of nitric media and the formula of commercial salt used used during the experiments. Give rationale for selecting low concentrations of chloride salt and high concentrations of nitrate salt for your study. Provide the quantification limits of your analytical method (MP-OES).

Brief description on the past material study, and some additional discussion on its crystallinity, was added to the first paragraph, but the details and comprehensive characterization remains as a reference to the previous work.

The non-radioactive work was done by MP-AES, but reported as OES by mistake (now fixed). Some details on this were added. The paragraph with effect of salt conc. was further altered. The MP-AES was utilized for the non-radioactive work only: the breakthrough experiment. As the MP-AES proved extremely sensitive for Eu (detected at 381.967 nm) without any spectral interferences, perfect linearity from 0.05 to 20 ppm was achieved. The samples were diluted so that 100% feed levels would hit the 15 ppm mark. Lanthanum at 394.910 nm was used as the internal standard. The formula: Detection limit = 10*STDn*PITstd/(INTstd-INTn) was used for the detection limit, where STDn is the standard deviation in blank measurements (6 to 10), PITstd is the conc. of the lowest standard used (50 ppb), INTstd is the intensity value of the lowest standard used, and INTn is the average intensity of the blank measurements. In the first nine samples of the breakthrough curve, no Eu is detected (the measurement is below the explained limit), and in the first sample with detected levels, the conc. level is 0.07 ppm (= about 0.5% of the feed levels). This information is not added to the manuscript for brevity. Instead, more information about the limits and uncertainty values in the numerous radioanalytical measurements were added to the text.

 

R&D

In the Binary batch uptake experiment, you should improve your discussion by adding the potential formation of other Eu/Am complexes with more than one nitrate ion in concentrated nitric media. In the Effect of salt on Eu uptake, you may discuss the potential formation of chloride Eu complexes. In the Effect of Eu/Am cc on uptake, you should add more emphasis on the speciation of both metals in PWR used nuclear fuel. The presence of others An and FPs may affect significantly your separation method. In the kinetic experiment, you have proven the physical stability but more testing / discussion are needed to assess chemical stability. In the Breakthrough experiment, you reported low experimental capacity that should be compared to other technologies (SX & IX). In the load elution experiment, very good separation factors are reported but the use of high bed volume for elution may led to very low concentration factors for your method and need to be estimate. In the constant feed experiment, how the feed trace concentration compared to what is expect in the treatment of real used nuclear fuel?

Please revise your conclusion, which should be a short summary of the results obtained against your objectives and a short discussion of your findings in regards to future development of your separation method.

During the previous work, when potential complexes in the equal-to-this-work experiment conditions with various nitrates, carbonates etc. were studied, we saw only the mentioned mononitrate species present in significant concentrations, even in highly concentrate nitric acid. This topic was only briefly touched on through PHREEQC modelling, but it did indeed include multinitrate species. Reference was mistakenly missing but now it is added.

Many of the other great points given will be the focus on future work, as we feel like real life applications are greatly out of scope for this paper, and thus the discussion should also be so. Comparison with other technologies and the stability in real harsh environments remains to be discussed when the next level of experiments will be conducted and reported. Although the column experiments reported here are a step to this direction, all of the discussion will be in the following work (and is very important, thank you for the ideas!).

But then, talks on the objectives and future development discussion, among some other topics, have now been added to conclusions (and intro), as several points were inadequate or missing.

Reviewer 3 Report

The paper called „Column Separation of Am(III) and Eu(III) by α-Zirconium Phosphate Ion Exchanger in Nitric Acid“ by Elmo Wiikinkoski and co-authors is a clear and well-written paper that brings new results, and, therefore, should be published in the ChemEngineering after minor revisions. The authors interpreted all obtained results and suggested that they can be useful for a supportive or alternative role in minor actinides-lanthanides separation.

 

Here are some details that can be considered and adjusted:

… lanthanide-actinide separations are one of the major challenges… the whole process is still dealing with more issues (line 8) Introduction – line 35: I suggest to use „hydrochemical and pyrometallurgical“ instead of „aqueous and pyrochemical“ processes. It would be beneficial to add one more paragraph about Ln(III)/minor An(III) solid-phase extractants and compare them with α-Zirconium Phosphate in the Conclusion. I suggest using the term „weight distribution coefficient“ or „weight distribution ratio“, which reflects to solid-phase extraction. The distribution coefficient is used in liquid-liquid processes. What are the approximate errors, for example for Kd values in Table 1? There are some errors shown in Figure 1… Because of the very high values of Kd(Eu), they must be also relatively high. It should be at least mentioned in the text and the Table 1 can be without them for better clarity. What was the detection limit for your measurements?

Author Response

 Dear reviewers

Thank you for your numerous corrections, suggestions and for the further discussion they have provoked. All the notes have been considered and replied to, while 95% have resulted in changes to the manuscript. Sincere apologies for slow reply, but the quality of this manuscript has improved greatly based on your critical notes. Please see the response for point-by-point changes.

 

Here are some details that can be considered and adjusted:

… lanthanide-actinide separations are one of the major challenges… the whole process is still dealing with more issues (line 8) Introduction – line 35: I suggest to use „hydrochemical and pyrometallurgical“ instead of „aqueous and pyrochemical“ processes.

Good catch, these terms are now corrected in the text, but a little bit differently: we now used hydro- and pyrometallurgical. Although in the industry many terms are used perhaps wrongly as synonyms these seem to be the ones currently in most use. Pyrometallurgy seems to be a clear case, but for aqueous nuclear reprocessing, both terms hydrochemical and hydrometallurgical are competing. For PUREX specifically, it seems like the hydrometallurgy term is winning, so we are going by that term for this text.

It would be beneficial to add one more paragraph about Ln(III)/minor An(III) solid-phase extractants and compare them with α-Zirconium Phosphate in the Conclusion.

Detailed talk on the subject will be added in future manuscripts where a more real life -ish applications/solutions will be studied and comparison with alternative methods will be reported. Same thinking goes with the discussion chapter, and this is naturally a very important topic. However, we strongly feel that such comprehensive comparison is out of the scope for this text, as here we are still dealing with clean laboratory tests with synthetic solutions.

I suggest using the term „weight distribution coefficient“ or „weight distribution ratio“, which reflects to solid-phase extraction. The distribution coefficient is used in liquid-liquid processes.

We discussed this, however this time there is a big but. In radionuclide separations specifically, the plain “distribution coefficient, Kd” has been widely used when dealing with especially the solid sorbents and liquid streams, in addition to the usual liquid/liquid case. Thus, this time we prefer to keep our text unchanged.

What are the approximate errors, for example for Kd values in Table 1? There are some errors shown in Figure 1… Because of the very high values of Kd(Eu), they must be also relatively high. It should be at least mentioned in the text and the Table 1 can be without them for better clarity. What was the detection limit for your measurements?

The error indeed becomes very high with very high Kd values as the values approach background, and similarly with very low Kd values as the values approach the method blank values. These datapoints from the high-end and low-end of the Kd curves, with huge uncertainty (e.g. +-100%) we commonly omit for this reason (or include, but write: high/low).

Numerically, the relative errors are commonly between 1 to 15% for the all of the shown data points in the figures and tables. These are not the relative errors for only measurement replicates, but rather the uncertainty for whole method replicates (replicate samples gone through the whole procedure). This information was added to the text to the corresponding locations, next to the tables, or to the figure captions. Note: the highest uncertainties were in Table 1 for pH 0.5, for Am. Luckily, here this pH 0.5 is not of interest (both the Kd’s are too low, and the separation factor), so the values were left in. Perhaps in this case it would have been an option to leave out the separation factors as N/A since the Kd(Am) is in the denominator, affecting even more on the final s.f. uncertainty. But in the end we decided to leave these in, as the numerical values for uncertainties are now added in the text for reference.

Round 2

Reviewer 2 Report

Thanks for the responses provided. 

Best regards