Removal of Fluorine from RECl3 in Solution by Adsorption, Ion Exchange and Precipitation
Round 1
Reviewer 1 Report
Review of paper ‘Removal of fluorine from RECl3 in solution by adsorption, ion exchange and precipitation’ prepared by Dong-Liang Zhang, Kai Gao, Xiao-Wei Zhang, Mi-Tang Wang.
The manuscript Minerals - 1487815 is focused on fluorine removal from mixed rare earth chloride solutions. The authors investigated different methods: fluorine removal agent or CO2 precipitation. The effects of temperature and concentration were also investigated. In my opinion this article is worth publishing in Minerals after a minor revision. I have some suggestions that authors may consider prior to publication of this work:
- Information on the repeatability of measurements should be added to the manuscript.
- Correction should be made in reactions 5 and 9 (see pages 11 and 12) - appropriate notation of anionic forms of reaction products is missing.
- The authors should explain why they used only one temperature (see results presented in Figure 5) for the carbon dioxide precipitation studies.
- From a practical point of view, it would be useful to assess to what extent the use of relatively high temperatures will be applicable. It should be noted that heating is an expensive operation. A comment on the feasibility of solving this problem should be added to the manuscript.
Author Response
Dear reviewer,
On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewers very much for their positive and constructive comments and suggestions on our manuscript.
We have studied reviewer’s comments carefully and have made revision which marked in red in the paper. We have tried our best to revise our manuscript according to the comments. Attached please find the revised version, which we would like to submit for your kind consideration.
We would like to express our great appreciation to you for comments on our paper. Looking forward to hearing from you. Thank you and best regards. Kind regards,
Yours sincerely,
Dong-liang Zhang
E-mail: btzdl85@163.com
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this study, the effects of some technical factors on objective function of %fluorine removal are assessed. The idea of the work is fair; however the methodology should be enhanced widely due to following notes:
- Why dear authors have not worked with Design of Experiment DoE? Of course DoE can conceptually and comprehensively enhance your experiment investigation. The factors are all studied individually, while you had to study the intersection of factors. How are the simultaneous effects of two or more factors studied? As well why you have used only curves for factor effects? It is better you use surfaces 3D diagrams for such immense factors. Because your response is engaged with surfaces and it’s better to study an RSM. On the other hand, How are the factor ranges derived, for example why only Temperatures of 25, 70 and 90?! Why not 25 (coded -1), 57.5 (coded 0) and 90 (coded +1)? You can receive very helps from Minitab or Design Expert software.
- The optimization of only one objective function -%Fluorine removal- is not so suitable. I highly advise to optimize both objective functions of 1) Cost –either total or operational- and 2) Performance - %Fluorine Removal together. Actually reaching the most amount of %F Removal at what cost?
- And the most important aspect is that what is the recommended standard value for Fluorine outlet to environment? The function of %F Removal needs to be transformed to Remained Fluorine Concentration or dose to be compared to environmental standards. Perhaps for one sample only 40% F removal is enough to reach the recommended standard value while for another sample even a 90% F Removal is not enough to reach the standard. What is the amount of outlet concentration target?
English language needs a thorough correction, some sentences seem meaningless like “ In order to avoid the adverse effect of fluorine on the extraction of mixed rare earth chlo-ride solution.”
About Figure 3, you may use a redistributer or sprinklers after injection line in the vessel for enhanced diffusion. I guess ventury is not capable to handle the effective flow regime all through the vessel.
As it is mentioned in conclusion ” The experimental results showed that the fluorine removal percentage of rare earth chloride solution can reach 99.60% under the conditions of 8% lanthanum carbonate, initial conc. of rare earths 240g/L, initial solu-tion pH≤1, reaction temperature 90℃, reaction time 2h.” I believe this process is too costly and needs some design variables to be traded off for lowering the cost of the process. About Figure 14, I find no meaningful difference between times 2h and 2.5h. So it is better to note the 2h as the best point. On the other hand initial concentration of Rare Earths cannot be served as a design variable, because it is very dependent upon extracted mineral environment and it is not due to engineer!
Finally two points from above advices are critically important which may not be ignored. 1) Your design variables must be traded off for optimizing process cost. And 2) the outlet standard target for F Concentration or its outfall Dose must be known for optimization of process performance.
Author Response
Dear reviewer,
On behalf of my co-authors, we thank you very much for giving us an opportunity to revise our manuscript, we appreciate reviewers very much for their positive and constructive comments and suggestions on our manuscript.
We have studied reviewer’s comments carefully and have made revision which marked in red in the paper. We have tried our best to revise our manuscript according to the comments. Attached please find the revised version, which we would like to submit for your kind consideration.
We would like to express our great appreciation to you for comments on our paper. Looking forward to hearing from you. Thank you and best regards. Kind regards,
Yours sincerely,
Dong-liang Zhang
E-mail: btzdl85@163.com
Author Response File: 
Author Response.pdf
Round 2
Reviewer 2 Report
As it is accepted worldwide, we use design of experiment methods in order to systematize and tidy the process of effective parameter exploration by regular experiments especially for the process of optimization. I addressed the ranges of all parameters not T 0C only. About other factors this problem encounters too. Even for temperature as you mentioned, 25 0C is very far from 70 0C, not applicable and actually not symmetric. About 90 0C how do you ascertain that another temperature -like for example 85 0C or 95 0C- does not optimize the program better? If you used a BBD design with 70 0C (coded as 0), 115 0C (coded as +1) and 25 0C (coded as -1), you could observe the true optimized amount for temperature to be calculated for example around 97 0C. So you have not kept this amount in your range. Especially because your response directly increases with T 0C and you undoubtedly need another response -like the most applied: the cost- for optimization process. In present case your work is only a rapid investigation and cannot be served as an optimization program.
About Fig.4 I meant 3D surfaces not near 2D curves being in one Figure! Altogether this part is better now.
When we talk about cost we mean the cost arouse from all effective factors like T 0C, speed, pH, facilities etc and actually the most important ones, not removal agents only! In present case we cannot determine the most expensive parameter and its sensitivity actually. Even for temperature you cannot underestimate the cost of T 0C for previous stages because the process is integrated and you encounter a big optimization program in which all factors are linked from the first part of component i removal to the last part which is the removal of Fluorine, and even the wastewater treatment. You cannot keep away the processes of various component separations; it is harshly against conceptual design and process integration ideas and not accepted in any convention.
About point 3 you must find a world-known standard for limits of F concentration disposal. Please add the standard limits in text. As you mentioned “The fluorine content of the mixed rare earth chloride solution obtained by concentrated sulfuric acid roasting process is very low, the conc. of rare earth solution is 330 g/L, the fluorine content is only 0.03 g/L” If you use the RECl3 Solution by naming process, the initial concentration should be around 330 g/L –constant- as well for other processes different from the naming one; your initial RE solution must be a constant amount –at most changing for a very small range not from 60 to 300 g/L!- hence assuming this factor as a design variable is meaningless. You are designing a factory for a definite feed and you cannot change the quality of the feed for your own aims. And you must keep the consideration of the worst case for example 60g/L and of course not changing. So Initial Dose is not only a design variable but also a limiting factor which affects both other factors and the response(s) actually. It is better to work with this parameter as a limiting factor and not inserting to optimization process.
Another point about the final remained F value is that for a sample specified by Table 3, the F concentration is 0.57 g/L which needs only 94% F removal to reach the recommended standard of 0.03 g/L as mentioned in your target. So determining a 99.6% for optimization is overestimating and you can reach the target by only 1.3h and even not stirring or below 50 r.min-1 as that of figure 17. You should work more and more on your data, factors, ranges and responses.
Finally I guess the idea and innovation of the work is fair, however the structure, design, results and discussion of the study are all really poor. I can accept the article only for its novelty of idea.
Author Response
Dear reviewer:
Hope you are well.
We have studied your comments carefully and have made revision which marked in red in the paper. We have tried our best to revise our manuscript according to the comments. Attached please find the revised version, which we would like to submit for your kind consideration.
We would like to express our great appreciation to you for comments on our paper. Looking forward to hearing from you. Thank you and best regards.
Yours sincerely,
Dongliang Zhang
E-mail: btzdl85@163.com
Author Response File: Author Response.docx
