Extraction of Lanthanum Oxide from Different Spent Fluid Catalytic Cracking Catalysts by Nitric Acid Leaching and Cyanex 923 Solvent Extraction Methods

Round 1

Reviewer 1 Report

The subject of REE recovery from spent industrial catalysts is a vital issue nowadays. The authors propose a multistep process to produce lanthanum oxide from spent FCC catalyst, which is a very interesting attitude. However, more data should be given to justify the conclusions. Moreover, scientific discussion is scarce. This is rather a technical note, not a scientific publication. In my opinion, a major revision is necessary to recommend the manuscript for publishing in Metals. 

The most important remarks that should be addressed:
1.  Values of La concentration in the leachate should be shown. It would be good to show also concentrations of Al, Ti and Fe in the leachates.
2. There is no statistical analysis for the presented experiments - for each step of the process.
3. The final composition of the leachates after the leaching of each catalyst should be given.
4. You should show also coextraction of other metal ions.
5. Eqs. 3 and 7 - generally, small "k" letter is ascribed to reaction rate constant, not to reaction constant. So, here you should change it for a capital "K" letter.
6. Before characterization of the final product the authors should show results for stripping experiments. There are neither stripping efficiencies nor metal ion concentrations in the stripping solutions. Then yields of product formation should be calculated, one in relation to the initial amount of spent catalyst taken to the leaching and another one also in relation to the amount of La in the stripping solution.
7. In Conclusions the authors say about "industrial scale procedure". If it is "industrial scale procedure" - the authors should show clearly amounts of the reactants and products - how many kilograms of the product they are able to produce? It would be useful to show a flowsheet with mass balance for the proposed process.
8. English quality must be improved.

More detailed remarks are included in the attached pdf file.

Comments for author File: Comments.pdf

Author Response

Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts, by Lorena Alcaraz, Olga Rodríguez Rodriguez Largo, Francisco J. Alguacil, Margarita Alvarez Montes, Carmen Baudín, and Félix A. López, (Manuscript ID: metals-1517358)

 

Response to reviewer #1

 

We would like to thank the referee for his/her interesting and useful comments. In the following lines, we answer his/her questions on a point by point basis and indicate how the text has been modified.

1. 
   Values of La concentration in the leachate should be shown. It would be good to show also concentrations of Al, Ti and Fe in the leachates.

Due to the principal aim of the present work is the lanthanum recovery, Al, Ti and Fe concentrations in the leachates are not consider since lanthanum was subsequently selectively separated by liquid-liquid extraction process.

La concentration is collected in the following table, and also added to the manuscript:

Table 2. Lanthanum concentration in the leaching solutions for both spent FCC powders.

La (mg/L)	SC1	SC2
HCl	1.55	3.60
HNO3	1403	3275
OA	0.2	0.4
NaOH	<0.05	<0.05

 

2. 
   There is no statistical analysis for the presented experiments - for each step of the process.

As shown in the title, the aim of the present work is the "Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts". This process was widely described in the manuscript, so the statistical analyses are not importance.

3. 
   The final composition of the leachates after the leaching of each catalyst should be given.

Only lanthanum concentration was followed by ICP-MS in the leachates. In the revised version, lanthanum concentrations are summarized in Table 2.

4. 
   You should show also coextraction of other metal ions.

As indicated in the original manuscript, lanthanum was quantitatively selectively extracted under the conditions assessed.

5. 
   Eqs. 3 and 7 - generally, small "k" letter is ascribed to reaction rate constant, not to reaction constant. So, here you should change it for a capital "K" letter.

As suggested by the reviewer, “k” letter in the equations 3 and 7 has been replaced by capital "K" letter.

6. 
   Before characterization of the final product the authors should show results for stripping experiments.

The reviewer is right. In the revised version, a new section related to the stripping experiments has been added in the revised version.

There are neither stripping efficiencies nor metal ion concentrations in the stripping solutions.

Stripping experiments were carried out from organic phases. It should be noted that in the organic phases the concentration of metals cannot be measured.

Then yields of product formation should be calculated, one in relation to the initial amount of spent catalyst taken to the leaching and another one also in relation to the amount of La in the stripping solution.

“3.2.2. Stripping process

Finally, organic phases with a lanthanum concentrated were stripped using 1 M oxalic acid solution. Mixtures were mechanically stirred until the formation of a solid precipitate. After some minutes, the final mixtures were centrifugated and the solids were dried at 80 ºC for 24 hours to obtain the corresponding lanthanum oxalates. Considering the initial concentration of the organic phases (i.e. 7.8 g/L), stripping yields higher than 87 % were obtained in both cases. The obtained results demonstrate that it is possible recover 8.7 g and 20.7 g of lanthanum from 100 g of SC1 and SC2 spent fluid catalytic cracking catalysts, respectively.”

7. 
   In Conclusions the authors say about "industrial scale procedure". If it is "industrial scale procedure" - the authors should show clearly amounts of the reactants and products - how many kilograms of the product they are able to produce? It would be useful to show a flowsheet with mass balance for the proposed process.

It is a mistake. The obtention of lanthanum oxide from different spent fluid catalytic cracking catalysts was evaluated a laboratory-scale procedure in the present work. In the revised version, this sentence has been modified.

8. 
   English quality must be improved.

The English has been revised by a native speaker.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents interesting results for the lanthanum oxide production from different spent fluid catalytic cracking catalysts. The paper is generally well-written with contribution of new results and will have an impact on Metals readers in the industry and academia. However, there are some revisions to be done before publishing:

Please find enclosed comments annotated on the PDF-document of your submission.

Comments for author File: Comments.pdf

Author Response

Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts, by Lorena Alcaraz, Olga Rodríguez Rodriguez Largo, Francisco J. Alguacil, Margarita Alvarez Montes, Carmen Baudín, and Félix A. López, (Manuscript ID: metals-1517358)

 Response to reviewer #2

We would like to thank the referee for his/her interesting and useful comments. In the following lines, we answer his/her questions on a point by point basis and indicate how the text has been modified.

• The title must be changed. Extraction of Lanthanum Oxide from Spent Fluid Catalytic Cracking Catalysts Using HNO₃ Leaching and Solvent Extraction by Cyanex 923.

The authors don't agree with the reviewer. The authors consider that the initial title describe the principal aim of this work. For example, title suggested by the reviewer say "using HNO₃ leaching". However, several conditions have been evaluated (not only nitric acid) such as different leaching reagents, and different spent fluid catalytic cracking catalysts were also investigated.

 

• The abstract should contain the values obtained in this study: the extraction degree, technological parameters, metals content, etc. Authors should write the methods by which they analyzed the results and the main conclusion of the article in one sentence. In this form, the abstract contains only general words, there is no detailed information.

As suggested by the reviewer, Abstract section has been modified in the revised version:

“A laboratory-scale procedure has been developed to obtain lanthanum oxide from spent fluid catalytic cracking catalyst, commonly used in the cracking the heavy crude oil process. Two different spent fluid catalytic cracking catalysts, which are mainly formed by silica and alumina, and a certain amount of rare earths were leached under several conditions to recover the rare earth from the solids waste. Nitric acid leaching leads to a higher recovery of lanthanum, reached a recovery percentage greater than 95% when a 1.5 M concentration is used. Subsequently, liquid phases were subjected to a liquid-liquid extraction process using Cyanex 923 diluted in Solvesso 100. Then, lanthanum was quantitatively extracted. Lanthanum was also quantitatively stripped using oxalic acid to obtain the corresponding lanthanum oxalates as reveal X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), and Fourier Transform Infrared (FTIR) techniques. After the corresponding thermal treatment at 1200 ^oC for 2 hours, these solids were transformed into lanthanum oxide.”

 

• Line 65-73. Write more detailed the reagent's name and formulas. Don’t use basic media – use alkali (NaOH).

All reagents used were Laboratory Reagent (LR Grade chemicals). In the revised version a new line has been added:

“Based in previous investigations related to REE recovery from spent FCC [2, 21-23], hydrochloric acid (HCl), nitric acid (HNO₃), oxalic acid (C₂H₂O₄, OA), and sodium hydroxide (NaOH) were used. All the chemicals used in the present work were of Laboratory Reagent (LR Grade chemicals).”

• The authors should describe the novelty of the study. These words are not in the introduction.

The present work describes the obtention of lanthanum oxide obtention from different spent fluid catalytic cracking catalysts. Previous investigations have been reported the recovery of rare earths from these types of waste, but the influence of the synthesis conditions has scarcely evaluated. Thus, the authors describe several leaching conditions to recover lanthanum, followed by liquid-liquid extraction which leads a pure lanthanum oxide as final product:

“Several conditions were analyzed to recovery lanthanum from the spent fluid cat-alytic cracking catalyst initial solids by a leaching process. Different leaching agents, as well as concentrations, were evaluated. Subsequently, liquid-liquid extraction was carried out to selectively separate the rare-earth of interest. Various conditions were also assessed. Finally, lanthanum stripped in the liquid phase was precipitated, and the solid formed was thermally treated to obtain pure lanthanum oxide as products.”

 Section 2. Where did the authors get the raw materials? Add XRD with mineral compositions of two raw samples.

As suggested by the reviewer, XRD patterns of the raw materials have been added:

“Figure 1 exhibit the XRD patterns of both initial spent fluid catalytic cracking powders. In both cases, more intense diffraction maxima correspond to a Y-type zeolite (marked as triangle) as the main crystalline phase. Some reflections that can be attribute to ZSM-5 zeolite can be also appreciated (marked as circle in the Figure 1). These results are according to the previously reported studies, where spent fluid catalytic cracking catalysts usually contains Zeolite-Y and ZSM-5 zeolite [24–26].”

Figure 1: X-ray diffraction patterns of the (a) SC1 and (b) SC2 samples.

 

24. Madeti, M.; Lande, S. V.; G, K.; Mewada, R.K.; Jasra, R. V. A Green Approach. Int. J. Green Nanotechnol. 2013, 1, 194308921350702, doi:10.1177/1943089213507024.
25. Gusev, A.A.; Psarras, A.C.; Triantafyllidis, K.S.; Lappas, A.A.; Diddams, P.A.; Vasalos, I.A. ZSM-5 Additive Deactivation with Nickel and Vanadium Metals in the Fluid Catalytic Cracking (FCC) Process. Ind. Eng. Chem. Res. 2020, 59, 2631–2641, doi:10.1021/acs.iecr.9b04819.
26. Ferella, F.; Leone, S.; Innocenzi, V.; De Michelis, I.; Taglieri, G.; Gallucci, K. Synthesis of zeolites from spent fluid catalytic cracking catalyst. J. Clean. Prod. 2019, 230, 910–926, doi:10.1016/j.jclepro.2019.05.175.

 

and the origin of the starting spent fluid catalytic cracking powders has been indicated in the revised version:

“The two different spent fluid catalytic cracking powders investigated were named SC1 and SC2. Raw materials were provided by the Research Center of CEPSA (Spain).”

 

• Line 95. Don’t use the pulp density. Use the liquid to solid ratio (L/S ratio). In your research the L/S ratio = 10.

The reviewer is right. It is a mistake. In the revised version, this sentence has been modified: “SC1 and SC2 powders were put in contact with a leaching solution into a glass reactor at 60 ^oC for 4 hours using a solid/liquid ratio (S/L) equals to 10.”

 

• Line 94-95. Why authors use this T, leaching time and L/S ratio? Wy authors didn’t write information about leaching reagent and its concentration?

Experiments were carried out considering previous investigations reported which rare earths recovery from spent fluid catalytic cracking powders were assessed. In this sense, mineral acids (such as HCl and HNO₃), organic acids (oxalic acid) as well as sodium hydroxide (NaOH) were studied to efficiently recover rare earths. These publications reported that an increase of the temperature lead to highest rare earths recovery.

In the revised version, a new paragraph with this respect has been added:

“Based in previous investigations related to REE recovery from spent FCC [2, 21-23], hydrochloric acid (HCl), nitric acid (HNO₃), oxalic acid (C₂H₂O₄, OA), and sodium hydroxide (NaOH) were used. SC1 and SC2 powders were put in contact with a leaching solution into a glass reactor at 60 ^oC for 4 hours using a solid/liquid ratio (S/L) equal to 10. The leaching process was carried out into a great-capacity glass reactor. Previous inves-tigations have been reported that the leaching efficiencies of the metals increase with the temperature [2].”

 

• Table 2-3. Give this information in one Figure with columns.

As suggested by the reviewer, Table 2 and 3 are shown as Figure in the revised version:

“Figure 2 show lanthanum recovery percentages from both starting powders, modifying the leaching agent.

Figure 2. Experimental conditions and lanthanum recovery of the different test carried out from SC1 (blue) and SC2 (orange) powders.”

 

• Table 4. Why authors chose the HNO₃ acid? Add the reason to the article text.

As indicated in the original version, “Therefore, these experimental conditions were discarded. The highest extraction percentages of lanthanum were obtained when HCl and HNO₃ were used as leaching agents”

 

• Authors must write the full chemical compositions of the acid solution (g/L) after the leaching process.

Due to the principal aim of the present work is the lanthanum recovery, Al, Ti and Fe concentrations in the leachates are not consider since lanthanum was subsequently selectively separated by liquid-liquid extraction process.

La concentration is collected in the following table, and also added to the manuscript:

Table 2. Lanthanum concentration in the leaching solutions for both spent FCC powders.

La (mg/L)	SC1	SC2
HCl	1.55	3.60
HNO3	1403	3275
OA	0.2	0.4
NaOH	<0.05	<0.05

 

- Figure 1-3. Use the different colors for points. Y-axis – La or HNO₃ extraction (%).

As suggested by the reviewer, Figures 1 to 3 have been modified in the revised version:

 

Figure 1. Lanthanum extraction at various Cyanex 923 concentrations. Temperature: 20 ^oC.

 

Figure 2. Nitric acid extraction at various Cyanex 923 concentrations. Temperature: 20 ^oC.

 

• Section 3.4.1. How were the final solid products were obtained?

As indicate in the section 2.3, “The stripping step was carried out with oxalic acid using the organic extracted solution under the optimal conditions. These experiments were performed with 1 M oxalic acid solution as stripping phase according to the next equation:

The precipitates were then centrifuged, and subsequently calcinated at 1200 ^oC for 2 hours in order to yield the La₂O₃ phase.”

 

• Figure 4. Sigh all peaks. Add information about phase and chemical formulas.

As suggested by the reviewer, all diffraction maxima have been indexed, and Figure 4 has been modified in the revised version:

Regarding the chemical formulas of the obtained samples, as indicate in the original version: “All diffraction maxima can be indexed to a La₂O₃ phase.”

 

• Figure 5. Authors must sign all extremums. Write temperatures and mass losses information.

In the original version, both temperatures as well as mass losses are described for each peak registered. 

 

• Section 3.4.4. Authors can add information about the particle size distribution of powder by laser diffraction method and BET (m²/g). What are the chemical compositions of powder? What is the impurities content?

As shown in the title, the aim of the present work is the "Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts". For this reason, particle size distribution of powder is not important.

With respect to the chemical composition of the powder, XRF analyses of both initial and leached solids are shown in the original manuscript.

 

Table 1. Chemical composition (wt %) for both spent FCC powders.

Oxide (wt %)	SC1	SC2
Al2O3	50.00	52.20
SiO2	45.60	39.10
La2O3	1.82	4.32
V2O5	nd	0.24
Na2O	0.19	0.30
P2O5	0.94	0.27
TiO2	0.89	0.64
Fe2O3	0.43	0.36
CeO2	nd	0.26
NiO	0.12	nd
MgO	nd	0.88
SO3	nd	1.25

 

Table 5. Chemical composition (wt %) for both spent FCC insoluble residue powders.

Oxide (wt %)	SC1-B	SC2-B
Al2O3	38.6	44.5
SiO2	59.2	52.7
La2O3	0.33	0.52
V2O5	nd	0.15
Na2O	nd	nd
P2O5	0.25	0.096
TiO2	1.12	0.87
Fe2O3	0.26	0.23
CeO2	nd	0.28
NiO	0.15	<0.05
MgO	nd	0.47
SO3	nd	0.18
Al2O3/SiO2	0.65	0.84

 

• The authors should add a process flowsheet for the extraction of lanthanum oxide.

In the revised version, a schematic procedure of the tests carried out has been included:

 

“Schematic procedure of the tests carried out is summarized in Figure 1.

 

Figure 1. Schematic process for the obtention of lanthanum oxide.”

 

• What will be done with the solid residue after the leaching of lanthanum? It contains a lot of silica and alumina.

As indicated in the original version, “In subsequent work, the evaluation of the insoluble residues obtained from the process as raw materials for refractories is reported.”

 

• The conclusions should be more detailed, add the main values and parameters.

Conclusions section has been rewritten:

 

“An effective process to obtain lanthanum oxide from spent fluid catalytic cracking (sFCC) catalysts has been assessed. Two different sFCC solids were used in the investigated work. Initially, several leaching conditions was evaluated under to extract lanthanum from the initial solids. Highest lanthanum recover percentage was found using nitric acid with a 1.5 M concentration proved to be the most effective condition for the recovery of lanthanum for both samples investigated. Subsequently, the liquid-liquid extraction process using Cyanex923 undiluted and diluted using Sovesso100 was investigated to selectively separate lanthanum from nitric acid. Optimal separation was found for aqueous/organic (A/O) ratio of 8. Finally, lanthanum was stripped from the organic phases using oxalic acid to precipitate the corresponding lanthanum oxalate. After thermal treatment at 1200 ^oC for 2 hours, pure lanthanum oxide was effectively obtained. The present work demonstrates that it is possible to obtain lanthanum oxide from different spent fluid catalytic cracking catalysts powders.”

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript ID: metals-1517358

Title: Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts

Authors: Lorena Alcaraz et al.

The title must be changed. Extraction of Lanthanum Oxide from Spent Fluid Catalytic Cracking Catalysts Using HNO₃ Leaching and Solvent Extraction by Cyanex 923.

The abstract should contain the values obtained in this study: the extraction degree, technological parameters, metals content, etc. Authors should write the methods by which they analyzed the results and the main conclusion of the article in one sentence. In this form, the abstract contains only general words, there is no detailed information.

Line 65-73. Write more detailed the reagent's name and formulas. Don’t use basic media – use alkali (NaOH).

Introduction. The authors should give a detailed description of the previous methods, show their advantages and disadvantages. Write the optimal parameters and the extraction degree of rare earth metals.

The authors should describe the novelty of the study. These words are not in the introduction.

Section 2. Where did the authors get the raw materials? Add XRD with mineral compositions of two raw samples.

Line 95. Don’t use the pulp density. Use the liquid to solid ratio (L/S ratio). In your research the L/S ratio = 10.

Line 94-95. Why authors use this T, leaching time and L/S ratio? Wy authors didn’t write information about leaching reagent and its concentration?

Table 2-3. Gibe this information in one Figure with columns.

Table 4. Why authors chose the HNO₃ acid? Add the reason to the article text.

Authors must write the full chemical compositions of the acid solution (g/L) after the leaching process.

Line 202-203. Add references.

Figure 1-3. Use the different colors for points. Y-axis – La or HNO₃ extraction (%).

Section 3.4.1. How were the final solid products were obtained?

Figure 4. Sigh all peaks. Add information about phase and chemical formulas.

Figure 5. Authors must sign all extremums. Write temperatures and mass losses information.

Section 3.4.4. Authors can add information about the particle size distribution of powder by laser diffraction method and BET (m²/g). What are the chemical compositions of powder? What is the impurities content?

The authors should add a process flowsheet for the extraction of lanthanum oxide.

What will be done with the solid residue after the leaching of lanthanum? It contains a lot of silica and alumina.

The conclusions should be more detailed, add the main values and parameters.

Author Response

All corrections proposed by the reviewer have been incorporated into the corrected manuscript.

Round 2

Reviewer 1 Report

The Authors took into account some of my remarks, however, they did not address the remarks from the pdf file which was attached by me previously (e.g. what "responsible equilibrium" means, in lines 302 and 305 still a wrong number of eqs.). For example, the first sentence from the Introduction "Fluid catalytic cracking catalyst (FCC catalyst) is a widely process used in crude oil 27 processing in petroleum refineries...", as I marked before "Fluid catalytic cracking catalyst" is not a process. The process is called FCC - fluid catalytic cracking. There are still more such errors. 

Another thing is concerned with the responses - in the case of stripping the Authors added results to the manuscript which is noteworthy. However, in Materials and Methods, more details about the stripping procedure are necessary, e.g. volumes of the loaded organic and stripping phases, time of stripping, calculation of the stripping yield (given as a value of 87% in section 3.2.2).

Some responses seem to be superficial and I am not sure whether the Authors are aware of the scientific responsibility:

1. The response "As shown in the title, the aim of the present work is the "Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts". This process was widely described in the manuscript, so the statistical analyses are not importance." shows that the Authors do not realize that EACH result is burden with an error, and the statistical analysis is important to show that the results are not accidental/random. It means that the statistical analysis in research works is a basic procedure to show the significance of the obtained results (the results are affected by various errors which can occur during all phases of a study).
2.  The Authors write about selective separation of lanthanum, and I asked for showing concentrations of other accompanying metal ions, which seems to be crucial to speak about selectivity. However, the Authors answer that "Only lanthanum concentration was followed by ICP-MS in the leachates." and further "As indicated in the original manuscript, lanthanum was quantitatively selectively extracted under the conditions assessed." The quantitative La extraction does not mean that ions of other metals are also quantitatively extracted. That's why proof for the selective extraction of La must be shown in the research investigation. But if the Authors determined only La concentration then they cannot speak about selectivity because they do not know the extent of extraction of other metal ions.
3. I asked for stripping efficiencies or metal ion concentrations in the stripping solutions. And the Authors answered: "Stripping experiments were carried out from organic phases. It should be noted that in the organic phases the concentration of metals cannot be measured." It sounds as if the Authors misunderstood my question. The question was about concentrations in STRIPPING solutions which are AQUEOUS, not organic solutions. It is obvious that stripping efficiencies are always calculated from the mass balance for the stripping phase after stripping and the loaded organic phase (calculated from the mass balance after extraction).
4. Unfortunately, the statement that "The English has been revised by a native speaker." is NOT TRUE. There are still a lot of grammar mistakes in the text what would not be missed by a native speaker. Such quality of English cannot be accepted in such a high-value journal as "Metals".

I am sorry to conclude that this manuscript should not be published in Metals. It can be resubmitted after substantial revision.

Author Response

Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts, by Lorena Alcaraz, Olga Rodríguez Rodriguez Largo, Francisco J. Alguacil, Margarita Alvarez Montes, Carmen Baudín, and Félix A. López, (Manuscript ID: metals-1517358)

 Response to reviewer #1

 

We would like to thank the referee for his/her interesting and useful comments. In the following lines, we answer his/her questions on a point by point basis and indicate how the text has been modified.

The Authors took into account some of my remarks, however, they did not address the remarks from the pdf file which was attached by me previously (e.g. what "responsible equilibrium" means, in lines 302 and 305 still a wrong number of eqs.). For example, the first sentence from the Introduction "Fluid catalytic cracking catalyst (FCC catalyst) is a widely process used in crude oil processing in petroleum refineries...", as I marked before "Fluid catalytic cracking catalyst" is not a process. The process is called FCC - fluid catalytic cracking. There are still more such errors.

 

Another thing is concerned with the responses - in the case of stripping the Authors added results to the manuscript which is noteworthy.

It should be noted that these added results were included by a suggestion of another reviewer.

 

However, in Materials and Methods, more details about the stripping procedure are necessary, e.g. volumes of the loaded organic and stripping phases, time of stripping, calculation of the stripping yield (given as a value of 87% in section 3.2.2).

The authors are agreed with the reviewer. In the revised version, these data are now including in the manuscript.

 

 

Some responses seem to be superficial and I am not sure whether the Authors are aware of the scientific responsibility:

1. The response "As shown in the title, the aim of the present work is the "Lanthanum oxide obtention from different spent fluid catalytic cracking catalysts". This process was widely described in the manuscript, so the statistical analyses are not importance." shows that the Authors do not realize that EACH result is burden with an error, and the statistical analysis is important to show that the results are not accidental/random. It means that the statistical analysis in research works is a basic procedure to show the significance of the obtained results (the results are affected by various errors which can occur during all phases of a study).

We may agreed with you, however, we have a wide experience (over 40 years) using these methodologies and we are confident with the data presented in the work. Based in this experience we feel that a manuscript not presenting these data does not decrease its importance. Also, please note that we include the analytical error associated with the analytical work. It is also true that these statistical data are not always given in published manuscripts in relation to our work. Please see below some few recent publications in which these data do not appear:

-Hydrometallurgy 208 (2022) 105780. DOI: 10.1016/j.hydromet.2021.105780

-Hydrometallurgy 208 (2022) 105702. DOI: 10.1016/j.hydromet.2021.105782

-Hydrometallurgy 208 (2022) 105798. DOI: 10.1016/j.hydromet.2021.105798

-Hydrometallurgy 208 (2022) 105818. DOI: 10.1016/j.hydromet.2022.105818

-Metals 2021, 11, 1987. DOI: 10.3390/met11121987

-Metals 2021, 11, 1300. DOI; 10.3390/met11081300

-Solvent Extraction and Ion Exchange 2022. DOI: 10.1080/07366299.2021.2024650

-Solvent Extraction and Ion Exchange 2021. DOI: 10.1080/07366299.2021.2016935  

       Please note that in some cases (not necessarily these listed above), not even the analytical error was given in the published manuscript.

 

2. 2. The Authors write about selective separation of lanthanum, and I asked for showing concentrations of other accompanying metal ions, which seems to be crucial to speak about selectivity. However, the Authors answer that "Only lanthanum concentration was followed by ICP-MS in the leachates." and further "As indicated in the original manuscript, lanthanum was quantitatively selectively extracted under the conditions assessed." The quantitative La extraction does not mean that ions of other metals are also quantitatively extracted. That's why proof for the selective extraction of La must be shown in the research investigation. But if the Authors determined only La concentration then they cannot speak about selectivity because they do not know the extent of extraction of other metal ions.

The sentence “lanthanum was quantitatively selectively extracted under the conditions assessed” was somewhat not complete, since it was referred to the separation La/nitric acid using the A/O conditions given in the text (and figures). We indicated the above in the revised manuscript.

Thought other elements are partially soluble, they were not extracted (or marginally extracted) by Cyanex 923 under these limiting situations, i.e. A/O= 8.

3. 
   I asked for stripping efficiencies or metal ion concentrations in the stripping solutions. And the Authors answered: "Stripping experiments were carried out from organic phases. It should be noted that in the organic phases the concentration of metals cannot be measured." It sounds as if the Authors misunderstood my question. The question was about concentrations in STRIPPING solutions which are AQUEOUS, not organic solutions. It is obvious that stripping efficiencies are always calculated from the mass balance for the stripping phase after stripping and the loaded organic phase (calculated from the mass balance after extraction).

We did not measure these concentrations by two reasons:

1. i) as we stated above, the element was not extracted(or poorly extracted) under the limiting extraction conditions,
2. ii) under the stripping conditions, only lanthanum(III) oxalate precipitated, this is corroborated from further analysis of this solid and the lanthanum(III) oxide yielded in the work.

Thus, we considered the analysis of these elements of residual interest, and since the target was lanthanum.

4. 
   Unfortunately, the statement that "The English has been revised by a native speaker." is NOT TRUE. There are still a lot of grammar mistakes in the text what would not be missed by a native speaker. Such quality of English cannot be accepted in such a high-value journal as "Metals".

We checked the English and after correction of the grammar mistakes, we think that it is correct, other thing is that:

1. i) you do not like the style that we use to write the manuscript,
2. ii) some of the nomenclature, that it is very specific to the methodology that we utilize in each case.

Reviewer 3 Report

The authors did not provide a separate file with answers to questions. The authors did not answer a big part of the questions. In this regard, I change my review to reject.

Authors must either accept comments or answer why comments are not corrected. Most of my comments are ignored. I can't understand why.

Author Response

We believe that we have responded to the questions raised by the reviewer in round 1 of the review, both in the PDF he sent and in the point-by-point responses.

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Dear Authors,

as responsible scientists, we have to take care of good practices, not the bad ones, i.e. the basic statistical analysis should be carried out to prove the reliability of the data. In my opinion, the lack of statistical analysis in other works is not an argument.

You should hire a professional English translator to correct and improve the English quality of the manuscript. There are still basic errors such as: "were analyzed to recovery lanthanum", "lanthanum oxide as products", "Aqueous feed solutions from the highest lanthanum recovery", and many others. So, this is not a question if I like your style of writing, this is a question of basic rules of English grammar.

Author Response

Extraction of lanthanum oxide from different spent fluid cata-lytic cracking catalysts by nitric acid leaching and Cyanex 923 solvent extraction methods, by Lorena Alcaraz, Olga Rodríguez Rodriguez Largo, Francisco J. Alguacil, Margarita Alvarez Montes, Carmen Baudín, and Félix A. López, (Manuscript ID: metals-1517358)

 

Response to reviewer #1

We would like to thank the referee for his/her interesting and useful comments.

It should be noted that the title has been chenged in the revised version by the suggestion of one referee.

Dear Authors, as responsible scientists, we have to take care of good practices, not the bad ones, i.e. the basic statistical analysis should be carried out to prove the reliability of the data. In my opinion, the lack of statistical analysis in other works is not an argument.

The referee is right. There isn´t doubt that a statistical analysis would improve the quality of the present work. The authors appreciate the suggestion by the referee and take it into account for future works.

 

You should hire a professional English translator to correct and improve the English quality of the manuscript. There are still basic errors such as: "were analyzed to recovery lanthanum", "lanthanum oxide as products", "Aqueous feed solutions from the highest lanthanum recovery", and many others. So, this is not a question if I like your style of writing, this is a question of basic rules of English grammar.

The authors are agree with the reviewer. There were still some grammar errors in the manuscript. In the revised version, English has been thoroughly revised.

Reviewer 3 Report

Several errors have been corrected in the article. However, additional corrections need to be made:

• The title must be changed to “Extraction of Lanthanum Oxide from different spent fluid catalytic cracking catalysts by nitric acid leaching and Cyanex 923 solvent extraction methods”
• Authors must mark the phases in Figure 2 (triangle and circle).
• Figure 3. Authors must add the X and Y-axis.
• Authors must sign all mass changes in Figure 8. The y-axis usually shows the change in mass relative to 100% of the raw material. The authors must correctly draw up this figure.
• The authors characterized the final product by XRD and SEM. What are the average particle size distribution (laser diffraction) and specific surface area (BET, m²/g) of the lanthanum oxide powder? Authors must add this information.
• How many impurities are in it? The authors write “pure lanthanum oxide” in line 434. Add the chemical composition of pure lanthanum oxide.

Author Response

Extraction of Lanthanum Oxide from different spent fluid catalytic cracking catalysts by nitric acid leaching and Cyanex 923 solvent extraction methods, by Lorena Alcaraz, Olga Rodríguez Rodriguez Largo, Francisco J. Alguacil, Margarita Alvarez Montes, Carmen Baudín, and Félix A. López, (Manuscript ID: metals-1517358)

 

Response to reviewer #3

Several errors have been corrected in the article. However, additional corrections need to be made:

The title must be changed to “Extraction of Lanthanum Oxide from different spent fluid catalytic cracking catalysts by nitric acid leaching and Cyanex 923 solvent extraction methods”

The authors are agree with the reviewer. As suggested by the reviewer, the title had been changed in the revised version.

 

Authors must mark the phases in Figure 2 (triangle and circle).

In the revised version, Figure 2 had been modified. In the new Figure 2, the phases marked by triangle and circle are identified. New Figure 2 are shown below:

Figure 2. X-ray diffraction patterns of the (a) SC1 and (b) SC2 samples.

 

Figure 3. Authors must add the X and Y-axis.

As suggested by the reviewer, Figure X and Y-axis have been added. New Figure 3 are shown below:

Figure 3. Experimental conditions and lanthanum recovery of the different tests carried out from SC1 (blue) and SC2 (orange) powders.

 

Authors must sign all mass changes in Figure 8. The y-axis usually shows the change in mass relative to 100% of the raw material. The authors must correctly draw up this figure.

As suggested by the reviewer, Figure 8 has been changed in the revised version. New Figure 8 are shown below:

 

Figure 8. DTA/TGA curves of the obtained lanthanum oxalates.

 

The authors characterized the final product by XRD and SEM. What are the average particle size distribution (laser diffraction) and specific surface area (BET, m²/g) of the lanthanum oxide powder? Authors must add this information.

As suggested by the reviewer, both average particle size distribution (laser diffraction) have been added in the revised version. New Figure 10, as well as the text added in the revised version is shown below:

3.4.5. Granulometric analyses

The particle size distribution graph of lanthanum oxide is shown in Figure 10. The curve of the granulometric distribution (sigmoidal line) represents the particle-size distribution expressed as % volume. Classical granulometric parameters D50, and D90 were used to characterize the final product. DX designates the diameter for which X % of the particles have a smaller size. The calculated D50 (medium), and D90 particle sizes were 14.3 µm and 168 µm, respectively.

Figure 10. Particle size distribution of lanthanum oxide.

 

In addition, as suggested by the reviewer, specific surface area (S_BET) measurements were carried out. The obtained lanthanum oxides exhibit a low BET surface (2.0186 m²/g). For this reason, the authors consider that these results are not enough relevant to include in the manuscript. The obtained results are shown below:

BET Surface Area: 2.0186 m²/g

 

 

How many impurities are in it? The authors write “pure lanthanum oxide” in line 434. Add the chemical composition of pure lanthanum oxide.

The reviewer is right. In the revised version, the chemical composition of lanthanum oxide is added. The obtained results are shown below:

 

“In addition, the chemical composition of the final lanthanum oxides was analyzed by XRF. The obtained results are shown below (Table 5). Some minor impurities of cerium and aluminium were found. However, the obtained results reveal that the final oxides are mainly composed of lanthanum.

These results demonstrate that it is possible to recover lanthanum from spent FCC catalysts and to reach a yield lanthanum oxide.”

 

Table 5. Chemical composition (wt %) for the obtained lanthanum oxides.

Oxide (wt %)
La2O3	98.06
CeO2	1.38
Al2O3	0.22

 

 

Author Response File: Author Response.pdf