Preparation of La(III), Fe(III) Modified Zeolite Molecular Sieves for the Removal of Fluorine from Water
Round 1
Reviewer 1 Report
In this study, La-Fe zeolite absorbent was prepared and characterized, and its application for adsorption of fluoride ion was investigated. The results showed that the removal rate of fluoride ion at 240 min was 99.04%. The adsorption kinetics of La-Fe zeolite was in line with the pseudo-second kinetic model, and the adsorption isotherms was well fitted with Freundlich isotherm model. The adsorption thermodynamics indicated that the adsorption was an endothermic spontaneous process. The tests of dynamic adsorption column showed that the adsorption efficiency of fluoride ion on La-Fe zeolite was higher than 85 % for 9 h of continuous adsorption. La-Fe zeolite absorbent showed good adsorption capacity and stability. In addition, the mechanisms for fluoride adsorption was discussed. Some important results and conclusions were obtained. The experimental content is relatively complete. Overall, the study is interesting and helpful to the application of adsorption in wastewater treatment. However, the scientific background of this version is limited, thus I recommend a minor revision before it is accepted:
Minor concerns:
ü Q1. It is necessary to unify the formatting and writing of the manuscript, and some formatting and writing problems need to be corrected, such as “change Fig.2c and 2d” to “Fig.2c and Fig.2d”; “2θ range of of 10 ~ 80°” should be “2θ range of 10 ~ 80°”; change “La2O3” to “La2O3”; (1) should be ( Eq.1), etc.
ü Q2. The adsorption mechanisms suggested are relatively simple, and the adsorption mechanisms have not been deeply ascertained. In the report "Highly efficient fluoride removal from water using 2D metal-organic frameworks MIL-53 (Al) with rich Al and O absorptive centers", the adsorption mechanisms of fluoride ion on MIL-53(Al) were well studied by the density functional calculation, and the main adsorption sites were confirmed by the change of bond energy of removing fluoride by MIL-53(Al). Thus, is it possible to add some quantum chemical calculations or refer to some articles to discuss the adsorption mechanisms in depth?
ü Q3. All abbreviations in the manuscript should be given full names when they first appear, so the first abbreviation, such as 3.1: "EDS" should be revised.
ü Q4. In general, the regeneration methods include physical regeneration and chemical regeneration. Acid regeneration and alkali regeneration are the most common method. Why did the author choose aluminum sulfate for regeneration? The regenerated adsorbent still has good capacity for simulated wastewater, but could it be used in practical applications?
ü Q5. The adsorption properties of La-Fe zeolite for fluoride ions were studied. However, there were many metal-modified zeolites have been used. A comparison should be incorporated with the previously reported adsorbents, and the discussion for the differences in the performance should be provided.
ü Q6. Authors are suggested to add some typical documents to improve the scientific background of this manuscript. For example, some new type of de-fluoridation adsorbents could be introduced, which makes the article more readable and interesting. For example:
n Pan B , Xu J , Wu B , et al. Enhanced Removal of Fluoride by Polystyrene Anion Exchanger Supported Hydrous Zirconium Oxide Nanoparticles[J]. Environmental Science & Technology, 2013, 47(16):9347-9354.
n Zhang X , Lu Z , Li Z , et al. Rational Design of Antifouling Polymeric Nanocomposite for Sustainable Fluoride Removal from NOM-Rich Water[J]. Environmental Science and Technology, 2017, 51(22).
ü Q7. For the unit of all graphs, “Binding energy(eV)” should be “Binding energy (eV)”. “cm.-1” should be “cm−1”. Please check the manuscript.
ü Q8. For tables 1 and 2, in addtion to R2, it is suggested that the authors can provide RMSE values.
The authors can add the following sentence in section 2.4:
“The kinetic parameters were calculated using the non-linear regression and the least-squares method in MATLAB. The fitting performance of different kinetic models was evaluated using two statistical criteria, “R2 - coefficient of determination and RMSE – root mean square error”[ref.].
”
Ref.:
Kinetic modeling and optimization of flotation process in a cyclonic microbubble flotation column using composite central design methodology, International Journal of Mineral Processing2016, 157, 175-183
ü Q9. Some grammar mistakes should be revised. The authors should be further improve the language level.
Line 285: “the increase of CO3 and HCO3 concentration” should be “the increase of CO3 and HCO3 concentrations”
Line 297: pH values between 5 and 7; thus “pH 10.0” (line 298) should be “pH 10”; line 305, “pH>8.0” should be “pH>8”
Line 309: “the zeta potential of ...” should be “pH>8.0” “the zeta potentials of ...”
Author Response
Reviewer #1:
In this study, La-Fe zeolite absorbent was prepared and characterized, and its application for adsorption of fluoride ion was investigated. The results showed that the removal rate of fluoride ion at 240 min was 99.04%. The adsorption kinetics of La-Fe zeolite was in line with the pseudo-second kinetic model, and the adsorption isotherms was well fitted with Freundlich isotherm model. The adsorption thermodynamics indicated that the adsorption was an endothermic spontaneous process. The tests of dynamic adsorption column showed that the adsorption efficiency of fluoride ion on La-Fe zeolite was higher than 85 % for 9 h of continuous adsorption. La-Fe zeolite absorbent showed good adsorption capacity and stability. In addition, the mechanism for fluoride adsorption was discussed. Some important results and conclusions were obtained. The experimental content is relatively complete. Overall, the study is interesting and helpful to the application of adsorption in wastewater treatment. However, the scientific background of this version is limited, thus I recommend a minor revision before it is accepted:
Response: We extremely appreciate your precise comments and suggestions. We have made careful revisions accordingly to improve the research rationale and quality of our manuscript.
Q1. It is necessary to unify the formatting and writing of the manuscript, and some formatting and writing problems need to be corrected, such as “change Fig.2c and 2d” to “Fig.2c and Fig.2d”; “2θ range of of 10 ~ 80°” should be “2θ range of 10 ~ 80°”; change “La2O3” to “La2O3”; (1) should be ( Eq.1), etc.
Response: We are thankful for your suggestions, which are helpful to improve the quality of our manuscript. We have revised these mistakes in the revised manuscript.
Revisions in the revised manuscript:
Page 3, line 119-121:
The crystalline structure of the adsorbent was analyzed by Nanoco Empyrean X-ray diffractometer (XRD) at the scanning rate of 2 °/min and 2θ range of 10 ~ 80°.
Page 5, line 213-215:
In addition, the peaks of La2O3 were found at near 30.7° and 48.06°, and the diffraction peaks at 33.9° and 43.59° were attributed to La2Si2O7.
Page 6, line 229-230:
The FT-IR analysis for the functional groups of natural zeolite and La-Fe zeolite were shown in Fig. 2c and Fig. 2d, respectively.
Page 10-11, line 353-363:
As shown in Table 4, the ΔG0 of all the processes of three temperatures fluoride ions adsorption were negative, indicating that the adsorption processes were spontaneous. The absolute value of the ΔG0 increases with the temperature rise, indicating that raising the temperature has a significant influence on the adsorption process. ΔH0 ＞ 0 reveals the characteristics of adsorption process is endothermic, and ΔS0 ＞ 0 demonstrates that the chaos degree increases in the process of adsorption[42]. Therefore, the adsorption process of fluoride ions by La-Fe zeolite is an entropic increase reactions, which is spontaneous endothermic.
Table 4 Thermodynamic properties of La-Fe zeolite absorbing fluoride ions
Q2. The adsorption mechanisms suggested are relatively simple, and the adsorption mechanisms have not been deeply ascertained. In the report "Highly efficient fluoride removal from water using 2D metal-organic frameworks MIL-53 (Al) with rich Al and O absorptive centers", the adsorption mechanisms of fluoride ion on MIL-53(Al) were well studied by the density functional calculation, and the main adsorption sites were confirmed by the change of bond energy of removing fluoride by MIL-53(Al). Thus, is it possible to add some quantum chemical calculations or refer to some articles to discuss the adsorption mechanisms in depth?
Response: Thanks for your valuable comments. We greatly agree with your comments and study the mechanism with quantum chemical calculations. Nevertheless, we think that the zeolite adsorption mechanism is not required to apply quantum chemical calculations.
Quantum chemical calculations can play a key role in the study of adsorption mechanism, which can be studied at a deep mechanistic level with changes in chemical-bond energy and atomic orbitals. Due to the simple principle of zeolite fluorine adsorption, our research has clearly depicted the adsorption mechanism. If there is an opportunity in the future, the mechanism will be researched more deeply by quantum chemical calculations.
Q3. All abbreviations in the manuscript should be given full names when they first appear, so the first abbreviation, such as 3.1: "EDS" should be revised.
Response: Special thanks for your valuable comments. According to your comments, we revised it in the revised manuscript.
Revisions in the revised manuscript:
Page 3, line 118-119:
The functional groups on the adsorbent surface were detected by Fourier Transform infrared spectroscopy (FT-IR) (Thermo Scientific Nicolet iS20).
Page 5, line 2013-205:
Combined with the Energy Dispersive X-ray Spectroscopy (EDS) (Fig. 1c) and mapping diagram (Fig. 1 d–i) of the La-Fe modified zeolite, it can be known that La and Fe were successfully loaded on the natural zeolite.
Page 6, line 225-228:
The isotherms shown in Fig. 2b are type V adsorption-desorption curves and the hysteresis loop is H3, which indicates that the mesoporous structure is a slit hole formed by stacking flaky particles, which is consistent with the SEM image.
Q4. In general, the regeneration methods include physical regeneration and chemical regeneration. Acid regeneration and alkali regeneration are the most common method. Why did the author choose aluminum sulfate for regeneration? The regenerated adsorbent still has good capacity for simulated wastewater, but could it be used in practical applications?
Response: We are thankful for your suggestions, which are helpful to improve the quality of our manuscript. Although acid and alkali are common regenerants, we found that alkali regeneration was not effective. While we used 0.1 mol/L hydrochloric acid and nitric acid solutions as regenerants, the removal of regenerated adsorbent had less than 90%, and the adsorption time became shorter and couldn’t be regenerated after two cycles. The adsorbent regenerated with aluminum sulfate solution not only had high efficiency but also had long adsorption time, and the removal rate could reach more than 85% after regeneration for four times, so the aluminum sulfate solution was selected as regenerant. In the practical mine water adsorption experiments, the results indicated that the treated mine water did not meet WHO discharge standards. Subsequently, we will re-optimize the adsorbent to meet the discharge standards.
Q5. The adsorption properties of La-Fe zeolite for fluoride ions were studied. However, there were many metal-modified zeolites have been used. A comparison should be incorporated with the previously reported adsorbents, and the discussion for the differences in the performance should be provided.
Response: We are appreciated for your suggestions, which are helpful to improve the quality of our manuscript. We added the capacities of different adsorbents for fluoride removal in Table 3 in the revised manuscript.
Revisions in the revised manuscript:
Page 10, line 352: Table 3
To understand the adsorption capacity of La-Fe zeolite, the maximum adsorption capacities of reported adsorbents were shown in Table 3.
Table 3 Comparison of the maximum adsorption capacities of various adsorbents with La-Fe zeolite
|
Absorbents |
Q0 (mg/g) |
References |
|
Lanthanum hydroxide modified magnetite |
1.42 |
[1] |
|
Fe(III)–Sn(IV) mixed oxide |
10.47 |
[2] |
|
Fe(III)-STI zeolite |
2.31 |
[3] |
|
KMnO4-modified carbon |
15.90 |
[4] |
|
Hydrous aluminum oxide-iron oxide mixture |
4.18 |
[5] |
|
Layered double hydroxides |
16.10 |
[6] |
|
Marble apatite-CM |
4.23 |
[7] |
|
La-Fe zeolite |
22.77 |
this work |
Q6. Authors are suggested to add some typical documents to improve the scientific background of this manuscript. For example, some new type of de-fluoridation adsorbents could be introduced, which makes the article more readable and interesting. For example:
Pan B , Xu J , Wu B , et al. Enhanced Removal of Fluoride by Polystyrene Anion Exchanger Supported Hydrous Zirconium Oxide Nanoparticles[J]. Environmental Science & Technology, 2013, 47(16):9347-9354.
Zhang X , Lu Z , Li Z , et al. Rational Design of Antifouling Polymeric Nanocomposite for Sustainable Fluoride Removal from NOM-Rich Water[J]. Environmental Science and Technology, 2017, 51 (22).
Response: We gratefully appreciate for your valuable suggestions. According to your suggestions, some typical literatures in the chapter of introduction were added in the revised manuscript.
Revisions in the revised manuscript:
Page 2, line 50-59:
Pan et al. [8]designed a novel nanocomposite adsorbent HZO-201 for preferable and sustainable defluoridation from NOM-rich water. HZO-201 can treat > 3000 BV of the acidic effluent per run at pH 3.5, compared to only ~4 BV with D201. Zhang et al. [9] synthesized the nanocomposite HZO@HCA by encapsulating hydrated zirconia nanoparticles (HZO NPs) in hyper-cross-linked polystyrene anion exchanger (HCA) combined with tertiary amine groups. The synthesized fluorinated groundwater can pass through the HZO@HCA fixed bed and finally produce ∼80 bed volume (BV) effluent to meet the drinking water standards (<1.5 mg/L). Thus, developing a highly efficient and selective adsorbent for fluoride ions from wastewater is highly needed.
Q7. For the unit of all graphs, “Binding energy(eV)” should be “Binding energy (eV)”. “cm.-1” should be “cm−1”. Please check the manuscript.
Response: Thank you very much for your suggestions. According to your suggestions, we revised these errors in the figures and carefully checked all the figures.
Revisions in the revised manuscript:
Page 6, line: Fig. 2
Page 7, line 254: Fig. 3
Q8. For tables 1 and 2, in addition to R2, it is suggested that the authors can provide RMSE values. The authors can add the following sentence in section 2.4:
“The kinetic parameters were calculated using the non-linear regression and the least-squares method in MATLAB. The fitting performance of different kinetic models was evaluated using two statistical criteria, “R2 - coefficient of determination and RMSE – root mean square error” [ref.].”
Ref.: Kinetic modeling and optimization of flotation process in a cyclonic microbubble flotation column using composite central design methodology, International Journal of Mineral Processing2016, 157, 175-183
Response: We really appreciate your comments. We fully agree with the comments you made. It is evident from the literature that the fitting performance of different kinetic models can be accurately calculated by least squares in MatLab, which plays a key role in the adsorption analysis. Nevertheless, we can also explain the adsorption of fluoride ions well by kinetic fitting of the coefficient of determination R2. In the future study, we will learn the programming calculation of REMS in MatLab in order to better analyze the adsorption principle.
Q9. Some grammar mistakes should be revised. The authors should be further improve the language level.
Line 285: “the increase of CO32- and HCO3- concentration” should be “the increase of CO32- and HCO3- concentrations”
Line 297: pH values between 5 and 7; thus “pH 10.0” (line 298) should be “pH 10”; line 305, “pH>8.0” should be “pH>8”
Line 309: “the zeta potential of ...” should be “pH>8.0” “the zeta potentials of ...”
Response: We are thankful for your suggestions, which are helpful to enhance the quality of our manuscript. We carefully checked the spelling and revised the grammatical mistakes in the revised manuscript.
Revisions in the revised manuscript:
Page 8, line 284-287:
The results showed that the increase of CO32- and HCO3- concentrations led to the increase of pH of the solution, and OH- in the solution showed a competitive effect on the adsorption of fluoride, occupying the position of fluoride ion adsorption.
Page 8, line 303-305:
The adsorption capacity decrease significantly and the removal rate drops below 20 % in alkaline pH range (pH > 8).
Page 8, line 308-309:
To understand the changes in the surface charge of the adsorbent, the zeta potentials of natural zeolite and La-Fe zeolite at different pH values were investigated.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The problem of removing fluorides from water and wastewater is current.Development of F- removal methods is necessary,
thus the work should be published.
Author Response
Reviewer #2:
The problem of removing fluorides from water and wastewater is current. Development of F- removal methods is necessary, thus the work should be published.
Response: We thank the reviewer for reading our manuscript carefully and giving the above positive comments.
Reviewer 3 Report
The manuscript presents a study on La-Fe zeolite for removal of fluoride. The following comments should be addressed by the authors for further consideration.
1) Novelty of work should be clearly highlighted. 2) The purpose of adding TISAB II solution should be more clearly explained in section 2.3 3) Any term appearing for the first time should have a full name followed by an acronym in brackets. 4) In 2.7, what does r/min denote? Flow rate is a more suitable term than penetration rate. Is there any specific reason for using the penetration rate term? 5) Please justify the selection of competing ions. 6) The maximum adsorption capacity should be stated in abstract. 7) Future directions should be discussed such as optimization, developing treatment systems for removal and recovery of resources, etc.. The following references are relevant in this context for including in the discussion https://doi.org/10.1515/gps-2020-0039- https://doi.org/10.1016/j.chemosphere.2021.132690
Author Response
Reviewer #3:
The manuscript presents a study on La-Fe zeolite for removal of fluoride. The following comments should be addressed by the authors for further consideration.
Response: Thank you very much for your valuable comments. We made careful revisions accordingly to improve the research rationale and quality of our manuscript.
Comment 1: Novelty of work should be clearly highlighted.
Response: Thanks greatly for your valuable suggestions. As you suggested, we added the novelty statement in the introduction in the revised manuscript.
Revisions in the revised manuscript:
Page 2, line 50-60:
In previous studies, there were a few examples of zeolite modification with both La and Fe, and most of the zeolites were modified by monometallic La or Fe. In present study, the modification with La and Fe has achieved considerable results, and La is a precious metal, which reduces the cost compared with the modified zeolite with the single metal La. When the dosage was 10 g/L, the pH was 4.59±0.02, and the temperature was 313 K, the maximum adsorption capacity of the modified zeolite synthesized by LAI et al [10] for fluoride in simulated zinc sulfate was 23.04 mg/g. In contrast, the optimal pH environment of this experiment is about 7. Under the condition of 318 K and dosage of 8 g/L, the maximum adsorption capacity of modified zeolite to simulated mine water was 22.8 mg/g, which was more economical and environmental friendly.
Comment 2: The purpose of adding TISAB II solution should be more clearly explained in section 2.3.
Response: We gratefully appreciate for your valuable suggestions. The clear explanation about TISAB II solution was added in the revised manuscript.
Revisions in the revised manuscript:
Page 3, line135-143:
This is because in the overly acidic solution, hydrogen ions will form hydrogen fluoride or difluoro-hydride ligands with fluoride ions, reducing the concentration of fluoride ions. Some ions can form complexes with fluoride ions or insoluble precipitation ions such as iron ions, aluminum ions, calcium ions, magnesium ions, etc. can interfere with the determination, and the citric acid in TISAB â…¡ can mask them. In the analysis of potentiometric methods, the potential value is often linearly related to the activity of the analyzed ion, rather than the logarithm of the concentration, and the total ionic strength of the adjusted buffer solution is quite important for the accuracy of the analysis.
Comment 3: Any term appearing for the first time should have a full name followed by an acronym in brackets.
Response: Thank you for pointing out these suggestions in manuscript. According to your suggestions, we revised it in the revised manuscript.
Revisions in the revised manuscript:
Page 3, line 118-119:
The functional groups on the adsorbent surface were detected by Fourier Transform infrared spectroscopy (FTIR) (Thermo Scientific Nicolet iS20).
Page 5, line 2013-205:
Combined with the Energy Dispersive X-ray Spectroscopy (EDS) (Fig. 1c) and mapping diagram (Fig. 1 d ~ i) of the La-Fe modified zeolite, it can be known that La and Fe were successfully loaded on the natural zeolite.
Page 6, line 225-228:
The isotherms shown in Fig. 2b are type V adsorption-desorption curves and the hysteresis loop is H3, which indicates that the mesoporous structure is a slit hole formed by stacking flaky particles, which is consistent with the SEM image.
Comment 4: In 2.7, what does r/min denote? Flow rate is a more suitable term than penetration rate. Is there any specific reason for using the penetration rate term?
Response: Thanks for your valuable suggestions. In 2.7, rpm/min represents the speed of the peristaltic pump. We fully agree with your suggestions that the term flow rate is more appropriate than penetration rate. The original intent of the term permeability was to describe the amount of solution per minute through the adsorbent. Since we did not understand and express it clearly, we accepted your suggestions to change the penetration rate to flow rate in manuscript.
Comment 5: Please justify the selection of competing ions.
Response: Thanks greatly for your valuable comments. In the practical mine water, other anions such as chloride ions, sulfate ions, bicarbonate ions, nitrate carbonate ions and sulfate ions are always present at the same time. The studies by Yin et al. [11] and Jun et al. [12] showed that bicarbonate ions and carbonate ions have a great influence on the adsorption of fluoride ions, and the efficiency of fluoride removal decreases as the ion concentration increases, while sulfate and nitrate ions have almost no influence to fluoride removal. Therefore, sulfate, bicarbonate and carbonate ions were selected as competing ions for comparative discussion.
Comment 6: The maximum adsorption capacity should be stated in abstract.
Response: We are thankful for your suggestions, which are helpful to improve the quality of our manuscript. We added the appropriate content in the revised manuscript.
Revisions in the revised manuscript:
Page 9, line 346-348:
As can be seen from Fig. 5c, the Langmuir isotherm can also agreement with the data. The adsorption capacity increased with increasing temperature and the maximum adsorption capacity was 22.77 mg/g.
Comment 7: Future directions should be discussed such as optimization, developing treatment systems for removal and recovery of resources, etc. The following references are relevant in this context for including in the discussion.
https://doi.org/10.1515/gps-2020-0039
https://doi.org/10.1016/j.chemosphere.2021.132690
Response: Thanks for your valuable question. We have added the future direction of adsorbent development in the revised manuscript.
Revisions in the revised manuscript:
Page 13, line 452-460:
In future research, it is necessary to improve the adsorption capacity of adsorbent and also to pay attention to the environmental impact of adsorbent after adsorption saturation. Specifically, composite modification is a good measure to improve the adsorption performance of adsorbent materials, because it can combine the advantages of multiple modified materials. Moreover, if the adsorbed saturated material is not properly treated, it may cause serious secondary pollution to the environment. Some measures can be considered to reuse the saturated adsorbent resourcefully. For instance, the utilization of nitrogen, phosphorus and potassium by crops can be improved when the adsorption-saturated zeolite is used with fertilizers.
Comment 8: A comparison of fluoride removal performance of this adsorbent vs various adsorbents reported in literature should be included.
Response: Extremely thanks for your valuable comments. We added the capacities of different adsorbents for fluoride removal in Table 3 in the revised manuscript.
Revisions in the revised manuscript:
Page 10, line 352: Table 3
To understand the adsorption capacity of La-Fe zeolite, the maximum adsorption capacities of reported adsorbents were shown in Table 3.
Table3. Comparison of the maximum adsorption capacities of various adsorbents with La-Fe zeolite
|
Absorbents |
Q0 (mg/g) |
References |
|
Lanthanum hydroxide modified magnetite |
1.42 |
[1] |
|
Fe(III)–Sn(IV) mixed oxide |
10.47 |
[2] |
|
Fe(III)-STI zeolite |
2.31 |
[3] |
|
KMnO4-modified carbon |
15.90 |
[4] |
|
Hydrous aluminum oxide-iron oxide mixture |
4.18 |
[5] |
|
Layered double hydroxides |
16.10 |
[6] |
|
Marble apatite-CM |
4.23 |
[7] |
|
La-Fe zeolite |
22.77 |
this work |
Author Response File: Author Response.pdf
