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Peer-Review Record

A Novel and Facile Method to Characterize the Suitability of Metallic Iron for Water Treatment

Water 2019, 11(12), 2465; https://doi.org/10.3390/w11122465
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Water 2019, 11(12), 2465; https://doi.org/10.3390/w11122465
Received: 30 September 2019 / Revised: 15 November 2019 / Accepted: 21 November 2019 / Published: 23 November 2019
(This article belongs to the Section Wastewater Treatment and Reuse)

Round 1

Reviewer 1 Report

The paper is competently and carefully written. Well-throughout design of experiments, providing reasoned results during the discussion. However, some minor revisions should be taken into account before publishing the work in Water Journal.

- Relevant conclusions should be arisen (a few sentences) in the abstract.

- It is not clear at all the objective of the work. It should be better explained (pros and cons of using conventional and new method). Especially in the introduction, a better explanation should be given, as it is very difficult to understand the core purpose of the work.

- Table. 1. Units of elemental composition should be provided (%). Could the impurities (in different proportions) influence the oxidation progress of the Fe0 samples? The same with the diameter, which is probably influencing the oxidation reaction, what is the aim of comparing samples with different sizes if then, diameter is not taking into account in the discussion? What is the aim of providing the information of the origin of all samples? Not clear at all.

Author Response

The paper is competently and carefully written. Well-throughout design of experiments, providing reasoned results during the discussion.

Many thanks for this evaluation!

However, some minor revisions should be taken into account before publishing the work in Water Journal.

Noted with thanks!

Comments 1: Relevant conclusions should be arisen (a few sentences) in the abstract.

Many thanks, the following is added:

The apparent iron dissolution rate in EDTA (kEDTA) and in Phen (kPhen) were such that 0.53 kEDTA (g h-1) 4.81 and 0.07 kPhen (g h-1) 1.30. Higher kEDTA values, relative to kPhen, are a reflection of disturbing FeIII species originating from FeII oxidation by dissolved O2 and dissolution of iron corrosion products.


Comments 2: It is not clear at all the objective of the work. It should be better explained (pros and cons of using conventional and new method). Especially in the introduction, a better explanation should be given, as it is very difficult to understand the core purpose of the work.


Many thanks, the last paragraph of the introduction now reads:

The present work is a continuation of an effort to characterize the intrinsic reactivity of Fe0 specimens based on the kinetics of their dissolution in a dilute solution of complexing agents. Previous works were based on Fe0 dissolution in (EDTA) [9,20,21,45,50,51]. The interpretation of achieved results was complicated by the evidence that EDTA dissolves amorphous FeIII-components of iron corrosion products (FeCPs) as well [51,52]. This is due to the extreme stability of the FeIII-EDTA complex [53-56]. Therefore, characterizing the intrinsic reactivity of very reactive Fe0 material such as steel wool specimens (Fe0 SW) was very challenging [51]. In other words, developing a tool to reliably characterize the intrinsic reactivity of Fe0 SW would be a progress for the Fe0 remediation community. The purpose of this study was to develop an experimental method to characterize the intrinsic reactivity of Fe0 SW using their initial dissolution in 1,10-Phenanthroline (ortho-Phenanthroline or Phen). Nine (9) commercial Fe0 SW are used. The selection of Phen is justified by the extreme stability of the FeII-Phen complex [53,55]: (i) avoiding any further oxidation of FeII from Fe0 dissolution and (ii) non-addressing any FeIII species already available in the system [52]. Parallel experiments using EDTA are performed and the results are comparatively discussed.


Comments 3: Table. 1. Units of elemental composition should be provided (%). Could the impurities (in different proportions) influence the oxidation progress of the Fe0 samples? The same with the diameter, which is probably influencing the oxidation reaction, what is the aim of comparing samples with different sizes if then, diameter is not taking into account in the discussion? What is the aim of providing the information of the origin of all samples? Not clear at all.

The unit was in (mg/L) but intentionally omitted and replaced by computed % for easiness of comparing composition.

The impurities in different propositions were proven to have an insignificant effect, especially in such minute composition (expressed in prospective unpublished work)

The diameter strictly defines material (SW) grades; hence, all discussions regarding behavioral trends concerning steel wool grade implied the diameter.

The aim of providing information on the origin of all samples was based on identifying locally available materials and their origin. This will enable future implications on field studies when selecting suitable grades for specific remediation tasks with respect to cost issues and necessary economies of scale in their production.


Reviewer 2 Report

The manuscript ”A Novel and Facile Method to Characterize the Suitability of Metallic Iron for Water Treatment” has a very interesting topic: characterization of the intrinsic reactivity of Fe(0) materials. For the research group headed by Dr. Noubactep this work it is certainly the continuity of numerous previous investigations on developing and revisiting tools for the characterization of Fe(0) reactivity (the EDTA test, the methylene blue discoloration method). With this work, the authors present a new, simple and affordable experimental protocol that can be applied for the characterization of Fe(0) intrinsic reactivity, regardless of its type (e.g.,  granular or filamentous), more rapid, accurate and reliable than the EDTA test. The manuscript is written in a well-organized and systematic way, with a necessary chronological overview on the currently existing methods on characterization of Fe(0) reactivity. The objectives of this study, clearly presented in the ”Introduction” section, are followed consistently throughout the paper, and the obtained results are consistent. Therefore, I would recommend publishing this paper after considering the following suggestions:

 

1) Maybe adding photographs of the 9 tested steel wool materials and/or of the experimental design (the beakers) would be useful;

 

2) Table 1, line 111: ”Al, As and Zn were not detected (n.d.).”

I believe this information could be omitted from the table caption, since Al, As and Zn were not included in the ”elemental composition” section of the table.

 

3) Line 124: Section ”2.3.2. Iron dissolution”

I am sure that this study will become the experimental protocol for the ”phenantroline-test”. Therefore, I would suggest providing as much detail as possible about the quiescent experimental protocol of iron dissolution (e.g.: narrow beakers, not shaken, protected from sunlight etc.), instead of sending the reader to reference 45, which is not open access. It would be also important to know how was the steel wool added in the 50 mL solution; probably cut in small pieces, but how small?

 

4) Line 141: ” Therefore, the goal of this study is to identify the time frame for the linearity of Eq. 1.”

I believe this is an extremely important outcome of this study: how long should be the duration of the phenantroline-test”? Therefore, an exact answer should be given in the ”Conclusion” section. In the present form of the ”Conclusion” we have a rather vague time: ” takes just about one day”. Please give a more exact duration (24 h?).

 

5) Line 148: ”It is seen that all 9 specimens are made up of at least 98.6 % Fe”

Table 1 shows that SW 5 contains the smallest percentage of Fe, only 98.37%

 

6) Line 156: ”Comparison of the dissolution rate of SW9 in ……. solutions quiescent conditions for 83 h.

As I see from Fig.1, the duration of experiment was 100 h, not 83 h.

Author Response

The manuscript ”A Novel and Facile Method to Characterize the Suitability of Metallic Iron for Water Treatment” has a very interesting topic: characterization of the intrinsic reactivity of Fe(0) materials. For the research group headed by Dr. Noubactep this work it is certainly the continuity of numerous previous investigations on developing and revisiting tools for the characterization of Fe(0) reactivity (the EDTA test, the methylene blue discoloration method). With this work, the authors present a new, simple and affordable experimental protocol that can be applied for the characterization of Fe(0) intrinsic reactivity, regardless of its type (e.g., granular or filamentous), more rapid, accurate and reliable than the EDTA test. The manuscript is written in a well-organized and systematic way, with a necessary chronological overview on the currently existing methods on characterization of Fe(0) reactivity. The objectives of this study, clearly presented in the ”Introduction” section, are followed consistently throughout the paper, and the obtained results are consistent. Therefore, I would recommend publishing this paper after considering the following suggestions:

Many thanks for this evaluation!


1) Maybe adding photographs of the 9 tested steel wool materials and/or of the experimental design (the beakers) would be useful;

We are trying to have a picture with good resolution. This idea is also good for the graphical abstract!


2) Table 1, line 111: ”Al, As and Zn were not detected (n.d.).”

I believe this information could be omitted from the table caption, since Al, As and Zn were not included in the ”elemental composition” section of the table.

Done, thanks!

3) Line 124: Section ”2.3.2. Iron dissolution”

I am sure that this study will become the experimental protocol for the ”phenantroline-test”. Therefore, I would suggest providing as much detail as possible about the quiescent experimental protocol of iron dissolution (e.g.: narrow beakers, not shaken, protected from sunlight etc.), instead of sending the reader to reference 45, which is not open access. It would be also important to know how was the steel wool added in the 50 mL solution; probably cut in small pieces, but how small?

The following is added:

SW materials were cut into 2-3 cm, satisfying the prescribed weight and submerged in 50 ml graduated plastic cell-star tubed (narrow beakers) containing respective chelate solution (EDTA and O-Phen). All experiments were protected from light.


4) Line 141: ” Therefore, the goal of this study is to identify the time frame for the linearity of Eq. 1.”

I believe this is an extremely important outcome of this study: how long should be the duration of the phenantroline-test”? Therefore, an exact answer should be given in the ”Conclusion” section. In the present form of the ”Conclusion” we have a rather vague time: ” takes just about one day”. Please give a more exact duration (24 h?).

16 hours, it is now specified, thanks!

5) Line 148: ”It is seen that all 9 specimens are made up of at least 98.6 % Fe”

Table 1 shows that SW 5 contains the smallest percentage of Fe, only 98.37%

Done, Thanks

6) Line 156: ”Comparison of the dissolution rate of SW9 in ……. solutions quiescent conditions for 83 h.

As I see from Fig.1, the duration of experiment was 100 h, not 83 h.

100 h is indicated from the graph based on the scale using for plotting (i.e 10 h interval). But the actual experimental duration was 83 h as elaborated in the caption.

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