Thermal Behavior of Hydrated Iron Sulfate in Various Atmospheres
, Nour-Eddine Menad 2, Etleva Ostrosi 3, Seit Shallari 4, Frederic Diot 1, Eric Allain 1 and Jacques Yvon 1Round 1
Reviewer 1 Report
The authors ought to be congratulated on producing a fine piece of work. The manuscript covers a well-defined topic nicely. The introduction sets an appropriate context for the reader, the methods are very suitable for the investigation, and a sensible range of techniques were cross-checked to validate the conclusions. This is good work.
This reviewer would like to have a few points clarified;
Of the two samples (the IND and the LAB samples), the IND sample is proven to be essentially-pure FeSO4.H2O. This is excellent. The LAB sample is contaminated by ~half FeIIISO4.OH. The fact that this FeIII compound is formed by drying ferrous sulfate heptahydrate in air is very pertinent, and should definitely be reported. But the apparent activation energy of dehydration for the LAB sample under N2 is not reflective of the activation energy of FeSO4, nor of FeIIISO4.OH, nor of the activation energy in any foreseeable industrial process (an industrial process would either be performed wholly in air, or wholly in N2, not in air up to 150°C then in N2 up to ~600°C). Please justify what utility the LAB sample brings in the isothermal decomposition section (section 3.3)?
Non-isothermal decomposition of iron sulfate yielded Fe2O3 by 1000°C, as proven very neatly by the authors. However, isothermal decomposition at ~500-600°C appears to reach a plateau of consistent mass loss short of the Fe2O3 theoretical composition. Was there any XRD or Mossbauer spectroscopy done of the products of the isothermal decomposition to verify that the decomposition did, in fact, proceed completely to Fe2O3 in these tests?
In Line 130, you refer to the transformation of FeSO4.OH into anhydrous ferric sulfate upon heating under nitrogen. The stoichiometry of this transformation is not clear to this reviewer; anhydrous ferric sulfate is Fe2(SO4)3, so there seems to be a sulfur deficit in the indicated transformation. It seems possible that you meant that a portion of the FeSO4.OH is transformed to Fe2(SO4)3, with the remainder transformed to Fe2O3 [viz. 6 FeSO4.OH --> 2 Fe2(SO4)3 + Fe2O3 + 3 H2O]. Or possibly there is a typo, and you intended that it transforms to a ferric oxysulfate, Fe2O(SO4)2? Can you please provide a chemical equation for the process you intended, to alleviate my confusion?
There are also a few items of grammar or clarity that this reviewer would encourage the authors to consider;
Line 15; "titanium dioxide and surface treatment" should be "titanium dioxide production and surface treatment".
Line 20, 88 & 92; This reviewer prefers that acronyms be enclosed in brackets rather than apostrophes after they are introduced. But my preferences aside, if you are to use apostrophes, please be consistent with either a single or a double, rather than mixing the two.
Line 33; Please remove the "...".
Line 46; "consistent" should be assumed of any review - perhaps you meant to say "thorough", or "extensive", or "holistic"?
Line 48; "As mentioned early" should be "As mentioned earlier".
Line 50; "a few part of" is unclear. Either "a few parts of" or "a small part of". If you have an approximate percentage that is reused, that would make your claim even more convincing.
Line 53; H2SO4 is sulfuric acid. Hydrosulfuric acid is a different chemical. Delete the "hydro".
Line 77; "samples were subjected to different analysis in order to observe their composition" is not the most clear way to present that you mean. Consider "samples were subjected to a variety of analyses in order to determine their composition".
Line 78; You state that Fe(II) was determined by "chemical analysis". I'm sure this is true, but can you please specify what chemical analysis this was? This reviewer would assume a digestion followed by dichromate titration, but there are many other techniques, so please specify.
Line 85; "occurred at about 150°C" should be "occurred by 150°C".
Lines 100-103; You reference XRD and Mossbauer results. Consider including them as figures.
Figure 2 and Figure 3; Please state the heating rate employed - Figures 4 and 5 demonstrate the importance of heating rate in these experiments, so it needs to be noted for each experiment.
Line 106-107; You mention the valence of iron in N2 and in Cl2+O2. What was the results in straight O2?
Line 109; "temperatures close to 675°C" should be "temperatures up to 675°C".
Line 129; "This can be only attributed to" should be "This can be attributed to".
Line 136; "higher and /or equal to" should be "higher than and/or equal to".
Line 138; "in order to avoid" is a little too confident. Consider "in order to minimise" instead.
Figure 9; You show decomposition rates as a function of temperature. Can you please elaborate a little in the text on how you quantified the decomposition rate? Was it an exponential decay function fitted to a section of the mass loss curve, or rate at a defined degree of reaction completion, or some other quantification? A single sentence of clarification would be sufficient to assuage my curiosity.
Line 183; "and their full decomposition depends on the heating rate in the furnace" is a little ambiguous, since full decomposition is eventually achieved regardless of heating rate. I believe you mean "and the final temperature of their full decomposition depends on the heating rate in the furnace".
Overall, a well-written and clearly-articulated paper. In this reviewer's opinion, once these minor matters are addressed the paper shall be fit for publication in Metals.
Author Response
Response to the Comments of Reviewers
Reviewer 1
Thank You for your remarks to improve the quality of this paper. You find below our responses and corrections, when necessary, regarding to your queries.
Additional modifications were also made according to the Editor’s remarks and suggestions.
Reviewer #1: The authors ought to be congratulated on producing a fine piece of work. The manuscript covers a well-defined topic nicely. The introduction sets an appropriate context for the reader, the methods are very suitable for the investigation, and a sensible range of techniques were cross-checked to validate the conclusions. This is good work.
This reviewer would like to have a few points clarified:
Of the two samples (the IND and the LAB samples), the IND sample is proven to be essentially-pure FeSO4.H2O. This is excellent. The LAB sample is contaminated by ~half FeIIISO4.OH. The fact that this FeIII compound is formed by drying ferrous sulfate heptahydrate in air is very pertinent, and should definitely be reported. But the apparent activation energy of dehydration for the LAB sample under N2 is not reflective of the activation energy of FeSO4, nor of FeIIISO4.OH, nor of the activation energy in any foreseeable industrial process (an industrial process would either be performed wholly in air, or wholly in N2, not in air up to 150°C then in N2 up to ~600°C). Please justify what utility the LAB sample brings in the isothermal decomposition section (section 3.3)?
Good point! However, authors would like to mention that the tests of heating samples up to 150° C were performed for the purpose of obtaining iron (III) compounds such as FeIIISO4·OH which is suitable for the synthesis of alkali ferrates (iron compounds containing iron at hexavalent state). Furthermore, a previous investigation of several stock-pile samples of iron sulfate heptahydrate showed the oxidation possibility of Fe(II) into Fe(III).
Indeed, such a decomposition process at large scale must be performed in air (at least, from the economic point of view). But, as you may have noticed, it took several weeks to carry out these experimental tests (with equipment maintenance). Hence, to minimize the effect of the “atmosphere air composition, especially humidity”, the use of pure nitrogen was favorably considered. In fact, in the beginning of experimental tests, different intersect kinetics for the decomposition of IND sample (100 % Fe(II)) and LAB sample (about 45 % Fe(II) and 55 % Fe(III)) were suspected. In addition, the use of oxygen during the IND sample treatment resulted certainly in the oxidation of Fe(II) into Fe(III) with the temperature rise under non-isothermal treatment. At the end of this kinetic investigation, it was obvious that the thermal behaviors of both the samples were similar.
However, a sentence for the use of LAB sample in the isothermal decomposition was inserted.
Non-isothermal decomposition of iron sulfate yielded Fe2O3 by 1000°C, as proven very neatly by the authors. However, isothermal decomposition at ~500-600°C appears to reach a plateau of consistent mass loss short of the Fe2O3 theoretical composition. Was there any XRD or Mossbauer spectroscopy done of the products of the isothermal decomposition to verify that the decomposition did, in fact, proceed completely to Fe2O3 in these tests?
You are right. The XRD results of the final products issued from treatment at 560 and 575 °C under isothermal conditions showed the presence of Fe2O3 as only crystallized phase of iron bearing compounds.
However, as mentioned in the text, The IND sample contains about 31 % Fe, that is lower than theoretical value of iron (32.87 % Fe) in FeSO4·H2O. This can partially explain the mass loss short for IND sample lower than that of LAB sample, although the mass loss for the transformation of FeSO4·H2O into FeSO4·is higher in the case of IND sample.
In Line 130, you refer to the transformation of FeSO4.OH into anhydrous ferric sulfate upon heating under nitrogen. The stoichiometry of this transformation is not clear to this reviewer; anhydrous ferric sulfate is Fe2(SO4)3, so there seems to be a sulfur deficit in the indicated transformation. It seems possible that you meant that a portion of the FeSO4.OH is transformed to Fe2(SO4)3, with the remainder transformed to Fe2O3 [viz. 6 FeSO4.OH --> 2 Fe2(SO4)3 + Fe2O3 + 3 H2O]. Or possibly there is a typo, and you intended that it transforms to a ferric oxysulfate, Fe2O(SO4)2? Can you please provide a chemical equation for the process you intended,to alleviate my confusion?
That’s also a good point! The most probable product of the FeSO4·H2O transformation is Fe2O(SO4)2. The modification was included in the revised manuscript.
The chemical reactions for both transformations should be:
FeSO4(s)→ Fe2O3(s) + SO2(g) (1)
2FeSO4(s)→ Fe2O3(s) + 2SO2(g) + 1/2O2(g) (2)
and
2FeSO4·OH(s) → Fe2O(SO4)2(s) + H2O(g) (3)
Fe2O(SO4)2(s) → Fe2O3(s) + 2SO3(g) (4)
Authors would like to point out that in absence of sufficient elements that could confirm the formation of Fe2O(SO4)2, the insertion of these equations in the article was considered unnecessary.
There are also a few items of grammar or clarity that this reviewer would encourage the authors to consider:
Line 15; "titanium dioxide and surface treatment" should be "titanium dioxide production and surface treatment".
Modification is made.
Line 20, 88 & 92; This reviewer prefers that acronyms be enclosed in brackets rather than apostrophes after they are introduced. But my preferences aside, if you are to use apostrophes, please be consistent with either a single or a double, rather than mixing the two.
Modification is made.
Line 33; Please remove the "...".
Modification is made.
Line 46; "consistent" should be assumed of any review - perhaps you meant to say "thorough", or "extensive", or "holistic"?
Modification is made.
Line 48; "As mentioned early" should be "As mentioned earlier".
Modification is made.
Line 50; "a few part of" is unclear. Either "a few parts of" or "a small part of". If you have an approximate percentage that is reused, that would make your claim even more convincing.
Modification is made.
Line 53; H2SO4 is sulfuric acid. Hydrosulfuric acid is a different chemical. Delete the "hydro".
Modification is made.
Line 77; "samples were subjected to different analysis in order to observe their composition" is not the most clear way to present that you mean. Consider "samples were subjected to a variety of analyses in order to determine their composition".
Modification is made.
Line 78; You state that Fe(II) was determined by "chemical analysis". I'm sure this is true, but can you please specify what chemical analysis this was? This reviewer would assume a digestion followed by dichromate titration, but there are many other techniques, so please specify.
Modification is made.
Line 85; "occurred at about 150°C" should be "occurred by 150°C".
Modification is made.
Lines 100-103; You reference XRD and Mossbauer results. Consider including them as figures.
A reference is added for this item.
Figure 2 and Figure 3; Please state the heating rate employed - Figures 4 and 5 demonstrate the importance of heating rate in these experiments, so it needs to be noted for each experiment.
The heating rates are included in Figures 2 and 3 of the revised manuscript. The heating rates for the non-isothermal part of the sample treatment in nitrogen (section 3.3.) were also inserted.
Line 106-107; You mention the valence of iron in N2 and in Cl2+O2. What was the results in straight O2?
As it is mentioned in the previous paragraphs and Table 1, the heating of FeSO4·H2O in air (PO2 » 0.21 atm) at 150 °C led to partial oxidation of Fe(II) into (Fe(III).
Line 109; "temperatures close to 675°C" should be "temperatures up to 675°C".
Modification is made.
Line 129; "This can be only attributed to" should be "This can be attributed to".
Modification is made.
Line 136; "higher and /or equal to" should be "higher than and/or equal to".
Modification is made.
Line 138; "in order to avoid" is a little too confident. Consider "in order to minimise" instead.
Modification is made.
Figure 9; You show decomposition rates as a function of temperature. Can you please elaborate a little in the text on how you quantified the decomposition rate? Was it an exponential decay function fitted to a section of the mass loss curve, or rate at a defined degree of reaction completion, or some other quantification? A single sentence of clarification would be sufficient to assuage my curiosity.
The mean reaction rate is defined for the decomposition degree corresponding to 12.5 % ≤ ML ≤ 22.5 % and it is added in the revised manuscript.
Line 183; "and their full decomposition depends on the heating rate in the furnace" is a little ambiguous, since full decomposition is eventually achieved regardless of heating rate. I believe you mean "and the final temperature of their full decomposition depends on the heating rate in the furnace".
Modification is made.
Overall, a well-written and clearly-articulated paper. In this reviewer's opinion, once these minor matters are addressed the paper shall be fit for publication in Metals.
Again, authors would like to thank you for reviewing this manuscript. Your remarks and positive opinion with respect to our work are very much appreciated.
Reviewer 2 Report
Dear Authors,
this paper uses TG for iron sulfate transitions with various atmosphere and this topic is essential.
I have checked carefully and this paper is fine to publish only small following correction.
under chloride atmosphere, chloride reaction is not happened?
Reference 11, Chu, M.-S.; Ying, Z.-W.; Liu, Z.-G. -> Chu, M.S.; Ying, Z.W.; Liu, Z.G.
Reference 12, Oolitic -> oolitic
Author Response
Response to the Comments of Reviewers
Reviewer 2
Thank You for your remarks to improve the quality of this paper. You find below our responses and corrections regarding to your queries.
Additional modifications were also made according to the Editor’s remarks and suggestions.
Dear Authors,
This paper uses TG for iron sulfate transitions with various atmosphere and this topic is essential.
I have checked carefully and this paper is fine to publish only small following correction.
Under chloride atmosphere, chloride reaction is not happened?
In this paper we developed only the results under oxygen and oxygen + chlorine atmosphere. The chlorination reaction takes place also in the chlorine atmosphere.
Reference 11, Chu, M.-S.; Ying, Z.-W.; Liu, Z.-G. -> Chu, M.S.; Ying, Z.W.; Liu, Z.G.
Yes, the correction is made.
Reference 12, Oolitic -> oolitic
Yes, the correction is made.
Reviewer 3 Report
Was just one sample tested for each of the experimental conditions? There don't seem to be any uncertainty levels in the individual experimental results. Industrial samples are rarely consistent enough to justify conclusions from a single experiment.
Author Response
Response to the Comments of Reviewers
Reviewer 3
Thank You for your remarks to improve the quality of this paper. You find below our responses to your queries.
Additional modifications were also made according to the Editor’s remarks and suggestions.
Was just one sample tested for each of the experimental conditions? There don't seem to be any uncertainty levels in the individual experimental results. Industrial samples are rarely consistent enough to justify conclusions from a single experiment.
This work is a part of the results obtained from the large valorization program of the ferrous sulfate generated by the TiO2 production and the surface treatment of steel. A good number of industrial samples (seven samples) of ferrous sulfate hepta and mono hydrate were collecte).
They had similar composition and purity since the ferrous sulfates (FeSO4·7H2O and FeSO4·H2O) were separated from the treatment liquor by the crystallization method which assures a higher purity than the other physical routes of separation of the constituents resulting from hydrometallurgical treatments.
