Technological Challenges of Phosphorus Removal in High-Phosphorus Ores: Sustainability Implications and Possibilities for Greener Ore Processing

Round 1

Reviewer 1 Report

The paper is very wide ranging in the topics it covers and so the large number of references.

Generally the paper is well written although sentences often are very long with multiple ideas in them. They could be shortened.

Considering the length of the paper and the number of references, section 7 on recent efforts to remove P from iron ores is not a particularly extensive coverage of the literature, especially acid leaching.

I understand that this is a sustainability journal but I doubt that the ideas in section 11, to recover P from iron ores for use as a fertilizer, could not be done economically.

A major problem is with the numbering of references in the text. 
In line 35, references for fertility of soils is given as [2-6]. BUT in the reference list there are 6 references given [2-7] so all subsequent references are out by 1. The easiest fix is to remove one of the [2-7] references from the reference list.

lines 95 - 111   Use pm OR Å but do not use both.

Table 1  Remove %Fe and %P from the table as they are the units given at the top.  Convert %P2O5 to %P.

Table 2  Remove solubility data from the top of table.
            Fit hydroxyapatite in properly. 
            In the footnote  replace constitution with composition.

Table 3  subscript 4  second entry.

line 86  Add be      prone to be present

Spelling errors noted. 
line 113  maintaining,  line 146  over, lines 412 & 423 the   line 685 phosphorus

Reference list:  Generally the references are done well. Some minor changes required.
In paper titles use capitals OR lower case.
Line 734, 846 & 882  Remove the capitals
Subscripts required lines 802, 829, 888, 897, 1023, 1027, 1033, 10381046, 1053, 1063, 1067, 1074, 1095, 1111, 1122, 1123, 1131, …………..
Superscripts required 1063, 1077, 1095, 1123 ………………...

Author Response

SUSTAINABILITY MDPI ARTICLE, REVIEWER 1 COMMENTS AND RESPONSES TO REVIEWER'S COMMENTS ROUND 1

Reviewer 1: General Comments:

The paper is very wide ranging in the topics it covers and so the large number of references.

Reviewer 1 Comment 1:

Generally, the paper is well written although sentences often are very long with multiple ideas in them. They could be shortened.

Response to Reviewer 1 Comment 1:

Efforts have now been made to shorten sentences. However, in some cases it has been difficult to shorten a few sentences without losing intended meaning or the trend of the arguments.

Reviewer 1 Comment 2:

Considering the length of the paper and the number of references, section 7 on recent efforts to remove P from iron ores is not a particularly extensive coverage of the literature, especially acid leaching.

Response to Reviewer 1 Comment 2:

I totally agree with your esteemed observation.

However, acid leaching had been almost synonymous with leaching of iron ores for P removal.  It had been the principal leaching method and is well-known. Hence a robust discussion of the acid leaching method for P-removal/recovery was intentionally avoided to maintain focus on the challenge of sustainable P-recovery from high-P iron ores. In this regard works on acid leaching with results most relevant to the focus of the review was discussed extensively.

Reviewer 1 Comment 3:

I understand that this is a sustainability journal but I doubt that the ideas in section 11, to recover P from iron ores for use as a fertilizer, could not be done economically.

Response to Reviewer 1 Comment 3:

I totally agree with your perspective and actually argued in this line in lines 697 to 699 of the manuscript with this statement; “Hence, development of technologies for sustainable valorization of high phosphorus iron ores through phosphorus removal and recovery can provide an alternative source for phosphorus thus diluting the demand for phosphate rocks with significant global economic, environmental and socio-political benefits.”

The recovery of phosphorus for agricultural purposes from high-phosphorus iron ore beneficiation  is a side product which reduces the cost of the high P-iron ore beneficiation process.

Similar strategy is employed in waste-water/sewage treatment in which the major aim is to treat water but recovery of phosphorus from the treatment system for agricultural use becomes an added revenue source which enhances the economy of the treatment process. More robust analysis of the economic prospects and challenges of this strategy have been highlighted in these references

Ueno, Y., & Fujii, M. (2001). Three years experience of operating and selling recovered struvite from full-scale plant. Environmental Technology, 22(11), 1373-1381.

Li, B., Boiarkina, I., Yu, W., Huang, H. M., Munir, T., Wang, G. Q., & Young, B. R. (2019). Phosphorous recovery through struvite crystallization: challenges for future design. Science of the Total Environment, 648, 1244-1256.

Reviewer 1 Comment 4:

A major problem is with the numbering of references in the text.  
In line 35, references for fertility of soils is given as [2-6]. BUT in the reference list there are 6 references given [2-7] so all subsequent references are out by 1. The easiest fix is to remove one of the [2-7] references from the reference list.

Response to Reviewer 1 Comment 4:

The mis-match in the references have now been corrected. It was due to the URL for reference one shifting during formatting to wrongly appear as Ref No.5. This has now been corrected.

Reviewer 1 Comment 5:

lines 95 - 111   Use pm OR Å but do not use both.

Response to Reviewer 1 Comment 5:

The pm unit has now been uniformly adopted in discussions of ionic radii and inter-ionic distances. The earlier use of both units was due to different authors reporting their values in different units. I had attempted to give the reader an idea of the conversion scale between the two units in Line 111. This has now been deleted and all values reported in angstroms converted to pm in discussion in this work

Reviewer 1 Comment 6:

Table 1  Remove %Fe and %P from the table as they are the units given at the top.  Convert %P2O5 to %P.

Response to Reviewer 1 Comment 6:

Thanks do much for pointing these out.

The conversions have now been made and phosphorus content is uniformly presented in %P in Table 1. The superfluous insertion of %P2O5 and %P in the Table have now been deleted.

Reviewer 1 Comment 7:

Table 2  Remove solubility data from the top of table.
            Fit hydroxyapatite in properly. 
            In the footnote  replace constitution with composition.

Response to Reviewer 1 Comment 7:

Solubility data has been removed from the top of column 3 of Table 2

The width of Column 1 has been adjusted so that hydroxyapatite now fits into a single line.

The footnote has been updated as suggested.

Reviewer 1 Comment 8:

Table 3  subscript 4  second entry.

Response to Reviewer 1 Comment 8:

The “4” in both items have been subscripted.

Reviewer 1 Comment 9:

line 86  Add be      prone to be present

Response to Reviewer 1 Comment 9:

Thanks for pointing out this omission. “be” has now been inserted.

Reviewer 1 Comment 10:

Spelling errors noted.  
line 113  maintaining, 

 line 146  over,

lines 412 & 423 the  

line 685 phosphorus

Response to Reviewer 1 Comment 10:

The spelling errors have all been  now been corrected.

Reviewer 1 Comment 11:

Reference list:  Generally the references are done well. Some minor changes required.
In paper titles use capitals OR lower case.
Line 734, 846 & 882  Remove the capitals

Response to Reviewer 1 Comment 11:

The cases were capital case letters were used in paper titles have now been amended. The lower case has been uniformly adopted for all the manuscript references.

Reviewer 1 Comment 12:
Subscripts required lines 802, 829, 888, 897, 1023, 1027, 1033, 1038,1046, 1053, 1063, 1067, 1074, 1095, 1111, 1122, 1123, 1131, …………..

Response to Reviewer 1 Comment 12:

The references have now been carefully cross-checked and subscripts have now been effected in all these lines and other lines were it was necessary.

Reviewer 1 Comment 13:
Superscripts required 1063, 1077, 1095, 1123 ………………...

Response to Reviewer 1 Comment 13:

The references have now been carefully cross-checked and superscripts have now been effected in all these lines and other lines were it was necessary.

Author Response File: Author Response.pdf

Reviewer 2 Report

Nice paper on Phosphorus Removal in High Phosphorus Ores assessing Sustainability Implications and aiming Greener Ore Processing.

Extensive and comprehensive review, properly done, well supported by abundant and recent references.

Very good Introduction, with a sound state of art and presenting the main goals of the paper.

Author not only review recent past and present of the focused thematics but also the near future expected developments.  

Theoretical and empirical approaches are correct and well explained and discussed. 

Just a few comments to improve this excellent paper:       :

Author Response

SUSTAINABILITY MDPI ARTICLE, REVIEWER 2 COMMENTS AND RESPONSES TO REVIEWER'S COMMENTS ROUND 1

Reviewer 2, General Comments:

Nice paper on Phosphorus Removal in High Phosphorus Ores assessing Sustainability Implications and aiming Greener Ore Processing.

Extensive and comprehensive review, properly done, well supported by abundant and recent references.

Very good Introduction, with a sound state of art and presenting the main goals of the paper.

Author not only review recent past and present of the focused thematics but also the near future expected developments.  

Theoretical and empirical approaches are correct and well explained and discussed. 

Just a few comments to improve this excellent paper:      

Reviewer 2 Comment 1:

Mineral names must be written according to uniform criteria (not sometimes goethite, others Goethite, for instance);

Response to Reviewer 2 Comment 1:

Mineral names have now been corrected and harmonized throughout the manuscript.

Reviewer 2 Comment 2:

Explain what means some components in Bold, on Tables 2 and 3

Response to Reviewer 2 Comment 2:

Thanks so much for pointing out this error.

The appearance of these items Bold type was a mistake and has no significance. Normal type case has now been affected.

Reviewer 2 Comment 3:

Conclusions are too much straightforward. 

Response to Reviewer 2 Comment 3:

The conclusions section has now been enhanced by highlighting the approach suggested for use in the main body of the article for addressing the challenge.

Author Response File: Author Response.pdf