Processing of Phosphoric Solid Waste by Humic Acid Leaching Method

Round 1

Reviewer 1 Report

It would be useful if you could specify the novelty in the abstract and the conclusions section.

Materials and Methods section: The description should be sufficiently detailed to ensure an understanding of research results.

It would be useful if you could specify the experimental design.

There is no discussion. In the results and discussion section, only some descriptive references and the most relevant results obtained are presented.

The conclusions are too general and do not represent a contribution to the problem. The most important quantitative and qualitative values ​​​​obtained from this research could be included in the conclusions. It would be useful if you could specify the process efficiency in the conclusions.

Author Response

Reviewer 1

It would be useful if you could specify the novelty in the abstract and the conclusions section.

The scientific novelty of the article is the use of humic acid for leaching phosphoric solid waste, as opposed to traditional methods. This new method may offer improved efficiency, reduced environmental impact, and a potential alternative solution for the processing of phosphoric waste. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Materials and Methods section: The description should be sufficiently detailed to ensure an understanding of research results.

Additions have been made to the Materials and Methods section, taking into account the reviewer's comment. Corresponding changes have been made to the text of the manuscript (highlighted in red).

It would be useful if you could specify the experimental design.

Experimental design is described in the form of Figure 1.

There is no discussion. In the results and discussion section, only some descriptive references and the most relevant results obtained are presented.

Corresponding changes have been made to the text of the manuscript (highlighted in red).

The conclusions are too general and do not represent a contribution to the problem. The most important quantitative and qualitative values ​​​​obtained from this research could be included in the conclusions. It would be useful if you could specify the process efficiency in the conclusions.

The necessary changes have been made to the text of the Conclusion (highlighted in red).

Author Response File: Author Response.docx

Reviewer 2 Report

 

This paper introduces a method for recycling P from waste by humic acid leaching. The results might be of interest to relevant researchers. However, the authors should provide more scientific discussions in terms of physical chemistry in the process.

 

Line 104

The meaning of the numerator in the equation need to be explained. How to determine it by experiment?

 

Fig. 1

How to obtain the fraction of each phase by XRD? Explanation is needed.

 

Line 142

The reviewer could not understand the statement “phosphoric sludge and cottrel dust have an amorphous structure”. XRD suggests that both wastes contain several crystal phases. What is the amorphous structure?

 

Fig.2

The dependence of degree of decomposition on temperature is not quite clear. For example, in Fig.2a, the value decreases as the temperature increases. More explanation is needed.

 

Fig.4

The unit of T is degree C in this figure. Why not Kelvin? Data in Fig. 4 do not agree well with the data in Table 3.

 

Equation （3）

The authors should explain the meaning of each item in the equation.

 

Table 5

The authors should explain more the difference between P2O5 total and P2O5 assimilable in the table.

 

Author Response

Reviewer 2

This paper introduces a method for recycling P from waste by humic acid leaching. The results might be of interest to relevant researchers. However, the authors should provide more scientific discussions in terms of physical chemistry in the process.

Line 104. The meaning of the numerator in the equation need to be explained. How to determine it by experiment?

"Assimilable P2O5" or "available P2O5" refers to the portion of the total P2O5 in the fertilizer that can be taken up by plants and used for growth. It is the amount of phosphorus that is readily soluble in soil and can be absorbed by plant roots. The determination of assimilable P2O5 (Phosphorus Pentoxide) in fertilizers using Trilon B is a colorimetric method that measures the portion of the total P2O5 in the fertilizer that can be taken up by plants and used for growth.

Corresponding changes have been made to the text of the manuscript (highlighted in red).

Fig. 1. How to obtain the fraction of each phase by XRD? Explanation is needed.

The phase composition was studied using a Bruker D8 diffractometer (Germany), It uses X-rays to excite the atoms in a sample and measure the diffraction pattern of the X-rays as they pass through the sample (Shooting angle 3-180О degrees). The dif-fraction pattern can be used to determine the crystal structure of the sample and its atomic arrangements. The Bruker D8 diffractometer is equipped with a high-power X-ray source, a detector, and a goniometer (sample stage) that allows for precise posi-tioning of the sample in the X-ray beam. It can also be equipped with advanced data collection and analysis software that automates the process of data collection and analysis, making it an efficient and reliable tool for structural analysis.

 The data obtained were interpreted in the Diffrac Plus Search database. The software provides a search function that can match the peaks in the diffraction pattern to those in the database and provide a list of possible matches. The database of PDF2 radiographic standards was also used, containing about 450,000 cards of radiographs of known compounds, each of which contains diffraction, crystallographic and bibliographic data, as well as experimental conditions. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 142. The reviewer could not understand the statement “phosphoric sludge and cottrel dust have an amorphous structure”. XRD suggests that both wastes contain several crystal phases. What is the amorphous structure?

This is explained by the fact that no sharp diffraction peaks are observed, and the diffraction pattern is typically featureless or exhibits broad, weak diffraction peaks. The presence or absence of sharp, well-defined diffraction peaks in the XRD pattern is a good indicator of whether a solid is amorphous or crystalline. Crystalline solids exhibit sharp, well-defined diffraction peaks, while amorphous solids exhibit broad, weak, or featureless diffraction peaks. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Fig.2. The dependence of degree of decomposition on temperature is not quite clear. For example, in Fig.2a, the value decreases as the temperature increases. More explanation is needed.

This is explained by a growth in the proportion of the formation of insoluble CaHPO₄, which blocks the decomposed grains of the initial phosphate with a dense crystalline film. Since there is saturation of calcium phosphates with liquid-phase acid and actually the main reaction of acid decomposition.

Fig.4. The unit of T is degree C in this figure. Why not Kelvin? Data in Fig. 4 do not agree well with the data in Table 3.

In the figures, the temperature values are given in Celsius, but the Kelvin temperature was used in the calculations. Table 3 represents Reaction rate constant and confidence value of linear approximation from Figure 3. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Equation （3）. The authors should explain the meaning of each item in the equation.

Е_а - apparent activation energy; R - gas constant (8.314 J/mol·K); tgα - The tangent of the angle of inclination of the resulting straight line. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Table 5. The authors should explain more the difference between P2O5 total and P2O5 assimilable in the table.

Total P₂O₅ content refers to the amount of phosphorus pentoxide (P₂O₅) present in a sample. It represents the total amount of phosphorus available in the sample. Assimilable P₂O₅ refers to the portion of the total P₂O₅ that is readily available for plant uptake. This is the portion of the total P2O5 that can be absorbed and utilized by the plant for growth and development. The difference between total P₂O₅ content and assimilable P₂O₅ is that total P₂O₅ content represents the total amount of phosphorus present, while assimilable P₂O₅ represents the portion of that phosphorus that is available for plant uptake. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Author Response File: Author Response.docx

Reviewer 3 Report

The article “Processing of phosphoric solid waste by humic acid leaching method” is dealing with the leaching process of phosphoric sludge and cottrel dust.

However there are still many issues which require more explanation and consideration, including re-interpretation, reformulation and additional data.

If authors are willing to consider these comments and questions and perform an in-depth revision, the revised paper can be reconsidered for publication. I do not recommend publication of the manuscript in its present form.

A general and detailed list of comments and questions are addressed to the authors.

General comments

1. Statistics and error bars should be included in Tables and Figures since these are essential when comparing experimental data.  

2. More detailed information should be given on the analytical methods used and the experimental set-up of the applied leaching method.

3. What will be effect of repeating the leaching procedure at least two times with a new portion humic acid to overcome the problem of formation of a crystalline film which is blocked further leaching and to enhance the alfa value?

4. What is amorphous/crystalline ratio in both phosphorous wastes?

5. The relationship between reaction (1) describing the decomposition of the phosphate waste materials under study and the reaction in line 240 is not explained.

6.  The description of the internal diffusion should be better explained using a Figure with the different layers of particle and the frontal displacement of the  reaction zone.

7. Chemical composition of Karatau phosphorites should be included for the composition of both wastes under study.

8. The composition (impurities) of production phosphoric acid should be induced in the manuscript for comparison results of Table 5 for obtained H3PO4.

9. Conclusions should be adapted according to the comments of the reviewer.

10. What is the fate and amount of the insoluble resiude obtained after the leaching process (sustainability of the process)?

A detailed list of comments and questions   

1. Introduction

Line 30: “electrofilter” instead of “electric filter”.  

Line 32: “The chemical composition of both wastes is different” instead of “Their difference is in the chemical composition”.

Line 46: “in special installations” instead of “on special installations”.

Line 68: “during electrothermia”? Please comment.

Lines 79-80: “to the research plan” instead of “to the plan”.

 

2. Materials and Methods

Lines 91-94: References or used analytical methods should be included. Please comment.

Lines 92-93: “photometry” instead of “photometroc”. 

Line 93: “gravimetry” instead of “gravimetric”.

Line 93: “atomic absorption spectrophotometry” instead of “atomic absorption”

Line 94: “complexometry” instead of “complexometric”.

Lines 96-97: How pH and acid value of obtained humic acid are determined? Please comment.

Lines 98-104: More details should be given on the experimental set-up: amount of waste? Concentration of humic acid? Type and dimensions of vessel? Stirring or not?

A scheme of the experimental set-up should be included. Please comment.

Line 104: How P2O5 assimilable is determined? Applied analytical method should be described. Please comment.

3. Results and discussion

Line 117 Table 1: Statistics (standard deviations) should be included. Please comment.

Line 120: Chemical composition of Karatau phosphorites should be included in Table 1 for comparing results. Please comment.

Line 125: How free carbon is determined and what is the relationship with total C content in Table 1? Please comment.

Line 127: “X-ray diffraction analysis” instead of “the method of diffraction analysis”  

Line 128: “XRD results” instead of “the results of which”

Line 130: What are the broad bands in the XRD pattern? Please comment. Since XRD is given only information on the crystalline fraction the sum of detected crystalline minerals is presented as 100% but what is the amorphous fraction and what is the amorphous/crystalline ratio for both phosphorous wastes? Please comment. Reference pattern number from the ICDD International database should be included. Please comment.

Line 139: Are described as quartz? Are assigned to quartz? Please comment.

Lines 140-141: Is quartz an amorphous material?? Please comment.

Line 152: Will there be a reaction between HF and H3PO4? Please comment.

Line 161: Taken into account the main factors? Which ones? Please comment.

Line 163: ”conditions” instead of “parameters”.  

Line 163 Figure 2: Error bars should be included. Please comment. 

Lines 169: “In” instead of “On”.    

Lines 172: “In both acids to its lowering”. Not clear to me. Please comment.

Lines 175-177:” Since there is saturation of calcium phosphates with liquid-phase acid and actually the main reaction of acid decomposition”. Not clear to me. Please comment.

Lines 168-185: What will be the effect of repeating the leaching procedure at least two times with a new portion humic acid  to overcome the problem of formation of a crystalline film which is blocked further leaching? In that case alfa value will increase also at a lower PS-CD/HA ratio (1/1) and higher pH (pH= 1.92). Please comment.

Lines 186/190: What is the ratio crystalline phase / amorphous phase in both phosphorous wastes under study? Please comment.

Line 197: Equation (2) should be better explained in terms of the resistance to diffusion through the waste particles which controls reaction kinetics in a heterogeneous fluid- (spherical) particle system (eventually in supporting information).

Line 200: ”conditions” instead of “parameters”. 

Line 200 Figure 3: Error bars should be included. Please comment.

Line 206: a), b), c) and d) are not defined in the legend of Table 3. Please comment.

Lines 208-210: This statement is not clear to me.  Since maximum rate constant and trend is different depending on conditions:

A): increasing trend up to 80°C (=kmax), b): no clear trend with kmax at 80°C, c): no clear trend with kmax at 60°C and d) no clear trend with kmax at 60°C. Please comment.

Line 206: Error bars should be included in Figure 4. Please comment.

Line 233: Statistics are essential when comparing activation energies in Table 4 and should therefore be included. Please comment.

Line 240: The relationship between reaction (1) describing and the reaction in line 240 ((number) should be included) is not explained.  It is not clear why only CaHPO4 is formed and not CaF2 or other compounds. Please comment.

Line 246-250: the description of the internal diffusion should be better explained using a Figure with the different layers and the frontal displacement of the of the reaction zone. See also my comment on equation (2) in line 197. Please comment.

Lines 253-255: Ea values for decomposition reactions between natural phosphates with mineral acids (including conditions: acid concentration, ratio mineral/acid, time and pH) should be included in the manuscript for a better comparison. Please comment.   

Lines 263-270: Part of this paragraph should be transferred to Materials and Methods section. Please comment.

Line 264. Which type of filter was used? Please comment.

Line 271: Which analytical method was applied for determination P2O5 total and P2O5 assimilable? Please comment. What is the ratio between phosphoric acid and the insoluble residue under the given experimental conditions? Please comment.

Line 271: The composition (impurities) of production phosphoric acid should be induced in the manuscript for comparison with results of Table 5 for obtained H3PO4.   Please comment.

Line 274: “Content of potassium is more dominant present in phosphoric acid” instead of “Potassium is more in phosphoric acid”.

Line 280: “The XRF identified compounds are…” instead of “The XRD identified compounds in the form of …”.

Line 281: Apart of a crystalline fraction is there also an amorphous fraction and what is the ratio? Please comment.

 

4. Conclusions

Conclusion should be adapted taken in account the comments of the reviewer. Please comment.

Line 295: The composition (impurities) of production phosphoric acid should be included in the manuscript for comparison with results of obtained H3PO4 in Table 5. Please comment.

Line 297: See my comments on line 2946-250.

Line 300: “kinetic models are proposed for different variations. Not clear to me. Please comment.

 

                  

Author Response

Reviewer 3

The article “Processing of phosphoric solid waste by humic acid leaching method” is dealing with the leaching process of phosphoric sludge and cottrel dust.

However there are still many issues which require more explanation and consideration, including re-interpretation, reformulation and additional data.

If authors are willing to consider these comments and questions and perform an in-depth revision, the revised paper can be reconsidered for publication. I do not recommend publication of the manuscript in its present form.

A general and detailed list of comments and questions are addressed to the authors.

General comments

1. Statistics and error bars should be included in Tables and Figures since these are essential when comparing experimental data.

The comment is taken into account by the authors. Corresponding changes have been made to the Tables and Figures of the manuscript.

2. More detailed information should be given on the analytical methods used and the experimental set-up of the applied leaching method.

The comment is taken into account by the authors. Corresponding changes have been made to the structure of the manuscript.

3. What will be effect of repeating the leaching procedure at least two times with a new portion humic acid to overcome the problem of formation of a crystalline film which is blocked further leaching and to enhance the alfa value?

Repeating the leaching procedure with a new portion of humic acid can help to overcome the problem of the formation of a crystalline film that blocks further leaching and to enhance the alpha value. However, this is not economically advantageous and destroys the uniformity of the process. If you noticed, the process in its current form consists of several stages. Adding an additional stage will only increase the complexity of the process, which in turn is undesirable. The alpha value has reached a maximum of 91%, which is a good result in this case.

4. What is amorphous/crystalline ratio in both phosphorous wastes?

Characterization of the ratio of amorphousness and crystallinity in both phosphoric wastes is difficult, but we can say that these wastes have an amorphous structure. When a material is described as having an amorphous structure, it means that the atoms within the material are not arranged in a regular, repeating pattern, as in a crystalline structure. Instead, the atoms are arranged in a random, disordered fashion. Amorphous materials do not have well-defined crystal planes, which makes them difficult to analyze using X-ray diffraction (XRD).

When it's said that phosphoric sludge and cottrel dust have an amorphous structure, it means that a portion of the material does not have a crystal structure that can be identified by XRD. It's possible that the material has a mixture of amorphous and crystalline phases.

5. The relationship between reaction (1) describing the decomposition of the phosphate waste materials under study and the reaction in line 240 is not explained.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

6. The description of the internal diffusion should be better explained using a Figure with the different layers of particle and the frontal displacement of the reaction zone.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

7. Chemical composition of Karatau phosphorites should be included for the composition of both wastes under study.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

8. The composition (impurities) of production phosphoric acid should be induced in the manuscript for comparison results of Table 5 for obtained H3PO4.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

9. Conclusions should be adapted according to the comments of the reviewer.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

10. What is the fate and amount of the insoluble resiude obtained after the leaching process (sustainability of the process)?

As can be seen from the results of chemical analysis and X-ray diffraction analysis, phosphoric anhydride is present in the insoluble residue in an amount of 14%, of which more than 8% is in the form assimilated by plants. In addition, potassium, aluminum, and magnesium-containing compounds are found in the composition. The reaction shows that the main part is occupied by calcium compounds in the form of calcium humates. This means that the insoluble residue can be used as an organomineral fertilizer of the quality of a simple superphosphate.

A detailed list of comments and questions  

1. Introduction

Line 30: “electrofilter” instead of “electric filter”. 

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 32: “The chemical composition of both wastes is different” instead of “Their difference is in the chemical composition”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 46: “in special installations” instead of “on special installations”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 68: “during electrothermia”? Please comment.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Lines 79-80: “to the research plan” instead of “to the plan”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

2. Materials and Methods

Lines 91-94: References or used analytical methods should be included. Please comment.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Lines 92-93: “photometry” instead of “photometroc”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 93: “gravimetry” instead of “gravimetric”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 93: “atomic absorption spectrophotometry” instead of “atomic absorption”

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 94: “complexometry” instead of “complexometric”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Lines 96-97: How pH and acid value of obtained humic acid are determined? Please comment.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Lines 98-104: More details should be given on the experimental set-up: amount of waste? Concentration of humic acid? Type and dimensions of vessel? Stirring or not? A scheme of the experimental set-up should be included. Please comment.

The comment has been corrected. The experimental setup and the stages of the experiments are shown in Figure 1. A magnetic stirrer of the IKA brand was used to stir the reaction mass. Filtration was carried out using a KNF vacuum pump at a pressure of 0.06 MPa. Glassware has been used for as reaction vessels, Erlenmeyer flasks for sampling, chemical analysis and solution heating.

Line 104: How P2O5 assimilable is determined? Applied analytical method should be described. Please comment.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

3. Results and discussion

Line 117 Table 1: Statistics (standard deviations) should be included. Please comment.

The value of the standard deviation is included in Table 1.

Line 120: Chemical composition of Karatau phosphorites should be included in Table 1 for comparing results. Please comment.

The chemical composition of Karatau phosphorites is included in Table 1 for comparison

Line 125: How free carbon is determined and what is the relationship with total C content in Table 1? Please comment.

Carbon was determined by the gas-volume method. The presence of carbon in both studied samples is associated with the use of coke in the thermal reduction of phosphorus in ore-thermal furnaces. The presence of carbon in Karatau phosphorites is associated with carbonate-containing minerals in the form of dolomite, calcite.

Line 127: “X-ray diffraction analysis” instead of “the method of diffraction analysis” 

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 128: “XRD results” instead of “the results of which”

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 130: What are the broad bands in the XRD pattern? Please comment. Since XRD is given only information on the crystalline fraction the sum of detected crystalline minerals is presented as 100% but what is the amorphous fraction and what is the amorphous/crystalline ratio for both phosphorous wastes? Please comment. Reference pattern number from the ICDD International database should be included. Please comment.

Characterization of the ratio of amorphousness and crystallinity in both phosphoric wastes is difficult, but we can say that these wastes have an amorphous structure. When a material is described as having an amorphous structure, it means that the atoms within the material are not arranged in a regular, repeating pattern, as in a crystalline structure. Instead, the atoms are arranged in a random, disordered fashion. Amorphous materials do not have well-defined crystal planes, which makes them difficult to analyze using X-ray diffraction (XRD).

When it's said that phosphoric sludge and cottrel dust have an amorphous structure, it means that a portion of the material does not have a crystal structure that can be identified by XRD. It's possible that the material has a mixture of amorphous and crystalline phases.

Reference samples from the PDF2 database are shown in the corresponding figures.

Line 139: Are described as quartz? Are assigned to quartz? Please comment.

More precisely, it will be "assigned to quartz". Fixed it.

Lines 140-141: Is quartz an amorphous material?? Please comment.

In these works, the study of the phase structure revealed that silicon occurs in the form of its amorphous variety. This is logical, since during the thermal processing of phosphate raw materials, along with coke and quartz, the structures of these compounds undergo changes. As it was written above, the low intensity of the diffraction waves of the samples under study suggests that they have an amorphous structure.

Line 152: Will there be a reaction between HF and H3PO4? Please comment.

This reaction roughly describes the ongoing process between phosphorus-containing waste and humic acids. According to the reaction, the solid phase is an insoluble residue in the form of calcium humate, the liquid phase is production phosphoric acid, and hydrogen fluoride can also be released as a gas phase.

Line 161: Taken into account the main factors? Which ones? Please comment.

Taking into account the main factors: time, temperature and PS-CD/HA ratio, pH of HA. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 163: ”conditions” instead of “parameters”. 

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 163 Figure 2: Error bars should be included. Please comment.

The comment has been corrected. Corresponding changes have been made to the Figure

Lines 169: “In” instead of “On”.  

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Lines 172: “In both acids to its lowering”. Not clear to me. Please comment.

An increase in the time and temperature of the process in both cases leads to a decrease in the alpha value. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Lines 175-177:” Since there is saturation of calcium phosphates with liquid-phase acid and actually the main reaction of acid decomposition”. Not clear to me. Please comment.

Rephrased to “Since in this case, the reaction mass is saturated with the production liquid-phase acid, which in turn proves the course of the acid leaching reaction.”

The above statement refers to the saturation reaction of calcium phosphates with liquid-phase acid, and the fact that this saturation is proof of the acid leaching reaction.

Lines 168-185: What will be the effect of repeating the leaching procedure at least two times with a new portion humic acid  to overcome the problem of formation of a crystalline film which is blocked further leaching? In that case alfa value will increase also at a lower PS-CD/HA ratio (1/1) and higher pH (pH= 1.92). Please comment.

Repeating the leaching procedure with a new portion of humic acid can help to overcome the problem of the formation of a crystalline film that blocks further leaching and to enhance the alpha value. However, this is not economically advantageous and destroys the uniformity of the process. If you noticed, the process in its current form consists of several stages. Adding an additional stage will only increase the complexity of the process, which in turn is undesirable. The alpha value has reached a maximum of 91%, which is a good result in this case.

Lines 186/190: What is the ratio crystalline phase / amorphous phase in both phosphorous wastes under study? Please comment.

As it was written, the characterization of the ratio of amorphousness and crystallinity in both phosphoric wastes is difficult, but we can say that these wastes have an amorphous structure. When a material is described as having an amorphous structure, it means that the atoms within the material are not arranged in a regular, repeating pattern, as in a crystalline structure. Instead, the atoms are arranged in a random, disordered fashion. Amorphous materials do not have well-defined crystal planes, which makes them difficult to analyze using X-ray diffraction (XRD).

When it's said that phosphoric sludge and cottrel dust have an amorphous structure, it means that a portion of the material does not have a crystal structure that can be identified by XRD. It's possible that the material has a mixture of amorphous and crystalline phases.

Line 197: Equation (2) should be better explained in terms of the resistance to diffusion through the waste particles which controls reaction kinetics in a heterogeneous fluid- (spherical) particle system (eventually in supporting information).

Reaction kinetics in a heterogeneous fluid-spherical particle system refers to the study of chemical reactions that occur between the fluid and the solid particles in the system. In this system, the reaction rate can be described by the Ginstling-Brounstein rate equation, which relates the reaction rate to the concentration of the reactants and other system parameters. In a heterogeneous fluid-spherical particle system, the reaction can occur both on the surface of the particles and in the fluid phase. The reaction rate on the particle surface can be described using surface reaction kinetics, while the reaction rate in the fluid phase can be described using fluid reaction kinetics. The overall reaction rate in the system can be obtained by combining the surface and fluid reaction rates, taking into account the mass transfer of reactants between the particle surface and the fluid phase.

Line 200: ”conditions” instead of “parameters”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 200 Figure 3: Error bars should be included. Please comment.

The comment has been corrected. Corresponding changes have been made to the Figure

Line 206: a), b), c) and d) are not defined in the legend of Table 3. Please comment.

Table 3-Reaction rate constant and confidence value of linear approximation refers to Figure 4. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Lines 208-210: This statement is not clear to me.  Since maximum rate constant and trend is different depending on conditions:

A): increasing trend up to 80°C (=kmax), b): no clear trend with kmax at 80°C, c): no clear trend with kmax at 60°C and d) no clear trend with kmax at 60°C. Please comment.

The statement we've provided describes the results of an experiment in which the rate constant of a reaction was measured under different conditions. The results of the experiment indicate that the trend in the rate constant depends on the conditions of the experiment.

In condition (a), the rate constant (k) shows an increasing trend up to 80°C and reaches its maximum value (kmax) at this temperature.

In conditions (b) and (c), the rate constant does not show a clear trend, and the maximum value of the rate constant (kmax) is observed at 80°C and 60°C, respectively.

In condition (d), the rate constant does not show a clear trend, and kmax is observed at 60°C.

These results suggest that the rate of the reaction may be influenced by temperature and that the maximum reaction rate may be achieved at different temperatures depending on the conditions of the experiment.

Line 206: Error bars should be included in Figure 4. Please comment.

The comment has been corrected. Corresponding changes have been made to the Figure

Line 233: Statistics are essential when comparing activation energies in Table 4 and should therefore be included. Please comment.

Statistical analysis of the found activation energy values by the least squares method: correlation coefficient – 0.99; linear correlation coefficient – 0.984, i.e. on the Cheddock scale, the relationship between the signs is noticeable and direct; the approximation error is 5.4%.

Line 240: The relationship between reaction (1) describing and the reaction in line 240 ((number) should be included) is not explained.  It is not clear why only CaHPO4 is formed and not CaF2 or other compounds. Please comment.

This scheme has a relationship with the reaction (1), where calcium humates, as expected, is a solid insoluble residue, while phosphoric acid belongs to the liquid phase. CaF2 is present in the very structure of phosphoric sludge and cottrel dust, naturally it refers to an insoluble residue. CaHPO4 is an intermediate of the reaction.  

Line 246-250: the description of the internal diffusion should be better explained using a Figure with the different layers and the frontal displacement of the of the reaction zone. See also my comment on equation (2) in line 197. Please comment.

Internal diffusion refers to the movement of reactants within the solid particles in a heterogeneous fluid-spherical particle system. The reactants can diffuse from the interior of the particles to the surface, where they can participate in the chemical reaction. The rate of internal diffusion can be influenced by several factors, including the particle size and shape, the porosity and permeability of the particles, and the concentration and diffusivity of the reactants.

In a heterogeneous fluid-spherical particle system, the reaction zone can form at the front of the solid particles, where the reactants diffuse to the surface and participate in the reaction. The position of the reaction zone can move as the reaction progresses, and it can be influenced by the rate of internal diffusion and the velocity of the fluid.

The different layers within the solid particles can also play a role in the internal diffusion and reaction kinetics. For example, the outer layers of the particles can be more porous or have a different composition than the inner layers, which can affect the rate of internal diffusion and the reaction kinetics.

It is important to consider the effects of internal diffusion and the frontal displacement of the reaction zone when modeling and simulating the reaction kinetics in a heterogeneous fluid-spherical particle system. Accurately accounting for these factors can provide a more complete understanding of the reaction kinetics and the behavior of the system under different conditions.

Lines 253-255: Ea values for decomposition reactions between natural phosphates with mineral acids (including conditions: acid concentration, ratio mineral/acid, time and pH) should be included in the manuscript for a better comparison. Please comment.  

Data on acid leaching of phosphorite rocks (from China and Turkey) are given in the text of the manuscript.

Lines 263-270: Part of this paragraph should be transferred to Materials and Methods section. Please comment.

Corrected.

Line 264. Which type of filter was used? Please comment.

Vacuum filter (described in Materials and Methods section).

Line 271: Which analytical method was applied for determination P2O5 total and P2O5 assimilable? Please comment. What is the ratio between phosphoric acid and the insoluble residue under the given experimental conditions? Please comment.

The method of determination P2O5 total and P2O5 assimilable is given in the Materials and Methods section.

The ratio of phosphoric acid-insoluble residue according to the results of the experiments was 1/4. If we take into account that the reaction mass was initially 450 g at PS-CD/HA ratio = 1/2, then after leaching the ratio of the liquid and solid phases, respectively, is 87 g / 363 g.

Line 271: The composition (impurities) of production phosphoric acid should be induced in the manuscript for comparison with results of Table 5 for obtained H3PO4.   Please comment.

Data for comparing the chemical composition of the obtained phosphoric acid are given in Table 5

Line 274: “Content of potassium is more dominant present in phosphoric acid” instead of “Potassium is more in phosphoric acid”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 280: “The XRF identified compounds are…” instead of “The XRD identified compounds in the form of …”.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 281: Apart of a crystalline fraction is there also an amorphous fraction and what is the ratio? Please comment.

As in the phase structure of the feedstock, low intensity is also observed here, which in turn allows us to conclude about the amorphous structure of the insoluble residue. Corresponding changes have been made to the text of the manuscript (highlighted in red)

4. Conclusions

Conclusion should be adapted taken in account the comments of the reviewer. Please comment.

Line 295: The composition (impurities) of production phosphoric acid should be included in the manuscript for comparison with results of obtained H3PO4 in Table 5. Please comment.

Data for comparing the chemical composition of the obtained phosphoric acid are given in Table 5. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 297: See my comments on line 2946-250.

The comment has been corrected. Corresponding changes have been made to the text of the manuscript (highlighted in red)

Line 300: “kinetic models are proposed for different variations. Not clear to me. Please comment.

Yes, different kinetic models can be proposed to describe the reaction kinetics under different variations of conditions such as temperature, LS ratio, concentration, and others. The kinetic model can be used to describe the rate of reaction, determine the rate constant, and study the effect of various factors on the reaction kinetics.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Check the final document to make minor improvements text editing in order to harmonize the paper.

All of the comments were considered by the authors in the preparation of the final text.

Author Response

Check the final document to make minor improvements text editing in order to harmonize the paper.

All of the comments were considered by the authors in the preparation of the final text.

All necessary changes and improvements have been made to the text of the manuscript. The authors thank the reviewer for the high-quality processing of our manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Ref [1] introduces a new concept of preparing yellow phosphorus by molten salt electrolysis. This method is very different from the traditional carbothermal reduction. The statement in line 28 is not correct. 

Author Response

Reviewer 2:

Ref [1] introduces a new concept of preparing yellow phosphorus by molten salt electrolysis. This method is very different from the traditional carbothermal reduction. The statement in line 28 is not correct.

 

The comment is taken into account by the authors. Corresponding changes have been made to the Reference list.

The authors thank the reviewer for the high-quality processing of our manuscript.

Author Response File: Author Response.docx

Reviewer 3 Report

I have read the revised article “Processing of phosphoric solid waste by humic acid leaching method” including the answers of the authors to the reviewers.

Authors have addressed the comments and questions of the reviewers in a detailed way and have implemented changes and additional information.

However considering the answers on my comments and questions and the revised manuscript with new data, new questions popped up when reading this revised version, including answers to the reviewers.

I hope authors will again consider these questions and comments for a better understanding and improvement of this paper.

I regret that I do not recommend the publication of this manuscript in its current form.

Detailed list of additional comments and questions on the revised paper.   

1. Introduction

Line 72: “during electrothermia as a phosphorus additive to increase it.”? This is still an unclear formulation. What is electrothermia? Electrostatic? Electrothermal? Please comment and reformulate.

2. Materials and Methods

Lines 93: “Bruker D8 diffractometer (Germany). It” instead of “Bruker D8 diffractometer (Germany), It”

Lines 95: “3-180°” instead of “3-180° degrees”. 

Line 93: “It can also be equipped with advanced data collection and analysis software that automates the process of data collection and analysis, making it an efficient and reliable tool for structural analysis”. This paragraph can be omitted since in the next paragraph more information is given on the used analysis software and library.

Line 116-117: Indicator and specific wavelength for photometric measurements should be included. Please comment. Type and supplier of flame photometer and atomic absorption spectrometer should be included. Please comment.

Lines 137-138: Methods for the determination of cation exchange capacity and acid value are different. It is not clear which method is used for total acid value (potentiometric determination?). Please comment.   

3. Results and discussion

Line 166: In Table 1 standard deviations for CaO and Fe2O3 are higher than the mean value. What is the reason for this observation? Please comment.

Line 166: It is not clear if in Table 1, C is related to free carbon or total carbon. Since according to the authors “The presence of carbon in both studied samples is associated with the use of coke in the thermal reduction of phosphorus in ore-thermal furnaces. The presence of carbon in Karatau phosphorites is associated with carbonate-containing minerals”. How free C and total C is defined? How carbides can be determined with cited method? Please comment.

Line 190: When SiO2 is referred to quartz a crystalline phase should be present (as mentioned in line 189 and confirmed by XRD in Figure 2). If SiO2 is amorphous because of a heat treatment, it is referred to a glass, not to quartz. Please comment.

Line 202: It is still unclear if there is no competition between the formation of Ca-phosphate and Ca-humate. Please comment.

Lines 203-205: Authors state that ”According to the reaction, the solid phase is an insoluble residue in the form of calcium humate, the liquid phase is production phosphoric acid, and hydrogen fluoride can also be released as a gas phase.”

However according to experimental set-up (Figure 1) and lines 147-150 glassware was used for the leaching procedure.

How is this compatible with the presence of HF? Additionally what will be the fate of the very aggressive and corrosive gaseous HF from an environmental point of view and the safety of such process? Please comment.

Line 306-307: It is still unclear if there is no competition between the formation of Ca-phosphate and Ca-humate. Since ”Reaction kinetics in a heterogeneous fluid-spherical particle system refers to the study of chemical reactions that occur between the fluid and the solid particles in the system” (Lines 245-254).Why a reaction between Ca-humate and phosphoric acid in such heterogeneous system is not possible while stirring of this mixture is used?  See also my comment on line 202. Please comment.

Lines 355-363: P2O5 is used to express total and available P content. However P speciation is dependent on the pH of the solution and can be present as mixtures of  phosphoric acid and hydrogen phosphates which is important when used as a fertilizer to a soil. Please comment. 

Lines 364-368: The same comment for the insoluble residue. Phosphorous will not be present as P2O5 but in different species and compounds (potassium and calcium (hydrogen) phosphates amongst others. Please comment. From XRD results only limited information can be obtained of crystalline species which are present as a minor fraction since the amorphous fraction is the most important one. Please comment.

Lines 387-390: Authors should discussed why decomposition with humic acid has less environmental impact that other methods and in which way it affects the composition of obtained products.

Lines 391-393: I do not agree with this statement: Authors stated that HF is released (line 205) which is an extreme corrosive and toxic compound especially when released as gaseous HF during the decomposition process. Please comment.

Lines 397-398:  This statement should be documented since isolation of humic acid requires also expensive mineral acids and processing costs and waste streams/by products which should be compared with overall costs of traditional methods. Differences in waste streams/by products should be documented. Please comment.

Lines 309-401: No information is found in the paper on the selectivity of this process compared to traditional methods. Please comment.

4. Conclusions

Lines 407-409: As mentioned in previous comments the eco-friendly and techno-economic features of this process should be better documented.

Lines 411-412: From results in Table 7 obtained phosphoric acid contains significant impurities (18% K2O and 10% CaO) compared to production phosphoric acid (less than 0.1%K2O and less than 0.5% CaO) and can therefore not be considered as a substitute. Please comment.  

 

                  

Author Response

Reviewer 3:

I have read the revised article “Processing of phosphoric solid waste by humic acid leaching method” including the answers of the authors to the reviewers.

Authors have addressed the comments and questions of the reviewers in a detailed way and have implemented changes and additional information.

However considering the answers on my comments and questions and the revised manuscript with new data, new questions popped up when reading this revised version, including answers to the reviewers.

I hope authors will again consider these questions and comments for a better understanding and improvement of this paper.

I regret that I do not recommend the publication of this manuscript in its current form.

Detailed list of additional comments and questions on the revised paper.  

1. Introduction

Line 72: “during electrothermia as a phosphorus additive to increase it.”? This is still an unclear formulation. What is electrothermia? Electrostatic? Electrothermal? Please comment and reformulate.

 

This process is known as the Electric Furnace Process and is used to produce elemental phosphorus, also known as white phosphorus. In this process, phosphate rock is ground into a fine powder and formed into pellets. The pellets are then heated with coke or silica in an electric furnace at high temperatures. The heat causes a chemical reaction that releases the phosphorus from the phosphate rock and converts it into white phosphorus, which is then collected and further purified for various applications. This process is widely used due to its high efficiency and low cost, and is an important source of phosphorus for the production of fertilizers, flame retardants, and other chemicals.

 

Reformulate to: “Also, cottrel dust can be used in the ore preparation process at the Electric Furnace Process as an additive to increase the phosphorus component”.

 

2. Materials and Methods

 

Lines 93: “Bruker D8 diffractometer (Germany). It” instead of “Bruker D8 diffractometer (Germany), It”

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

 

Lines 95: “3-180°” instead of “3-180° degrees”.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

 

Line 93: “It can also be equipped with advanced data collection and analysis software that automates the process of data collection and analysis, making it an efficient and reliable tool for structural analysis”. This paragraph can be omitted since in the next paragraph more information is given on the used analysis software and library.

 

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript

 

Line 116-117: Indicator and specific wavelength for photometric measurements should be included. Please comment. Type and supplier of flame photometer and atomic absorption spectrometer should be included. Please comment.

 

Indicator and specific wavelength for photometric measurements: λ=440 nm and alphanumeric LCD with backlight.

- potassium by FPA-2-01 flame photometry (Russia), calcium and magnesium by Kvant-2m1 atomic absorption spectrophotometry (Russia).

 

Lines 137-138: Methods for the determination of cation exchange capacity and acid value are different. It is not clear which method is used for total acid value (potentiometric determination?). Please comment.  

Removed from the text of the manuscript.

 

3. Results and discussion

 

Line 166: In Table 1 standard deviations for CaO and Fe2O3 are higher than the mean value. What is the reason for this observation? Please comment.

This may have happened due to an error during the calculation. The specified data has been recalculated.

 

Line 166: It is not clear if in Table 1, C is related to free carbon or total carbon. Since according to the authors “The presence of carbon in both studied samples is associated with the use of coke in the thermal reduction of phosphorus in ore-thermal furnaces. The presence of carbon in Karatau phosphorites is associated with carbonate-containing minerals”. How free C and total C is defined? How carbides can be determined with cited method? Please comment.

 

As is known, free carbon refers to carbon that is not chemically bound to any other elements, and total carbon refers to the sum of free carbon and carbon that is chemically bound to other elements in the sample. In our case, we can say that this is total carbon. In the context of our study, the presence of carbon in both studied samples is likely to be due to the use of coke in the thermal reduction of phosphorus in ore-thermal furnaces. The presence of carbon in the Karatau phosphorites is also associated with carbonate-containing minerals. A gas volume method was used to determine the amount of total carbon.

 

Line 190: When SiO2 is referred to quartz a crystalline phase should be present (as mentioned in line 189 and confirmed by XRD in Figure 2). If SiO2 is amorphous because of a heat treatment, it is referred to a glass, not to quartz. Please comment.

 

In the electric furnace process, SiO2 can act as a flux, which helps to reduce the melting point of the minerals in the phosphorite and facilitates the separation of impurities from the desired product. SiO2 can also react with other components in the furnace, such as phosphorus and carbon, to form compounds such as SiO2-P-C slag or silicates.

The behavior of SiO2 also depends on the temperature and time of the furnace process. At high temperatures, SiO2 can react with other components to form silicates, while at lower temperatures it may act as a flux to facilitate the separation of impurities. The duration of the furnace process also affects the behavior of SiO2, as longer processing times can result in more complete reactions and the formation of more complex compounds. Overall, the formation of glass, as you note, is impossible in this process.

In addition, the authors cited the scientific work of other authors here (Imanbetov, K.M.; Kerembayev, A.B.; Koshkarbaeva, S.T. Improvement of the technology of processing cottrel milk into PK fertilizer. Bulletin of Science of South Kazakhstan 2018, 1(1), 70-74).

 

Line 202: It is still unclear if there is no competition between the formation of Ca-phosphate and Ca-humate. Please comment.

 

As it was noted here, the decomposition products of humic acids (HA) "can be" calcium humate in the form of an insoluble residue, phosphoric acid and hydrogen fluoride in the form of a gas phase. According to the results of experimental studies, it can be seen that an increase in the assimilable phosphoric pentoxide indicates a predominance of the formation of Ca-phosphates than Ca-humates.

 

Lines 203-205: Authors state that ”According to the reaction, the solid phase is an insoluble residue in the form of calcium humate, the liquid phase is production phosphoric acid, and hydrogen fluoride can also be released as a gas phase.”

 

However according to experimental set-up (Figure 1) and lines 147-150 glassware was used for the leaching procedure.

 

How is this compatible with the presence of HF? Additionally what will be the fate of the very aggressive and corrosive gaseous HF from an environmental point of view and the safety of such process? Please comment.

 

The above reaction (1) presumably describes the process under study. In XRD, it was found that fluorine occurs in the composition of phosphorite and calcium fluoride. The authors assumed whether humic acid would be able to decompose fluoride compounds. However, as a result, it turned out that fluoride compounds remain intact in the solid phase (from the results of XRD). Thus, the formation of hydrogen fluoride is impossible.

 

Line 306-307: It is still unclear if there is no competition between the formation of Ca-phosphate and Ca-humate. Since ”Reaction kinetics in a heterogeneous fluid-spherical particle system refers to the study of chemical reactions that occur between the fluid and the solid particles in the system” (Lines 245-254).Why a reaction between Ca-humate and phosphoric acid in such heterogeneous system is not possible while stirring of this mixture is used?  See also my comment on line 202. Please comment.

 

According to the process under study, when chemical reactions occur between liquid and solid particles in the system, the solid particle is the intermediate products of formation in the form of CaHPO4. The final product is phosphoric acid and calcium humate. Due to the saturation of the pulp with the CaHPO4 compound, no further reaction takes place.  From the XRD analysis it can be seen that the compounds in the form of fluorapatite are not completely decomposed by humic acid. If we assume your statement, then the reaction between calcium humate and weak phosphoric acid does not take place in principle. The main reason for this is the same result of the XRD analysis.

Lines 355-363: P2O5 is used to express total and available P content. However, P speciation is dependent on the pH of the solution and can be present as mixtures of phosphoric acid and hydrogen phosphates which is important when used as a fertilizer to a soil. Please comment.

 

Lines 364-368: The same comment for the insoluble residue. Phosphorous will not be present as P2O5 but in different species and compounds (potassium and calcium (hydrogen) phosphates amongst others. Please comment. From XRD results only limited information can be obtained of crystalline species which are present as a minor fraction since the amorphous fraction is the most important one. Please comment.

In phosphoric acid, there are two types of compounds in the form of monetite with the formula CaHPO4 and potassium dihydroorthophosphate KH2PO4. Both compounds are acid salts of phosphoric acid. Phosphorus is known to occur in these compounds in the form of P2O5. Regarding the insoluble residue, there are also compounds in the form of monetite. The presence of an amorphous structure in the studied samples is explained by the low intensity. Phosphorite ore has higher intensities in XRD.

 

Lines 387-390: Authors should discussed why decomposition with humic acid has less environmental impact that other methods and in which way it affects the composition of obtained products.

 

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript

 

Lines 391-393: I do not agree with this statement: Authors stated that HF is released (line 205) which is an extreme corrosive and toxic compound especially when released as gaseous HF during the decomposition process. Please comment.

The above reaction (1) presumably describes the process under study. In XRD, it was found that fluorine occurs in the composition of phosphorite and calcium fluoride. The authors assumed whether humic acid would be able to decompose fluoride compounds. However, as a result, it turned out that fluoride compounds remain intact in the solid phase (from the results of XRD). Thus, the formation of hydrogen fluoride is impossible.

 

Lines 397-398:  This statement should be documented since isolation of humic acid requires also expensive mineral acids and processing costs and waste streams/by products which should be compared with overall costs of traditional methods. Differences in waste streams/by products should be documented. Please comment.

Removed from the text of the manuscript.

 

Lines 309-401: No information is found in the paper on the selectivity of this process compared to traditional methods. Please comment.

Removed from the text of the manuscript.

 

4. Conclusions

 

Lines 407-409: As mentioned in previous comments the eco-friendly and techno-economic features of this process should be better documented.

Removed from the text of the manuscript.

 

Lines 411-412: From results in Table 7 obtained phosphoric acid contains significant impurities (18% K2O and 10% CaO) compared to production phosphoric acid (less than 0.1%K2O and less than 0.5% CaO) and can therefore not be considered as a substitute. Please comment.

 

Removed from the text of the manuscript.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

I have read the 2^nd revised article “Processing of phosphoric solid waste by humic acid leaching method” including the answers of the authors to the reviewers.

Authors have addressed the new comments and questions of the reviewers in a detailed way and have implemented changes and additional information where needed.

Some interpretations and statements have been reconsidered and reformulated.

I am convinced that the overall quality of the article has improved considerably and I support the publication of this revised version of this paper.

There are still a few paragraphs which require rephrasing.

Minor comments

Line 129: “photometer” instead of “photometry”

Line 130: “photometer” instead of “photometry”

Line 201-203: “It follows from the above reaction that the products of humic acid (HA) 201 decomposition can be calcium humate in the form of an insoluble residue, phosphoric acid and hydrogen fluoride in the form of a gas phase.” Authors responded that

“according to the results of experimental studies, it can be seen that an increase in the assimilable phosphoric pentoxide indicates a predominance of the formation of Ca-phosphates than Ca-humates”; Authors answered to the reviewer that “the authors assumed whether humic acid would be able to decompose fluoride compounds. However, as a result, it turned out that fluoride compounds remain intact in the solid phase (from the results of XRD). Thus, the formation of hydrogen fluoride is impossible.”

If that case authors should change lines 201-203 accordingly, otherwise there is a conflict between statements and experimental findings. Additionally there will be a considerable conflict which will be in conflict with the environmental impact of this process (lines 391-396).

Line 401: “to obtain production phosphoric acid with enhanced Ca and K impurities.” instead of “to obtain production phosphoric acid”.

 

Author Response

Reviewer’s comment:

I have read the 2nd revised article “Processing of phosphoric solid waste by humic acid leaching method” including the answers of the authors to the reviewers.

Authors have addressed the new comments and questions of the reviewers in a detailed way and have implemented changes and additional information where needed.

Some interpretations and statements have been reconsidered and reformulated.

I am convinced that the overall quality of the article has improved considerably and I support the publication of this revised version of this paper.

There are still a few paragraphs which require rephrasing.

Minor comments

Line 129: “photometer” instead of “photometry”

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 130: “photometer” instead of “photometry”

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

Line 201-203: “It follows from the above reaction that the products of humic acid (HA) 201 decomposition can be calcium humate in the form of an insoluble residue, phosphoric acid and hydrogen fluoride in the form of a gas phase.” Authors responded that “according to the results of experimental studies, it can be seen that an increase in the assimilable phosphoric pentoxide indicates a predominance of the formation of Ca-phosphates than Ca-humates”; Authors answered to the reviewer that “the authors assumed whether humic acid would be able to decompose fluoride compounds. However, as a result, it turned out that fluoride compounds remain intact in the solid phase (from the results of XRD). Thus, the formation of hydrogen fluoride is impossible.”

If that case authors should change lines 201-203 accordingly, otherwise there is a conflict between statements and experimental findings. Additionally there will be a considerable conflict which will be in conflict with the environmental impact of this process (lines 391-396).

Revised to: “It follows from the above reaction that the products of humic acid (HA) decomposition can be calcium humate in the form of an insoluble residue and phosphoric acid in liquid phase. The formation of hydrogen fluoride in this reaction is impossible, since in this case the fluoride compounds are presented in the form of calcium fluoride (from the XRD analysis). Humic acid cannot decompose calcium fluoride (CaF2) because calcium fluoride is a very stable compound with a high lattice energy, which makes it difficult to break down. Humic acid, on the other hand, is an organic acid with relatively low reactivity towards inorganic compounds like calcium fluoride. In addition, the bond between calcium and fluoride in CaF2 is a strong ionic bond, which requires a significant amount of energy to break. As a result, even under normal conditions, humic acid is not able to decompose calcium fluoride, and the compound remains intact in the solid phase.”

Line 401: “to obtain production phosphoric acid with enhanced Ca and K impurities.” instead of “to obtain production phosphoric acid”.

The comment is taken into account by the authors. Corresponding changes have been made to the text of the manuscript (highlighted in red).

 

The authors are immensely grateful to the reviewer for such a careful and reverent attitude to the manuscript under consideration.

Author Response File: Author Response.docx