Thermodynamics and Kinetics Research of the Fluorination Process of the Concentrate Rutile

Round 1

Reviewer 1 Report

This article deals with fluorine technology for processing titanium-containing minerals. Rutile was used as a raw material in the work. Thermodynamic and kinetic parameters of the process have been calculated. The authors have done significant work, including experiments and calculations.

The experimental part is well described. But it is worth noting a strong deficiency in the presentation of the article, namely: in some places, there is no logical structure of the text, no smooth transitions from one thought to another, as well as the sloppy design of the document.

Abstract

Unfortunately, the Abstract does not give a complete picture of the work done. It is necessary to logically structure this section.

The authors at the beginning report that the article provides a rationale for the need to develop a new fluoride technology: “Disadvantages of current titanium technology have been described and have shown the need for the introduction of new advanced fluoride technologies”. It may be better to list the main factors driving this need rather than referring to the main text.

Further, the authors immediately proceed to thermodynamic calculations of the process without presenting the proposed process. Thus, it is completely unclear which method / process is being discussed, and why its parameters are calculated, and why this calculation is carried out.

Introduction

The introduction does not fully reflect the relevance/content of the chosen topic. It is sufficiently written about the environmental harm of existing methods, but there is no information about the fluoride technology. Further, the authors move quite sharply to the statement of the research problem, but the goal looks like a result that has already been achieved. It is worth noting the lack of information about the need for kinetic and thermodynamic calculations, which could justify the importance of the work.

Conclusions

In the conclusions, it is necessary to add a generalized result or a recommendation about the possibility of using the obtained data. In accordance with the stated purpose in the introduction section: "In this paper, a method of processing titanium-containing minerals are introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a plan to introduce titanium-containing minerals. industrial production".

Typos and superscripts and subscripts throughout the text need to be corrected. Some of them are: “The chloride method is considered to be better and more complete in terms of the environment. However, the limitation of the method is that a large amount of gaseous, liquid and solid industrial chloride waste is discharged, and the total amount of titanium extracted to pure titanium chloride does not exceed 89% (mass fraction). first]. “ “… (under the condition that all factories are equal. switch to chloride technology) [ 3, 4].” “In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a plan to introduce titanium-containing minerals. industrial production” “All Rutile concentrates used in the experiment were selected and refined with high TiO2 content from the Tasky region (Omsk), Russia. In which, the content of TiO2: 93.2%; FeO + Fe2O3: 2.7%; SiO2: 1.8%; Al2O3: 1%; MnO: 0.6%; CaO: 0.4%; MgO: 0.2% and V2O5:….”, and so on in the text of the article.

References 4. 4. Krishnan A., Lu X.G. and Pal U.B. Solid Oxide Membrane (SOM) technology for environmentally sound production of tantalum metal… and etc.

Comments for author File: Comments.pdf

Author Response

Point 1: 

Abstract

Unfortunately, the Abstract does not give a complete picture of the work done. It is necessary to logically structure this section.

The authors at the beginning report that the article provides a rationale for the need to develop a new fluoride technology: “Disadvantages of current titanium technology have been described and have shown the need for the introduction of new advanced fluoride technologies”. It may be better to list the main factors driving this need rather than referring to the main text.

Further, the authors immediately proceed to thermodynamic calculations of the process without presenting the proposed process. Thus, it is completely unclear which method / process is being discussed, and why its parameters are calculated, and why this calculation is carried out.

Respone 1: We would like to rewrite

Abstract: The growth in the production of titanium metal and its compounds leads to an increase in the amount of toxic waste. As a result, at the legislative level, emissions of such wastes are limited, which leads to a drop in the production of titanium-containing products and a shortage of titanium in the international market. This paper presents the results of the process of fluorination of rutile concentrate from the Tarsky deposit (Russia, Omsk region) with elemental fluorine using a laboratory setup of a special design. For fluorination, samples of rutile concentrate weighing 0.1–1.0 g were used. The particle size distribution of particles varied from 2·10^–6 to 2·10^–5 m. To determine the possibility of carrying out the process, the calculation of the change in the logarithm of the equilibrium constant versus temperature was performed. The influence of the following operating parameters on the fluorination process has been studied: various concentrations of F₂ in a fluorinating mixture of fluorine with nitrogen; process time from 0 to 9 minutes; different ratios of the initial solid phase to fluorine (10 and 50 % excess of fluorine and 10 and 50 % of its deficiency); fluorination temperature in the range of 300-1800 K. A kinetic equation is selected that most accurately describes the fluorination process. The values of the activation energy and the preexponential factor in the kinetic equation are determined. The obtained results shows that with an increase in the fluorine content in the fluorinating gas mixture and the temperature of the process, the fluorination rate increases. Optimal conditions for fluorination: temperature - 680 K; time - 5 minutes; excess fluorine in the fluorinating mixture - 20-25 %. The obtained results allow to propose and consider the conditions of process execution on industrial equipment.

Point 2: 

Introduction

The introduction does not fully reflect the relevance/content of the chosen topic. It is sufficiently written about the environmental harm of existing methods, but there is no information about the fluoride technology. Further, the authors move quite sharply to the statement of the research problem, but the goal looks like a result that has already been achieved. It is worth noting the lack of information about the need for kinetic and thermodynamic calculations, which could justify the importance of the work.

Respone 2: According to the opinion of reviewer 1 combined with the opinion of reviewer 2, we have supplemented and rewritten introduction:

1. Introduction

With the development of science-intensive technologies, the need for the creation of structural materials that work in critical conditions is sharply increasing. These materials include titanium alloys. Creation of technological processes allowing to ensure high quality of titanium alloys and their minimum cost is the key task of technologies for obtaining high-tech structural materials. The development of modern technologies for the chemical processing of titanium concentrates and the synthesis of high-purity metallic titanium is one of the main processes preceding the creation of titanium alloys, since the physicochemical properties and cost of products made of titanium and its alloys depend on the content of impurities in a titanium product.

Currently, two main methods are used in industry for processing titanium-containing concentrates: sulfate (sulfuric acid) and chloride. The main problem, as well as the disadvantage of sulfate technology, is environmental pollution due to the need to discharge a large amount of waste in the form of CaSO₄ into the environment. As a result, the production cost of titanium dioxide using sulfate technology is very high. However, the sulfate method has the advantage that it does not require a high titanium feedstock [1]. The chloride method is considered to be more advanced and environmentally friendly. However, the main disadvantage of the method is that a large amount of gaseous, liquid and solid toxic chloride waste is discharged, and the total amount of titanium extracted into pure titanium chloride does not exceed 89 % of the mass. In addition, for the chlorination process to be highly efficient, the titanium content (as TiO₂) in the starting material must be high (> 90 %). In this case, it becomes necessary to carry out auxiliary operations for the purification of raw materials and the recycling process in order to increase the titanium content in the raw materials to a level corresponding to technological requirements. As a result, only 10 to 50 % of titanium metal can be obtained from raw materials, which significantly increases its cost [2].

The current production rate of titanium dioxide in the world is about 2750 thousand tons/year, corresponding to the amount of harmful solid waste by chlorination method of about 1467 thousand tons/year (under the condition that all factories are equal. switch to chloride technology) [3, 4].

In the last decade, the development of the sulfate method associated with the introduction of various reagents (additives) sulfuric acid. For example, in [5] a water technology is described, in which it is recommended to use a mixture of H₂SO₄ (10 % vol.) - HF (15 % vol.) To open titanium ores. At opening, TiF₆^2– is first formed, which, upon subsequent interaction with H₂SO₄, forms Ti(SO₄)₂ [5]. In [6, 7, 8], the process of sulfate-fluoride leaching of titanium from ilmenite and the formation of fluorotitanate ions in aqueous solutions and the subsequent synthesis of Ti(SO₄)₂ in a sulfuric acid medium is proposed. In fact, this is a modification of the well-known sulfate technology of titanium ore opening. The main disadvantage of this technology is the formation of a large amount of calcium sulfate, which must be separated from production waste and spend significant funds on its storage.

An aquatic technology is being developed for opening titanomagnetite ore by selective extraction of titanium with solutions containing ammonium fluoride (ammonium and fluorine ions) [9]. A technology based on the use of metal and ammonium hydrofluorides for opening titanium ores and concentrates is presented [10]. As a result of the interaction of titanium and iron oxides with aqueous solutions of ammonium fluoride, aqueous solutions of HF (hydrofluoric acid) are formed, which, under the conditions of the process, have a strong corrosive effect on the material of the apparatus. This does not allow the use of this method in an industrial environment.

A high-temperature technology for the synthesis of titanium slag based on TiO₂, suitable for metallothermal reduction and synthesis of metallic titanium, has been described [11]. However, if magnesium is used as a metal-reducing agent in the reduction of slag, then this is actually the well-known Kroll process, which is the only method used in industrial conditions to obtain titanium sponge.

The process of synthesis of rutile from titanium slags from the Panzhihua deposit (China) by oxidative roasting of these slags at 1100 °C for 2 hours is presented [12]. However, this method is not new, since it is described in the preparation of various titanium ores for the Kroll process - the reduction of TiO₂ with magnesium.

Recently, various types of titanium electrolytic reduction processes in fluoride-chloride-salt melts have been intensively developed. TiO₂ is used as a starting material. These are FFC-, MER-, PRP-, Osaka-, Suzuki- and Chinuka-processes [13-18]. However, these processes have not yet passed the stage of laboratory tests and research using "pilot" installations.

In the near future, we can expect a breakthrough in the creation of new titanium technologies, which will significantly reduce its prime cost. In this case, the cost of titanium can become commensurate with the cost of stainless steel. As a result, titanium consumption could skyrocket and replace stainless steel and other materials in the global market.

In the opinion of the authors of the article, in order to expand the areas of application of titanium and its alloys, it is necessary to develop a technology that makes it possible to effectively separate titanium from impurities, and then convert the volatile titanium compound into metallic titanium (powder or sponge). The number of stages of such a process should be minimal (no more than 3-4 stages). Such a process can be the process of direct fluorination of titanium concentrates with elemental fluorine, which makes it possible to transfer titanium into a gaseous compound, for example, TiF₄, and at the same time effectively separate non-volatile impurity fluorides from TiF₄. Subsequently, the reduction of TiF₄ should be carried out in a high-frequency pulse discharge, and the resulting elemental fluorine should be recycled again into the fluorination process. In order to study the mechanism of chemical processes occurring in this proposed technology, it is necessary to start from basic studies, namely thermodynamic and kinetic.

In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a schematic diagram of a facility for fluorination of rutile concentrate in industrial conditions.

Point 3: 

Conclusions

In the conclusions, it is necessary to add a generalized result or a recommendation about the possibility of using the obtained data. In accordance with the stated purpose in the introduction section: "In this paper, a method of processing titanium-containing minerals are introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a plan to introduce titanium-containing minerals. industrial production".

Respone 3: We rewrote the stated purpose in the introduction: In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a schematic diagram of a facility for fluorination of rutile concentrate in industrial conditions.

In the conclusions added recomendation: 

6. The obtained results allow to propose and consider the conditions of process execution on industrial equipment.

Point 4: 

Typos and superscripts and subscripts throughout the text need to be corrected. Some of them are: “The chloride method is considered to be better and more complete in terms of the environment. However, the limitation of the method is that a large amount of gaseous, liquid and solid industrial chloride waste is discharged, and the total amount of titanium extracted to pure titanium chloride does not exceed 89% (mass fraction). first]. “ “… (under the condition that all factories are equal. switch to chloride technology) [ 3, 4].” “In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a plan to introduce titanium-containing minerals. industrial production” “All Rutile concentrates used in the experiment were selected and refined with high TiO2 content from the Tasky region (Omsk), Russia. In which, the content of TiO2: 93.2%; FeO + Fe2O3: 2.7%; SiO2: 1.8%; Al2O3: 1%; MnO: 0.6%; CaO: 0.4%; MgO: 0.2% and V2O5:….”, and so on in the text of the article.

References 4. 4. Krishnan A., Lu X.G. and Pal U.B. Solid Oxide Membrane (SOM) technology for environmentally sound production of tantalum metal… and etc.

Respone 4: We also rewrote this part because we had to rewrite the entire introduction, but in English we also ask for help with editing the writing.

Author Response File: Author Response.pdf

Reviewer 2 Report

This article is devoted to the study of the thermodynamics and kinetics of the fluorination process of TiO₂ ore concentrate to produce titanium tetrafluoride. The obtained data are of theoretical and practical interest and can be published. Unfortunately, the quality of the article preparation is not high.

Key comments are the next:

1. The Introduction section discusses very briefly the advantages and disadvantages of only two methods of processing titanium ores. When describing them, there are no references to literature. The fluoride method is not considered at all. Only 4 references are used for the whole section. Obviously, this is not enough. The following literature, I suggest the author to read, may be helpful to your discussion:

https://doi.org/10.3390/met10040497

https://doi.org/10.3390/min8010002

https://doi.org/10.3390/app11031153

https://doi.org/10.4028/www.scientific.net/SSP.265.542

https://doi.org/10.1016/j.jmrt.2020.05.044

https://doi.org/10.3390/pr9111922

https://doi.org/10.3390/min10060538

https://doi.org/10.3390/pr8060640

2. The calculation results of the thermodynamic equilibrium constants of the studied reactions are shown in the Materials and Methods section. This material should be presented in the Results section.
3. The chemical reactions were indicated in the first version of the article. But they are removed in this version. However, they are important because reactions show what was ultimately calculated.
4. Comparing Figures 1 in both article versions shows that the new version has significant errors in the values ​​of the equilibrium constants. There are no points in the figure for a temperature of 300 K. Therefore, the course of the lines shown in Fig. 1 is not clear.
5. Figure 2 should not be in the Materials and Methods section too. It is not clear why the authors studied reactions with a lack of fluorine.
6. When describing the experimental equipment, the phrase “The collected gas is measured by a dedicated gas analysis system, determining the composition and volume of each gas” is not enough. It is necessary to describe in detail how the analysis of gas streams was carried out.
7. The Results section contains two pages of text about known models of heterogeneous processes. How does it relate to the obtained results? And one sentence about the result: “The results of the kinetic study are shown in Fig. 4, which was carried out in the temperature range of 670-850 K ". At the same time, Figure 4 is not shown in this section.
8. Information about models of heterogeneous processes is repeated in the Discussion section. Some part of the above material is not described. What does mean the data in Table 3? For example, why the activation energies are of 3.7-6.7 kJ mean if then it is again determined as 24.6 kJ/mol? Figure 5 shows seven lines, and only 6 of them are described.
9. The conclusions show: «Thermodynamic calculations of the fluorination reactions of rutile concentrate by elemental fluorine, the dependences of the change in the Gibbs energy (ΔG°_T) and the equilibrium constant (lnKp) of the indicated reactions in the temperature range of 298-2000 K were determined». There is nothing about Gibbs energies in the article. The temperature range of 298-2000 K is also unclear.
10. The article text contains many typos and mistakes. Their listing does not make sense, since the text of the article needs significant revision.

Author Response

Point1: 

1. The Introduction section discusses very briefly the advantages and disadvantages of only two methods of processing titanium ores. When describing them, there are no references to literature. The fluoride method is not considered at all. Only 4 references are used for the whole section. Obviously, this is not enough. The following literature, I suggest the author to read, may be helpful to your discussion:

https://doi.org/10.3390/met10040497

https://doi.org/10.3390/min8010002

https://doi.org/10.3390/app11031153

https://doi.org/10.4028/www.scientific.net/SSP.265.542

https://doi.org/10.1016/j.jmrt.2020.05.044

https://doi.org/10.3390/pr9111922

https://doi.org/10.3390/min10060538

https://doi.org/10.3390/pr8060640

Respone 1: We additionally wrote an analysis of these suggested references and rewrote the entire introduction:

1. Introduction

With the development of science-intensive technologies, the need for the creation of structural materials that work in critical conditions is sharply increasing. These materials include titanium alloys. Creation of technological processes allowing to ensure high quality of titanium alloys and their minimum cost is the key task of technologies for obtaining high-tech structural materials. The development of modern technologies for the chemical processing of titanium concentrates and the synthesis of high-purity metallic titanium is one of the main processes preceding the creation of titanium alloys, since the physicochemical properties and cost of products made of titanium and its alloys depend on the content of impurities in a titanium product.

Currently, two main methods are used in industry for processing titanium-containing concentrates: sulfate (sulfuric acid) and chloride. The main problem, as well as the disadvantage of sulfate technology, is environmental pollution due to the need to discharge a large amount of waste in the form of CaSO₄ into the environment. As a result, the production cost of titanium dioxide using sulfate technology is very high. However, the sulfate method has the advantage that it does not require a high titanium feedstock [1]. The chloride method is considered to be more advanced and environmentally friendly. However, the main disadvantage of the method is that a large amount of gaseous, liquid and solid toxic chloride waste is discharged, and the total amount of titanium extracted into pure titanium chloride does not exceed 89 % of the mass. In addition, for the chlorination process to be highly efficient, the titanium content (as TiO₂) in the starting material must be high (> 90 %). In this case, it becomes necessary to carry out auxiliary operations for the purification of raw materials and the recycling process in order to increase the titanium content in the raw materials to a level corresponding to technological requirements. As a result, only 10 to 50 % of titanium metal can be obtained from raw materials, which significantly increases its cost [2].

The current production rate of titanium dioxide in the world is about 2750 thousand tons/year, corresponding to the amount of harmful solid waste by chlorination method of about 1467 thousand tons/year (under the condition that all factories are equal. switch to chloride technology) [3, 4].

In the last decade, the development of the sulfate method associated with the introduction of various reagents (additives) sulfuric acid. For example, in [5] a water technology is described, in which it is recommended to use a mixture of H₂SO₄ (10 % vol.) - HF (15 % vol.) To open titanium ores. At opening, TiF₆^2– is first formed, which, upon subsequent interaction with H₂SO₄, forms Ti(SO₄)₂ [5]. In [6, 7, 8], the process of sulfate-fluoride leaching of titanium from ilmenite and the formation of fluorotitanate ions in aqueous solutions and the subsequent synthesis of Ti(SO₄)₂ in a sulfuric acid medium is proposed. In fact, this is a modification of the well-known sulfate technology of titanium ore opening. The main disadvantage of this technology is the formation of a large amount of calcium sulfate, which must be separated from production waste and spend significant funds on its storage.

An aquatic technology is being developed for opening titanomagnetite ore by selective extraction of titanium with solutions containing ammonium fluoride (ammonium and fluorine ions) [9]. A technology based on the use of metal and ammonium hydrofluorides for opening titanium ores and concentrates is presented [10]. As a result of the interaction of titanium and iron oxides with aqueous solutions of ammonium fluoride, aqueous solutions of HF (hydrofluoric acid) are formed, which, under the conditions of the process, have a strong corrosive effect on the material of the apparatus. This does not allow the use of this method in an industrial environment.

A high-temperature technology for the synthesis of titanium slag based on TiO₂, suitable for metallothermal reduction and synthesis of metallic titanium, has been described [11]. However, if magnesium is used as a metal-reducing agent in the reduction of slag, then this is actually the well-known Kroll process, which is the only method used in industrial conditions to obtain titanium sponge.

The process of synthesis of rutile from titanium slags from the Panzhihua deposit (China) by oxidative roasting of these slags at 1100 °C for 2 hours is presented [12]. However, this method is not new, since it is described in the preparation of various titanium ores for the Kroll process - the reduction of TiO₂ with magnesium.

Recently, various types of titanium electrolytic reduction processes in fluoride-chloride-salt melts have been intensively developed. TiO₂ is used as a starting material. These are FFC-, MER-, PRP-, Osaka-, Suzuki- and Chinuka-processes [13-18]. However, these processes have not yet passed the stage of laboratory tests and research using "pilot" installations.

In the near future, we can expect a breakthrough in the creation of new titanium technologies, which will significantly reduce its prime cost. In this case, the cost of titanium can become commensurate with the cost of stainless steel. As a result, titanium consumption could skyrocket and replace stainless steel and other materials in the global market.

In the opinion of the authors of the article, in order to expand the areas of application of titanium and its alloys, it is necessary to develop a technology that makes it possible to effectively separate titanium from impurities, and then convert the volatile titanium compound into metallic titanium (powder or sponge). The number of stages of such a process should be minimal (no more than 3-4 stages). Such a process can be the process of direct fluorination of titanium concentrates with elemental fluorine, which makes it possible to transfer titanium into a gaseous compound, for example, TiF₄, and at the same time effectively separate non-volatile impurity fluorides from TiF₄. Subsequently, the reduction of TiF₄ should be carried out in a high-frequency pulse discharge, and the resulting elemental fluorine should be recycled again into the fluorination process. In order to study the mechanism of chemical processes occurring in this proposed technology, it is necessary to start from basic studies, namely thermodynamic and kinetic.

In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a schematic diagram of a facility for fluorination of rutile concentrate in industrial conditions.

Point 2: The calculation results of the thermodynamic equilibrium constants of the studied reactions are shown in the Materials and Methods section. This material should be presented in the Results section.

Respone 2: This material removeded in the Results section:

Results

The thermodynamic study of the fluorination of rutile ore concentrates was conducted at temperatures from 300 ^oC to 1800 For the main reaction of interest is the reaction between TiO₂ and F₂, at different temperatures. The reaction goes like this:

TiO_{2 (solid)} + 2F_{2 (gas)} → TiF_{4 (gas)} + O_{2 (gas)}   

Point 3:     

The chemical reactions were indicated in the first version of the article. But they are removed in this version. However, they are important because reactions show what was ultimately calculated.

Respone 3: The chemical reactions were added:

In addition, reactions occur between F₂ and other components of the original rutile concentrate:              

SiO₂ + 2F₂ → SiF₄↑ +O₂,                                    (2)

MgO + F₂ → MgF₂↓ + 0,5O₂,                             (3)

MnO + F₂ → MnF₂↓ + 0,5O₂,                              (4)

Al₂O₃ + 3F₂ → 2AlF₃↓ + 1,5O₂,                            (5)

FeO + 1,5F₂ → FeF₃↓ + 0,5O₂,                              (6)

Fe₂O₃ + 3F₂ → 2FeF₃↓ + 1,5O₂,                           (7)

CaO + F₂ → CaF₂↓ + 0,5O₂,                                  (8)

V₂O₅ + 5F₂ = 2VF₅↑ + 2,5O₂.                               (9)

 Point 4:        Comparing Figures 1 in both article versions shows that the new version has significant errors in the values ​​of the equilibrium constants. There are no points in the figure for a temperature of 300 K. Therefore, the course of the lines shown in Fig. 1 is not clear.

 Respone 4: Point in the figure for a temperature of 300 K was added and  Figure 1 has been redrawn more clearly.

Point 5: Figure 2 should not be in the Materials and Methods section too. It is not clear why the authors studied reactions with a lack of fluorine.

Respone 5: Figure 2 has been moved to the Materials and Methods section.

The need to conduct research under conditions of 10% and 50% fluorine deficiency is determined by the fact that in industrial conditions the fluorination process is carried out in two stages: the first - in an excess of fluorine, the second - in a fluorine deficiency. This is necessary to ensure the full use of fluorine in the process. In this case, at the first stage, the completeness of the fluorination of the rutile concentrate is ensured. For this, it is necessary to provide an excess of fluorine. In the second stage, it is necessary to capture the excess fluorine from the first stage. For this, the solid phase (rutile concentrate) is supplied in excess relative to the amount of fluorine leaving the first stage. As a result, titanium oxyfluorides and other components (solids) are formed, which are then returned to the first stage together with the rutile concentrate. 

Point 6: When describing the experimental equipment, the phrase “The collected gas is measured by a dedicated gas analysis system, determining the composition and volume of each gas” is not enough. It is necessary to describe in detail how the analysis of gas streams was carried out.

Respone 6:

The concentration of fluorine and gaseous fluorides in the gas phase removed to the ventilation system was determined by infrared spectrometry.

For this, a was used continuous method based on the interaction of fluorine with sulfur dioxide:

SO₂ + F₂ → SO₂F₂.                                                                                                                      

Sulfuryl fluoride formed in this process was analyzed by infrared spectroscopy on a 4300 DTGS spectrometer (Agilent Technologies) in a continuous mode.

Point 7: The Results section contains two pages of text about known models of heterogeneous processes. How does it relate to the obtained results? And one sentence about the result: “The results of the kinetic study are shown in Fig. 4, which was carried out in the temperature range of 670-850 K ". At the same time, Figure 4 is not shown in this section.

Point 8: Information about models of heterogeneous processes is repeated in the Discussion section. Some part of the above material is not described. What does mean the data in Table 3? For example, why the activation energies are of 3.7-6.7 kJ mean if then it is again determined as 24.6 kJ/mol? Figure 5 shows seven lines, and only 6 of them are described.

Respone 7 and 8: These two questions indicate major errors of the author team in presentation and calculation, so we have reviewed all the data, carefully recalculated and uploaded the content of the article for readers easy to follow. We have rewritten a lot of kinematics content.

This edit is very long, I would like to hope you read it in the article we resubmitted.

Point 9: The conclusions show: «Thermodynamic calculations of the fluorination reactions of rutile concentrate by elemental fluorine, the dependences of the change in the Gibbs energy (ΔG°_T) and the equilibrium constant (lnKp) of the indicated reactions in the temperature range of 298-2000 K were determined». There is nothing about Gibbs energies in the article. The temperature range of 298-2000 K is also unclear.

Respone 9: A calculation of the Gibbs energy (ΔG°_T) is presented in Appendix, because the article is too long, we have omitted this part, only stopping the value of Kp to assess the possibility of the reaction and the temperature value has also been corrected to the part. experimental data mentioned above.

"Thermodynamic calculations of the fluorination reactions of rutile concentrates by elemental fluorine, the dependences of the change in the equilibrium constant (lnKp) of the indicated reactions in the temperature range of  300-1800K were determined."

Point 10: The article text contains many typos and mistakes. Their listing does not make sense, since the text of the article needs significant revision.

Respone 10: We are pleased to provide English editing services

Author Response File: Author Response.pdf

Reviewer 3 Report

It is very difficult to get a clear message of the manuscript. The technical writing is quite weak and should be considerably improved to bring the best out of the manuscript. Authors are encouraged to correlate their findings with global samples. Also, estimate the theoretical activations using the Coats Redfern method and OSW methods. What is the actual meaning of activation as it is determined under several speculative assumptions?

Avoid abbreviations in abstract

Lot of typo errors in the first para of introduction (no subscript usage)

The introduction is not written well, it lacks scientific rationale, inadequate references and connecting parts

The concentrate should contain LOI and volatiles, it is incorrect to write no impurities

 

Author Response

Point 1: It is very difficult to get a clear message of the manuscript. The technical writing is quite weak and should be considerably improved to bring the best out of the manuscript. Authors are encouraged to correlate their findings with global samples. Also, estimate the theoretical activations using the Coats Redfern method and OSW methods. What is the actual meaning of activation as it is determined under several speculative assumptions?

Respone 1: Study the kinetics of the process to help calculate kinetic parameters such as activation energy and reaction rate constants, which help with reaction time calculations and mechanism evaluation. To calculate these parameters, we need to find and provide models and mathematical equations describing the change in reaction rate over time. Here, the authors have determined the mathematical model and the kinematic equation. Quantitative and activation energy values will give us an estimate of the control domain of a chemical reaction. If the value is large from 60kJ/mol, the process is in the kinetic domain, while the low value is below 5kJ/mol, the process is controlled by gas adsorption on the solid phase surface.

In the conculations:

4. Kinetic studies of the fluorination process of rutile concentrates with elemental fluorine, depending on temperature and pressure, have been carried out. Mathematical processing of quantitative data on their interaction of components according to the equations of Gistling, Yander and the «reduced» sphere was carried out.

It has been found that the process is most accurately described by the equation of a «reduced» sphere.

5. As a result, the value of the apparent activation energy 4654,2 J/mol and the value of the pre-exponential coefficient k₀ = 0,717 min^–1 of the process of fluorination of titanium dioxide with elemental fluorine were determined. The kinetic equation for fluorination of concentrate rutil with elemental fluorine was found:

(formula)

This process takes place in the control – limited stage - chemical adsorption of F2 gas on the solid phase surface – rutile thermal equalization, and mass equalization fluorination reactions.

Point 2: 

Avoid abbreviations in abstract

Lot of typo errors in the first para of introduction (no subscript usage)

Respone 2: We edited (manuscrips attached)

Point 3: The introduction is not written well, it lacks scientific rationale, inadequate references and connecting parts

Respone 3: We rewrote

1. Introduction

With the development of science-intensive technologies, the need for the creation of structural materials that work in critical conditions is sharply increasing. These materials include titanium alloys. Creation of technological processes allowing to ensure high quality of titanium alloys and their minimum cost is the key task of technologies for obtaining high-tech structural materials. The development of modern technologies for the chemical processing of titanium concentrates and the synthesis of high-purity metallic titanium is one of the main processes preceding the creation of titanium alloys, since the physicochemical properties and cost of products made of titanium and its alloys depend on the content of impurities in a titanium product.

Currently, two main methods are used in industry for processing titanium-containing concentrates: sulfate (sulfuric acid) and chloride. The main problem, as well as the disadvantage of sulfate technology, is environmental pollution due to the need to discharge a large amount of waste in the form of CaSO₄ into the environment. As a result, the production cost of titanium dioxide using sulfate technology is very high. However, the sulfate method has the advantage that it does not require a high titanium feedstock [1]. The chloride method is considered to be more advanced and environmentally friendly. However, the main disadvantage of the method is that a large amount of gaseous, liquid and solid toxic chloride waste is discharged, and the total amount of titanium extracted into pure titanium chloride does not exceed 89 % of the mass. In addition, for the chlorination process to be highly efficient, the titanium content (as TiO₂) in the starting material must be high (> 90 %). In this case, it becomes necessary to carry out auxiliary operations for the purification of raw materials and the recycling process in order to increase the titanium content in the raw materials to a level corresponding to technological requirements. As a result, only 10 to 50 % of titanium metal can be obtained from raw materials, which significantly increases its cost [2].

The current production rate of titanium dioxide in the world is about 2750 thousand tons/year, corresponding to the amount of harmful solid waste by chlorination method of about 1467 thousand tons/year (under the condition that all factories are equal. switch to chloride technology) [3, 4].

In the last decade, the development of the sulfate method associated with the introduction of various reagents (additives) sulfuric acid. For example, in [5] a water technology is described, in which it is recommended to use a mixture of H₂SO₄ (10 % vol.) - HF (15 % vol.) To open titanium ores. At opening, TiF₆^2– is first formed, which, upon subsequent interaction with H₂SO₄, forms Ti(SO₄)₂ [5]. In [6, 7, 8], the process of sulfate-fluoride leaching of titanium from ilmenite and the formation of fluorotitanate ions in aqueous solutions and the subsequent synthesis of Ti(SO₄)₂ in a sulfuric acid medium is proposed. In fact, this is a modification of the well-known sulfate technology of titanium ore opening. The main disadvantage of this technology is the formation of a large amount of calcium sulfate, which must be separated from production waste and spend significant funds on its storage.

An aquatic technology is being developed for opening titanomagnetite ore by selective extraction of titanium with solutions containing ammonium fluoride (ammonium and fluorine ions) [9]. A technology based on the use of metal and ammonium hydrofluorides for opening titanium ores and concentrates is presented [10]. As a result of the interaction of titanium and iron oxides with aqueous solutions of ammonium fluoride, aqueous solutions of HF (hydrofluoric acid) are formed, which, under the conditions of the process, have a strong corrosive effect on the material of the apparatus. This does not allow the use of this method in an industrial environment.

A high-temperature technology for the synthesis of titanium slag based on TiO₂, suitable for metallothermal reduction and synthesis of metallic titanium, has been described [11]. However, if magnesium is used as a metal-reducing agent in the reduction of slag, then this is actually the well-known Kroll process, which is the only method used in industrial conditions to obtain titanium sponge.

The process of synthesis of rutile from titanium slags from the Panzhihua deposit (China) by oxidative roasting of these slags at 1100 °C for 2 hours is presented [12]. However, this method is not new, since it is described in the preparation of various titanium ores for the Kroll process - the reduction of TiO₂ with magnesium.

Recently, various types of titanium electrolytic reduction processes in fluoride-chloride-salt melts have been intensively developed. TiO₂ is used as a starting material. These are FFC-, MER-, PRP-, Osaka-, Suzuki- and Chinuka-processes [13-18]. However, these processes have not yet passed the stage of laboratory tests and research using "pilot" installations.

In the near future, we can expect a breakthrough in the creation of new titanium technologies, which will significantly reduce its prime cost. In this case, the cost of titanium can become commensurate with the cost of stainless steel. As a result, titanium consumption could skyrocket and replace stainless steel and other materials in the global market.

In the opinion of the authors of the article, in order to expand the areas of application of titanium and its alloys, it is necessary to develop a technology that makes it possible to effectively separate titanium from impurities, and then convert the volatile titanium compound into metallic titanium (powder or sponge). The number of stages of such a process should be minimal (no more than 3-4 stages). Such a process can be the process of direct fluorination of titanium concentrates with elemental fluorine, which makes it possible to transfer titanium into a gaseous compound, for example, TiF₄, and at the same time effectively separate non-volatile impurity fluorides from TiF₄. Subsequently, the reduction of TiF₄ should be carried out in a high-frequency pulse discharge, and the resulting elemental fluorine should be recycled again into the fluorination process. In order to study the mechanism of chemical processes occurring in this proposed technology, it is necessary to start from basic studies, namely thermodynamic and kinetic.

In this paper, a method of processing titanium-containing minerals is introduced by fluorine technology with rutile as the raw material, and some thermodynamic and kinetic parameters are calculated to evaluate and propose a schematic diagram of a facility for fluorination of rutile concentrate in industrial conditions.

Point 4: The concentrate should contain LOI and volatiles, it is incorrect to write no impurities

Respone 4:

All Rutile concentrates used in the experiment were selected and refined with high TiO₂ content from the Tasky region (Omsk), Russia. The refining process is a heat treatment process so there is no LOI and volatiles. This concentrates has the following composition, % (mass): 93,2 TiO₂;1,8 SiO₂; 2,7 FeO + Fe₂O₃; 1,0 Al₂O₃; 0,6 MnO; 0,4 CaO; 0,2 MgO; 0,1 V₂O₅. The total content of the main components reaches 100%, which means that it does not contain other impurities.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors took into account most of the previous comments. However, the article still has several (technical) remarks. After correcting, I can recommend the article for publication.

1. The authors changed their conclusions about the activation energy value in comparison with the previous version of the article. However, even now there are questions about this. The point is that the activation energy was calculated with unreasonably high accuracy. The rate constants and the pre-exponential coefficient k₀ were calculated with an accuracy of 3 significant digits. The logarithm of the rate constants was shown with an accuracy of 4 significant digits?! And the activation energy was calculated with an accuracy of five significant digits: 4.6542 J/mol. It is not right. The number of significant digits in all values ​​should not be more than 3. All tables need to be edited.
2. The activation energy is written with the units of J in Table 1. Correctly should be J/mol.
3. The data presented in APPENDIX have no scientific value. I suggest, this APPENDIX should be removed because it consists well-known formulas and their transformations. It is not clear, for example, why Fig. 8b and 8c are needed. Authors can take a dozen other mathematical models for heterogeneous processes and show that they are not suitable for describing the process under study (since they will have low values ​​of the correlation coefficients). It is customary to show only the best options. Therefore, Figure 8a is enough to illustrate this conclusion. However, this figure repeats the data in Table 2 and Fig. 6. Therefore, this figure is shown twice and it should be removed too.

Author Response

Point 1: The authors changed their conclusions about the activation energy value in comparison with the previous version of the article. However, even now there are questions about this. The point is that the activation energy was calculated with unreasonably high accuracy. The rate constants and the pre-exponential coefficient k₀ were calculated with an accuracy of 3 significant digits. The logarithm of the rate constants was shown with an accuracy of 4 significant digits?! And the activation energy was calculated with an accuracy of five significant digits: 4.6542 J/mol. It is not right. The number of significant digits in all values ​​should not be more than 3. All tables need to be edited.

Respone 1: We fixed the error

Point 2: The activation energy is written with the units of J in Table 1. Correctly should be J/mol.

Respone 2: We fixed the error.

Point 3: The data presented in APPENDIX have no scientific value. I suggest, this APPENDIX should be removed because it consists well-known formulas and their transformations. It is not clear, for example, why Fig. 8b and 8c are needed. Authors can take a dozen other mathematical models for heterogeneous processes and show that they are not suitable for describing the process under study (since they will have low values ​​of the correlation coefficients). It is customary to show only the best options. Therefore, Figure 8a is enough to illustrate this conclusion. However, this figure repeats the data in Table 2 and Fig. 6. Therefore, this figure is shown twice and it should be removed too.

Respone 3: we removed this part.

We have added reference number 19, which is our previous conference paper.

Author Response File: Author Response.pdf