Deposition of Arsenic from Nitric Acid Leaching Solutions of Gold–Arsenic Sulphide Concentrates
, Evgeniy Kuzas, Oleg Dizer, Dmitry Golovkin and Maksim TretiakRound 1
Reviewer 1 Report
Manuscript ID: metals-1211634
Title: Deposition of arsenic from nitric acid leaching solutions of sulfide-containing non-ferrous metal raw materials
Authors: Kirill Karimov et al.
Title must be rewrite. Authors need to describe raw materials. For example: Precipitation of arsenic from solutions obtained after nitric acid leaching of gold-arsenic sulfide concentrates
Abstract very long, it is necessary to reduce the number of words, for example, to exclude sentences: Previously, weakly acidic effluents containing As (III) and solutions for processing converter dust from copper smelting production are neutralised with sodium hydrosulfide to fix As (III) in a sulfide form (As2S3), containing 30–60% arsenic.
According to SEM/EDS and XRF sediment data, results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulfide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that ...
Introduction. Authors should more clearly highlight the novelty of this study.
Line 43. Authors must describe harmful impact to the environment of pyrometallurgical methods.
Line 48-52. This text is taken from the abstract. Authors do not need to write the same words. Choose what to keep and what to delete.
Line 90. What is the deposit of gold-arsenic sulfide concentrates are used in this research?
Line 99. What are the “other chemicals”?
Line 148. Add reference for solubility data.
Figure 2-4. Authors should use the same abbreviations in Figures and Figure captions: precipitation degree of arsenic (III) or removal efficiency of As.
Figure 6. Why the labels on the x-axis are: 38, 51, 64, 77 °C?
Figure 7. Why the labels on the x-axis are: 7 14, 21, 28, 35 g/L?
In all chemical reactions, it is necessary to indicate in what form each reagent is (solid, liquid, gas) and which of them precipitates (by an arrow ↓)
In Figure 9, only one mage shows the morphology of the particle, the remain of the images show the surface. Can the authors add image of individual particles of the precipitates?
Figure 10. Authors must add the second XRD figure.
- The authors can add a flowchart with the leaching and further precipitation processes to showing the optimal parameters and mass balance for arsenic.
- Authors should add discussion about the application of their results in industry. What are the further methods to utilization of the arsenic sediments?
The level of English is average. I read a previous article by these authors in Hydrometallurgy "Kinetics and mechanism of arsenopyrite leaching in nitric acid solutions in the presence of pyrite and Fe (III) ions". The level of English there is much higher. I ask the authors to improve the quality of the English.
Technical errors:
Line 49, 64. Authors must write full chemical formula of arsenopyrite, enargite, tennantite, goethite.
Figure 6. Use “T” for temperature.
Author Response
Dear reviewer, thank you for your work, it helped us to improve our article.
Title must be rewrite. Authors need to describe raw materials. For example: Precipitation of arsenic from solutions obtained after nitric acid leaching of gold-arsenic sulfide concentrates
It is corrected on «Deposition of arsenic from nitric acid leaching solutions of gold-arsenic sulfide concentrates».
Abstract very long, it is necessary to reduce the number of words, for example, to exclude sentences: Previously, weakly acidic effluents containing As (III) and solutions for processing converter dust from copper smelting production are neutralised with sodium hydrosulfide to fix As (III) in a sulfide form (As2S3), containing 30–60% arsenic.
According to SEM/EDS and XRF sediment data, results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulfide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that ...
The first sentence is excluded.
Introduction. Authors should more clearly highlight the novelty of this study.
The novelty of this study is the investigation of the arsenic sulfide precipitation from leaching solutions containing oxidants with minimization of sodium hydrosulfide oxidation.
Line 43. Authors must describe harmful impact to the environment of pyrometallurgical methods.
It is added.
Line 48-52. This text is taken from the abstract. Authors do not need to write the same words. Choose what to keep and what to delete.
Some words were deleted from the abstract.
Line 90. What is the deposit of gold-arsenic sulfide concentrates are used in this research?
The studies used solutions obtained after nitric acid leaching of gold-arsenic sulfide concentrates of Uderey deposit, containing, %: 21,6 Fe, 12,2 As, 20,0 S, 3,5 Al; 30 g/t Au [26,27].
Line 99. What are the “other chemicals”?
H2SO4 and NaOH used in this work were of analytical grade.
Line 148. Add reference for solubility data.
We added the following reference: Stephen, H., Stephen, T. Solubilities of Inorganic and Organic Compounds. Volume 1: Binary Systems. Part 1. Oxford: Pergamon Press, New York, USA. 1963. 975. [https://doi.org/10.1016/B978-0-08-009923-1.50006-9
Figure 2-4. Authors should use the same abbreviations in Figures and Figure captions: precipitation degree of arsenic (III) or removal efficiency of As.
It is corrected.
Figure 6. Why the labels on the x-axis are: 38, 51, 64, 77 °C?
It is corrected.
Figure 7. Why the labels on the x-axis are: 7 14, 21, 28, 35 g/L?
It is corrected.
In all chemical reactions, it is necessary to indicate in what form each reagent is (solid, liquid, gas) and which of them precipitates (by an arrow ↓)
It is corrected.
In Figure 9, only one mage shows the morphology of the particle, the remain of the images show the surface. Can the authors add image of individual particles of the precipitates?
It is added.
Figure 10. Authors must add the second XRD figure.
It is added.
The authors can add a flowchart with the leaching and further precipitation processes to showing the optimal parameters and mass balance for arsenic.
It is added.
Authors should add discussion about the application of their results in industry. What are the further methods to utilization of the arsenic sediments?
The applications of research results in industry allow to reduce consumption of expensive NaHS.
The hydrothermal mineralization stabilization can be adopted to improve the stability of amorphous As2S3. The results showed that the As leaching concentration of mineralized As2S3 was only 4.82 mg/dm3. Furthermore, the amorphous As2S3 could be transformed into crystallized As2S3 (orpiment) in the presence of mineralizer Na2SO4. Simultaneously, the As leaching concentration of crystallized As2S3 was further re-duced to 3.86 mg/dm3 [20].
The level of English is average. I read a previous article by these authors in Hydrometallurgy "Kinetics and mechanism of arsenopyrite leaching in nitric acid solutions in the presence of pyrite and Fe (III) ions". The level of English there is much higher. I ask the authors to improve the quality of the English.
We add certificate a to confirm the translation by the native speaker competence.
Technical errors:
Line 49, 64. Authors must write full chemical formula of arsenopyrite, enargite, tennantite, goethite.
These chemical formulas are written full.
Figure 6. Use “T” for temperature.
It is corrected.
Reviewer 2 Report
Dear authors, the manuscript deals about an interesting topic. However, the manuscript needs important major revisions before their potential publication.
Authors need to perform a wide description of currently technologies that were studied for the recovery of gold from refractory ores. The nitric acid leaching is one of the potential methods but there are other that could be classified as most promising. Also, the traditional technology with cianure needs to be cited.
In addition, it was necessary a wide characterization of ore used. What is the concentration of gold in the leaching? The main objective is the recovery of gold form refractory ores and then, the As precipitation. So, it is necessary to show the gold content in the ore and if leaching conditions are the best.
Reaction 1 or 7 correspond to H2SO4 solution. It is the same mechanism in HNO3 medium? The research is perfomed in HNO3 medium and H2SO4 is obtained by oxidation of sulfides? A better description was necessary in order to a better understanding of the document.
Figures needs to be improved. For example, the Figure 6. The x-axys. Why 38, 51, 64 and 77ºC? it is better to use 40, 50, 60, 70 and 80ºC. Figure 4, select only one. Both Figures represent the same data? Temperature is better to write as T(ºC) not t (ºC).
When authors said that oxidation of sulfide by Fe(II) lead to sulfur, is is confirmed by any analysis?
How was performed the determination of Fe(II) in the solution? A wide description was necessary.
The title is not related with the content of the manuscript as the manuscript do not refer to leaching solutions. Only, the behaviour of As was studied.
Author Response
Dear reviewer, thank you for your work, it helped us to improve our article.
Authors need to perform a wide description of currently technologies that were studied for the recovery of gold from refractory ores. The nitric acid leaching is one of the potential methods but there are other that could be classified as most promising. Also, the traditional technology with cianure needs to be cited.
It is added.
In addition, it was necessary a wide characterization of ore used. What is the concentration of gold in the leaching? The main objective is the recovery of gold form refractory ores and then, the As precipitation. So, it is necessary to show the gold content in the ore and if leaching conditions are the best.
The studies used solutions obtained after nitric acid leaching of gold-arsenic sulfide concentrates of Uderey deposit, containing, %: 21,6 Fe, 12,2 As, 20,0 S, 3,5 Al; 30 g/t Au [26,27]. The method and conditions of leaching were previously described in detail [26].
Reaction 1 or 7 correspond to H2SO4 solution. It is the same mechanism in HNO3 medium? The research is perfomed in HNO3 medium and H2SO4 is obtained by oxidation of sulfides? A better description was necessary in order to a better understanding of the document.
The solution after nitric acid leaching does not contain free nitric acid because in order to remove free nitric acid and increase the degree of its utilisation, a new batch of the concentrate with an excess (t = 80 °C) was added to the solution following leaching until the end of the evolution of nitrous gases. Nitrate ions are most likely associated with Fe(III) ions. Reactions 6-8 were added.
Figures needs to be improved. For example, the Figure 6. The x-axys. Why 38, 51, 64 and 77ºC? it is better to use 40, 50, 60, 70 and 80ºC. Figure 4, select only one. Both Figures represent the same data? Temperature is better to write as T(ºC) not t (ºC).
It is corrected.
When authors said that oxidation of sulfide by Fe(II) lead to sulfur, is is confirmed by any analysis?
It is confirmed by the increased content of sulfur (53 %) and a reduced arsenic content (35 %) in cakes relative to the precipitate obtained from pure model solutions containing 25–36 % sulfur and EDS, EDS mapping data.
How was performed the determination of Fe(II) in the solution? A wide description was necessary.
The Fe (II) concentration in the solution was determined by potassium dichromate (K2Cr2O7) titration. To determine the Fe (II) concentration the sample solution transfers into an Erlenmeyer flask. Using a graduated cylinder, add 25 mL of 1 M H2SO4 to flask. Then add 10 cm3 of the phosphoric acid solution and 8 drops of sodium diphenylamine sulfonate indicator to the flask. The intense purple color produced by the first drop of excess K2Cr2O7 signals the end point for the titration.
The title is not related with the content of the manuscript as the manuscript do not refer to leaching solutions. Only, the behaviour of As was studied.
It is corrected.
Reviewer 3 Report
Deposition of arsenic from nitric acid leaching solutions of sulfide-containing non-ferrous metal raw materials
by Kirill Karimov, Denis Rogozhnikov, Evgeniy Kuzas, Oleg Dizer, Dmitry Golovkin and Maksim Tretiak
The topic is interesting and relevant to sustainable extractive metallurgy; the experiments seem well designed and carried out; and the manuscript is very well written and easy to follow. Removing arsenic from the leaching solution is a very important step in extractive metallurgy. The authors reviewed a few options and provided detailed study on the option of precipitating arsenic sulfide. In my opinion, this is not a good option because arsenic sulfide is easily dissolved in the presence of water and oxygen. This kind of oxidative dissolution reactions occur globally in sulfide minerals, forming acid mine drainage. In spite of this limitation, the results have some values for comparison of the available options. The authors should provide more discussions on the limitations of this technique, such as oxidative dissolution of arsenic sulfide, overconsumption of reagent NaHS due to formation of FeS, and oxidation of NaHS due to residue nitrate in the leaching solution, and ways for safe disposal of arsenic sulfide without causing oxidative dissolution.
Other minor revisions are:
Line 128: provide mole concentration of H2SO4 and NaOH solutions.
Line 151: Figure 1. Provide more parameters of the Purbaix diagram, i.e., total concentration of sulfur species and total concentration of arsenic species.
Line 159-160: The should be the
Line 330: Figure caption suggests 2 XRD patterns (a) and (b) but there is only 1 XRD pattern provided.
Author Response
Dear reviewer, thank you for your work, it helped us to improve our article.
The topic is interesting and relevant to sustainable extractive metallurgy; the experiments seem well designed and carried out; and the manuscript is very well written and easy to follow. Removing arsenic from the leaching solution is a very important step in extractive metallurgy. The authors reviewed a few options and provided detailed study on the option of precipitating arsenic sulfide. In my opinion, this is not a good option because arsenic sulfide is easily dissolved in the presence of water and oxygen. This kind of oxidative dissolution reactions occur globally in sulfide minerals, forming acid mine drainage. In spite of this limitation, the results have some values for comparison of the available options. The authors should provide more discussions on the limitations of this technique, such as oxidative dissolution of arsenic sulfide, overconsumption of reagent NaHS due to formation of FeS, and oxidation of NaHS due to residue nitrate in the leaching solution, and ways for safe disposal of arsenic sulfide without causing oxidative dissolution.
The hydrothermal mineralization stabilization can be adopted to improve the stability of amorphous As2S3. The results showed that the As leaching concentration of mineralized As2S3 was only 4.82 mg/dm3. Furthermore, the amorphous As2S3 could be transformed into crystallized As2S3 (orpiment) in the presence of mineralizer Na2SO4. Simultaneously, the As leaching concentration of crystallized As2S3 was further reduced to 3.86 mg/dm3 [25].
Line 128: provide mole concentration of H2SO4 and NaOH solutions.
It is added.
Line 151: Figure 1. Provide more parameters of the Purbaix diagram, i.e., total concentration of sulfur species and total concentration of arsenic species.
Concentrations of As, S, Fe are 1 mol/dm3.
Line 159-160: The should be the
We don’t understand.
Line 330: Figure caption suggests 2 XRD patterns (a) and (b) but there is only 1 XRD pattern provided.
It is added.
Round 2
Reviewer 1 Report
The authors have corrected all comments. The scientific data of the article looks good.
However, I asked the authors to make a significant improvement in the English. The certificate sent by the authors is not even a certificate, but just a signed letter.
This letter is not a confirmation of the high level of English.
If the authors used the service of English Editing by MDPI, Elsevier, or similar resources and provided a certificate with a unique number, this would be an argument.
The article does not contain any revision of the English language. This is very sad fact.
I would like to draw the attention of the Metals editor to this fact.
Author Response
Dear reviewer, thank you for your time and attention to our work. We coordinated our manuscript with English-speaking proofreader, and the corresponding letter from him was forwarded to Academic Editor.
Reviewer 2 Report
Dear authors
The manuscript has been improved. However, there are some questions and some comments that need to be improved.
Introduction: Line 51. Authors need to performed a wide description of nitric acid leaching process in order to know the best advantages not only that was necessary to take like this research about the arsenic deposition.
Authors said that remove free nitric acid. However, there are NO3- and acid medium. It is an efficient method to heat the leaching for the evolution of nitrous gases? It is expensive and contaminant.
Revise Figures 6 and 7. It is low size and difficult to see the data
Revise the numbers in the X-axis. I think is better to use numbers without decimals.
Authors said that with increasing temperature the amount of As in the solution increases. One reason could be that solubility of precipitate (Kps) increases with temperature
Please, change Purbaix by Pourbaix diagram
Authors said that the Fe(II) content is calculated by K2Cr2O7. However, this oxidant could react with other reduced species.
Authors need to show in the document and specially, in the conclusions the advantage of this method comparing to traditional used for the removal of As
Author Response
Dear reviewer, thank you for your work, it helped us to improve our article.
Introduction: Line 51. Authors need to performed a wide description of nitric acid leaching process in order to know the best advantages not only that was necessary to take like this research about the arsenic deposition.
It is added (Line 53-58).
Authors said that remove free nitric acid. However, there are NO3- and acid medium.
NO3- ions are mostly in the form of Fe(NO3)3 into solution since solution contains 4 g/l Fe (II) ions and the stability constant of Fe(NO3)3 is larger than that of Fe2(SO4)3 (its 10 and 0.000066 respectively). Nitric acid is widely used in chemical analysis as an oxidizer agent for Fe (II) ions at sulfate solutions. If the solution contains Fe (II) then the concentration of free nitric acid should be minimal.
It is an efficient method to heat the leaching for the evolution of nitrous gases? It is expensive and contaminant.
It is added (Line 59-62).
Revise Figures 6 and 7. It is low size and difficult to see the data
It is corrected.
Revise the numbers in the X-axis. I think is better to use numbers without decimals.
It is corrected.
Authors said that with increasing temperature the amount of As in the solution increases. One reason could be that solubility of precipitate (Kps) increases with temperature
The increase in temperature leads to a significant decrease in the deposition of arsenic (III) sulfide it is different from that obtained when precipitating arsenic from pure model solutions [33]. When the temperature increased from 25 to 85 ◦C, no difference was observed in the precipitation efficiency of As at pure model solutions without Fe(III) ions.
Please, change Purbaix by Pourbaix diagram
It is corrected.
Authors said that the Fe(II) content is calculated by K2Cr2O7. However, this oxidant could react with other reduced species.
According to Pourbaix diagram (Fig. 1) the solution does not contain any other reduced species of sulfur in presence arsenic. Cation exchange column allows to separate iron cations from arsenic anions that is said at line 126.
Authors need to show in the document and specially, in the conclusions the advantage of this method comparing to traditional used for the removal of As
As compared to the traditional neutralisation method, the production of arsenic (III) sulfide without the formation of free acid or the use of additional oxidants and lime as a neutraliser contributes to the production of a more concentrated arsenic sludge for a given volume (42 % As). Arsenic trisulfide is stable under reducing conditions at pH < 4.
Author Response File: 
Author Response.pdf
