Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes
Round 1
Reviewer 1 Report
Thank you for submitting this work to metals.
Below a few comments on how I think you can improve this manuscript.
-line 68 - see typo
-MDPI will ask you to specify the company, city, country of all materials and machines used for the experiment.
This is a straight forward manuscript that can be published as is.
It is fine the way you present it. The analysis is thourough and nothing is missing.
When we did experiments like this we found that we have very good results with synthetic solutions that do not show other impurities,
but not necessarily similar good data with the actual industrial solutions, that often show larger amounts of impurities
So again, this manuscript is fine as it is - I just fear that it is of only limited value to industry.
If you could add an industrially relevant solution, I think you can make a much stronger case.
I leave that up to you.
Author Response
Response to Reviewer 1 Comments
Point 1: line 68 - see typo
Response 1: corrected
Point 2: MDPI will ask you to specify the company, city, country of all materials and machines used for the experiment.
Response 2:
Corrected:
АВ-17-8 (Russian Federation)
Purolite S 985 (United Kingdom)
АН-31 (Russian Federation)
Point 3: This is a straight forward manuscript that can be published as is.
It is fine the way you present it. The analysis is thourough and nothing is missing.
When we did experiments like this we found that we have very good results with synthetic solutions that do not show other impurities,
but not necessarily similar good data with the actual industrial solutions, that often show larger amounts of impurities
So again, this manuscript is fine as it is - I just fear that it is of only limited value to industry.
If you could add an industrially relevant solution, I think you can make a much stronger case.
I leave that up to you.
Response 3:
Added:
«Application of sulfate-chloride leaching of chromite concentration tailings, which are obtained during the processing of the Inagli and Konder deposits (Aldan region, Russian Federation, Russian Platinum PLC)…»
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes is very interesting paper. Some improvement is required:
Line 20: the platinum Group metals (PGM)
Line 90: The initial iridium concentration was 3.61 g/l. What is the concentration of the impurities (Ba,...)?
Line 97: What is reason for the choice of HCl and H2SO4 for this work?
line 93, 94: platinum was prepared by dissolving chloroplatinic
acid in concentrated hydrochloric acid/ H2PtCl6 in HCl. Why not only H2PtCl6?
Line 102, 103: distribution coefficient (D), PGM recovery into the sorbent (R, %), and separation coefficient (S) were calculated using the following Equations:
Line 124: at which temperature? What is the influence of temperature at the sorption Efficiency of Pt and Ir?
Line 132: The obtained negative values of the standard Gibbs energy (which chemical reactions?)
Line 137-138: Can you put units for К,R2, ΔG in Table 3?
Line: 144 What is the meaning of 1/EC (can you add it)
Line 175: Sorption Degree (%) at Y-Axis
Line 203: from the chromite waste heap leaching (what is the concentration of Chromium?)
Author Response
Response to Reviewer 2 Comments
Point 1: Line 20: the platinum Group metals (PGM)
Response 1: corrected
Point 2: Line 90: The initial iridium concentration was 3.61 g/l. What is the concentration of the impurities (Ba,...)?
Response 2: Barium peroxide decomposes with the release of oxygen and barium oxide, which can be converted in the presence of hydrochloric acid to BaCl2. The solubility of this chloride decreases rapidly with increasing concentration of hydrochloric acid; BaCl2 is practically insoluble at 20-30° C in acid with a concentration above 20%.
Added: « The content of trace impurities in the solution, including barium, was lower than the sensitivity of the analysis.»
Point 3: Line 97: What is reason for the choice of HCl and H2SO4 for this work?
Response 3:
Hydrochloric acid is necessary for the conversion of kinetically inert sulfate complexes of platinum metals (such as [Pt2(H2O)2(SO4)4]2 and others), which cause a significant complication in the sorption of PGM, into more labile chloride forms. However, hydrochloric acid is expensive. The sulfate-chloride process is known in industry.
Added reference: [29] Heap Leaching of Noble Metals / ed. by M. I. Fazlullin. Moscow. Mining Science Academy Publ., 2001. 647 p.
Point 4: line 93, 94: platinum was prepared by dissolving chloroplatinic
acid in concentrated hydrochloric acid/ H2PtCl6 in HCl. Why not only H2PtCl6?
Response 4:
To prepare working solutions, we used solid crystals of hydrochloric platinum acid. Hydrochloric acid was used to increase the degree of dissolution.
Point 5: Line 102, 103: distribution coefficient (D), PGM recovery into the sorbent (R, %), and separation coefficient (S) were calculated using the following Equations:
Response 5:
Added:
where C0 - concentration of PGM in the initial solution, mmol/l; CE - equilibrium concentration of PGM in solution after sorption, mmol/l; V - volume of the solution, l; Q - ionite suspension, g.
Point 6: Line 124: at which temperature? What is the influence of temperature at the sorption Efficiency of Pt and Ir?
Response 6:
The temperature of the production solutions of heap leaching is in the range of 15-20 °C. For this reason, the studies in this paper on the sorption extraction of platinum and iridium were carried out at a temperature of 20 °C.
Added (Line 63): «The initial concentrations, medium acidity and temperature selected are based on the approximation of the experiment to the real conditions that occur during the processing of platinum metal mining wastes by heap leaching…».
Point 7: Line 132: The obtained negative values of the standard Gibbs energy (which chemical reactions?)
Response 7:
corrected: «Based on the calculated values of the apparent constants of ion-exchange equilibria for individual sulfate-chloride solutions:
-Pt(II,IV)-HCl-H2SO4-H2O;
-Ir(III,IV)-HCl-H2SO4-H2O;
where - anionite in chloride form,
it can be concluded that the affinity of ion exchangers AH-31 and AB-17-8 to iridium is greater than to platinum, while the sorbent Purolite S985 is quite the opposite. The obtained negative values of the standard Gibbs energy confirm the thermodynamic probability of ion-exchange recovery of PGM complexes from the studied individual sulfate-chloride solutions (Table 3).»
Point 8: Line 137-138: Can you put units for К,R2, ΔG in Table 3?
Response 8: We have put unit for ΔG in Table 3.
Point 9: Line: 144: What is the meaning of 1/EC (can you add it)
Response 9: 1/EC=f(1/CE) – is a convenient graphical form for calculating the thermodynamic parameters (the equilibrium constant and the Gibbs energy) according to the Langmuir equation.
Point 10: Line 175: Sorption Degree (%) at Y-Axis
Response 10: corrected
Point 11: Line 203: from the chromite waste heap leaching (what is the concentration of Chromium?)
Response 11:
Added: «The chromium content in the solutions similar to production ones from the chromite waste heap leaching is less than 2 mg/l, which is due to the extremely low solubility of chromite, sulfates and chromium chlorides in sulfate-chloride media and, accordingly, does not affect the sorption parameters.»
Response to Reviewer 2 Comments
Point 1: Line 20: the platinum Group metals (PGM)
Response 1: corrected
Point 2: Line 90: The initial iridium concentration was 3.61 g/l. What is the concentration of the impurities (Ba,...)?
Response 2: Barium peroxide decomposes with the release of oxygen and barium oxide, which can be converted in the presence of hydrochloric acid to BaCl2. The solubility of this chloride decreases rapidly with increasing concentration of hydrochloric acid; BaCl2 is practically insoluble at 20-30° C in acid with a concentration above 20%.
Added: « The content of trace impurities in the solution, including barium, was lower than the sensitivity of the analysis.»
Point 3: Line 97: What is reason for the choice of HCl and H2SO4 for this work?
Response 3:
Hydrochloric acid is necessary for the conversion of kinetically inert sulfate complexes of platinum metals (such as [Pt2(H2O)2(SO4)4]2 and others), which cause a significant complication in the sorption of PGM, into more labile chloride forms. However, hydrochloric acid is expensive. The sulfate-chloride process is known in industry.
Added reference: [29] Heap Leaching of Noble Metals / ed. by M. I. Fazlullin. Moscow. Mining Science Academy Publ., 2001. 647 p.
Point 4: line 93, 94: platinum was prepared by dissolving chloroplatinic
acid in concentrated hydrochloric acid/ H2PtCl6 in HCl. Why not only H2PtCl6?
Response 4:
To prepare working solutions, we used solid crystals of hydrochloric platinum acid. Hydrochloric acid was used to increase the degree of dissolution.
Point 5: Line 102, 103: distribution coefficient (D), PGM recovery into the sorbent (R, %), and separation coefficient (S) were calculated using the following Equations:
Response 5:
Added:
where C0 - concentration of PGM in the initial solution, mmol/l; CE - equilibrium concentration of PGM in solution after sorption, mmol/l; V - volume of the solution, l; Q - ionite suspension, g.
Point 6: Line 124: at which temperature? What is the influence of temperature at the sorption Efficiency of Pt and Ir?
Response 6:
The temperature of the production solutions of heap leaching is in the range of 15-20 °C. For this reason, the studies in this paper on the sorption extraction of platinum and iridium were carried out at a temperature of 20 °C.
Added (Line 63): «The initial concentrations, medium acidity and temperature selected are based on the approximation of the experiment to the real conditions that occur during the processing of platinum metal mining wastes by heap leaching…».
Point 7: Line 132: The obtained negative values of the standard Gibbs energy (which chemical reactions?)
Response 7:
corrected: «Based on the calculated values of the apparent constants of ion-exchange equilibria for individual sulfate-chloride solutions:
-Pt(II,IV)-HCl-H2SO4-H2O;
-Ir(III,IV)-HCl-H2SO4-H2O;
where - anionite in chloride form,
it can be concluded that the affinity of ion exchangers AH-31 and AB-17-8 to iridium is greater than to platinum, while the sorbent Purolite S985 is quite the opposite. The obtained negative values of the standard Gibbs energy confirm the thermodynamic probability of ion-exchange recovery of PGM complexes from the studied individual sulfate-chloride solutions (Table 3).»
Point 8: Line 137-138: Can you put units for К,R2, ΔG in Table 3?
Response 8: We have put unit for ΔG in Table 3.
Point 9: Line: 144: What is the meaning of 1/EC (can you add it)
Response 9: 1/EC=f(1/CE) – is a convenient graphical form for calculating the thermodynamic parameters (the equilibrium constant and the Gibbs energy) according to the Langmuir equation.
Point 10: Line 175: Sorption Degree (%) at Y-Axis
Response 10: corrected
Point 11: Line 203: from the chromite waste heap leaching (what is the concentration of Chromium?)
Response 11:
Added: «The chromium content in the solutions similar to production ones from the chromite waste heap leaching is less than 2 mg/l, which is due to the extremely low solubility of chromite, sulfates and chromium chlorides in sulfate-chloride media and, accordingly, does not affect the sorption parameters.»
Response to Reviewer 2 Comments
Point 1: Line 20: the platinum Group metals (PGM)
Response 1: corrected
Point 2: Line 90: The initial iridium concentration was 3.61 g/l. What is the concentration of the impurities (Ba,...)?
Response 2: Barium peroxide decomposes with the release of oxygen and barium oxide, which can be converted in the presence of hydrochloric acid to BaCl2. The solubility of this chloride decreases rapidly with increasing concentration of hydrochloric acid; BaCl2 is practically insoluble at 20-30° C in acid with a concentration above 20%.
Added: « The content of trace impurities in the solution, including barium, was lower than the sensitivity of the analysis.»
Point 3: Line 97: What is reason for the choice of HCl and H2SO4 for this work?
Response 3:
Hydrochloric acid is necessary for the conversion of kinetically inert sulfate complexes of platinum metals (such as [Pt2(H2O)2(SO4)4]2 and others), which cause a significant complication in the sorption of PGM, into more labile chloride forms. However, hydrochloric acid is expensive. The sulfate-chloride process is known in industry.
Added reference: [29] Heap Leaching of Noble Metals / ed. by M. I. Fazlullin. Moscow. Mining Science Academy Publ., 2001. 647 p.
Point 4: line 93, 94: platinum was prepared by dissolving chloroplatinic
acid in concentrated hydrochloric acid/ H2PtCl6 in HCl. Why not only H2PtCl6?
Response 4:
To prepare working solutions, we used solid crystals of hydrochloric platinum acid. Hydrochloric acid was used to increase the degree of dissolution.
Point 5: Line 102, 103: distribution coefficient (D), PGM recovery into the sorbent (R, %), and separation coefficient (S) were calculated using the following Equations:
Response 5:
Added:
where C0 - concentration of PGM in the initial solution, mmol/l; CE - equilibrium concentration of PGM in solution after sorption, mmol/l; V - volume of the solution, l; Q - ionite suspension, g.
Point 6: Line 124: at which temperature? What is the influence of temperature at the sorption Efficiency of Pt and Ir?
Response 6:
The temperature of the production solutions of heap leaching is in the range of 15-20 °C. For this reason, the studies in this paper on the sorption extraction of platinum and iridium were carried out at a temperature of 20 °C.
Added (Line 63): «The initial concentrations, medium acidity and temperature selected are based on the approximation of the experiment to the real conditions that occur during the processing of platinum metal mining wastes by heap leaching…».
Point 7: Line 132: The obtained negative values of the standard Gibbs energy (which chemical reactions?)
Response 7:
corrected: «Based on the calculated values of the apparent constants of ion-exchange equilibria for individual sulfate-chloride solutions:
-Pt(II,IV)-HCl-H2SO4-H2O;
-Ir(III,IV)-HCl-H2SO4-H2O;
where - anionite in chloride form,
it can be concluded that the affinity of ion exchangers AH-31 and AB-17-8 to iridium is greater than to platinum, while the sorbent Purolite S985 is quite the opposite. The obtained negative values of the standard Gibbs energy confirm the thermodynamic probability of ion-exchange recovery of PGM complexes from the studied individual sulfate-chloride solutions (Table 3).»
Point 8: Line 137-138: Can you put units for К,R2, ΔG in Table 3?
Response 8: We have put unit for ΔG in Table 3.
Point 9: Line: 144: What is the meaning of 1/EC (can you add it)
Response 9: 1/EC=f(1/CE) – is a convenient graphical form for calculating the thermodynamic parameters (the equilibrium constant and the Gibbs energy) according to the Langmuir equation.
Point 10: Line 175: Sorption Degree (%) at Y-Axis
Response 10: corrected
Point 11: Line 203: from the chromite waste heap leaching (what is the concentration of Chromium?)
Response 11:
Added: «The chromium content in the solutions similar to production ones from the chromite waste heap leaching is less than 2 mg/l, which is due to the extremely low solubility of chromite, sulfates and chromium chlorides in sulfate-chloride media and, accordingly, does not affect the sorption parameters.»
Author Response File: Author Response.pdf
