Comparative Analysis of Lead Ions and Ammonium Salts in Malachite Sulfurization-Assisted Flotation Based on Surface Layer Durability
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe submitted manuscript is devoted to the investigation on the sulfurization of malachite using Pb2+, ammonium salts and Na2S and its effect on flotation.
The topic of this paper aligns with the scope of Metals and will be of interest to the readership.
The obtained results are clear and supported by various analyses.
However, the following points should be clearly addressed before considering publication.
- Experiments with only Pb2+ and Na2S are required to clarify the effects of ammonium salts.
- Fig. 2: The authors mentioned that over-sulfidization hindered the flotation of malachite. It needs to further explain why the formation of more hydrophobic sulfurized layers reduces the floatability of malachite.
- The results clearly indicate the addition of Pb2+ and ammonium salts together with Na2S improves the efficiency of malachite flotation; however, the underlying reasons for this improvement remain unclear. What are the functions of Pb2+ and ammonium salts? Why three ammonium salts show different performance? Why the addition of Pb2+ and ammonium salts improve the formation of copper sulfides?
- ToF-SIMS analysis: The authors need to add Pb+ data to check the amount of PbS formed on the surface of malachite.
- Lines 315-316: How did the authors confirm this statement?
- Lines 321-322: This statement needs to be verified with the distribution of Pb+ ion.
- Lines 325-327: How did the authors check the durability of the sulfurized layer?
- Fig. 10: Why there's no Pb signal?
- The resolution of Figs. 3, 4, and 6 should be improved.
Author Response
Comment 1: Experiments with only Pb2+ and Na2S are required to clarify the effects of ammonium salts.
Response 1: Many studies have investigated the effects of Pb²⁺ and Na₂S, using Pb²⁺ as an activator reagent, which has shown good improvements in the malachite sulfurization process. However, this study explores the combined effects of Pb²⁺ and NH₄⁺ ions in sulfurization systems. The results indicate a significant enhancement, suggesting that the presence of both Pb²⁺ and NH₄⁺ ions plays a crucial role in improving the activation mechanism of the sulfurization process.
Comment 2: Fig. 2: The authors mentioned that over-sulfidization hindered the flotation of malachite. It needs to further explain why the formation of more hydrophobic sulfurized layers reduces the floatability of malachite.
Response 2: Over-sulfidization can lead to the formation of a thick, continuous copper sulfide layer on the malachite surface, potentially hindering the sites that enable optimal interaction with the collector and air bubbles.
Comment 3: The results clearly indicate the addition of Pb2+ and ammonium salts together with Na2S improves the efficiency of malachite flotation; however, the underlying reasons for this improvement remain unclear. What are the functions of Pb2+ and ammonium salts? Why three ammonium salts show different performance? Why the addition of Pb2+ and ammonium salts improve the formation of copper sulfides?
Response 3: The combined use of Pb²⁺ and NH₄⁺ salts before sulfurization activates the malachite surface and optimizes its hydrophobicity, allowing sodium sulfide to further alter the surface chemistry. This sequence forms more reactive species (Cu-S and Pb-S), enhancing collector attachment and improving flotation efficiency. The varying performances of the three ammonium salts, along with Pb²⁺ and ammonium salts' role in copper sulfide formation, can be attributed to their chemical properties and interactions with the malachite surface and flotation reagents. The chloride anion from (NH₄Cl) is simple and does not form strong complexes with metal ions, resulting in minimal surface modification. Ammonium nitrate (NH₄NO₃), an oxidizing agent, regulates pH and may promote oxidation but does not contribute sulfide ions or aid in sulfide formation. In contrast, ammonium sulfide (NH₄₂S) releases sulfide ions (S²⁻), which react with copper ions on the malachite surface to form copper sulfide (CuS), increasing the surface’s hydrophobicity and enhancing the mineral's attraction to collectors and air bubbles, thus improving flotation.
Comment 4: ToF-SIMS analysis: The authors need to add Pb+ data to check the amount of PbS formed on the surface of malachite.
Response 4: The Pb⁺ data has been included in the ToF-SIMS analysis after re-analyzing the samples, and the amount of PbS formed on the malachite surface was also assessed.
Comment 5: Lines 315-316: How did the authors confirm this statement?
Response 5: Previous studies have confirmed that both Pb²⁺ and NH₄NO₃, when used separately as chemical activators, significantly improve the flotation of copper oxide and zinc minerals, demonstrating excellent effects on floatability. This enhances the mineral surface before sulfurization, resulting in a higher recovery rate. The increased intensities of S⁻ and S₂⁻ (0.02634 and 0.03281, respectively) suggest that these sulfur species were more abundantly produced, likely because sulfurization is enhanced by forming more stable Cu-S species, due to the catalytic role of Pb²⁺ and NH₄⁺ ions.
Lines 315 and 316 have been carefully reviewed and modified in the revised manuscript.
Comment 6: Lines 321-322: This statement needs to be verified with the distribution of Pb+ ion.
Response 6: Thank you for your valuable comments. After re-analyzing the samples under different conditions, the Pb⁺ ion distributions on the mineral surface were measured. These results confirmed significant formation of Pb-S and Cu-S species when malachite was treated with Pb²⁺ and various NH₄⁺ ions, creating more active sites for xanthate-assisted adsorption and promoting the growth of sulfurized species. Notably, all statements have been updated throughout the revised manuscript.
Comment 7: Lines 325-327: How did the authors check the durability of the sulfurized layer?
Response 7: The author evaluated the durability of the sulfurized layer using ToF-SIMS analysis after treating malachite with Pb²⁺ and various NH₄⁺ ions prior to sulfurization. The durability was assessed by monitoring the increased signal intensities of sulfur species on the mineral surface under different conditions. This enhanced hydrophobicity improves the mineral's attraction to the collector and air bubbles, boosting flotation efficiency.
Comment 8: Fig. 10: Why there's no Pb signal?
Response 8: In Fig. 10, Pb-S vibrations typically occur in the 400–600 cm⁻¹ range. However, malachite and its alteration products, such as copper sulfides, have vibrational modes in this region, which may overlap and obscure the Pb-S signal.
Comment 9: The resolution of Figs. 3, 4, and 6 should be improved.
Response 9: In the updated version of the manuscript, we have improved the resolution of Figures 3, 4, and 6. All images were captured with high resolution using AFM, FESEM, and ToF-SIMS instruments.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper studies the possibilities to increase the efficiency of sulfurization-assisted flotation of malachite (basic copper carbonate). The authors propose the combination of lead ions and ammonium salts in sulfurization. It also seems to be a research gap that requires in depth studies. The authors study the effects of the above-mentioned factors on the durability of the sulfurized surface layer surface through micro-flotation tests. This is a detailed, extensive experimental paper that might lead to later applications. The results should, of course, be validated in a bigger scale. I recommend it for publication almost as it is. I have only a few minor comments:
- Why are the copper concentrations of malachite on line 139 and in Table 1 different? How does this concentration (56.14 wt. % on line 139) confirm “the presence of malachite”? I guess that the authors do not mean this, but this is rather a language problem.
- 2: It would be easier to compare the Figures with the similar scaling. Are there recoveries over 100%? Figure gives the SBX concentration as x10-4 mol/l, but the text speaks about x10-3. mol/l. The values are correct, but once again the similar format is recommended. What is the lead ion concentration in Fig. 2a?
- Check the writing of the authors names in ref. 9 in the reference list.
Author Response
Comment 1: Why are the copper concentrations of malachite on line 139 and in Table 1 different? How does this concentration (56.14 wt. % on line 139) confirm “the presence of malachite”? I guess that the authors do not mean this, but this is rather a language problem.
Response 1: Thank you for your thorough review. This was a mistake, and the author did not intend to write that. The sentence has been corrected on line 139, along with the Cu concentration (55.78%) mentioned in Table 1: 'Quantitative analysis revealed that the sample contained 55.78 wt.% Cu, confirming its purity.
Comment 2: It would be easier to compare the Figures with a similar scaling. Are there recoveries over 100%? Figure gives the SBX concentration as x10-4 mol/l, but the text speaks about x10-3. mol/l. The values are correct, but once again the similar format is recommended. What is the lead ion concentration in Fig. 2a?
Response 2: The Pb²⁺ concentration in Fig. 2a is 2 × 10⁻³ mol/L, with no recovery rate exceeding 100%. The highest recovery obtained was 93.7%, and the SBX concentration is × 10⁻⁴ mol/L. However, the text refers to a concentration of 2.5 × 10⁻³ mol/L, equivalent to 25 × 10⁻⁴ mol/L. In the updated version, all concentrations are standardized to the SBX concentration of × 10⁻⁴ mol/L.
Comment 3: Check the writing of the authors names in ref. 9 in the reference list.
Response 3: Thank you for pointing this out. I have carefully checked the authors' names in reference 9 in the reference list and have corrected them in the updated version.
Reviewer 3 Report
Comments and Suggestions for AuthorsComparative Analysis of Lead Ions and Ammonium Salts in Malachite Sulfurization-Assisted Flotation Based on Surface Layer Durability is very interesting paper in extractive non-ferrous metallurgy and flotation processes! Minor improvements are required.
Line 15, 16: Sulfurization-assisted flotation is a key process that uses sulfur compounds to modify mineral surfaces, enhancing hydrophobicity and flotation efficiency, especially for copper oxide minerals (in what temperature interval?)
Line 49: This challenge has driven a focus on sustainable solutions such as enhanced recycling, alternative sources, and advanced smelting technologies (such as..)
Line 150. and adjusting the pulp pH using NaOH or HCl (in what pH-range?)
Line 344, 345: Compared to conventional sulfidation (what are parameters for conventional sulfidation?), without competing Pb²⁺ ions, sulfide ions preferentially react with Cu, resulting in higher Cu⁺ and S²⁻ intensities and lower free S⁻ levels.
Line 421; Fig. 10 shows the FTIR spectra of malachite treated with Pb²⁺ + NH₄NO₃ + Na₂S system (in what time?) Did you study kinetics of this process?)
Line 457: likely due to the development of larger copper sulfide crystals (copper (II) sulfide? Or copper (I) sulfide?)
Conclusion
Line 477: The adsorption of copper sulfide and the durability of the sulfurized surface layer were also assessed (in what time?)
Author Response
Comment 1: Line 15, 16: Sulfurization-assisted flotation is a key process that uses sulfur compounds to modify mineral surfaces, enhancing hydrophobicity and flotation efficiency, especially for copper oxide minerals (in what temperature interval?)
Response 1: Thank you for this comment. Sulfurization-assisted flotation of copper oxide minerals typically occurs within a temperature range of 20°C to 60°C. In our study, we used an approximate temperature range of 20–25°C, which yielded satisfactory results. Higher temperatures (up to about 60°C) can accelerate reaction rates and enhance the effectiveness of sulfurization; however, temperatures above 60°C may lead to undesirable side reactions or reagent degradation.
Comment 2: Line 49: This challenge has driven a focus on sustainable solutions such as enhanced recycling, alternative sources, and advanced smelting technologies (such as..)
Response 2: One of the significant future challenges in copper production is the decline of primary copper resources. Alternative raw material sources, such as recycled scrap, mine tailings, low-grade ores, and industrial by-products, offer promising solutions. To address this, researchers are exploring advanced, eco-friendly, and cost-effective methods. One such approach is bioleaching (biomining), which uses microorganisms like Acidithiobacillus ferrooxidans to naturally oxidize sulfide minerals and release copper into solution. This method is particularly effective for low-grade ores and has minimal environmental impact. Additionally, advanced smelting technologies, such as oxygen-enriched smelting and flash smelting, help reduce greenhouse gas emissions and toxic byproducts.
Comment 3: Line 150, and adjusting the pulp pH using NaOH or HCl (in what pH range?)
Response 3: In this study, the pulp pH was adjusted to 9 ± 0.05 using NaOH or HCl, and added in the updated version with highlighting.
Comment 4: Line 344, 345: Compared to conventional sulfidation (what are parameters for conventional sulfidation?), without competing Pb²⁺ ions, sulfide ions preferentially react with Cu, resulting in higher Cu⁺ and S²⁻ intensities and lower free S⁻ levels.
Response 4: The conventional sulfidation parameters used were sodium sulfide at approximately 2 × 10⁻³ mol/L, pH= 9, and room temperature.
Comment 5: Line 421; Fig. 10 shows the FTIR spectra of malachite treated with Pb²⁺ + NH₄NO₃ + Na₂S system (in what time?) Did you study kinetics of this process?)
Response 5: Thank you for your valuable comment. Figure 10 presents the FTIR spectra of malachite treated with Pb²⁺ and various ammonium salts. Additionally, we conducted separate kinetic analyses for each condition, including the Pb²⁺ + NH₄NO₃ + Na₂S system.
Comment 6: Line 457: likely due to the development of larger copper sulfide crystals (copper (II) sulfide, or copper (I) sulfide?)
Response 6: The larger copper sulfide crystals were identified as copper(I) sulfide (Cu₂S), which enhances floatability by forming a more hydrophobic mineral surface compared to copper(II) sulfide (CuS).
Comment 7: Conclusion {Line 477: The adsorption of copper sulfide and the durability of the sulfurized surface layer were also assessed (in what time?)}
Response 7: The durability of the sulfurized surface layer on malachite was assessed using micro-flotation tests, AFM, ToF-SIMS, FESEM–EDS, FT-IR, and contact angle measurements, focusing on the stability of hydrophobic characteristics during flotation and their impact on mineral recovery efficiency after reagent addition.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors- Regarding Comment 1:
Although many studies have confirmed that the use of Pb²⁺ and Na₂S is effective in enhancing the sulfurization of malachite, they should be included as controls in the manuscript to clearly demonstrate the effectiveness of ammonium salts. Without this, it is difficult to justify the necessity of using ammonium salts. - Regarding Comment 2:
The authors' response is unconvincing. Even if a thicker sulfurized layer forms on the surface of malachite, it can still exhibit hydrophobicity, allowing interaction with the collector and air bubbles. - Regarding Comment 3:
Please add this explanation in the main text.
Author Response
Comment 1: Although many studies have confirmed that the use of Pb²⁺ and Na₂S is effective in enhancing the sulfurization of malachite, they should be included as controls in the manuscript to clearly demonstrate the effectiveness of ammonium salts. Without this, it is difficult to justify the necessity of using ammonium salts.
Response 1: We acknowledge that including Pb²⁺ and Na₂S as controls would strengthen the comparison and provide a clearer context for evaluating the effectiveness of ammonium salts in the sulfurization process. Therefore, additional experiments and discussions have been included in the updated manuscript, which has improved the manuscript's quality.
Comment 2: The authors' response is unconvincing. Even if a thicker sulfurized layer forms on the surface of malachite, it can still exhibit hydrophobicity, allowing interaction with the collector and air bubbles.
Response 2: Thank you for your valuable comment. We understand the concern regarding the potential hydrophobicity of the thicker sulfurized layer on malachite and its interaction with the collector and air bubbles. While a thicker sulfurized layer may exhibit some hydrophobic characteristics, our study explicitly focuses on its durability and stability under flotation conditions.
Based on previous studies and our experience, a thicker sulfur layer forms with increased sulfurization. However, excessive sulfurization leads to an overabundance of sulfur ions in the solution, which consumes the added collector and destabilizes the sulfur layer, resulting in poor sulfurization.
Comment 3: Please add this explanation in the main text.
Response 3: The explanation has been added to the main text in the new version.
