Slag after Smelting of Anode Mud: Role of Sulphiding Sintering

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Good work, English is fine but some minor revisions:

- Table 1: units are missing for the composition of the charge and the sintered mass weight.

- Page 2 in section "Materials and Methods": please provide more information on the XRF used to characterize the original samples.

- In the conclusion, please describe more the final purpose of the resulting cake (more explanation than it will go to hydrometallurgical processes. Will you use it in froth flotation?).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Article refers to the study of the composition of pyrometallurgical slags, treated by sintering for further leaching process. 

The  proposed process is not presented clearly enough, and a deeper  explanation of said process is required, indicating the relevance of the composition of the sintering process.

The slags processed are from the Balkhash Smelter, but no basic informations is provided about the production process in order to asses the type of slags, and how particular they are. The lead content for example is very high, so a discussion about that is recommended.

Some terms used in the article are not well understood, like electrolyte slag, copper electrolyte residues or dehydration slag.

Methodology is incomplete. There is no explanations about the sintering process, raw materials, or sampling methods.

Chemical analysis for the slag provided is not clear if it is a typical assay or corresponds to the sample used.

The proposed mechanism for the formation of the sup hides is repeated throughout the article several times.

Several assertion throughout the article are poorly supported or are questionable. Among them:

- That the sintering process determines the efficiency of the entire process is poorly supported. No connection with te leaching step is analyzed.

- No presence of sulphur detected according to chemical analysis. A thermodynamic analysis is recommended to explain the Copper content.

Incorporate units in Table 1.

There is no information of the sintering at 600 C and the explanation about selecting 800 C should be more thorough, specially on the assertion that 800 C there is complete transformation to sulfides.

Consequently, the conclusion should be revised. The conditions reported as optimum are not fully supported by the results and/or the discussion.

Comments on the Quality of English Language

Minor editing of certain phrases should be performed to improve understanding. For example in page 3 it says:

"It should be noted that the basis of deep selection is the sintering operation ..." This paragraph is not clear enough and might get some poor understanding of the author's idea.

Also some technical terms used seems to be particular to the authors, like electrolyte slag, as mentioned before. It is suggested the use of terminology which is  widely accepted.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper provides an interesting overview of sulphiding sintering as applied to copper smelter slag.  The chemical phenomena observed is interesting, however revisions are needed to better contextualize the results both with prior engineering art, previously reported chemical phenomena, and thermodynamics.  Furthermore, additional information surrounding experimental methods are needed.  The following revisions are recommended:

1. Please provide further literature review with regards to sulphiding / sulfidation processes for the treatment of slags and mineral bodies.  Referencing prior art from both laboratory benchtop and industrial scale testing of sulphiding / sulfidation processes will help contextualize the scalability and feasibility of the process and the relevant chemical phenomena observed in the study.

2. Please elaborate on the experimental design, equipment, and methods employed.  Please also discuss further gas atmosphere control in the experiment, as this is very important to set oxygen and sulfur partial pressures for your sulphiding reactions.  Please elaborate on the particle bed morphology used (particle size, porosity, etc.) and its role in the process.

3. Please include thermodynamic data to contextualize the results obtained.  Predominance area (Kellogg) diagrams for metal compound phase formation as a function of oxygen and sulfur partial pressures will help inform why some elements had a higher affinities to form sulfides versus oxides. 

4.  Please consider and discuss the results of element partitioning between oxide, sulfide, and metallic phases in the context of known chalcophilic-lithophilic-siderophilic trends.

Comments on the Quality of English Language

Please improve the text and abstract by replacing vague statements with more descriptive text.  Example from the abstract: "The main transformations in the sintering process were determined, and the optimal modes were identified. The structures of slags and sintered materials obtained during the experiments were studied by electron-probe microanalysis." - Why not state what the optimal modes and structures are? 

Please also correct any typos / unusual phrasing in the text as appropriate.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Firstly, I appreciate the authors' efforts in revising the article to address the reviewers' comments. While the article has improved, additional revisions are necessary to make it suitable for publication. Here are some further comments:

1.     Title: The new title can be misleading. The article discusses the characterization of products from a sintering process using slags from the pyrometallurgical treatment of anodic slimes. The proposed title suggests that the article is about slags from the treatment of anodic slimes, which is not entirely accurate. 

2.     Language and Style: The English language and overall writing style still require significant improvement. A thorough review of the style is recommended before resubmission. 

3.     Bibliographic References: Please exercise caution when using references. Here are some specific issues:

a.     Line 34: “The work [1] is dedicated to the use of sulfidation for the extraction of heavy metals in the waste from low-grade mining.” The cited article actually discusses low-grade ores, not wastes. Consider citing as "Lan et al. [1] report..."

b.     Line 59: “The authors in work [8] investigated the application of sulfidation to stabilize heavy metals in mineral processing wastes. The materials of articles [9] are very interesting. These works provide a fundamental understanding of the thermodynamic and kinetic aspects of sulfidation processes for the recovery of metals from various mineral sources.” This paragraph is unclear as it seems to refer to references [8] and [9] together. Additionally, the phrase “it is very interesting” lacks supporting discussion or data. 

c.     Line 67: “There is considerable focus on further processing copper smelting residues, including those derived from anode mud in copper smelting [11–17].” References [11], [12], [13], [14], [16], and [17] pertain to copper smelting, while [15] refers to iron converting slags. None of these references mention anodic slime slags, which are distinct.

d.     Line 74: Check references [8, 19, 918]. There appears to be a typographical error with reference [918].

e.     Line 81: “…has led to the discovery of novel properties in superionic conductors and p-type semiconductors [20–28].” It is unclear how this information is relevant to the article’s objectives.

f.      Line 89: “The technology for processing cyclone dusts from lead production, achieving a rhenium extraction of up to 84.3% in solution and arsenic extraction up to 70%, is detailed in reference [30].” Reference [30] actually discusses phase relations in sulphides, not the stated technology.

4.     Line 101: Figure 1 is clear, except that the Kaldo process is related to smelting and not melting. Smelting refers to pyrometallurgical refining, while melting refers to a phase change. Please review and correct similar references throughout the article.

5.     Line 122: “Besides, elemental composition of original slag was subjected with X-ray fluorescence spectrometer with wave dispersion AXIOS.” This phrase needs to be clearer and more precise.

6.     A more detailed description of the sintering process is needed, including the selected experimental conditions. Table 2 implies that an experimental design methodology was used, which should be mentioned in the Materials and Methods section.

7.     Line 139: “The proposed technology intended for processing of such slags includes sintering of the charge with sodium sulphate and carbonate, leaching of the sintered mass with a sulphate-carbonate solution, decomposition of the resulting solutions with the release of selenium, tellurium, antimony, arsenic, melting of the sintered mass with the release of lead containing gold and silver, as well as matte containing copper.” This paragraph should be restructured for clarity, with parts included in the methodology or introduction sections.

8.     Line 143: “It should be noted that the basis of deep selection is the sintering operation where the intensity…” Please clarify what is meant by "deep selection."

9.     Line 155: “The negative value of the Gibbs energy indicates the possibility of these reactions” Probable meaning is that the reactions are spontaneous. This phrase needs to be clarified.

10.  Line 156: “The use of Na₂S as a sulphidizer during sintering is due to the fact that this reagent is a poison. Elemental sulphur, which can also be used as a sulphidizer, is expensive. Therefore, Na₂SO₄was used as a sulphidizer.” This writing requires substantial improvement.

11.  Line 186: “Before mixing and sintering all the components of the charge were milling. More than 90 % of the particles were less than 74 microns in size. Sintering was carried out in alumina crucibles in the NTS 08/16 Nabertherm GmbH furnace by atmosphere pressure. The main technological parameters of the sintering process are specified in Table 2.” This should be part of the Methodology section.

12.  Line 199: “The most significant changes occurred in sintered mass samples 6 and 7.” Please mention the corresponding figure

13.  Line 268: “...extraction of metals from solution into marketable products.” This topic has not been addressed throughout the article.

14.  Line 252: “The optimal amount of additives based on the weight of the slag 282 is Na2SO4 – 45 %, Na2CO3 – 15 %...” The previous discussion should explain how these numbers were determined as optimal. They appear to be derived from experiments, but there is no discussion about optimization.

15.  Line 292: “As a result of sintering the slag of the Kaldo furnace with reagents, a redistribution of the forms of metal content took place 294 in accordance with the Goldschmidt classification - in the slag forming – Si, Al, Na remained, in the sulphide form - Pb, Cu, Sb, As, Se, Te..” This was not previously discussed.

16.  Line 298: “This technology of sulphidization of metals in slag can be used for other types of slag before its flotation beneficiation.” This has not been discussed or demonstrated in the article.

Comments on the Quality of English Language

Writing can be greatly improved. Thorough revision before submission is recommended.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for making the revisions.  Please address the following minor points:

- please include references to current or former industrial scale operations of mineral sulfidation processes such as at Falconbridge, PT Inco/Vale, Eramet / Le Nickel, and Tsingshan for nickel/ferronickel/NPI with various sulfur sources.  While these sulfur sources and products may be different, references to these commercial sulfidation processes will help support claims of the scalability of your process.

- the process is suggested to be economical and sustainable -this claim has not been sufficiently supported by emissions or environmental impact data projections in the paper, references to published LCA, or cost data by others.  For example, published data for sulfidation of oxides with elemental sulfur is available. Alternatively, please further clarify that further analysis is needed to understand sustainability and cost.

Author Response

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Author Response File: Author Response.pdf