Selective Cementation of Gold Using an Iron Oxide and Zero-Valent Aluminum Galvanic System from Gold–Copper Ammoniacal Thiosulfate Solutions
, Sanghee Jeon 3, Akuru Kuze 1, Nako Okada 1, Ilhwan Park 4, Mayumi Ito 4, Yogarajah Elakneswaran 4 and Naoki Hiroyoshi 4,*Round 1
Reviewer 1 Report
Thiosulfate has been regarded as one of the most promising lixiviants that have potential to replace the highly toxic cyanide for gold extraction. One issue that severely impedes the large-scale application of the thiosulfate leaching technology is few effective methods for gold recovery from thiosulfate leach solutions. This paper proposes a novel strategy to recover gold from its thiosulfate leachate, in which galvanic interaction between iron oxides (electron mediator), i.e., hematite (Fe2O3) or magnetite (Fe3O4) and Al0 powders (electron donor) occurs promoting the preferential cementation of gold over copper onto iron oxides. The results from leaching and electrochemistry tests as well as morphology and composition analyses are interesting and significant. Overall, the work in this paper is good and suitable for publication in the journal “Metals”. Despite this, some revision is needed before its acceptance.
1. There are some grammatical errors in language, which need careful language polish.
2. Many format errors were found in the text and figures, and please correct.
3. The scan rate of 20 mV/s was used for electrochemical experiments in this paper. It is known that scan rate has a significant effect on electrochemical behavior such as current density, peak shape, peak number. The authors can explain why 20 mV/s was used?
4. Lines 305, 309: Inconsistent with the results shown in Fig. 4, the data of “94%”, “87%’, and “95” could not be found for Au/Cu recoveries.
5. The selectivity so-called for gold in this work seems exaggerated compared with copper. Although the copper recovery was significantly decreased from 99.9% for the AC/ZVAl system to 15% – 25% for the Hem/ZVAl or Mag/ZVAl system, the amount of copper (15% – 25%) co-cemented with gold onto iron oxides cannot be ignored, which should be stressed in this paper. In other words, if the selectivity of gold is much higher than that of copper, why as higher as 15% – 25% of copper was cemented together with gold using iron oxides as electron mediator.
Line 41: consist → consisting
Line 46: poster → posters
Line 72: researched → research
Lines 113 – 119: The sentence should be revised.
Line 294: ZVAI → ZVAl
In Fig. 6: there were two “AH- 2”.
Line 354: Cu(NH3)42- → Cu(NH3)42+
Line 389: Au3+ → Au+
Line 396: NH3 → 3 NH3
Line 298: The reaction is unbalanced.
Line 404: Cu(NH3)42 → Cu(NH3)42+
Author Response
Question no. 1: All grammatical errors were revised and highlighted in red colour.
Question no. 2 : All typo errors were revised and highlighted in red colour.
Question no. 3: The following paper will highlight a parametric study on the electrochemical behaviour of iron oxides. In the meantime, 20mV/s was used since the optimized scan rate gives us more defined voltammogram peaks.
Question no. 4: Sorry for the confusion. It was revised and highlighted in red colours.
Question no. 5: The following paper will highlight a parametric study on the electrochemical behaviour of iron oxides. In the meantime, a cementation model of iron oxides was presented. Theories have been thoroughly investigated for why iron oxide was selective only to gold. We are pleased to inform the reviewers that we already have a leading mechanism concerning the selective cementation of gold, which might be presented in the following paper.
Reviewer 2 Report
As we known, ammonium thiosulfate leaching is a promising alternative to the conventional cyanide method to extract gold from ores. The present study investigated the recovery of gold from the leachate using iron oxides (hematite, Fe2O3 or magnetite, Fe3O4),which gives new result and possibly propose a new strategy to recovery gold. After answering the following questions, it can be published in metals:
1) Some terms are not strict. ZVAl and Al seem the same material but have not the name.
2) Figs. 5-7, the lightness of Au and Cu elements does not show the drastically selective Au recovery on the oxides, which has been shown in Fig. 4. Why?
3) Fig. 8, the reference electrode name should be labeled.
4) Fig.11 has wrong codes. Other figures or tables have the same error.
5) Fig. 12, Au grows in different orientations under two conditions. Hence, is it possible to use magnetic field to enhance the recovery of Au?
6) References need to be rechecked.
English should be improved
Author Response
No. 1: Researchers hope to can get a more specific suggestion on this. (Should we change ZVAl to Al0 ?).
No. 2: The researchers highlighted the discussions regarding the evidence of selectivity concerning the intensity of copper signals between the different binary systems upon SEM-EDX point analysis, as shown in Figures 5-7. We suggested that copper deposition is limited for iron oxide/Al systems. (Line 329-336).
No. 3: Already modified.
No.4: Already Modified.
No.5: Researchers have already conducted different recovery processes. Yes, it is possible to use a magnetic field. This technique might be presented in the following paper.
No.6: Already cross-examined.
Reviewer 3 Report
The paper investigated the recovery of gold from the leachate using iron oxides. It has certain guiding significance to recovery of gold. Along with English editing the following comments should be addressed:
1. In the introduction, ZVAL and AC should be full names when they first appear. Their interpretation should be on line 66, not line 69.
2. In the introduction, the recovery method of gold in this study should be clarified.
3. In this paper, the format of many chemical formulas and units are not correct, please carefully check the MS and correct them. For example, line 78, 79, 80,81, 106, 111, 119, 120,142, 225 and 514.
4. The Figure 1 in the paper is not clear.
5. The font size of the chemical formula and horizontal and vertical coordinates of the two figures in Figure 8 should be consistent. Same as the Figure 10.
I think the English language needs to check carefully. There are many grammatical errors in the whole MS.
Comments for author File: 
Comments.pdf
I think the English language needs to check carefully. There are many grammatical errors in the whole MS.
Author Response
Comment No. 1: Already modified and highlighted in the paper.
Comment No.2: Researchers request the reviewer to be specific in the comment. "In the introduction part, the recovery method of gold in this study should be clarified."
Comment No. 3: Already modified and highlighted in the paper.
Comment no. 4: Already Modified.
Comment No. 5: Already Modified.
Reviewer 4 Report
Interesting article, current topic. No objections to the research methodology. The results were presented graphically and tabulated and discussed accordingly.
Some comments:
- fig. 2 - line numbers are confused with the drawing, the drawing is difficult to read
Fig. 3 - situation as above
Fig. 5, 6 and 7 - inscriptions on dark figures are practically unreadable, require changes
- the reference in the text to table 1 appears far after Table 1, first the information in the text, then only the table should appear
- Table1 - the row number merged with the table, which made the equations in the table practically illegible
- is equation (2) in table 1 balanced?
Fig. 8 - no information and description of points 1, 2, 3, 4, 5
- Fig. 9 and 10 - inscriptions on dark drawings are practically impossible to read, requires changes
Fig. 11 - row numbers have merged with the drawing, requires changes
Fig. 13 - as above
Author Response
Comment No. 1: Already Modified.
Comment no. 2: Already Modificed.
Comment no. 3: Already Modified.
Comment no. 4-6: Already Modified.
Comment no. 7: Figure 8 was discussed in the revised manuscript starting from line 352-418.
Comment 8-10: Already Modified.
