Chlorination Treatment for Gold Extraction from Refractory Gold-Copper-Arsenic-Bearing Concentrates

Round 1

Reviewer 1 Report

Authors have made an attempt to extract gold from gold-copper-arsenic bearing refractory concentrates. The combined process of reductive sintering and chlorinating sintering was developed. However, it needs two times of high temperature roasting. Chlorine is toxic and strong corrosive at high temperature. The gold extraction yield is only 88.4%. Existing methods is still needed for the extraction of copper.These means that this combined process is not competitive, economic and safe. Matte smelting process is recommend to deal with the gold-copper-arsenic bearing refractory concentrates. The gold extraction yield have been proved to be possible as high as 98% in practice.

The following corrections/revisions essentially required to be addressed as given below:

1) In Line 73, what is the meaning of calcined at 923-973 K?

2) The occurrence forms of As, Cu, S and Fe are not given in detail.

3)In Section 2.6, the chlorination with CaCl₂ and SiO₂ is not properly described. Silica binds to calcium oxide to form calcium-silicate, which is then removed from the reaction zone?

4)The formation of As2O5 and the reaction of CuAsS is not given in Group l of Table 3.

5) Why the reaction product of Group 2 of Table 3 is CO₂ rather than CO?

6) In Line 213 and Line 218, the sublimation of Sn is higher in this work both with chlorine and calcium chloride without carbochlorination. It is not reasonable. The chlorination of Sn is similar to that of Ti and carbochlorination is needed.

Author Response

Response to Reviewer 1 Comments

 

The authors agree with the reviewer that the extraction of gold and other precious metals from any metallurgical products and wastes (electronic waste, spent car catalysts ets) during their melting in a furnace with a copper, lead, iron bath or with any other metal collector is easier and more obvious for any metallurgist. Noble metals almost completely pass into the metallic or matte phase, from where they are then extracted. But, unfortunately, this requires an existing metallurgical plant with a full production cycle (preparation, smelting, converting, electrolysis). The proposed process can be implemented on a small scale in the any suitable placewithout building a metallurgical plant.

The authors also want to note that the use of chlorine in industry is not a big and dangerous problem. Existing titanium and magnesium plants have been using these processes with chlorine gas for many years.

 

Thefollowingcorrections/revisionsessentially required to be addressed as given below:

 

Point 1: In Line 73, what is the meaning of calcined at 923-973 K?

 

Response 1: The authors agree with the reviewer. There is an error on line 73. Correct text: Cu-Au-As concentrate was obtained from mine fields located in East Kazakhstan (Table 1).

 

Point 2: The occurrence forms of As, Cu, S and Fe are not given in detail.

 

Response 2: The study of the forms of As, Cu, S and Fe in the concentrate was not the subject of this work. For thermodynamic calculations, arsenopyrite and arsenic sulfide were chosen in accordance with the literature data.

 

Point 3: In Section 2.6, the chlorination with CaCl₂ and SiO₂ is not properly described. Silica binds to calcium oxide to form calcium-silicate, which is then removed from the reaction zone?

 

Response 3: The addition of silica leads to an improvement in the chlorination process. The authors agree with the reviewer that silica binds with calcium oxide to form calcium silicate, which is then removed from the reaction zone.

 

Point 4: The formation of As2O5 and the reaction of CuAsS is not given in Group l of Table 3

 

Response 4: The reaction of the As2O5 production is not shown in the manuscript, as this compound decomposes to give As2O3 at temperatures above 588K. Reactions with CuAsS (Lautite) is not presented in the manuscript, because in the reference literature lacks thermodynamic constants (enthalpy and entropy) for Lautite.

 

Point 5:  Why the reaction product of Group 2 of Table 3 is CO₂ rather than CO?

 

Response 5: Thermodynamic calculations show that both reactions (both with the production of CO2 and with the production of CO) are thermodynamically possible, but a comparison of the Gibbs energy of these reactions shows that reactions with the production of CO2 are much more thermodynamically probable (Table). The authors believe that this is due to the presence of oxygen in the gas phase, which oxidizes CO to CO2.

Table.

#	Reactions	Gibbs energy (ΔG), kJ/mol
		Temperature, K
		473	673	873	1073	1273	1473

4	FeAsS(s) + 0.5 CH4(g) + 3.25 O2(g) = = FeO (s) + 0.5 As2O3 (g) + SO2(g) + + 0.5 CO2(g) + H2O(g)	-1040	-1020	-1000	-978	-956	-932
4a	FeAsS (s) + 0.5 CH4(g) + 3O2(g) = FeO + 0.5 As2O3(g) + SO2(g) + 0.5 CO(g) + H2O(g)	-219	-217	-214	-211	-207	-204
5	As2S3 + 1.5CH4(g) + 3O2(g) = = As2O3(g) + 1.5CO2(g) + 3H2S(g)	-888	-931	-963	-991	-1016	-1032
5a	As2S3 + 1.5CH4(g) + 2.25O2(g) = As2O3(g) + 1.5CO(g) + 3H2S(g)	-125	-142	-156	-169	-181	-192
6	ReS2(s) + 0.5CH4(g) + 4.75O2(g) = = 0.5Re2O7(g) + 0.5CO2(g) + 2SO2(g) + H2O(g)	-1326	-1299	-1271	-1244	-1216	-1187
6a	ReS2 + 0.5 CH4(g) + 4.5O2(g) = 0.5 Re2O7(g) + 0.5 CO(g) + 2SO2(g) + H2O(g)	-287	-283	-279	-274	-270	-265

 

Point 6: In Line 213 and Line 218, the sublimation of Sn is higher in this work both with chlorine and calcium chloride without carbochlorination. It is not reasonable. The chlorination of Sn is similar to that of Ti and carbochlorination is needed.

 

Response 6: Unfortunately, the authors did not find in the manuscript the remark given by the reviewer about the sublimation of tin in the process of chlorination. But the authors note that the work is devoted only to the process of gold removing from arsenic-containing products.

Reviewer 2 Report

The manuscript describes a process for gold recovery from Au-Cu-As containing ore. The submission is a good attempt. However, revisions are required before considering the publication.

1. In abstract, it is missing logic in structure. The problem statement and background to adequately motivate the essence of the research are not clear.

2. In the literature review, the main paragraph that speaks to the theme of the research work requires adequate literature review. Intensive literature review for the specific research problem state in the manuscript is required. A lot of research has been investigated in a refractory gold treatment in the field. It is very weak in the shape.

3. Lack of information for sample analysis. How did you get values for gold, silver and rhenium in Table 1?

4. Figures 1 and 2 could be improved for the better visualisation or could be emerged with separated two section for different parts.

5. A minor language improvement is required.

Author Response

Response to Reviewer 2 Comments

 

The manuscript describes a process for gold recovery from Au-Cu-As containing ore. The submission is a good attempt. However, revisions are required before considering the publication.

Point 1:  In abstract, it is missing logic in structure. The problem statement and background to adequately motivate the essence of the research are not clear.

Point 2: In the literature review, the main paragraph that speaks to the theme of the research work requires adequate literature review. Intensive literature review for the specific research problem state in the manuscript is required. A lot of research has been investigated in a refractory gold treatment in the field. It is very weak in the shape.

Point 3:  Lack of information for sample analysis. How did you get values for gold, silver and rhenium in Table 1?

 

Response 3: Sample preparation for all analytical measurements included milling and averaging. Material composition, prior to and following gold extraction, was characterized by solution inductively coupled plasma mass spectroscopy (ICP-MS, Agilent Technologies). The ICP-MS measurements required preliminary aqua regia leaching of the sample at boiling temperature. For ICP-MS samples containing compounds, which are insoluble in aqua regia, the following protocol was used: a 250 mg sample was mixed with 1.5 g lithium tetraborate (Li₂B₄O₇) and fused at 1373 K in a platinum crucible. After cooling to room temperature, the melt was dissolved in 10vol.% hydrochloric acid and then analyzed.

 

Point 4:  Figures 1 and 2 could be improved for the better visualisation or could be emerged with separated two section for different parts.

Point 5:  A minor language improvement is required.

 

Reviewer 3 Report

It's a very intriguing research for establishing the optimal conditions and process in order to extract gold with high arsenic content. The test procedure is systematically well established and the results are presented accordingly.

I recommend authors to give some geological and mining information about the ore deposit in Kazakhstan where the samples are taken.

I found it unclear about the number of the repeat tests, (the number of the sample sets used for each experiment conditions).  should be stated. Has only one test conducted for each condition? If it's the case, wouldn't it be better to have repeat tests to confirm the each outcome?

According to the results, the authors have concluded a final solution for the maximum extraction of gold for this type of ore and given a path to follow; At this point, I think the adaptability of this process on an industrial scale (most probably for the same mine that the samples were taken from) should also be discussed.

Other than these, I like the research and it is explained in a very clear structure.

Author Response

Thank you for your interest in the article. We are sending you the final version of the manuscript.

Reviewer 4 Report

This manuscript suggested the pre-treatment methods for removing the arsenic to increase the gold recovery of Au-Cu-As complex ore. The writing and figures were well organized. This manuscript is really interesting. Please find my comments and suggestion below:

- Page 2 Line 75: "74u" must be "74um"

- 2.3 Thermodynamic Calculation: more explanations are needed.

- Fig. 1, 2, and 3: the resolution is low. Please try to check it.

Good luck !!

Author Response

Thank you for your interest in the article. We are sending you the final version of the manuscript.

Round 2

Reviewer 1 Report

Their process needs two times of high temperature roasting and the final calcines as a kind of copper ores are sold to Copper smelting Enterprise. The gold extraction yield by their process is low. If the refractory gold-copper-arsenic-bearing concentrates are sold to Copper smelting Enterprise, the gold extraction yield has been proved to be possible as high as 98% in practice. From both the CO2 emissions and economic perspective, their process is not recommended.

Authors think that their process can be implemented on a small scale in the any suitable place without building a metallurgical plant. And the use of chlorine in industry is not a big and dangerous problem. Existing titanium and magnesium plants have been using these processes with chlorine gas for many years. In fact, only few industries could use chlorine. It is not widely used and needs professional safety precautions

From above, their process is unsafe, environmentally-unfriendly and not economic compared with the existing process in Copper smelting Enterprise.

From the viewpoint of research, the following corrections/revisions essentially required to be addressed as given below:

1) The occurrence forms of As, Cu, S and Fe are not given in detail.

2)The reaction of CuAsS, Cu2S is not given in Table 3.

 

Author Response

Response to a review 1 Comments

Point 1:     The occurrence forms of As, Cu, S and Fe are not given in detail.

Response 1: The study of the forms of As, Cu, S and Fe in the concentrate was not the subject of this work. A detailed study of the form of As, Cu, S and Fe in the concentrate is expected to be carried out in the next investigation.

Point 2: The reaction of CuAsS, Cu2S is not given in Table 3.

Response 1: Reactions with CuAsS (Lautite) is not presented in the manuscript, because in the reference literature lacks thermodynamic constants (enthalpy and entropy) for Lautite.

Reactions with Cu2S have inserted to the Table 3 of the manuscript, although the authors see no rational reason for including these reactions in the manuscript. Cu2S is not involved in the reactions of removing gold from products and in the sublimation reactions of arsenic and rhenium.