A Brief Note on the Heap Leaching Technologies for the Recovery of Valuable Metals

Round  1

Reviewer 1 Report

Manuscript is recommended for publication after some small revision of the points shown in below.

Line126. Figure 1. Chart of a gold heap-leach operation (adopted and modified from the reference [22]).

Lines 151, 152. Figure 2. Flow diagrams of heap leaching processes of gold, copper, and uranium (adopted and modified from reference [35]).

Author Response

Answers to the 1^st Reviewers comments to the article Sustainability- 491086  

General Comments:

Manuscript is recommended for publication after some small revision of the points shown in below.

Ans: Thank you very much for your valuable suggestions and comments.

1. Line126. Figure 1. Chart of a gold heap-leach operation (adopted and modified from the reference [22]).

Ans) Yes. We modified the graphs in revised manuscript

2. Lines 151, 152. Figure 2. Flow diagrams of heap leaching processes of gold, copper, and uranium (adopted and modified from reference [35]).

Ans) Yes. We modified the graphs in revised manuscript

We modified the manuscript as per reviewer suggestions. Please accept this manuscript.

Author Response File: Author Response.doc

Reviewer 2 Report

In the scientific literature of his last years, there are many contributions on the subject. In this sense, we could expect novelties that have not been addressed in recent reviews (Yousef Ghorbani et al., 2015): Heap leaching technology - current state, innovations and future directions: A review, Mineral Processing and Extractive Metallurgy Review, DOI: 10.1080 / 08827508.2015.1115990).

Unfortunately, some points in my opinion have not had an appropriate development in this review and was damaged. Environmental concerns related to heap leaching require critical discussion and at least one paragraph in this review. The problem of the environment was briefly mentioned in one sentence in the introduction, however, it is the limiting factor of this extraction method.

Another point that we would have liked to be addressed is bioleaching, a biotechnology that has developed a lot in recent years.

This work can be a very good contribution if you amend it and give it originality in relation to all reviews on the subject in the last 10 years.

Author Response

Answers to the 2nd Reviewers comments to the article Sustainability- 491086

1.In the scientific literature of his last years, there are many contributions on the subject. In this sense, we could expect novelties that have not been addressed in recent reviews (Yousef Ghorbani et al., 2015): Heap leaching technology - current state, innovations and future directions: A review, Mineral Processing and Extractive Metallurgy Review, DOI: 10.1080 / 08827508.2015.1115990).

Ans) Yes sir. My paper focused mainly on heap leaching applications in Rare earths extraction. We saw that outstanding review paper by Jochen Peterson, from South Africa (Hydrometallurgy Editor), they covered all most all aspects except rare earths extraction by heap leaching and cost effective analysis. We added this reference in a revised manuscript.

2. Unfortunately, some points in my opinion have not had an appropriate development in this review and was damaged. Environmental concerns related to heap leaching require critical discussion and at least one paragraph in this review. The problem of the environment was briefly mentioned in one sentence in the introduction, however, it is the limiting factor of this extraction method.

Ans) This paper I am going to mention about environmental concerns of heap leaching, cost effective analysis and also advantages and disadvantages of heap leaching method in the revised manuscript.

3.Another point that we would have liked to be addressed is bioleaching, a biotechnology that has developed a lot in recent years.

Ans) Definitely sir. I added the bioleaching and bio technology methods in the revised manuscript.

4.This work can be a very good contribution if you amend it and give it originality in relation to all reviews on the subject in the last 10 years.

Ans) ok sir. We prepared a summary table for the last ten years heap leaching method developments.

We modified the manuscript as per reviewer suggestions. Please accept this manuscript.

Author Response File: Author Response.doc

Reviewer 3 Report

Heap leaching is an important hydrometallurgical method to process low-grade raw materials. The objective of the submitted manuscript is of interest of not only professionals but also of the general public. But the manuscript must be revised in order to be published. The main reasons are as followed:

Introduction is too generic without clear reasoning of the purpose and importance of the manuscript.

It is hard to understand why the last paragraph (l64-68) was added in Introduction. It is more or less a statement, which is not connected with any previous paragraph or it can serve as an argument for the purpose of the manuscript.

Writing about heap leaching, it is suitable to mention shortly its history, when and where the technology was applied firstly. 

More details, data and/or examples should be added to support the conclusions or statements in the manuscript, for example "low capital requirements and low operating costs...."- l100-108: how much is CAPEX and OPEX of heap leaching comparing to traditional tank leaching and autoclave leaching, what do moderate-grade ores or low grade gold mean? How long does the heap leaching take place? What is temperature in the heaps? Leaching efficiencies?

The authors should also outline the disadvantages of heap leaching as well.

The diagrams are too small, hard to read.

Part 3.1 is not necessary. 

The authors should rewrite the manuscript to be more concise, remove unnecessary and repeated statements and add data to support their statements.

Author Response

Answers to the 3rd Reviewers comments to the article Sustainability- 491086

Heap leaching is an important hydrometallurgical method to process low-grade raw materials. The objective of the submitted manuscript is of interest of not only professionals but also of the general public.

Ans: Thank you very much for your valuable suggestions and comments on this manuscript.

But the manuscript must be revised in order to be published. The main reasons are as followed:

1. Introduction is too generic without clear reasoning of the purpose and importance of the manuscript.

Ans) Yes. We modified the introduction part including the purpose and importance of this study in revised manuscript in the line no.s 74-76.

2. It is hard to understand why the last paragraph (l64-68) was added in Introduction. It is more or less a statement, which is not connected with any previous paragraph or it can serve as an argument for the purpose of the manuscript.

Ans) Yes. We removed that sentences in revised manuscript

3. Writing about heap leaching, it is suitable to mention shortly its history, when and where the technology was applied firstly. 

Ans) Yes. We followed your suggestions and heap leaching history, the first applications of this technology etc. are added into the revised manuscript in the line no.s 32-41.

4.More details, data and/or examples should be added to support the conclusions or statements in the manuscript, for example "low capital requirements and low operating costs...."- l100-108: how much is CAPEX and OPEX of heap leaching comparing to traditional tank leaching and autoclave leaching, what do moderate-grade ores or low grade gold mean? How long does the heap leaching take place? What is temperature in the heaps? Leaching efficiencies?

Ans) Yes. We added the all information suggested by reviewer in revised manuscript in the Table 1.

what do moderate-grade ores or low grade gold mean?

Low grade ore has pebble sizes ranging from 8.6 mm to 29 mm and poorly packed, poorly sorted, sub-angular to sub-round. For medium and high grade ore, pebble sizes are up to 31 mm, moderate to well sorted with occasional rounded and well packed pebbles. Very high grade ore has restricted pebble size of about 13.4 mm or 24.2 mm and may be well-rounded.  (G. M. Tetteh, E. O. Lartey, Texture and Gold Grade as Guides to Blending of Conglomerate Ore, International Journal of Scientific & Technology Research, 2018, 7(9), 61-66.)

How long does the heap leaching take place? What is temperature in the heaps? Leaching efficiencies?

Ans)  In Table 1. I gave the time and leaching efficiency of different metals, now I added the temperature information in the revised manuscript.

5. The authors should also outline the disadvantages of heap leaching as well.

Ans) Yes. We added the disadvantages of heap leaching in revised manuscript

6.The diagrams are too small, hard to read.

Ans) Yes. We modified the diagrams in revised manuscript

7.Part 3.1 is not necessary. 

Ans) Yes. We deleted the part 3.1 in revised manuscript

8.The authors should rewrite the manuscript to be more concise, remove unnecessary and repeated statements and add data to support their statements.

Ans) Yes. We followed the reviewers suggestions and presented in revised manuscript

We modified the manuscript as per reviewer suggestions. Please accept this manuscript.

Round  2

Reviewer 2 Report

Dear Karen

I read the last version, it's ok for me for the article to be published.

Author Response

Answers to the 2nd Reviewers comments to the article Sustainability- 491086

I read the last version, it's ok for me for the article to be published

Ans) Thank you very much for your comments. Thank you for accepting this paper for publication

Author Response File: Author Response.doc

Reviewer 3 Report

The revised manuscript is considerably improved.

Author Response

Answers to the 3rd Reviewers comments to the article Sustainability- 491086

The revised manuscript is considerably improved.

Ans: Thank you very much for your accepting this paper. Thank you for your valuable comments to improve the manuscript quality. Thank you very much sir.

Author Response File: Author Response.doc