Experimental Study on the Permeability of Rare Earths with Different Particle Composition for a Novel Heap Leaching Technology
Round 1
Reviewer 1 Report
The article certainly arouses interest. The authors describe the research methodology quite well. In my opinion, an analytical literary review of the work is insufficient. Authors are recommended to conduct a more serious analysis of the literature and patent information. In addition, it is not entirely clear from the work how this process will be implemented on a large-volume pile in the absence of a stubborn rock (Bedrock) and certain landschaft conditions. The main point that must certainly be added to the work is the impact of the effectiveness of the use of this technology. It is necessary to add data on the efficiency of extraction of valuable components using this method and the classical heap leaching technology. For a journal of this level, an ecological and economic justification is also necessary.
When making a recommendation, the work can be recommended for publication in the journal Applied Sciences.
Author Response
Point 1:
Reviewer
The article certainly arouses interest. The authors describe the research methodology quite well. In my opinion, an analytical literary review of the work is insufficient. Authors are recommended to conduct a more serious analysis of the literature and patent information.
Authors
Thank you for your recognition of our work. According to your comment, we have added more literature reviews and conduct a more serious analysis of the literature. Related references are also added in the list.
Point 2:
Reviewer
In addition, it is not entirely clear from the work how this process will be implemented on a large-volume pile in the absence of a stubborn rock (Bedrock) and certain landschaft conditions.
Authors
In order to implemented the a large-volume pile, a suitable site is identified with preliminary exploration, where a vertical impermeable bedrock is required. When a vertical bedrock is absent, it can be replaced by a manually constructing concrete wall. Before stacking of the rare earth ore in the heap leaching site, the bottom of the site needs to be treated. For example, any protruding areas around the site should be shoveled and any depressed areas should be filled in. According to the reviewer's suggestion, a supplementary explanation has been added in in Section 1 of the revised manuscript.
Point 3:
Reviewer
The main point that must certainly be added to the work is the impact of the effectiveness of the use of this technology. It is necessary to add data on the efficiency of extraction of valuable components using this method and the classical heap leaching technology.
Authors
It is really a good comment for improving our manuscript. According to the reviewer’s suggestion, we have conducted numerical simulations of the seepage of the leaching liquid in the piles for the traditional heap leaching technology and the novel heap leaching technology. The numerical results show that the leaching area on the cross section can reach 91.3% of the total area for the traditional heap leaching. While the ratio is 88.5% for the novel heap leaching technology. Although the leaching efficiency of the novel heap leaching technology is slightly lower, it is more environmentally friendly. The above explanation has been added in Section 1 of the revised manuscript.
Point 4:
Reviewer
For a journal of this level, an ecological and economic justification is also necessary.
Authors
According to the reviewer’s suggestion, an analysis of the economic and environmental justification has been added in Section 1 of the revised manuscript. Related references are also added in the list.
Reviewer 2 Report
The study aimed the permeability of rare earth elements in heap leaching of ion-adsorbed material. The manuscript is important due to the search of new sources of critical metals. The literature review must contain the recent works about extraction of rare earth elements from primary and secondary sources, for instance:
- https://www.mdpi.com/2075-4701/12/7/1133 (primary)
- https://link.springer.com/10.1007/s40831-021-00434-3 (secondary)
The search of new sources for critical metals must be highlighted in the manuscript.
What is the main difference between the heap leach and direct leaching of rare earth elements?
The composition and XRD data of the sample must be presented in the main document
Results must highlight the leaching of rare earth elements
Conclusions numbered is great for the readers. Great job!
Author Response
Point 1:
Reviewer
The study aimed the permeability of rare earth elements in heap leaching of ion-adsorbed material. The manuscript is important due to the search of new sources of critical metals. The literature review must contain the recent works about extraction of rare earth elements from primary and secondary sources, for instance:
The search of new sources for critical metals must be highlighted in the manuscript.
Authors
Thank you for your recognition of our work. According to your comment, we have added the literature reviews on the recent works about search of new sources for critical metals. Related references are also added in the list.
Point 2:
Reviewer
What is the main difference between the heap leach and direct leaching of rare earth elements?
Authors
Heap leaching is one of the rare earth mining technologies. Heap leaching requires a large amount of rare earth minerals to be stacked in a specific heap leaching site. After heap leaching, the leachate is collected and then subjected to processes such as edulcoration, precipitation and scorching to obtain rare earth products. Therefore, the leaching efficiency and pile stability are highly dependent on the seepage characteristics of leaching liquid in the rare earth pile. Different from direct leaching, extraction of rare earth elements from the leachate does not need to be considered. According to the reviewer’s suggestion, a supplementary explanation has been provided in Section 1 of the revised manuscript.
Point 3:
Reviewer
The composition and XRD data of the sample must be presented in the main document
Authors
According to the reviewer’s suggestion, the composition of soil samples and the chemical composition of the minerals have been added in Section 2.2 of the revised manuscript. The data were provided by the first research group of the National Key Research and Development Program of China. The authors of this paper are in the fifth research group of the program. This research was funded by the National Key Research and Development Program of China (2019YFC0605005 and 2019YFC0605001).
Point 4:
Reviewer
Results must highlight the leaching of rare earth elements
Authors
The leaching efficiency and pile stability are highly dependent on the seepage characteristics of leaching liquid in the rare earth pile. Therefore, the study in this paper focuses on the permeability of the rare earth pile under lateral liquid injection conditions. The relationship between the permeability and the leaching of rare earth elements is beyond the scope of this paper, and is not considered in this study. Notwithstanding its limitations, it can still provide guidance for the implementation of the novel heap leaching technology.
Round 2
Reviewer 1 Report
I believe that the authors' article corresponds to the level of the journal and is recommended for publication.
However, I consider the lack of data on the leaching of elements to be a major drawback. It is strongly recommended to conduct research in this direction and publish it in the near future.
