Leaching of Gold and Copper from Printed Circuit Boards under the Alternating Current Action in Hydrochloric Acid Electrolytes

Round 1

Reviewer 1 Report

Please, see attachment.

Comments for author File: Comments.pdf

Author Response

Please see attachmnet

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Author,

please find below and attached comments to your work.

The result proves the feasibility of AC leaching of Au and Cu from PCBs with HCl solution. The content fits the journal scope and interesting for the readers. The author was able to achieve a high gold and copper leaching of more than 80 % with the application of AC in HCl solution. Better leaching efficiency was achieved in cited papers in the introduction chapter, yet still a more environmentally sound potential approach. 

Determination of chemical composition clearly described, but the achieved results with gold recovery = 100 % are very unlikely in the present system (many less noble metals in system would generate a high reagent consumption or cause cementation of gold). The chemical composition of the input material does not fit expectation of published PCB compositions. This should be further discussed and explained, displaying the concentration of gold and copper in solution. Some experimental design can be adjusted and more references trials could be done to ensure the reproducibility and reliability of the result.

The solution of metals, especially Cu, in HCl solution without current application has to be displayed for comparison to determine the impact.

Further comments:

·         Generally good structured, however the innovative part of the paper is not clearly addressed;

·         Leaching of PCBs with AC is an innovative approach, no similar literature found in google scholar;

·         The reason for the choice of finest fraction missing;

·         8 from 39 cited papers are within 5 years, proper amount

·         English fluent. Some expressions should be adjusted to avoid misunderstanding.

Comments for author File: Comments.pdf

Author Response

Please see attachmnet

Author Response File: Author Response.pdf

Reviewer 3 Report

The author proposed a new scheme for leaching metals from computer printed circuits (PCBs) pre-crushed in a disintegrator. The results showed that the developed process of implementing the method applies to leaching gold and copper from the disintegrator-crushed waste PCBs in fine fractions <90 μm, 90~180 μm, and 180~350 μm, and the particle size had a great influence on the leaching rate of gold and copper. It was found that complete leaching of gold is achieved from fine fractions of raw materials containing 0.03% and 0.01% of the gold at an experiment duration of 2 hours, a current density of 0.66 A·cm^-2 and a solid/liquid ratio of 8.6 g·L^-1. Applying AC and the increase in the electrolyte temperature have a more significant effect on the gold leaching efficiency than copper. However, I have some major concerns that should be addressed before this manuscript is suitable for publication in metals. Please find below my comments:

1. In the Introduction, the composition of PCB should be more clearly described, and more literature on precious metal recycling in PCB should be reviewed. Please refer to the following literature.

[1]PVC gel bio-inspired adhesives with variable modulus and its application in a gripper. J. Cent. South Univ. 2022, 29, 1778–1787. https://doi.org/10.1007/s11771-022-5050-5

[2]Metals Content in Printed Circuit Board Waste, Polish Journal of Environmental Studies, 2014, 23(6): 2365-2369

[3]A Potential Alternative for Precious Metal Recovery from E-waste: Iodine Leaching. SEPARATION SCIENCE AND TECHNOLOGY, 2015, 50(16): 2587-2595, DOI: 10.1080/01496395.2015.1061005

[4] Two-step bioleaching of copper and gold from discarded printed circuit boards (PCB). WASTE MANAGEMENT, 2016, 57: 149-157, DOI: 10.1016/j.wasman.2015.11.033

2. The clarity of Figure 5 is far too low, please upload pictures with high definition. Figures 6, 13 and 14 also need to be replaced with clearer pictures.

3. Please ensure that the text format in all pictures is uniform.

4. The particle size has a great influence on the leaching rate of gold and copper. Could such a phenomenon be explained?

5. Some references lack “doi”, such as Reference 15, 16, 17, etc.

Author Response

Please see attachmnet

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper discussion is interesting note, but needs significant improvements. Please follow the comments carefully.

1.       Add some quantitative results to the abstract.

2.      Add more detail to the conclusion.

3.      Add more discussion about figure 2 “Scheme of the experimental setup: the electrical”.

4.      Provide a thorough discussion of reported results in 3.1 “raw material treatment…”.

5.      Add more results to your conclusion.

6.      3D printing has many usages in different industries. To highlight your work, add a short note in the introduction by using the following papers and mention the privilege of 3D printing in manufacturing.

·        Electron beam powder bed fusion of copper components: a review of mechanical properties and research opportunities

·        A review of Industry 4.0 and additive manufacturing synergy

·        Fatigue life optimization for 17-4Ph steel produced by selective laser melting

·        Electrothermal response optimization of nozzle structure for multi-material rapid prototyping based on fuzzy adaptive control

Author Response

Please see attachmnet

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Author,

the article can be published in this form. 

I am looking forward to read more articles from you about e-waste recycling in future.

Best regards

Author Response

Thank You very much for your valuable comments !

Reviewer 3 Report

The reviewer searched the relevant literature on WOS to expand the knowledge of the Introduction and enable the readers to better understand the research background. These references are not related to the reviewer. Citing the references is not mandatory. However, it is a pity that the authors did not take the suggestions of reviewers seriously. The first reference is in English, but the authors even did not open it. As for the second reference, the authors answered directly that they could not find it, without making more attempts. 

As for the author's other replies to the questions raised by the reviewer of last time, the author just simply answered "corrected". This makes it difficult for reviewers to judge whether the revision is appropriate.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper is ready to publish. 

Author Response

Thank You !