Validation of Bromide Leaching through Response Surface Methodology and Separation of Gold from Waste Printed Circuit Boards

Round 1

Reviewer 1 Report

The authors provided a relatively complete route to recover gold from PCBs. They emphasized the optimization study of the bromide leaching process, which would be a feasible alternative to the current toxic cyanide leaching. However, throughout the manuscript, some essential experimental descriptions are missing, hence the authors should complement them.

1. In the abstract, "elemental mapping" is repetitive with SEM-EDS and can be deleted.

2. In the abstract, the economic feasibility is mentioned but there is no implication on this aspect found in the article. Therefore, the author should add the corresponding discussion.

3. There are few articles involving critical metal recycling in the citations [6-11] due to the low concentration of critical metals used in PCBs. Actually, a recent article showing the feasibility of Nd (REEs) recycling (https://doi.org/10.1016/j.cej.2022.135886) can be cited here to support the statement. 

4. In figure 1, the stripping step is missing after solvent extraction.

5. In 2.1 Pre-treatment, did the authors use any grinder to further reduce the particle size of metal fractions, otherwise, how to assure the homogeneous nature of samples? Besides, The pre-treatment to separate metals and non-metals should be more specified.

6. In 2.2 Experimental design, why did the author choose a certain concentration of NaBr and H2SO4, please specify.

7. Did the authors use ICP-OES or ICP-MS to quantitatively measure metal concentrations? There is no method describing how to measure and calculate the gold leaching rate, which is a  key parameter supporting the article.

8. In line 125, please specify or provide the molecular structure of 3° amide in the article.

9. In lines 213-214, is the statement obtained from the present study or the citation [16]? In fact, according to the context, it should be from the authors' results.

10. In line 239. the concluded stirring speed is inconsistent with the results.

Author Response

Dear Reviewer

We have tried our best to respond to all queries raised by you and revise the paper significantly. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors present a complete process flow for sustainable gold recovery from waste printed circuit boards (WPCB). The topic seems very interesting, but some revisions are suggested prior to its acceptance.

1.     There are some grammatical and spelling errors as well as format problems. Please polish the language and correct the format issues.

For example:

Line 58: “……, as represented in Equation. 1-3.” → “……, as represented in Eqs. 1-3.”

Line 59: “Studies of reduction potential (Eh) vs pH diagram ……” → “Studies of reduction potential (Eh) vs. pH diagram ……”.

2. There is an equation that is not balanced (Eq. 1). Please check and correct.

3. Please add the meaning of each parameter in Eq. 6.

Author Response

Dear Reviewer

We have tried our best to respond to all queries raised by you and revise the paper significantly. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript ID: minerals-2333486

Title: Validation of bromide leaching through response surface methodology and separation of gold from waste printed circuit boards

Authors: Mudila Dhanunjaya Rao et al.

Line 33. «consumption of gold at 263.3 Mt/year» Does it correct information? May be authors write 263.3 t/year? Because global gold production in 2022 is ~3,478 tonnes.

Line 38-39. Authors write «million Mt». It is an incorrect term.

Line 44. Avoid more than 3 references for a fact. Maximum only 3 is allowed for Minerals.

Section 2. Authors should add information about calculation the Au extraction degree. Please add the equation.

Authors should add characterization for raw material (Waste printed circuit boards). Add the chemical composition (wt. %), phases by XRD and the particle size distribution of the sample.

Section 3.2. Why did the author use only one equation to calculate the kinetics? What about the shrinking core model (SCM)? Using one model is not relevant, there must be 2 or 3.

Figure 6-7. Authors should add the equation for each curve type, y= ax+b type.

If the Ea = 22.76 kJ/mol, it would be more relevant to use an internal or external diffusion equation for the calculation.

What is the value of the recovery of gold from the raw material into gold powder?

Why do the authors estimate the chemical composition using the SEM/EDX method? This is a semi-quantitative analysis. Other methods must be used: XRF or ICP.

The conclusions are too general, clear results should be given, and the data obtained in this study should be stated. For example, there is no information on activation energy etc. in the conclusions.

Author Response

Dear Reviewer

We have tried our best to respond to all queries raised by you and revise the paper significantly. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript can be accepted in its present form.

Reviewer 3 Report

Article can be accepted in the present form.