Gold Bioleaching from Printed Circuit Boards of Mobile Phones by Aspergillus niger in a Culture without Agitation and with Glucose as a Carbon Source
Round 1
Reviewer 1 Report
Reviewer's comments:
Review report for International Journal of ‘Metals’ (metals-490283): Gold bioleaching from printed circuit boards of mobile phones by Aspergillus niger in a culture without agitation and with glucose as a carbon source
This paper evaluates the capacity of Au bioleaching by either A. niger or one fungal consortium in culture medium with glucose as a carbon source, an excess of manganese and without agitation. The topic is highly relevant for the extractive metallurgy applications. The authors have well designed and executed the experiments. The material is well presented with strategic use of tables and figures. I strongly believe that paper data may be useful to other researchers. This reviewer has few comments and/or corrections that the authors need to address for improving the paper’s quality. All comments and suggestions are as follows;
Specific Comments:
P1, L15: The authors need to justify the necessity of this research shortly at the beginning of the abstract section.
P2, L73-75: Please form a separate paragraph which will explain the originality and core objectives of this paper.
P7, L252-260: Please summarize the present study shortly and then switch to its main findings.
P7, L327: Please give some research suggestions on this issue for researchers and also make recommendations for readers. This reviewer suggests a) The authors should investigate if gold recovery is more effective by bioleaching, comparing the works present in the literature; and b) The authors should also do a research on the availability of acidic bacteria in gold recovery by bacterial leaching.
P7, L261-262: Please delete the first sentence, redundant.
This is a good paper!
As a reviewer, I am pleased to suggest the manuscript to be accepted for publication in the International Journal of ‘Metals’ through the aforementioned minor revisions.
Author Response
Suggested changes are found in the manuscript, underlined in yellow.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
What are the characteristics of A.niger MXPE 6 and MX7?
Line 169. What was the reason of difference between test and findings of Madrigal-Arias?
Line 246. Wasn’t the mass of gold accumulation too low? 8.5 mg/g is very low number to achieve proper justification.
Line 256. What about other metals like Cd, Hg? It may also leach following metals and get contaminated solution, which will be harder to process later?
Is it feasible to do kind of study further?Author Response
Suggested changes are found in the manuscript, underlined in blue. Except for the following Comments.
Line 246. Wasn’t the mass of gold accumulation too low? 8.5 mg/g is very low number to achieve proper justification.
In the study, fungal biomass is increased in PCB treatments compared to those that do not have PCB.
Line 256. What about other metals like Cd, Hg? It may also leach following metals and get contaminated solution, which will be harder to process later?
The possibility of finding metals such as Cd and Hg in the solution depends on the composition of the PCB, the culture medium and the microorganism used. However, under the conditions of the present study, these elements were not detected. Although, some bioleaching tests with PCB from computers, using fungi of the genus Trichoderma and Fusarium show that it is possible to detect Cd and Pb in the solution.
Is it feasible to do kind of study further?
The objective of this study was to prove that the bioleaching of gold by A. niger MXPE6 and a fungal consortium was possible in a culture without agitation. Because the agitation generates an energy cost. The aim was to make a biological process as simple as possible without generating high costs, considering that the laboratories of the University do not have high-tech bioractors. Our research group is getting economic resources to deepen the present study and other studies in order to find the organic acids and enzymes involved in the fungal bioleaching. In addition, to identify the chemical complexes formed with Au.
Author Response File: Author Response.pdf
Reviewer 3 Report
“metal recovery 1; energy saving 2; filamentous fungi 3; fungal consortium 4; electronic wastes 5”
Please delete numbers after “keywords”
Furthermore, “metal recovery” is not used in the text. Please check and modify, if necessary.
The authors stated:
“These devices are composed of valuable materials such as plastics (50 %), glass-ceramics (15 %), Cu (15 %), and metals, including Fe, Al, Au, Ag, In, and Pd (15 %), as well as toxic compounds such as Pb, Cd, As, Hg, and Br [5]”.
It seems that this Reference [5] did not give the “devices composition” in percent.
Please check and modify.
…Cu (15 %), and metals, including Fe, Al, Au, Ag, In, and Pd (15 %),…
should be:
…Cu (15 %), and other metals, including Fe, Al, Au, Ag, In, and Pd (15 %),…
…as well as toxic compounds such as Pb, Cd, As, Hg, and Br [5]…
should be:
… as well as toxic elements such as Pb, Cd, As, Hg, and Br [5].…
…ceramics, PCB contain approximately 28 % metals (0-20 % Cu, 1-5 % Pb, 1-3 % Ni, 41 and 0.3-0.4 % Ag, Pd and Au) [6,7]
“0-20 % Cu” should be “10-20 % Cu” ?.
Please check and modify if necessary.
In addition, did the Reference [7] give the initial composition of PCB?
Therefore the authors are invited to revise the text related to the bibliographic/literature review as well the References in the “Reference section” for correctness.
…Natarajan and Ting [25] report that bioleaching…
should be:
…Natarajan and Ting [25] reported that bioleaching…
It has even been reported the construction of a strain…
Please modify to:
The development of a strain … was reported…
2.3. Cultural conditions
Please modify to: 2.3. Cultivation conditions (if necessary).
…it was not possible to compare our results.
Please modify to:
it was not possible to compare our results to other research ones.
While the treatments inoculated with A. niger MXPE6 in the presence of PCB, they lower the pH to…
Please modify to:
While the treatments inoculated with A. niger MXPE6 in the presence of PCB lowers the pH to…
…leaching of metals leads an increase on pH…
Please modify to
…leaching of metals leads to an increase of pH…
Figure 5, Y axis legend: “Biolixiviación de Au (%)”
Please modify to :
“Biolixiviation of Au (%)”
Figure 5, X axis legend: “Tiempo”
It should be: “Time”
Including the environmental benefits that could be obtained in this type…
Please modify to :
Additionally, there are environmental benefits that could be obtained by using this type…
Author Response
Suggested changes are found in the manuscript, underlined in green.
Author Response File: Author Response.pdf
