Review Reports - Leaching Kinetics of Iron Collector Containing PGMs

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Metals

Article

Leaching Kinetics of Iron Collector Containing PGMs

Review

The leaching kinetics of Fe and Si from the iron PGM collector in HCl and HF solutions were studied.

In our previous work [15], it was shown that if the melting of automotive catalysts is carried out to obtain an iron-based collector, then it can be effectively dissolved using HCl or H2SO4 solutions to extract PGMs

it would be necessary to briefly describe this process in a few sentences, at the beginning there is Fe-collector and then ferrosilicon matrix Is it an iron alloy or a Fe-Si-ferro-silicon ferroalloy?

composition: 41.6% SiO2, 39.8% Al2O3, 7.8% MgO, 4.9% ZrO2, 3.3% CeO2, 1.4% P2O5, 1.0% Fe2O3, 0.17% Pd, 0.07% Pt, 0.02% Rh. The alloy was pre-ground

it is not an alloy (this name applies to metals), it is waste (post-use) from catalysts for recycling,

X=Eel/100^,

“^,”?

Besides the shrinking core model (SCM), the full factorial experiment model (FFEM) was used to study the

it would be advisable to provide reference literature for beginner readers

The SCM [15]

it's a bit further but it could be earlier

The extraction of Fe into solution and Si into the gas phase was 17.8–100.0% and 19.2–100.0%, respectively. Pd, Pt, and Rh were not detected in solutions. The cake yield varied in the range of 9.2–61.1%.

Very unclear description of what cake leaching is all about - we dissolve Fe into the solution, we drive off Si as a gas and the PGM remains in the cake?

it is visible only in Table 3. XRF and EDS results of the cakes, %. it is enough to add the cake after leaching the Fe-collector alloy

or …. Leaching the initial iron collector

because Fe precipitates on the surface of the iron collector in the form of thin-film conglomerates of FeF2 [15].

therefore it is a pity that there are no maps of Fe analysis maps, it would be possible to see the common occurrence and local increases in the density of Fe and F (FeF₂)

The positive effect of the HCl concentration and the HF concentration on the

The positive effect of the HCl and HF concentrations on the

deposition of secondary phase (FeF2) on the surface of the iron collector. At the same time,

Is it still Fe- collector or is it already a leaching product - cake (PGM collector)

Author Response

Dear reviewer!

The authors have carefully read your comments. Below are the answers:

Q1) In our previous work [15], it was shown that if the melting of automotive catalysts is carried out to obtain an iron-based collector, then it can be effectively dissolved using HCl or H2SO4 solutions to extract PGMs.

It would be necessary to briefly describe this process in a few sentences, at the beginning there is Fe-collector and then ferrosilicon matrix Is it an iron alloy or a Fe-Si-ferro-silicon ferroalloy?

A1) This article is a continuation of the article published in Metals earlier (https://doi.org/10.3390/met14091077). In the first article, issues related to the description of the collector and methods of its production are described in sufficient detail. These issues are not considered in this article to reduce its volume.

Q2) …composition: 41.6% SiO2, 39.8% Al2O3, 7.8% MgO, 4.9% ZrO2, 3.3% CeO2, 1.4% P2O5, 1.0% Fe2O3, 0.17% Pd, 0.07% Pt, 0.02% Rh. The alloy was pre-ground…

It is not an alloy (this name applies to metals), it is waste (post-use) from catalysts for recycling.

A2) Fixed.

Q3) X=Eel/100,

“,”?

A3) This is a comma.

Q4) Besides the shrinking core model (SCM), the full factorial experiment model (FFEM) was used to study the…

It would be advisable to provide reference literature for beginner readers.

The SCM [15]…

It's a bit further but it could be earlier.

A4) We have added links in the introduction.

Q5) The extraction of Fe into solution and Si into the gas phase was 17.8–100.0% and 19.2–100.0%, respectively. Pd, Pt, and Rh were not detected in solutions. The cake yield varied in the range of 9.2–61.1%.

Very unclear description of what cake leaching is all about - we dissolve Fe into the solution, we drive off Si as a gas and the PGM remains in the cake?

it is visible only in Table 3. XRF and EDS results of the cakes, %. it is enough to add the cake after leaching the Fe-collector alloy

or …. Leaching the initial iron collector

A5) We have removed the information on PGM recovery to avoid confusion. An iron collector containing iron, silicon and PGM is leached in a mixture of hydrochloric and hydrofluoric acids. Iron goes into the solution and silicon fluoride goes into the gas phase. PGMs remain in the cake.

Q6) Because Fe precipitates on the surface of the iron collector in the form of thin-film conglomerates of FeF2 [15].

Therefore, it is a pity that there are no maps of Fe analysis maps, it would be possible to see the common occurrence and local increases in the density of Fe and F (FeF2).

A6) We have added mappings of Fe.

Q7) The positive effect of the HCl concentration and the HF concentration on the…

The positive effect of the HCl and HF concentrations on the…

A7) Fixed.

Q8) …deposition of secondary phase (FeF2) on the surface of the iron collector. At the same time…

Is it still Fe- collector or is it already a leaching product - cake (PGM collector)

A8) This is a cake. We have changed the name.

Thank you.

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the comment in the attached file.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

I am not sure, because I am not English speaker, but It should be English-polished.

Author Response

Dear reviewer!

The authors have carefully read your comments. Below are the answers:

Q1) It is very complicated that the composition mentioned in section 2.1 and that in Table 1 were much different. There is no explanation.

A1) Section 2.1 provided the composition of the initial catalysts that were used in the melting process. The resulting collector was used in the experiments in this paper. To eliminate confusion, this information has been removed. Table 1 provides the composition of the collector.

Q2) Related to comment 1, Table 1 and 3 should be combined for comparison.

A2) Table 1 shows the composition of the collector. Table 3 shows the composition of the cakes. This is different information that cannot be combined.

Q3) For the experiments shown in Figure 2, only one factor should be changed!? If the plural factors are changed, it seems to be difficult for identifying the affecting factor.

A3) Figure 2 shows the results of the cakes analysis obtained under soft, medium and hard leaching parameters. The purpose of these figures (and Figure 3) is to show the presence of fluorine on the surface (and the composition of the cakes, too). The influence of individual parameters on the leaching process is shown in Figures 4-6.

Q4) In Page 8 line 5 from the bottom, the authors described Le Chatelier’s principle for equation 2.1. However, Le Chatelier’s principle is based on equilibrium state. The equation 2.1 includes gas generation and not be under equilibrium.

A4) Deleted.

Q5) Why do the modeling plots show two steps? The authors may explained it in Page 10 lines 1-3 from the bottom, but it is a bit complicated.

A5) Because after 120 min, the extraction of Fe and Si is zero (Figures 4-6). Added in sec. 4.1.

Q6) In Page 2 line 2 from the bottom; “Tables 1,2” should be ”Tables 1 and 2”.

A6) Fixed.

Q7) In Page 6 line 8; “Tables 3,4” should be ”Tables 3 and 4”.

A7) Fixed.

Q8) In Page 8 line 2; “The resulting in Figure 4” should be ”Figure 4”.

A8) Changed.

Q9) In Page 8 line 4; “from 2.74 mol/L to 6.86 mol/L” should be ”from 2.74 to 6.86 mol/L”.

A9) Fixed.

Q10) In Page 8 line 5; “from 64.2 % to 75.3 %” should be ” from 64.2 to 75.3 %”. Related to comments 9 and 10, please revise the similar ones in Page 8 line 10, Page 9 line 3, Page 9 lines 9 and 10, Page 10 lines 3, 4 and 11, Page 12 lines 3 and 3

A10) Fixed.

Q11) In Page 8 line 2 from the bottom; “Chapter 3.1” should be “Section 3.1”.

A11) Changed.

Q12) Experimental condition includes two acid concentrations, so the captions in figures should include such information.

A12) We have checked all the figures; the information has been added.

Thank you.