High-Efficiency Desulfurization of High-Sulfur Bauxite Calcined in a Conveyor Bed: Kinetics, Process, and Application

Round 1

Reviewer 1 Report

This article is a very interesting research of characterization and technological methods for desulfurization of high-sulfur bauxite originated from Nanchuan, Chongqing, China, calcined in a conveyor bed.

-        The abstract clearly and fully reflects the content of the manuscript. The main results are presented with an emphasis on applied laboratory analysis methods and technological solutions.

-        Introductory considerations are extensive, comprehensive and based on adequate references. Among other things, the authors set themselves a clear task: "...to establish an accurate desulfurization kinetic model to provide a basis for process design and production control." The same authors in previous research (reference 23): "...developed a method to calculate complex reaction kinetics based on the release characteristics of gaseous products using a combined thermal analysis-IR analysis technique. Satisfactory results were obtained for the calcination reaction mechanism and kinetic analysis of coal gangue using this method, providing a basis for the desulfurization mechanism and kinetic analysis of high-sulfur bauxite.” As the main result of this research they state: "After calcination at 600°C–650°C for around 3.5 s, the removal rate of negative divalent sulfur from the high-sulfur bauxite was >99%, and the relative dissolution rate of alumina was > 99%, which meets the requirements of the Bayer process.”

-       The applied analytical methods, experiments and calculations are presented clearly and in detail.

 

Suggestions:

For the readers, special geologists, it would be important to show the basic data about the high-sulfur bauxite deposit Nanchuan, such as: genetic type, age, mineral composition, geochemical characteristics, average content of the main oxides and trace elements (especially REE`s), distribution of the main components (especially of total S) in the deposit, geological reserves, deposit status (exploration and/or exploitation).

Is the high-sulfur bauxite from the Nanchuan deposit or another deposit with similar characteristics already used for alumina production?

How much high-sulfur bauxite was used in the experiments?

Is this a representative sample of bauxite from the Nanchuan deposit?

Briefly describe the method of high-sulfur bauxite sampling.

Are the results shown in Table 1 an average of the analysis of multiple samples or a single analysis of a composite sample? Mention in the text.

 

-       The Thermal Analysis–IR Analysis Combined Experiment, based on TG and DTG data and IR spectroscopic analysis of the gaseous product, is very well presented and analytically documented.

-   The figures are clear, the results are explained in the text of the manuscript.

-  By comparing theoretical data and data obtained during the experiment, as well as their mathematical processing, the authors come to the conclusion that: "The complete desulfurization of high-sulfur bauxite in the temperature range of 575°C–650°C required only a few seconds, showing that it provides a theoretical basis for transport bed suspension calcination technology.”

-   Desulfurization rate analysis shows that with the applied methods: "...the negative divalent sulfur and total sulfur content of the high-sulfur bauxite decreased significantly, but the sulfur content in sulfate increased gradually.", but also: "Sulfate exhibits good thermal stability and cannot be decomposed <650°C.”. And besides: "...at a calcination temperature of >550°C, the negative divalent sulfur content in high-sulfur bauxite was to <0.27 wt.%, which meets the requirements of the Bayer extraction process (<0.4 wt.%) ". The results are clearly shown in Table 4 and Figure 9.

-          The XRD patterns show the decomposition of the main minerals, carriers of Al, Si, Fe and S at temperatures from 500°C to 650°C, in a defined calcination time of 3.5 s.

-    The analysis of SEM images clearly shows that after the calcination of high-sulfur bauxite there were significant positive effects in terms of grain size reduction and pore size increase.

-      In the conclusions, the authors state the claims previously expressed in the text of the manuscript, now in a concise form.

- The results of experiments, applied analytical methods and technological procedures clearly show the efficiency of the process, because the negative divalent sulfur content in high-sulfur bauxite was reduced to less than 0.03 wt.%, in the range of 600°C–650°C for around 3.5 s. At the same time the desulfurization rate was >0.98 and the relative dissolution rate was >99%.

-      I recommend that the article be accepted for publication, after minor additions listed in suggestions.

Author Response

Thanks for your valuable comments and suggestions on our paper. We have carefully considered the comments and suggestions and have revised the manuscript accordingly.

Author Response File: Author Response.pdf

Reviewer 2 Report

High-efficiency desulfurization of high-sulfur bauxite calcined in a conveyor bed: kinetics, process, and application

Authors: Shaowu Jiu et al.

Year: 2022.

This paper might be accepted after a minor revision of the manuscript.

The manuscript presents a sound and robust kinetic model of desulfurization of high-sulfur bauxite in a conveyor bed. However, the manuscript requires more detail in some sections and fixing of minor issues. Overall, this work is suitable and relevant to Processes.

Some comments to this manuscript are given below.

1.     Overall, English is good, but consider proofreading the whole manuscript for style, grammar, and mistakes once corrections are made and issues identified here are addressed. The only suggestion here is to use another verb instead of "parsed" on page 3, line 113, to make clear what the authors are trying to state.

2.     Regarding the manuscript's scientific content, the authors must provide further details of their findings. The following are some issues that require attention:

a.      In the last paragraph of the introduction section, page 2, line 75, in this reviewer's opinion, all the sentences starting there seem to be conclusions and are misplaced within the manuscript.

b.     The last sentence of page 2, within materials and methods, is unclear to this reviewer: "The barium sulfate gravimetric method was adopted for analysis of the sulfur phase." Could the authors confirm? I reckon, after reading the paper that the authors meant sulfur oxidation state, not a phase (i.e., gas, liquid, monoclinic, orthorhombic). And if that is the case, correct the sentence.

c.      According to this reviewer, on page 4, line 128, the sentence should state "Equation (3) can be substituted…" instead of "Equation (2)"

d.     The last method of characterization described by the authors was alumina digestion. However, no results correspond to this process.

Suddenly, with no previous mention or justification, the authors discuss the dissolution of alumina in section 3.3.4 and even offer conclusions corresponding to this process.

Are alumina digestion and alumina dissolution related?

It is not yet clear to this reviewer why the authors did not describe the methodology for alumina dissolution. Moreover, it is not clear the importance of this result and its connection with the kinetic model. This methodology and its relevance should be clearly explained within the manuscript.

e.      I want to suggest flipping Figure 4b horizontally, so both figures present the same scale. This change makes it easier for the readership to associate peaks in both figures.

f.       In section 3.1, the authors mention and present the thermochemical reactions (9-13) that yield water vapor, carbon dioxide, and sulfur dioxide. The authors inadvertently, I guess, forgot to present the muscovite decomposition reaction. Could the authors provide such a reaction?

g.      Could the authors provide more detail on how the release flow curves were obtained in this section? These curves are of utmost importance to this reviewer since the spectra overlapping of the gaseous products in figure 4.

h.     I do not see any relevant discussion on SEM micrographs in this reviewer's opinion. In particular, I do not see its relation with kinetic studies. I suggest complementing such micrographs with EDS analysis. Otherwise, that should be considered supplementary information.

This paper might be accepted after a minor manuscript revision based on the above.

Author Response

Thanks for your valuable comments and suggestions on our paper. We have carefully considered the comments and suggestions and have revised the manuscript accordingly.

Author Response File: Author Response.pdf