Characterization Analysis of Airborne Particulates from Australian Underground Coal Mines Using the Mineral Liberation Analyser

Round 1

Reviewer 1 Report

The article presents the results of the monitoring and health surveillance of coal mines in Australia. The idea presented is very interesting, and the results shall be implemented. Although the paper is very well-written, it needs a revision in some points as indicated below:

• The bibliography presented is appropriate and exhaustive. However, each of the bibliography cited shall be written according to the journal policies.
• The affiliations shall be indicated according to the journal policies. It can be helpful to compare the affiliation indicated in this paper with the affiliation(s) indicated in any other article published by minerals, MDPI.  
• The paper must be integrated with maps where the position of the mines investigated and the sampling points are clear. The map can also indicate the samples and mines discussed in this paper and published in previous work.
• Check if table 1 and figure 1 are well described in the text, especially from line 80 to line 88.
• Table 2 shall be fixed. Name, formula, and, eventually, abbreviations of the minerals indicated must respect the indication of the International Mineralogical Association. Check the latest list of approved minerals. The formulas must respect the subscripts and superscripts. The column related to “formula” must be completed.
• Which is the mineral reference library used?

I believe that overall, the paper deserves to be published in a prestigious journal like Minerals after the indicated improvements.

Author Response

• The bibliography presented is appropriate and exhaustive. However, each of the bibliography cited shall be written according to the journal policies.

-I have updated the Endnote setting to include all Authors, it previously was only including the first one if there were more than four. Reference 1 updated to report type and 2 updated to webpage. Title of 5 updated.

• The affiliations shall be indicated according to the journal policies. It can be helpful to compare the affiliation indicated in this paper with the affiliation(s) indicated in any other article published by minerals, MDPI.  

-These have been fixed

• The paper must be integrated with maps where the position of the mines investigated and the sampling points are clear. The map can also indicate the samples and mines discussed in this paper and published in previous work.

-The mines have asked to remain anonymous. There are only 11 operating underground mines in the whole state of Queensland. So if I start narrowing down locations and putting them on a map their anonymity will be threatened.

• Check if table 1 and figure 1 are well described in the text, especially from line 80 to line 88.

-Added a second reference to Table 1 and changed the order of paragraphs. Figure 1 referenced in lines 121-122.

• Table 2 shall be fixed. Name, formula, and, eventually, abbreviations of the minerals indicated must respect the indication of the International Mineralogical Association. Check the latest list of approved minerals. The formulas must respect the subscripts and superscripts. The column related to “formula” must be completed.

• Updated the list and added IMA abbreviations. Added notes of elements and compounds that are included, which do not fit the minerals list

• Which is the mineral reference library used?

-We typically use the stoichiometric composition and standard mineral formulae, which has been noted in the text

Reviewer 2 Report

Overall, very interesting work.  I enjoyed reading this paper.

Line 152 Define what is meant by "carbon" here.  From Table 2 it seems to be a particle that contains solely carbon and no other EDS-identifiable elements, but since "carbon" is not really a mineral this warrants a brief clarification in the text, particularly since this is the major class of particles in most samples.

Line 223 But are diesel engines indeed made of stainless steel?

Lines 256-259 Here carbon is attributed to either coal or DPM - this could be mentioned and discussed in slightly more detail in the earlier section (line 152). Even though the earlier publication is referenced, a brief explanation is relevant and clarifying here.

Discussion and conclusions:

Lines 280-283 "Mine dust lung disease prevalence rates have been found to vary by mine and region and the logical next step in establishing that correlation lies in the characterization of the dust [13]. This characterization work serves as an important precursor to the future research needs to determine the extent of the variation on toxicity." How generalizable and scalable is this method? It seems possible that it may be necessary to sample individual mines to know anything meaningful about the characteristics of the dust - is that feasible? How specialized and costly is this type of analysis?

Lines 304-305 "This method has shown its potential in mining and should be expanded to more commodities and industries to gain insights into their exposures." This seems to be a research tool with limited generalizability due to the nature of the sampling and the degree of potential variability.  Could the feasibility in coal mines differ from its feasibility in other types of mining operations? What if the level of consistency for similar types of samples is lower than was observed here?

Author Response

Line 152 Define what is meant by "carbon" here.  From Table 2 it seems to be a particle that contains solely carbon and no other EDS-identifiable elements, but since "carbon" is not really a mineral this warrants a brief clarification in the text, particularly since this is the major class of particles in most samples.

-I have clarified what are mineral groups and carbon as an element as opposed to the minerals in Table 2.

Line 223 But are diesel engines indeed made of stainless steel?

Yes. Updated to specify mining equipment in the first instance and personnel transport vehicles with diesel engines in the second.

Lines 256-259 Here carbon is attributed to either coal or DPM - this could be mentioned and discussed in slightly more detail in the earlier section (line 152). Even though the earlier publication is referenced, a brief explanation is relevant and clarifying here.

-Added discussion and more detail at line 152.

Discussion and conclusions:

Lines 280-283 "Mine dust lung disease prevalence rates have been found to vary by mine and region and the logical next step in establishing that correlation lies in the characterization of the dust [13]. This characterization work serves as an important precursor to the future research needs to determine the extent of the variation on toxicity." How generalizable and scalable is this method? It seems possible that it may be necessary to sample individual mines to know anything meaningful about the characteristics of the dust - is that feasible? How specialized and costly is this type of analysis?

I’ve added a section on this to the manuscript. The method is very generalizable and scalable. It would need to be done on an individual mine basis. All mines could be taking their own samples and sending them for MLA analysis. They would just have to be sent the filters, and that is what currently happens with gravimetric filters for compliance monitoring.

The cost for MLA analysis is coming down as we standardise the method to go from research to routine analysis with less time for sample prep and scanning. These samples analysed up to 750k particles on the filter. The US samples only needed 1400 particles to achieve the desired confidence limit with 8 mineralogies. We are working out how many particles need to be sampled for our 25 mineralogies, and what mineralogies can be combined into groups and still give meaningful data. I’m hoping that in 10 years this is a routine analysis for mines. There is an additional paper planned that will go into the specifics of sample prep and the MLA analysis issues that had to be overcome including measurement artefacts and selection of measurement areas (from this work and 5 metals mines). I’m hoping this becomes a commercially available service in the coming years.

Lines 304-305 "This method has shown its potential in mining and should be expanded to more commodities and industries to gain insights into their exposures." This seems to be a research tool with limited generalizability due to the nature of the sampling and the degree of potential variability.  Could the feasibility in coal mines differ from its feasibility in other types of mining operations? What if the level of consistency for similar types of samples is lower than was observed here?

I have also subsequently sampled and analysed five underground metals mines and several smelters using this methodology with both respirable and inhalable samples. It works very well there with good consistency in paired sample and even more mineralogies are present. The metals results are actually more interesting that the coal data.

Reviewer 3 Report

The MS, titled "Characterization Analysis of Airborne Particulates from Australian Underground Coal Mines using the Mineral Liberation Analyser", reports data about the mineralogical compositions of coal mine dust using MLA and SEM methods. The organisation of the MS is good; nevertheless, the authors could provide some additional data. Since the authors mentioned that the SEM equipment was also used in this study, providing SEM-BSE images from selected coal dust in different size fractions could increase the scientific soundness of the MS. Furthermore, if it is possible, the authors could provide data about the mineralogical composition of mined coal. Because, such data could also help us understand the importance of parent material on coal dust. I added some corrections and suggestions in the revised MS. Overall, I could suggest a minor revision and would like to see the revised MS after suggested corrections are made by the authors.

Comments for author File: Comments.pdf

Author Response

The organisation of the MS is good; nevertheless, the authors could provide some additional data. Since the authors mentioned that the SEM equipment was also used in this study, providing SEM-BSE images from selected coal dust in different size fractions could increase the scientific soundness of the MS.

-BSE image has been added to supplement the false colour images of the particles.

Furthermore, if it is possible, the authors could provide data about the mineralogical composition of mined coal. Because, such data could also help us understand the importance of parent material on coal dust.

-Information and references added on the general mineralogical composition of coal.

I added some corrections and suggestions in the revised MS.

-These have all been addressed and references added where applicable. The mines have asked for anonymity and since there are so few (11 in QLD) giving a location narrows it down very quickly.

Round 2

Reviewer 1 Report

The paper has been corrected according to the reviewers' indications. There is just one minor correction to be made. 

According to the authors' affiliation reported in the last version, there are just three different affiliations. The affiliations n. 3 and 5 are repetitions of 2 and 1, respectively. The authors should correct the affiliation according to the following scheme: LaBranche and Cliff are 1 (The University of Queensland, Minerals Industry Safety and Health Centre, Sustainable Minerals Institute), Teale and Wightman are 2 (The University of Queensland, Julius Kruttschnitt Mineral Research Centre, Sustainable Minerals Institute), and Johnstone is 3 (The University of Queensland, School of Earth and Environmental Sciences).