The Significance of Hydrophobicity for the Water Retention Properties of Sand and Coal

Round 1

Reviewer 1 Report

Review: The significance of hydrophobicity for water retention properties of sand and coal

The paper presents experimental work to study the effect of formation hydrophobicity for water retention. Different samples were used including crushed and uncrushed coal and sandstone sample.

• The abstract need to add a sentence at the end to show the novelty and the application of the paper findings.
• What is the mineral analysis for the rock samples? For coal what is the thermal maturity, carbon content, ash content?
• More details of sample preparation for CA measurements are needed.
• What is the effect in the findings for using consolidated rock samples comparing to cemented samples?

Here is some papers for the measurements and sample preparation of CA for coal and sandstone.

Ibrahim, Ahmed Farid, and Hisham A. Nasr-El-Din. "Effect of water salinity on coal wettability during CO2 sequestration in coal seams." Energy & Fuels 30.9 (2016): 7532-7542.

Ibrahim, Ahmed Farid, and Hisham A. Nasr-El-Din. "Effects of Water Salinity, CO₂ Solubility, and Gas Composition on Coal Wettability." Paper presented at the EUROPEC 2015, Madrid, Spain, June 2015. doi: https://doi.org/10.2118/174371-MS

• Figures caption needs to be rewritten to include more description about the experiment, conditions.
• In Fig. 7, the caption defines what the arrows referring to.
• Figures 11,12 need to improve their quality
• Separate the discussion from the conclusion section.
• A discussion section can be combined with the results section or can stand-alone section to add more interpretation for the results and comparison with the literature results.
• The conclusion section should highlight and generalize the main findings in the paper.
• The paper needs proofreading to improve its readability

Author Response

Please see the attachment for our response to your comments. If viewing the revised manuscript, please forgive any formatting errors that may appear, due to "Track Changes" being used.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have provided a cogent and thorough examination of the effect of hydrophobicity on the soil water retention curve for a mixture of sand, coal, and crushed rock. The results are applicable to mine tailings management, a vital area of inquiry.

The methods were careful and appropriate. The authors provided thoughtful explanations as to their experimental decisions and their consequences. These results were predictable in a general sense, i.e., the reduction of saturation at any level of suction with increased hydrophobicity. However, the careful approach and detailed results provide definitive confidence and increase the likelihood that this phenomena will be recognized, if not accounted for, in subsequent modeling approaches. The authors provide several meaningful insights, including the discussion of menisci relative to prevailing saturation. 

Some comments for consideration:

-What method was used for experimentally measuring the water retention curves? The manuscript provides a figure, and cites an article that presumably contains the method - the article cited is entitled "The mechanics of cone penetration". Is the hanging column method described in that article? If so, then state that (this reviewer was unable to verify the method was contained in that reference). Better yet, state the actual source method (e.g., ASTM D6836).

-The use of the shoe waterproofing spray is reasonable for a study whose objectives are to evaluate the effects of initial hydrophobicity. The authors noted how they disaggregated particles prior treatment. Is there any concern that chemical coating/bridges between particles remained, and that such bridges could be misinterpreted as water during the ESEM analysis?

Author Response

Please see the attachment for our response to your comments. If viewing the revised manuscript, please forgive any formatting errors that may appear, due to "Track Changes" being used.

Author Response File: Author Response.docx