Reactive Transport Modeling during Uranium In Situ Leaching (ISL): The Effects of Ore Composition on Mining Recovery
, Aidarkhan Kaltayev 2 and Jean-Jacques Royer 3Round 1
Reviewer 1 Report
General Comments
This manuscript reports on the experimental data and modelling of in-situ uranium leaching from ore material, which was subsequently used to model the extraction of uranium from the Budenovskoe uranium deposit. Overall, the manuscript reads well, but there are several occasions which require a greater level of detailed to improve clarity (see detailed comments below). One major concern is Section 3.3 as the information provided is great, except it is positioned around 6-7 pages after the original description of the data fit, resulting in the reader having to go back and attempt to find the corresponding Figure (this is not helped by the lack of Figure and Equation cross-references). Thus, having this information in its own separate sub-section is a nuisance. I would strongly encourage the authors to split out Section 3.3 into Sections 3.1 and 3.2, so that the modelling details, fit quality discussion and model assumption justifications are located with the original Figure description.
Overall, minor changes are required before this manuscript can be considered for publication.
Detailed Comments
1) Title. The word “modelling” is misspelt in the title; it should contain two l, not one as currently shown.
2) Often the Figures and Tables were placed before the first mention rather than immediately after, making it difficult for the reader to follow as they end up looking at the wrong figure/table. Prime examples of this confusion are Figure 9 and Table 11 where the former is located in Section 3.2.1 but not described until Section 3.2.2, and the latter is placed in Section 3.3.3 but not referred to until Section 4. Please amend.
3) Throughout: Following on from point 1 above, a lot of key information is missing from the Figure and Table captions making it difficult to distinguish between each one, especially when the Figures and Tables are misplaced. The missing information that needs adding includes (but not limited to): symbol and abbreviation definitions; what the different colour lines represent (e.g., Figure 8a); and the difference between multiple lines on the plot (e.g., while most of this information is shown in the key to Figure 10, it is unclear from the key alone what is being presented).
4) Section 1, pg 1, line 31. “IAEA” is not defined.
5) Section 1, pg 1, line 33. In the sentence beginning “The ISL method consists in…” the word “in” should be replaced with “of”.
6) Section 1, pg 1, line 44. “… mostly UO2 and UO3 oxides…” would read better as “mostly as UO2 and UO3 oxides.”
7) Section 1, pg 1, line 45. “…different dissolution rates in sulfuric acid solution.” the word “solution” should be pluralised, especially as your paper focuses on multiple sulfuric acid concentrations (i.e., solutions).
8) Section 1, pg 2, line 52. “… remaining available reserved in uranium.” replace “in” with “of”.
9) Section 1, pg 2, lines 61-62. You state that the presence of fine clay particles increases the amounts of acid, but not explained how. Is this through chemical reactions or is less of the acid absorbed into the clay? Please provide further details.
10) Section 1, pg 2, line 78. “Kazakh uranium deposits…”, I’m guessing “Kazakh” should be Kazakhstan?
11) Section 1, pg 3, lines 88-90. All reaction equations should be labelled as (R1), (R2), (R3), etc… enabling them to be distinguishable from mathematical equations (1), (2), (3), etc… Also, when you are describing these reactions equations in the main text you need to state which reaction is being referred to; for example, UO3 reacts with sulfuric acid (Reaction R1). Please change throughout. Also, please check reaction R2 as your text states that uranyl sulfate and hydrogen (H2) are produced whereas the equation shows uranyl sulfate and protons (H+); this typo could also explain why the charges are not balanced in Reaction R2.
12) Section 1, pg 3, line 92. The location details (i.e., state and country) for the Shu-Sarysu uranium province are missing.
13) Section 1, pg 3, line 99. The sentence part “… acid bulk dissolves partially impurities…” would read better as “acid bulk partially dissolves”.
14) Section 1, pg 3, lines 100-102. The clarity of this sentence needs improving. I would recommend the phase identification (e.g., solid) to be formatted in the same style as in its corresponding reaction equation (i.e., subscribe and no spaces). Also add in a cross-reference to this reaction equation to improve clarity (e.g., The reagent reaction in the leaching solution is shown in Reaction R3…).
15) Section 2, pg 4, line 110. “Experimental observation measurement…” should be replaced with either Experimental observations, or Experimental measurements.
16) Section 2, pg 4, line 111. “…the same all over the chemical reactions…” reads better as “the same over all the chemical reactions.”
17) Section 2, pg 4, lines 119-120. This sentence is too long. I would recommend ending the sentence after the term definitions, and start the next sentence by replacing “due to the” with “Based on the…”
18) Section 2, pg 4, lines 123-124. What do you mean by “invade”? Please use the correct chemistry terminology. Also, change the following to “the ability of the acid” and “rock for to reaching the uraninite inclusions.”
19) Section 3, pg 4, line 132. This sentence would read better if changed to “…in situ composition of the uranium compounds in the ore.”
20) Section 3, pg 4, line134. Location details for the Tortkuduk deposit are missing.
21) Section 3, pg 4, line 135. “These experimental data were…” reads better as “The experimental data was…”
22) Section 3, pg 4, line 137. What was the pressure of the solution? You state that it was constant but not gave a value or range of values used.
23) Section 3, pg 4, line 139. Which part of the apparatus is the ore material located in? I’m guessing it is in the leaching tube (part 3), but you need to state/correct this. Furthermore, how tightly packed was the ore material in this region (i.e., was the whole volume filled)? Was the ore material cut as a single block, or compacted into a block, or was it kept as loose sediment? Did you use any fittings (e.g., filters) in order to keep the ore material in this section? A little more information is required.
24) Section 3.1, pg 5, line 158. The text reads better if “in the function of the dimensionless” is replaced with “as a”; especially as you go on to state that L/S is typically given in mass units of…
25) Section 3.1, pg 5, line 164. Missing and between “time [day]” and “Q the flow rate”. Also, all symbols used in equations must be placed in italics; this needs correcting throughout the manuscript.
26) Section 3.1, pg 5, line 166. You state that two modes for L/S are used, but you have not stated what they are. Please add these details into the main text. Also, are these two modes (i.e., sulfuric acid concentrations) representative of the concentrations used in the field? Can you justify your findings from these two models alone (usually a minimum of 3 values are required)?
27) Section 3.1, pg 6, line 170. What do the authors mean by “… reaction rates of the solution with rock…”? Does the word “rock” refer to the ore material? Please clarify.
28) Section 3.1, pg 6, line 173. This sentence follows on from the equation above and, so, should continue in lower-case (“Where” currently starts with an upper-case letter).
29) Section 3.1, pg 6, line 175. It is unclear what the porosity (ϕ) is referring to; I’m guessing the ore material? Also, the rest of this sentence would read better by changing it to “and r and l the tube radius and length [m], respectively.”
30) Section 3.1, pg 6, lines 175-180. The sentence describing equation 11 needs re-writing as it is unclear how you derived/found this equation. I tried to obtain equation 11 myself based on the text given but ended up with a different formula.
31) Section 3.1, pg 6, lines 201-205. Is your assumption for an equal mass of UO2 to UO3 based on any field measurements or previous modelling studies? Without this information, it is difficult for the reader to judge how reliable this assumption is for the Tortkuduk deposit. If no measurements have been reported in the literature, then at least state that you explore the effect of the reliability of this assumption later in the paper with a cross-reference to Figure 11.
32) Section 3.2, pg7-8. This whole section needs checking as I was unable to reproduce your values for cUO3, cUO2 or cMineral. Using equation 12 and the variables given in Tables 2 and 4, I obtained a value of 10 m-3 for cUO3 and cUO2; not only is this inconsistent with your findings but the units for cU also doesn’t match. Either there is a mistake with Equation 12, and/or Tables 2 and 4, and/or the text description.
33) Section 3.2.1, pg 8, lines 216-222. What are the units for kU(VI), kU(IV) and kMinerals and are these values for dissolution or reaction rates?
34) Section 3.2.1, pg 9, Figure 6. While your numerical fit agrees well with the experimental data obtained using 30 g L‑1 of sulfuric acid, it is not the case when using 20 g L-1 - the leading edge is too steep, the peak is noticeably shifted by at least 0.05 L/S to lower values, and the falling edge is too shallow. Given that the results from this numerical fit are heavily applied in the rest of this paper, I would strongly encourage the authors to refit the data in Figure 6b.
35) Section 3.2.1, pg 9, line 248. Should “E/S” read L/S?
36) Section 3.2.1, pg 9, lines 250-255. The description of Figure 7d would be easier for the reader to follow if the discussion always described the results from the inlet to the outlet.
37) Section 3.2.1, pg 10, Figure 7 caption. Plot d is positioned bottom right, not “left, down” as currently described in the caption.
38) Section 3.2.2, pg 10, line 265. Remove the second “(a)” from this sentence, you have already referred to this plot.
39) Section 3.2.2, pg 10, lines 266-278. The authors state they use “different values for the solution filtration rate imposed in the tube during simulation” but do not include the values used. This information is also missing from Figure 8 and its caption. Three values for velocity are given in the key for Figure 8b (only), but there is no mention of “velocity” in the description of Figure 8b.
40) Section 3.2.2, pg 10, lines 271-272. The authors state “the peak amplitude is flow rate dependent according to a decreasing function (Figure 8, a)” but what is this function of (e.g., solution filtration rate, time, sulfuric acid concentration?). More details and clarity are required.
41) Section 3.2.2., pg 11, lines 284-285. The authors state that “a decrease in the filtration rate leads to an increase in the peak value” but what is this peak value of? More details and clarity are required here.
42) Section 3.2.3, pg 12, line 302. This sentence would read better if it was change to “It should be noted that the U(VI) to (VI) ratio may vary from one location to another in the same deposit…”
43) Section 3.3, pg 13, lines 334-341. This is a fantastic explanation of what is being shown in Figures 3 and 4, but you do not give this level of description when you originally discuss these plots 7 pages ago. In fact, the whole of Section 3.3 seems like an afterthought when in truth this information really needs to be incorporated at the points where the corresponding graphs and fits are discussed as it explains and justifies why you originally made these assumptions or chose those sets of variables or fit type. I would suggest the authors merge Section 3.3 into Sections 3.1 and 3.2.
44) Section 3.3.1, pg 13, line 350. The variable K is not defined.
45) Section 3.3.1, pg 14, Figure 12. Please rescale your axes as it is difficult to see how well the different fits correlate with your experimental data. Moving the information in the key to the caption would aid this.
46) Section 3.3.1, pg 14, line 366. Insert the word “are” between “t1*” and “given”.
47) Section 3.3.1, pg 14, line 368. This sentence would read better if the word “were” is placed between “R2” and “fitted”.
48) Section 3.3.1, pg 14, line 370. What do the authors mean by the phrase “they are quite identical”? I’m guessing this should read “the data agrees with” or “the data reproduced the same relationship as described by…”
49) Section 3.3.3, pg 15, lines 396-403. This paragraph describes your fitting results well, but you have not cross-reference which Figure this corresponds to – I’m guessing Figure 6 which would answer my Comment 34. If this is so, then this sub-section needs to be moved back 6 pages to where you originally discuss the results shown in Figure 6 as it would justify why you believe this poorer fit is acceptable; especially as then when on to use the values extracted from this numerical fit.
50) Section 3.3.3, pg 16, Figure 13. There is no mention of this Figure in the main text. Plus, the experimental data appears to be from Figures 3 and 4; if this is the case, then add this information in the caption. Also, should the x-axes read “L/S” rather than “E/S”?
51) Section 4, pg 16, lines 425-526. This sentence would read better is the word “the” is added between “keep” and “flow balance”.
52) Section 4, pg 17, Figure 14. I’m guessing that L here represents length? However, the authors have already assigned L to the liquid uranium part in the L/S ratio; thus, a different symbol is required for Figure 14 and a description of what this symbol represents needs to be added to the caption.
53) Section 4, pg 17, Figure 15. There is some confusion in the definition of Q; in the text, Q is the total flow rate divided by the productivity whereas the Figure 15 caption defines Q as the total flow rate which can also be described as the productivity. So, which is it? Also, why did the authors choose a poly numerical fit and what does this fit show? Further information is required, both in the caption and the main text.
54) Section 4, pg 17, Table 12. The authors have used a very similar caption for another table earlier in this manuscript, but neither of then state which set of experimental data the error analysis has been applied to. Please provide this information in the caption; a link to the correspond Figure where the experimental data is plotted would also be helpful.
55) Section 4, pg 18, lines 443-445. Either insert a reference to the Mass Conservative Law or remove the square brackets directly afterwards. This sentence would also read better if “under the action of a well network” was placed in brackets and the word “the” is removed from “the velocity field”.
56) Section 4, pg 18, line 454. Did the authors mean Figure 16 here (Figure 15 is cross-reference)? Also, the sentence would read better if it was change to “…changes in uranium content over time in the solution…”.
57) Section 4, pg 18, line 457. The authors state that an average value was used, but do not state what this value is or represents. Please provide details.
58) Section 4, pg 18, line 461. Units are missing for MAE and ME values.
59) Section 4, pg 18, Figure 16. There are no details provide explaining the numerical fit applied to the data shown in Figure 16. Can the authors state what this fit represents and why it fits the experimental data poorly (e.g., incorrect assumption used, or no/limited data was available for one or more of the variables, etc…).
60) Section 4, pg 19, Figure 17. Again, there are no details provided for the numerical fit applied to the data shown in Figure 17 (see above comment). Also, it is unclear what the “total recovery” corresponds to in the caption – is it the total recovery of ore material or leached uranium? Please provide the missing information.
61) Section 5, pg 19, line 484. Earlier in the paper the authors state that L/S is a dimensionless mass ratio, but here it is described as a dimensionless time unit – which is it? Also, this change also occurs in the Appendix.
62) Section 5, pg 19, line 488. What do the authors mean by “reduce the service time”? Is this time scale between introducing sulfuric acid into the injection wells and extracting uranium from the productive wells? Please clarify.
63) Section 5, pg 19, lines 489-490. The authors state that “intensification methods is recommended, for example, by addition to the solution of oxidizing agents such as Fe3+ and Mn2+ or by using bacterial leaching”; however, there is no discussion of this finding in the Results and Discussion section. How did the authors reach this conclusion?
Comments for author File: 
Comments.pdf
Author Response
Thank you for valuable remarks. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Initial Comments:
The manuscript “Reactive Transport Modeling during Uranium In-Situ Leaching (ISL): Effects of Ore Composition on Mining Recovery”, proposes a uranium reaction and transport model for the injected leach mining method. for this, the authors used mathematical and kinetic models of chemical reactions to compare with the real results.
It is an interesting manuscript, with a relevant theme, since after being extracted from unconsolidated sands, the presence of other minerals such as clay and oxides directly impact the process, and the definition of a methodology capable of approaching and predicting the reactions and processes involved, can be of great value to improve the efficiency of the extraction method, both from an economic and environmental point of view
Introduction
In general, I found the introduction very explanatory, covering several aspects of the uranium extraction system by leaching. The authors used appropriate references and the text is very clear and concise.
I suggest that topic "2", be part of the introduction, as item "1.2". It seems to me to be a complement to the introduction and I think it would be clearer for readers.
I also suggest that topic 3 be presented with material and methods, thus following a standard for scientific manuscripts. As it stands, it is difficult to distinguish where the introduction ends, and where the materials and methods used in the experiment begin.
Still in this context, I suggest that the authors define where the section of the results of the experiment itself begins, using a topic 4, which can be just the results, or results and discussions together. The way the paper is written, it is confusing to understand where the explanation of the previous work cited ends (Poezhaev, I.P. et al 2017), and where the results of the experiment itself begin.
L.26. In my opinion, don’t put the year (2021) between parenthesis. It’s looks like a reference in the text. I suggest “In 2021, it reaches up to ….”.
Table 4. The authors first present the table and afterwards explain the contents of the table. I suggest inverting the order, first citing the contents of the table in the text, and then presenting the table.
Table 6. Again, in Table 6, the authors first present the table and then discuss it. I suggest reversing, first discussing the results, and then presenting the table. This type of procedure is almost standard in scientific manuscripts.
Figure 7. Figure (7d) is left down or left right? Please clarify better.
Figure 9. Please first discuss the results of the figure and then insert into the text. the way it is, figure 9 (very interesting by the way) is a apparently "loose" in the middle of the text.
Figure 10. The same. First text, afterwards the figure.
Figure 12 and tables 7 and 8. The same thing. Please revise all figures and tables and be sure that the explanations texts are presented before the figures and tables.
Results
The results are in accordance with the data end results showed by Authors. It’s clearly and concise, and in my opinion reflect what was done in the experiments. The results are interesting and may have practical application for an improvement in the efficiency of uranium extraction in this type of geological context.
General comments
The manuscript addresses an interesting topic and fits into the context of the newspaper.
I only make a few reservations and some specific suggestions, but I strongly recommend that authors better organize the manuscript into appropriate topics, in order to make the paper read more clearly, as suggested above.
Author Response
Thank you for a valuable remarks. Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This is an interesting study about understanding ISL of U, through experiments as well as modeling, from actual ores and is acceptable for publication with following corrections:
1. Pg. 3; Eq. 2: Is any oxidizing agent added to ensure uranyl sulphate formation for uraninite. Please specify conditions with references.
2. It is mentioned in the manuscript that U(IV): U(VI) of deposits is unknown. Is it due to inhomogeneity? For homogeneous samples, amongst other methods, it can be determined by O/M measurements potentiometrically or thermogravimetrically.
3. How does the major component silica for all the deposits influence extent of leaching? Any correlation with % of other impurities?
4. What were the dissolved percentages of other metal ions in sulphuric acid? Authors mention it is 1 % in total. What is the distribution and is it deposit dependent?
Author Response
Thank you for a valuable remarks. Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Acceptable for publication
