Review Reports - Technological Studies on the Production of Spodumene Concentrate and Lithium Carbonate from Low-Grade Pegmatite Ores

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript contains promising experimental work and industrial relevance; however, substantial revisions are required regarding mineralogical characterization, process description, quantitative analysis, mass balance presentation, and scientific discussion before publication can be recommended.

1. The manuscript lacks sufficient mineralogical characterization. Since beneficiation performance strongly depends on spodumene liberation and gangue association, detailed mineralogical analysis is necessary.

2. The manuscript would benefit significantly from more quantitative discussion, mass balance analysis, and comparison with published literature.

3. Were mica, lepidolite, petalite, or clay-associated lithium phases present? What was the modal abundance of spodumene in the ore? Without detailed mineralogical characterization, it is difficult to assess the beneficiation behavior and

process applicability.

4. The authors should also discuss whether the excellent recovery is related to favorable spodumene liberation characteristics.

5. The authors should also compare their roasting conditions with literature data, since industrial conversion temperatures are often between 950-1100 °C.

6. The lithium concentration of 12.1 g/L is promising, but leaching efficiency and impurity dissolution data should also be reported.

7. The authors should provide XRD and SEM characterization of the final lithium carbonate product.

Author Response

Comments 1: [The manuscript lacks sufficient mineralogical characterization. Since beneficiation performance strongly depends on spodumene liberation and gangue association, detailed mineralogical analysis is necessary.]

Response 1: [Thank you to the reviewer for this comment. The mineralogical characterization of the investigated ore was carried out using a combination of modern analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and elemental mapping. These analyses enabled the identification of the major gangue-forming and lithium-bearing minerals, as well as the distribution of the principal elements within the studied material. It should be noted that a dedicated mineral liberation study using Mineral Liberation Analysis (MLA) was not conducted within the scope of the present work. Nevertheless, the high degree of Li₂O upgrading achieved through dense medium separation (DMS), together with the preferential concentration of lithium in the coarser size fractions, indicates favorable conditions for the separation of spodumene from gangue minerals. To further support the mineralogical interpretation, published data on lithium-bearing pegmatites from the Akhmetkino deposit and the Karagoin-Saryozek ore zone have been incorporated into the Discussion section. According to these studies, lithium mineralization in the region is predominantly associated with albite–spodumene pegmatites, where spodumene occurs in association with quartz and feldspars and is often present as coarse crystalline aggregates. These findings are in good agreement with the mineralogical results obtained in the present study]

Comments 2: [The manuscript would benefit significantly from more quantitative discussion, mass balance analysis, and comparison with published literature.]

Response 2: [The manuscript has been revised to provide a more quantitative discussion of the beneficiation and lithium extraction results. Additional comparison with published literature has been included for the dense media separation, thermal conversion of spodumene, sulfation roasting, and lithium carbonate precipitation stages. It should be noted that the primary objective of the present study was not the optimization of lithium recovery, but rather the evaluation of the technological feasibility of processing an ultra-low-grade pegmatite ore containing approximately 0.26 wt.% Li₂O using an industrially applicable processing route. In contrast to many published studies, the present work reports not only concentrate grades and recoveries for selected fractions, but also lithium distribution among size fractions and overall lithium recovery into the final lithium carbonate product. To improve clarity, the discussion of lithium distribution and recovery throughout the process has been expanded in the revised manuscript. In addition, the overall lithium recovery throughout the process flowsheet was recalculated based on the updated lithium mass balance and is reported in the revised manuscript]

Comments 3: [Were mica, lepidolite, petalite, or clay-associated lithium phases present? What was the modal abundance of spodumene in the ore? Without detailed mineralogical characterization, it is difficult to assess the beneficiation behavior and process applicability]

Response 3: [Detailed mineralogical characterization of the investigated ore was performed using XRD, SEM and EDS analyses. The XRD results showed that the ore consisted predominantly of quartz (66%), anorthite (24%), muscovite (8%) and spodumene (virgilite) (approximately 3%). Therefore, the modal abundance of spodumene in the investigated sample was approximately 3%. Muscovite was identified as a gangue mineral, whereas no lepidolite, clay-associated lithium minerals or other significant lithium-bearing phases were detected in the investigated sample. Although petalite and lithium-bearing mica minerals have been reported elsewhere in the Akhmetkino deposit, they were not identified in the ore sample used in the present study. The obtained mineralogical data indicate that lithium in the investigated ore is predominantly associated with the spodumene phase, which forms the basis for the beneficiation strategy applied in this work].

Comments 4: [The authors should also discuss whether the excellent recovery is related to favorable spodumene liberation characteristics]

Response 4: [We agree that mineral liberation may influence the efficiency of dense media separation. However, in the present study a formal Mineral Liberation Analysis (MLA) was not conducted. Therefore, the degree of spodumene liberation cannot be quantitatively assessed. In our opinion, the high lithium recovery achieved during DMS is primarily related to the density contrast between spodumene (approximately 3.1–3.2 g/cm³) and the major gangue minerals, including quartz and feldspars (approximately 2.5–2.7 g/cm³), combined with the selected suspension density of 3.0 g/cm³. This provided favorable conditions for density-based separation of spodumene-bearing particles from the gangue minerals. Additional discussion has been added to the revised manuscript].

Comments 5: [The authors should also compare their roasting conditions with literature data, since industrial conversion temperatures are often between 950-1100 °C.]

Response 5: [Thank you for this valuable comment. Additional discussion comparing the selected roasting conditions with published literature has been included in the revised manuscript. The decrepitation temperature range applied in this study (1000–1100 °C) falls within the range commonly reported for industrial and laboratory α→β spodumene conversion (950–1100 °C). Relevant references have been added and the consistency of the selected thermal treatment conditions with previously published studies has been discussed]

Comments 6: [The lithium concentration of 12.1 g/L is promising, but leaching efficiency and impurity dissolution data should also be reported.]

Response 6: [We appreciate the reviewer’s observation. During revision of the manuscript, it was identified that the reported concentration corresponded to Li₂O rather than elemental lithium. The manuscript has been corrected accordingly, and the concentration is now reported as 12.1 g/L Li₂O. In addition, the lithium leaching efficiency was calculated based on the Li₂O content of the sulfated concentrate and the measured Li₂O concentrations in the productive solution and wash waters. Considering the obtained solution volumes, the overall lithium leaching efficiency reached approximately 87.1%. Furthermore, impurity dissolution behavior is discussed in greater detail in the revised manuscript. Concentrations of dissolved impurity elements, including Al, Si, Fe, S, As, Nb, Cd, and Sn, are presented in Table 5 and discussed in the corresponding section]

Comments 7: [The authors should provide XRD and SEM characterization of the final lithium carbonate product.]

Response 7: [The XRD characterization of the final lithium carbonate product is already included in the manuscript (Figure 11), confirming the formation of lithium carbonate as the dominant crystalline phase. SEM characterization of the final lithium carbonate product was not included because scanning electron microscopy combined with EDS is not suitable for reliable lithium identification due to the very low atomic number of lithium (Z = 3) and its weak characteristic X-ray emission. Therefore, SEM-EDS cannot provide direct confirmation of lithium-bearing phases. In the present study, the identity and purity of the lithium carbonate product were confirmed by XRD analysis and chemical analysis, which demonstrated a lithium carbonate purity of not less than 98.8 wt.% Li₂CO₃]

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript deals with lithium recovery from low grade spodumene by dense media separation (DMS), conversion of alpha to beta spodumene, sulfation and precipitation of lithium carbonate. The proposed method for processing low grade spodumene is not new in the industry. In the current form the manuscript is not recommended to be published in Metals.

I highly recommend the authors focus more on the Dense Medium Separation (DMS) step. Establishing the relationships between processing conditions (including suspension density, residence time, and mixing dynamics etc.) and lithium recovery is crucial. Since this Kazakhstan spodumene deposit is unique, obtaining these specific processing boundaries will provide the metallurgical community with valuable, highly localized baseline data.

To enhance the manuscript, the authors also should expand the methodology section to accurately reflect how the experiments were executed, specify the commercial equipment, experimental configurations, and process conditions utilized during testing. The specific analytical methods employed to determine the chemical compositions and phase formations should also be clearly detailed.

In addition the authors indicated in the Abstract that lithium carbonate was obtained under conditions close to the industrial ones, which are not totally true. The conversion of spodumene does not last for 2-4 hours at the industrial scale.

Author Response

Commets 1: [The manuscript deals with lithium recovery from low grade spodumene by dense media separation (DMS), conversion of alpha to beta spodumene, sulfation and precipitation of lithium carbonate. The proposed method for processing low grade spodumene is not new in the industry. In the current form the manuscript is not recommended to be published in Metals. I highly recommend the authors focus more on the Dense Medium Separation (DMS) step. Establishing the relationships between processing conditions (including suspension density, residence time, and mixing dynamics etc.) and lithium recovery is crucial. Since this Kazakhstan spodumene deposit is unique, obtaining these specific processing boundaries will provide the metallurgical community with valuable, highly localized baseline data. To enhance the manuscript, the authors also should expand the methodology section to accurately reflect how the experiments were executed, specify the commercial equipment, experimental configurations, and process conditions utilized during testing. The specific analytical methods employed to determine the chemical compositions and phase formations should also be clearly detailed. In addition the authors indicated in the Abstract that lithium carbonate was obtained under conditions close to the industrial ones, which are not totally true. The conversion of spodumene does not last for 2-4 hours at the industrial scale.]

Response 1: [Thank you to the Reviewer for this valuable comment. Additional discussion has been added regarding the influence of DMS operating parameters. The effect of suspension density was evaluated experimentally. At suspension densities of 2.8, 2.9 and 3.0 g/cm³, lithium recoveries remained relatively constant (97.8–98.0%), whereas the Li₂O grade of the concentrate increased from 4.1 wt.% to 5.77 wt.%. This behavior indicates that increasing suspension density primarily reduces gangue entrainment and improves concentrate quality rather than significantly affecting lithium recovery. The mixing time used during DMS was 1–2 min, while separation occurred within several seconds after agitation. Longer settling periods were found to be undesirable because they promoted ferrosilicon settling and reduced suspension stability. These observations have been added to the revised manuscript. A more comprehensive optimization of DMS parameters, including residence time and hydrodynamic conditions, is considered an important subject for future investigation. The Materials and Methods section has been expanded to provide a more detailed description of the dense media separation procedure. Additional information has been included regarding suspension preparation, suspension density (2.8–3.0 g/cm³), sample mass, mixing conditions (1-2 min), separation procedure, and operational observations related to ferrosilicon settling. These additions improve the reproducibility of the experimental procedure and provide a clearer description of the technological parameters used during DMS beneficiation. We agree with the reviewer that the wording in the Abstract could be interpreted too broadly. The intention was to emphasize the use of an industrially applicable ferrosilicon-based suspension for dense media separation, rather than to state that all stages of lithium carbonate production were conducted under fully industrial conditions. To avoid ambiguity, the sentence in the Abstract has been revised. The phrase “under conditions close to industrial practice” has been removed and replaced with “using an industrially applicable ferrosilicon-based suspension”. The manuscript now more accurately reflects that the present study was conducted at laboratory scale to evaluate the technological feasibility of the proposed processing route.]

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript has been improved significantly. After minor revision it would be suitable for publication.

There are suggestions that the authors should take into account for the revision:

Table 1: add the type of minerals from each deposit.
Table 2: round the numbers to the nearest thousandth of a percent, 4 digits are irrelevant.
Fig2, 3: use SEM/EDX instead of only SEM
Table 3: the capital letters in the titles
Fig. 1,5,9,11: X-ray patterns - unify the styles, every fig has a different presentation
Line 499: showing content of Li2O in solutions is not appropriate, use Li concentration
Line 518, 537: add % wt before each element
Line 570: unify same digits for Li2O content

Author Response

Comments 1: [Table 1: add the type of minerals from each deposit.]

Response 1: [Thank you for the comment. We added type of minerals for each deposit]

Comments 2: [Table 2: round the numbers to the nearest thousandth of a percent, 4 digits are irrelevant]

Response 2: [The values in Table 2 have been rounded to three decimal places (nearest thousandth of a percent) as suggested.]

Comments 3: [Fig2, 3: use SEM/EDX instead of only SEM]

Response 3: [Thank you for the valuable comment. In the revised manuscript, Figures 2 have been supplemented with EDS (EDX) elemental mapping results to provide additional information on the elemental distribution within the studied samples. Since a large number of EDS spectra were collected during the SEM–EDS investigation, including all spectra in the main manuscript would significantly increase the size and complexity of the figures. Therefore, the complete set of EDS spectra and quantitative elemental analyses has been provided as Supplementary Material for the convenience of readers, while only the most representative spectra are presented in the main text.]

Comments 4: [Table 3: the capital letters in the titles]

Response 4: [The titles and column headings in Table 3 have been revised and formatted consistently using capital letters (Title Case) throughout the table.]

Comments 5: [Fig. 1,5,9,11: X-ray patterns - unify the styles, every fig has a different presentation]

Response 5: [Thank you for this observation. However, some diffraction patterns were originally processed using different software packages, which resulted in minor differences in graphical presentation. These differences do not affect the interpretation of the phase composition or the scientific conclusions of the study.]

Comments 6: [Line 499: showing content of Li2O in solutions is not appropriate, use Li concentration]

Response 6: [Thank you for the comment. We agree with you and chaneged to Li concentration]

Comments 7: [Line 518, 537: add % wt before each element]

Response 7: [Thank you for the comment. The notation has been corrected, and the unit "wt.%" has been added to the elemental compositions reported in Lines 518 and 537 to improve clarity and consistency.]

Comments 8: [Line 570: unify same digits for Li2O content]

Response 8: [Thank you for the comment. The Li₂O contents have been revised and formatted consistently throughout the manuscript. The number of decimal places has been unified to ensure consistency in data presentation.]