Skip to main content

Elucidation of the Nature of Structural Heterogeneity During Alkali Leaching of Non-activated and Mechanically Activated Boehmite (γ-AlOOH)

An Erratum to this article was published on 20 May 2015


Crystal joints and faces in non-activated boehmite and, state of agglomeration of particles, degree of amorphization, microcrystallite dimension and, strain in mechanically activated boehmite are indicators of structural heterogeneity which influences reactivity of the solid phase. The focus of this paper is on understanding the manifestation of the heterogeneity during alkali leaching of a boehmite (specific surface area—263 m2/g), without and with mechanical activation using planetary milling up to 240 minutes. A two-prong strategy is used for this purpose which involved analysis of the kinetics of leaching by a model-free approach using ‘isoconversional method’ and, in parallel, characterization of the reacting solid after different durations of leaching. Unlike model-fitting methods, the kinetic analysis revealed sample-dependent variation of apparent activation energy with fraction leached. Changes observed in the morphology of samples (by SEM), particle size distribution (by laser diffraction), and crystalline nature (by powder X-ray diffraction) are used to explain activation energy changes and propose mechanisms of leaching. The effect of mechanical activation on rate constant is assessed and it has been found that up to ~23-fold increase in rate is possible depending on the activation time, leaching temperature, and fraction leached. Further, based on binary correlations between activation energy at different fractions leached and initial characteristics of the samples, it is found that the leaching is predominantly influenced by structural changes during milling, namely, degree of amorphization, microcrystallite dimension, and strain, vis-à-vis specific surface area. Significantly, the paper highlights limitation of model-fitting methods used by most researchers to analyze the kinetics of leaching, especially for mechanically activated minerals.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13


α :

Fraction leached

a, b, c :

Lattice parameters (nm)

a/c :

Alkali to caustic weight ratio

A m :

Degree of amorphization (pct)

d 10, d 50, d 90 :

Characteristic particle diameters (µm)

ε :


E a :

Activation energy (kJ/mol)

E aα , E *aα :

α dependent E a (kJ/mol)

ΔE *aα :

Stored energy E aα  − E *aα (kJ/mol)


Functional form of integrated reaction model

k/k* :

Rate constant ratio


Microcrystallite size (nm)

R :

Gas constant

R 2 :

Correlation coefficient

r xy :

Binary correlation coefficient

SSAGeo :

Geometrical specific surface area (m2/g)


BET specific surface area (m2/g)

t MA :

Milling or mechanical activation time (min)

t :

Leaching or reaction time (min)

t α :

Leaching time for fraction leached α (min)

T :

Temperature (K)

Z,Z* :

Pre-exponential factor


  1. C. Marquez-Alvarez, N. Zilkova, J. Perez-Pariente and J. Cejka : Catalysis Reviews, 2008, vol. 50, pp. 222-286.

    Article  Google Scholar 

  2. T.C. Alex, Rakesh Kumar, S.K. Roy and S.P. Mehrotra: in Light Metals 2012, C.E. Suarez, ed., The Minerals, Metals & Materials Society (TMS), Warrendale, PA, 2012, pp. 15–19.

  3. J.J. Kotte: in Light Metals 1981, P.G. Campbell, ed., The Minerals, Metals & Materials Society (TMS), Warrendale, PA, 1981, pp. 46–81.

  4. R.A. Peterson, G.J. Lumetta, B.M. Rapko and A.P. Poloski, Sep. Sci. Technol., 2007, vol. 42, pp. 1719-1730.

    Article  Google Scholar 

  5. A.S. Russell, J.D. Edwards and C.S. Taylor, Journal of Metals, 1955, vol. 203, pp. 1123-1128.

    Google Scholar 

  6. R.F. Scotford and J.R. Glastonbury, Can. J. Chem. Eng., 1971, vol. 49, 611-616.

    Article  Google Scholar 

  7. R.F. Scotford and J.R. Glastonbury, Can. J. Chem. Eng., 1972, vol. 50, 754-758.

    Article  Google Scholar 

  8. A. Packter and H.S. Dhillon, Z. Phys. Chem., 1975, vol. 256, pp. 801-807.

    Google Scholar 

  9. A. Packter, Colloid Polym. Sci., 1976, vol. 254, 1024–1029.

    Article  Google Scholar 

  10. T. Ejima, K. Shimakage and K. Agatsuma, Journal of Japan Institute of Light Metals, 1980, vol. 30(2), pp. 98-105 (in Japanese with English abstract).

    Article  Google Scholar 

  11. N.S. Maltz, V.M. Sizyakov and N.S. Shmorgunenko: in Light Metals 1983, E.M. Adkins, ed., The Minerals, Metals & Materials Society (TMS), Warrendale, PA, 1983, pp. 99–107.

  12. D. Panias, P. Asimidis and I. Paspaliaris, Hydrometallurgy, 2001, vol. 59, pp. 15-29.

    Article  Google Scholar 

  13. R.L. Russell and R.A. Peterson, Ind. Eng. Chem. Res., 2010, vol. 49, pp. 4542-4545.

    Article  Google Scholar 

  14. H. Grénman, T. Salmi, D.Y. Murzin and J. Addai-Mensah, Hydrometallurgy, 2010, vol. 102, pp. 22-30.

    Article  Google Scholar 

  15. I. Djuric, I. Mihajlovic, Z. Zivkovic and R. Filipović, Chem. Eng. Comm., 2010, vol. 197, 1485.

    Article  Google Scholar 

  16. I. Djuric, I. Mihajlovic and Z. Zivkovic, Can. Metall. Q, 2010, vol. 49(3), pp. 209-218.

    Article  Google Scholar 

  17. B. Li, Z. Ting-an, D. Zhi-he, L. Guo-zhi, G. Yong-nan, N. Pei-yuan, W. Xu-jian and M. Jia, T. Nonferr. Metal. Soc., 2011, vol. 21, pp. 173-178.

    Article  Google Scholar 

  18. T.C. Alex, Rakesh Kumar, S.K. Roy and S.P. Mehrotra, Powder Technol., 2011, vol. 208, pp. 128-136.

    Article  Google Scholar 

  19. T.C. Alex, Rakesh Kumar, S.K. Roy and S.P. Mehrotra, Hydrometallurgy, 2013, vol. 137, pp. 23-32.

    Article  Google Scholar 

  20. W.H. Casey and B. Bunker, Reviews in Mineralogy and Geochemistry, 1990, vol. 23(1), pp. 397-426.

    Google Scholar 

  21. A.P. Prosser, Hydrometallurgy, 1996, vol. 41(2-3), pp. 119-153.

    Article  Google Scholar 

  22. Z. Juhasz and L. Opoczky, Mechanical Activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Akademiai kiado, Budapest, 1990.

    Google Scholar 

  23. P. Baláž, M. Achimovičová, M. Baláž, P. Billik, Z. Cherkezova-Zheleva, J.M. Criado, F. Delogu, E. Dutková, E. Gaffet, F.J. Gotor, Rakesh Kumar, I. Mitov, T. Rojac, M. Senna, A. Streletskii and K. Wieczorek-Ciurowa, Chem. Soc. Rev., 2013, vol. 42, pp. 7571-7637.

    Article  Google Scholar 

  24. F. Pawlek, M.J. Kheiri, and R. Kammel: in Light Metals 1992, E.R. Cutshall, ed., The Minerals, Metals and Materials Society (TMS), Warrendale, PA, 1992, pp. 91–95.

  25. P. G. McCormick, T. Picaro and P.A.I. Smith, Miner. Eng., 2002, vol. 15, pp. 211-214.

    Article  Google Scholar 

  26. T.C. Rakesh Kumar, M.K. Alex, Z.H. Jha, S.P. Khan, S.P. Mahapatra, and C.R. Mishra : in Light Metals 2004, P. Crepeau, ed., The Minerals, Metals & Materials Society, Warrendale, PA, pp. 31–34.

  27. T.C. Rakesh Kumar, Z.H. Alex, S.P. Khan, Mahapatra, and S.P. Mehrotra: in Light Metals 2005, H. Kvande, ed., The Minerals, Metals & Materials Society, Warrendale, PA, 2005, pp. 77–79.

  28. S. Fortin and G. Forté: in Light Metals 2007, M. Sorlie, ed., The Minerals, Metals & Materials Society, Warrendale, PA, 2007, pp. 87–92.

  29. E. Taskin, K. Yidiz and A. Alp: Miner. Metall. Process., 2009, vol. 26(4), pp. 222-225.

    Google Scholar 

  30. G. Greifzu: Diploma Thesis, Institute of Nonferrous Metallurgy and Purest Materials, TU Freiberg, 2012.

  31. T.C. Alex, Rakesh Kumar, S.K. Roy and S.P. Mehrotra, Hydrometallurgy, 2014, vol. 144-145, 99-106.

    Article  Google Scholar 

  32. V. K. Smolyakov, O. V. Lapshin and V. V. Boldyrev, Theor. Found. Chem. Eng., 2008, vol. 42(1), pp. 54-59.

    Article  Google Scholar 

  33. E. V. Bogatyreva, A. G. Ermilov and K. V. Podshibyakina, Inorg. Mater., 2009, vol. 5(12), pp. 1375-1381.

    Article  Google Scholar 

  34. N.J. Welham and D.J. Llewellyn, Miner. Eng., 1998, vol. 11, 827-841.

    Article  Google Scholar 

  35. A.M. Kalinkin and E.V. Kalinkina, Hydrometallurgy, 2011, vol. 108, pp. 189-194.

    Article  Google Scholar 

  36. S. Vyazovkin, Thermochim Acta, 2000, vol. 355, p. 155-163.

    Article  Google Scholar 

  37. A. Khawam and D.R. Flanagan, Thermochim. Acta, 2005, vol. 429, pp. 93-102.

    Article  Google Scholar 

  38. A. Khawam and D.R. Flanagan, J. Pharm. Sci., 2006, vol. 95(3), 472-498.

    Article  Google Scholar 

  39. A.I. Vogel: Vogel’s Textbook of Quantitative Chemical Analysis, 5th ed. (revised by G. H. Jeffery et al.), Longman Group U.K. Limited, 1989.

  40. M. Kitamura and M. Senna, Adv. Powder Technol., 2001, vol. 12(2), pp. 215-226.

    Article  Google Scholar 

  41. D. Panias and I. Paspaliaris, ERZMETALL, 1999, vol. 52(11), pp. 585-595.

    Google Scholar 

  42. W. Chesworth, Clay Clay Miner., 1972, vol. 20, pp. 369-374.

    Article  Google Scholar 

  43. K. Wefers, Metall, 1967, vol. 25(5), pp. 422-431.

    Google Scholar 

  44. K. Wefers and C. Misra: Oxides and Hydroxides of Aluminum, Alcoa Technical Paper No. 19, Revised, Alcoa Laboratories, 1987.

  45. J.A. Apps, J.M. Neil, and C. Jun: “Thermochemical Properties of Gibbsite, Bayerite, Boehmite, Diaspore and the Aluminate ion Between 273 K and 623 K (0 °C and 350 °C)”, Report No. LBL-21482, US Department of Energy, August 1988.

  46. P. Baláž, Extractive Metallurgy of Activated Minerals, Elsevier, Amsterdam, 2000.

    Google Scholar 

  47. A.N. Zelikman, G.M. Voldman and L.V. Beljajevskaja, Theory of Hydrometallurgical Processes, Metallurgija, Moscow 1975 (in Russian) (cited in Reference 46).

    Google Scholar 

  48. P. Baláž, Mechanochemistry in Nanoscience and Minerals Engineering, Springer-Verlag, Heidelberg/Berlin, 2008.

    Google Scholar 

  49. J.J.C. Jansz, Hydrometallurgy, 1984, vol. 12(2), pp. 225-243.

    Article  Google Scholar 

  50. A. Lüttge, R.S. Arvidson and C. Fis, Elements, 2013, vol. 9(3), pp.183-188.

    Article  Google Scholar 

Download references


The authors acknowledge the constructive criticism of this work and useful suggestions from Prof. S.P Mehrotra (formerly Director CSIR-NML and presently at IIT Gandhinagar, India). This work was carried out as a part of Department of Science and Technology sponsored project (ILTP/A-2.55).

Author information

Authors and Affiliations


Corresponding author

Correspondence to Rakesh Kumar.

Additional information

Manuscript submitted August 13, 2014.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Kumar, R., Alex, T.C. Elucidation of the Nature of Structural Heterogeneity During Alkali Leaching of Non-activated and Mechanically Activated Boehmite (γ-AlOOH). Metall Mater Trans B 46, 1684–1701 (2015).

Download citation

  • Published:

  • Issue Date:

  • DOI:


  • Leaching
  • Apparent Activation Energy
  • Boehmite
  • Gibbsite
  • Isoconversional Method