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. 2024 May 4;29(9):2135.
doi: 10.3390/molecules29092135.

Exploring the Efficiency of Algerian Kaolinite Clay in the Adsorption of Cr(III) from Aqueous Solutions: Experimental and Computational Insights

Karima Rouibah  1 , Hana Ferkous  2 , Meniai Abdessalam-Hassan  3 , Bencheikh Lehocine Mossab  3 , Abir Boublia  4 , Christel Pierlot  5 , Amdjed Abdennouri  6 , Ivalina Avramova  7 , Manawwer Alam  8 , Yacine Benguerba  9 , Alessandro Erto  10
Affiliations

Exploring the Efficiency of Algerian Kaolinite Clay in the Adsorption of Cr(III) from Aqueous Solutions: Experimental and Computational Insights

Karima Rouibah et al. Molecules. .

Abstract

The current study comprehensively investigates the adsorption behavior of chromium (Cr(III)) in wastewater using Algerian kaolinite clay. The structural and textural properties of the kaolinite clay are extensively characterized through a range of analytical methods, including XRD, FTIR, SEM-EDS, XPS, laser granulometry, N2 adsorption isotherm, and TGA-DTA. The point of zero charge and zeta potential are also assessed. Chromium adsorption reached equilibrium within five minutes, achieving a maximum removal rate of 99% at pH 5. Adsorption equilibrium is modeled using the Langmuir, Freundlich, Temkin, Elovich, and Dubinin-Radushkevitch equations, with the Langmuir isotherm accurately describing the adsorption process and yielding a maximum adsorption capacity of 8.422 mg/g for Cr(III). Thermodynamic parameters suggest the spontaneous and endothermic nature of Cr(III) sorption, with an activation energy of 26.665 kJ/mol, indicating the importance of diffusion in the sorption process. Furthermore, advanced DFT computations, including COSMO-RS, molecular orbitals, IGM, RDG, and QTAIM analyses, are conducted to elucidate the nature of adsorption, revealing strong binding interactions between Cr(III) ions and the kaolinite surface. The integration of theoretical and experimental data not only enhances the understanding of Cr(III) removal using kaolinite but also demonstrates the effectiveness of this clay adsorbent for wastewater treatment. Furthermore, this study highlights the synergistic application of empirical research and computational modeling in elucidating complex adsorption processes.

Keywords: COSMO-RS; DFT; adsorption; chromium; kaolinite; quantum theory of atoms in molecules (QTAIM).

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Structural characterization of kaolin: X-ray diffraction patterns of kaolin (a) and FTIR spectrum of kaolin after and before Cr3+ adsorption (b,c).
Figure 2
Figure 2
SEM images of kaolin at magnifications ×10.00 (a), ×5.00 (b,c), and ×2.00 µm (d).
Figure 2
Figure 2
SEM images of kaolin at magnifications ×10.00 (a), ×5.00 (b,c), and ×2.00 µm (d).
Figure 3
Figure 3
Kaolin EDS microanalysis.
Figure 4
Figure 4
Particle size distribution of kaolin: (a) focal distance of 300 mm and (b) focal distance of 45 mm.
Figure 5
Figure 5
XPS survey spectra of kaolin.
Figure 6
Figure 6
High resolution of XPS spectra of (a) Al 2p, (b) Si 2p, (c) O 1s, and (d) C 1s.
Figure 7
Figure 7
N2 adsorption–desorption and pore size distribution.
Figure 8
Figure 8
TGA–DTA curves of kaolin.
Figure 9
Figure 9
(a) Kaolin point of zero charge measurement and (b) zeta potential values of kaolin as a function of pH.
Figure 10
Figure 10
Effect of the contact time (a) and initial concentration (b) on the adsorption capacity of the adsorbent under constant conditions: pH = 5, T = 22 °C, V = 300 rpm, and r = 10 g/L.
Figure 11
Figure 11
Effect of (a) pH and (b) solid–liquid ratio on the removal percentage of Cr(III) under constant conditions: C0 = 10 mg/L, T = 22 °C, tc = 120 min, V = 300 rpm, and r = 10 g/L.
Figure 12
Figure 12
Ionic strength’s effect on the adsorption capacity of adsorbent under constant conditions: pH = 5, T = 22 °C, V = 300 rpm, and r = 10 g/L.
Figure 13
Figure 13
(a) Temperature’s effect for the conditions C0 = 10 mg/L, pH = 5, V = 300 rpm, and r = 10 g/L and (b) variation of the adsorption constant of Cr(III) as a function of temperature.
Figure 14
Figure 14
Adsorption isotherm of Cr(III) on kaolin with the conditions V = 300 rpm, pH = 5, T = 22 °C, and r = 10 g/L.
Figure 15
Figure 15
Detailed description with side and top views for the structure model of the kaolinite surface.
Figure 16
Figure 16
Detailed description of the COSMO-RS distribution with side and top views for the adsorbed Cr(OH)3 onto kaolinite surface in Al–O(H) (a) and Si–O (b) layers.
Figure 17
Figure 17
Frontier orbital distributions of the structure models for the adsorbed Cr(OH)3 onto kaolinite surface in Al–O(H) (a) and Si–O (b) layers.
Figure 18
Figure 18
The visualized IGM weak interaction regions (isosurface value = 0.05 a.u.) and the RDG scatter map of the kaolinite surface attached to Cr(OH)3 in Al–O(H) (a,c) and Si–O (b,d) layers.
Figure 19
Figure 19
The QTAIM maps of the kaolinite surface attached to Cr(OH)3 in Si–O (a) and Al–O(H) (b) layers.
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