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. 2023 Jul 27;9(8):e18634.
doi: 10.1016/j.heliyon.2023.e18634. eCollection 2023 Aug.

RSM optimization studies for cadmium ions adsorption onto pristine and acid-modified kaolinite clay

L S Mustapha  1 , A S Yusuff  2 , P E Dim  1
Affiliations

RSM optimization studies for cadmium ions adsorption onto pristine and acid-modified kaolinite clay

L S Mustapha et al. Heliyon. .

Abstract

Clay has been reported as an active absorbent for the removal of toxic heavy metals from aqueous medium. In this study, pristine and acid modified kaolinite clays (PKC and AMKC) were prepared, characterized using various analyses, and tested for Cd2+ ion adsorption from textile industry wastewater. After acid modification, the specific surface area of clay increased from 84.2 to 389.4 m2/g. Adsorption isotherm, kinetics and thermodynamics behaviour process were examined. The pH at (pHpzc) of 8.5 indicate that AMKC surface is positively charged for pH below the pHpzc attracting anions. Response surface methodology was used to investigate the effect of adsorption process factors on Cd2+ ion removal uptake. At the optimum process conditions of 45.3 °C temperature, 0.63 g/L adsorbent dosage, and 120.9 min contact time, the percentages of Cd2+ adsorbed by PKC and AMKC were 77.82% and 99.19%, respectively. Various models were employed to analyzed the kinetic and equilibrium data. The Pseudo-first order, Pseudo-second order and Intra-particle diffusion were used to evaluate the kinetic data, while the Langmuir, Freundlich and Temkin isotherm models were applied to analyzed the equilibrium data. The sorption kinetics was found to be best described by Pseudo-second order considering the high correlation coefficient (R2), smaller Chi-square (ᵪ2) and sum of square error (SSE). The Freundlich model was the most accurate in describing the equilibrium data followed by Langmuir and Temkin respectively. The thermodynamic reveal that the reaction is spontaneous and endothermic in nature, and increase in randomness between the adsorbent and adsorbate. The obtained activation energy (Ea) value suggest that the adsorption mechanism of Cd(II) is a physisorption dominated.

Keywords: Adsorption; Cadmium ions; Kaolinite clay; Optimization; Response surface methodology.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
SEM images of (a) PKC and (b) AMKC.
Fig. 2
Fig. 2
FTIR spectra of PKC and AMKC samples.
Fig. 3
Fig. 3
XRD pattern of PKC and AMKC samples.
Fig. 4
Fig. 4
Combined effect of process factors (a) dosage and temperature (b) time and temperature (c) time and dosage on percentage removal of Cd(II) on AMKC.
Fig. 5
Fig. 5
Combined effect of process factors (a) dosage and temperature (b) time and temperature (c) time and dosage on percentage removal of Cd2+ ions on PKC.
Fig. 6
Fig. 6
a. Plot of a Normal % probability versus residual error b. Actual values versus predicted values for AMKC.
Fig. 7
Fig. 7
a. Plot of a Normal % probability versus residual error b. Actual values versus predicted values for PKC.
Fig. 8
Fig. 8
Determination of pH at point zero charge (pHpzc) on surface (a) PKC and (b) AMKC.
Fig. 9
Fig. 9
Effect of pH on Cd(II) ions adsorption by AMKC. (Adsorbent dosage of 0.63 g/L, temperature of 45.3 °C and time of 120 min).
Fig. 10
Fig. 10
Predicted curve fits for equilibrium isotherm for Cd(II) adsorption on AMKC.
Fig. 11
Fig. 11
Predicted curve fits for kinetics of Cd(II) adsorption onto AMKC.
See this image and copyright information in PMC

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