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6.0. Desorption of adsorbed metal ions from metal-loaded leached residue and its regeneration ability were also studied. The results obtained could be useful for considering the leached manganese nodules residue as adsorbent for removal of heavy metal ions from contaminated water bodies.
doi:10.1016/j.jhazmat.2006.10.046 
Copyright © 2006 Published by Elsevier B.V.
Kinetic and thermodynamic studies of the adsorption of lead (II) ions onto phosphate-modified kaolinite clay
Received 31 March 2006;
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Abstract
This study is on the kinetics and thermodynamics of the adsorption of Pb2+ onto phosphate-modified and unmodified kaolinite clay obtained from Ubulu-Ukwu in Delta State of Nigeria. Increasing initial Pb2+ concentration increased the rate of Pb2+ adsorbed with increase in initial Pb2+ concentration from 300 to 1000 mg/L. Increasing Pb2+ concentration also increased the initial sorption rate h, from 1.404 to 13.11 mg g−1 min−1 for phosphate-modified kaolinite clay and 1.04–3.48 for unmodified kaolinite clay as Pb2+ concentration. Increase in temperature was found to increase the initial sorption rate of Pb2+ adsorption onto phosphate-modified adsorbent from 3.940 to 8.85 and 2.55 to 4.16 mg g−1 min−1 for the unmodified adsorbent. The overall sorption rate k, increased only slightly from 5.1 × 10−2 to 9.7 × 10−2 g mg−1 min−1 for phosphate-modified adsorbent, 3.8 × 10−2 to 5.4 × 10−2 g mg−1 min−1 for unmodified adsorbent. The adsorption reaction on both adsorbents was found to be chemically activated reaction and endothermic with energy of activation, E, at 500 mg/L of Pb2+ in solution as 19 and 10.68 kJ mol−1 for phosphate-modified and unmodified adsorbents, respectively. The positive values of both ΔH° and ΔS° obtained suggest an endothermic reaction and in increase in randomness at the solid–liquid interface during the adsorption of Pb2+ onto the adsorbents. ΔG° values obtained were all negative indicating a spontaneous adsorption process. The presence of Cd2+ decreased both initial sorption rate and the amount of Pb2+ adsorbed on phosphate-modified and unmodified adsorbents at equilibrium. The adsorption process follows a pseudo-second-order reaction scheme.
Keywords: Kaolinite; Phosphate-modified; Activation energy; Spontaneous; Endothermic
Article Outline
- 1. Introduction
- 1.1. Materials and methods
- 1.2. Modification of clay sample
- 1.3. Kinetics of Pb2+ adsorption
- 1.4. The pseudo-second-order model
- 2. Results and discussions
- 2.1. Mineralogical composition of kaolinite clay
- 2.2. Effect of temperature on kinetics lead ion adsorption
- 2.3. Thermodynamic parameters of adsorption
- 2.4. Adsorption mechanism
- 2.5. Effect of the presence of cadmium on the adsorption of lead
- 3. Conclusion
- References
