Kinetic and Thermodynamic Aspects of the Adsorption of Pb2+ and Cd2+ Ions on Tripolyphosphate-Modified Kaolinite Clay.
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Date
2007
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Elsevier: Chemical Engineering Journal
Abstract
Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with tripolyphosphate reagent to obtain TPP-modified Kaolinite
clay. The kinetics and thermodynamics of the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay were studied. Increasing temperature and initial
metal ion concentration increased the sorption capacity of the adsorbent. The rates of adsorption of both Pb2+ and Cd2+ increased with increasing
temperature but decreased with increasing initial metal ion concentration and time. The pseudo-second-order initial sorption rates for the sorption of
Pb2+ were found to be higher than those of Cd2+. Pseudo-first-order model was found to only describe well, the data obtained in the first 8 min of the
adsorption process. The sorption of both metal ions was endothermic and spontaneous with H◦ values of +13.94 kJ mol−1 and +24.93 kJ mol−1
for Pb2+ and Cd2+, respectively. Activation energy values obtained were between +8 kJ mol−1 and +22 kJ mol−1. These values suggest that the
rate-controlling step in the adsorption of Pb2+ and Cd2+ by TPP-Kaolinite clay was diffusion-controlled. The sorption of metal ions from binary
solutions of both metal ions at different initial metal ion concentrations reduced the initial sorption rates of the adsorption of Pb2+ by TPP-Kaolinite
clay and increased that for Cd2+. The adsorption capacity of TPP-Kaolinite clay for both metal ions was also decreased by simultaneous presence
of both metal ions.
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Keywords
Kaolinite clay, Adsorption of metals, Endothermic, Tripolyphosphate