Sequestering of Zn((Ⅱ) ions at the surface of rice husk has been studied as a function of contact time, adsorptive concentration, temperature and pH, using the radiotracer technique employing a↑(65)Zn radiotracer. A relatively slow uptake of metal ion increasing with bulk dilution (10↑(-2) to 10↑(-7) mol/dm↑(3)) was seen, which obeys the first-order rate law and agrees well with the classical Freundlich adsorption isotherm. The removal of metal ions from the bulk increases with the increase in pH (3.2-10.2) and temperature (293-323K) and evaluation of the thermodynamic data shows that the process involved is endothermic and apparently irreversible in nature, suggesting an ion exchange mechanism along with surface complexation. On the other hand Cd(Ⅱ) was not adsorbed on the surface of the rice husk at pH 6.2. #1997 Elsevier Science Ltd
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