Kinetics and Thermodynamics Studies for the Adsorption of Nickel(II), Lead(II) and Cadmium from Aqueous Solution using Illite Clay - Silica Nanocomposite

Heavy metals in their elemental form as well as chemical form pose a threat to nature. There is the need therefore to explore and develop a simple, efficient, inexpensive and more eco-friendly method for removing these heavy metals from the environment and waste water to their permissible limits. Illilite clay - silica nanocomposite was successfully synthesized as the adsorbent for the removal of Ni2+,Cd2+ and Pb2+ ions from aqueous solution. The optimum percentage removal of Ni2+,Cd2+ and Pb2+ ions were 98.4, 93.15 and 93.23 % respectively, at 5 ppm with 0.4g adsorbent dose. Equilibrium data were subjected to Langmuir and Freundlich adsorption models in which the adsorption of Nickel fitted well with both models with correlation coefficient (R2) of 0.9852 and 0.9956 while Cadmium fitted well only with the Freundlich model with Correlation Coefficient (R2) of 0.9967. The kinetics or adsorption process was tested with pseudo first order and pseudo second rate laws. The kinetic studies followed pseudo-second order kinetics for all the three metal ions studied. The standard (H) enthalpy changes were found to be: 35.7, 25.2 and 38.4 kJ/mol for Ni2+, Cd2+ and Pb2+ respectively, hence indicate an endothermic process of adsorption. The standard entropy changes (S for Ni2+, Cd2+ and Pb2+ were also respectively found to be 0.1240,, 0.0878 and 0.1326 kJ/ mol/1 thus resulting into negative free energy changes and spontaneous adsorption processes for the removal of all the metal ions. The work has shown that enriched rich husk with silica nanoparticles is an efficient devise for the removal of the heavy metals studied.