Turmeric was found to sequester toxic metal ions from their aqueous solutions but thorough understanding of metal-adsorbent interaction requires assessment of adsorption rates. Therefore, in present work reaction and diffusion based kinetic models were applied on adsorption data to evaluate adsorption efficiency of turmeric. The correlation of coefficient, R2, for linear regression of pseudo second-order and Elovich kinetic models were found to be close to unity indicating that adsorption of aqueous Cu (II) onto turmeric was chemisorption process and its kinetics followed pseudo-second-order and Elovich models. The value of qe (theoretical) calculated from pseudo-second order model and qe (experimental) were also close to each other. On raising temperature from 298K to 313K, initial adsorption rate, ho, increased from 0.0031 to 0.032 gmmol-1min-1 and second-order kinetic constant, k2, increased from 2.74 to 12.27 g mmol-1min-1 indicating that Cu (II) adsorption onto turmeric powder is of endothermic nature. On the other hand, Elovich model parameters α (mmol g-1 min 1) and βE (gmmol-1) initially increased and then decreased on raising temperature from 298K to 313K. Intraparticle diffusion plot showed multi-linearity suggesting involvement of two step diffusion process. The presence of pores on adsorbent surface was confirmed by Scanning Electron Micrograph. The value of activation energy was found to be 75.29 kJ mol-1.On the basis of kinetic parameters determined at different temperatures and value of activation energy, chemisorption can be assumed as rate controlling mechanism for aqueous Cu (II) adsorption onto turmeric surface.

Amtul Qayoom, Syed Arif Kazmi and Saeeda Nadir Ali