OPTIMIZATION OF CHROMIUM BIOSORPTION BY AGERATUM CONYZOIDES LEAF POWDER FROM AQUEOUS SOLUTIONS: EQUILIBRIUM KINETICS AND THERMODYNAMICS

The study on low - cost adsorbent such as Ageratum conyzoides leaf powder was used to remove chromium from aqueous solutions. Experiments were conducted in batch mode to observe the influence of various parameters such as effect of contact time (1 - 180 min.), pH (2 - 8), biosorbent dosage (5 - 60gL - 1), effect of temperature (283 - 323 K), biosorbent siz e (53 - 152), initial metal concentration (20 - 200 mgL - 1), the equilibrium agitation time for chromium biosorption was found to be 50 minutes. The % removal of Cr increased significantly with increase in pH (6), biosorption dosage (35gL - 1) and temperature (3 03K). The percentage removal of chromium decreased by increasing the initial concentration of chromium and absorption size. The experimental biosorption data were modeled using Langmuir, Freundlich and Temkin isotherms. Based on R2 values, the Freundlich ( R2 = 0.9967) model fitted the equilibrium biosorption data best, confirming monolayer adsorption of chromium on to the biosorbent surface followed by Langmuir (R2 = 0.987) and Temkin (R2 = 0.9535). The biosorption kinetics of chromium was best described by pseudo - second order (R2 =0.9890) kinetics since at all concentrations, the R2 values were higher than the corresponding pseudo - first order (R2 =0.9534) values. Based on thermodynamic parameters the biosorption of Cr by A.conyzoides leaf powder was found t o be spontaneous, endothermic and feasible under given conditions.