Adsorption of cadmium from aqueous solutions onto coffee grounds and wheat straw: equilibrium and kinetic study.

AbstractThe adsorption kinetics of cadmium (Cd) from wastewater onto coffee grounds and wheat straw was ascertained under various process conditions. Batch tests were performed to study the effect of pH, adsorbent concentration, contact time, and initial metal concentration on the removal of Cadmium. The adsorption kinetics was envisaged by fitting the experimental data to the pseudo-first-order and pseudo-second-order kinetic models; and based on linear regression analysis, the best fit was found to be for the pseudo-second-order kinetic model for both adsorbents. Equilibrium conditions were achieved in less than 30 min. Two isotherm equations, namely Langmuir and Freundlich models, were also used to fit the experimental adsorption equilibrium data. The results showed that both physisorption and chemisorption mechanisms controlled the adsorption rate and capacity. The maximum adsorption capacity of coffee grounds and wheat straw was calculated to be 16.2 and 31.6  mg/g, respectively.