Batch sorption dynamics and equilibrium for the removal of cadmium ions from aqueous phase using wheat bran

Studies on a batch sorption process using wheat bran as a low cost sorbent was investigated to remove cadmium ions from aqueous solution. The influence of operational conditions such as contact time, cadmium initial concentration, sorbent mass, temperature, solution initial pH, agitation speed and ionic strength on the sorption kinetics of cadmium was studied. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The sorption of cadmium was found to be dependent on initial concentration, sorbent mass, solution pH, agitation speed, temperature, ionic strength and contact time. The value of activation energy (12.38 kJ mol(-1)) indicates that sorption has a low potential barrier corresponding to a physical process. Sorption equilibrium isotherms at different temperatures was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to well fit the isotherm data but a worse correlation was obtained by the Freundlich model. The five Langmuir linear equations as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Thermodynamic parameters such as Delta H degrees, Delta S degrees and Delta G degrees were calculated. These parameters indicate that the sorption of cadmium by wheat bran is a spontaneous process and physical in nature involving weak forces of attraction and is also endothermic. (C) 2007 Elsevier B.V. All rights reserved.