Kinetic and equilibrium studies for cadmium biosorption from contaminated water using Cassia fistula biomass

Cadmium (Cd) contamination of the water resources is one of the serious environmental issues. The present study aims to (1) evaluate the biosorption potential of Cassia fistula biomass for the removal of Cd from contaminated water and validate the experimental results with kinetic and equilibrium sorption models, (2) assess the removal of Cd from groundwater samples in the presence of other competing ions in the solution. The C. fistula biomass was characterized using Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller technique and scanning electron microscopy to understand the role of its physical properties in Cd biosorption and removal. The effects of biosorbent dose, initial Cd concentrations, contact time and presence of competing cations in groundwater samples at constant pH and temperature (27 +/- 1.5 degrees C) were studied. At equilibrium (90min), Cd removal (98-16%) and biosorption (6.26-0.34mg/g) were recorded depending on the experimental conditions. The Langmuir model yielded a better approximation of the experimental data at equilibrium rather than Freundlich model. The pseudo-second-order kinetic model explained well the kinetic behavior of Cd biosorption. Results revealed a decline in the Cd removal (12.7 and 6% at 0.25 and 1.0g/100mL, respectively) in the presence of cations in the water samples. The results proved that C. fistula is a very effective and environment friendly alternative adsorbent for the removal (98%) of Cd from the aqueous system.