Materials and Methods

Tamarind pod shells were obtained from a de-hulling unit in Bangalore, Karnataka, India. The tamarind shells were washed thoroughly with distilled water and boiled to remove colour and impurities. They were dried in a hot air oven at 105°C and ground to a uniform size of 0.8 mm. So prepared tamarind pod shell particles were used for further studies. The stock solution (1000 mgl^-1) of Cr (VI) was prepared using potassium dichromate salt. Biosorption studies were performed in batch process. The processed tamarind shells equivalent to 1g dry weight were added to 100 ml of an aqueous solution of chromium (pH 2.0; adjusted with 0.1M H₂SO₄) of required concentration. The concentration of the unadsorbed chromium was determined spectrophotometrically at 540 nm using the diphenylcarbazide reagent. The effect of several parameters such as pH, metal concentration, contact time and quantity of biosorbent on adsorption is studied. The pH of the chromium aqueous solution was adjusted using 0.1 N HCl/NaOH. To study the functional groups responsible for the biosorption of Cr (VI), the biomass (tamarind pod shells) was analyzed using  a Fourier transform infrared spectrometer (FTIR). Adsorption of Cr (VI) on the walls of the glassware is found to be negligible and is determined by running blank experiments.