Materials and Methods

Biomass and dye solution preparation

The tamarind pod shells (TH) were collected from dehulling unitand were washed extensively in running tap water to remove dirt and other particulate matter. This was later subjected to colour removal through washing and boiling in distilled water repeatedly. Subsequently the husks were oven dried at 105C for 24 hours, stored in a desiccator and used for biosorption studies in the original piece size. Methylene blue and amaranth has been used in this study as model molecules for cationic and anionic dyes. Stock solutions were prepared by dissolving accurately weighed samples of dye in distilled water to give a concentration of 1000 mg/L and diluting when necessary. Initial pH was adjusted by adding dilute solutions of HCl or NaOH. Batch adsorption experiments Batch adsorption studies were conducted in a routine manner. The 250 ml flasks containing 100 ml of the dye solution was contacted with the predetermined amount of the biosorbent at equilibrium time. The flasks were agitated at a 120 rpm constant shaking rate to ensure that equilibrium is achieved. The dye solution was separated from the biosorbent using Whatman No.1 filter paper. Adsorption uptake values were determined as the difference between the initial dye concentration and the one in the supernatant. All the experiments were carried out in duplicates and the average values were used for further calculations. Analysis of the dyes The concentration of the unadsorbed amaranth and methylene in the biosorption medium was measured colorimetrically using a spectrophotometer. The absorbance of the colour was read at 665 and 520 nm for methylene blue and amaranth respectively.