Removal of a Cationic Dye from Aqueous Solution using Bentonite

Pollution of water by use of dyes is a widespread phenomenon and malachite green has been most often associated with aquatic pollution. This paper reports the ability of bentonite to remove malachite green from aqueous solutions by varying the amount of adsorbent, pH, temperature, and contact time and dye concentration in batch adsorption studies. It was found that adsorption increased with increasing pH up to 11 and temperature up to 50°C and equilibrium was achieved within 30 minutes of contact time between bentonite and malachite green. More than 99% of the dye could be removed by using only 3 g bentonite per litre of dye. Adsorption of malachite green onto bentonite could be described by the first order kinetic model and could be well described by the Freundlich adsorption isotherm. Using the Freundlich isotherm, the absorption capacity of bentonite was found to be 17.56 ug^1–1/n ml^1/n g⁻¹ at 30°C and hence is a promising low cost material for removal of dyes from waste water.