Colour removal from synthetic dye wastewater using a bioadsorbent

Removal of dyes (Crystal Violet, Methylene Blue, Malachite Green and Rhodamine B) from aqueous solutions at different concentrations, pH and temperatures by Neem sawdust has been carried out successfully. The percentage of the dye adsorbed by Neem sawdust decreased from 91.56 to 78.94 and 84.93 to 71.25 for Crystal Violet and Malachite Green, respectively, when the concentration of the dye was increased from 6 to 12 mg L-1 at a temperature 30 +/- 1 degrees C and pH 7.2. Adsorption of other dyes (Methylene Blue and Rhodamine B) also decreased with increasing concentration of the dye in solutions. The values of the rate constant of adsorption (k(ad)) of Crystal Violet at 25, 35 and 45 degrees C were found to be 10.80, 10.52 and 10.25 x 10(-2) min(-1), respectively. The values of the Langmuir constant for adsorption capacity (Q(o)) of Crystal Violet on the adsorbent varied from 4.44 to 3.99 mg g(-1), respectively, with the increase of temperature between 25 to 45 degrees C. The equilibrium data followed the Langmuir model of adsorption. The variation in the extent of removal with pH has been explained on the basis of surface ionisation and complexation. Thermodynamic parameters (Delta G, Delta H and Delta S) have also been determined to explain the results.