Process development for the batch and bulk removal and recovery of a hazardous, water-soluble azo dye (Metanil Yellow) by adsorption over waste materials (Bottom Ash and De-Oiled Soya)

Bottom Ash and De-Oiled Soya have been used as adsorbents for the removal of a hazardous azo dye-Metanil Yellow from its aqueous solutions. Adsorption of Metanil Yellow on these adsorbents has been studied as function of time, temperature, concentration and pH. Batch adsorption studies, kinetic studies and column operations enabled extraction of lethal dye from wastewaters. Adsorption equilibrium data confirms both Langmuir and Freundlich isotherm models and monolayer coverage of dye over adsorbents. Kinetic data have been employed to calculate specific rate constants, indicating thereby involvement of first order kinetics in the on-going adsorption and activation energy was determined as 0.813 and 1.060 kJ mol−1 for Bottom Ash and De-Oiled Soya, respectively. For both adsorbents, the adsorption process has been found governing by film diffusion, over the entire concentration range. Column operations have also been performed for the bulk removal of the dye and also to examine the practical utilization of fixed bed adsorption technique in elimination of dangerous effluent. Saturation factors for Bottom Ash and De-Oiled Soya columns have been calculated as 99.15 and 99.38%, respectively. Attempts have also been made to regenerate the dye from the exhausted columns using aqueous sodium hydroxide as eluent.