Anuja Agarwal, Babita Kapil
Abstract: Adsorption appears to offer the best prospects for overall treatment of waste water as the process is useful for a broad range of substances and is normally excepted to be reversible so that regeneration of the adsorbent with resultant economy of operation may be possible. Lignin; an adsorbent obtained by precipitating it with concentrated hydrochloric acid from black liquor; a by product formed after digestion of mixed wood during pulping which was managed from a pulp mill in northern India. Lignin is inexpensive; mostly non-toxic; and also available in large quantities so it was investigated as a replacement for the current expensive methods of removing lead; a toxic and hazardous metal. The toxicity symptoms are mild anemia; brain damage; vomiting; lose of appetite; convulsions; uncoordinated body movements and stupor; eventually producing coma and death when lead accumulation is greater than 500 mg. Adsorption studies on lignin have been performed to remove lead from water as a function of equilibrium time; temperatures; pH; concentration and particle size of lignin. The data fits very well into Langmuir model. The Langmuir constants have been evaluated. Low desorption results are observed with a number of desorbing solutions. Adsorption kinetics has also studied by batch method and kinetic data suggests that the rate determining step is diffusion through the particle. Kinetic parameters like diffusion coefficient; activation of energy and entropy of activation have also evaluated. Studies proved that bio adsorbent lignin has good potential as an adsorbent for removing lead metal ions from water and waste water. It acts as a good scavenger of lead metal and the capacity of this adsorbent is quite significant.
Keywords: Lignin, adsorbent, isotherm, pH, diffusion