ADSORPTION STUDIES OF SOME SURFACE ACTIVE AGENTS ON LIGNIN

Abstract

Biochemically resistant detergents present some of the most wide spread and severe problems in wastes and receiving waters. A • regular discharge of synthetic surfactants into municipal sewage causes frothing troubles in operation tanks. The toxicity of the synthetic surfactants to fish and aquatic flora as well as human beings is well known. Of the various treatment methods adsorption method appears to offer the best overall treatment especially for those which can not be removed by other methods. Activated carbon, the most effective adsorbent has not found favour in view of regeneration difficulties and economic considerations. A number of other adsorbents like fly ash, alumina, lime stone, solids, sludge, ash etc. have also been tried but the results are not encouraging. Lignin is a waste material present in the black liquor of pulp and paper industry whith possess problems for its Osposal. Studies have shown that it can adsorb a number of dyes and other compounds from their aqueous solutions. Hence lignin has been chosen for the study of adsorption of synthetic surfactants, to explore its utility for the removal of surfactants from waste water. EXPERIMENTAL Kraft lignin has been isolated from spent liquor .obtained by pulping of Eucalyptus chips in the laboratory. The pulp was filtered and the filterate was acidified with dilute hydrochloric acid to precipitate crude lignin. It was purified by Ahlm's method. Two cationic surfactants namely Cetyl pyridinium chloride (CPC) and Cetyl trimethyl ammonium bromide (CTAB) and two nonion-ic surfactants namely Tween20 (T2()) and Tween40 (T40) have been chosen for adsorption studies. The estimation of cationic sur-factants have been performed by the method of Few and Ottewill. The method involves the extraction of cationic surfactant Oran-geII dye complex into chloroform and measuring spectrophotometri- cally the colour intensity of chloroform phase at 485 nm. The estimation of nonionic surfactants have been performed by stand- ard method. The method essentially involve the extraction of nonionic surfactant cobaltothiocyanate comple:< into dichloro methane and measuring spectrophotometrically the colour intensity of dichloromethane phase at 620 nm. The study of sorption characteristics and sorption kinetics provide very useful information for fully exploiting the poten-tial of an adsorbent. Batch method because of simplicity and ease of evaluation of adsorption parameters, has been used for the study of adsorption and adsorption kinetics experiments. Adsorption isotherms are shown by determining the adsorption at different concentration of surfactants (1-14 mg/1 and 16-117 mg/I in cases of cationic and nonionic surfactants respectively). The isotherms have been plotted to study the effect of temperature, pH, particle size of lignin and salt solutions on adsorption.