REMOVAL OF ZINC USING TEA FACTORY WASTE AS AN ADSORBENT

Abstract

Heavy metal pollution has become an important environmental issue all over the world. The heavy metal, such as lead, copper, cadmium, mercury, zinc, and nickel are among the most common pollutants. These heavy metals even at low concentrations pose threat to ecosystem and human life. The toxic metal ions are released into environment in a number of ways, e.g. industrial effluents, municipal sewage, fossil fuel combustion, mining activities. A number of methods are available for the removal of metal ions from aqueous solutions. These include ion exchange, solvent extraction, reverse osmosis, sorption and activated carbon adsorption. However, these techniques have certain disadvantages, such as high capital and operational cost or the treatment and disposal of residual metal sludge. Since the cost of these processes are rather expensive, so use of agricultural residues or industrial by product having biological activities have been received considerable attention. A variety of adsorptive material, such as coconut husk, a sugar industry waste, green algae, fly ash and lignite are used in heavy metal removal. Recently, tea factory waste is also gaining grounds due to its potential to overcome heavy metal pollutants. Tea leaves are largely made up of cellulose and hemicelluloses, lignin, condensed tannins and structural proteins. So one third of the total dry matter in tea leaves have good potential as metal scavengers from solution and wastewaters since the above constituents contain functional groups. In India, yearly production of tea is approximately 857000 tonnes which is 27.4% of total world produce. Amount of tea factory waste produced per after processing is about 190400 tonnes. The present study has been undertaken with the objective to investigate the suitability of tea factory waste as a low cost adsorbent for the removal of heavy Zinc as replacement of conventional activated carbon. Adsorption studies have been carried out for evaluating the suitability of tea factory waste as a low cost adsorbent. The effects of various parameters like pH, adsorbent dose, initial concentration of heavy metal was studied using tea factory waste (TFW). The detailed characterization pertaining to iii physio-chemical, structural and morphological properties of tea factory waste have also been carried out. The straight line plot of log (Qe-Qt) versus time (t) for adsorption of zinc shows, the validity of Lagergren equation. Various steps involved in adsorbate transport from the solution to surface of the adsorbent particles have been dealt with by using Weber-Moriss plot, Q, versus t0'5 for the tea factory waste. The rate controlling parameters kid,i and k,d,2 have been determined and it is found that macro pore diffusion is much larger than micro pore diffusion rate. Equilibrium data obtained from the experiments were analyzed for various isotherms such as, Freundlich, Langmuir, Redlich-Peterson and Tempkin. All these isotherms have been found fitted with the equilibrium data and based on percent relative and absolute error it is concluded that the Redlich-Peterson shows best fit followed by Langmuir isotherm. iv