REMOVAL OF LEAD FROM WASTE WATER BY ADSORPTION

Abstract

The pollution of water resources due to indiscriminate disposal of heavy metals has been causing worldwide concern for the last few decades. Unlike organic pollutants, the majority of which are susceptible to bio-degradation, heavy metals are non-degradable to harmless end products. They are toxic to aquatic flora and fauna even in relatively low concentrations. Metals, which are significantly toxic to human beings and ecological environments, include arsenic (As), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), manganese (Mn), cadmium (Cd), nickel (Ni), zinc (Zn) and iron (Fe), etc. Lead, an element which has been used by man for years, can be regarded as a longstanding environmental contaminant. All the chemicals/compounds containing lead are considered as cumulative poisons that usually affect the gastrointestinal track, nervous system and sometimes both. The chief sources of lead in water are the effluents of processing industries. Apart from this lead is also used in storage batteries, insecticides, plastic water pipes, food, beverages, ointments and medicinal concoctions for flavoring and sweetening. Lead poisoning causes damage to liver, kidney and reduction in hemoglobin formation, mental retardation, infertility and abnormalities in pregnant women etc. There are several methods for removing toxic/heavy metals from aqueous solutions, such as chemical precipitation, membrane filtration, ion exchange, biosorption and adsorption. Removal of lead from contaminated water bodies has been attempted by several researchers employing a wide variety of techniques. Majority of these are adsorption on various surfaces like activated carbon, peat, goethite mineral, hydrated iron etc. In the present study laboratory scale experiments have been carried out using the Coconut Jute Activated Carbon (CJAC) and Commercial Activated Carbon (CAC) as adsorbents for the removal of Lead. The present study has been undertaken with the objective to iii investigate the suitability of CJAC as a low cost adsorbent for the removal of Lead as replacement of CAC. Batch experiments were carried out to determine the effect of various factors such as contact time, initial concentration, pH, adsorbent dose, adsorbent particle size and temperature on adsorption process. Kinetic study shows that adsorption of Pb(II) on CJAC and CAC follows the Pseudo-second order kinetics. Langmuir isotherm best-fitted the isotherm data for Pb(II) adsorption on CJAC and CAC at almost all temperatures. However, the error analysis values and the non-linear correlation coefficients, R2, are comparable for Langmuir, Temkin isotherms (for CJAC) and Langmuir, Temkin, Redlich-Peterson (for CAC). Adsorption rate increases with increase in temperature for both the adsorbents, showing the endothermic nature of adsorption. From thermodynamic study AG° , L\H ° and AS° values are also calculated for both adsorbents. iv