Removal Of Lead, Cadmium And Nickel By Sawdustmodified Tropical Clay For Use As Landfill Liner Material

ABSTRACT

Access to groundwater, a major source of direct drinking water in many developing countries, should not be assumed as access to safe drinking water. There is a need to prevent or minimize the contamination of groundwater, especially arising from solid waste disposal. This research work investigated the suitability of using clay and bentonite modified with sawdust as landfill liner materials for minimizing the migration of Pb2+, Cd2+ and Ni2+ in order to protect the environment and public health. Series of laboratory tests were carried out to determine the chemical and mineralogical composition, microstructural analysis of the clay and bentonite in order to characterize the samples. The effects of adding varying percentages of sawdust to the clay and bentonite on their geotechnical properties were determined. The removal of each of Pb2+, Cd2+ and Ni2+ by the clay, bentonite, sawdustmodified-clay and sawdust-modified-bentonite was investigated using the batch equilibrium adsorption technique for varying initial metal ion concentrations and contact times, while the pH, adsorbent dosage and temperature were kept constant. Results obtained show that the application of up to 8% sawdust to the clay satisfies standard geotechnical properties requirements for use as clay landfill liner, whereas the bentonite and its modification with sawdust did not. Each of the sawdust-modified-clay and sawdust-modified-bentonite removed more Pb2+, Cd2+ and Ni2+ than the clay and bentonite without sawdust, respectively. The Dubinin-Radushkevich model was found to be the best adsorption isotherm that described the Pb2+, Cd2+ and Ni2+ adsorption by the sawdust-modified-clay, while the pseudo-second-order kinetic model best described the rate of adsorption of these metal ions by the sawdust-modified-clay. The adsorption by the modified clay can be described as physical adsorption due to weak van der Waals forces. The order of removal of the metals by the clay and sawdust-modified-clay followed a trend of Pb2+ > Cd2+ > Ni2+, while that of bentonite and sawdust-modified-bentonite followed a trend of Pb2+ > Ni2+ > Cd2+. The clay and sawdust-modified-clay removed Pb2+ and Cd2+ better than the bentonite and sawdustmodified-bentonite, respectively, while the bentonite removed Ni2+ better than the clay. Clay modified with sawdust was found suitable and recommended for use as a landfill liner material in a composite lining system, thereby providing a low-cost and sustainable approach to improving the capacity of the clay to minimize the migration of Pb2+, Cd2+ and Ni2+ from landfills, and protecting the environment (particularly groundwater resources) and public health.