EFFECT OF ORGANIC MODIFICATION ON BENTONITE AND LOCALLY SOURCED CLAYS FOR THE REMOVAL OF HEAVY METALS FROM WASTEWATER.

Abstract

Heavy metal pollution has increased in recent decades due to increased industrial activities and technological development. This pollution is posing significant threats to the environment and public health, because of its toxicity, non-biodegradability and bio-accumulation. Lead (II) and Nickel (II) have been discovered to be highly toxic, causing allergy in human organs and kidney damage respectively. Clays have been used as adsorbents for the removal of some toxic metal ions from aqueous solution and they have been found to be effective and efficient due to heterogeneity of their surfaces and their ion exchange capacities. These potentials can be improved upon when natural clays are modified. This study investigated the workability of using modified and unmodified local clays to sequester Lead (II) and Ni (II) ions from aqueous solutions, using natural clays obtained from two sites: Ajegunle in Ilaje Local Government of Ondo State and Umbuluko Village in Orumba Local Government in Anambra State as adsorbents. The natural local clays were organically modified by using cationic Genamine CTAC as compatibility tool and monomer Vinyl acetate solution to produce the composite clay. The standard used in this study was commercial Bentonite clay. Each Local Clay sample was used to prepare three different forms of adsorbents powder and the six different adsorbents were used in this study, namely: Natural Clay samples, Hexadecyltrimethylammoniumchloride (CTAC) – Organoclay and Vinyl acetate composite of the natural clay. Morphological characterization of these adsorbents before metal removal was investigated using Scanning Electron Microscope (SEM) while the quantitative and qualitative elemental composition of the adsorbents were determined using Energy Dispersive X-ray Spectroscope(EDX) before the adsorption process. The FTIR analysis showed possible involvement of the functional groups of the different natural clay in modification of the clay .The mineralogical contents and structures of the different adsorbents were studied by using X-ray Diffractometer. Batch experiments were carried out to investigate the effects of pH, contact time, adsorbent dose, temperature and initial metal concentration. The optimum conditions established for each metal – adsorbent system was applied to sequester the same set of metals from industrial wastewater. Scanning Electron Micrographs showed that there were significant changes in the morphological appearance of the surface of clay after different chemical modifications. The XRD analysis showed the presence of SiO2, Al2O3, MgO, TiO2, Fe2O3, FeO and H2O in natural Ajegunle clay and SiO2, Al2O3, MgO, CaO, Fe2O3, FeO and H2O in Umbuluko natural clay. MgO, Al2O3 and H2O contents were reduced in the organoclay and the composite of both clays. The adsorption efficiency increased with increase in time, temperature, dosage and metal concentration. Langmuir, Freundlich and DubininRadushkevich models were used in the study The best fit was obtained with Langmuir isotherm, indicating monolayer adsorption. The mean free energy of adsorption obtained from Dubinin-Radushkevich model showed that the adsorption mechanism involve physical and ion exchange processeses .The kinetics study of the adsorption process indicated that the adsorption mechanism followed second order reaction .The thermodynamics studies data depict that the adsorption processes were feasible and spontaneous