Comparative Study of Rates of Biosorption for Selected Single and Mixed Metal Ions using Natural Products

Abstract

Heavy metals are usually found in low concentrations in natural aquatic ecosystem. In recent times, however, the occurrence of metal contaminants especially heavy metals in excess of natural loads has become a problem of increasing concern. The contributing factors are rapid growth of population, increased urbanization and expansion of industrial activities, exploration and exploitation of natural resources, extension of irrigation and other modern agricultural practices as well as lack of environmental regulations. This therefore, calls for efficient, cheap, available and non polluting method of controlling presence of heavy metals in water bodies. Use of natural biosorbents such as algae has demonstrated great potential to remove heavy metals from wastewater. An investigation of the effect of contact time, reaction kinetics, influence of ionic sizes and influence of presence of other metal ions in biosorption of heavy metals Cu, Zn and Pb using Ascophyllum nodosum has been done. Model wastewater solution containing a known concentration of the given heavy metal ions was prepared for both single and mixed at a fixed pH of 5. A 0.25g mass of dry algae was introduced for every 100 mL solution. Change in level of concentration was monitored at intervals of 10 minutes using AAS until the rate of biosorption was almost constant.  The sorption process occurred in two stages; first being rapid adsorption and then gradual adsorption that was almost constant. Pb was most biosorbed while Zn was least for both systems, adopting the order Pb > Cu > Zn. The data obtained fitted both Langmuir isotherm and experimental parameters were determined. The order of reaction was found to follow pseudo second order after comparison of R2 values that were deduced from first and second order linearized plots.Key words: Biosorption, heavy metals, algae, wastewater, pollution