KINETIC STUDY OF LIQUID-PHASE ADSORPTIVE REMOVAL OF HEAVY METAL IONS BY ALMOND TREE (TERMINALIA CATAPPA L.) LEAVES WASTE ABSTRACT. The kinetic sorption of five metal ions - Al3+, Cr6*, Zn2+, Ag+ and Mn2+ - from aqueous solution onto almond tree leaves (ATL) waste in single component system has been studied. The experimental data was analyzed in terms of intraparticle diffusion and rate of adsorption, thus comparing transport mechanism and chemical sorption processes. The sorption rates based on the pseudo-second order rate constants for the five metal ions are 0.018 (Al3+), 0.016 (Cr6+), 0.023 (Zn2+), 0.021 (Ag+) and 0.022 (Mn2+) g/mg.min. The adsorption rates are rapid and within 180 min of agitation more than 85 percent of these metal ions has been removed from solution by the ATL waste biomass. The kinetic data suggest that the overall adsorption process is endothermic, and that the rate-limiting step is a surface diffusion controlled process. The results from this study have revealed that the ATL waste, which is hitherto an environmental nuisance, has the ability to adsorb metal ions from solution and the data are relevant for optimal design of wastewater treatment plants. The low cost and easy availability of ATL waste make potential industrial application a strong possibility. KEY WORDS: Kinetic sorption, Heavy metal ions, Almond tree leaves waste, Wastewater treatment plants INTRODUCTION
Adsorption kinetic studies are important in predicting the rate of pollutant removal from aqueous systems. Kinetic studies provide information for selecting optimum operating conditions, identifying reaction pathways, understanding rate-limiting steps and are also essential for scaling-up of laboratory studies to industrial applications. The use of cheap adsorbents for the treatment of aqueous effluents to remove inorganic and organic pollutants has been recognized as a major development in the area of biosorption during the past ten years [1-10]. Some of the adsorbent studied for metal ions adsorption in aqueous solution includes modified groundnut husks (Arachis hypogea) , oil-palm fibres , sphagnum moss peat , tree fern , and waste tea leaves , just to mention a few. The literature search reveals that no information is presently available on kinetic study of metal ion removal by almond tree leaves waste. The almond tree (Terminalia catappa L) has been known for its usefulness in the medical world. However, in Nigeria the almond tree is predominantly found and is known locally as "umbrella" tree because it gives shade for relaxation during hot weather. There are two extreme seasons in Nigeria, the dry and rainy seasons. During the rainy season the almond tree leaves are evergreen but begins to drop continuously during the dry season and therefore constitute environmental nuisance. In order to keep places like industries, schools and residential houses tidy of almond tree leaves waste, the wastes are gathered by cleaners/gardeners and are burnt regularly. This process releases dangerous gases into the atmosphere. In order to find solution to the waste liter, land pollution, as well as air pollution, the almond tree leaves waste was used for metal ion adsorption studies.
This paper describes the adsorption kinetics of five metal ions (Al3+, Cr6+, Zn2+, Ag+, Mn2+) in aqueous solution using almond tree leaves (ATL) waste. The kinetic models employed to fit the experimental data are discussed in terms of intra-particle diffusion and rate of adsorption. EXPERIMENTAL
Sample collection and preparation
The adsorbent for this work is the almond tree (Terminalia catappa L) leaves (ATL) waste. The dried leaves were gathered into clean plastic bags. In order to ensure that homogeneous samples were collected, standard technique were applied. The air dried ATL wastes were further oven dried (Gallen Kamp, model OV-160, England) at 105 oC to constant weight and ground using a food processor (Magimax Cuisine...
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