International Journal of Scientific & Engineering Research, Volume 5, Issue 10, October-2014 102 ISSN 2229-5518 IJSER © 2014 http://www.ijser.org Kinetics of Fluoride Adsorption on Mixed Oxide Nanocomposites: Analysis Joseph Govha,T. Bala Narsaiah, Milton Manyangadze, P. Akhila swathanthra Abstract:The prevalence of high fluoride concentration in water is a global problem. High fluoride concentration is a health hazards which results in dental and skeletal fluorosis. In an effort to reduce the detrimental effects of fluoride a number of technologies are in use but adsorption has proved to be the most effective and economic fluoride removal technology. The advent of nanotechnology introduced nanoadsorbents as an alternative to bulk adsorbents. Nanocomposites are an important class of adsorbents that have gained wide interest from researchers.Sorption kinetics is one of the most important parameters that are used in evaluation of the efficiency of an adsorbent. There are various mathematical models in use but in this paper attention is paid to adsorption reaction models which are mainly used by researchers to fit kinetic data for nanoadsorbents. Index Terms: adsorption; Fluoride; reaction models; nanocomposites;kinetic models ———————————————————— 1 INTRODUCTION T he dissolution of fluoride rich rocks and industrial waste streams with high fluoride concentration are the main source of high fluoride concentration in drinking water [1]. Drinking water with high fluoride concentration may cause dental and skeletal fluorosis and according to World Health Organization (WHO) the maximum acceptable concentration is below 1.5mg/L [2]. Fluorosis has been described as an endemic disease of the tropical climate but high fluoride waters occur in many geographical regions.Endemic of fluorosis is found inArgentine, U.S.A., Morocco, Algeria, Libya, Egypt, Jordan, Turkey, Iran, Iraq, Kenya, Tanzania, S. Africa, China, Australia, New Zealand, Japan, Thailand, Canada, Saudi Arabia, Persian Gulf, Sri lanka, Syria, India, etc [3, 4]. In many cases communities living in areas with high fluoride in drinking water have no alternative source of health clean water. Hence their water has to be treated if it’s to be safe for drinking. There are many reported methods for reducing fluoride concentration in water and these are adsorption, ion exchange, precipitation, electro-dialysis and reverse osmosis [5]. Adsorption has been found to be one of the most effective, economic and environmentally friendly as compared to the other techniques [6]. There are many adsorbents that are available in literature such as bone char, activated alumina, amorphous alumina, activated carbon, red mud and some low cost adsorbent [7]. The emergence of nanotechnology has introduced nanoadsorbents which are unique and have excellent physical and chemical properties which aid adsorption process. The nanoadsorbents have small size and high to surface ratio which results in high adsorption capacity and fast kinetics as active adsorption sites are on the surface [8] The objective of this work is to provide a detailed analysis of fluoride sorptionon nanocomposite. This is because nanocomposites have shown good results in reducing fluoride to below the recommended limit hence they are going to be an important part of fluoride removal technology. Adsorption kinetics is very important for designing of continuous flow system and a detailed understanding will result in excellent adsorption equipment design. The mathematical models will be discussed and the various manipulations that are done to linearly fit the data to the models. A brief analysis of application of these models to nanocomposites is also included. 2 KINETIC MODELS The kinetics of adsorption is significant in the evaluation of the performance of a given adsorbent and it provides insight into the reaction pathways and the mechanism of reaction. . In general adsorption kinetics is the basis that is used to determine the performance of any flow-through system [9]. A number of mathematical models have been proposed to describe adsorption data and it is mainly divided into adsorption reaction model and diffusion models. Adsorption diffusion models are based on three steps which are liquid film diffusion, diffusion in the liquid which is internal diffusion and adsorption of adsorbate on active sites. The reaction models are based on chemical reaction kinetics where the whole process is considered not individual process [10]. Adsorption reaction models are the ones that apply to adsorption of nanoadsorbent as the active adsorption sites are found on the surface. 3 ADSORPTION REACTION MODELS There are a number of reaction models in use and the models which are discussed here have been applied mainly to nanoadsorbents. Nanoadsorbents have their active adsorption sites on the surface hence they are characterized by fast sorption kinetics as pore diffusion length is very small or reduced. The models discussed in this paper are IJSER