Full Length Research Paper
Elemental analysis of rice husk ash using X – ray fluorescence technique Omatola, K. M1* and Onojah, A. D.2
Department of Physics, Kogi State University, Anyigba, Kogi State, Nigeria. Department of Physics, University of Agriculture Markudi, Benue State, Nigeria. Accepted 17 March, 2009
Rice husk ash is one of the most silica rich raw materials containing about 90 – 98% silica after complete combustion among the family of other agro wastes. Ash samples from rice husks of five o different origins were prepared at two different temperatures, 500 and 1000 C, respectively and the ash content was evaluated at each temperature. The interestingly high percentage of silica (taking up from the soil during paddy growth) in rice husk ash which has various industrial and domestic applications necessitated the process of determining the presence and amount of impurities or trace elements in ash taking up from the soil during paddy growth. Small quantities of impurities present at concentrations below one part per billion can have a significant effect on the quality of devices constructed form the silica obtained from the ash. The X – Ray Fluorescence (XRF) technique was used to analyze each 0 sample heated to a temperature of 1000 C at which excellent chemical activity could be exhibited to characterize the ash in terms of the purity of the silica level by the determination of the trace (impurity) elements present that has a nature that can determine their removal method to get the pure silica. The result of the XRF showed that rice husk ash (RHA) had a very low impurity concentration of 1.1 (sample 1) to 5.58% (sample 4) corresponding to 98.9% (sample 1) and 94.42% (sample 4) purity level of silica indicating that rice husk which is an agricultural waste is a potential source of silica with a high purity level of 94 - 98.9%. Key words: Rice husk, ash composition, fluorescence, impurity, silica. INTRODUCTION Rice husks are the natural sheaths that form on rice grains during their growth. Removed during the refining of rice, these have no commercial interest however can be made useful through a variety of thermochemical conversion process. The major compounds from rice husks are silica and cellulose which yields carbon when thermally decomposed (Adylov et al., 2003). On the majority of rice producing countries much of the husks produced from the processing of rice is either burnt or dumped as a waste. Rice husk is unusually high in ash compared to other biomass fuels – close to 20% (Adylov et al., 2003). The ash is 92 – 95% silica, highly porous and light weight, with a very external surface area. With such a large ash content and silica content in the ash it becomes economimical to extract silica from ash which takes care of ash Rice husk ash (RHA) is a term describing all types of ash produce from burning rice husks which vary considerably according to burning techniques. The silica in the ash undergoes structural transformations depending on conditions (time, temperature etc) of combustion. At 550 o to 800 C amorphous ash is formed and at temperature greater than this, crystalline ash is formed (Joseph et al., 1989). The change from amorphous to crystalline ash o occurs at approximately 800 C, although the process is 0 often ‘incomplete’ until 900 C is achieved (Sugita, 1993). All the combustion processes devised to burn rice husks 0 remain below 1440 C, which is the rice husk melting point 0 (Sugita, 1993). The rice husk ash obtained at 1000 C will exhibit excellent chemical activities and will be white in colour (Sugita, 1993). These types of silica have different properties and it is important to produce ash of the correct specification for the particular end use. Rice husk ash has so many applications due to...