CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the Study
Rice is a major crop grown in some states in Nigeria. After rice grain milling, rice husks remain as an agricultural waste material. Many people have tried to use this waste to produce useful materials such as silica, silicon carbide, silicon nitride or silicon for solar cells (Yalcin and Sevinc, 2001). Rice husk is one of the largest readily available but most unutilised biomass resources and has long been an ideal fuel for electricity generation (kumar and Venugopal, 2013).
Numerous silicate based wastes, such as coal ash, slag from steel production, fly ash and filter dusts from waste incinerators, mud from metal hydrometallurgy, different types of sludge as well as glass cullet or mixtures of them have been considered for the production of glass ceramics (Rawlings et al., 2009).
Rice husk (RH) is one of the by-products obtained during milling of rice. It is reported that approximately 0.23 tonnes of rice husk is formed from every tonne of rice produced (Jain et al., 1996). Global production of rice, the majority of which is grown in Asia, is approximately 550 million tonnes per year. The milling of rice generates a waste material, the husk surrounding the rice grain. This is generated at a rate of about 20% of the weight of the product rice, or some 110 million tonnes per year globally. The husk in turn contains between 15 and 20% of mineral matter the majority of which is amorphous silica (Groszek and Laughin, 2015).
In Nigeria, rice production is reported as 4.7 million tonnes in the year 2013 by the (FAOSTAT in GEOHIVE, 2015), the National Rice Development Strategy produce; in 2010 put national paddy production in 2007 at 3.4 million tonnes and a projection of 13.27 million tonnes for 2018 (Adesina, 2014). Three types of rice are cultivated in Nigeria. These are the African rice, Oryza glaberrima; Asian rice, Oryza sativa; and the recently introduced, West African Rice Development Association (WARDA) hybrid rice, New Rice for Africa (NERICA) available only to farmers under WARDA's programme. The major rice type grown in Nigeria is the Asian rice Oryza sativa (Longtau, 2003). There are varieties of the rice the grown in various geo-location of Nigeria which include: Upland, Hydromorphic, Rain fed Lowland, Irrigated Lowland, Deep Inland Water and Mangrove Swamp. Rice cultivated in Kujama in Chikun Local government area of Kaduna state is classified under the rain fed lowland rice.
Burning rice husk as fuel to generate energy, results in the waste product, rice husk ash (RHA). RHA is rich in silica (about 60%) and can be an economically viable raw material for production of silica gels and powders (Chakraverty and Kaleemullah, 1991; Kamath and Proctor, 1998). RHA has been evaluated and use as an adsorbent of minor vegetable oil components (Proctor et al., 1995, Proctor and Palaniappan, 1990). Although various uses for rice husk and RHA have been suggested in literatures, their disposal or utilisation remains a major concern. Soluble silicates produced from silica are widely used in the glass, ceramics, cement as a major component, in pharmaceuticals, cosmetics and detergents industries as a bonding and adhesive agents. (Laxamana, 1982, Anon., 1997). Rice husk is sometimes used as a fuel for parboiling paddy in the rice mills and to power steam engines. The partially burnt rice husk in turn
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