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extraction of silica from burnt paddy husk pdf

Abstract

Zeolite Y in sodium form (NaY) was synthesized using silica source from rice husk. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), BET. As results, we verify that NaY zeolite obtained from the two-step route, presents a good degree of crystallinity and then can be suitable for using in various applications.

Introduction
Silica is the most abundant oxide in the earth’s crust, yet despite this abundance, silica is predominantly made by synthetic means for its use in technological applications and it is one of the valuable inorganic multipurpose chemical compounds (Londeree et al., 2002). Naturally occurring silica, especially those found in agro waste, can provide an alternative source to replace commercial silica precursors. Rice husk saw dust (Venkat and Vijay Babu, 2011), and rapeseed stalk (Seung et al., 2011) are among the widely studied agro wastes which have been converted into more valuable end products.

Rice husk (RH) is therefore an agricultural residue abundantly available in rice producing countries. Much of the husk produced from the processing of rice is either burnt or dumped as waste. Even though some of this husk is converted into end products such as feedstock (Maiti et al., 2006) and adsorbent (Hyun et al., 2009) most is burnt openly, causing environmental and health problems especially in poor and developing countries. Therefore, it is very important to find pathways to fully utilize the rice husk. Silica can be pyrolyzed at elevated temperatures to form rice husk ash (RHA) or it can be extracted from rice husk in the form of sodium silicate by using a solvent extraction method. In most applications, rice husk ash is more favorable compared to rice husk. Rice husk ash is a general term describing all forms of the ash produced from burning rice husk. It would be beneficial to the environment to recycle the waste to produce eco-material having a high end value (Pijarn et al., 2010).

Nowadays, zeolites as well as the other molecular sieves find several application in a diverse areas. In particular, zeolites are hydrated, crystalline aluminosilicates constructed from TO4 tetrahedra (T = Al, Si) where each apical oxygen atom is shared with an adjacent tetrahedron. Zeolite Y is a highly versatile molecular sieve from the faujasite family of zeolites whose 7.4 Å, three-dimensional pore structure and solid acidity make it useful as a catalyst, ion exchanger, adsorbent, etc. Zeolite Y is commonly prepared with a high aluminum content, but in most cases it is employed in a silicon-enriched form.

The objective of this paper is to explore the synthesis of zeolite from RHA as a source of silica after extraction in the amorphous form by acid leaching of husks. Two different synthetic routes one-step and two-step, and crystallization time were applied. Also, characterizations of RHA were investigated including; chemical analysis, XRD and SEM. The physical properties and crystallinity of the synthesized zeolites are discussed based on the results obtained by means of various spectroscopic techniques including XRD, N2 adsorption and SEM.