EXTRACTION OF SILICA FROM RICE HUSK ASH

ABSTRACT

This study was carried out on the extraction of silica from rice husk ash. One of the main components of rice husk ash (RHA) is silica, which can be used as raw material for fertilizer. The study examined influences of various volume and concentration on silica extraction. The silica was extracted using a technical alkaline grade solvent (NaOH) with a variation in volume/ the ratio of RHA to the amount of solvents (1: 4, 1: 5, and 1: 6) and the solvent concentration (0.50, 0.75 and 1 N). The highest average yield was found in the concentration of 1 N solvent with the ratio of RHA to the number of solvents 1: 6 is 62.83%. Based on the physical characteristics of silica from RHA which include whiteness (93.2496.66%), moisture content (0.49-2.81%), and density (0.56-0.95 g / mL) indicates that the use of technical alkaline solvents tends to decrease the purity of the proven silica also with the presence of major contaminants such as Na and Cl and other elements through SEM-EDX, XRF, and XRD test. In saline soils, the presence of contaminants in silica with an amorphous phase (2θ = 22.29°) especially Na and Cl may have a negative effect if used as raw material for fertilizers. 

CHAPTER ONE

INTRODUCTION

1.1    Background of the study

Critical economic and environmental situations of the current days encourage companies and researchers to develop and improve technologies intended to reduce or minimize industrial wastes. As a consequence, much effort has been expended in different areas, including the agricultural production. Rice is the second largest produced cereal in the world. Its production is geographically concentrated in Asia with more than 90 percent of world output. The United States and Brazil are the most important non-Asian producers and Italy ranks first in Europe. The rice world production was approximately 400 million tons of milled rice in 2003. In most varieties rice is composed by approximately 20 % of rice hull, which contains a fibrous materials and silica; however, the amount of each component depends on the climate and geographic location of rice crop.

Naturally, silica in rice husk ash is amorphous and has a large surface area, but when combustion above 650 ºC will change the silica phase to crystalline [4]. Amorphous silica can be used as fertilizer [5]. Various types of silica fertilizers are potassium silicate slag, calcium silicate hydrate, liquid potassium silicate, and silica gel [6]. The use of silica-based materials in industrial fields is adsorbents, filter media, glass industry, refractory industry, ceramic materials and raw materials for the production of silicates, silicones and alloys [7]. Therefore, RH can be used as raw materials of bio-silica that are very useful and can increase the added value.

Silica gel is a synthetic silica compound that can be extracted from rice husk ash by the sol-gel method. Silica is removed from residual ash in the form of sodium silicate, and in a later stage of the process, treatment with acid converts the silica into gel. This type of extraction can be done at ambient temperatures, making it an alter- native to the thermal treatment, which is often used in the production of highly reactivate pozzolanas.1-5 Previous studies on the preparation and characterization of extracted silica gel from rice husk ash have resulted in a simplified method for obtaining pure silica,6-9 and this process is called the sol-gel method.