18*' International Mining Congress and Exhibition of Turkey-IMCET 2003, ic> 2003, ISBN 975-395-605-3 The Effect of Chemical Treatment on The Production of Active Silica from Rice Husk H. Kurama Osmangazi University, Mining Engineering Department, Batı -Meşelik, Eskişehir, Turkey S. K. Kurama Anadolu University, Department of Material Science and Engineering, Eskişehir, Turkey ABSTRACT : In this study the effect of chemical treatment on the production of high purity silica from rice husk was investigated. Rice husk, supplied from Kastomonu region-Turkey, was used as a sources of silica. They were washed with water to remove the contaminants present in them then dried in an oven at 100"C for 24 h. The dried husks were then subjected to the chemical treatment before calcinations in order to increase silica contents of husk ash. In experiments, HCl was used as a leaching reagent for extracting inorganic impu- rities from the husk and the affect of leaching temperature, reactive concentration, leaching time and solid percent on the purity of silica ash were systematically investigated. The results of leaching test showed that high purity amorphous silica could be produced with a 99.74 °/t grade. The surface properties of both rice hush and husk ashes were analyzed by Scanning Electron Microscope (SEM). 1 INTRODUCTION Rice husk are the natural sheaths that form on the rice grains during their growth. Removed during the refining of rice, these husks have no commercial in- terest. When it burns, the silica rich ash (87-97 %) from 13-29 % by weight is produced depending on the variety, climate and geographic location (Amick 1982). The silica in husk is in hydrated amorphous form, either opal or silica gel. Due to the high silica content, rice husk has become a source for prepara- tion of number of silicon compounds such as solar grade silicon (Ikram et al. 1988), silicon carbide (Sharma et al. 1984, Krishnarao et al. 1992, Romero et al. 1996), silicon nitride (Rahman 1994), zeolite and concrete and cements surfactant (Real et al. 1996). Presently, the word production of rice is ap- proximately 500 million tons a year containing 50- 100 million tons of rice husks (Andreoli et al. 2000). In Turkey the annual rice production is about 240000 tons, equivalent to 2.4x10 4 tons of rice husk. These husks are mostly thrown away as waste. The husk is mainly consisted of 70 - 75 % or- ganic matters such as lignin. cellulose and sugar and remaining silica with small amount of alkali and other trace elements. Utilization of rice husk as a source of silica is based on removal of impurities with a low effort. Many authors (Riveros et al. 1986, Patel et al. 1987, Chakraverty et al. 1988, Krısh- naroa et al. 2001, Delia et al. 2002) have concluded that preliminary simple acid leaching of rice husk before thermal treatment proved to be effective in substantially removing most of the metallic impuri- ties and producing silica ash with a high specific surface area (<250 m7g) and small particle sizes (<5qm). However, except for some studies on the thermal treatment of rice husk, few systematic work has been done to determine the optimum conditions for the acid leaching steps of silica ash production. The objective of the present work is to determine the effect of acid treatment parameters such as percent solid, leaching temperature, and reactive concentra- tion and leaching time on the production of high pu- rity silica ash from rice husk. 2 EXPERIMENTAL 2. / Material and Methods The rice husk sample was supplied from Kastomonu region-Turkey. They were washed with water to re- move the contaminants present in them then dried in an oven at 100"C for 24 h. The chemical composi- tion of the sample is shown in Table 1. SiOi was found to be 13.66 %, the carbon and water content is 84%. There are several leaching agent that can be used in the extraction of inorganic impurities from rice husk such as HCl, HiSOjand HNO,. However using H2SO4 leads to formation of metallic sulphates, some of which are not easily soluble in water. Again HCl 431