A simple method for production of pure silica from rice hull ash

Rice hull ash (RHA), a waste product of the rice industry is rich in silica. A simple method based on alkaline extraction followed by acid precipitation was developed to produce pure silica xerogels from RHA, with minimal mineral contaminants. The silica gels produced were heated to 80 degrees C for 12 h to obtain xerogels. Silica and mineral contents of xerogels were determined by energy dispersive X-ray (EDX) and inductively-coupled plasma (ICP) emission spectrometers, respectively. Xerogels produced from RHA had 93% silica and 2.6% moisture. The major impurities of silica produced from RHA at an extraction yield of 91% were Na, K, and Ca. Acid washing prior to extraction resulted in silica with a lower concentration of Ca (<200 ppm). However, final water washing of the xerogel was more effective in producing silica with lower overall mineral content (Na < 200 ppm and K < 400 ppm). X-ray diffraction patterns revealed the amorphous nature of silica xerogel. Fourier transform infrared (FTIR) data indicated the presence of siloxane and silanol groups. (C) 2000 Elsevier Science Ltd. All rights reserved.