Optimizing Amorphous Silica Recovery from Rice Husk Cultivated under Different Soils for Supplementary Cementitious Material Application

Abstract

Amorphous silica (a-SiO₂), found in rice husk ash, is a valuable material due to its high silica content, large surface area, excellent pozzolanic properties, and strong binding ability with cement. These characteristics make it ideal for use as a supplementary cementitious material and a sustainable alternative for the partial replacement of ordinary Portland cement. This study aims to optimize the recovery process of amorphous silica from rice husks cultivated under various soil conditions (normal, drought, saline, and acidic soils), which are experiencing significant fluctuations due to climate change in many rice-producing countries. Experiments were conducted on rice husks under different pyrolysis conditions at temperatures of 700 °C, 800 °C, and 900 °C, with varying calcination durations. Through comprehensive analysis using Scanning electron microscopy (SEM) and X-ray Diffraction (XRD), along with the evaluation of amorphous silica recovery efficiency, we identified the optimal conditions for producing amorphous silica from rice husks. The analysis revealed that the highest recovery efficiency was achieved at a pyrolysis temperature of 700 °C for 1 hour. Under these conditions, the recovery efficiencies were 87.9% for normal soil RHA, 96.5% for saline soil RHA, 94.8% for drought soil RHA, and 95.6% for acidic soil RHA. The phase structure, surface morphology, and particle size of the RHA-derived amorphous silica, ground to micrometer sizes, were found to be similar to commercial products such as ordinary Portland cement and silica fume. This study provides a foundation for scaling up the production of amorphous silica from rice husk ash on an industrial scale, considering the relationship between optimal recovery efficiency and the origin of the rice husk ash, thus contributing to the development of environmentally friendly construction materials.

Keywords

• pyrolysis
• rice husk ash
• amorphous silica
• recovery efficiency
• rice husk
• supplementary cementitious material