Characterisation of high purity rice husk silica synthesised using solvent-thermal treatment with different concentration of acid leaching

In recent years, research on bio-based materials, such as rice husk is steadily gaining momentum. Despite their huge developmental potential, rice husks are often left unutilised following the harvesting season, wasting a natural wealth that could be explored. Their high silica content makes them potential fillers to replace commercial precipitated silica in the polymer industry, composites and building materials for construction. In this study, highly pure silica with small particle size and high surface area was extracted from rice husks via solvent-thermal treatment, followed by leaching with different concentrations of hydrochloric acid (HCl). This treatment method was modified from TAPPI T204 (2007) and TAPPI T264 (1997) standards, which are used for wood extraction in the pulp and papermaking industry. By using this method, rice husk silica (RHS) that was leached with 1.0 M HCl recorded the highest particle purity with 99.99% of SiO2 content and the highest BET surface area of 234.25 m2/g compared with RHS leached with 0.01 M, 0.1 M, 2.0 M, and 3.0 M HCl. All RHS samples were in the amorphous state following incineration at 700 degrees C for 4 hours. This proved that RHS synthesised by solvent-thermal treatment method can be further developed as one of the alternatives to commercial silica in the market.