A comparative study on rice husk and rice straw as bioresources for production of carbonaceous adsorbent and silica

Abstract

The conversion of rice crop residues into activated carbon (AC) and nanosilica was performed via an integrated procedure including successive carbonization, K2CO3 activation, and extraction steps. For the first time, rice husk and rice straw were utilized comparatively as the raw materials for parallel AC and silica production, and the main characteristics of the corresponding products were compared. However, AC produced from rice straw at 1000 °C and impregnation ratio of 1.5 showed a larger surface area and total pore volume (2229 m2/g and 1.6 cm3/g) than AC produced from rice husk (1941 m2/g and 1.5 cm3/g); no definite and general conclusion can be made about the superiority of rice straw as the raw material. This is attributed to the close characteristics of the products, the large variety of rice crop residues, and the strong influence of the operating conditions on the properties of products. The rice husk– and rice straw–based activated carbons had no significant difference in their functional groups and chemical characteristics. The amorphous silica nanosize particles (< 50 nm) were obtained from both raw materials; however, the presence of little crystalline phase impurities (potassium chloride) and silica (tridymite and coesite) was also observed. The most important superiority of rice husk to rice straw was its larger silica production yield from the initial biochar (40% compared to 25%).