This study examined the influence of rice husk (RH) particle size, carbonization temperature, and their interaction on the availability of Silicon (Si) in RH biochar obtained from the carbonization of different particle sizes of RH (<= 1 mm, >1 mm, and the original size, i.e., the unmodified RH biomass (O_RH)) at varying carbonization temperatures from 300 to 700 degrees C. Silicon content in the biochar was extracted with 0.01 M CaCl2. Results showed that the influence of RH particle size on available Si is modified by temperature. The maximum available Si from the RH biochar were 2145 mg kg(-1) at 700 degrees C for O_RH, 2428 mg kg(-1) at 600 degrees C for > 1 mm RH and 2562 mg kg(-1) at 500 degrees C for <= 1 mm RH. These were an increase of 171%, 207% and 224% respectively, compared to the uncarbonized original rice husk (790 mg kg (-1)). Smaller particle sizes attained the maximum values of available silicon at lower temperatures compared with the original RH probably due to the efficient heat transfer to the smaller RH particle surface because of the smaller packing/void volume between the particles. Thus, the carbonization of smaller particles of RH will produce higher available Si content at a lower carbonization temperature than that required to achieve the same effect in the original RH biomass, thereby saving energy and time.
