The petroleum sorption by adsorbent materials is dependent on the specific surface area of the latter and hence on the adsorbent preparation process. The effect of the heating temperature on the surface area of rice husks is shown in Fig. 4. The specific surface area increased with increasing heating temperature up to 700 °C, however, the further increase of temperature caused a decrease of the specific surface area. The increasing of the specific surface area can be explained by formation of new micro- and mesopores during the thermal treatment [33]. The decrease of specific surface area after stronger heating of rice husks may be connected with the increase of density due to phase transformation of amorphous SiO2 into its cristobalite form. A similar result was reported by Chandrasekhar et al. [34]. The largest surface area of TRH was obtained at 700 °C and hence the adsorbent obtained that way had the highest sorption capacity for petroleum products.