caused a phase transformation of silica from amorphous to crystalline form and hence decreasing the sorption capacity of TRH [27]. Comparing the experimental data shows that TRH had the highest sorption ability, while virgin rice husk (RH) had the lowest one; this is likely to be connected with the high density of thermally untreated rice husk. For further studies, thermally treated rice husk (TRH700)was selected as petroleum adsorbent. The experimental observations show that TRH float on the surface water after petroleum sorption because the TRH has a lower density than virgin rice husk [32]. The effect of contact time on the sorption capacity of TRH700 was studied. Fig. 2 shows that the sorption capacity of TRH700 increased with the contact time from the first 5 min on, then it reached equilibrium. Also, this curve consists of two phases (rapid phase and slow phase). This effect can be explained as follows: the thermally treated rice husk first absorbed petroleum by macropores and afterwards it penetrated into the micropores until reaching equilibrium time. The equilibrium times for heavy crude petroleum on TRH700 and RH were 25 and 10 min, respectively. Summarizing the results, following optimum conditions can be inferred for heavy crude petroleum sorption by TRH700: heating temperature 700 °C and sorption time 25 min (Figs. 1 and 2).