Rice Husk Silica Adsorbent for Removal of Hexavalent Chromium Pollution from Aquatic Solutions

The present study investigates the effectiveness of a new adsorbent prepared from agricultural wastes, namely rice husk silica as well as raw rice husk and rice bran to remove Cr +6 from aquatic solutions. The raw rice husk was collected from North of Iran. But rice husk silica was prepared by burning of clean rice husk inside a muffle furnace at a temperature of 800°C for 4 hours after acid leaching. The effects of four parameters: contact time (30 to 90 min), pH values (2 to 9), adsorbents dosages (0.5 to 1.5 g/L) and initial concentration (1.0 to 15 mg/L) were investigated to remove Cr+6. The silica derived from rice husk showed a high percentage of SiO2 up to 94.24%. But 􀁆arbon􀀃 was􀀃 the highest 􀀃element in raw rice husk up to 35.92%. The maximum removal efficiency (RE) of Cr +6 was obtained by rice bran up to 98.8% at 5.0 mg/L initial concentration of Cr, 60 min of contact time, pH = 2 and adsorbents dosage of 1.0 g/L. However, at the same condition the maximum RE by raw rice husk and rice husk silica were 82.3 and 88.4%, respectively. Moreover, a negative strong significant correlation between increasing of initial concentration of Cr+6 and RE was detected by the three adsorbents (p<0.01). In conclusion, raw rice husk and adsorbents prepared from it such as rice husk silica could be considered as effective and inexpensive adsorbents for removal of Cr +6from aquatic solutions .