BACKGROUND AND OBJECTIVE: Lately, extensive attention has been devoted to the study of heavy metals removal from water and wastewater by the adsorbents resulted from agricultural wastes. The aim of this study was to investigate the removability of cadmium (Cd) from aqueous solutions using raw rice husk, rice bran and Silica from rice husk in different conditions.

METHODS: In this experimental research, the adsorption of cadmium using three adsorbents (raw rice husk, rice bran and rice husk silica) carried out in bath reactors. Raw rice husk and rice bran were collected from north of Iran. Rice husk silica was prepared in a furnace at 800 ºC for four hours, after acid leaching. The efficiency of the adsorbents was studied in four different statuses: different values of pH (5, 6, 7, 8 and 9), different concentrations of cadmium (1, 5, 10 and 15), different dosages of adsorbents (0/5, 1 and 1/5) and different contact times (30, 45, 60, 75 and 90). The standard method of atomic adsorption was used to measure the concentration of cadmium.

FINDINGS: The maximum removal efficiency of cadmium was obtained by rice bran up to 96.8% at 5 mg/l initial concentration of Cd, 90 min of contact time and adsorbents dosage of 1.0 g/l. However, at the same condition, the maximum removal efficiency of cadmium by raw rice husk and rice husk silica was 69.3% and 74.7%, respectively. Moreover, this study showed that there was a significant relationship between the increase of the contact times and removal efficiency of Cd in aquatic environments by three adsorbents (p<0.01).

CONCLUSION: Rice husk and the adsorbents derived from it could be considered as effective and inexpensive adsorbents for removal of cadmium.