Rice husk was modified by ultrasound assisted (UA) and supercritical CO2 (SCO2) technologies, to improve its adsorption characteristics regarding to Co(II). The Co(II) adsorption was studied with respect to the pH effect, kinetic curves and equilibrium isotherms. The UA and SCO2 treatments provided increases of 7 and 4 times in the surface area, respectively. The maximum experimental adsorption capacities were 17.6, 20.8 and 35.0 mg g(-1), for raw rice husk, SCO2-rice husk and UA-rice husk, respectively. These results demonstrated that mainly the ultrasound assisted technology was adequate to improve the rice husk characteristics for adsorption purposes. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.