Activated carbons obtained from rice husk: Influence of leaching on textural parameters

Activated carbons obtained from rice husk exhibit low specific surface areas when physical activation is applied due to its high silica content. The purpose of this work was to improve textural parameters of powdered activated carbons obtained from rice husk. To avoid the negative influence of the raw material ash content, a leaching step was included in the preparation process. Hydrofluoric acid, in two concentrations (25 and 50 wt %), was used as leaching agent and applied in different stages of the process. Physical activation using water vapor as activating agent was applied. Specific surface area and porosity were evaluated from nitrogen adsorption data. When a leaching step was included, specific surface area values between 700 and 1200 m(2)/g were obtained. These values are higher than that corresponding to the activated carbon prepared from rice husk not treated with acid (290 m(2)/g). Pore size distribution depends on the step sequence of the preparation process and on the HF concentration.