Physically activated charcoal from waste and low-cost biomass: Adsorptive and porosity studies

ABSTRACT

Different plant raw materials (corn stalk, wheat straw, saw dust, corn cobs, broom grass and Sudan grass) were carbonized and secondary activated in the rotating kiln with the action of water vapor as activation agent under different temperatures and lasting times. Optimum carbonization parameters such as temperature and lasting time were found to be 750°C and 45 min, while optimal conditions for powdered activated carbon obtained by water vapor activation at a temperature of 1,000 C and contact time of 120 min were determined. All obtained activated carbons were distinctly macroporous with mercury intrusion total specific pore volume in the range from 2.04 to 4.86 cm³/g for activated carbons originating from sawdust and broom grass, respectively. Activated carbon prepared from broom grass had the largest specific surface area of 1,190 m²/g. Freundlich, Langmuir, Dubinin-Radushkevitch and Temkin adsorption isotherm models were applied for groundwater humic matter adsorption modeling. Broom grass-originated activated carbon was found to have excellent adsorption affinities toward natural organic matter with regard to the Langmuir model, with maximum adsorption capacity of 90.1 mg TOC/g. The Freundlich isotherm was best fitted with the obtained experimental data. Adsorption experiment followed a physical process as can be seen from heat of sorption of 118.82 J/mol estimated by the Temkin isotherm model, and mean free energy of 0.158 kJ/mol estimated by the Dubinin-Radushkevitch isotherm model.

KEYWORDS:

• Activated carbon
• adsorption modeling
• broom grass
• macroporosity
• steam activation