Thermal regeneration of spent coal-based activated carbon using carbon dioxide: Process optimisation, Methylene Blue decolorisation isotherms and kinetics

Spent coal-based activated carbon from the silicon industry has been used as raw material for the regeneration of activated carbon, with carbon dioxide as the regenerating agent. The regeneration process was optimised using response surface methodology and the optimum regeneration conditions were: regeneration temperature 985°C; regeneration time 120min; and carbon dioxide flow rate of 600ml/min. The iodine number and yield of the activated carbon obtained under the optimum regeneration conditions were 1071mg/g and 67%, with a Brunauer-Emmet-Teller surface area of 1270m ²/g and pore volume of 0.91cm ³/g. The regenerated carbon was tested for the removal of Methylene Blue dyes. The maximum adsorption capacity was found to be 395mg/g and the equilibrium data fitted to the Langmuir isotherm model. The kinetic data indicated that the best fit corresponds to the pseudo-second-order kinetic model.