Single step carbonating and activating fir sawdust to activated carbon by recyclable molten carbonates and steam

Molten carbonate pyrolysis with steam on fir sawdust was conducted to produce activated carbon, in which physical and recycling chemical activation was combined with carbonization as a single step process. The effects of temperature, molten carbonate pyrolysis and steam flow rate on the activated carbon were investigated. The BET results showed an excellent specific surface area of 822.02 m²/g and a pore diameter of 2.39 nm. The adsorption capacities of the activated carbon achieved ideal values on methylene blue and iodine and reached a removal capacity of 196.5 mg/g for the elimination of Cr(VI) in wastewater. There were four stages in developing the porous structure of activated carbon by the joint effects of molten carbonates and steam as the temperature rising. The activated carbon had abundant micropores inside the macropore structure at temperatures ranging from 700 °C to 750 °C. Molten carbonates promoted the formation of mesopores and macropores and reduced the reaction temperature as a catalyst and heat transfer medium, while steam promoted micropore generation by water-gas shift reactions. A recycling study indicated that the Cr(VI) adsorption capacity of the activated carbon generated after five recycling cycles of molten carbonates was still reached 195 mg/g.