Microwave-assisted pyrolysis of rape stalk to prepare biochar for heavy metal wastewater removal

Cd(II) adsorption performance and energy storage potential of biochar produced from microwave pyrolysis of rape stalk are investigated. Adsorption experiment indicates that Cd(II) adsorption data fits well with the Langmuir model with the adsorption capacity of 53.17 mg/g. The effective Cd(II) wastewater volume is 700 mL in the column adsorption experiment. The adsorption mechanism analysis indicates that π-electron is the primary adsorption mechanism for Cd(II) removal with the contribution percentage of 56.22 %. The density functional theory analysis result shows that Cd(II) is easier to bind with the hydroxyl groups compared to carboxyl group. The coexisted ions have little influenced on Cd(II) adsorption. Biochar still has large Cd(II) adsorption capacity after three times adsorption-desorption experiment. Biochar is used as the lithium ion battery anode material for energy storage with the specific capacity of 195 mA g−1. Besides, pyrolysis gas is recycled to prepare bio-gas with large heating value. Our findings provide a successful example of rape stalk waste converting into the high-quality biochar for Cd(II) removal/energy storage and bio-gas.