Utilization of biochar produced from invasive plant species to efficiently adsorb Cd (II) and Pb (II)

[Display omitted] •Ragweed and horseweed were directly pyrolyzed to biochars without modification.•The properties and sorption capacity of biochars varied with pyrolysis temperature.•RB450 showed unprecedented adsorption capacity for both Cd and Pb.•RB450 was characterized by better adsorption capacity than most reported biochars.•Precipitation and cation exchange were important mechanisms for Cd and Pb sorption. Global expansion of invasive plant species has caused serious ecological and economic problems. Two such invasive species, ragweed and horseweed, were pyrolyzed at temperatures of 350, 450 and 550 ℃ for biochar production (RB350, RB450, RB550 and HB350, HB450, HB550). The biochars produced were used for Cd(Ⅱ) and Pb(Ⅱ) removal in aqueous solutions. The results indicated that the properties of the biochars varied with pyrolysis temperature, which further affected their adsorption performance. The maximum adsorption capacity of RB450 for Cd(Ⅱ) (139 mg·g−1) and Pb(Ⅱ) (358.7 mg·g−1) was much higher than that shown in previous studies. The immobilized Cd(Ⅱ) and Pb(Ⅱ) fraction on RB450, RB550, HB450 and HB550 was mainly attributable to the acid soluble and non-available fractions. These findings suggested that pyrolysis of invasive plants at 450 ℃ could not only be an option to control invasive plants but also could be of benefit in using biochar as excellent adsorbent.