Competitive adsorption of heavy metals onto sesame straw biochar in aqueous solutions

• Sesame straw biochar demonstrated an excellent adsorption capacity for heavy metals.
• Adsorption fitted best with Langmuir model as compared to the Freundlich model.
• High interference among the metals was observed under multimetal sorption condition.
• The highest reduction in adsorption capacity was found for Cd.
• Adsorption behaviors was well described by three-dimensional simulation.

Objective of this research was to evaluate adsorption of heavy metals in mono and multimetal forms onto sesame straw biochar (SSB). Competitive sorption of metals by SSB has never been reported previously. The maximum adsorption capacities (mg g−1) of metals by SSB were in the order of Pb (102) ≫ Cd (86) ≫ Cr (65) > Cu (55) ≫ Zn (34) in the monometal adsorption isotherm and Pb (88) ≫ Cu (40) ≫ Cr (21) > Zn (7) ⩾ Cd (5) in the multimetal adsorption isotherm. Based on data obtained from the distribution coefficients, Freundlich and Langmuir adsorption models, and three-dimensional simulation, multimetal adsorption behaviors differed from monometal adsorption due to competition. Especially, during multimetal adsorption, Cd was easily exchanged and substituted by other metals. Further competitive adsorption studies are necessary in order to accurately estimate the heavy metal adsorption capacity of biochar in natural environments.