Comparison of Cd(II) adsorption performance on two phosphate modified straw biochar

Abstract

Phosphate-modified biochar is a good material for the heavy metals removal from wastewater.However, different phosphate modified straw biochar have dissimilar adsorption performance for heavy metals.In this work, Na 3 PO 4 -modified straw biochar (PBC) and Na 2 HPO 4 -modified straw biochar (SPBC) were used to remove Cd(II) from aqueous solution.Moreover, the effects of dosage, solution pH, coexisting ions, adsorption time, temperature and initial concentration on the Cd(II) removal by the sorbent were investigated.The result shown that SPBC possessed richer pore structure and O-containing functional groups.The adsorption experiments indicated that the optimum adsorption performance could be obtained at pH = 6.0 and dosage 25 mg.K + , Na + , Ca 2+ and Mg 2+ had little effect on the removal of Cd(II) by biochar, while Cu 2+ and Pb 2+ had strong inhibitory effect.Notably, SPBC reached the time of adsorption equilibrium much faster than biochar (BC) and PBC.The pseudo-second-order kinetic model and Langmuir model could describe the adsorption process of Cd(II) well.The theoretical maximum adsorption capacities of BC, PBC and SPBC for Cd(II) were 54.55, 114.79 and 154.13 mg/g at 25°C, respectively.The removal mechanisms included complexation, ion exchange, Cd(II)-π interaction, electrostatic interaction and co-precipitation.This work suggested that Na 2 HPO 4 -modified straw biochar held greater potential to remove Cd(II) from wastewater than Na 3 PO 4 -modification.