Characterization and Pb(II) removal potential of corn straw- and municipal sludge-derived biochars

Corn straw- and municipal sludge-derived biochars (CS-BC and MS-BC, respectively) were used to remove Pb(II) from aqueous solutions. Despite being pyrolysed at the same temperature (723 K), MS-BC showed higher porosity and hydrophobicity than CS-BC. The optimum biochar loading and pH values allowing efficient Pb(II) removal (greater than 80%) were 0.2 g l^-1 and 7.0, respectively. The presence of PO₄^3- (greater than 0.01 mol l^-1) significantly affected the adsorptive performance of Pb(II) on the biochar samples. The adsorption data fitted well to a pseudo-second-order kinetic model and a Langmuir model, and the maximum Pb(II) adsorption capacities were 352 and 387 mg g^-1 for CS-BC and MS-BC, respectively. The main mechanisms involved in the adsorption of Pb(II) on biochar were electrostatic attraction and surface complexation. When comparing both biochars, CS-BC showed better cost-effectiveness for the removal of Pb(II) from aqueous solutions.