Enhanced removal of aqueous Cd(II) by a biochar derived from salt-sealing pyrolysis coupled with NaOH treatment

Activated biochar (A-BC550) that was prepared by salt-sealing pyrolysis (at 550 degrees C) and coupled with NaOH treatment was used to remove cadmium (II) from an aqueous solution. The FTIR spectroscopy and XPS analysis showed that the content of carboxyl and methoxy (CH3-O-) groups was increased by the NaOH impregnation that occurred before pyrolysis. The complexation and precipitation that occurred played a leading role in the subsequent adsorption. Adsorption occurred on the surface of the biochar, and the adsorption equilibrium was achieved in approximately 10 min of reaction following the pseudo second-order kinetic model and the Redlich-Peterson isotherm model. The maximum adsorption capacity of A-BC550 was determined by the Sips isotherm model to be 216.2 mg g(-1) at pH = 7, which was 4.6 times that of the unmodified biochar without the NaOH treatment (47.13 mg g(-1)). Thermodynamic parameters showed the increase of adsorption temperature was conducive to the adsorption process. This work provides a low-cost and environmentally friendly method to pyrolyze biochar. The A-BC550 is a favorable material for treating heavy metal-contaminated wastewater.