| Biochar has large surface and may be used to adsorb heavy metals from water. A lab experiment was carried out to investigate the effects of time, temperature（288.15~318.15 K）, solution pH, and biochar particle size on adsorption of aquatic Cd2+ by biochar. The surface characteristics of biochar before and after Cd2+ adsorption were examined using X-ray diffraction analysis（XRD）, Fourier transform infrared spectroscopy（FTIR） and X-ray Photoelectron Spectroscopy（XPS）. The results showed that the equilibrium adsorption was better fit by Langmuir model than Freundlich model. The maximum adsorption capacity of the biochar for Cd2+ at different temperatures was 18.49 mg·g-1（288.15 K）, 23.51 mg·g-1（298.15 K）, 23.59 mg·g-1（308.15 K） and 24.43 mg·g-1（318.15 K）, respectively. The adsorption kinetics could be well described by pseudo-second order kinetics model. The adsorption process was quick and the equilibrium was attained within 40 minutes. The optimum adsorption pH value was 5.0. The particle size of biochar had no significant effects on Cd2+ adsorption. The biochar adsorbed Cd2+ mainly via Cd2+ chelation with hydroxyl（-C-OH） and carbonyl（-C=O） as confirmed by XRD, FTIR and XPS. |
