Marked Changes in Biochar's Ability to Directly Immobilize Cd in Soil: Implication for Biochar Remediation of Cd Contaminated Soil

Abstract

To investigate the change in biochar’s ability to directly immobilize Cd in soil，a successive wheat cultivation with experiment was conducted. Three biochar with different Cd adsorption mechanisms were added into soils and a mesh bag was used to separate the soil particles (> 1 μm) from biochar. The results showed that the ash contents and anionic contents (CO₃ ^2- and PO₄ ^3-) of the biochar decreased with the cultivation time, while the oxygen-containing functional groups content and CEC of the biochar increased. Resultly, the Cd concentration on biochar decreased, while unstable Cd species (acid soluble and reducible fraction of Cd) on biochar increased with successive cultivation. Correspondingly, the ability of biochar to inhibit Cd accumulation in wheat decreased. The results of this study illustrated that the ability of biochar to directly immobilize Cd in soil is not permanent, it gradually decreases with aging in soil. The adsorption mechanism of Cd on biochar changed from precipitation to complexation and ion exchange processes could be the main reason.

Keywords: Biochar, Cd, immobilization, rhizosphere, soil aging