Adsorption of Cadmium on Degraded Soils Amended with Maize-Stalk-Derived Biochar

Biochar has been extensively proven to distinctively enhance the sorption capacity of both heavy metal and organic pollutants and reduce the related environmental risks. Soil pollution and degradation widely coexist, and the effect of biochar addition on adsorption behavior by degraded soils is not well understood. Four degraded soils with different degrees of degradation were amended with maize-stalk-derived biochar to investigate the adsorption of cadmium using batch methods. The maximum adsorption capacity (Q_m) of degraded soil remarkably decreased in comparison with undegraded soil (5361 mg·kg^-1→170 mg·kg^-1), and the Q_m of biochar increased with increasing pyrolysis temperature (22987 mg·kg^-1→49016 mg·kg^-1) which was much higher than that of soil. The addition of biochar can effectively improve the cadmium adsorption capacity of degraded soil (36⁻328%). The improving effect is stronger when increasing either the degradation level or the amount of added biochar, or the pyrolysis temperature of biochar. Contrary to the general soil⁻biochar system, adsorption of Cd was not enhanced but slightly suppressed (7.1⁻36.6%) when biochar was incorporated with degraded soils, and the adsorptivity attenuation degree was found to be negatively linear with SOM content in the degraded soil⁻biochar system. The results of the present study suggest that more attention on the adsorption inhibition and acceleration effect difference between the soil⁻biochar system and the degraded soil⁻biochar system is needed.