Sorption mechanisms of lead on soil-derived black carbon formed under varying cultivation systems

The knowledge about lead (Pb) sorption on soil-derived black carbons (SBCs) under different cultivation intensities of soils is limited. In this study, chemical and spectroscopic methods were applied to investigate the Pb sorption mechanisms on SBCs in soils from a forest land, a rubber plantation area, and a vegetable farm with none, less and highly intensive cultivation, respectively, that are located in the Hainan Island of China. Results showed that the specific surface area and cation exchange capacity of the SBCs from the less and highly intensive cultivation soils were 4.5- and 2.7-fold, and 1.3- and 1.8-fold higher compared to that of SBC from the no-cultivation soil, which subsequently enhanced the Pb sorption capacities of SBCs in iron exchange fraction. Ion exchange and hydrogen bonded Pb fractions together accounted for about 80% of total Pb sorbed on all SBCs at an externally added 1000 mg L^-1 Pb solution concentration. The OC-O groups also played key roles in Pb sorption by forming complexes of OC-O-Pb-O and/or OC-O-Pb. Overall, SBCs in soils under all studied cultivation intensities showed high potential to sorb Pb (with the maximum absorbed Pb amount of 46.0-91.3 mg g^-1), and increased Pb sorption capacities of the studied soils by 18.7-21.1 mg kg^-1 in the stable fraction (complexation). Therefore, SBC might be a potential environment-friendly material to enhance the Pb immobilization capacity of soil.