Mobility, Speciation and Bioavailability of Zn and Pb in Artificially Polluted Soils by Magnetic Biochars from Siraitia Grosvenorii Residues

The effects of magnetic biochar (SMBC) prepared from Siraitia grosvenorii residues on the mobility, speciation and bioavailability of Pb and Zn in the soil were studied. SMBC was characterized by N₂ adsorption–desorption isotherm, Scanning electron microscope, Fourier infrared spectroscopy and X-ray diffraction. Three different extractions of Pb and Zn by TCLP, CaCl₂ and PBET were used to simulate mobility, availability and bioaccessibility, respectively. SMBC was incubated with contaminated soils at rates of 0, 1, 2.5, and 5.0% by weight for 5 days and 30 days. SMBC was effective for both Zn and Pb immobilization, and the immobilization effect increased with the increase of SMBC dosage. It was observed that there was a slight rebound of TCLP-extractable Pb and CaCl₂-extractable Pb in the SMBC-treated soils after 30 days of incubation. The chemical fractions of Pb and Zn from sequential extractions were used for evaluating mobility and availability. After 30 days of incubation, the chemical species of Pb in the control distributed in the decreasing order of OX (26.5%) > CB (20.99%) > OM (18.52%) > RS (18.02%) > EX (15.95%) and RS (27.35%) > OX (24.88%) > EX (19.95%) > OM (17.42%) > CB (10.38%) for Zn in the soil. Siraitia grosvenorii residues has a broad application prospect in the remediation of heavy metal polluted soil in the future.