Performance and mechanism for cadmium and lead adsorption from water and soil by corn straw biochar

Cadmium (Cd) and lead (Pb) in water and soil could be adsorbed by biocharproduced from corn straw. Biocharpyrolyzed under 400°C for 2 h could reach the ideal removal efficiencies (99.24%and 98.62% for Cd and Pb, respectively) from water with the biochardosage of 20 g·L–1 and initial concentration of 20 mg·L–1. The pH value of 4–7 was the optimal range for adsorption reaction. The adsorption mechanism was discussed on the basis of a range of characterizations, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman analysis; it was concluded as surface complexation with active sorption sites (-OH, -COO-), coordination with π electrons (C = C, C = O) and precipitation with inorganic anions (OH-, CO3 2–, SO4 2–) for both Cd and Pb. The sorption isothermsfit Langmuir model better than Freundlich model, and the saturated sorption capacities for Cd and Pb were 38.91 mg·g-1 and 28.99 mg·g–1, respectively. When mixed with soil, biocharcould effectively increase alkalinity and reduce bioavailability of heavy metals. Thus, biocharderived from corn straw would be a green material for both removal of heavy metals and amelioration of soil.