Abstract:

Corn straw biochar may be of an important role in improving soil fertility and controlling nonpoint source pollution of nitrogen and phosphate. Three  biochars named B250,B350 and B450 were produced from corn straw biomass materials at  temperatures  250,350 and 450 ℃, respectively. The characteristics of structure and surface of the biochars were measured by  SEM (scanning electron microscopy) and FTIR (Fourier Transform infrared spectroscopy), and the adsorption characteristics of the biochars for nitrogen and phosphate  were also investigated by laboratory simulation. The results from SEM and FTIR show that the pore deformation and the stalk roughness increased as the carbonization temperature rose, furthermore making the pore canal effect easier and the adsorption properties more excellent. Meanwhile, the biochars were of a higher degree of stability enhancement with temperature rising. The results from nitrogen and phosphate adsorption kinetics and thermodynamics on biochars show that B250 released some phosphate from itself during the adsorption process, so adsorption results of B250 is negative, while the adsorption kinetic processes of B350 and B450 were consistent with the Lagergren pseudosecond order kinetic model, and the adsorption isotherms of three  biochars agreed well with the Langmuir formulae. The shortest time to reach the adsorption equilibrium is 5 h for B450, and the longest time to reach the adsorption equilibrium is 12h for B350, while adsorption capacity is in descending order of B450>B350>B250. In addition, the adsorption kinetic process for nitrogen is consistent with the Lagergren pseudosecond order kinetic model, the adsorption isotherms agree well with the model of Langmuir. Adsorption rate of nitrogen on the biochars is in descending order of B450>B350>B250, while adsorption capacity is in descending order of B450>B350>B250.

Key words: adsorption characteristic, structure characteristic, nitrogen, phosphate, corn straw biochar