Impact Of Biochar On The Sorption Behavior Of Benzonitrile And Atrazine Onto Loess Soil Of The North-Western Part China

In the present study, benzonitrile and atrazine were selected as the target pollutants to investigate the effect of biochar produced from wheat residue at different temperatures on the adsorption of benzonitrile and atrazine onto loess soil in the northwestern China. The results showed that the adsorption equilibrium of benzonitrile and atrazine onto loess were both about 8h without biochar, and after the addition of biochar into loess soil, the adsorption equilibrium time of benzonitrile and atrazine were shortened, meanwhile, with the increase of pyrolysis temperature of biochar added into soil, the adsorption equilibrium time was obviously reduced, while the saturation adsorption amounts of benzonitrile and atrazine onto loess soil were also significantly increased. The kinetic data showed that the adsorption of benzonitrile and atrazine onto loess soil could be better described by a pseudo-second-order kinetic model, the boundary layer control and intraparticle diffusion were both involved in the adsorption process. Besides, the adsorption equilibrium data were well described by the Freundlich isothermal model. The saturated adsorption capacity was improved as temperature increased with or without the biochar, suggesting a spontaneous endothermic process for benzonitrile, whereas for atrazine the process was found to be an exothermic process. The average adsorption free energies E were in the range of 1.865-3.171kJ/mol and 0.635-1.058kJ/mol, respectively, which indicated that adsorption processes of benzonitrile and atrazine onto loess, were physical adsorptions with or without biochar. Thermodynamic parameter analysis showed that Gibbs free energy (?G~?) was less than zero, while Entropy (?S~?) and Enthalpy (AH~?) were greater than zero, indicating an endothermic process for adsorption of benzonitrile onto loess soil and negative values for atrazine indicating that the atrazine adsorption onto loess soil was exothermic. The results indicated that the adsorption process of benzonitrile and atrazine onto loess with the addition of biochar involved a surface adsorption, diffusion within the particles, and external film diffusion mechanism.