| Biochar can not only improve soil fertility,but also lock the organic and inorganic pollution in the environment to reduce the risk of pollutant migration.The primary objective of this study was to investigate the effect of biochar produced from maize and pine needles residue at different temperatures on the adsorption of diuron and carbaryl onto loess soil.Meanwhile,the effect of the systemic temperature,p H values and the initial concentration were also investigated for the adsorption of diuron and carbaryl onto losses soil.And Kinetic parameters,such as rate constants,equilibrium adsorption capacities and related correlation coefficients were also calculated and discussed.Based on the adsorption of petroleum pollutants onto loess soil inthis study,the exogenous substances?MBC-200,MBC-400,MBC-600,PBC-200,PBC-400,PBC-600?were characterized via thermal gravimetric analysis?TG-DTG?,elemental analysis,fourier transform infrared spectroscopy?FTIR?,the surface area detection and scanning electron microcopytometer?SEM?.The effect of the different exogenous substances on the adsorption of loess was investigated.The results were as follows:?1?The results of biochar characterization showed that the surface of the biochar contains hydroxyl groups,carboxyl groups and carbonyl groups.With the increase of pyrolysis temperature,the biochar ash content increases,the degree of carbonization increases,and the rate of organic matter decreased.The distinct surface characteristics of biochar from the maize straw and pine needles regulated by the pyrolytic temperature,and the hole-wall of biochar got thin gradually with increasing pyrolytic temperature.Furthermore,the internal pore structure of biochar increased gradually,and then a large number of micropores of the biochar appeared.With the increase of pyrolysis temperature of biochar,the carbon content gradually increased,the hydrogen and oxygen contents decreased gradually.The biochar become “carbon-rich particles”,and its aromaticity?H/C ratio?and hydrophobicity?O/C ratio?were enhanced dramatically,while its polarity [?O+N?/C] was sharply decreased.?2?The adsorption experiment of diuron and carbaryl on loess soil showed that the adsorption process is divided into a fastand slow adsorption stages,Carbaryl reached the adsorption equilibrium at 14 h,while diuron reached the adsorption equilibrium at around 16 h.The results showed that the adsorption of diuron and carbaryl onto loess soil could be described by the pseudo-second-order kinetic model and intraparticle diffusion model.Theadsorption thermodynamics of diuron and carbaryl onto loess soil is non-linear by nature,and well fitted with the Freundlich isothermal model.The p H has different effects on adsorption of diuron and carbarylon loess soil,At the p H in a range of 3 to 10,the adsorption capacity of carbaryl onto loess soil has a great chance,but the adsorption capacity of diuron onto loess soil changed a little.?3?The adsorption experiment of diuron and carbaryl on biochar showed that the adsorption capacity of two kinds of organic pesticides onto MBC-600 and PBC-600 was much higher than that of biochar produced at 200? and 400?.It could be described by the pseudo-second-order kinetic model,and the adsorption thermodynamic well fitted with the Freundlich isothermal model.Thermodynamic parameter analysis of diuron onto loess soil by adding biochar showed that Gibbs free energy??G??was less than zero,while Enthalpy??H??and Entropy??S??were greater than zero,indicating a spontaneous endothermic adsorption,which increases the degree of disorder during the process.The results showed that the adsorption of diuron and carbaryl on the biochar at low temperature was mainly the distribution.With the increase of pyrolysis temperature of biochar,the contribution of surface adsorption increased.The adsorption of organic pollutants were mainly adsorbedby the distribution and surface adsorption.?4?The results showed that the adsorption of diuron and carbaryl onto loess soil by adding biochar could be described by the pseudo-second-order kinetic model,and followed the intraparticle diffusion model,but diffusion is not only the rate controlling step.The adsorption thermodynamics of diuron and carbaryl well fitted with the Freundlich isothermal model.The average adsorption free energy E was less 8k J·mol-1 when the temperatures increased from 25 to 45 ?,indicated that adsorption of diuron and carbaryl onto loess was a physical adsorption.The results also suggested that the effected factors of diuron and carbaryl have significant effects on the adsorptive behavior on loess soil by adding biochar.With the pyrolysis temperature of biochar increasing,the equilibrium concentration of diuron and carbaryl in solution decreased,while the amount of adsorption on loess soil increased.The adsorption of organic matter on loess is mainly controlled by biochar,and most of the organic pollutants are absorbed by biochar.When the initial concentration of diuron and carbaryl increased,the adsorption capacity showed a rapidly increasing trend,then when the initial concentration increases the adsorption capacity showed a slow increasing trend and gradually tends to the balance.The p H had only a great effect on the adsorption of carbaryl,and had nosignificant effect on the adsorption capacity of diuron.?5?The results showed that the adsorption equilibrium time of diuron and carbaryl onto the diesel-contaminated loess has no significant change.And the adsorption equilibrium time of diuron and carbaryl onto the diesel-contaminated loess by adding biochar has shortened.The kinetic process is more consistent with the pseudo-second-order model.Whether it is adsorption of diuron or carbaryl,thermodynamic parameter analysis onto loess soil by adding biochar showed that Gibbs free energy??G??was less than zero,while Enthalpy??H??and Entropy??S??were greater than zero,indicating a spontaneous endothermic adsorption,which increases the degree of disorder during the process.The adsorption capacity showed an increasing trend when MBC-400 is added to the diesel-contaminated loess.But the adsorption may be affected by the intensity of diesel pollution,and the adsorption capacity decreased with the increase of pollution intensity. |
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