The Effects And Mechanism Of Chicken Manure Biochar And Its Modification Materials On Immobilization Remediation Cd And Pb Contamination

In this study,chicken manure biochar(BC)(BC200,BC400,BC600 and BC800)and ball milling biochars(QBC)were produced through pyrolysis under oxygen-limited condition at the temperature of 200,400,600℃ and 800℃ and ball milling method.The structure characteristics and interaction mechanism with heavy metals of biochar were detected by BET surface area,scanning electron microscopy(SEM),transmission electron microscope(TEM),CP-MAS 13C NMR and adsorption model,and then the effect of BC and QBC on immobilization remediation on Cd and Pb contamination was studied.The purpose of this study is developed to investigate the effects and mechanisms of chicken manure biochar and its modification materials to heavy metals Cd and Pb,In order to provide scientific basis for the resource utilization of poultry and chicken manure and the remediation of heavy metal contaminated soil.The main research results are as follows:(1)The results showed that ash content,pH values,BET surface area,and average pore diameter increased with the increases of pyrolysis temperature,the surface of BC had lots of irregular pore structure,mainly being mesoporous,while the yields of BC was significantly reduced with the increase of temperature.BC prepared at high temperature has a high degree of carbonization and a high cation exchange capacity.Its main components are CaCO3,SiO2,KCl and other elements with a low content.And high temperature(>600℃),the preparation of BC is more suitable for the repair of heavy metals and carbon emission reduction.(2)The adsorption of Cd2+and Pb2+in BC included an initial fast sorption phase and a second slow phase,and Elovich equation could better simulate the processes of kinetic adsorption,and the maximum adsorption capacities at equilibrium reached 45.50(BC200),49.17(BC400),52.02(BC600)and 49.34(BC800),respectively,and the maximum adsorption capacity at equilibrium reached 180.21,200.80,239.59 and 242.57 mg·g-1,respectively,showing BC200<B400<BC600<BC800.The processes of isotherms adsorption of Cd2+ and Pb2+ on BC could fit well with Langmuir.Under the condition of 35℃,the adsorption of Cd2+ and Pb2+ on BC was higher.The optimal pH value for Cd2+ and Pb2+ adsorption on four kinds of BC was 4.5～7.5.When the pH value was 4.5,the adsorption of Cd2+ and Pb2+ are most favorable.The mainly adsorption mechanisms of heavy metals on BC were involved in surface complexation,cationic-π action,precipitation and cation exchange.(3)The maximum adsorption capacities of Cd2+ on BC after treatment with ball milling was increased from 47.30 mg·g-1 to 104.13 mg·g-1,and from 240.46 mg·g-1 to 806.01 mg·g-1 for Pb2+.The adsorption of QBC and BC on the Cd2+ and Pb2+ could be well fitted by the pseudo-second-order equation and Langmuir isotherms adsorption model.With the increase of temperature,the equilibrium adsorption capacity increased,and the adsorption capacity of Cd2+ and Pb2+ increased with the increased of pH within the range of pH 2.5～7.5,and the highest of adsoption capacity of Cd2+and Pb2+ on QBC and BC was obtained at pH 4.5.The adsorption processes of QBC and BC to Cd2+ and Pb2+ were dominated by chemical adsorption,and its adsorption mechanism was mainly precipitation reaction.(4)The application of BC significantly increased soil pH value(P<0.05),while the contents of TCLP-Cd and-Pb were decreased,with the maximum reduction of 16.5%and 14.5%,respectively,in contrast with the blank treatments.When compared with CK,the ratios of weak-acid-extractable,reducible and oxidizable fraction of Cd and Pb was decreased to some extent,but the percentage of residue fraction of Pb and Cd decreaed by 5.49%-15.14%and 2.51%-6.30%,respectively.