A Preliminary Study On The Remediation Of Cadmium Contaminated Soil By Modified Pennisetum Giganteum Z.x.lin Biochar

In this study,Pennisetum giganteum z.x.lin was taken as a raw material to get biocar?JBC?,and then impregnated by potassium permanganate and hydrogen peroxide solution to obtain modified biocars?JMB1 and JMB2?.Afterwards,the modified biochars were pyrolyzed under blowing N2 and held at 300°C for 1 h.The physic-chemical charactersistics of biocars,including the main surface element content,surface morphology characteristics,specific surface area and porosity,crystal structure,surface functional group and the main surface elements'valence,were analyzed by scanning electron microscope and energy spectrum?SEM-EDS?,specific surface area analysis,X-ray diffraction?XRD?,Fourier Transform Infrared Spectrometer?FTIR?and X-ray photoelectron spectroscopy?XPS?,respectively.To analysis the adsorption mechanism of Cd???by modified biochars,the following factors such as reaction time,initial Cd???concentration,pH value and reaction temperature in solution were taken into consideration.To analysis the stabilization and passivation mechanism of modified biochar in soil,the effects of soil pH value and cation exchange capacity?CEC?were tested after adding biochars into both simulated and actural soil.And the changes of the cadmium forms,exchangeable base ions and available manganese were further studied in actual Cd-contaminated soil after adding biochars.The main conclusions were as followings:?1?In the batch experiment,the Cd???adsorption of JBC and JMB1 fit the pseudo second order model?PSOM?better,indicating the dominant adsorption mechanism was chemical adsorption.And JMB1 had performed a better Cd???adsorption effect.While the adsorption process of JMB2 tended to fit the pseudo first order model?PFOM?better,suggesting physical adsorption dominant.Compared with Freundlich model,Langmuir model could better describe the adsorption process of three biochars,and the maximum adsorption capacity occurred in the following order:JMB1?90.32 mg/g?>JMB2?45.18mg/g?>JBC?41.79 mg/g?.?2?JMB1 was selected as a likely better adsorbent to further discuss the Cd???adsorption mechanism.The effect of solution pH value on the material adsorption was investigated.Meanwhile,the changes of surface valence were analyzed by XPS.It showed that?aromatic group disappeared when Cd???was absorbed onto biocars and the hydroxyl group that connected to the center of Cd???formed the surface complexes,by which we could conclude that the adsorption mechanisms of Cd???by biocars were mainly precipitation,surface complexation and the effect of cationic?.?3?After adding the biochars into simulated soil,the soil pH value and cation exchange capacity?CEC?improved significantly after adding JBC and JMB1.After adding bioars into actual Cd-contaminated soil,the soil pH value also increased obviously from 5.60 to 7.80.The soil organic matter content also increased to a certain extent.The soil exchangeable Cd decreased and transferred into more stable forms,such as residue state.In different culture times,the stabilization effect was in the following order:JMB1>JBC>CK.Compared with the controlled?CK?,the soil Cd exchangeable decreased a lot with different culture time after adding JMB1,which expreseed in the following order:90d?15.02%?>120d?11.18%?>60d?13.9%?>30d?6.66%?.At the same time,the addition of biocars also had obvious impacts on soil exchangeable K⁺,Ca²⁺,Na⁺,Mg²⁺and available Mn²⁺.It suggested that the loaded Mn²⁺by JMB1 might have exchanged with Cd???in the actural Cd-contaminated soil,leading to the increase of soil Mn²⁺content and decrease of soil exchangeable Cd???content.