Mechanism Of Crayfish Shell Biochar On Remediation Of Arsenic And Its Ecological Effect

Arsenic（As）pollution in groundwater and soil in China has been a serious threat to animal and plant health.Biochar has been widely used in arsenic pollution remediation due to its well-developed pores and abundant surface functional groups.Crayfish shell biochars（CS300,CS500 and CS700）were produced through pyrolysis under anoxic atmosphere at the temperature of 300-700℃.The surface chemical properties and structural characteristics of crayfish shell biochars were tested by elemental analyzer,thermogravimetric differential thermogravimetry（TG-DTG）,scanning electron microscopy（SEM）,energy dispersive analysis（EDS）,X-ray diffraction（XRD）,Fourier infrared spectroscopy（FTIR）,Raman spectroscopy（Raman）,¹³C-solid state nuclear magnetic resonance(¹³C-NMR).The performance and mechanism of crayfish shell biochar for adsorbing arsenic in solution were studied by batch equilibrium experiment,column adsorption experiment and spectral characterization.The remediation effect and ecological effect of crayfish shell biochar on arsenic-contaminated soil were investigated by culture experiment.The main research results are as follows:（1）Pyrolysis temperature significantly affected the physicochemical and structural characteristics of crayfish shell biochar.With the increase of pyrolysis temperature,the yield,C,N and H contents of crayfish shell biochar decreased gradually,while the p H value,the content of ash,pore volume and average pore size increased gradually.Meanwhile,with the increase of pyrolysis temperature,the change intensity of-OH was greater than that of-CH₂ in the band of 3600-2800 cm^-1,and the change order of-OH in was superior to that of-CH₂.In the 1850-700 cm^-1,the changes of C=O,CO₃^2-,C-O and C=C led to the formation of related peaks.The intensity of change was CO₃^2->C=C>C-O>C=O and the order of change was C-O>CO₃^2->C=C>C=O.（2）The pseudo first order kinetic model was more suitable for describing the adsorption process of As（Ⅲ,Ⅴ）on CS300,and the pseudo second order kinetic model was more suitable for describing the adsorption process of As（Ⅲ,Ⅴ）on CS500 and CS700.At adsorption equilibrium,the maximum adsorption capacity of As（Ⅲ）by crayfish shell biochars were as follows:CS300(5.17 mg·g^-1)>CS700(3.55mg·g^-1)>CS500(0.86 mg·g^-1)and the maximum adsorption capacity of As（Ⅴ）by crayfish shell biochars were as follows:CS300(9.20 mg·g^-1)>CS700(3.58 mg·g^-1)>CS500(1.14 mg·g^-1).The isothermal adsorption of As（Ⅲ,Ⅴ）on crayfish shell biochar fitted well with Langmuir model.The Thomas model fitted well the dynamic adsorption process of As（Ⅲ,Ⅴ）by CSBC.The mainly adsorption mechanisms of As（Ⅲ,Ⅴ）onto CS300 and CS500 were involved in physical pore filling,electrostatic attraction and complexation of hydroxyl,carboxyl and nitrogen-containing functional.However,CS500 absorbed As（Ⅲ,Ⅴ）through physical pore filling and electrostatic attraction.（3）Crayfish shell biochar significantly reduced the available arsenic content in alkaline soil compared with the control,and CS700 had the best remediation effect,which decreased by 9.9%.However,crayfish shell biochar increased the content of available arsenic in acidic soil by 19.58%-26.80%.Compared with the control,adding biochar could increase the proportion of calcium-bound arsenic in the soil.After adding CSBC,the content of dissolved organic carbon in acidic soil was significantly increased by 58%-256%.In alkaline soil,only CS300 treatment significantly increased soil dissolved organic carbon content by 114%.The addition of crayfish shell biochar affected the content and proportion of compounds of soil dissolved organic.With the increase of pyrolysis temperature of biochar,humic-like substances in DOM of acidic soil changed preferentially,and the change order of various functions of DOM was-OH>-COOH>C=O>C-O>C=C,while in the alkaline soil DOM,the change of fulvic-like substances was preferred,and the change order of functional groups was-COOH>-OH>C=O>C=C>C-O.（4）Compare the treatment of control,the contents of soil p H,organic matter,alkali-hydrolytic nitrogen,nitrate nitrogen,available phosphorus,available potassium,total nitrogen and total phosphorus increased by 0.64%-67.72%,16.06%-40.24%,2.74%-75.12%,28.20%-172.23%,18.69%-78.74%,14.17%-363.97%,36.62%-167.01%,11.03%-44.38%and 7.76%-37.78%,respectively,after the addition of crayfish shell biochar.CS300 had the best effect on improving soil nutrient.Crayfish shell biochar reduced the richness and diversity of microbial community in acidic soil.In alkaline soil,crayfish shell biochar did not change the richness of soil microbial.CS300 decreased the diversity of microbial in alkaline soil,while CS500 and CS700 increased the diversity of microbial.Crayfish shell biochar prepared at low temperature has greater potential to change soil microbial community structure.