| Five types of biochars(MS,referred as MS350-MS750)were prepared by maniocs wastes,a typical agricultural waste in Hainan province,at different pyrolysis temperatures(350-750 ?)under an oxygen-limited condition.The properties of biochars were determined by precise instruments.The effects of biochar on the soil improvement and adsorption of heavy metal and antibiotics in the environment were studied.This paper aims to reveal the adsorption isolation rule and mechanism of biochar to the typical heavy metal and pollutant in the soil and provide the basis for the agricultural application of biochar and pollution control and risk assement of heavy metal and antibiotics in the soil.The main conclusions of this paper are as follows:(1)The C content of five bio chars is far greater than other elements.With the increase of pyrolysis temperature,pH value of biochar was gradually increasing,and when the pyrolysis temperature was greater than 650?.biochar was alkaline.C/H value also increased with the increase of pyrolysis temperature.Alkaline group increased with the increase of pyrolysis temperature,while other four kinds of functional groups decreased with the increase of pyrolysis temperature.Moreover,with the increase of pyrolysis temperature,the specific surface area,CEC and ash content of biochars increased.(2)Biochar amended into decreased soil bulk density and specific gravity,while increased soil porosity and field capacity.With the increase pyrolysis temperature and addition amount(0.1-5%)of biochars,bulk density and specific gravity decreased,while total porosity and field moisture capacity increased.Soil saturated water content and residual water content increased with the increase of the addition amount of biochar.Furthermore,with the pyrolysis temperature increasing saturated water contents were also enlarging.When adding 5%ofMS650 into soil can most significantly improve the water-holding capacity of soil.(3)Adding biochar into soils can effectively increase the soil pH and decrease soil acidity.When 5%of biochars prepared under high temperature amended into soils,the soil pH values were greater than 7.Biochar can significantly increase organic material content of soils.With the increase of adding amount of biochar,the organic material content was gradually increasing.CEC of laterite with biochars amended also showed a significantly increasing trend.Bio char can improve available nutrients(available N,P,K)in the soil.All nutrients contents increased with the increase of adding amount of biochar.In this study,when 5%of MS650 added into soils,the improvement effect was relatively better than other biochars amened into soils.(4)The adsorption process of heavy metal and antibiotics can be divided into fast and slow process.The pseudo second-order model can describe the relation of adsorption and reaction time well.With the increased of pyrolysis temperature and addition amount,the adsorption affinity of biochar for heavy metals and antibiotics gradually strengthened.The significant bending of adsorption isotherm illustrated the adsorption and desorption processes of heavy metals and antibiotics in soils with biochars amendedwere very complicated.Adsorption isotherm and desorption isotherm indicated that the adsorption mechanisms of antibiotics in the tested soil with biochar added were the interaction of surface filling and distribution,heavy metals basing surface filling.(5)The thermodynamic studies indicated that the adsorption of heavy metals and antibiotics in biochars-added soils was spontaneous and endothermic reaction.The absolute values of AGo were all less than 40kJ/mol,indicating that the adsorption process was primarily controlled by physisorption,which was the effect of hydrogen bond.(6)In conclusion,when adding 5%of MS650 into soils,the adsorption and improvement effects were the best. |
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