| Biochar is a carbon-rich solid product with high nutrient content,large specific surface areaand loose porosity produced by high-temperature pyrolysis of agricultural and forestry wastes under anaerobic or oxygen-limited conditions.Because of its good structural characteristics and physicochemical properties,biochar can not only improve soil quality,increase fertilizer efficiency,increase crop yield,but also achieve the effect of adsorbing heavy metals.Therefore,before studying the soil improvement effect of biochar,it is particularly important to clarify the basic physicochemical properties and stability of biochar.In this research,biochars were fabricated from rice straw and corn straw through pyrolysis in vacuum environment at 400~700℃ for 10 min,30min,and 60 min,respectively.Scanning electron microscopy(SEM)and specific surface area-pore size analyzers were used to analyze the structural characteristics of biochar.The physicochemical properties of biochar were characterized and analyzed by means of Fourier transform infrared spectroscopy(FTIR)and elemental analysis.The aim is to clarify the physicochemical properties and structural characteristics of straw biochar under different preparation conditions and the optimization conditions.Finally,the carbon loss rate calculation method was used to compare the stability of biochar under different materials and preparation conditions.With a view to deepening the relationship between raw materials,preparation conditions and the nature and stability of biochar,it will provide data support and theoretical basis for biochar’s characteristic production and application.The main research results are:(1)With the increase of pyrolysis temperature and increase of residence time,the carbonization degree of biochar increased,the aromaticity of biochar increased,the content of C increased,and the content of H and O decreased.Ash,fixed carbon,pH,and conductivity increase,but yield and volatile content decrease.Under the same preparation conditions,the yield and ash content of rice straw biochar were higher than that of corn straw biochar.(2)By Fourier transform infrared spectroscopy(FTIR)analysis of two kinds of straw biochar,it can be seen that there are many types of biochar functional groups obtained by low temperature pyrolysis.As the pyrolysis temperature increases,the absorption peaks of most functional groups gradually weaken or even disappear.(3)The increase of pyrolysis temperature and prolongation of residence time are consistent with the above-mentioned basic physical and chemical properties of biochar and stability,but the effect of pyrolysis temperature on biochar is greater than the effect of residence time.(4)Scanning electron microscopy and specific surface area,pore size and pore volume of biochar showed that with the increase of pyrolysis temperature and residence time,the pores of biochar increased,the specific surface area increased,the pore volume increased,and the pore size decreased.(5)Under the same residence time,the stability of the two types of straw biochar was ranked according to the pyrolysis temperature was 600°C>700°C>500°C>400°C;at the same pyrolysis temperature,the stability was ranked according to the residence time was 60min>30min >10min.Under the same preparation conditions,the stability of corn straw carbon is stronger than that of rice straw carbon.(6)There was a significant negative correlation between the volatile matter,H/C and O/C and the stability of straw biochar.There was a very significant positive correlation between the fixed carbon and stability of straw biochar. |
