The Physical And Chemical Properties Of Rice Straw Biochar Under Different Temperature Treatments And Its Effect On The Bioavailability Of Heavy Metals In Soil

How to deal with the large amount of straw produced in China's grain production process involves environmental pollution and recycling of resources.The incineration method often used in the past not only caused serious air pollution,but also caused a lot of waste of straw resources.In recent years,the application of straw to biochar has been applied to the soil,which can hide carbon in the soil,reduce the concentration of carbon dioxide in the atmosphere,and improve soil structure and fertility.In recent years,it has been found that biochar also has the ability to adsorb and passivate heavy metals in soil,which can be used as a repairing material for heavy metal contaminated soil.Therefore,research in this area has become a hot spot in the field of new environmental material development and soil pollution repair.When using plant straw to produce biochar,different preparation temperatures may result in differences in the structural and physicochemical properties of the prepared biochar.In theory,this difference will inevitably affect the ability of biochar to absorb heavy metals.When biochar is actually applied to soil remediation,this holding capacity not only affects the passivation effect of biochar on the soil's original heavy metals,but also affects the difficulty of re-release of the heavy metals being absorbed,and ultimately involves pollution remediation.The actual effect.Therefore,to clarify the relationship between the preparation temperature and structural characteristics of biochar and the actual passivation effect,it can provide a scientific basis for the temperature setting in the process of preparing high-efficiency biochar by using straw.To this end,two kinds of rice straw biochar were prepared at 400? and 600?.The apparent structure,group characteristics and basic physical and chemical properties were determined.The isothermal adsorption of heavy metals Cu,Cd and Pb was analyzed.The characteristics of the soil,Cu,Cd,Pb in the two biochar passivation soils were evaluated by pot experiment.It is hoped to provide a theoretical reference for the utilization of rice straw biochar.The test results are as follows:(1)As the cracking temperature increases,the degree of carbonization also increases,and mineral elements such as Na,K,Ca,Mg,etc.remain,resulting in an increase in the ash content of the biochar and an increase in alkalinity,but the yield of biochar,cation The amount of exchange is reduced.(2)The surface structure of the prepared biochar is slightly different at different temperatures:the biochar treated at 400? has a long strip shape,neatly arranged,and the surface is smooth;the biochar treated at 600? is relatively short.The shape is irregular and the surface is rough.On the whole,high temperatures make biochar charification more complete.(3)After analysis of elemental analysis,infrared spectroscopy,polycrystalline diffraction,etc,it can be seen that the biochar obtained at 600 C has more aromatic structure and more polar groups than the biochar at 400?.The process of preparing biochar can contain more plagiocl in the inorganic component of biochar at 600?,so it can adsorb more Cu,Cd and Pb.(4)The isothermal adsorption tests of biochar on heavy metals Cu,Cd and Pb at different initial concentrations showed that the adsorption performance of biochar at 600? was better;the adsorption curves of two biochars for Cu,Cd and Pb and The fitting between the Langmuir isotherm adsorption models is better than that between the Freundlich models,indicating that the adsorption of heavy metals is more monolayer-based;the desorption test shows that the two-temperature rice straw biochar pairs The adsorption of heavy metals Cu,Cd,and Pb is not only ion exchange,but also chelation.Since the surface of the 400? biochar particles is flatter than the surface of the 600? biochar particles,it is more conducive to the distribution of adsorbed heavy metal ions on the surface.(5)Bioavailability tests show that biochar has a strong "passivation" effect on the original heavy metals Cu,Cd and Pb in the soil,and also obviously prevents the re-release of heavy metals adsorbed by itself.Greatly reduce the bioavailability of heavy metals in the soil.Relatively speaking,the biochar produced at 600 C has a stronger passivation and inhibition release effect,which may be due to the fact that the 600? biochar contains more aromatic structures,more polar groups and higher.The pH is related.(6)The simple addition of biochar can increase the pH and conductivity of the soil,improve the physical and chemical properties of the soil,increase the available phosphorus,available potassium and organic matter in the soil,and the biochar effect at 600? is better.After adding the biochar adsorbed by heavy metals,the total nitrogen,available potassium and available phosphorus of the soil changed greatly,and other nutrients also changed,and the fluctuations were not large.It is known that the change of heavy metals is also related to the change of nitrogen,phosphorus and potassium.