Preparation Of Biochar By Low Temperature Pyrolysis Of Wheat Straw And Its Properties And Application

As an important green resource,biochar can not only be used as clean energy,carbon materials,etc.,but also can be directly applied to the soil as a carbon-based fertilizer base to improve soil fertility and nutrient utilization,adjust p H,improve structure,and microbial survival environment,and adsorb and fix heavy metal in the soils,so as to improve and repair the soil.Wheat straw is one of the main straw biomass resources in China,which has the advantages of tremendous yield and renewable.In this paper,wheat straw biochar is prepared by low-temperature pyrolysis of wheat straw,and its application effects on the adsorption of heavy metal and the fixation of heavy metal in soil to improve the growth and quality of crop are of great significance for solving and reducing agricultural straw burning,efficient utilization of agricultural waste,and promoting green development.It was found through thermal weight loss analysis that the pyrolysis process of wheat straw can be roughly divided into four stages: drying,pre-pyrolysis,pyrolysis and carbonization.The drying stage is the process of wheat straw heating and surface water detachment;the pre-pyrolysis stage is the process of wheat straw combining water detachment and a small amount of depolymerization reaction;the pyrolysis stage is the process of hemicellulose and cellulose being largely decomposed;The carbonization stage is the process of slow decomposition and carbonization of lignin and residues.The temperature range of the pyrolysis stage is 260?370?.At this stage,the quality of wheat straw was significantly reduced,and the weight loss rate was as high as 50%.By investigating the effects of different pyrolysis temperatures on the properties of wheat straw biochar,it was found that as the pyrolysis temperature increased,the yield decreased,the specific surface area and p H increased,the light components escaped,the C content increased,and the degree of carbonization increased.FTIR showed that the higher the pyrolysis temperature,the weaker the intensity of the-OH,C-O and C=O absorption peaks,and the long carbon chain breaks.By examining the adsorption conditions for the adsorption of Pb(?)on wheat straw biochar,it was found that the removal rate and adsorption amount of Pb(?)by biochar increased with the increase of solution p H.The removal rate of Pb(?)increased with the increase of solid-liquid ratio.When the solid-liquid ratio is 1.5?2 g / L and the p H is 5?6,the adsorption of Pb(?)by wheat straw biochar is more favorable.Adsorption isotherms and thermodynamic studies have found that the process of wheat straw biochar adsorption of Pb(?)conforms to the Langmuir isotherm model and is a spontaneous endothermic process.The investigate of adsorption kinetics found that the adsorption process conformed to the pseudo-second-order kinetic model,which may be controlled by both surface adsorption and intra-particle diffusion.The adsorption process may involve both physical and chemical adsorption.The prepared wheat straw biochar is used to apply different doses to the soil,and mix different concentrations of Pb(?)solution to plant pakchoi.By studying the role of biochar in fixing Pb(?)in soil and its effect on crop quality,it was found that the application of biochar in soil can effectively reduce the content of Pb(?)in pakchoi tissues.The content of Pb(?)in pakchoi tissue decreases with the increase of the proportion of biochar application,which indicates that biochar can effectively adsorb and fix Pb(?)in the soil,and the adsorption amount of Pb(?)in pakchoi.Under the conditions of this research,by adding 1% biochar to the soil,the content of Pb(?)in pakchoi tissues meets the limit value for lead content of fresh vegetables in GB 2762-2012.A carbon-based fertilizer was prepared by mixing wheat straw biochar with compound fertilizer,and the effects of different fertilizers on tomato growth and quality were investigated.It was found that biochar has a certain inhibitory effect on tomato plant height and diameter.Carbon-based fertilizers and compound fertilizers promote the growth of tomato plant height and diameter.With the application of biochar,carbonbased fertilizer and compound fertilizer,the vitamin C,soluble sugar content,and sugar-acid ratio of tomatoes all increased in different degrees.However,the effects on the content of organic acids were different.Among them,when carbon-based fertilizer was applied,the content of organic acids decreased significantly,reaching a maximum of 22.2%.Compared with biochar and compound fertilizer,carbon-based fertilizer reduces the organic acid content of tomato,increases the sugar-acid ratio,and improves the nutritional quality.Biochar can partially replace compound fertilizer,while the quality of tomato will not decrease.