Study On Molding And Release Property Of Slow Release Fertilizer Based On Rice Husk Charcoal

Biochar has rich porous structures and hydroxyl radicals,which is helpful for improving the air permeability and waterholding capacity of soil and will provide nutrients to soil.The utilization efficiency of fertilizer in China is lower,the production of slow-release fertilizer with biochar as carrier will not only decrease the release rate of nutrients in fertilizer,improve the utilization efficiency of fertilizer,reduce environmental pollution,but also will provide a new approach for the utilization of biomass resource.With agricultural residue-rice husk as raw material,its carbonization characteristics have been studied,the rice husk charcoal has been produced and a kind of modified starch was developed as binder for producing charcoal based slow-release urea fertilizer,the processing parameters for slow-release fertilizer molding,the mechanic properties and release characteristics of the fertilizer have also been studied.The main results are as following:1?The pyrolysis characteristics of rice husk have been analyzed by TG-DSC,the results show that the pyrolysis process of rice husk has three stages which are drying stage,pyrolysis stage and carbonization stage;along with the increase of heating rate,the comprehensive release index D of volatiles will be increased and the time for reaching the pyrolysis temperature is reduced;the first order kinetic model for rice husk carbonization has been set up,the activation energy at the volatile release stage is 44.39⁵5.49 kJ/mol,which indicates that the activation energy of rice husk pyrolysis is not higher and this will favor the carbonization.2?The rice husk charcoal have been produced by self-made biomass pyrolysis device,the influence of pyrolysis temperature on the characteristics of rice husk charcoal has been study.The results show that:Along with the increase of pyrolysis temperature,the volatiles in rice husk charcoal and the charcoal yield rate are gradually reduced while the ash content and the fixed carbon in rice husk charcoal show the trend of increase;meanwhile,along with the increase of pyrolysis temperature,the iodine adsorption value is gradually increased while the Methylene blue adsorption value shows the counter tendency,the iodine adsorption value reaches the maximum of 312.40mg/g at pyrolysis temperature of 600?,while the Methylene blue adsorption value reaches the minimum of 5.68mg/g.The SEM picture shows that the porous structure of biochar are improved while the pyrolysis temperature increases.The FT-IR spectrum shows that the various kind of functional groups are found at lower pyrolysis temperature and gradually disappear at higher pyrolysis temperature.3?With maize starch,cassava starch and potato starch as raw material,H₂O₂ as oxidant,FeSO₄ as catalyst and cross-linking agent,the influences of the varieties of starch,the gelatinization temperature and the dosage of gelatinization agent on the characteristics of the cross-linking agent have been studied.The evaluation on the cross-linking agent are carried out from four aspects which are appearance,initial viscosity,fluidity,stability for storage and bio-toxicity.The results show that:when the mass ratio of starch and ion removed water is 1:8,at the gelatinization temperature of 25?,adding 1.5mL of H₂O₂solution at the concentration of 26%,3mL of FeSO₄ solution at the concentration of 6%,1.5mL of 1.5mL NaOH solution at the concentration of 10%in sequence,the binder produced from modified maize starch shows brown color,and its viscosity of 268.6mPa·s is higher,its fluidity is fine while its bio-toxicity is lower,it is suitable for charcoal based fertilizer production.4?The introduction of binder will obviously improve the molding properties of fertilizer pellet,which has higher pressure resistance and fine anti-impact performance,thus the fertilizer is more suitable for storage,transportation and utilization.The dosage of 5%for starch is recommended in order to obtain the fertilizer pellet of fine molding properties.The moisture content,molding temperature,molding pressure,ratio of charcoal to fertilizer and etc.have remarkable influences on the molding properties of fertilizer pellet.At the dosage of 5%for starch,the ratio of charcoal to fertilizer could be 5:1,comprehensively considering the mechanic properties of fertilizer pellet and the volatilization loss of fertilizer in the molding process,the moisture content,the molding temperature and the molding pressure should be 20%?45??6kN respectively.5?By leaching experiment,the study on the influences of binder dosage,ratio of charcoal to fertilizer and molding pressure on the release characteristics of slow-release fertilizer pellet have been carried out.The results show that the release performance tends to be improved along with the increase of binder dosage,ratio of charcoal to fertilizer and molding pressure,when the binder dosage is 5%,the ratio of charcoal to fertilizer is 3:1,the moisture content is 20%and the molding pressure is 6kN,the cumulative release rate is63.1%.This indicates that,by comparison with urea fertilizer,the release performance of charcoal based fertilizer with modified maize starch as binder could be remarkable improved,and the charcoal based fertilizer could be more suitable for agricultural production.