| Biochar fertilizers have numerous advantages compared with conventional fertilizer,such as releasing slowly fertilizer nutrient,improving soil environment and reducing pest damage.Meanwhile,it is more effective to solve the serious problems of biomass resource,reduce the usage of conventional fertilizer and to achieve the goal of energy-saving and environmental protection in agricultural production when combining with biochar and conventional fertilizer.This study took the rice husk biochar and urea fertilizer as raw material to prepare three kinds of novel rice husk biochar fertilizer with sustained release character,and had explored the effects of technical parameters on the molding and nutrient releasing performance of the rice husk biochar fertilizer.Besides,structure characterization were performed on the internal structure of the rice husk biochar fertilizer to investigate the possible forming mechanism between rice husk biochar and urea,and provided theoretical and experimental basic for commercial extended application.The specific research contents and conclusions are as follows:1.The influence rule on the physical and chemical properties of rice husk biochar(RHBC)on pyrolysis temperature was systematically studied,and the adsorption mechanism of urea-N in water solution was also explored.The results showed that yield of rice husk biochar,content of volatile and number of functional groups gradually decreased along with the increase of pyrolysis temperature,while that of p H value,content of fixed carbon and the specific surface area gradually increased.The results of the adsorption experiment suggested that the ability of by rice husk biochar increased with the rising pyrolysis temperature.Furthermore,the adsorption isotherm and profile of adsorption kinetics were fitted by several empirical model showed that the mechanism of the urea-N adsorption was cooperatively controlled by mononuclear and binuclear physical adsorption,surface chemical adsorption and intraparticle diffusion.2.The rice husk biochar fertilizer(RHBF)was prepared by an innovative process of melting urea permeation,which was based on the theory of heating melting and cooling crystallization of the urea.The effect of technical parameter on the molding performance,nutrient releasing performance and structural characteristics of the RHBF were investigated.The results showed that the RHBF pellets formed at the heating temperature of 150-155℃,heating time of 18-22 min,biochar to urea ratio of 1:1-1:1.5,biochar particle size of 75-120μm and biochar pyrolysis temperature of 550-650 ℃,exhibited better molding performance to be handled.The results of structural analysis revealed that recrystallized urea had entirely permeated into the inner pores of RHBC and showed a well interface combination,and the bonding strength between molecule was enhanced by formation of solid bridge,mechanical interlocking and hydrogen bonding between urea and RHBC particles.The results of nutrient release suggested that the nutrient release presented “S” type of profile and the releasing process of RHBF can be divided into three stages of slow-release,fast-release and extreme slow-release.The release rate of nutrient was mainly controlled by the fore of H-bonding,RHBC pore adsorption.3.The rice husk biochar fertilizer with pressure(P-RHBF) was produced in an universal testing machine by the way of hot extrusion.The mechanical property and nutrient release performance of P-RHBF were studied and regulated by controlling the technical parameter.The results of single-factor experiments suggested that by considering molding density,compressive strength and specific energy consumption,better molding conditions of P-RHBF pellets were obtained with 130-135℃ heating temperature,1.0-1.5KN molding pressure,2:1 biochar to urea ratio and 2%-4% acetate starch(AS)addition content.Comparing with of molding process of RHBF,the hot extrusion process of P-RHBF largely shortened the molding time and decreased the heating temperature.The results of leaching experiment suggested that AS can effectively reduce the nutrient release rate as an additive int the P-RHBF pellets,and the release period of P-RHBF pellets gradually prolonged along with the increase of AS addition content,exhibiting excellent slow-release performance.4.The rice husk biochar/acetate starch-urea(RHBC/AS-UR)composite films were prepared by casting method,and the coated urea fertilizers using composite films as coated material were also made in a spouted fluidized bed coating equipment.The microstructural property,mechanical property and thermostability were investigated.The results showed that RHBC can be uniformly dispersed in the RHBC/AS-UR composite film and forming the crosslinking structure with AS-UR,exhibiting a good interface combination.Furthermore,due to the enhanced bonding strength and the improvement of the ductility,the thermostability and tensile strength of the RHBC/AS-UR composite film improved comparing with pure acetate starch film.Finally,the results of nutrients release suggested that the release rate of coated urea fertilizer decreased at first and then increased with the urea addition content. |
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