Interaction Of Coal-Based Humic Acid With Urea And Nitrogen Regulation

The combination of clean utilization of lignite and improving the utilization rate of nitrogen fertilizers is an important research direction.In this thesis,Heihe lignite was used as raw material to extract coal-based humic acid,and combined with elemental analysis,infrared spectra,fluorescence spectra,XRD and thermogravimetric analysis to explore the effect of coal-based humic acid and humic acid complex on urea.The solid waste produced in the process of extracting humic acid from lignite was treated by carbonization,and its adsorption of NH₄⁺-N was studied.According to the important reasons for the rapid decomposition of urea in soil,the possibility of coal-based humic acid as urease inhibitor was explored.The findings are as follows:The dissolution of humic acid in urea solution is affected by temperature,reaction time,urea concentration and humic acid content.When the temperature is less than 60℃,the dissolution of humic acid in urea solution is slow.When the temperature is greater than 60℃,the dissolution rate of humic acid in urea solution is accelerated.The dissolution process of humic acid was accompanied by the hydrolysis of urea and the increase of system pH.There are many reactions between humic acid and urea solution.Dehydration reaction occurs between carboxyl group of humic acid and amide group of urea.Hydrogen bonds are formed between the carboxyl or hydroxyl groups of humic acid and the amide groups of urea.NH₄⁺ produced by hydrolysis of urea has ion exchange with carboxyl group of humic acid.The interaction between humic acid and molten urea is mainly through carboxyl and amide groups,and a small amount of water-soluble humic acid is generated during the reaction process.Humic acid solution can inactivate urease,and potassium humate solution can promote the decomposition of urea by urease by adjusting the pH of the solution.The humic acid applied to the soil can inhibit the urease activity in the soil in the early stage,and promote the urease activity in the later stage,which is related to the change of soil pH.Humic acid has an irregular structure,and humps appear in the 2θ range of 20-27°,while crystal peaks appear in water soluble urea humate.300-600℃ is the main stage of pyrolysis of water-soluble humic acid urea,and this stage will produce a large amount of CO₂,and the content of CO₂ in the pyrolysis component at 550℃ is more than 70%.Combined with elemental analysis and gel chromatography analysis,the molecular weight of water-soluble humic acid was determined to be 1493,and the molecular formula was C₇₆H₈₃O₂₇N₅.The molecular model of UHA was preliminarily constructed by infrared spectroscopy,pyrolysis-gas chromatography-mass spectrometry and solid ¹³C nuclear magnetic resonance.The molecular weight was adjusted to 1503 and the molecular formula was C₇₆H₈₉O₂₇N₅.The molded fertilizer prepared with humic acid bentonite complex as the carrier can effectively delay the release of urea in water.The residue after extracting humic acid from lignite was carbonized.Through nitrogen adsorption and desorption curves,it was found that when the ratio of residue to alkali was 1:2,the specific surface area of the carbonized product exceeded 1000 m²/g,with rich pore structure and adsorption of NH₄⁺-N.There are 60 figures,19 tables and 104 references in this thesis.