Study On Adsorption And Application Of Humic Acid-Zeolite Composites For Ammonia Nitrogen

Excessive use of nitrogen fertilizer and low utilization rate not only increase the input cost of crops,but also pose a threat to the environment and cause eutrophication of water bodies.In order to improve the utilization rate of nitrogen fertilizer and reduce the use of nitrogen fertilizer,the nitro humic acid-modified zeolite composite material（NHA-HZ）was prepared by compression molding.The NHA-HZ after adsorption of ammonia nitrogen was applied to agriculture to supplement the nitrogen element required by plants.At the same time,the advantages of nitro humic acid（NHA）and modified zeolite（HZ）in plant growth and soil improvement were utilized to achieve the purpose of reducing the abuse of nitrogen fertilizer and promoting crop growth.Firstly,NHA and HZ were prepared,and NHA-HZ was prepared by compression molding.Secondly,the effects of different conditions on the adsorption/desorption of ammonia nitrogen were investigated by adsorption/desorption experiments,and the adsorption/desorption characteristics of ammonia nitrogen were analyzed by kinetic model and isothermal model.Finally,the effects of NHA-HZ adsorbing ammonia nitrogen（NHA-HZ-N）on the growth of lettuce and the physical and chemical properties of soil were investigated by plant experiments,and the advantages of reuse after adsorbing ammonia nitrogen were analyzed.NHA was extracted from lignite by alkali-soluble acid precipitation method.The optimum preparation conditions of NHA were obtained by single factor experiment combined with response surface method.The optimum preparation conditions were KOH concentration 0.67 mol/L,liquid-solid ratio 10 m L/g,and reaction temperature70 ^oC.Under these conditions,the yield of NHA can reach 72.36%.After the coal sample is oxidized by HNO₃,the carboxyl content in the NHA structure increases,which is beneficial to the adsorption of ammonia nitrogen.The zeolite modified by 0.10mol/L H₂SO₄ solution had the largest adsorption capacity for ammonia nitrogen.The phase composition of zeolite did not change after modification,but the hydroxyl content increased,the surface changed from smooth to rugged,the pores increased,the pores deepened,and the roughness increased.When the mass ratio of NHA and HZ is 7:3,it can better meet the requirements of adsorption and reuse.The adsorption capacity of NHA-HZ to ammonia nitrogen decreases with the increase of NHA-HZ dosage.The coexisting cations K⁺,Ca²⁺and Na⁺all inhibited the adsorption of ammonia nitrogen by NHA-HZ,and the higher the concentration of coexisting cations,the greater the influence on the adsorption process.The influence of different cations on the adsorption of ammonia nitrogen by NHA-HZ was K⁺>Ca²⁺>Na⁺.The weakly alkaline environment（p H=9）is more conducive to the adsorption and desorption process of ammonia nitrogen.Reducing temperature is beneficial to the adsorption process of ammonia nitrogen,and increasing temperature is beneficial to the desorption process of ammonia nitrogen.The pseudo-second-order kinetic model is more suitable for describing the adsorption and desorption process of ammonia nitrogen,and the Freundlich isotherm model is more suitable for describing the adsorption process of ammonia nitrogen.Compared with NHA-HZ,the relative content of O-C=O in NHA-HZ-N is lower,and the thermal stability is reduced.It is speculated that O-C=O may be involved in the adsorption process of ammonia nitrogen.The pot experiment showed that the application of NHA-HZ and NHA-HZ-N was helpful to the growth of lettuce,which was mainly manifested in the vigorous growth of seedlings,the increase of leaves,the increase of chlorophyll content and soluble sugar content,and the promotion effect of NHA-HZ-N on the growth of lettuce was more obvious.The addition of NHA-HZ and NHA-HZ-N can also increase soil cation exchange capacity,and the effect of NHA-HZ-N is more obvious.This thesis has 51 figures,14 tables and 111 references.