Preparation And Application Of Fly Ash-based Soil Conditioner With Nitrogen And Phosphorus Adsorption Properties

Excessive phosphate and ammonium salts in the water system will lead to eutrophication,which will bring serious ecological pollution to the water environment,and serious soil degradation will lead to the reduction of crop yields.In this paper,a low-cost solid waste fly ash（FA）was used as raw material to prepare a FA-based soil conditioner with excellent nitrogen and phosphorus adsorption properties,and its adsorption properties and removal mechanism for nitrogen and phosphorus were studied.The improvement of FA-based soil conditioners on the soil quality of red loam and the effects on agronomic characters,yield and quality of tomatoes were investigated.The specific research results are as follows:（1）Mesoporous tobermorite（TFA）prepared with FA can effectively remove phosphate and ammonium salts from water.The physicochemical properties of TFA were determined by X-ray fluorescence（XRF）,X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,Brunauer-Emmett-Teller（BET）,X-ray photoelectron spectroscopy（XPS）and scanning electron spectroscopy Microscopy-energy dispersive spectroscopy（SEM-EDS）was used for characterization.The results showed that TFA had larger specific surface area,pore volume and average pore size,which increased from 22.05 m2/g,0.04589 cm3/g and 8.323 nm for FA to 84.17 m2/g,0.2668 cm3/g and 12.68 nm for TFA.The removal efficiency of phosphate and ammonium salts increased from 26.57%and 14.40%of FA to 54.40%and 19.53%of TFA.The adsorption kinetic data of phosphate and ammonium salts on FA and TFA were more in line with the pseudo-second-order model.The mechanism of phosphate removal by TFA is due to electrostatic attraction and the formation of Ca HPO₄·2H₂O precipitation.Meanwhile,TFA removes ammonium salts through adsorption and interaction with-OH in TFA to generate NH₃·H₂O.Therefore,TFA can be used as an efficient and economical adsorbent for the adsorption of phosphate and ammonium salts in water,and the TFA after adsorption of nitrogen and phosphorus can be used as an effective nitrogen and phosphorus slow-release fertilizer.（2）FA-based soil conditioners can improve the physical and chemical properties of red loam:soil bulk density is reduced by 4.84%,soil porosity,water content and water retention performance are increased by 11.44%,17.93%and 58.41%,respectively.Plough layer structure of soil;soil p H value and soil organic matter content also increased,especially soil available silicon content increased significantly,increased by165.19%,indicating that soil fertility was significantly enhanced;and heavy metal ions such as Cr,As,Cd,and Pb in soil The content is far lower than the screening value of agricultural land soil pollution risk.At the same time,the plant height and stem diameter of tomatoes increased by 48.26%and 33.69%,respectively;the horizontal diameter,vertical diameter,fruit number and single fruit weight of the fruit increased by 21.31%,22.71%,81.08%,and 49.26%,respectively.The results showed that the FA-based soil conditioner showed a good growth advantage to tomato plants at the seedling stage,and maintained until the late growth stage.Appropriate application of fly ash-based soil conditioner can significantly improve the soluble sugar,soluble protein,vitamin C,nitrate content and other qualities of tomato fruit,and the content of heavy metal elements such as Cr,As,Cd,Hg,and Pb in tomatoes is far lower than Corresponding national standard limits.This research will provide a certain theoretical and technical basis for the high-value resource utilization of fly ash,soil improvement in red loam planting areas,and improvement of tomato yield per unit.