Study On The Occurrence Mechanism Of Phosphorus At The Interface Of Typical Minerals In Variable Charge Soils In South China

Southern China is an important agricultural production base in China.Phosphorus,as an important nutrient element,restricts the development of local agricultural production.At the same time,the eutrophication of slow flow water caused by nitrogen,phosphorus and other nutrients has also attracted much attention in recent years.Most of the soils in southern China are variable charge soils.The soil pH is acidic and rich in iron and aluminum oxides,has a strong fixation effect on phosphorus and form closed storage phosphorus easily,which is difficult to be absorbed and utilized by plants,and is easy to enter the water body,resulting in the risk of non-point source pollution.The high content of iron and aluminum oxides is a significant feature different from other soils in southern China.Therefore,the migration and transformation process of phosphorus in soils in southern China is studied,It is necessary to clarify the environmental behavior of phosphorus at the iron oxide interface.In addition,heavy industries such as metallurgical industry and battery manufacturing are developed in the south of China.In addition,due to the soil forming parent material,all kinds of anion and phosphorus often coexist in the soil environment,which has an impact on the environmental behavior of phosphorus.Moreover,the high temperature and rain in the south,frequent and intense hydrothermal processes,make the soil prone to isomorphic substitution in the process of soil formation,and form various aluminum substituted iron oxides,which further affect the interface chemical behavior and characteristics of iron oxides.Based on this,the purpose of this research is to explore the environmental behavior process of phosphorus from the following three aspects:（1）the environmental behavior process of phosphorus at the typical mineral interface in variable charge soil;（2）The effect of cation and anion on phosphorus adsorption at typical iron oxide interface;（3）Effect of aluminum substitution on adsorption and fixation of phosphorus by iron oxide.Taking the adsorption experiment as the main research method,this thesis explores the adsorption behavior of phosphorus at the interface of iron oxide through basic adsorption experiments such as p H effect,ionic strength effect,adsorption isotherm and adsorption kinetics.Combined with Zeta potential,X-ray diffraction spectroscopy（XRD）,high-resolution transmission electron microscopy（HRTEM）,X-ray photoelectron spectroscopy（XPS）and infrared spectrum（IR）,analyzed the micro chemical mechanism of phosphorus adsorption at different mineral interfaces,coexistence with anion and cation at goethite interface and adsorption and fixation at aluminum substituted iron oxide interface from the micro level.Through the analysis of experimental data,the following main conclusions are drawn in this experimental system:（1）The adsorption capacity of iron oxide for phosphorus is greater than that of aluminum silicon oxide,and the adsorption efficiency of goethite is higher than that of hematite,The adsorption kinetics of phosphorus adsorption at the interface of goethite and hematite fit the pseudo-second-order kinetic model well,which belongs to chemical adsorption,the adsorption isotherms fit Langmuir model well,mainly monolayer adsorption.（2）When phosphorus and anions coexist at the goethite interface,the inhibition of arsenate ions with similar structure is the strongest,and there is electrostatic repulsion and co-adsorption site competition,The coexistence of phosphorus and cationic Cd（Ⅱ）is controlled by different mechanisms at different concentration ratios,which are electrostatic attraction,forming ternary complexes and coprecipitation.（3）Aluminum isomorphic substitution will change the grain size,crystallinity,morphology,Zeta potential,surface functional groups and specific surface area of iron oxide.Aluminum substituted goethite has higher crystallinity,smaller particles and lower adsorption efficiency for P（V）,the crystallinity of aluminum substituted hematite becomes weaker and the particles become larger,and the adsorption efficiency of P（V）increase.