Preparation Of Magnetic Layered Double Hydroxides And Its Removal Of Phosphate From Water

In recent years,excessive discharge of nitrogen and phosphorus has led to serious eutrophication of water,which has become one of the most serious water environmental problems in China.Phosphorus is the main element that causes water environment problems.Reducing the concentration of phosphorus in water is always the main research direction of water pollution control.Adsorption method has attracted much attention in the field of phosphorus pollution control because of its advantages such as low cost,controllable reaction and phosphorus resource recovery.Magnetic layered double hydroxides(magnetic LDHs)adsorbent has high adsorption capacity and rapid solid-liquid separation performance,which provides a necessary prerequisite for recycling.However,its industrial application is seriously hindered due to the cumbersome preparation procedures of its existing methods.To solve the above problems,a new method of preparing magnetic LDHs adsorbent with simple preparation process was developed in this paper,which was based on aluminum ferroalloy and introduced magnesium salt.Studied the best condition of preparation of magnetic LDHs,and carries on the characterization analysis,under the condition of different phosphorus removal performance of magnetic LDHs and recycling performance,and stability test,the isothermal adsorption kinetics of phosphate,and thermodynamics data is analyzed,combined with SEM,XRD,FTIR,Zeta potential before and after adsorption and XPS characterization methods,to explore the mechanism of adsorption.Results show that the best alkali etching time is 4 h,stirring time is 2 h after add magnesium salt,sodium hydroxide solution concentration is 1 mol L1,particle size of the alloy mesh for 20-40 mesh,iron content is 10%,the best conditions LFe10(Fe account for 10%of the total mass),specific surface area of 106.09 m2 g-1 to 40 mg L-1 phosphate removal rate can reach more than 99%,and saturated magnetization can reach 6.51 emu g-1,can be achieved within 20 s fast solid-liquid separation,its largest adsorption capacity can reach 81.2 mg g-1.SO42-,Cl-and NO3-have little inhibition effect on phosphate adsorption by LFe10.Na2CO3 is the best regenerating agent for magnetic hydrotalcite.When the concentration is 0.1 mol L-1,the regeneration rate can still reach more than 70%after 5 cycles.The magnetic LDHs before and after calcination had lower release rates of Mg,Al and Fe metal ions.The presence of Fe3O4 improves the adsorption capacity and chemical stability of the composites.The adsorption of phosphate by magnetic LDHs conforms to the pseudo-second-order kinetics and Langmuir adsorption isotherm model,indicating that chemical adsorption is the main adsorption mechanism.Thermodynamic analysis shows that the adsorption is spontaneous and goes in the direction of increasing entropy.According to the comprehensive characterization analysis,the adsorption mechanism of magnetic hydrotalcite on phosphate is mainly electrostatic attraction,inner sphere complexation and anion exchange between layers.It provides a theoretical basis for the further treatment of phosphorus pollution in water environment and the modification of adsorbents.