NaP Zeolite By Mass Transfer Intensification With Ultrasound And Its Adsorption Performance For Pb(Ⅱ)

In the hydrothermal process,the mass transfer by ultrasonic intensification was beneficial to achieve the regulation on the synthesis process of NaP zeolite.In the ultrasonic hydrothermal synthesis system,the effects of reaction parameters on the aging process and crystallization process as well as the hydrolysis pretreatment of silica sources on the synthesis of NaP zeolite were investigated,and the samples were characterized by the X-ray diffractometer,Scanning electron microscope,Specific surface area tester,Fourier infrared,Nuclear magnetic and other characterization methods,which were carried out to explore the regulation mechanism of ultrasonic intensification on the systhesis process of NaP zeolite,and the adsorption and regeneration properties for Pb（Ⅱ）of NaP zeolite were investigated,and the primirary conclusions were as follows:（1）NaP zeolite was synthesized by ultrasonic hydrothermal method successfully.The molar ratio of reaction materials was n（SiO₂）:n（Al₂O₃）:n（Na₂O）:n（H₂O）=1.00:0.22:0.65:100.00,and the optimized synthesis conditions were as follows.The synthesis conditions were:the aging time was 2 h,the crystallization time was 4 h,and the crystallization temperature was 120℃.The NaP zeolite synthesized under this condition had high crystallinity（85.56%）,uniform size（average particle size of 2.78μm）,good ball-like morphology,and relatively uniform pore size distribution（21.90nm）.（2）Ultrasonic external field could provide more energy for the synthesis of NaP zeolite,thereby shortening the crystallization reaction time,reducing the particle size of zeolite,increasing the specific surface area,and improving the pore structure.By comparing the crystallization kinetics results of the NaP zeolite synthesized by the ultrasonic method and the hydrothermal method,it was found that the nucleation time of ultrasonic crystallization was shortened 5/6（from 554 min to 92 min）,compared to the hydrothermally induced nucleation time,and the crystallization time of NaP zeolite was shortened from 12 h to 4 h.The particle size of NaP zeolite synthesized by ultrasound reduced 2/3（from 8.4μm to 2.78μm）in contrast with the average particle size of the hydrothermal synthesis.In addition,the NaP zeolite synthesized by the ultrasonic hydrothermal method had a larger specific surface area（14.08 m²/g）and pore volume（0.058 cm³/g）than the static hydrothermal method.（3）The pore structure of NaP zeolite was closely related to the existing forms of silicon precursors:the three-dimensional cage-like silicon gel produced by acid treatment of TEOS was conducive to the synthesis of NaP zeolite with large pore size and high specific surface area.The chain or cyclic silicons produced by alkali modification was conducive to improving the porosity of small pores.With the increase of TEOS hydrolysis time,the specific surface area and pore size of NaP zeolie increased.The optimal acid hydrolysis conditions of TEOS were 4 h at p H=1.（4）The maximum removal rate of Pb（Ⅱ）by NaP zeolite could reach 99.12%,and the maximum adsorption capacity was 59.45 mg/g.At the same time,the adsorption process of Pb（Ⅱ）by NaP zeolite was more in line with the Langmuir isothermal adsorption model,indicating that the adsorption process was the monolayer adsorption.Through the study of adsorption thermodynamics,it was found that the adsorption process of Pb（Ⅱ）by NaP zeolite was an endothermic process and could proceed spontaneously.（5）With the EDTA-2Na as the regeneration aid agent,when the concentration of the agent was 100 mg/L,the regeneration temperature was 40^oC,and the regeneration time was 1 h,the removal rate of Pb（Ⅱ）by NaP zeolite after four times adsorption-regeneration cycles reached 96.94%,indicating that the NaP zeolite synthesized by ultrasound hydrothermal had good regeneration performance.