Preparation And Preparation Of Spherical Y₂O₃ Nanoflowers And La(OH)₃/SiO₂ Aerogels Study On The Adsorption Of Phosphorus In Water

Phosphate is an important element causing eutrophication of water body.Efficient removal of excess phosphate in water body has become a research focus in water environmental governance.Therefore,it is very necessary to set up a phosphate removal process before the discharge of phosphate-containing wastewater.There are many phosphate removal methods in water body,but the adsorption method is recognized as one of the phosphate removal technologies with great application prospects because of its advantages of simple operation,high selectivity and economic and effective treatment process.Rare earth compounds have been widely studied because of their special adsorption activity to phosphate.However,common rare earth metal oxides or hydroxides tend to have low adsorption capacity,insufficient utilization of active sites and low efficiency due to their structural shortcomings such as low surface area and small pore volume.Therefore,it is a great significance to study the adsorption sites for efficient utilization of rare earth metal oxides and hydroxides to save resources and improve adsorption efficiency.In this study,spherical Y₂O₃ nano-flower phosphate removal adsorbent and La（OH）₃/Si O₂aerogel phosphate removal adsorbent were prepared by hydrothermal method and impregnation precipitation method respectively.The preparation method of spherical Y₂O₃ nano-flower phosphate removal adsorbent was to use yttrium nitrate hexahydrate,polyethylene pyrrolidone（PVP）and urea as raw materials.In the polytetrafluoroethylene high-pressure reaction kettle,using hydrothermal self-assembly to get a tightness spherical Y（OH）CO₃ precursor.Then,the precursor was placed in muffle furnace,calcination at high temperature under empty atmosphere.Finally,the spherical Y₂O₃ nano-flower sample was obtained.The preparation method of La（OH）₃/Si O₂ aerogel phosphate removal adsorbent was to use lanthanum nitrate hexahydrate and Si O₂ aerogel as raw materials.Put Si O₂ aerogel in lanthanum nitrate solution,and impregnated for a certain time.Then,sodium hydroxide solution was dropped into the above solution to adjust the p H value of the solution,and aging for a certain time.Finally,La（OH）₃ was load on Si O₂ aerogel successfully.The static adsorption experiment of simulated phosphate containing wastewater was carried out by using the two adsorbents mentioned above.The effects of single factor variables such as initial p H,coexisting ions and dosage on phosphate removal were studied.The adsorption kinetics,isothermal adsorption model and adsorption thermodynamic model were fitted.The zero-point potential of adsorbent was determined by potential drift method.SEM,TEM,XRD,BET,FTIR and XPS were used to analyze the adsorbent samples and explore the adsorption mechanism of adsorbent.The adsorption mechanism was also discussed.BET characterization results of spherical Y₂O₃ nano-flower showed that the specific surface area of the material was 14.15 m²·g^-1,which was nearly 14 times that of purchasing Y₂O₃.The adsorption experiment results showed that when the dosage of adsorbent was 0.6g·L^-1,the removal rate of adsorbent was closely to 100%.Spherical Y₂O₃ nano-flower maintain a high adsorption capacity in a wide p H range.When coexisting with Cl^-,SO₄^2-,CO₃^2-and NO₃^-ions,except CO₃^2-,the ions had little effect on the adsorption capacity of phosphate,indicating that spherical Y₂O₃nano-flower had high selectivity for phosphate.In this experiment,the correlation coefficient of pesudo second-order kinetic model fitting was good,indicating that the adsorption process of spherical Y₂O₃ nano-flower on phosphate was mainly controlled by chemisorption.The Langmuir isothermal adsorption model was well fitted,and the adsorption of phosphate on spherical Y₂O₃ nano-flower was single-layer adsorption,and the maximum theoretical adsorption capacity was 103.7 mg·g^-1.The adsorption thermodynamics showed that the adsorption capacity increased with the raising of temperature,which proved that the adsorption process of spherical Y₂O₃ nano-flower on phosphate was endothermic process.The△G value was negative,indicating that the adsorption reaction was spontaneous.Combined with FTIR,XPS and other characterization methods,it was speculated that the main adsorption effect of spherical Y₂O₃ nano-flower on phosphate might be electrostatic attraction and coordination exchange.When the adsorption capacity was calculated in unit of La element,the adsorption experiments of La（OH）₃/Si O₂aerogel showed that the adsorption capacity of AER-La0.2reached 294.1 mg·g^-1（La）.When the dosage of adsorbent was 0.4 g/L,the adsorption capacity was the highest.AER-La0.2 maintained high adsorption capacity in weak acid and neutral solution.When coexisting with Cl^-,SO₄^2-,CO₃^2-and NO₃^-ions,except CO₃^2-,the ions had little effect on the adsorption capacity of phosphate,indicating that AER-La0.2 has high selectivity for phosphate.The fitting correlation coefficient of pesudo second-order kinetic model was good,indicating that the adsorption process of AER-La0.2 was mainly controlled by chemisorption.The Langmuir isothermal adsorption model was well fitted.The adsorption of phosphate by AER-La0.2 was single-layer adsorption,and the maximum theoretical adsorption capacity was 19.31 mg·g^-1.Adsorption thermodynamics showed that the adsorption capacity increases with the rasing of temperature,which proved that the adsorption process of AER-La0.2 on phosphate was endothermic.The value of△G was negative,which proved that the adsorption reaction was spontaneous.Combined with FTIR,XPS and other characterization methods,the main adsorption action of La（OH）₃/Si O₂aerogel on phosphate may be electrostatic attraction and coordination exchange,among which the complex forms obtained after coordination exchange were mononuclear single tooth,mononuclear double tooth and binuclear double tooth.