Preparation Of FeCl₃ Modified Ceramsite And Its Study On The Mechanism Of Adsorption For Phosphorus Removal

In recent years,China’s ecological environment has been dramatically improved,but eutrophication is still severe in some regions.The excessive input of nitrogen and phosphorus is the leading cause of eutrophication,and the influence of phosphorus is more prominent.Therefore,to reduce the concentration of phosphorus pollutants in water,it is imperative to find an economical and efficient technology for phosphorus removal.Among many phosphorus removal technologies,the adsorption method has attracted much attention because of its advantages of good phosphorus removal effect,simple operation,and so on.The selection of adsorbent materials has an important influence on the effect of phosphorus removal by adsorption.Among many adsorption materials,ceramsite has attracted extensive attention due to its easy access to raw materials,easy modification of functions,and renewable utilization.However,the adsorption capacity of traditional ceramsite is relatively low,and the adsorption rate is not high enough.To improve the adsorption performance of ceramsite,the modification of ceramsite has become the focus of research.The core content of this paper is to study the modified ceramsite,including modifier ratio,modification conditions optimization,modified ceramsite performance index test and microstructure characterization,adsorption and phosphorus removal characteristics,and desorption and regeneration performance research.On this basis,the microscopic mechanism of phosphorus adsorption and removal was further explored employing comparative analysis of the microstructure of modified ceramsite before and after phosphorus absorption,which made a beneficial exploration for the application of Fe Cl₃ modified ceramsite in phosphorus adsorption and removal.The main conclusions of this study are as follows:（1）Study on preparation and characterization of modified ceramsite:compared with Al Cl₃ and Fe（NO₃）₃,the Fe Cl₃ modifier has a better effect in the experiment of modifier selection.The optimal conditions were determined as Fe Cl₃ concentration of1.5 mol/L,roasting temperature of 300℃,and roasting time of three hours through the single factor test and orthogonal test.Under these conditions,Fe Cl₃ modified ceramsite was prepared with a void fraction of 45.7%,an apparent density of 1.69 g/cm³,and a bulk density of 0.92 g/cm³.SEM shows that the surface of the modified ceramsite is rough,and the pore structure is rich.EDS shows that the relative content of Fe on the surface of modified ceramsite is 8.69%.XRD shows that the main phases of the modified ceramsite are Al₂O₃,Si O₂,Ca CO₃,Fe₂O₃,and Fe（OH）₃.（2）Study on adsorption and phosphorus removal characteristics and regeneration performance of Fe Cl₃ modified ceramsite:In the single factor experiment of adsorption phosphorus removal,6.0 g/L modified ceramsite was added to the phosphorus solution with a concentration of 2.0 mg/L,and the reaction was carried out at 25℃and 120r/min for 14 hours.The phosphorus removal rate was 88.6%,and the effect was good.Under the same conditions,the phosphorus removal rate of 3.0 g modified ceramsite for 500 m L of 1-12 mg/L,p H=3-9 phosphorus solution is higher than 67.8%,and its adaptability to phosphorus concentration and p H is good.In the regeneration experiment,the desorption rate of phosphorus was 74.8%when 3.0 g modified ceramsite after phosphorus adsorption was desorbed in 0.1 mol/L Na OH solution for 6hours.The desorbed ceramsite was adsorbed in 500 m L of 2.0 mg/L phosphorus solution for 14 hours,and the phosphorus removal rate was 86.5%,only 3.1%different from the initially modified ceramsite,indicating that the modified ceramsite could be effectively regenerated.In the kinetic and isothermal adsorption experiments,the adsorption and dephosphorization process of the modified ceramsite matches the Langmuir model,which indicates that monolayer adsorption mainly occurs at the solid-liquid interface.It also follows the quasi-second-order kinetic model,indicating that the modified ceramsite mainly depends on chemisorption for phosphorus removal.（3）Study on the microscopic mechanism of adsorption phosphorus removal of Fe Cl₃ modified ceramsite:The characterization results of SEM and XRD show that the surface of the modified ceramsite is wrapped by a large amount of Al PO₄ and Fe PO₄flocculent,which indicates the chemical precipitation reaction of Al³⁺,Fe³⁺,and PO₄^3-is one of the adsorption and removal mechanisms of modified ceramsite.After phosphorus absorption,the characteristic peaks of M-OH and M-PO₄ appeared in FT-IR and XPS spectra,the area of the CO₃^2-distinct peak decreased,and the Fe 2p peak changed.These results show that there are M-O-P coordination between M-OH and phosphate/hydrogen phosphate,ion exchange between CO₃^2-and phosphate/hydrogen phosphate,and strong O-M-O=P coordination between metal atoms in metal oxides and phosphate/hydrogen phosphate in the adsorption system,which are consistent with the results obtained by using density functional theory to simulate the bonding mode between the main components of modified ceramsite and the adsorbent phosphate/hydrogen phosphate.In addition,Fe（OH）₃ and Fe₂O₃ introduced after modification have smaller LUMO energy level and electron energy level difference,indicating that Fe（OH）₃ and Fe₂O₃ have stronger attraction to phosphate/hydrogen phosphate and are more likely to participate in their adsorption process,which also verifies the reason why the modified ceramsite have more advantages in phosphorus removal.Based on the current situation of phosphorus pollution and the demand for phosphorus removal,a new adsorbent phosphorus removal material,Fe Cl₃ modified ceramsite,was prepared in this paper.The results of the research on the effect of modified ceramsite on simulated wastewater phosphorus removal and the mechanism of micro-adsorption phosphorus removal show that the modified ceramsite prepared in this paper have good phosphorus removal effect and regeneration performance,indicating that it has a good application prospect in the field of wastewater phosphorus removal.