Removal Of Phosphorus Pollutants In Water By Hydrated Oxide Nanocomposite And Its Mechanism

Eutrophication of water bodies is a recognized global problem that seriously affects the safety of the ecological environment and threatens the sustainable development of human society.One of the reasons for the eutrophication of the water body is the excessive phosphorus input into the water body.Therefore,how to quickly and efficiently treat the eutrophication of the water body and control the endogenous phosphorus pollution in the lake has become a hot issue in our research.Lanthanum modified adsorbent has become one of the most widely studied phosphorus removal materials due to its excellent phosphorus removal effect.In order to further reduce the cost of phosphorus removal and improve the stability and biological safety of the phosphorus removal agent,this paper selected two-dimensional(2D)layered kaolin and one-dimensional(1-D)halloysite nanotubes as the adsorption material substrate,using Co-precipitation method loaded the lanthanum and aluminum in lanthanum chloride and aluminum chloride onto the substrate,and measured and analyzed the basic physical and chemical properties of the lanthanum aluminum modified layered kaolin adsorbent and halloysite nanotube adsorbent.The adsorption-desorption characteristics of orthophosphate in water by these three modified materials under different environmental conditions were studied,and the metal leaching amount of the adsorbent was analyzed in conjunction with ICP-MS to explore the stability of the material during the adsorption process.The main findings are as follows:(1)Using porous two-dimensional(2D)layered kaolin as the base material,the lanthanum and aluminum ions with a molar ratio of 1:10(La/Al)are loaded on the kaolin material by co-precipitation method to prepare the lanthanum aluminum modification Kaolin-LA kaolin,and the structure of lanthanum aluminum modified kaolin was analyzed.The results show that the specific surface area of the lanthanum-aluminum modified kaolin is nearly 100 m2g-1 higher than that of the commercial phosphorus locking agent Phoslock(?),which is about 9 times higher than that of the kaolin before modification.In the XRD spectrum,the characteristic peaks of aluminum hydroxide and lanthanum hydroxide were seen,and it was observed in the image of the high-resolution field emission projection electron microscope that the surface of the modified material changed from an irregular lattice arrangement to a regular lattice arrangement.At the same time,it can be clearly seen in the scanning electron microscope and transmission electron microscope images that the surface of the modified layered kaolin changed from smooth to rough,which confirms that the surface structure of the material has changed.According to the X-ray energy spectrum mapping,it is confirmed that this structural change is due to the uniform loading of lanthanum and aluminum on the surface of kaolin,and shows that the lanthanum element accounts for 6.4 wt%,and the aluminum element accounts for 3.4 wt%.(2)Using one-dimensional(1-D)halloysite nanotubes as the main material,the lanthanum and aluminum ions with a molar ratio of 1:10(La/Al)are loaded on the hallosite by thermal modification and co-precipitation On the stone material,HNT-LA and HNT400-LA(calcined at 400℃)were prepared,and the characteristics of halloysite nanotubes were analyzed and determined.The results show that the specific surface area of HNT-LA is about 77.8 m2g-1,which is nearly 55 m2g-1 higher than that of the halloysite nanotubes before modification,and the specific surface area of HNT400-LA is about 94.0 m2g-1.It was nearly 70 m2g-1 before modified.XRD results showed that the modified material showed obvious diffraction peaks of aluminum hydroxide and lanthanum hydroxide,proving the existence of lanthanum hydroxide.In the high-resolution field emission projection electron microscope image,it can be observed that both HNT-LA and HNT400-LA have lattice fringes with a spacing of 3.3,and the diffraction peak of lanthanum hydroxide with a 20 of about 26.6 on XRD is calculated by the Bragg equation The results are consistent.At the same time,the scanning electron microscope and transmission electron microscope images also confirmed that the surface structure of the material changed,and this change was caused by the presence of lanthanum hydroxide and aluminum hydroxide.(3)The effect and mechanism of three lanthanum and aluminum modified adsorbents on the removal of orthophosphate in water were studied.The effect of pH on the adsorption effect was studied,and it was found that as the pH increased,the adsorption capacity of the adsorbent gradually decreased.At a pH of 4.0,HNT-LA adsorbed 27.2 mgP g-1 of orthophosphate,due to Kaolin-LA and HNT400-LA.At the same time,at pH=6.5,the desorption rate of phosphate by Kaolin-LA is 0.017%,compared with the other two adsorption materials,it has the best ability to fix orthophosphate.The adsorption isotherm is more suitable for Freundlich adsorption isotherm equation,so it is speculated that the adsorption process of these three lanthanum aluminum modified adsorbents for phosphate is mainly irregular multimolecular layer adsorption.According to the kinetics of adsorption in accordance with the quasi-second-order equation,it can be inferred that during the adsorption reaction,the reaction mechanism is dominated by chemical adsorption,that is,the adsorption reaction may be controlled by electron sharing or electron transfer between the adsorbent material and the phosphate ion.In addition,the leaching concentration and leaching amount of lanthanum ion and aluminum ion were determined in the range of pH=6.0,7.0 and 8.0 combined with ICP-MS analysis.The results showed that the three adsorbents of Kaolin-LA,HNT-LA and HNT400-LA The leaching amount of aluminum ions is much lower than the leaching amount of aluminum ions in Phoslock,indicating that Kaolin-LA,HNT-LA and HNT400-LA three adsorbents have excellent biological safety compared with commercially available phosphorus locking agents.The adsorption contribution of the adsorbent was discussed,and it was found that lanthanum hydroxide and aluminum hydroxide on the adsorbent dominated Compared with the phosphorus-locking agent,the cost of phosphorus removal also shows superior economic benefits,which provides a certain guiding significance for the subsequent study of the biological safety of phosphorus-removing adsorbents and cost reduction.