Study On Preparation,Loading Of Magnesium Oxide-based Nanomaterials And Their Adsorption Properties For Fluoride And Heavy Metals In Water

In many areas of China,especially where groundwater is the source of water,the phenomenon of excessive fluorine content in drinking water is very common.At the same time,the unauthorized discharge of heavy metal wastewater has also caused the heavy metal content in many inland lakes,reservoirs and groundwater to exceed the standard to a certain extent.These pollution problems not only damage the natural ecological environment,but also pose a huge threat to the health of the people.In the process of water treatment,the adsorption method is widely used as a treatment method that is environmentally friendly,simple to operate,economical in cost,and stable in effect.However,most of the existing adsorbents generally have the problems of low adsorption capacity for fluoride ions and heavy metal ions,long adsorption time,easy to be affected by pH and coexisting ions,etc.,and have certain limitations in the actual application process.Due to the advantages of larger specific surface area and higher surface free energy,magnesium oxide nanomaterials is considered to be an ideal adsorbent material which can provide more active sites than traditional adsorbent materials in adsorption.But the larger surface energy also makes the nanomaterials unavoidably prone to agglomeration problems,which greatly reduces the adsorption performance of such materials in practical applications.Therefore,it is important to develop an adsorbent with good dispersibility,excellent adsorption performance,wide pH range and less influence by coexisting ions.Based on the above problems,this study started from designing and preparing magnesium oxide-based nano-adsorbent materials,regulating the morphology of the materials and the loading of the materials,studied the adsorption properties of the prepared magnesium oxide-based nano-adsorbent materials to simulated pollutants,and further explored adsorption mechanism of magnesium oxide-based nano-adsorption materials.The main research contents of this paper are as follows:?1?Five groups of Mg-Al composite oxides with different ratios of magnesium and aluminum were prepared by hydrothermal method,the phase composition and morphology structure of the materials were compared,and the adsorption properties of the materials to fluoride ions and heavy metal ions were studied.The results show that when the magnesium-aluminum ratio is 3:1,the synthesized Mg-Al composite oxide has a good dispersibility and a uniform flower-like three-dimensional structure,and it has good adsorption effect on F^-,Pb²⁺,Cd²⁺,Mn²⁺and Cr⁶⁺in water.The maximum adsorption capacity can reached 125,934.58,1027,380.23 and 129.03 mg/g,respectively.The adsorption process can also be well fitted with Langmuir isothermal model and pseudo-second-order kinetic model.The pH range has little effect on the adsorption of fluoride ions,but the presence of CO₃^2-,HCO₃^-and PO₄^3-in water will significantly reduce the adsorption efficiency.In addition,the hydroxyl groups and carbonate co-exchange adsorption mechanism was also discovered.According to the above conclusions,the prepared Mg-Al composite oxide has certain application prospects as an adsorbent for removing fluoride ions and heavy metals in water.?2?The magnesium oxide hollow microsphere structure with good dispersibility was synthesized under the conditions of high temperature,high pressure and high solution viscosity.The phase composition and morphological structure were studied by characterizing,the effects of its adsorption performance on fluoride and heavy metal ions in water,pH and co-existing ions were discussed,and the adsorption mechanism was also analyzed.The results show that the unique hollow microsphere structure gives magnesium oxide excellent adsorption properties for fluoride ions and heavy metal ions.The saturated adsorption capacities of F^-,Pb²⁺and Cd²⁺in water are 198.02,1553.62 and 1562.47 mg/g,respectively.The adsorption process can be well fitted with Langmuir isotherm model and pseudo-second-order kinetic model,indicating that the adsorption process is monolayer chemical adsorption.In the wide pH range of 2¹2,magnesium oxide hollow spheres can have a high removal rate of F^-,and can also keep a high removal rate of Pb²⁺and Cd²⁺in the pH range of 3⁸.The results of co-existing ions show that the presence of CO₃^2-and HCO₃^-in solution will reduce the adsorption efficiency of F^-.Through mechanism analysis,the adsorption of fluoride ions by magnesium oxide hollow spheres is mainly based on the co-exchange mechanism of hydroxyl groups and carbonate,the mechanism of cationic heavy metal ions is the exchange of surface hydrogen ions with heavy metal ions,then heavy metals are adsorbed on the surface of the magnesium hollow sphere through oxygen atoms in the hydroxyl group.Based on the above conclusions,as an economical,environmentally friendly and efficient adsorbent,magnesium oxide hollow sphere material has a strong application prospect in practical treatment.?3?Four groups of magnesium oxide adsorption materials with different morphologies were successfully synthesized using hydrothermal method by adjusting the viscosity of the reaction system,and studied the adsorption properties of the four groups of materials for fluoride ions and heavy metal ions.The results show that with the increase of the viscosity value of the solution,the morphology of magnesium oxide will gradually change from an irregular bulk structure to a uniformly dispersed spherical hierarchical structure.Through comparison and selection,it was found that the magnesium oxide material prepared at the viscosity of 27.7 mPa·s had the best adsorption performance,and its saturated adsorption capacity of F^-,Pb²⁺,Cd²⁺and Mn²⁺in water can reached 209.64,1988.2,1579.04 and 649.35 mg/g,respectively.The adsorption process can be well fitted with Langmuir isotherm model and pseudo-second-order kinetic model,indicating that the adsorption process is monolayer chemical adsorption.The above conclusions indicate that the magnesium oxide nanomaterials synthesized by viscosity control have good adsorption performance,and the magnesium oxide hierarchical microspheres prepared at high solution viscosity values can efficiently remove fluoride ions and cationic heavy metal ions in water.?4?A composite adsorption material with magnesium oxide micro-nano hierarchical structure loading on pumice was designed and prepared,and its adsorption performance for fluoride ion in water was studied preliminarily.The results show that the loading of magnesium oxide greatly improves the adsorption performance of pumice,and the adsorption performance of the composite material on F^-is improved by 2.3 times compared with pumice under the same conditions.The adsorption process can be well fitted with Freundlich isotherm model.The pumice-loaded magnesium oxide composite adsorbent material overcomes the shortcomings that nano materials are difficult to separate in water treatment applications,and provides a solution for the loading of magnesium oxide micro-nano hierarchical structure.Figure[46]table[27]reference[153]...