Study On The Removal Of Water Pollutants By Modified MAl₂O₄ Adsorbents

In recent years,the continuous development of industry has caused people's living standard increase steadily.However,pollutants such as heavy metals and dyes in water bodies have caused serious threats to the environment and human health with the increase of anthropic production activities and improper management.At present,adsorption is still a practical method in water pollution treatment technology.One of the hot research directions in this field is researching and developing adsorbent materials with abundant resources,cheap,easy to prepare,and exhibiting excellent performance.Aluminate MAl₂O₄ has excellent properties such as high thermal stability,low surface acidity,and corrosion resistance,which cause it has a wide range of applications in the fields of catalysis,electronics,optics,and materials,but there are few studies on its use in adsorption.In this paper,aluminate modified materials NiAl₂O₄-NH₂ and CuAl₂O₄-EDTA were synthesized and applied to the study of adsorption and removal of heavy metal ions and organic dyes in water.The basic research work is summarized as follows:Using Ni?NO₃?₂·6H₂O and Al?NO₃?₃·9H₂O as the metal source and urea as the modifier,the template-free hydrothermal method and the subsequent annealing process were used to synthesize three-dimensional Tremella-like Ni Al₂O₄-NH₂adsorbent,the adsorption properties of Pb²⁺,Cr³⁺,Cd²⁺,Cu²⁺,Co²⁺,Zn²⁺,methyl blue and Congo red were also studied.Under the best experimental conditions,the adsorption removal efficiencies of this material for the above six metal ions and two anionic dyes were 92.42%,96.53%,96.78%,95.37%,75.17%,99.80%and 95.3%,98.8%,respectively.The adsorption process can be described by the Langmuir adsorption isotherm model,the adsorption capacities of Pb²⁺,Cr³⁺,Cd²⁺,Cu²⁺,Co²⁺,Zn²⁺,methyl blue,and Congo red can reach 97.63 mg·g^-1,99.53 mg·g^-1,28.22mg·g^-1,118.86 mg·g^-1,22.71 mg·g^-1,43.38 mg·g^-1,163.10 mg·g^-1,144.68 mg·g^-1,respectively.NiAl₂O₄-NH₂ adsorption of heavy metal ions and dyes follows quasi-second-order kinetic model,and each target can reach adsorption equilibrium within 60 minutes.The adsorption process is controlled by both surface adsorption and intraparticle diffusion,of which surface adsorption dominates.Using the isoelectric point of the adsorbent itself and the changes in the infrared spectrum before and after the adsorption reveal the adsorption mechanism:adsorption of metal ions through chelation and ion exchange,and adsorption of methyl blue and Congo red through hydrogen bonding and electrostatic interaction.Sequential adsorption experiments show that after washing and drying the adsorbent which was firstly used to adsorb six heavy metal ions was then used to adsorb the dyes,the adsorption efficiencies for methyl blue and Congo red were hardly affected,and vice versa.Using Cu?NO₃?₂·3H₂O,Al?NO₃?₃·9H₂O,urea and ammonium fluoride as raw materials,CuAl₂O₄ was synthesized by hydrothermal method,then EDTA was modified to its surface by low temperature water bath method to prepare a bulk CuAl₂O₄-EDTA adsorbent.The adsorption properties of the adsorbent for Pb²⁺,Cr³⁺,Cd²⁺,malachite green,and toluidine blue in single-component metal ion system,single-component dye system and mixed metal ion-dye system were investigated.The experimental results show that the adsorbent exhibits excellent adsorption performance for all five target pollutants.When pH=5,it can reach more than 80%adsorption after shaking at room temperature for 30 minutes,and the saturated adsorption capacities are 105.34 mg·g^-1,117.64 mg·g^-1,44.10 mg·g^-1 and 145.00mg·g^-1,160.85 mg·g^-1,respectively.The adsorption process can be described by Langmuir monolayer isothermal adsorption model and quasi-second-order kinetic model.The fitting result of Weber-Morris model shows that the speed control steps are surface adsorption and intra-particle diffusion,in which surface adsorption plays a major role.The adsorbent has different action sites for heavy metal ions and dyes:adsorption of heavy metal ions is through chelation of functional groups on the surface of the material;dyes are adsorbed through electrostatic action.Therefore,the adsorption of heavy metal ions and dyes did not interfere with each other in sequential adsorption experiments and metal-dye mixed system co-adsorption experiments.