Limestone-based Hydroxyapatite-coated And Its Composite Materials For Removing Cu(?) From Wastewater

In recent years,with the development of the global economy and rapid population growth,water pollution has become an increasingly serious problem worldwide.Due to human activities,a large number of industrial and agricultural and domestic pollutants are discharged into the water environment,causing water pollution and posing a serious threat to the health of aquatic organisms and human bodies.In addition,there are many types of water pollutants,the heavy metal copper is one of the refractory water pollutants,it does not naturally degrade when it enters the water environment.Therefore,it has become a domestic and foreign research to find scientific and effective methods to remove metal copper in water one of the key points.Adsorption is the most widely used method and has proven to be an economical alternative to remove trace metals from water.Hydroxyapatite(HAP)is one of the components of bones and teeth of vertebrates,and is usually used as a biological material,HAP structure is also often used as an adsorbent due to its porous structure and surface active sites.Due to the limited pore structure and surface active sites in pure HAP,poor mechanical properties,and greater brittleness,the application of pure HAP in the actual adsorption process is limited.Chitosan(CS)has good biodegradability and adsorption properties for heavy metals.Incorporation of CS into HAP to form composite materials has attracted widespread attention in recent years.The purpose of this thesis is to improve the adsorption performance of HAP and the stability of the material.limestone-based HAP-coated,limestone-based doped HAP-coated,and limestone-based CS/HAP-coated composites were successfully prepared by the blending method,and experiments were designed to study the adsorption of Simulate the adsorption performance of heavy metal copper in aqueous solution.Characterization and analysis of materials by technologies such as X-ray diffraction(XRD),Fourier infrared spectroscopy(FT-IR),thermogravimetric analyzer(TGA),specific surface and pore size distribution analyzer(BET),and scanning electron microscope(SEM),the material adsorption mechanism for heavy metal copper is further drawn,which provides enlightening suggestions for the practical application of the adsorbent.The main research contents of this paper are as follows:(1)First,limestone-based HAP-coated was successfully prepared and used as an adsorbent to treat simulated copper-containing wastewater.We studied the effects of time,temperature,initial copper ion concentration,coexisting anions and cations on copper ion removal.The results show that the limestone-based HAP-coated can efficiently and stably remove copper ions in the aqueous solution,and the adsorption reaction basically reaches an equilibrium state within 120 minutes.When the temperature was 30? and the initial copper ion concentration was 20 mg·L-1,the adsorption capacity of limestone-based HAP-coated for Cu2+ in the solution was 90.90 mg·g-1.When the initial concentration of the solution was from 20 to 50 mg·L-1,the adsorption capacity of Cu2+ in the solution by limestone-based HAP-coated gradually increased,and when the temperature was from 20?50?,The adsorption capacity of limestone-based HAP-coated for Cu21in solution also sriowed an increasing trend.Through the study of adsorption isotherm,adsorption kinetics and thermodynamics,the adsorption mechanism of Limestone-based HAP-coated on copper ions is ion exchange and electrostatic interaction on the surface of the adsorbent.In addition,the study have shown that the limestone-based HAP-coated prepared by us is a low-cost and highly efficient adsorbent,and has a strong practical application prospect.(2)Then the effects of Mg2+ and Sr2+ ions on the structure and adsorption properties of limestone-based HAP-coated were studied.In the process of preparing limestone-based HAP-coated chlorides containing two kinds of ions Mg2+ and Sr2+were mixed to obtain two kinds of metal ion doped limestone-based HAP-coated,and copper ion adsorption experiments were performed using the limestone-based doped HAP-coated.According to the experimental results,it can be seen that the adsorption performance:Limestone-based doped Mg2+ HAP-coated>Limestone-based doped Sr2+HAP-coated>Limestone-based HAP-coated,limestone-based doped Mg2+ HAP-coated has a better structure and a larger specific surface area.During the preparation of materials,the incorporated Mg2+ and Sr2+ can replace the position of Ca2+ on the surface of the limestone-based HAP-coated and change the structure of the limestone-based HAP-coated.The mechanism of limestone-based doped HAP-coated to adsorb copper ions is still ion exchange and electrostatic interaction.However,the incorporation of Mg2+ and Sr2+ enhanced these two effects,especially Mg2+.The research shows that limestone-based doped Mg2+ HAP-coated has better structural properties and adsorption capacity,and has low preparation cost and non-toxicity of the adsorbent,which has certain prospective significance for the development of efficient and low-cost adsorbents.(3)Finally,the effect of chitosan(CS)on the adsorption properties of limestone-based HAP-coated was studied.During the experiment,limestone-based CS/HAP-coated composites were prepared by changing the amount of chitosan added(0.5 g,1.0 g,1.5 g,2.5 g).The adsorption of copper ions by limestone-based CS/HAP-coated composites was studied by adsorption experiments performance.The effects of adsorption parameters such as time,temperature,and initial copper ion concentration on copper ion adsorption were investigated.The results show that limestone-based CS/HAP-coated prepared by adding 0.5 g of CS shows the best adsorption performance.At a temperature of 30? and an initial concentration of copper ions of 20 mg·L-1,the adsorption capacity of limestone-based CS/HAP-coated for Cu2+ was 122.84 mg·g-1.In addition,as the amount of CS added increased,the adsorption performance of limestone-based CS/HAP-coated on Cu2+ showed a downward trend,and compared with limestone-based HAP-coated,limestone-based CS/HAP-coated composites exhibit better thermal stability.The study showed that the introduction of chitosan further enhanced the limestone-based HAP-coated ability to adsorb copper ions and the thermal stability of the adsorbent material,greatly expanding the practical application range of limestone-based CS/HAP-coated composites.