The Influence Of Organic Matter On The Process Of Coagulation To Remove Fluoride And The Application Of New Hydroxyapatite

With the rapid development of technology in China,the sanitation and safety of drinking water environment are getting more attention,excessive fluoride in drinking water has always affected human health at present.The pollutants in high-fluorine drinking water are often not single,such as organic matter.However,the current basic research on the coagulation treatment of organic fluoride water bodies is still insufficient,which increases the cost of the treatment.Based on this,this study has an in-depth understanding of the effect and mechanism ofε-KAl₁₃⁷⁺(Al₁₃)coagulation to remove fluoride under organic conditions,reveals the specific influence process of organic matter on Al₁₃ fluoride removal,and provides theoretical knowledge for the wider application of Al₁₃ fluorine removal.At the same time,a new type of hydroxyapatite material with more active sites and larger specific surface area is prepared by doping modification based on Al₁₃ and used in the fluorine removal process.The specific results of this research are as follows:（1）The fluorine removal effect of Al₁₃ under the condition of organic matter,the influencing factors,and the dosage of coagulant are visually displayed by the coagulation area diagram.Electrospray time-of-flight mass spectrometry（ESI-TOF-MS）,differential absorption spectroscopy（DOAS）,and X-ray photoelectron spectroscopy（XPS）were used to analyze the competitive relationship between organic matter and fluorine in the coagulation process,as well as the complex product of Al₁₃and F,in-depth understanding of the mechanism of the influence of organic matter on the defluorination of Al₁₃.The study found that under the optimal dosage,the removal rate of fluorine by Al₁₃ increased by more than 10%under the influence of organic matter,the residual aluminum content decreased,and the coagulation effluent flocs were more tightly combined and easy to settle.According to DOAS analysis,at the beginning of the coagulation reaction,organic matter and fluorine have an advantage in the competition with Al₁₃.At this time,a complex of Al13 and organic matter is mainly formed.As the reaction continues,Al₁₃ is hydrolyzed to produce oligomeric Al nuclear material,at which time fluorine is mainly removed by ion exchange with Al-OH.At the same time,the coagulated flocs containing organic matter can further adsorb free fluorine by stronger netting and adsorption bridging effects.（2）A new type of hydroxyapatite materials were applied,and the materials were characterized by XRD,FTIR,SEM,BET.The influence of pH on fluorine removal efficiency were investigated by calculation of adsorption thermodynamics and adsorption kinetics.The results showed that the Al₁₃-HAP material was more porous than normal HAP.The specific surface area increased to 137.2 m²·g^-1,and the pore volume was 0.8217 cm³·g^-1.FTIR results indicated that the incorporation of Al₁₃brought lots of-OH groups.According to the characterization of materials before and after the adsorption,F^-is mainly removed by replacing the-OH in Al₁₃-HAP through ligand exchange.The maximum fluoride removal efficiency reached 5.03 mg·L^-1;the pH_PZCfor modified material is 8.46,which is greater than the pH_PZC of normal HAP,and the results showed that the materials could be applied in a wide pH range.The adsorption process fits well with the Langmuir adsorption model and the pseudo-second-order kinetic model,and the chemical adsorption is the main mechanism.The adsorption thermodynamics results showed that fluorine removal by Al₁₃-HAP is a spontaneous endothermic process.（3）In the engineering application of the new hydroxyapatite,its fluorine removal performance is reduced by the influence of organic matter.When the TOC concentration is less than 1.2 ppm,the fluorine removal rate of the new hydroxyapatite material is less affected.According to the concentration of organic matter in the experimental water body,the dosage of coagulant in the coagulation stage is controlled to reduce the organic matter in the coagulation effluent to less than 1.2 ppm,which provides good conditions for the subsequent adsorption process.Through the control of various process parameters,the coagulation and adsorption processes can play their respective strengths,reduce the consumption of chemicals,and at the same time can ensure that the effluent fluoride,residual aluminum and other indicators are up to the Standards for drinking water quality.