| Fluoride is one of the indispensable trace elements in the human body.Excessive or inadequate intake is harmful to the human body.China is one of the countries with high fluoride water in the world.As of 2017,the number of people affected by endemic fluorosis has reached more than 13 million people,especially in remote areas where China's economy is relatively backward,people are suffering from the harm caused by drinking high-fluorine water.In order to reduce the drinking water safety of residents in high-fluorine water areas,it is very meaningful to find an efficient,economical,and simple adsorbent.In this study,a new type of joint modification was synthesized with zeolite as the carrier,chitosan and aluminum sulfate as modifiers.Based on the optimization of chitosan,zeolite,kaolin clay material ratio,aluminum sulfate concentration,pH,and calcination temperature,this adsorbent is characterized and its defluorination performance and mechanism are explored.The results show:Orthogonal experiments were performed to optimize the material ratios of chitosan,zeolite,and kaolin,and the optimal modification conditions of aluminum sulfate concentration,pH,and calcination temperature were verified by single factor experiments.The optimal material ratio of chitosan,zeolite and kaolin is 0.6:1.0:0.5,the concentration of aluminum sulfate is 25 g·L-1,pH is 9.0,and the adsorbent is optimized under the conditions of calcination temperature 200?,which can make the adsorbent have the maximum adsorption capacity and removal Fluorine performance.The scanning electron microscope?SEM?,X-ray diffraction spectrum?XRD?,X-ray photoelectron spectroscopy?XPS?,energy spectroscopy?EDS?and other instruments were used to characterize and analyze the modified adsorbent.The results show that the particle porosity on the surface of the modified composite adsorbent increases and there are more externally expanded structures,which indicates that it can increase more adsorption active sites and enhance the adsorption capacity after modification;the main composition of the adsorbent mineral is found by XRD spectrum There are quartz,kaolin,silica,etc.,the XRD diffraction angle and peak intensity of the composite adsorbent before and after modification are basically the same,and the structural stability is good before and after modification;XPS spectrum and EDS results comprehensive analysis F-success Adsorbed to the surface of the adsorbent,indicating that the composite modified adsorbent has the ability to adsorb fluoride ions.Through the static adsorption test,the effects of the dosage of the adsorbent,the initial pH value of the solution,the initial fluoride ion concentration,and temperature on the removal of fluorine were explored.The results showed that the speculative amount of the adsorbent was 0.4 g·L-1,pH 4.0,the residual fluoride ion concentration was 0.89 mg·L-1,and the defluorination rate was over 90%,which met the national sanitary drinking water standard of 1.0 mg·L-1.The quasi-first-order kinetic model can well describe the adsorption kinetic curve of the adsorbent.The quasi-first-order kinetic model can well describe the adsorption kinetic curve of the adsorbent.The Langmuir model fits the adsorption isotherm of fluoride ion best.The saturated adsorption capacity of the adsorbent obtained by the Langmuir model fitting reaches 6.94 mg·L-1.Finally,the desorption regeneration performance of the adsorbent was explored.After five cycles of adsorption-desorption process,the fluorine removal rate dropped from 70%to about 40%,and the adsorption and defluorination performance became poor,indicating that the adsorbent studied in this paper can Repeated recycling.At the same time,through a preliminary discussion of the adsorption mechanism,it was found that the adsorption process is affected by the three mechanisms of electrostatic adsorption,ion exchange and surface complexation. |
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