Preparation Of Iron-based Composite Metal Oxides And Adsorption Of Fluorine In Water

Fluoride pollution in water has become a significant environmental problem worldwide.Adsorption method has the advantages of low cost,convenient operation,high removal rate and reusable adsorbent,which is a practical method to remove excess fluoride in water.Among them,due to the characteristics of large specific surface area and a large number of active sites,composite metal oxides can be used for fluoride fixation.However,at present,most metal oxide sorbents use rare metals,which make the preparation cost of adsorbent high,which are not suitable for large-scale adsorption of fluorine pollutants in water.Therefore,the efficient adsorption of fluoride can be realized by preparing iron based composite metal oxide adsorbent with low cost and environmental protection.（1）The flake precursor Ca-Fe-SO₄ LDH（CF）was prepared by co-precipitation of ferrous sulfate,a cheap by-product of titanium dioxide,and calcium oxide.The composite metal oxide Ca-Fe MMO（CCF）was synthesized after calcination to adsorb high concentration fluoride in aqueous solution.The adsorption capacity of CCF for fluorine was analyzed by batch adsorption experiments,and the adsorption process of fluorine was in accordance with Langmuir model,adsorption capacity was 160.66 mg/g.The pseudo-second-order kinetic model was more consistent with the actual adsorption process.According to the analysis of p H_zpc,FITR and XPS,complexation and electrostatic attraction were the main adsorption mechanisms of fluoride in water by CCF.In addition,the adsorbent had excellent and stable adsorption performance in the p H range of 3-12,with high selectivity,but poor reproducibility.Therefore,the adsorbent needed to be improved in subsequent experiments.（2）By introducing fluorophile magnesium to replace part of calcium in the previous material,the fluoride adsorbent precursor was synthesized by co-precipitation method,and the adsorbent Ca-Mg-Fe MMO（CCMF）was obtained by calcination to adsorb low concentration fluoride in aqueous solution and improve the reproducibility of the material.CCMF had good adsorption capacity for fluoride in water,and adsorption capacity was 18.11 mg/g.During the adsorption process,the adsorption of fluoride by CCMF followed Freundlich model and pseudo-second-order kinetic model.Batch adsorption experiments showed that CCMF has a high selectivity for fluoride,and after multiple reuse,it had a good removal ability of fluoride,and showed excellent adsorption performance in the range of p H 3-11.According to p H_zpc,FTIR and XPS analysis,electrostatic attraction and ion exchange were the main adsorption mechanisms of fluorine in water for CCMF.However,the long adsorption equilibrium time and slow adsorption rate of the material needed to be improved.（3）Because the by-product ferrous sulfate contains a small amount of manganese sulfate,manganese had a strong affinity for fluoride,in order to improve the adsorption rate,manganese with similar chemical properties to iron was introduced in the experiment.The adsorbent precursor was prepared by co-precipitation method.After calcination,the flake composite metal oxide Ca-Mg-Mn MMO（CCMM）was synthesized to adsorb low concentration fluoride in aqueous solution.During the adsorption process,CCMM followed Freundlich model and pseudo-second-order kinetic model for fluoride adsorption,and the adsorption capacity was 14.26 mg/g.In addition,batch adsorption experiments showed that the adsorbent had excellent and stable adsorption performance and high selectivity in the range of p H 3-11.Importantly,CCMM retained 63.66%of its initial adsorption capacity after repeated regeneration.According to p H_zpc,FTIR and XPS analysis,complexation,ion exchange and electrostatic adsorption were the adsorption mechanisms of CCMM adsorption of low concentration fluoride pollution in water.Therefore,CCMM was a potential adsorbent,which could achieve efficient adsorption of fluoride in water.