Efficient Preparation Of Chloride Ion Intercalation LDHs For The Nitrate Removal From Water

In surface water,the higher nitrate content was not only led to frequent eutrophication,but also posed a threat to the safety of drinking water due to the inadequate biological denitrification process in urban sewage treatment plants and the extensive use of agricultural nitrate nitrogen fertilizer.Therefore,a simple and practical nitrate treatment process with low consumption and high efficiency needs to be developed.Layered double hydroxides(LDHs)are layered nanomaterials composed by positively charged metal hydroxides,intercalated exchangeable anions and bound water with good selective adsorption for anions in water.In this paper,chloride intercalated Ni Fe-LDHs(CNF-LDHs)were successfully prepared by microwave-assisted coprecipitation double drop method for the exchange of low concentration nitrate in water.CNF-LDHs were synthesized simply and efficiently with large adsorption capacity and good ion selective adsorption,which provides new materials and data supporting for the removal of low concentration nitrate in surface water.The main results are as follows:(1)CNF-LDHs were successfully prepared by microwave-assisted co precipitation double drop method.The main preparation conditions were optimized by orthogonal experiment and single factor experiment.The optimum preparation conditions were as follows: the mole ratio of nickel to iron is 4:1,p H value was 10,and microwave temperature was 100 ℃ for 15 min.The results of XRD,FTIR and HRTEM show that the CNF-LDHs have obvious layered structure and typical hydrotalcite characteristics.(2)The influencing factors of CNF-LDHs exchange adsorption for nitrate in water were investigated,including adsorption time,stirring speed,initial concentration of nitrate and p H value,interfering ions and dosage.Among them,the adsorption time and the initial p H value of the solution have great influence,and the influence of high valence interfering anions is greater than that of low valence anions.When the initial concentration of nitrate was 10 mg/L and the dosage of CNF-LDHs was 4.0 g/L,the removal rate achieved at 89.6%.(3)The actual surface water samples from four places were selected for treatment.When the dosage of CNF-LDHs was 2.0 g/L,the nitrate removal rates of An zhou bridge,Nan liu zhuang,Dongfeng Park and Dong hu water samples were 61.9%,60.8%,66.7% and 64.7%respectively.The removal efficiency of nitrate by self-made CNF-LDHs was significantly better than that of market chlorine 717 anion exchange resin.(4)CNF-LDHs were desorbed by alkaline solution method and microwave-assisted alkaline solution method respectively,and the main influencing factors were optimized.Microwave assisted alkaline solution desorption has the advantages of short time and high speed.When the concentration of Na OH was 0.1 mol/L,microwave temperature was 100 ℃for 30 min,the regeneration rate of CNF-LDHs was 67.4%.In addition,in order to facilitate the separation of nano-adsorbents,magnetic CNF-LDHs were prepared and characterized by FTIR and HRTEM.