Removal Of Methylene Blue From Water By EDTA Grafted CMC Modified Sludge Based Adsorbent

With the development of industry and the expansion of social demand,the use of dyes has gradually become widespread.Methylene blue（MB）is one of the representative dyes.The wastewater produced by MB is harmful and needs to be treated.The adsorption method is simple and efficient,but the cost of large-scale use of commercial activated carbon is high.The preparation of adsorbent from sewage sludge,the by-product of sewage plant operation,not only reduces the use cost of activated carbon,but also solves the disposal of sludge resource.However,the traditional preparation method is easy to cause secondary pollution and has low adsorption performance.If the sludge based adsorbent is prepared by carbonization and surface modification,it will not only make the preparation environment-friendly,but also improve the adsorption performance of the product.It is a promising way to prepare sludge based adsorbent.In this study,sewage sludge was simply carbonized and loaded onto the surface of sludge based adsorbent with natural carboxymethyl chitosan（CMC）,then grafted with ethylenediamine tetraacetic acid（EDTA）to prepare functional solid waste and natural products composite which can efficiently adsorb methylene blue（MB）.The preparation effect of modified sludge based adsorbent（ECMS）under different preparation conditions was investigated.The physicochemical properties of ECMS were studied by various characterization methods.The removal performance of methylene blue by ECMs was studied by adsorption experiments such as influencing factors,kinetics and thermodynamics.The main results are as follows:（1）The results showed that carbonization temperature,CMC concentration and mass ratio of EDTA to CMC had different effects on the adsorption performance of ECMS.The results of orthogonal test showed that the order of influence of three factors from high to low was CMC concentration>mass ratio of EDTA to CMC>carbonization temperature,and the best preparation conditions were as follows:carbonization temperature was 800℃,CMC concentration was 1%,mass ratio of EDTA to CMC was 2.（2）Through the analysis of scanning electron microscope and specific surface area and pore structure,compared with the sludge based adsorbent（SBA）,the specific surface area and pore volume of ECMS decreased significantly,but the content of surface functional groups increased greatly,especially the carboxyl and hydroxyl groups were the most abundant,the zero charge point p Hpzc was lower,and the adsorption efficiency of positively charged pollutants was higher.In addition,Si O₂ is the main crystal of ECMS.The introduction of CMC destroys the order of the material,weakens the overall diffraction peak intensity and decreases the crystallinity.（3）The results showed that the adsorption capacity of ECMS for MB is much larger than that of SBA,and it is greatly affected by the initial p H of solution and the dosage of adsorbent.When the adsorption temperature is 25℃,the adsorption time is 12h,the p H of solution is 10,the dosage of ECMS is 1 g L^-1 and the ionic strength is zero,the adsorption capacity of MB reaches 675.3 mg g^-1.The adsorption kinetics showed that the pseudo second order and internal diffusion models could well fit the kinetic experimental data,indicating that the adsorption of MB on SBA and ECMs was mainly controlled by chemical adsorption.Thermodynamic studies show that the Langmuir model can describe the adsorption process better,which means that the adsorption process of MB tends to monolayer adsorption.The mechanism analysis showed that the adsorption of MB by ECMS was mainly chemical adsorption.The main adsorption mechanism was electrostatic attraction and hydrogen bonding,and-OH and-COOH participated in the chemical adsorption process.In addition,ECMS can remove cationic,neutral and anionic dyes effectively,which indicates that ECMS is an adsorbent for treating different types of dye wastewater.（4）The experimental results show that when the concentration of desorption agent is0.010 mol L^-1 and the desorption time is 120 min,the desorption effect has reached a high level,and after five cycles of use,it can still maintain 86.95%of the initial adsorption capacity,which has good stability and regeneration performance.