Preparation And Characterization Of Heavy Metal Copper Adsorbed Nonwovens Made From Ramie Fiber

With the rapid development of modern industrial and agricultural production,soil heavy metal pollution has become one of the most serious environmental problems in the world.Among the commonly used soil heavy metal remediation technologies,the ectopic remediation was costly to machinery,while in-situ leaching remediation has the problem of secondary pollution,which is not conducive to the restoration and subsequent utilization of soil ecological function.In this paper,modified ramie nonwovens combined with in-situ leaching method are used to explore how this method can effectively solve the problem of soil heavy metal pollution at high efficiency and low cost,and what is the process and mechanism of the method can effectively reduce the pollution in the process of remediation.In the first part of this paper,the long ramie spinning by ramie is used as the fiber raw material,and the amino carboxylic acid chelating agent ethylenediamine tetraacetic acid(EDTA)is used as the graft group to prepare the modified fiber,which is made into the heavy metal adsorption nonwovens material by needling.The modified fibers and the prepared nonwovens material are characterized by Fourier transform infrared spectroscopy,X-ray diffraction analysis,scanning electron microscope with energy dispersive spectrometer(SEM-EDS)and thermogravimetric analysis.The results have shown that the crystalline phase of modified ramie fiber is still cellulose type?,but the crystallinity decreased and the proportion of amorphous area increased,which is conducive to the adsorption of heavy metal ions.The modified graft group accounts for about 10%of the atomic concentration.The average pore diameter of the modified nonwovens is 251?m,maximum aperture less than 300?m and the porosity of the modified nonwovens is 97.77%.The heavy metal chelating nonwovens material has a good adsorption basis in fiber properties and nonwovens structure,and has the advantage of adsorption capacity compared with other materials made of micron order fibers.In the second part of the thesis,the box behnkendesign design of response surface method is used to optimize the process parameters of chelating and adsorbing copper ions.Referring to the results of single factors with factorial analysis,it is determined that the initial concentration of copper ion,temperature,reaction time and liquid-solid ratio are the main factors affecting the removal of Cu²⁺,and the four factor and three-level BBD experimental design is adopted to analyze the variance of the fitted quadratic model.The results show that the quadratic model of response function is significant and fittered a higher degree.As the influence of each factor on the removal amount of copper ion is analyzed,the impact of the initial concentration of copper ion is highly significant.The order of the influence of the selected four main factors on the total removal amount of copper ion is as follow:initial concentration of copper ion factor is greater than temperature one,which is similar to the time factor than liquid-solid ratio one.The optimal conditions calculated by the quadratic term model are that copper ion concentration of 30 mg/L,temperature of 35°C,time of 30 min and liquid-solid ratio of 15:1.For each gram of modified chelated nonwovens material,the removal amount of copper ion is 86.662 mg.The adsorption verification experiment has been carried out according to the optimized adsorption conditions.The actual adsorption capacity of copper ion is actually 92 mg/g.The predicted value obtained by fitting the model optimization is in great agreement with the verified experimental value,in which the relative error is 5.7%.The results above show that the quadratic term model fitted with BBD design response surface method can truly reveal the influence of various factors on the removal of heavy metals by modified adsorption materials.Thus,it can be used to predict the removal effect of heavy metals adsorbed by ethylenediamine tetraacetic acid modified-grafted nonwovens material.In the third part of the paper,the actual adsorption capacity data of modified nonwovens are brought into the classical adsorption thermodynamic model Langmuir and Freundlich adsorption isothermal model,where the correlation coefficient R~2 and the residual sum of squares for the fitting curve are used as the fitting evaluation criteria.The calculation results show that the adsorption mode of heavy metal ions on the modified nonwovens is more consistent with the Langmuir adsorption isothermal model(R~2 higher than 0.97),indicating that the adsorption process of heavy metals is dominated by uniform surface mono-layer adsorption.Through the calculation of apparent thermodynamic parameters,it is concluded that the main force between heavy metal ions and modified adsorption materials is coordination bond,and that main driving force of adsorption is electrostatic adsorption force.The adsorption process is increasing towards the direction of entropy,moreover,and the reaction process is spontaneous,which is more obvious with the increase of temperature.During the course which fitting three kinds of kinetic models,the correlation coefficient R~2 of quasi first-order kinetic equation and elovich model is higher than 0.9.The goodness of fit is as follows:elovich model is an integer greater than or equal to quasi first-order kinetic equation which is better than quasi second-order kinetic equation.The theoretical adsorption capacity of elovich model equation is closer to the actual measured equilibrium adsorption capacity data.Based on the particle diffusion control model,the adsorption stage of copper ion is analyzed.The correlation coefficient of the fitting equation of each stage is greater than 0.95.Therefore,the adsorption process of copper ion can be divided into three stages:In the first stage,the linear adsorption in the first stage is related to the surface diffusion,and the second stage is the intragranular diffusion process,and the third stage is the equilibrium dynamic process of adsorption and desorption.At this time,the boundary layer effect is the smallest.Besides,based on the thermodynamic model Langmuir adsorption isotherm and kinetic elovich model,the adsorption process of copper ion on the modified nonwovens is fitted.The two kinds of fitting curves can well coincide with the experimental data well.The fitting correlation coefficient R~2 is greater than 0.9 and the residual sum of squares is less than 14.Therefore,both equations can accurately describe the adsorption process and assist in the analysis of apparent thermodynamics and the study of adsorption mechanism.