Optimization Of Adsorption Performance And Its Influencing Factors Of Heavy Metals In Water By Eichhornia Crassipes Biochar

In this paper,Eichhornia crassipes biomass was used as raw material to prepare biochar,and its related physicochemical property characterization were analyzed.Based on the single factor experiment of heavy metals adsorption by Eichhornia crassipes biochar,the author adopted the response surface method to model and optimize the adsorption conditions of heavy metals by biochar.With isothermal adsorption and kinetic adsorption tests as well as characterization methods,the adsorption performance and adsorption mechanism were preliminarily analyzed.The main results were as follows:(1)Preparation and characterization of Eichhornia crassipes biomass were listed as follows.The pore structure on the surface of biochar was observed by scanning electron microscope(SEM).The test of specific surface area(BET)showed that the specific surface area of these four kinds of biochar(BC-1 was suitable for Pb(?),BC-2 for Cu(?),BC-3 for Cd(?)and BC-4 for Zn(II))were 337.167?4.299?4.436?8.065 m2/g,respectively,pore volume were 0.219,0.005,0.009,0.009 cm3/g,respectively,the average pore size were 3.009,21.686,48.637,8.357 nm,respectively.The results of FTIR characterization manifested that the surface of carbon particles contained abundant functional groups such as C=C,C=O,C-O and-COOH.X-ray diffraction(XRD)indicated that the carbon particles also contained many crystalline minerals,such as K and Ca.Zeta potential test results showed that the zero potential pH was between 2 and 3.(2)Optimization of heavy metal adsorption by adsorbent dosage(X1),adsorption time(X2)and solution pH(X3)of Eichhomia crassipes biochar was analyzed.The center point as well as the high and low points of the response surface method were obtained by single factor experiment analysis.The experiment design was tested by central composite design(CCD)molded for BC-1 and BC-2 before heavy metal adsorption experiments were carried out.At the same time,the response surface method was used for modeling.The results showed that X1 was remarkably effect on the removal rate of Pb(?)when BC-1 adsorbing Pb(?)while X2 was not significant.The optimal adsorption condition was when X,=0.27 g/L and X2=201 min;X1 and X2 were both remarkably effect on the removal of Cu(II)when BC-2 adsorbing Cu(?),but X2 was greater.The optimal adsorption condition was when X1=2.26 g/L and X2=210 min.With Box-Behnken Design(BBD)modeled for BC-3 and BC-4,the author carried out metal adsorption experiment by using the response surface method,finding that X1 and X3 were both remarkably effect on the removal of Cd(?)when BC-3 adsorbing Cd(?)while X2 was not significant,and the effect was X1>X2>X3.When X1-3.0g/L,X2=171 min,X3=7,the removal effect was the best.X1 and X3 were both remarkably effect on the removal of Zn(?)when BC-4 adsorbing Zn(?)while X2 was not significant,and the effect was X1>X3>X2,When X1=3.0 g/L,X2=163 min,X3=7,the removal of Zn(?)was the best.(3)Under the above optimized adsorption conditions,R2 of Langmuir model fitted by BC-1,BC-2,BC-3 and BC-4 were 0.966,0.994,0.924 and 0.994 respectively,and R2 of Freundlich model fitted by BC-1,BC-2,BC-3 and BC-4 were 0.975,0.986,0.995 and 0.988 respectively,and their correlation coefficients were all greater than 0.9.Therefore,single-molecular layer adsorption and multi-molecular layer adsorption should be taken into account in the adsorption process.But R2 of Langmuir model fitted by BC-1 and BC-3 were higher,indicating that the adsorption of Pb(?)by BC-1 and Cd(?)by BC-3 were mainly multilayer adsorption.What's more,R2 of Langmuir model fitted by BC-2 and BC-4 were higher than the former ones,showing that the adsorption of Cu(?)by BC-2 and Zn(II)by BC-4 were mainly monolayer adsorption.The theoretical maximum adsorption capacity Qm were 175.099?274.495?763.706 and 199.128 mg/g,respectively.The Freundlich model's n values were all greater than 1,indicating that Eichhornia crassipes biochar was conducive to the adsorption of heavy metals.The correlation coefficients of adsorption kinetic fit of the four biochar were all higher than that of the quasi-second-order kinetic equation,and all were greater than 0.9,which showed that the adsorption process of biochar was mainly chemisorption while chemisorption was generally single-molecule layer adsorption.Combined with the characterization of these four biochar,the experiment reflected that the adsorption of Cu(?)by BC-2 and Zn(?)by BC-4 were precipitation,complexation and ion exchange in chemical adsorption.And the adsorption of Pb(?)by BC-1 and Cd(?)by BC-3 involved chemisorption and physisorption,and its adsorption mechanism could be speculated to be precipitation,complexation,ion exchange,electrostatic adsorption and physical adsorption.