Effect Of Several Kinds Of Additives On The Preparation Of Hydrochars And Its Adsorption Of Pb(Ⅱ)

Hydrochar,prepared by hydrothermal carbonization of biomass,is a kind of carbon material which is green,environmental protection and non-toxic.Due to some common hydrochar’s adsorption properties are low,three kinds of chemical substances（KMnO₄,Fe（NO₃）3,Zn（NO₃）2）were added to the the hydrothermal carbonization process,using the situ chemical modification method in order to prepare hydrochars with high adsorption capacity.In this study,Pb（Ⅱ）was chosen as the model pollutant to evaluate the adsorption properties of hydrochars,and a series of hydrochar samples were characterized in detail.The main research contents and results of this thesis are as follows:1、Synthesis,characterization and adsorption properties of four KMnO₄ modified hydrochars for Pb（Ⅱ）removalThe typical biomass including peanut shell,willow,corn stalks and cow dung were used as raw materials,Pb（Ⅱ）as model pollutant,Peanut shell hydrochar（PSC）and Mn modified PSC（5%PSC 、 10%PSC and 15%PSC）,willow hydrochar（WHC）and Mn modified 5%WHC,corn stalks hydrochar（CSC）and Mn modified CSC（5%CSC、10%CSC and 15%CSC）,cow dung hydrochar（CDC）and Mn modified 5%CDC were synthesized by hydrothermal method in deionized water and KMnO₄ solution,respectively.The ash content and element composition of the synthesized hydrochars were measured,and simultaneously they were characterized by X-ray diffraction（XRD）and Fourier transform infrared spectroscopy（FTIR）.The adsorption properties for Pb（Ⅱ）of four kinds hydrochars were studied by the adsorption rate-pH curves,and the behavior of adsorption thermodynamics and kinetic were studied.The results show:（1）The ash content of four kinds of hydrochars were increased after modified by KMnO₄,but the contents of C,H,O and N were not consistent.（2）For peanut shell hydrochars,the adsorption isotherm of Pb（Ⅱ）on 15%PSC and 10%PSC were well fitted to Langmuir model（R2>0.99）,while those on 5% PSC and PSC were well fitted to Freundlich model（R2>0.96）,and the adsorption capacity of four hydrochars follow 15%PSC>10%PSC>5%PSC>PSC.（3）For willow hydrochars,theadsorption isotherm of Pb（Ⅱ）on WHC and 5%WHC were well fitted to Langmuir model（R2>0.94）,and their maximum adsorption capacities were 24.28 and 95.05 mg·g^-1respectively.（4）For corn stalks and cow dung hydrochars,the adsorption isotherm of Pb（Ⅱ）on CSC and CDC were well fitted to Freundlich model,while those on 5% CSC、10%CSC 、 15% CSC and 5%CDC were well fitted to Langmuir model（R2> 0.9）,and the adsorption for Pb（Ⅱ）was favorable after modified.（5）The adsorption kinetics of Pb（Ⅱ）on four kinds of hydrochars were well fitted by the pseudo-second order model（R2>0.9）.（6）The adsorption capacity of hydrochars prepared by four kinds of biomass were cow dung>willow>peanut shells>corn stalks.2、Effects of iron salt on preparation of willow hydrochars and adsorption performance for Pb（Ⅱ）The willow hydrochars modified by ferric nitrate were respectively prepared in aqueous solution,0.1 mol·L^-1HNO₃,0.1 mol·L^-1NaOH and 0.5 mol·L^-1HNO₃ solution,which marked NHC,H-NHC,OH-NHC and 5H-NHC in this study.These hydrochars’ s adsorption rate of Pb（II）at pH=5.5 were 5H-NHC>H-NHC>NHC>OH-NHC.5H-NHC and NHC with higher adsorption properties were characterized in detail,and the adsorption thermodynamics and kinetics of the two kinds of iron modified hydrochars were studied.The results show:（1）The ash content and aromaticity of NHC were higher than that of5H-NHC,but the polarity was less than 5H-NHC.（2）Both of NHC and 5H-NHC contained some pore structure,and they had similar surface functional groups and crystal structure.（3）The adsorption of Pb（II）on NHC and 5H-NHC were best when pH neared 5.5,and the optimal dosage was 1g·L^-1.（4）The adsorption kinetics of Pb（II）on NHC and 5H-NHC were in accordance with the pseudo-second order model,and the order of the equilibrium adsorption amount were 5H-NHC(42.900 mg·g^-1)> NHC(32.321 mg·g^-1).（5）The isothermal adsorption of Pb（II）on NHC and 5H-NHC were favorable,and the adsorption data were well consistent with Freundlich equation.3、Effects of medium acid-base property and zinc salt on preparation of willow hydrochars and the adsorption of Pb（II）The willow hydrochars modified by zinc nitrate were respectively prepared in 0.5mol·L^-1HNO₃ 、aqueous solution and 0.5 mol·L^-1NaOH solution,which marked H-ZHC、ZHC and OH-ZHC in this paper.Three kinds of modified hydrochars were characterized in detail,and at the same time the effects of medium acid-base property on the morphology,structure and properties of hydrochars were analyzed.The adsorption behavior of Pb（II）on three kinds of modified hydrochars were studied.The results show:（1）The yield of OH-ZHC was the lowest,but the ash content and the C content were the highest.The aromaticity was higher,and the microsphere particles supported on the surface of OH-ZHC were confirmed to be ZnO by XRD.（2）The specific surface area of these hydrochars prepared in three solution media were ZHC>H-ZHC>OH-ZHC.（3）The adsorption of Pb（II）on the three kinds of hydrochars were best when pH neared 5.5,and the optimal dosage was 1g·L^-1.（4）The adsorption properties of Pb（II）on three kinds of hydrochars were OH-ZHC>H-ZHC>ZHC when the initial concentration of Pb（II）solution was 50 mg·L^-1with the same dosage,and adsorption kinetics of Pb（II）were well fitted with the pseudo-second order model.（5）The Langmuir model can better described the isothermal adsorption behavior of Pb（II）on ZHC,H-ZHC and OH-ZHC,and adsorption on the three kinds of hydrochars were all favorable.