Preparation Of Powdered Activated Carbon Composite Material And Its Adsorption Performance And Mechanisms

For solving the problem of low efficiency about hydrophilic ions and slow precipitation rate for powdered activated carbon（PAC）,this study successfully prepares a kind of powdered activated carbon-based composites（PACMC）using potassium humate,PAC,polyaluminium chloride as raw materials through chemical precipitation method.The static adsorption experiments were carried out to investigate the adsorption properties of organic matter adsorption,heavy metal ions and oily sewage by PACMC.The structure and active functional groups of PACMC were characterized,the mechanism of performance improvement were revealed,the adsorption mechanisms of different types of pollutants by PACMC were analyzed.The influence factors of PACMC based water treatment technologies in real applications were also considered.This work provided new insights and theoretical supports for the application of PACMC in pollutant removal in wastewater.The results of this work were as follows:1.The optimal proportions and reaction conditions of PACMC were determined by orthogonal experiment and optimization experiment.PACMC was obtained by using polyaluminum chloride as the binder to rapidly combine humic acid and PAC effectively through chemical precipitation.We confirmed the micromorphology and chemical structure of PACMC by scanning electron microscopy energy-dispersive X-ray spectrometer（SEM-EDS）,Fourier infrared spectroscopy（FT-IR）,X-ray diffraction（XRD）,X-ray photoelectron（XPS）and Raman spectra.The results indicated that PACMC was synthesized by chemical bonds and PACMC has layered porous structure and functional group,which is beneficial to the transport and diffusion and chemical adsorption.2.The adsorption properties of Rh B by PAC、PACl and PACMC were investigated,which showed that the adsorption capacity of PACMC for Rh B was 2-3 times that of PAC,the p H value of the solution has a significant effect on the adsorption of Rh B,and the maximum adsorption was observed at a p H=4.5(q_e=28.56 mg·g^-1,C₀=40 mg·L^-1).The adsorption followed the pseudo-second-order kinetics.The intraparticle diffusion kinetics model indicated that the chemical adsorption and intraparticle diffusion played the important role during the whole adsorption process.The isothermal adsorption data were in accordance with the Dubinin-Radushkevich model which revealed the chemisorption mechanism.It is inferred that the adsorption mechanism includes chemical binding/chelation,hydrophobic effect,electrostatic adsorption.PACMC had the maximum adsorption on TCH in neutral environment.The adsorption followed the pseudo-second-order kinetic model and the isothermal adsorption data were in accordance with the Langmuir adsorption isotherm model which revealed both chemical adsorption and physical adsorption,and the adsorption capacity is 24.73 mg·g^-1.PACMC can remove 88.4%of organics from oily wastewater after oil removal.3.The adsorption performance of PACMC on heavy metal ions was investigated.p H had a significant effect on the adsorption capacity,and the adsorption capacity of PACMC on Cr（VI）was higher at lower p H values,which reflected that electrostatic interactions were the main driving force controlling the Cr（VI）binding mechanism.The kinetic process fitting indicated that both physical and chemical adsorption may exist simultaneously in the adsorption process,and the adsorption proceeds in multiple steps,with internal diffusion playing an important role in the mass transfer process.The adsorption of Cr（VI）on PACMC is a heat absorption and spontaneous process.The p H value of the solution has a significant effect on the adsorption of PACMC for Ni（Ⅱ）、Pb（Ⅱ）、Zn（Ⅱ）and sodium ion,and the optimal p H values were all near neutral,which were consistent with the pseudo-second-order kinetic model,indicating that chemical reactions occurred during all of adsorption process.However,the adsorption of Ni（Ⅱ）and Zn（Ⅱ）on PACMC is were endothermic reactions,and the adsorption of Pb（Ⅱ）on PACMC is were exothermic reactions,the isothermal adsorption data of PACMC for Ni（Ⅱ）and Pb（Ⅱ）were in accordance with the Temkin model which revealed the chemisorption mechanism.The adsorption of Zn（Ⅱ）by PACMC conforms to Freundlich model which revealed both chemical adsorption and physical adsorption.After PACMC treatment,the concentration of sodium ion in coalbed methane produced water decreased to 3.34 mg·L^-1.4.The static adsorption experiments were carried out to investigate the adsorption properties of organic pollutants in oily sewage by PACl、PAC and PACMC respectively.The results showed that the adsorption capacity of PACMC for organic pollutants in oily sewage was 2-3 times as high as that of PAC and PACl.The p H value of the solution had a significant effect on the adsorption of organic pollutants in oily sewage by PACMC,and the maximum adsorption was observed at p H=3(q_e=27.6mg·g^-1,C₀=300 mg·L^-1).The adsorption of organic pollutants in oily sewage by PACMC can be well described by the pseudo-second-order kinetics.The kinetic results revealed that the adsorption process involved several steps,where the chemical adsorption and intra-particle diffusion both played the important roles.The isothermal adsorption data were in accordance with the Dubinin-Radushkevich model,which indicated that the adsorption was dominated by the chemisorption mechanism.Therefore,the adsorption mechanisms included chemical binding/chelation effect,hydrophobic effect and electrostatic adsorption effect.PACMC was used to cleans actual oily sewage.The optimal dosage of PACMC is 130mg·L^-1,the oil removal rate reaches 94%.As the oil content decreases,the conductivity increases.