Study On The Co-Pyrolysis Behavior Of Sludge And Enteromorpha Prolifera And The Adsorption Mechanism Of Cr(Ⅵ) In Water By Pyrolysis Residue

The pyrolysis carbon residue of sludge has a special pore structure and extended specific surface area.Due to the high ash content and low fixed carbon content of sludge,the pore structure of pyrolysis carbon carbon is not developed,the specific surface area is low,and the adsorption effect is general.The pyrolytic carbon of Entermorpha prolifera has fibrous carbon skeleton and abundant pores,which can interact well with sludge in the process of co-pyrolysis.Based on this,this paper puts forward a new idea of preparing sludge-Entermorpha compound adsorbent with co-pyrolysis residue,which can be used for wastewater treatment and waste treatment,making full use of the resource value of both,and meeting the requirements of sustainable development in China.In this paper,the pyrolysis kinetics of sludge and Enteromorpha prolifera were analyzed and the pyrolysis behavior of the mixture was analyzed.Then,the optimum working parameters of sludge-Entermorpha prolifera composite adsorbent were found out by orthogonal experiment,and the physicochemical properties of the adsorbent were elucidated by means of various characterization methods.Finally,the adsorption experiment,adsorption kinetics calculation,isothermal adsorption,thermodynamic calculation and regeneration experiment were carried out to systematically and comprehensively describe the characteristics and optimization mechanism of sludge-Entermorpha prolifera composite adsorbent for Cr(Ⅵ)adsorption.The main results of this paper are as follows:Whether pyrolysis or co-pyrolysis,the pyrolysis process of sludge and enteromorpha can be divided into three stages,which are combined water stripping,decomposition of organic matter to and fixed carbonation bond breaking and carbonate splitting.The sludge-hustle co-pyrolysis process is not a simple superposition of the two,but there is an obvious synergistic effect,and the maximum value of the synergistic degree indexΔTG is-6 %.The model-free kinetic method was used to analyze the kinetics of co-pyrolysis of sludge and enteromorpha,and it was found that the corresponding activation energies of co-pyrolysis were 209.0126 kJ/mol,206.3775 kJ/mol and207.1607 kJ/mol.Combining thermodynamically relevant parameters such as enthalpy change ΔH,entropy change ΔS and Gibbs free energy ΔG,the co-pyrolysis process was found to be a non-spontaneous heat absorption process.The best performance of the adsorbent made was obtained by orthogonal experimental calculation and analysis: when the mass ratio of sludge in the blends was40 %,the concentration of zinc chloride was 0.1 mol/L,the pyrolysis temperature was500 °C and the pyrolysis time was 30 min.The experimental characterization results showed that from the microscopic morphology,the enteromorpha provided a good fibrous carbon skeleton structure for the sludge,and the two could fit together perfectly.The specific surface area of the adsorbent was 487.46 m2/g,the total pore volume was0.34 cm3/g and the micropore volume was 0.13 cm3/g.According to the peak value fitting before and after adsorption measured by XPS,it was found that Cr(Ⅵ)was reduced to Cr(Ⅲ),and the adsorption reaction was affected by the carbon-containing functional groups on the surface of the adsorbent.FTIR detection showed that there were abundant functional groups such as-OH,C=O and C=C on the surface of the adsorbent.The concentration of heavy metals in the leaching solution of adsorbent is far lower than the limit value of national standard,which is safe and reliable.It was found that the adsorption of Cr(Ⅵ)by the Sludge-Enteromorpha compound adsorbent was effective under acidic and neutral conditions and its adsorption rate could reach more than 97 %;the adsorption process of Cr(Ⅵ)by the adsorbent could be divided into three stages: fast,slow adsorption stage and equilibrium adsorption stage.The adsorption equilibrium was reached within 150 min,the adsorption amount of Cr(Ⅵ)by the adsorbent increased significantly with time,and the adsorption equilibrium time shifted left.The kinetic study found that the proposed secondary kinetic model was suitable to describe the adsorption of Cr(Ⅵ)by the Sludge-Enteromorpha compound adsorbent;the intraparticle diffusion model indicated that the adsorption process was the result of the combined effect of intraparticle diffusion and membrane diffusion;the activation energy of adsorption calculated by fitting the Arrhenius model was 20.9726KJ/mol.Isothermal adsorption and thermodynamic studies showed that the Freundlich(Freundlich)isothermal adsorption model is more suitable to explain the adsorption behavior of the adsorbent on Cr(Ⅵ),as a multilayer molecular adsorption on a non-uniform surface,with a maximum saturation adsorption capacity of 51.5536 mg/g at 313 K.The Polanyi adsorption potential decreases with the initial concentration of the solution;by calculating the thermodynamic parameters of the adsorption process,it is found that the adsorption process is a spontaneous heat absorption reaction.The regeneration experiments showed that the adsorption efficiency of the 3rd regeneration could still reach 68.72 %,which could meet the actual production requirements.