Preparation Of Cassava Sludge-based Activated Carbon And Study On Hexavalent Chromium Adsorption

Along with the increased number of sewage treatment plant and the more strictly discharge standard of sewage.Therefore,sludge utilization has become the focus of social attention.Sludge has rich organic matter,it can be used as raw material to prepare activated carbon which possessed excellent adsorption performance.It’s not only provided a new way for the treatment and disposal of sludge,but also reduce the traditional of activated carbon industry dependence on non-renewable energy.Accord with the requirement of sustainable development,economic and environmental benefits is well.In this study,cassava sludge-based activated carbon(CSAC)was prepared by chemical activation and cassava sludge as raw material,zinc chloride as activator.According to the orthogonal experiment to optimize the preparation of CSAC process parameters.Through a series of characterization methods analyzed the chemical and physical properties of CSAC under the optimum process parameters to prepared.CSAC as adsorbent,Cr(Ⅵ)as the adsorbate,from single factor influence,response surface experiments,adsorption kinetics,adsorption equilibrium,thermodynamics and activated carbon regeneration et al to system studied the characteristics and mechanism of CSAC removal of Cr(Ⅵ)in water.The prospect of industrialization is discussed by comparing and costing the CSAC.Orthogonal experiment results show that the optimal preparation process parameters of CSAC as follows:the sludge particle size 20 to 50,concentration of zinc chloride 20%,activation time 12h,carbonization temperature 500℃and carbonization time 60min.The iodine value of CSAC prepared by optimum conditions is 577.10 mg/g.The range analysis showed that the effects of five factors on the adsorption performance of CSAC were in the following order:sludge particle size>carbonization temperature>concentration of zinc chloride>activation time>carbonization time.The results of the characterization analysis show that the CSAC has a developed pore structure,and the pore diameter is similar to the slit of the parallel wall,the BET surface area was 509.03m~2/g,the average pore diameter was 29.5?,which belongs to the mesoporous activated carbon.FT-IR spectra found that the surface functional groups of CSAC were contained carboxyl group,hydroxyl group and internal ester group.Boehm titration and Zeta potential indicate that the surface of CSAC is acidic and the zero-charge point pHzpc is 4.8.The phase analysis shows that CSAC is belong to amorphous carbon.The leaching solution of CSAC show that the content of7 main heavy metals was lower than the national standard.The adsorption experiment results show that the initial pH,initial Cr(Ⅵ)concentration,adsorption time,adsorbent dosage and temperature have different effects on Cr(Ⅵ)removal,but the effect of temperature is small.The results of the response surface test showed that the optimal process parameters for Cr(Ⅵ)removal were:initial Cr(Ⅵ)concentration 4.02mg/L,activated carbon dosage 1.47g/L,adsorption time 42.34min,solution pH 4.44 and then the removal rate of Cr(Ⅵ)is98.64%.The influence degree of four factors on the removal of Cr(Ⅵ)is that:solution pH>activated carbon dosage>initial Cr(Ⅵ)concentration>adsorption time.Cr(Ⅵ)concentration and activated carbon dosage,activated carbon dosage and adsorption time have significant affect the removal of Cr(Ⅵ)on CSAC.At different temperatures and initial concentrations of Cr(Ⅵ),the adsorption kinetics processes of Cr(Ⅵ)both can be well described by the Elovich model,and the liquid film diffusion is the main rate limiting step.The calculation of activation energy can prove that the adsorption is physical adsorption.At different temperatures,the adsorption equilibrium of Cr(Ⅵ)on CSAC can be well described by Freundlich model.With the increase of the initial concentration of Cr(Ⅵ),the adsorption potential is decrease.The calculation of thermodynamic parameters indicates that the adsorption of Cr(Ⅵ)on CSAC is a spontaneous endothermic reaction,the high temperature is favorable to adsorption reaction.The adsorption mechanism of Cr(Ⅵ)on CSAC mainly included physical adsorption,electrostatic attraction and ion exchange reaction.The result of regeneration experimental of CSAC show that when HCl concentration is 0.5 mol/L,has good regeneration effect for CSAC.CSAC can be reused,but the repeated times were limited,after 8 times renewable,the removal rate of Cr(Ⅵ)from 81.52%to 81.52%.Compared with other activated carbon,CSAC has higher adsorption capacity.When Cr(Ⅵ)concentration is 10mg/L,solution pH is 2,the maximum adsorption capacity of Cr(Ⅵ)is 9.84mg/g.The cost calculation shows that the production cost of CSAC are about 2380 yuan/ton.