Preparation Of Sludge-Sawdust-based Activated Carbon And Its Adsorption To Methylene Blue

Sludge is an inevitable product in the process of sewage treatment.It contains many kinds of harmful substances.Handled improperly,it will have a considerable bad impact on the environment.And that's why how to properly treat sludge has become a very important study issue.In this paper,using sludge and sawdust as raw materials to prepare activated carbon by chemical activation,with zinc chloride as activator,and high temperature tubular furnace by adding powder activator directly.The effects of sawdust addition rate,salt-to-material ratio,activation temperature and activation time on the iodine adsorption value of activated carbon are investigated by conducting single factor experiments.The results show that when sawdust addition rate is 20%,salt-to-material ratio is 2.0,activation temperature is 550?,activation time is 15 min,the adsorption value of activated carbon is 679.25 mg/g.And,SEM(scanning electron microscopy)and BET(gas phase physical adsorption instrument)analysis show that activated carbon from sludge prepared by this method had developed pore size structure.At the same time the specific surface area can reach 609.68 m~2/g,the total pore volume is 0.51 cm~3/g,and the average pore diameter is 3.51 nm.All the results mentioned above verify the feasibility of this process for preparing activated carbon in this paper.The optimization interval of salt-to-material ratio,activation temperature and activation time are selected by single factor experiment.In this interval,the specific surface area of activated carbon is taken as the objective value,and the preparation process of activated carbon was optimized by response surface optimization method.The results show that the second-order model can accurately describe the preparation process of activated carbon by using response surface methodology.Its R~2 can reach0.9977,and the experimental value is highly consistent with the fitting value.Furthermore,in the range of solution,the maximum specific surface area of sludge-sawdust-based activated carbon is 699.87 m~2/g when the ratio of salt to material is 1.93,the activation time is 56.8 min and the activation temperature is 583.0?.The specific surface area is 712.35 m~2/g under the optimum condition.Meanwhile,the error between the predicted value and the experimental result is 1.75%,which verifies the effectiveness of the optimization.MB(methylene blue)dye wastewater is treated by the activated carbon obtained by optimization to study its adsorption mechanism.The results show that particle size and pH value have great influence on MB adsorption capacity.With the decrease of particle size,MB adsorption capacity increased gradually.With the increase of pH value,the adsorption capacity of MB increased;the adsorption capacity of MB on the activated carbon reaches saturation after 180 minutes;Redlich-Peterson model fits the experimental data best(R~2=0.9894);according to Langmuir isotherm model calculation,the maximum adsorption capacity of MB on the activated carbon is 186.40 mg/g;According to the kinetic fitting results,Pseudo-2st-order model fits best when MB concentration is 100 mg/L(R~2=0.9992).When MB concentration increases,Elovich model can fit well with the experimental data(R~2=0.9966~0.9990).Using the activated carbon obtained in this paper to compare with other activated carbons,it is found that the activated carbon in this paper has higher MB adsorption capacity and is suitable for the adsorption of MB dye wastewater.