Study On The Adsorption Of Modified Pine Needles To Methylene Blue

Now,the dye wastewater has made a serious impact on the environment,while the advantage of adsorption method to treat it is that it can not only remove the dye molecules but also the pollutants which are difficult to degrade in dye wastewater treatment methods.Among them,the modification of biomass materials such as agricultural and forestry waste as adsorbent can not only achieve the goal of turning waste into treasure,but also significantly improve the adsorption capacity to pollutants.Therefore,the pine needles are chosen as adsorbents and modified by various methods,it was finally determined that "the combination of zinc chloride-hydrochloric acid-isopropanol and ultrasonic" was the optimal modification method concluded by adsorption experiments and means of instrument characterization of different kinds of modified pine needles.A large number of pine needles modified by the optimal modification method are prepared and then launch the adsorption study to methylene blue.The effects of adsorption time,the dosage of modified pine needles,the experimental temperature,the initial concentration of methylene blue simulated wastewater,the pH value of solution and the dosage of dyeing assistants on adsorption are studied by static adsorption experiments,it was concluded that saturated adsorption capacity of the modified pine needles was 28.54 mg·g-1 when the modified pine needles dosage was 2 g·L-1,initial concentration of methylene blue simulated wastewater was 150 mg·L-1,pH value of solution was natural and oscillated continuously for 30h,the adsorption capacity was about 4 times of the unmodified pine needles' under the same conditions.Then study on adsorption kinetics and fit the experimental kinetic data by pseudo-first-order kinetic equation,pseudo-second-order kinetic equation,intra-particle diffusion equation and Elovich equation,adsorption kinetics studies showed that pseudo-second-order kinetic equation could well describe the adsorption behavior of methylene blue on modified pine needles,the results showed that the adsorption of methylene blue on modified pine needles existed the process of ion exchange and dominated by chemical adsorption.Establish the adsorption isotherm models,then fit the experimental data by Langmuir adsorption isotherm model and Freundlich adsorption isotherm model,it was concluded that the two models could both well describe the adsorption behavior of modified pine needles to methylene blue and the adsorption accorded with Langmuir adsorption isotherm better,analyses showed that the adsorption process was combined of homogeneous monolayer adsorption and heterogeneous multilayer adsorption,meanwhile,the adsorption process was mainly based on homogeneous monolayer adsorption,and heterogeneous multilayer adsorption was secondary.Adsorption thermodynamics showed that the adsorption was a spontaneous endothermic reaction and a process of entropy increase.Then the dynamic adsorption experiments are carried out and the dynamic adsorption models are established based on the optimal adsorption condition concluded by the static adsorption experiments of modified pine needles to methylene blue,analyses showed that Thomas model and Yoon-Nelson model could both well describe the dynamic adsorption behavior of modified pine needles to methylene blue.