| With the development of economy, modern industry has a large development and scale is increasingly great. However, emission of industrial wastewater is leap. And the pollution to our country's water resources is increasingly serious. The wastewater of dye is hard to be degraded, which can affect the ray propagation in water and is unfavorable for photosynthesis of water ecosystem. The wastewater including heavy metal ions can cause permanent toxicity to food chain. Thus adsorption method plays an important role in the removal of refractory pollutants. So our experiment used raw soluble starch as material to synthesize neutral starch microspheres and then continuely prepared an new anionic starch microspheres(ASMs) which can be green environmental protection and easy to be degraded using the neutral starch microspheres as materials. The new anionic starch microspheres were applied as an absorbent to adsorb the methylene blue as representative of positive dyes and copper and lead as the representative of heavy metal in wastewater. The adsorption characteristics were also studied through thermodynamics and kinetics research. The experiment results can supply theoretical basis and application basis for the wastewater treatment.Firstly, the neutral starch microspheres were prepared from soluble starch by inverse emulsion with epichlorohydrin as the crosslinking agent.Then the anionic starch microspheres were synthesized using the crosslinked neutral starch microspheres as materials with chloroacetic acid as anionic etherifying agent for the first time. Through the single factor experiment and orthogonal experiment, the results show that dosage of sodium hydroxide, dosage of chloroacetic acid, dosage of 80% ethanol, reaction temperature and reaction time all can affect the adsorption of ASMs. According to the results of orthogonal experiment design, a conclusion can be obtainted that dosage of ethanol affect the adsorption amount mostly and the dosage of chloroacetic acid affect leastly.Besides the dosage of sodium hydroxide showed a greater effect than reaction temperature and reaction time to adsorption amount. The optimum process conditions of synthesis are as follow:5.5 mL 80%ethanol, 0.9 g sodium hydroxide, 0.3 g chloroacetic acid, reaction time is 5 h and reaction temperature is 55℃.The anionic starch microspheres were characterized by Scanning Electron Microscopy(SEM), Fourier Transform Infrared spectroscopy(FT-IR) and Laser Particle Size Analyzer. The experiment results of SEM and particle size analysis indicated that the new anionic starch microspheres were spherical with smooth surface with many microporous. The average of particle size is 60-80μm. And the result of FT-IR indicated that the anionic starch microspheres has anionic group. Secondly, the anionic starch microspheres (ASMs) were applied to adsorb methylene blue as representative of positive dyes. The experiment results show that ASMs has a good adsorption on methylene blue and the adsorption process is adapted to Langmuir adsorption isotherm equation. And the maximum adsorption is 667.7 mg/g. Kinetic study shows that the pseudo-second-order kinetic model provided a better correlation of the experimental data in comparison with the pseudo-first-order model. And it may conclude that the adsorption rate is mainly controlled by chemisorption rather than mass transfer. The effect of temperature on the adsorption amount is not very significant and has a optimum temperature. That is 303 K.Lastly, ASMs were applied to adsorb copper and lead. The results indicated that the adsorption characteristics of Cu2+ and Pb2+ were conformed to the Langmuir and Freundlich isotherms within the experiment temperature. The results of linear fitting indicated that adsorption of Cu2+ is fit for the Langmuir isotherms equation and adsorption of Pb2+ is fit for the Freundlich isotherms equation. The adsorption thermodynamic parameters based on the Freundlich isotherms can reflect how the anionic starch microspheres adsorbed the heavy metal ions more clearly. The enthalpy change△H were negative and absolute values of△H are more than 30 kJ/mol and less than 60 kJ/mol, which proved ASMs adsorbed the adsorbates by means of physical adsorption, hydrogen bonding and the coordination adsorption between the metal ions and microspheres. With the increase of adsorption amount, the values of△H are increasingly small, which can prove the inhomogeneity of microspheres surface. However, with the increase of adsorption amount, the confusion degree of system is increasingly big, which indicate that solvent molecules is increasing when desorption. Kinetic study shows that the pseudo-second-order kinetic model provided a better correlation of the experimental data for the adsorption of Cu2+ and Pb2+. The adsorption was controlled by both surface diffusion and particles diffusion, but the adsorption rate was mainly controlled by particles diffusion. According to the absolute values of△H, it may find that adsorption affinity between Pb2+ and ASMs is stronger than the adsorption affinity between Cu2+ and ASMs.The innovative points of our experiment are as follows :( 1)A new green environmental protection and easily degradable anionic starch microspheres etherified by chloroacetic acid from neutral starch microspheres was synthesized for the first time. (2) The anionic starch microspheres were applied to adsorb methylene blue as representative of positive dyes and the adsorption characteristic of ASMs for positive dyes was investigated. Kinetic characteristics were studied. (3) Adsorption behavior and mechanism of ASMs for heavy metal ions were also studied through the thermodynamics and kinetics research. |
