Adsoption Study Of Humic Acid On Magnetic Anion Exchange Resin

Based on the contrast of common commercial resin adsorbents, this thesis studies the influence of humic acid adsorption by magnetic anion exchange resins’ skeleton structure and functional groups. The magnetic anion exchange resins were independently developed by our team called NDMP. The results show that anion exchange resins have a better adsorption performance on adsorbing humic acid than that on adsorption resins and active carbon due to the presence of functional groups. Among the anion exchange resins, the acrylic skeleton resin shows an adsorption advantage over the styrene skeleton resin. The acrylic skeleton resin with the higher exchange capacity gives a higher adsorption amount, and the pore size has very small effect on adsorption. Moreover, the acrylic skeleton resins also have a good performance on regeneration behavior because of their hydrophilic skeleton. In addition, a series of NDMP resins with different amount of magnetic materials was also conducted for the adsorption of humic acid. The result shows that the resin’s high water content is in favor of adsorption. On the basis of above results, the adsorption of humic acid fractions with different molecular size on NDMP resin was investigated. The different values of negative charged densities among four fractions were observed, resulting in the different adsorption behavior on NDMP resins. Finally, the effect of solution environment on adsorption was also studied. The results show that the solution with slight alkali and low content salt favors the adsorption, while the presence of high valence metal ions goes against the adsorption. The main research contents and conclusions are as follows:(1) The effects of resin’s chemical and physical properties on humic acid adsorption were explored. Through the study on adsorption kinetics, adsorption thermodynamics and desorption experiments, it was found anion exchange resins have a better performance on both adsorption and desorption than that of adsorption resins. Among anion exchange resins, the resin skeleton structure has the most effect on the performance. It shows the hydrophilic structure of resin is in favor of humic acid adsorption and desorption. The study of adsorption on the series of NDMP resins shows that resin’s high water content is in favor of adsorption.(2) The adsorption mechanism of humic acid fractions with different molecular size on NDMP resin was studied. Humic acid was fractionated into four components according to the different molecular size by using ultra-filtration technique. It was found that the aromaticity of humic acid fractions increased with molecular size, while the electro-negativity follows the order:HA2500-10000>HA>10000>HA1000-2500>HA<1000.The results of adsorption experiment show that the electro-negativity is a much more important factor for the adsorption than that of molecular size. Since the largest negative charged of the fraction with MW of2500-10000Da, their adsorption amount (25.94mg TOC/g) was the largest, while the fraction with MW smaller than1000Da was adsorbed hardly. Study on adsorption thermodynamics shows the force between HA2500-10000and NDMP resin is strongest, and the other interactions such as van der Waals’ force, hydrogen bonding force might take part in the adsorption process.(3) The effect of solution chemistry on adsorption was investigated. The results show that the adsorption amount of HA on NDMP resin increases with pH value of the solution (pH<10), decreases sharply after pH>10. The presence of salt (NaCl, Na2SO4) could enhance the adsorption amount due to the "salting-out" effect of inorganic ions. When the salt concentration is high enough, the adsorption amount decreases because of the competitive adsorption of anionic ions. The existence of high valence metal ion (Ca2+、Mg2+、Al3+、Fe3+) in solution can significantly reduce humic acid adsorption on NDMP resin because of the complexion between metal ion and humic acid.