Study On Simultaneous Sorption Of Organic Pollutants And Heavy Metals To Bentonite Modified By Surfactant And Organic Ligands From Water

A series of novel bentonite-based multifunctional adsorbent materials were syn-thesized by modifying bentonite with different organic chelating agents and a long-chain cationic surfactant. The simultaneous sorption of the organic pollutants and heavy metals onto the modified bentonites from the mixed solutions was investi-gated. The relationship between the structure of the modified bentonite and its sorp-tion behavior was extensively explored with the help of modern analytical techniques. The study put emphasis up on the cooperation mechanism, trend and influential fac-tors of the organic pollutants and heavy metals sorption to the following three modi-fied bentonites:the first class of bentonites with dual cationic modifiers, secondly with neutral organic ligand and quaternary cationics, and the last one with anionic organic ligand and quaternary cationics. This dissertation aimed to submit a useful theoretical evidence and technical basis for the functional modification of bentonite and its application in the wastewater treatment. The main original innovations of this work are as follows:(1) A novel modification method of bentonite was presented that both altered the surface property of bentonite and intercalated the functional modifying agents in the interlayer of bentonite. The results of the structural characterization and sorp-tion-desorption experiments indicated that the quaternary ammonium cation (CTMA) and the organic ligand (L) were stably intercalated into the lamellae of bentonites through ion exchange. The hydrophobicity of bentonite was enhanced, and the basal spacing and the specific surface area were changed markedly after modification. For example, compared to singly modified bentonite CTMA-Bent, the specific surface area of the dual organic cation bentonite modified by CTMA and AET was increased and its basal spacing was decreased, while the specific surface area of the bentonite modified by CTMA and TETA was decreased and its basal spacing was increased.(2) The cooperation mechanism, trend and influential factors for organic pollut-ants and heavy metals sorption to the modified bentonites CTMA-L-Bent were inves-tigated. The following main conclutions were given:i) the sorption of organic pollut-ants to the modified bentonite was controlled by a partition process. The organic compound which had weaker polarity, smaller solubility and larger octanol-water par-tition coefficient could be preferentially sorbed more easily. The sorption of heavy metals to the modified bentonite was dominated by the formation of complexes. The heavy metal which had the smaller hydration energy and the greater stability constant could be preferentially sorbed more easily. As an example, for CTMA-En-Bent, the sequence of its sorption for heavy metals was Pb2+>Cu2+>Cd2+ whereas the sequence of its sorption for organic pollutants was p-nitrophenol> phenylamine> phenol. ii) There were two important factors affecting the sorption behavior of the modified bentonite:one was the ratio of the modifiers, and the other was pH of solution. The results showed that the sorption of the organic pollutants and heavy metals to CTMA-L-Bent is excellently in the pH range ca.4-10. iii) There existed a strong syn-ergism in the sorption of organic pollutants and heavy metals to CTMA-L-Bent, that is, the better the sorption of organic pollutants, the stronger the sorption of heavy metals. When in the same concentration of modifiers, for instance, the sequence of their sorption was CTMA-TEPA-Bent> CTMA-TETA-Bent> CTMA-En-Bent for the bentonites modified by the organic ligands of En, TETA and TEPA respectively.(3) A regeneration technique of the modified bentonite, which is called acid-soaking method, was invented. The results indicated that organic pollutants and heavy metals could be desorbed efficiently from the spent modified bentonite respec-tively after immerged in a low concentration of HCl solution (0.1～1.0 mol·L-1). The regenerated sorbents could be use to retreat the solution containing both heavy metals and toxic organic compounds repeatedly and showed a good sorption behavior for the pollutants in water. For example, when CTMA-AET-Bent sorbed PNP and Pb2+ was saturated in a 0.1 mol·L-1 of HCl and shaked for 2 hours, the percentage of PNP de-sorption was 93.5% and that of Pb2+ desorption was even up to 97.8%. After regen-eration, the efficiency of PNP and Pb2+ sorption to CTMA-AET-Bent was almost the same with the original.