Surface Modification Of Natural Zeolite And Its Application In Wastewater Treatment With Organic Pollutants

Natural zeolites are a kind of hydrated alumina silicate minerals, which possess large specific surface areas due to their porous structures caused by frame structures. Therefore, they are often used as adsorbents in the field of environmental protection. In aluminum- oxygen tetrahedron of natural zeolites, an oxygen atom forms only one covalent bond, leading to the charge imbalance. In this way, aluminum- oxygen tetrahedron becomes negatively charged. To maintain an electrically neutral, some cations should offset the negative charge. In general, alkali metal and alkaline earth metal ions can offset the negative charge. This feature makes zeolites possess good ion exchange capability. Based on the above characteristics, natural zeolites have been widely applied in the field of environmental protection.However, in the actual treatment of waste waters, the compositions of waste waters are very complicated. They may contain some cationic or anionic pollutants. The raw natural zeolites are effective for the removal of cationic pollutants, but are not effective for the removal of anionic and neutral pollutants from wastewater. In order to take the advantages of natural zeolites and overcome their shortcomings, we designed and prepared three kinds of modified natural zeolites.In the first part of the work, we used three kinds of polysiloxane quaternary ammonium salts(PSQASs) for the surface modification of the natural zeolites. We prepared three kinds of modified natural zeolites(PSQAS-NZ1, PSQAS-NZ2 and PSQAS-NZ3) and then used them for the simulation experiment of Congo red adsorption. Results showed that the adsorption equilibrium data fitted well with Langmuir isotherm model and pseudo-second-order model. In the study of thermodynamics, we found that the adsorption process is a spontaneous endothermic reaction. In addition, PSQAS-NZ1, PSQAS-NZ2 and PSQAS-NZ3 which loaded 1.07′10-4 mol of quaternary ammonium salt functional groups per gram can adsorb 33.11, 12.08, and 10.97 mg/g of Congo red from 30 mg/L Congo red solution, respectively.In the second part of the work, we used three kinds of alkylene polysiloxanes(APSs) for the surface modification of natural zeolites. We prepared three kinds of modified zeolites(APS-NZ1, APS-NZ2 and APS-NZ3) and then used them for the simulation experiment of aniline adsorption. Results showed that the adsorption equilibrium data fitted well with Langmuir isotherm model and pseudo-second-order model. It also proves that the process of aniline adsorption is a typical chemical monolayer adsorption. Through thermodynamics research, we found that the process is more suitable to proceed at low temperature. For aniline solution of 50 mg/L, the adsorption capacity of the modified zeolite prepared by 0.02 g AS3 and 1.00 g of natural zeolite reached 25 mg/g. The durability testing under flowing water condition proved that the polymerized siloxane quaternary ammonium salts are durable on the surfaces of the modified zeolites. Also, it was found that the as-prepared modified zeolites have very good regenerabilties.In the third part of the work, we modified the surfaces of the natural zeolites with chitosan to prepare chitosan modified natural zeolites(CMNZs) and then used CMNZs for the simulation experiment of phenol adsorption. In addition, we explored the effect of p H on the adsorption process. In the research of dynamics, we found that phenol adsorption process fitted with pseudo-second-order model very well. The isothermal analysis showed that the adsorption process fitted with Langmuir isotherm model. It can be seen from the adsorption equilibrium data that CMNZs have strong phenol adsorption capacity. In conclusion, CMNZs have the potential to become effective adsorbents due to their easy preparation, cheap and accessible raw materials, and good adsorption performance.