Views: 74 Author: Site Editor Publish Time: 2022-03-04 Origin: Site
Deep nitrogen and phosphorus removal from wastewater is an important measure for the reuse of municipal wastewater resources and water pollution control.
The traditional biological treatment process mainly removes organic matter, and biological denitrification has problems such as additional carbon source input and complicated process technology. Adsorption method is a suitable method for treating low concentration pollutants, with the advantages of high treatment efficiency and stable effluent quality, which can be used for deep treatment of tailwater in sewage plants. Natural zeolite has rich pore channels and cation exchange adsorption properties, and has certain selective adsorption for NH4+.
However, its high mineral impurity content and uneven structural pore channels lead to small adsorption capacity, which is limited in engineering applications. The current research on the modification and regulation of natural zeolites has not fundamentally solved the defects in material composition and structure, and the adsorption performance is still not satisfactory.
In recent years, the artificial synthesis of molecular sieves from natural zeolites has become an effective method to solve this problem. The molecular sieve has the same basic structural unit as natural zeolite, which is silicon (aluminum) oxygen tetrahedra, and some of the silicon atoms of the silicon oxygen tetrahedra in its molecular skeleton are replaced by aluminum atoms to form negatively charged aluminum oxygen tetrahedra, which are combined with cations to achieve electric neutrality. The molecular sieve has a regular structure, uniform pore channel and low impurity content, which is an excellent adsorbent for ammonium ions.
The amount of soluble silicon dissolved after alkali soluble pretreatment of different zeolite raw materials is shown in Table 3. Combined with Table 3, which shows that C zeolite has the highest amount of soluble silicon, A zeolite is second, and D and B zeolites are lower. The soluble silicon dissolved is the main raw material for the next step of crystallization synthesis of molecular sieve, which has a decisive influence on the purity and quality of molecular sieve in the synthesis product.
And it is known from the test that the alkali solubility of mineral components in zeolite raw materials is related to their structural stability. Among them, quartz (SiO2) belongs to the tripartite crystal system, which generally has a tripartite bipyramidal or rhombic structure, and its polycyclic structure is more stable than that of plagioclase and smectite, so the general alkali solubility treatment cannot activate and dissolve it.
Compared with zeolite raw materials, the Si and impurity contents of the four synthesis products were relatively reduced, while the Al and Na contents were relatively increased, and the corresponding Si-Al ratios were reduced by 5-7 ratios, which was beneficial to improve the cation exchange adsorption performance of the synthesis products.
However, the difference of the Si-Al ratio of the four synthetic products was not obvious (varying in the range of 2.86-3.81), while the ammonia nitrogen adsorption amount was significantly different from the conclusion that the molecular sieve Si-Al ratio had an inverse relationship with the ammonia nitrogen adsorption amount, which was due to the fact that the synthetic products were a mixture of molecular sieve and other mineral components coexisting, and the purity of molecular sieve in the synthetic products was different.
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