What harmful substances can zeolite remove in water treatment?
Mechanism of wastewater treatment by zeolite
The internal structure of the zeolite lattice is very open. In addition to the stable [(Al,Si)O4] tetrahedrons that are connected to each other from the top of the corner to form a frame-shaped silicoalumina backbone, there are many holes and channels of uniform size. The holes pass through The channels of the open pores communicate with each other, making the zeolite have a huge specific surface area. According to relevant data, it can reach 400~800m2/g; and the negative charge in the cation lattice and the positive charge center of the balanced cation do not overlap in space There is a huge electrostatic attraction between molecules. In summary, the specific surface area is large, the electrostatic attraction is strong, and the zeolite has good adsorption performance. When the holes and channels in the zeolite lattice are vacant, the zeolite exhibits extremely strong adsorption performance for gas or liquid, especially for the adsorption of sensitive gases such as SO2, NH3, and some organic vapors. Compared with other adsorbents, zeolite has the characteristics of high selectivity, large adsorption capacity and high adsorption efficiency.
The most basic structural units of zeolite space are silicon oxygen (SiO4) tetrahedron and aluminum oxide (AlO4) tetrahedron. The valence electron of one oxygen atom is not neutralized, so that the entire aluminum-oxygen tetrahedron bears a negative charge. In order to maintain electrical neutrality, there must be a positively charged metal cation (M+) near the aluminum-oxygen tetrahedron. Counteract the negative charge it carries (usually alkali metal or alkaline earth metal ions). However, the metal cations such as Na+ and K+ in the zeolite are very weakly combined with the silicoalumina backbone. The cations that enter the surface of the zeolite are exchanged with the cations in the zeolite lattice, such as Na+ and K+. After the exchange, the zeolite structure is not destroyed. regeneration.
Because zeolite has a large adsorption surface and can accommodate a considerable amount of adsorbed substances, it can promote chemical reactions to proceed on its surface, so zeolite acts as an effective catalyst and catalytic carrier. In addition, the zeolite has aluminosilicate lattice charge and counterion charge, has a local high electric field and generates acidic positions on the lattice, so it can be used to accelerate carbon ion-type reactions. In addition, it can exchange catalytically active metals (such as Pt, Pa, etc.), so that it can be dispersed to the greatest extent, maintain high activity while reducing the amount of precious metals.
Application research of zeolite in water treatment
Remove ammonia nitrogen in water
Ammonia nitrogen exists in many industrial wastewaters. Ammonia nitrogen is discharged into water bodies, especially slow-moving lakes and bays, which can easily cause algal death in the water. Ammonia nitrogen also increases the amount of chlorine used in water supply disinfection and industrial circulating water sterilization; it is corrosive to certain metals, especially copper; when sewage is reused, ammonia nitrogen in reclaimed water can promote microorganisms in water pipelines and water equipment Multiply, form biofouling, block pipes and water equipment, and affect heat exchange efficiency. The use of zeolite to remove ammonia nitrogen in domestic sewage and industrial wastewater has been studied at home and abroad. There are certain cavities and pores in the zeolite framework, which determine its role in adsorption and ion exchange. Because natural zeolite is a cheaper mineral, the cost is lower than other adsorbents, and the regeneration cost is low. The regeneration liquid can be reused after being blown off, which shows that zeolite is an ideal denitrification adsorbent.
Remove heavy metal ions in wastewater
Heavy metal ions such as cadmium, mercury, lead, and zinc are substances that cause environmental pollution and are extremely harmful to the human body. The elimination method includes activated carbon
Adsorption method, solvent extraction method and ion exchange method, etc. Experiments show that zeolite, especially zeolite treated with NaOH, HCl and NaCl, has a better effect on the above heavy metal ions. The heavy metal ions adsorbed and exchanged by the zeolite can also be concentrated and recovered. The zeolite can also be regenerated after treatment.
Remove fluorine in water
Fluorine is the most electronegative element and is a very active non-metallic element. When fluoride ions are present in large amounts, it has a toxic effect. Too much fluoride in drinking water can easily cause children with fluorosis and skeletal fluorosis. With Hebei Guotou Shengshi high-quality clinoptilolite as raw material, the technological conditions for activation of natural zeolite with hydrochloric acid, aluminum sulfate and high temperature method were studied. The results show that the fluorine-containing drinking water treated with activated natural zeolite can basically reach the national drinking water standard.
Removal of organic matter in water
With the rapid development of modern industry, especially organic chemical industry, fine chemical industry and polymer industry, organic pollutants in water are characterized by diversification and complexity. For the removal of most organic pollutants, the most widely used method is still the biochemical method, especially the adsorption method. The adsorption capacity of zeolite for organic pollutants mainly depends on the polarity and size of organic molecules. Polar molecules are easier to be adsorbed than non-polar molecules. As the molecular diameter increases, the chance of being adsorbed into the cavity gradually decreases. When zeolite removes dissolved molecular substances in water, adsorption plays a major role, while the result of the combined action of ion exchange and adsorption when removing ionic pollutants in water is mainly ion exchange.
Removal of radioactive materials in wastewater
The radioactive elements Cs+ and Sr2+ are the main components of nuclear fission products and are usually discharged into wastewater. The thermal stability and radiation resistance of zeolite make it superior to Cs+ and Sr2+. In the atomic energy industry, when such substances are contained in radioactive waste liquids, they must be stored until they are transformed into a stable state before they can be excluded. Natural zeolite has extremely strong exchange and removal ability for cesium and strontium, and is not affected by radiation. Moreover, the zeolite exchanged with radioactive ions can be permanently fixed in the crystal lattice after melting to prevent its diffusion and pollution.
Application prospects of zeolite treatment of wastewater
Zeolite is a natural mineral with low cost and good treatment effect. It can reduce the cost of treatment in water pollution treatment. The treatment equipment using zeolite is relatively simple. Zeolite is used to remove ammonia nitrogen, organic pollutants, metal elements, Radioactive substances, sterilization, etc. have obvious effects, can be used to treat wastewater, and are a promising water treatment material.