Diatomite is a kind of biological siliceous sedimentary rock deposited from the siliceous remains of diatoms and other microorganisms. It has the characteristics of developed microporous structure, huge specific surface area, light weight, strong adsorption capacity, low thermal conductivity and good chemical stability. At the same time, it is cheap and easy to use, which makes it have broad application prospects in the field of environmental engineering.

1. Diatomite wastewater treatment materials

Diatomite has a huge specific surface area, and the particles contain a large amount of silicon hydroxyl. The silicon hydroxyl will dissociate H + in aqueous solution, so that the surface of diatomite has a strong negative charge. It is an adsorbent with excellent performance.

In order to further improve the adsorption performance of diatomite, a large number of researchers have carried out a series of modification work. The modified diatomite can be used to treat domestic sewage, wastewater containing heavy metal ions, papermaking wastewater and printing and dyeing wastewater.

Fan Yi et al. Synthesized zirconium modified diatomite by surface crosslinking method. It was found that the phosphorus adsorption capacity of zirconium modified diatomite was higher than that of pure zirconia adsorbent. For eutrophic lake water with phosphorus concentration of 2mg / L, when the dosage of zirconium modified diatomite was greater than 1.25g/l, the phosphorus concentration in the water body after reaction could meet the class III standard of lake and reservoir specified in the environmental quality standard for surface water. Wang Fang modified diatomite with transition metals (Fe, Cu, Zn). When the addition of Fe is 7%, the ammonia nitrogen adsorption capacity is 1.18mg/g, and the ammonia nitrogen removal rate is 2.19 times that of unmodified diatomite.

2. Diatomite organic pollutant adsorption material

Organic pollutants are the most complex pollutants in the field of environment. They will threaten human health and the growth of animals and plants, destroy the ecological balance and interfere with the ecosystem. By loading active components such as activated carbon, molecular sieve, MOF and metal oxide on the surface of diatomite, the positive and negative electricity of diatomite surface can be adjusted, the interface between diatomite and adsorbate can be improved, and various organic dye molecules, polluted oils, landfill leachate and other organic wastewater in water can be removed.

3. Diatomite heavy metal adsorption material

Heavy metal ions are discharged into the environmental water body through industrial wastewater. After a series of chemical actions, migration and transformation, they are finally retained in the water body in different forms, forming permanent potential hazards. The surface of nano metal oxide is rich in active hydroxyl groups, easy to combine with pollutants in solution and has high adsorption activity. Nano metal oxide is modified on the surface of diatomite, and the efficient adsorption of pollutants in water can be realized through the synergistic effect of the two. At present, surface treatment or modified diatomite for heavy metal ion adsorption has become a research hotspot.

4. Diatomite adsorption filler

As a cheap ore material with rich microporous structure, huge specific surface area, high porosity, strong adsorption capacity, good chemical stability and rich resources, diatomite can be used as a raw material for the preparation of fillers in activated sludge process and biofilm process to improve the treatment efficiency.

Zhu Jian and others prepared diatomite based porous adsorption filler with diatomite as the main raw material in a certain proportion with ultra-fine carbon powder, sintering additives and binder. Its adsorption capacity for Pb2 + in water is 78.0% higher than that of diatomite original soil (powder).

5. Diatomite microbial carrier

Diatomite has rich pores and specific surface area. If it is added to activated sludge, microorganisms can adhere through its porous structure, and diatomite can be used as a carrier of microorganisms, so as to improve the biological activity of microorganisms, reduce sludge bulking, and then improve the effluent index.

Zhang et al. Found that adding diatomite to the activated sludge system can improve the biomass in the wastewater treatment system containing phenolic compounds and enhance the sedimentation performance of sludge; The added diatomite can be used as the carrier of microorganisms to improve the biomass. The addition of diatomite can improve the removal rate of COD and total phenol in wastewater.

6. Diatomite filter aid and filter agent

Compared with the traditional fine filtration, the particle size of diatomite is relatively small, so the content and particle size of suspended solids in effluent are much smaller than that of conventional filtration process; Because the diatomite filter layer is easy to fall off, its filter membrane can be precoated repeatedly. Compared with ultrafiltration membrane or ceramic membrane filtration, these characteristics overcome the technical problems such as easy blockage and difficult backwashing of ultrafiltration membrane or ceramic membrane. It is a precision filter material with very good application prospect.

7. Diatomite air pollution control material

The adsorption method for VOCs treatment has the advantages of low energy consumption, high removal rate, low price and almost no secondary pollution. Diatomite has low price and good adsorption performance. In recent years, relevant scholars have greatly improved the adsorption capacity of diatomite for organic pollutants by modifying it.

In addition, diatomite loaded with photocatalytic components such as nano-TiO2 not only has the function of adsorbing organic pollutants such as formaldehyde, toluene and phenol, but also has the function of photocatalytic degradation of these organic pollutants.

8. Catalytic degradation of diatomite and synthesis of materials

The high specific surface area and porous structure of diatomite can provide effective surface and appropriate pore structure for the catalyst, increase the contact probability and area between active components and reactants, and improve the utilization efficiency of the catalyst; The mechanical stability and high temperature stability of diatomite can ensure that the active material will not be inactivated at high temperature; Diatomite has low cost and can reduce the production cost of catalyst.

In terms of using diatomite as photofenton heterogeneous catalyst, Yan et al. Prepared Fe2O3 supported diatomite matrix composites. Diatomite can also be used as a carrier of elemental catalyst materials. Brunner et al. Realized the loading of nano gold particles on the surface of diatomite and applied it as a catalyst for the catalytic oxidation of glucose.

9. Diatomite soil remediation material

Diatomite can effectively fix heavy metals in soil through chemical reaction in pores and reduce its bioavailability; In addition, the indefinite diatomite particles can absorb more than 1.5 times its own volume of water, and the effective water content of soil increases significantly. At the same time, the surface porous property is also a good carrier of fertilizer, and has a good slow-release effect on nitrogen, phosphorus and potassium. Therefore, it is also an excellent soil conditioner.

As a new type of environmental protection mineral material, diatomite has the advantages of low price and high efficiency in treating various pollutants, which makes its development prospect very broad. Therefore, it is necessary to deeply explore the adsorption mechanism and dynamic characteristics of diatomite in the treatment of industrial wastewater, waste gas and soil, and find the laws and influencing factors to meet the needs of diatomite for the treatment of different types of pollutants.

In addition, diatomite has limited pore structure and surface activity, and does not have good removal ability for all environmental pollutants. Therefore, researchers use various physical or chemical means to modify or compound the surface of diatomite, and develop different diatomite based composites to expand the application range of diatomite in the field of environment.