1. The diatomite is introduced

     Diatomite is by ancient silicon and siliceous remains of microbes, diatomite main composition is SiO2, and some, Al2O3, Fe2O3, CaO, MgO style and other substances. Because of diatomite performance stability, acid performance, has been in environmental, chemical, petroleum, building materials and many other industrial sectors as filter aid; Its entrance, large aperture can be used as adsorbent; Large specific surface area, adsorption ability strong, can absorb more than 1.5 ~ 4 times the mass of the liquid, 11 ~ 15 times the mass of the oil adsorption itself, etc., can be used as a filling agent, catalyst carrier, abrasive enhancer and animal feed supplements, etc widely application.

     Diatomite purification methods are divided into: physical, chemical and physical and chemical synthesis.

2.1 scrub method

     Scrubbing purification of diatomite before problem is through the scrub will play fine particle size, try to make consolidation of clay minerals such as impurities in diatom test out, create conditions for the separation and purification, and then according to the nature and scope of particles of different minerals, including clay, including iron ore, quartz sand particles is large, because of fast subsidence can be separated first, and the montmorillonite clay impurities writing stirring scrubbing has dispersed into small particles, and the same as the diatomite with negative charge, the same to each other, so it has good suspension and dispersion, thus can add oxygen in slurry dispersants such as sodium oxide to strengthen montmorillonite suspension and dispersion of montmorillonite particles are difficult to precipitation, and diatomite particles in the slurry settling velocity is much faster than montmorillonite particles, the predominantly montmorillonite suspension separated, can get the essence of diatom earth is given priority to with diatomite. Scrubbing Kong Wei by removing part of montmorillonite clay minerals and coarse sediment, the diatomite specific surface area and pore volume increased slightly. YiXianCheng in Inner Mongolia chifeng, such as low grade diatomite as a raw material, study the scrub concentration, washing time, scrubbing times, dispersant and other effects on the physical purification effect.

     Scrubbing method can remove algae shell out impurities, but diatom pores to remove impurities. Scrubbing purification of diatomite process is simple, less investment in equipment, easy to realize industrialized production, but covers an area of large, water consumption, production cycle is long, diatom fine soil drying energy consumption is bigger also. Table 1 is changbai linjiang Ⅱ grade diatomite, scrubbing purification results.

2.2 acid leaching method

     Through splittings after pickling, remove most of the iron and aluminum impurities in the pulp, sedimentation classification for the second time get the silicon content of 91.27% diatomite ore concentrate, through roughing, splittings, acid leaching processing of concentrate meet the expected requirements, silicon content from 71.86% to 71.86%, effectively removes impurities, improve the specific surface area, the whole process yield is about 40%.

     Guilong Zhang, such as acid leaching is studied in the modified effects of diatom pore structure, think acid leaching method not only increase the content of diatomite, can also by modifying diatom pore structure; Osman San and acid leaching of diatomite filtration performance is studied and the influence of porosity, and by using acid leaching diatomite diatomite filtration material and preparation of porous ceramic materials.

     Wen Fei and others through the strip after pickling, remove most of the iron and aluminum impurities in the pulp, then through a settlement of diatomite ore concentrate grade silicon content of 91.27%, after roughing, splittings, pickling treatment after the final concentrate meet the expected requirements, silicon content from 71.86% to 91.27%, can effectively remove impurities, than the surface also has a lot to improve, the entire process yield is about 40%.
     Guilong Zhang et al. studied the pickling for diatom pore structure modification effect, think acid leaching method not only can improve the diatom content, can also by modifying diatom pore structure; Osman San men such as acid leaching of diatomite filtration performance is studied and the influence of porosity, and by using acid leaching diatomite diatomite filter material with porous ceramic material preparation.

     But conventional acid leaching purification time is long, acid dosage, the high cost, environmental pollution and so on, is not conducive to industrial production, greatly affect its application prospect, microwave strengthen diatomite acid leaching purification technology research not only can shorten the leaching time, leaching rate and can make the improvement.

2.3 roasting method

     Roasting method for high fever vector type diatomite is one of the most economic and effective purification method. After roasting, micro holes and gaps in the material volatilize, diatomite specific surface area increase, performance enhancement. Roasting method has certain limitations, the clay impurities removal effect, generally need to be used with other methods. Through 600 ~ 800 ° C calcination, SiO2 content can significantly increase, pore size increases at the same time, the surface acid strength increase. Of diatomite specific surface area increases with the increase of calcination temperature, 450 ° C after calcination reaches the maximum, then along with the rise of roasting temperature drop. Above 900 ° C roasting of diatom shell structure damage.

     Nezahat Ediz et roasting process on the influence of diatomite filtration performance were studied, the results showed that the calcination temperature is 1000 ℃ calcination conditions of 1 h is calcined diatomite ores filtering performance is improved obviously; BulentY ı lmaz et al.
     studied the calcining process of diatomite, the influence of the cement additive application field results show that the calcined diatomite after compared with the run of mine ore can significantly improve the mechanical properties of cement.

     In addition to the above methods, as well as gravity settling, magnetic separation, thermal methods of flotation process, purification effect but each method has limitations, so generally used together. YiXianCheng by physical and chemical purification method of the joint in chifeng area of silicon and low iron high fever vector type diatomite purification processing (SiO2 content of 74.9%), with SiO293.82 1.96% %, Al2O3, Fe2O3 0.22% diatom fine soil quality. Some low grade diatomite Du Yucheng on scrubbing, pickling purified. Experiments show that the three scrubbing the SiO2 content can increase by 70.18% to 83.17%; The secondary pickling, can effectively remove the structure within the clay impurities, SiO2 content can increase nearly 5%.

     Clay of a mine shui-lin zheng on jilin diatomite, through the scrub and settlement separation, compared with the 36.43% yield, SiO2 content of 86.32% of the fine soil, recycling grinding and settlement separation, compared with the 31.18% yield of SiO2 content of 90.17% of the quality of diatomite. Cun-di wei the hot flotation - magnetic separation purification process acid cooking method, the ji Lin mou the low and middle grade diatomite purification research; Jin-chuan gu, dispersion, in addition to the impurity scrub - acid leaching iron - roasting process, will be one of qualified for the purification of diatomite ore in sichuan filter aid.

3 summary

     At present our country has been used diatomite purification methods and the latest scientific research achievements, the purification effect is better, but as a result of diatomite ores is different in nature, the processing method and the process parameters and there are differences, selection of quality essence of diatom earth is not the same. Selected diatomaceous earth method should consider the following principles: one must consider the physical and chemical properties of soil; Second, we must consider the diatoms of pure soil use. So the diatomite purification main purpose is to simplify the production process, meet the application requirements, obtain the best economic benefits.

     Though diatomite resources rich in China, but most of low and middle grade diatomite, good soil is less, from the variety and quality can not meet the requirement of the market, unable to make full use of in many areas. So, research on solving the problem of the purification of diatomite is particularly important, therefore, by physical and chemical purification methods will be low and middle grade diatomite purification for the level of soil, and the level of soil purification for soil with high quality, fine for diatomite provide high-quality raw materials, product processing, in turn, to develop new products excellent performance of diatomite, broaden the application field of diatomite, constantly create new opportunities for diatomite industry.