Effect of particle size and soaking time on filtration performance of diatomite filter aid
Diatomite filter aid is a powder product made from diatomite by roasting and grading process.
In industrial production filtration, diatomite filter aid has the advantages of good adsorption performance, microporous structure and anti compression performance. It can filter out fine suspended solids, and the particle size of small impurities that can be filtered is 0.11wm.
Therefore, diatomite filter aid is widely used in water treatment, agriculture, food and medicine, which can effectively improve the filtration speed and filtrate clarity.
It has been found that diatomite can obtain a filter aid with good permeability and good clarity of beer filtrate after adding a certain amount of flux such as sodium carbonate and sodium chloride in roasting.
In terms of the effect of particle size on the performance of diatomite filter aid for food and medicine, Jiang Yuzhi et al. Conducted some research, and concluded that the particle size range of diatomite filter aid melting roasted products should be 24.6131.4um, and the particle size range of diatomite filter aid roasted products should be 2.979.8um. However, they only investigated the effect of particle size on permeability, The effect of particle size on whiteness and impurity adsorption was not investigated.
Because the higher the whiteness of diatomite, the wider its application range, the better the adsorption of filter aid to impurities, and the clearer the filtrate. Therefore, the effects of particle size on permeability, whiteness and adsorption should be considered.
After diatomite is placed in the wetting environment for a certain time, its adsorption performance may be affected to a certain extent due to the adsorption of water in the pores. In the filtration application, with the progress of filtration, the wetting degree of filter aid becomes higher and higher, and the adsorption performance may decline slowly, The study on the influence of soaking time on the filtration performance of filter aid can provide a certain reference for the field service life of filter aid. In this paper, permeability, whiteness and beer filtration absorbance were used as indexes to evaluate the excellent filtration performance of diatomite, and the effects of particle size and soaking time on the performance of diatomite filter aid were investigated.
Test materials and methods
Diatomite samples for raw material test were taken from a company in Linjiang. X-ray fluorescence analysis of diatomite shows that its main chemical composition is Si02 6.41. XRD analysis shows that its main mineral composition is amorphous opal, and a small amount of quartz, illite and plagioclase.
Beer stock liquor is taken from the sample before filtration and sterilization in a brewery in Wuhan, with an absorbance of 1.900. 2.2. Sx2-8-13 box type energy-saving resistance furnace and equipment.
Yq-z-48a whiteness color measurement: invite particle size (UM) particle size condition test whiteness, permeability and beer filtration absorbance comparator.
V-1100d mapada visible spectrophotometer; The permeability measuring device is self-assembled according to the national standard gb24265-2009 diatomite filter aid.
Test method preparation process of filter aid: diatomite raw material is crushed and graded, evenly mixed with flux na2c3, roasted in high temperature furnace, cooled, dispersed and graded to obtain different particle sizes of filter aid.
The roasting process is carried out from 25 ° C to the method specified in the filter aid. After the permeability measurement is completed, add a certain amount of beer stock solution that has been stirred evenly. Like the permeability measurement, the vacuum degree is controlled at 7600 ± 100Pa. After the beer is filtered, measure the volume of beer filtrate, record the beer filtration time and calculate the beer filtration speed.
The filtered beer filtrate was tested for absorbance with a spectrophotometer, and the wavelength was 560nm. The whiteness of the products with particle size of + 150, + 37, – 150 + 37, – 150, – 37um in the calcined filter aid was determined.
The influence of particle size distribution on the properties of diatomite filter aid was explored. The preparation conditions of filter aid were as follows: the amount of flux na2c3 was 7% of the quality of diatomite, diatomite and flux were mixed evenly by dry method, calcined at 1000C, heated for 3H and kept warm for 2h. After crushing the obtained diatomite, the products with particle size of + 150, + 37, – 150 + 37, – 150, – 37um were obtained, The whiteness, permeability and absorbance were measured under the same conditions.
Although there are small fluctuations, the permeability is decreasing with the decrease of particle size.
As the average particle size increases, the specific resistance decreases and the permeability increases.
This may be because the coarser the particles in the solution, the larger the void in the filter aid, thus increasing the permeability.
The smaller the particle size, the lower the absorbance, the clearer the filtrate, and the better the filtration effect.
Whiteness generally has an obvious upward trend, but there is a certain fluctuation at – 150 + 37um. The causes of this phenomenon need to be further studied. However, in general, reducing the particle size can increase the whiteness. Considering that it will not affect the sensory performance and color of food filter solution, the higher the whiteness of filter aid, the better.
High quality diatomite filter aid should have high permeability, low absorbance of beer filter solution (the lower the absorbance, the clearer the filtrate, indicating the better filtering effect) and high whiteness.
Based on the above data, it can be concluded that the smaller the particle size, the higher the whiteness and the lower the absorbance, the better the filtering effect.
However, if the particle size is small, the permeability will be reduced. The reduction of permeability will slow down the filtration speed, and sometimes it can not even be filtered.
Therefore, an appropriate balance point must be selected between absorbance, whiteness and permeability, so that both higher whiteness and permeability and lower absorbance can be obtained.
Effect of soaking time because diatomite filter aid has a large number of holes and strong adsorption, it is investigated whether the filtration performance is affected after the filter aid is soaked in water for a long time. The diatomite filter aid modified with sodium carbonate was screened with a 150um sieve. Finally, the diatomite filter aid with – 150um particle size was selected to study the effect of soaking time on the permeability and absorbance of diatomite filter aid, which is basically consistent with the particle size of most commercial diatomite filter aid products.
To sum up, the longer the soaking time, the weaker the interception effect of filter cake on impurities, the worse the filtering effect, and the permeability decreases significantly after soaking for 4H. In the continuous filtration process, due to the accumulation of impurities in the filter cake and the adsorption of liquid in the pores, the filtration effect will gradually deteriorate. After the filter cake is used for 4h, the filtration speed will be significantly reduced.
For the diatomite filter aid calcined and modified with sodium carbonate, its filtration performance is greatly affected by the particle size. The smaller the particle size, the higher the whiteness, and the smaller the absorbance of beer filter solution, that is, the better the filtration effect. However, the decrease of particle size will reduce the permeability, and the decrease of permeability will prolong the filtration time. Therefore, in the process of practical application, the appropriate particle size must be selected according to the actual requirements, and an appropriate balance point must be selected between absorbance, whiteness and permeability.
The filtration performance of diatomite filter aid will also be affected by soaking time, which will affect the interception effect of diatomite filter aid on impurities, that is, the longer the soaking time, the lower the clarity of filtrate.