RU2104760C1 - Method of manufacturing filter element for deep purification of colloid systems from disperse phase - Google Patents

Abstract

FIELD: filtration technics. SUBSTANCE: layer of colloid particles is inwashed onto porous carrier with pore size 0.5-2.0 mcm by hematite dispersed to concentration no higher than 1.0 g/l in ferric chloride aqueous solution having concentration 1.0 g/l to attain specific density of inwash 40-80 mcg of hematite per 1 sq.cm on conversion to iron. EFFECT: achieved desired quality of filter element. 2 tbl

Description

 The invention relates to the field of filtration. The present invention is advisable to use for deep cleaning from colloidal and coarse impurities, as well as to determine the concentration of the dispersed phase in the analyzed medium.

 Currently, there are many ways to clean dispersed systems. The most common water purification methods are ion-exchange filtration and filtration through a layer of inert filter material - perlite, diatomite, magnetite, etc. [1,2].

 To increase the cleaning efficiency of dispersed systems, filter materials are preliminarily washed on a porous substrate (alluvial filters). The filter element of the alluvial filters is a perforated pipe entwined with a wire with a gap between the turns of wire 0.1 mm with a layer of filter material washed over it. All these methods have a significant drawback - the degree of removal of the dispersed phase does not exceed 60 - 85%.

 A more effective cleaning method is the method of filtering colloidal systems through porous membranes [3]. The efficiency of removing the dispersed phase by this method reaches 90%. Since when filtering dispersed systems through membranes, not only purely mechanical retention of particles on the surface and in the pores of the membrane occurs, but also their capture due to electrokinetic interaction with the membrane surface, the pH of the medium, the fractional and chemical composition of the dispersed phase significantly affect the cleaning efficiency, flow rate through the filter, pore size of the membrane, etc. Our studies have shown that the efficiency of trapping particles of corrosion products by domestic porous membranes with size rum then 0.12 - 4.0 microns do not exceed 80 - 40%, respectively.

- 5 мкм) и обладают полупроницаемыми свойствами все время, пока в поступающем на них растворе имеются примеси дисперсного материала. В случае небольшого механического повреждения намытого слоя возможно самовосстановление мембраны за счет отложения на подложке нового слоя дисперсных частиц.The closest analogue is a method of manufacturing filter elements for deep cleaning of dispersed systems on dynamic membranes [4]. Dynamic membranes are formed by filtering a solution containing impurities of a dispersed substance through porous substrates (pore size 30

- 5 microns) and possess semi-permeable properties all the time, while there are impurities of dispersed material in the solution arriving at them. In the case of slight mechanical damage to the washed layer, self-healing of the membrane is possible due to the deposition of a new layer of dispersed particles on the substrate.

Dynamic membranes have the following disadvantages:
A prerequisite for the effective operation of a dynamic membrane is the constant replenishment of the washed layer with fresh dispersed particles, which leads to a significant increase in the hydraulic resistance of the membrane over time. So, a membrane formed by dispersed additives of zirconium hydroxide with polyacrylic acid was used for wastewater treatment. With a differential pressure of 70 kg / cm ^{2, the} specific flow rate through the filter (S = 4 m ² ) was only 1 l / hcm ² .

 Insufficiently high cleaning efficiency (in the processing of radioactive waste, a decrease in activity of 88% was achieved).

 Aggregate instability of the alluvial layer. The problem solved by the invention is to increase the efficiency of cleaning dispersed systems from the dispersed phase while significantly reducing the hydraulic resistance of the filter.

The essence of the proposed method lies in the fact that a layer of dispersed hematite with a specific density of 40 - 80 μg / cm ^{2 is} washed on a porous substrate with a pore size of 0.5 - 2.0 μm (porous membrane, precoated pearlite filter, etc.) in terms of iron) containing a dispersed medium. For washing use a colloidal solution of hematite with a concentration of not more than 1 g / l in an aqueous solution of FeCl ₃ with the same concentration. When the value of the washout density is less than 40 μg / cm ² , the cleaning efficiency does not exceed 85 - 90%, and for filter elements with a wash density of more than 80 μg / cm ² , the hydraulic resistance sharply increases. The minimum pore size of the filter element substrate (0.5 μm) is due to the significant hydraulic resistance of the substrate itself, and when using a substrate with a pore size greater than 2.0 μm, the cleaning efficiency does not exceed 85 - 90%, since it is not possible to obtain a sufficiently high-quality alluvial hematite layer (tight, well adhered to the surface of the substrate). In addition, for substrates with a pore size of more than 2.0 μm, a slip of hematite particles into the filtrate is observed. The upper limit of the concentration of hematite and electrolyte (FeCl ₃ ) in the wash solution is determined by its aggregate stability. The lower limit of hematite concentration in the wash solution is determined only by its solubility (solubility does not exceed 1 • 12 ^-12 g / l at 25 ^o C. Dispersed system flow through the filter element (S = 2 cm ² ) at a working pressure drop of 0.2 kg / cm ² and in the given intervals of the parameters is 1 - 15 l / h, which is 100 - 200 times less than in the method - the closest analogue.

 The basis of the invention was the experimentally discovered phenomenon of almost complete retention of colloidal particles of various nature in the washed layer of fine hematite due to the interaction of this layer, which is a periodic colloidal structure, with a filtered dispersed phase.

 The main condition for the effective operation of the filter element is the aggregative stability of the layer being washed during washing and during filtration, i.e. the absence of spontaneous formation of irregularities in the layer.

 The novelty of this method lies in a new technique: washing on a porous substrate before filtering a layer of dispersed hematite. At the same time, during filtration, no additional washing of the dispersed phase is performed. The novelty is significant, because from the literature there are no known methods for almost complete purification of colloidal systems from the dispersed phase by filtration.

The essence of the proposed method is illustrated by the following examples:
Example 1

A layer of hematite with different specific gravity of the wash was washed on porous dacron membranes (S = 2 cm ² , pore size 0.12; 0.57; 1.1; 2.0; 2.5 μm) , 100 μg Fe / cm ² ) and then a colloidal solution of hematite with an iron concentration of 20 mg / L was passed through these membranes. The iron content was determined by the orthophenontraline method. The working pressure drop of 0.2 kg / cm ² . The results are presented in table 1.

As can be seen from the table, the goal is achieved by using a porous substrate with a pore size of 0.5 - 2.0 μm and a hematite washout density of 40 - 80 μg Fe / cm ² , i.e. within optimal parameter ranges.

 Example 2

A sample of a colloidal solution (H ₂ O - CaCO ₃ ) with a CaCO ₃ particle size of less than 1 μm was passed through a dacron membrane (pore diameter 2 μm) and through the same membrane with a washed-up hematite layer (60 μg Fe / cm ² ). The Ca content in the filtrate was determined by complexometric titration with complexon III. The results obtained are presented in table.2.

The detection limit of calcium by complexometric titration is 1 mg / L, which approximately corresponds to the solubility limit of CaCO ₃ . Thus, it can be seen from the table that a membrane with a pore size of 2 μm, processed by the proposed method, almost completely retains CaCO ₃ colloidal particles _of less than 1 μm.

 Example 3

A perlite layer with a specific wash density of ≈0.01 g / cm ² was washed onto a perforated pipe with a 0.1 mm gap between the turns of wire, after which a hematite layer with a wash density of 60 μg Fe / cm ² was washed on it. Tap water was passed through the filter element thus prepared and the content of iron PK in the feed water and the filtrate was analyzed by the sulfosalicylic method. When the iron PK content in the initial water was ≈1 mg / L, their concentration in the filtrate did not exceed the upper limit of determination (20 μg / L).

The advantages of this method compared to the closest analogue:
increase in cleaning efficiency up to almost 100%;
increase in hydraulic resistance of the filter element;
preservation of the filtering characteristics of the element with the washed layer for an unlimited time while the layer contains a dispersed medium (when the washed layer dries, a repeated hematite washing process is necessary).

Claims (1)

A method of manufacturing a filter element for deep cleaning of colloidal systems from the dispersed phase by washing on a porous substrate with a pore size of 0.5 to 2.0 μm hematite dispersed to a concentration of not more than 1 g / l in an aqueous solution of FeCl ₃ with a concentration of not more than 1 g / l to achieve a specific density of the washout 40 80 μg of hematite per 1 cm ² in terms of iron.

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