RU2216385C2 - Method of production of granulated filtering material - Google Patents

Abstract

FIELD: treatment of sewage; water supply systems. SUBSTANCE: proposed method includes introduction of powder-like dolomite into clay suspension followed by mechanical dehumidification of suspension simultaneously with molding, partial drying of molded mixture, crushing of partially dried molds into granules and roasting of granulated material; dolomite is introduced in the amount of 10-20% of mass of clay; partial drying is performed at temperature of 200-400 C and roasting of crushed material is performed at temperature of 800-900 C. EFFECT: enhanced efficiency of cleaning water from humus, suspended particles and ions of heavy metals. 5 tbl

Description

 The invention relates to the production of granular material and can be used in the technology of natural water purification for drinking water supply and wastewater treatment in filter facilities.

A known method of producing granular filter material [1], including the introduction of a suspension of kaolin inorganic additives of powdered dolomite in an amount of 20 ... 25% by weight of kaolin, granulating the mixture and firing the granules at a temperature of 900 ... 950 ^o C. However, the filter material obtained by this method does not provide the required efficiency of water purification from humus, suspended substances and heavy metal ions due to the insufficiently high adhesion force of the particles of contaminants extracted from water to the surface of the filter grains materials and a short duration of the filter cycle, during which the necessary degree of water purification is provided.

There is also known a method for producing granular filter material [2], which includes introducing into the suspension from kaolin an inorganic additive of magnesium carbonate in an amount of 15 ... 30% by weight of the suspension, followed by granulation and calcination at a temperature of 850 ... 900 ^o C. However, the filter material obtained by this method does not provide the required efficiency of natural water purification at its high color, due to humic substances, as well as industrial wastewater treatment at high concentrations of heavy metal ions.

There is also known a method for producing granular filter material [3], including the introduction into a clay suspension of powdered dolomite in an amount of 15.. .18% by weight of clay with its subsequent granulation and firing at a temperature of 800 ...... 880 ^o C (prototype). However, the filter material obtained in this way also does not provide the required efficiency of purification of natural waters with a high concentration of humic substances that determine the color of water, as well as wastewater containing heavy metal ions, such as zinc, copper, hexavalent chromium.

 The objective of the invention is to provide a method for producing granular filter material that provides a high degree and efficiency of purification of various waters from humic, suspended substances and heavy metal ions by increasing the adhesion force between the grain surface of the filter material, pollution particles represented by mechanical suspension, humic colloidal substances and heavy metal compounds.

The problem is solved in that in the proposed method for producing granular filtering material, including introducing into a clay suspension of powdered dolomite carbonate salt of magnesium and calcium in an amount of 10 ... 20% by weight of clay, mechanical dehydration of the obtained homogeneous mixture with molding in the process of dehydration of pellets, cake or briquettes, drying the molded mixture at a temperature of 200 ... 400 ^o C, crushing the dried molded material into granules and subsequent firing of the obtained granules a temperature of 800 ... 900 ^o C.

New in comparison with the prototype is mechanical dewatering with molding, subsequent drying and crushing of pellets, cakes or briquettes consisting of a homogeneous mixture of clay and powdered dolomite, as well as changing the boundaries of the amount of inorganic additives: lower - from 15 to 10% and upper - from 18 up to 20%, as well as changing the upper limit of the firing temperature from 880 to 900 ^o C. Therefore, this technical solution meets the criteria of the invention of "novelty."

Due to the fact that the suspension, consisting of a mixture of clay raw materials and powdered dolomite in an amount of 10 ... 20% by weight of clay, is mechanically dehydrated before firing, molding, subsequent drying of the formed material, crushing it into granules and firing granules at a temperature of 800.. .900 ^o C we obtain a porous filter material with a high sorption capacity for the absorption of contaminants present in water of various qualitative composition. The porosity of the granules of the filter material is ensured by the complete decomposition of the carbonate salt of magnesium and calcium already at the lower boundary of the recommended calcination temperature of 800 ^° C with the formation of a large amount of carbon dioxide and its practically unobstructed exit from the granule body, which contributes to the creation of a highly porous grain structure of the filter material.

Achieving these results by introducing into the suspension of powdered dolomite in an amount of 10 ... 20% by weight of clay, mechanically dehydrating the resulting mixture, drying and crushing the molded mass into granules and then firing them at a temperature of 800 ... 900 ^o С is not necessary for a specialist explicitly from the prior art, therefore, this technical solution meets the criterion of "inventive step".

For the manufacture of filter material according to the proposed method, as the clay raw materials, Cambrian clay of the following chemical composition is used: SiO ₂ 52.1%; Al ₂ O ₃ - 41.6%; F ₂ O ₃ 2.3%; MgO 0.83%; CaO 0.49%; Na ₂ O 0.1%; K ₂ O 0.05%. Vitebsk dolomite in the form of dolomite flour was adopted as an activating additive.

To prepare a suspension of 70% moisture, 10 kg of Cambrian clay was taken. 5 portions of 3.5 L were selected from the resulting suspension. A certain amount of dolomite flour was introduced into each portion, namely:
- in the first 0.12 kg (8 wt.% by weight of clay),
- in the second 0.15 kg (10 wt.% by weight of clay),
- in the third 0.225 kg (15 wt.% by weight of clay),
- in the fourth 0.30 kg (20 wt.% by weight of clay),
- in the fifth 0.33 kg With 22% weight by weight of clay).

 The resulting mixture was stirred until homogeneous.

 All five portions of the mixture were subsequently subjected to mechanical dehydration in a laboratory press filter unit.

 Pellets of 8 ... 10 mm in size were granulated from the dehydrated mixture of a dough-like state, counted in diameter, dried several weighed batches at various temperatures and crushed in a manual coffee grinder.

 Drying was carried out in order to give the granules sufficient mechanical strength to reduce the degree of grinding and abrasion during subsequent heat treatment in roasting apparatus.

To establish the optimum drying temperature, the granular mixture was dried at temperatures of 100, 150, 200, 300, 400 ^o C. The upper limit of the drying temperature (400 ^o C) was dictated by the fact that when the processing temperature of the mixture of clay with dolomite more than 400 ^o C the process of decomposition of dolomite with the formation of calcium and magnesium oxides and the release of a large amount of carbon dioxide. At the stage of drying the material in order to mechanically harden its decomposition, carbonate salt is not required, it (decomposition) is only necessary at the firing stage, when an intragranular porous structure of the granular filter material is formed.

 The criterion for assessing the sufficiency of the temperature of the drying of the granules was the degree of grindability and abrasion of them under mechanical action. The mechanical effect was carried out by shaking a portion of the granular mixture on a laboratory vibrating screen for 3 minutes. The size of the sample was 20 g; the mesh size of the sieve was 0.25x0.25 mm. After shaking, the screening was weighed, the screening value (g), referred to the sample size (20 g), characterized the degree of destruction (grinding and abrasion) of the material.

 The results of determining the degree of destruction of granules, dried at different temperatures and subjected to shaking, are presented in table. 1.

From the data of table 1 it follows that at a drying temperature of 100 and 150 ^o With the loss of granular material for grinding and abrasion is very large, which is economically disadvantageous. When the drying temperature is from 200 to 400 ^o With the total loss is much lower and range from 25 to 8.3%. These indicators are quite acceptable, therefore, the drying temperature from 200 to 400 ^o With accepted for use in the manufacture of granular filter material.

Dried and crushed samples of the material were fired in a muffle furnace at various temperatures in order to determine the mechanical strength of the granules depending on the firing temperature and to select a temperature range in which the granules of the filter material satisfy the mechanical strength requirements. The firing temperature was varied from 750 to 950 ^o C every 50 ^o C. Indicators of mechanical strength (grindability and abrasion) were determined by standard methods. The test results are presented in table.2.

As the data in table 2 show, at a firing temperature of less than 800 ^o C there is insufficient mechanical strength of the granules, while the loss is more than 4%. Raising the firing temperature over 900 ^o With the increase in mechanical strength practically does not.

For a comparative assessment of the filtering properties of the proposed material, a filter material (prototype) was taken, manufactured at an industrial plant for the production of granular filter material with the following characteristics: initial clay feed - Cambrian clay, additive - dolomite flour, the amount of additive 15 wt.% By weight of clay, firing temperature 850 ^o C.

The ability of filter materials to remove contaminants from water with a different amount of dolomite powder additive in clay raw materials and filter material made in accordance with the prototype is determined by the following method. A portion of each material in an amount of 10 g is placed in two sets of flasks. In each flask from the first set, pour 100 ml of water with a color of 210 ^o platinum-cobalt scale; 100 ml of water, which contains 21.6 mg / l of zinc ions, is poured into each flask from the 2nd set. The contents of all flasks are shaken slightly every 2 hours. The sorption capacity of the absorption of contaminants in each material is determined by the change in the color of the water, due to adsorption of humic substances on the surface of the granules of filter materials and a decrease in the concentration of zinc ions in the aqueous solution after 12 hours of contact.

 The test results are presented in table.3.

 From the data of table 3 it follows that the sorption ability of the material manufactured by the proposed method, the sorption of humic substances with any amounts of activator additives other than additives 8 wt.% By weight of clay) is higher by 20.. .35% than the material adopted for the prototype. The absorption capacity of heavy metal ions (zinc) of the proposed material is on average 35 ... 40% higher than that of a material manufactured by the method adopted as a prototype.

 Technological testing of the filter material manufactured according to the proposed method was carried out on a filtration stand. The tests consisted of two stages. At the first stage, the efficiency of purification of high-color water was determined, and at the second, the efficiency of purification of water containing heavy metal ions (zinc).

 At both stages of the technological tests, 5 filter columns were loaded with the obtained granular materials, differing from each other only in the amount of powdered dolomite introduced. The sixth column was loaded with granular material made according to the prototype.

 The filter media on all columns were characterized by the following parameters: grain size 0.6 ... 1.0 mm, layer thickness 400 mm.

 The water treatment efficiency was determined on all six columns. A filter column loaded with material made according to the prototype served as a reference for comparison.

At the first stage, natural water of the following qualitative composition was filtered through all six columns: suspended solids 4 mg / l, color 106 ^o . The filtration rate during the filter cycle was kept constant and amounted to 2.5 m / h. The coagulant was not added to the water before it was filtered. In this case, colloidal particles of humic substances, which impart color to water, were sorbed on the surface of the grains of filter materials without preliminary treatment with a coagulant. The criterion for the effectiveness of water purification from color is the degree of water discoloration and the duration of the filter cycle, during which the source water is purified to the requirements of SanPin 2.1.4.559-96 "Drinking water".

 At the second stage of testing, the imitate of wastewater of the following qualitative composition was filtered through all six columns: suspended solids 2 mg / l, zinc ion concentration 16.8 mg / l. The filtration rate was 2.5 m / h. The criterion for the effectiveness of the filter material was the degree of purification of the drain simulator from zinc ions.

 The results of technological tests at both stages are presented in table. 4 and 5.

Technological tests for water purification from color show that the duration of the filtering, during which the water is bleached to the requirements of SanPiN 2.1.4.559-96 (20 ^o ) on the filter material made by the proposed method with the addition of dolomite to clay in an amount of 10 ... 20 weight. % by weight of clay is 1.5 ... 2.0 times more than on material made in accordance with the prototype (Cambrian clay with the addition of dolomite in the amount of 15 wt.% by weight of clay). When dolomite is added to clay raw materials less than 10 wt.% Of the clay mass (for example, 8%), the decolorizing ability of the filter material is significantly reduced. It is comparable only with the material made according to the prototype.

 From the data of table 5, which shows the results of filtering the simulated effluent containing heavy metal ions of zinc, it follows that the material manufactured by the proposed method, much more efficiently cleans the drain of zinc ions than the material made in accordance with the prototype.

 The best results when cleaning the drain from zinc ions are given by filtering materials made of Cambrian clay with activating additives of dolomite in the amount of 10 ... 22 wt.% By weight of clay. Material made from Cambrian clay with the addition of dolomite in an amount of 8 wt.% By weight of clay is better than material made in accordance with the prototype, but not significantly. The filter material made of Cambrian clay with the addition of dolomite in an amount of 22 wt.% By weight of clay has practically the same absorption capacity of zinc ions with a material having an addition of dolomite in an amount of 20 wt.% By weight of clay.

 It should be noted that ground dolomite is significantly more expensive than clay raw materials. Therefore, the most rational amount of dolomite additives should be considered 10 ... 20 wt.% By weight of clay.

Sources of information
1. Copyright certificate of the USSR 1243807, cl. B 01 J 20/02, C 02, 05/08/84.

 2. USSR copyright certificate 1152650, cl. B 01 J 20/02 C 02, 02.17.02.84

 3. RF patent 2077380, cl. B 01 J 20/02, 20/04, 04/19/94

Claims (1)

A method of obtaining a granular filter material, including the introduction into a clay suspension of powdered dolomite in an amount of 10.. . 20 weight. % by weight of clay, followed by mechanical dehydration of the mixture, granulation and firing at a temperature of 800.. . 900 ^o C, characterized in that before granulation produce drying of the mixture at a temperature of 200.. . 400 ^o C.

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