RU2625114C1 - Process of producing finely dispersed amorphous microsilica by sol-gel method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: process for producing finely dispersed amorphous microsilica by sol-gel method. The process comprises a preliminary drying and milling diatomite. The micronized diatomite added 10-30% sodium hydroxide solution, incubated at 70-90°C for 2-3 hours at a ratio of liquid and solid phases 12: 1. Silicic acid precipitation is carried out from the filtrate by addition of concentrated hydrochloric acid solution. Separate the precipitate of silica and dried.

EFFECT: invention provides a dispersion of fine amorphous microsilica 0,062-0,097 micron with high purity from inexpensive mineral raw materials in a high yield the desired product.

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Description

The invention relates to the technology of the building materials industry and the processing of mineral raw materials for the creation of insulating materials, dry building mixtures, the production of modified additives for concrete, the manufacture of optical fiber.

The scope of finely dispersed amorphous silicon dioxide in the world economy is expanding every year, since amorphous silica is a multi-purpose material and is used in various industries, including in the field of high technology. It is used in the manufacture of glass, ceramics, concrete products, abrasive materials, as well as in radio engineering, ultrasonic installations, and in the manufacture of fiber optic cables.

Amorphous silicon dioxide in its pure form is almost not found in nature. It can only be obtained in a technological way. There are various methods for producing finely dispersed amorphous silica fume.

A known method of processing fine silicon-containing dust of gas cleaning electrothermal production of silicon and silicon ferroalloys, in which the processing of fine silicon-containing dust of gas cleaning is carried out in a rotating drum, compacting is carried out by removing electrostatic charge from particles by mass transfer of material in contact with an electrically conductive surface. Silicon-containing dust is loaded in an amount of 50-60% of the volume of the drum, the linear velocity of the material in the drum is maintained at 0.18-0.37 m / s, and processing is carried out for 2-4 hours (RU 2085488, IPC C01B 33/18, publ. 07.27.1997). The disadvantage of this method is that it is not sufficiently pure silica fume, therefore, additional costs for cleaning the product are necessary.

It is known to obtain an amorphous fine powder of silicon oxide under the influence of a solution of water glass with hydrochloric acid, repeatedly washing the precipitate of metacosilicic acid H ₂ SiO ₃ from the NaCl salt formed by the reaction, drying the gel formed, grinding the xerogel obtained and subsequent heat treatment (RU 2262544, IPC C22B 34/12, C22B 3/06, publ. 20.10.2005). The known method for producing silica is laborious, time consuming and allows to obtain small amounts of the final product.

Known methods for producing silicon dioxide, including the processing of fluoride solutions containing silicon in the form of fluoride compounds, as well as aluminum and iron (RU 2474535, IPC C01B 33/12, B82B 3/00, B82Y 40/00, publ. 02/10/2013; CN No. 1363511, publ. 08/14/2002); methods for producing amorphous silicon dioxide from a solution of ammonium hexafluorosilicate (HFSA) by alkaline hydrolysis to form a precipitate of silica and its separation from the solution (RU 1624923, IPC C01B 33/12, C01B 41/00, C22B 34/36, publ. 08/27/1999; RU 2048559, IPC C22B 34/14, publ. 11/20/1995; RU 2058408, C22B 34/12, publ. 04/20/1996). The disadvantages of the known methods are the use of fluoride compounds, which are aggressive products.

It is known to obtain silicon dioxide (silica) from natural mineral raw materials - rocks (perlite, obsidian, diatomite, nepheline, tripoli, from silicate raw materials, quartz sand and from "semi-finished products" - waste high-silicon ferrosilicon) (RU 2036836, IPC C01B 33/12 , publ. 09.06.1995), production of boron or borosilicate materials (RU 2170211, IPC C01B 33/142, C01F 7/26, publ. 10.07.2001), from apatite production waste (SU 856981, IPC C01B 33/18, publ . 23.08.1981) and ferroalloy production (RU 2002119217, IPC C01B 33/12, C01B 33/18, publ. 02.27.2004), however, the degree of extraction of silicon dioxide no more than 60%.

A known method of producing silicon dioxide, in which the silicon-containing material is used dust of exhaust gases from the production of silicon and / or high-silicon ferrosilicon, which is treated with a solution of alkali. Silicon dioxide is isolated from the resulting solution by the action of mineral acid (RU 2036836, IPC C01B 33/12, published 09.06.2015). The disadvantage of this method is the insufficiently high purity and low dispersion of the product obtained with its help, which limits the scope of this product, which is mainly used as a mineral filler in composite materials.

Known methods for producing high purity silicon dioxide (99.99%) from rice husk (CN 1063087, publ. 07.29.1992; RU 2191159, IPC C01B 33/12, publ. 20.10.2002). A disadvantage of the known methods is the use of a highly aggressive mixture of concentrated nitric acid and hydrogen peroxide and the associated need for special hardware design, which complicates the industrial application of the known method.

A known method of producing silicon dioxide of high purity from silicon-containing raw materials, which is used as blast furnace dust of the gas purification process of the electrochemical production of silicon at aluminum enterprises (RU 2031838, IPC C01B 33/12, publ. 03/27/1995). The disadvantages of the method are multioperational, use to neutralize sulfuric acid, and hence the formation of sulfate effluents.

A known method of producing silicon dioxide, in which fumed silica fume is obtained by burning silicon tetrachloride in a stream of oxygen and hydrogen, the result is a highly dispersed amorphous silica and hydrogen chloride in a gaseous state (RU 1791383, IPC C01B 33/12, publ. 30.01.1993 ) This production requires large energy costs and serious explosion safety measures.

A known method of producing finely dispersed SiO ₂ , including autoclaving solid silicon-containing products and fluorine-containing compounds (US 6217840, IPC C01B 33/12, C01B 33/08, C01B 7/19, publ. 04/17/2001). However, the known method is technologically complicated, since it requires appropriate hardware design, is energy-intensive, and is associated with increased safety measures due to the use of concentrated sulfuric acid and the subsequent utilization of fluorine-containing gases, as well as high temperatures and pressures.

Of great variety from the variety of methods for producing amorphous silica, methods of fusion of natural rocks with a high content of bound amorphous silica, with alkaline sludges and processing of silicon-containing raw materials with alkali deserve descent.

The closest in technical essence to the proposed technical solution is a method for producing finely dispersed amorphous silica fume, including preliminary grinding and grinding in an agate mortar to the state of powder dried and calcined in a muffle furnace diatomite weighing 5-8 g, grinding in a porcelain mortar 6 times the amount of alkaline fluff consisting of a mixture of anhydrous potassium and sodium carbonates, mixing diatomite and alkaline flux in an alundum or corundum crucible, fusion of the obtained mixture si in a muffle furnace in a crucible for 40-50 minutes, followed by pouring the melt onto a silicate base, transferring it to a heat-resistant glass, precipitating silicic acid first by leaching the melt with distilled water, and then, after controlling the pH of the medium by titration with 0.1 M a solution of potassium hydroxide with methyl orange, processing it with 100-200 ml of distilled water until complete dehydration of silicic acid. Precipitation of silicic acid is carried out by adding 30-40 ml of a concentrated solution of hydrochloric acid, and after slowing down the reaction, the solution is evaporated in a sand bath until the carbon dioxide evolution ceases. The precipitate is treated by adding 10-20 ml of concentrated hydrochloric acid solution, then 100-200 ml of distilled water is poured, and after evaporating the solution in a water bath for 5 min until the hydrated silicon oxide (IV) is completely dehydrated and the pH of the medium is controlled by titration 0, 1 mm solution of potassium hydroxide with methyl orange carry out the separation of silicon oxide (IV) by filtration, collecting the filtrate through a loose ashless filter in a glass and washing the precipitate with a 0.5% hydrochloric acid solution until negative share on iron (III) ions with thiocyanate. The pH of the medium is monitored by titration with a 0.1 M solution of potassium hydroxide with methyl orange. The precipitate is dried on a filter, then in a Petri dish in an oven at a temperature of 90-120 ° C (RU 2526454, IPC C01B 33/18, C09C 1/28, published on 08.20.2014).

The disadvantages of this method are the low yield (70-80%) and low dispersion (5-10 microns) of silica fume, in addition to its preparation, it becomes necessary to use expensive materials (platinum, alundum crucibles), and also require large energy costs for alloying diatomite with alkaline fluff (800-1000 ° C), which leads to a significant increase in the cost of the final product.

The technical result of the proposed method is to obtain finely dispersed amorphous silica fume of high purity from an inexpensive source of mineral silica-containing raw materials - diatomite, without expensive materials and sophisticated hardware, with minimal energy costs, an optimized technological scheme for industrial production and a wide range of specific surface for various industrial purposes , as well as increasing the yield of finely dispersed amorphous microsilica zema.

The essence of the invention lies in the fact that the method for producing finely dispersed amorphous silica fume sol-gel method involves pre-drying and grinding of diatomite. A 10-30% sodium hydroxide solution is added to the crushed diatomite, kept in a thermostat at 70-90 ° C for 2-3 hours, where the ratio of liquid to solid phase is 12: 1. The silicic acid is precipitated from the filtrate by adding a concentrated hydrochloric acid solution, the precipitate is treated, the silicon oxide (IV) is filtered, the precipitate is dried on the filter, then in a Petri dish in an oven at 90-120 ° C.

The method is as follows. The raw material used is sedimentary rock - diatomite, consisting mainly of the remains of diatoms, usually loose or slightly cemented, light gray or yellowish rock. Diatomite powder is insoluble in hydrochloric, nitric and sulfuric acids and refers to acidic rocks. To obtain finely dispersed amorphous silica fume, the Atemar diatomite deposit (Republic of Mordovia) was used.

A 50 g sample of diatomite, dried to 5-6% humidity, is preliminarily crushed in a ball mill to a fraction of 0.08 mm and ground in an agate mortar to a powder state. A weighed portion of diatomite in the bottle is transferred to a 1 L conical flask, 300 ml of sodium hydroxide solution of 10, 20, 30% concentration is added, stirred and incubated for 1-3 hours in an thermostat at 50, 70, 90 ° C, stirring occasionally . The ratio of solid and liquid phases is W: T = 12: 1. After termination of the temperature control, the unreacted residue is separated from the hot solution by filtration through a loose filter (white tape). The filtrate is a liquid glass. Silicic acid is isolated from the residue by the action of concentrated hydrochloric acid, which is added in small portions with continuous stirring to an acidic medium (pH≈2). The formed amorphous precipitate (silica sol) is difficult to separate from the solution by filtration; therefore, the silica sol is coagulated. The solution is evaporated to dryness in a water (sand) bath, small portions (3-5 ml of concentrated hydrochloric acid) are added to the dry residue to dehydrate silicic acid and the dry residue is dried again, then 200-300 ml of hot distilled water are added, kept under heating and stirring for complete dissolution of salts. Unreacted silica precipitate is separated from the solution by filtration through a loose filter (white tape), washed with 1% nitric acid solution and plenty of hot water until the Cl ^- - ions with silver nitrate (I) and ions Fe ^{3+ are} negatively negative reactions with potassium thiocyanate. Drying the washed precipitate, after separation from the filter, is carried out in a Petri dish in an oven at 90-120 ° C to constant weight.

In the table. 1 shows the output of silica from diatomite depending on the alkali concentration and temperature (thermostating time is 2 hours); in table 2 - elemental composition of silica fume obtained from natural diatomite depending on alkali concentration and thermostating time; in table 3 - dimension of the obtained silica fume particles.

The optimal conditions for the production of amorphous silicon dioxide were identified experimentally, taking into account changes in temperature, thermostating time, and alkali concentration (Table 1).

The results of elemental analysis of the synthesized silica powders by the X-ray fluorescence method showed that it consists of 95.00-99.97% silicon dioxide. The main impurity is sodium chloride. Oxides of iron, aluminum, calcium, potassium, titanium are contained in small quantities, which can be attributed to microcomponents (table. 2). An admixture of sodium chloride was sorbed on the surface of amorphous silica in the process of its synthesis from a solution of sodium hydroxide and the release of silicic acid with hydrochloric acid. Sodium chloride is removed by extensive washing with water and dialysis.

For comparison, the preparation of silica fume was studied under the following conditions: ratio of liquid and solid phases - W: T = 6: 1, temperature of thermostatting - 145 ° C, thermostatting time - 2 hours (composition 4, Tables 1, 2).

It was revealed that the optimal compositions are 2 and 3 (Table 1, 2), where the ratio of liquid to solid phase is W: T = 12: 1 at a temperature of temperature control - 70-90 ° C and a time of temperature control - 2-3 hours, so as silica fume get finer.

A ShimadzuSALD-3101 laser particle size diffraction analyzer established the minimum particle size of amorphous silica fume obtained from natural diatomite at different temperatures and alkali concentrations (W: T = 12: 1) (Table 3).

It was established that the obtained silica fume (L: T = 12: 1) from the Atemarskoye diatomite deposit is characterized by the following indicators:

The content of silicon dioxide is not less than 96.00-99.97%; The minimum particle size is 0.062-0.097 microns;

Impurity content: iron (III) oxide - 0.0169% and calcium oxide - 0.0041%.

Compared with the known, the proposed method allows to obtain finely dispersed amorphous silica fume with a dispersion of 0.062-0.097 μm of a high degree of purity (minimum impurity content) from an inexpensive initial siliceous mineral raw material - diatomite of the Atemarsky deposit, without expensive materials and complex hardware, with minimal energy costs, optimized technological scheme for industrial production, due to the absence of the need for fusion of diatomite with alkaline smooth flux and a wide range of specific surface area for various industrial purposes, as well as increase the yield of finely dispersed amorphous silica fume to 99.97%.

Claims (1)

A method of obtaining finely dispersed amorphous silica fume silica sol-gel method, including pre-drying, grinding diatomite, precipitation of silicic acid from the filtrate by adding concentrated hydrochloric acid solution, processing the precipitate, filtering the silicon oxide (IV), drying the precipitate first on the filter, then in a Petri dish in drying oven at 90-120 ° C, characterized in that a 10-30% sodium hydroxide solution is added to the crushed diatomite, kept in a thermostat at 70-90 ° C for 2-3 hours, where the liquid and solid phases are 12: 1.