RU2740995C1 - Method of producing microsilica from natural diatomite by precipitation of nitric acid solution - Google Patents

Abstract

FIELD: construction.SUBSTANCE: invention relates to construction materials, specifically to production of modified additives for concrete, mortar, dry construction mixtures, heat-insulating materials. Disclosed is a method of producing microsilica from natural diatomite by precipitation of a solution of HNO3, including preliminary calcination of diatomite at temperature of 500 °C for 30–120 minutes, grinding, after which ground and calcined diatomite is treated using 30 % NaOH solution, where the ratio of liquid and solid phases is equal to 14:1, at the temperature control temperature of 90 °C for 2 hours, then formed precipitate is separated and SiO2is precipitated with solution of concentrated HNO3to acid reaction of solution pH 1–2, followed by washing and drying the filter cake, which is then transferred into a Petri dish and dried at 100–160 °C in a drying cabinet to constant weight.EFFECT: technical result is invention increases output of finely dispersed amorphous chemically pure microsilica with minimum content of impurities from natural diatomite by precipitation of HNO3solution to 87.2 %, where content of SiO2is 95.36÷99.63 %, and also to save time for washing residue with water to remove chloride ions.1 cl, 3 tbl

Description

The invention relates to building materials, namely to the production of modified additives for concrete, mortars, dry building mixtures, thermal insulation materials.

Silicon dioxide is a substance of widespread use, which is necessary for the preparation of biocidal, fire-resistant fabrics, especially "pure" uviol glass, high-strength concretes, thermal insulation materials, ceramics, refractories, rubber, fiber-optic cable, in food (additive E 551), pharmaceutical and textile industry. Currently, there is a significant increase in the consumption of amorphous silicas in the world industry. In addition to their traditional use as additives in rubber, plastic (RU 2262544, IPC C22B 43/12, publ. 20.10.2005), paper, for the manufacture of adhesives, water glass, ceramics, adsorbents, etc. Consumption of nanodispersed chemically pure amorphous silica in high-tech industries is significantly increasing. Therefore, it is necessary to develop new technologies for the production of amorphous silica.

In Russia, silica-containing raw materials, which include diatomites, tripoli and flask, are used as a starting material for the production of amorphous silica. These rocks consist mainly of 60-80% by mass of various modifications of silicon dioxide.

The raw material base of silica-containing raw materials for obtaining silica in the Republic of Mordovia can be two diatomite deposits - Atemarskoye, Anuchinskoye with total reserves of 21 106 thousand m ³ .

Diatomite of the Atemarsky deposit is a cemented rock, light gray in color. A yellow tint appears in the powder. Diatomite powder is insoluble in acids (HCl, HNO ₃ , H ₂ SO ₄ ) and belongs to acidic rocks. To transfer it to solution, fusion is necessary.

A known method of producing silicon dioxide, including the processing of fluoride solutions, formed as a result of opening the titanium-silicon concentrate with an 8% solution of hydrofluoric acid (HF) to obtain a solution containing silicon in the form of fluoride compounds, as well as aluminum and iron. The solution is filtered, evaporated until dry salts are formed. In the filtrate, silicon is in the form of a compound H ₂ SiF ₆ , which has a high volatility. During evaporation, this compound passes into the gas phase. The latter is treated with a solution of ammonium hydroxide (NH ₄ OH), while silicon dioxide passes into the precipitate, and ammonium fluoride is concentrated in the solution (RU 2262544, IPC C22B 43/12, publ. 20.10.2005).

The disadvantages of this method are the use of fluoride compounds, which are aggressive products. This necessitates the use of expensive materials in the hardware design of the process, as well as to create increased security measures for the personnel serving the technical process. These disadvantages lead to a significant increase in the cost of silicon dioxide.

A known method of producing silicon dioxide, obtained by carbonization of liquid glass with carbon dioxide with a CO ₂ content _of 17-25% at a temperature of 78-82 ° C The carbonization process is carried out until a pH of 9-10.5 is reached. The resulting suspension is subjected to hydrodynamic activation, then the suspension is neutralized with sulfuric acid to pH 5.0-8.5 with exposure in the reactor, washed with hot water and spray dried (RU 2023664, IPC S01B 33/18, publ. 30.11.1994).

The disadvantage of this method is the multi-stage operation, the use of sulfuric acid to neutralize, and then the formation of sulfuric acid effluents. In addition, water glass is used as a feedstock, which is the target technological product. All this increases the cost of the process, complicates the hardware design and does not solve environmental problems.

A known method of producing silicon dioxide, in which pyrogenic highly dispersed silica is obtained by burning silicon tetrachloride in a stream of oxygen and hydrogen, as a result, highly dispersed amorphous silicon dioxide and hydrogen chloride in a gaseous state (RU 2474535, IPC C01B 33/12, B82B 3/00, B82Y 40/00, publ. 02/10/2013).

The disadvantage of the known method is that production requires high energy consumption and serious explosion safety measures.

In addition, for example, the method for processing finely dispersed silicon-containing dust from gas cleaning of electrothermal production of silicon and silicon ferroalloys (RU 2085488, IPC С01В 33/18) contains the disadvantage that insufficiently pure microsilica is obtained, therefore additional costs are required for cleaning the product. Methods for obtaining high-purity silicon dioxide from rice husks (RU 2480408, IPC S01V 33/12, B01J 19/10, publ. 04/27/2013, RU 94031518, IPC C01B 33/12, publ. 10.077.1994, RU 2488558 IPC C01B 33 / 12, publ. 27.07.2013, IN 148538, IPC C01B 33/12, publ. 03/28/1981, RU 94031518, IPC C01B 33/12, publ. 10.07.1996, GB 1508825, IPC S01B 33/12, publ. 03/26/1975, CN 86104705, IPC С01В 33/113, С01В 33/12, publ. 07/14/1986) are insufficiently rational and environmentally unsafe, or require complex and expensive cleaning systems.

A known method for producing highly dispersed silicon dioxide, including dissolving sodium silicate (lumps) in an autoclave in water under an overpressure of 0.57-0.59 MPa, with processing the solution with a gas mixture containing carbon dioxide (RU 2156734, IPC S01B 33/18, publ. 27.09.2000).

The disadvantage of this method is its multi-operation, obtaining a product of silicon dioxide (SiO ₂ ) of insufficient quality.

The closest technical solution to the claimed invention is a method for producing fine amorphous microsilica by a sol-gel method, which includes preliminary drying and grinding of diatomite. A 10-30% sodium hydroxide solution is added to the crushed diatomite, kept in a thermostat at a temperature of 70-90 ° C for 2-3 hours at a ratio of liquid to solid phases of 12: 1. The precipitation of silicic acid from the filtrate is carried out by adding a concentrated solution of hydrochloric acid. Separate the silicon dioxide precipitate and dry. The invention makes it possible to obtain fine amorphous microsilica with a dispersion of 0.062-0.097 microns of high purity from inexpensive mineral raw materials with a yield of the target product up to 99.97% (RU 2625114, IPC С01В 33/18, С01В 33/193, publ. 11.07.2017).

The disadvantage of the prototype is that this method of obtaining silica fume is laborious, time-consuming and allows you to get small amounts of the final product. At low pH values, there is a loss of silica due to the transition of silicic acid to a truly soluble state. Therefore, colloidal-dissolved silicic acid must be dehydrated and coagulated, true-dissolved silicic acid must be polymerized and dehydrated. To reduce the loss of silicic acid, repeated operations are carried out with the filtrate (evaporation) or the introduction of a gelatin solution. After precipitation of silicic acid with concentrated hydrochloric acid (HCl), a high content of chloride ions was found in the filtrate. Under these conditions, the sorption of chloride ions by silicic acid is possible. To remove chloride ions from the sediment, it requires prolonged washing with hot water acidified with nitric acid (HNO ₃ ).

The technical result achieved when using the claimed invention is to increase the yield of finely dispersed amorphous chemically pure microsilica with a minimum content of impurities from natural diatomite by precipitation of a solution of HNO ₃ to 87.2%, where the content of SiO ₂ is 95.36 ÷ 99.63%, and saving time for washing the precipitate with water to remove chloride ions.

The essence of the invention lies in the fact that the method of obtaining microsilica from natural diatomite by precipitation of a solution of HNO ₃ includes preliminary calcination of diatomite at a temperature of 500 ° C for 30-120 minutes, after which the crushed and calcined diatomite is processed using a 30% sodium hydroxide solution ( NaOH), where the ratio of liquid and solid phases is 14: 1, at a thermostatting temperature of 90 ° C for 2 h, then the formed precipitate is separated and SiO _{2 is} precipitated with a solution of concentrated HNO ₃ until the acidic reaction of the pH 1-2 solution, subsequent washing is carried out and drying the precipitate on the filter, which is then transferred to a Petri dish and dried at 100-160 ° C in a drying oven to constant weight.

Table 1 shows the elemental composition of natural diatomite depending on the time of calcination according to the data of X-ray fluorescence analysis (T = 500 ° C), in table. 2 - the yield of amorphous microsilica from calcined diatomite, depending on the concentration of alkali and calcination temperature (τ = 2 h, temperature control temperature 90 ° C), in table. 3 - elemental composition of amorphous microsilica powder synthesized from calcined diatomite (τ = 2 h) depending on the NaOH concentration and calcination temperature according to X-ray fluorescence analysis.

The method is carried out as follows.

Natural diatomaceous earth must always be calcined beforehand. When calcining, first of all, adsorption water is removed (in the temperature range 100-300 ° C), then pore water (in the temperature range 300-400 ° C), followed by the burning out of organic substances at temperatures above 400 ° C. Already at a temperature of 500 ° C and more, a phase transition of β-quartz to α-quartz is possible in diatomite.

The calcination time is from 30 to 120 minutes, since the duration of heat treatment of diatomite for more than 2 hours can lead to the decomposition of the rock structure. The heat treatment of diatomite is carried out at: 100, 200, 300, 400, 500, 600 ° C in a muffle furnace in alundum and corundum crucibles. In the process of calcination, a change in the color of the rock from gray to red-brown is observed. The chemical composition of natural diatomite, depending on the time of calcination at a stable temperature, is presented in table. one.

The table shows that the chemical composition of diatomite at a stable temperature (up to 500 ° C) is practically independent of the calcination time. The SiO ₂ content is 88.00% on average.

After heat treatment, the crushed and calcined diatomite is weighed on a technical balance weighing 25.00 - 50.00 g, placed in a conical flask of ~ 500 - 750 ml, 350 ml of NaOH solution of various concentrations are added: 10-, 20-, 30% , covered with a watch glass and kept in a thermostat at 90 ° C for 2 hours, stirring occasionally. The ratio of L-T phases is 6: 1 - 14: 1.

To maintain the temperature in operation, use a liquid cryothermostat TZH-TS-01 / 16K-40. At the end of the time, the hot solution is filtered through a loose filter. From the obtained filtrate, silicic acid is precipitated with concentrated acid HNO₃... The acid is added slowly, with stirring, until the acid reaction of the pH 1–2 solution. The solution is evaporated to dryness in a heat-resistant glass in a water or sand bath. The dry residue is treated 2-3 times with small portions of concentrated HNO₃ for dewatering hydrated SiO₂... Then add 200-250 ml of hot distilled water and continue heating in a water bath until the salts are completely dissolved. Only hydrated SiO remains insoluble₂in the form of a flaky mass. After standing, the precipitate is filtered through a loose ashless filter and washed on the filter until a negative reaction for iron (III) ion with thiocyanate.

The precipitate is dried on a filter, then transferred to a Petri dish and dried at a temperature of 100-160 ° C in a drying oven to constant weight. The yield of amorphous silica, depending on the concentration of alkali and calcination temperature, is presented in table. 2.

As you can see from the table. 2, the yield of amorphous microsilica depends on the calcination temperature, alkali concentration, L: S ratio, and the nature of the acid with which precipitation was carried out. The highest microsilica yield was obtained using 30% NaOH, calcination temperature 500 ° C, L: T ratio 14: 1, precipitating agent - concentrated HNO _{3, the} yield was 87.2%.

The results of the chemical analysis of powders of synthesized microsilica showed (Table 3) that it consists of 95.36 ÷ 99.63% of SiO ₂ . The main impurities are sodium oxide (Na ₂ O). Oxides of iron, aluminum, calcium, potassium, titanium are contained in small amounts, which can be attributed to microcomponents.

An admixture of sodium chloride (NaCl) during its synthesis from a sodium hydroxide solution and the isolation of silicic acid with hydrochloric acid is sorbed on the surface of amorphous silica. NaCl can be removed by washing with copious water. The chemical composition of the synthesized silica fume is practically independent of the calcination temperature, but depends on the concentration of alkali. With an increase in the concentration of alkali, the percentage of SiO ₂ decreases due to an increase in the content of aluminum oxide.

The filtrate obtained after separating the synthesized microsilica and washing it with hot water is analyzed for the content of silicon oxide (IV), chloride ions, iron (III) ions and pH. The results of the analysis indicate that after the separation of silicic acid with concentrated HNO ₃ , the pH of the filtrate is ~ 1, which is an important condition for obtaining finely dispersed silica. The filtrate must be acidic (pH 1 ÷ 2). However, this may increase the solubility of silicic acid.

After precipitation of silicic acid with concentrated HCl, a high content of chloride ions was found in the filtrate. Under these conditions, the sorption of chloride ions by silicic acid is possible. To remove chloride ions from the sediment, it requires prolonged washing with hot water acidified with HNO ₃ .

In order to save time for washing the precipitate with water to remove chloride ions, it is more convenient to use concentrated HNO ₃ as a precipitant of silicic acid from an alkaline solution. In this case, the content of chloride ions in the filtrate is minimal.

Compared with the known solution, the claimed invention makes it possible to increase the yield of finely dispersed amorphous chemically pure microsilica with a minimum content of impurities from natural diatomite by precipitation of an HNO ₃ solution to 87.2%, where the SiO ₂ content is 95.36 ÷ 99.63%, and also to save time to wash the precipitate with water to remove chloride ions.

Table 1

No.
p / p t, min W,% SiO ₂ Fe ₂ O ₃ Al ₂ O ₃ CaO TiO ₂ MgO P ₂ O ₅ SO ₃ one thirty 88.51 3.45 4.17 1.25 0.387 0.358 0.159 0.0267 2 60 88.11 3.81 4.08 1.31 0.418 0.335 0.150 0.0513 3 90 89.18 2.93 4.13 0.913 0.426 0.380 0.196 0.0313 4 120 87.13 4.07 4.18 1.48 0.466 0.430 0.224 0.0540

table 2

No.
p / p T, ° C Conc.
NaOH,% Diatomite SiO ₂ nH ₂ O, g Output, % Ratio
W: T The precipitant is concentrated HNO ₃ ten 500 ten 25.0 12.10 48.4 14: 1 eleven 20 25.0 17.30 69.2 14: 1 12 thirty 25.0 21.81 87.2 14: 1

Table 3

No.
p / p T, ° C Conc.
NaOH,
% SiO ₂ Na ₂ O Cl ^- P ₂ O ₅ Fe ₂ O ₃ Al ₂ O ₃ CaO TiO ₂ W,% Precipitator concentrated HNO ₃ ten 500 ten 99.13 0.48 - 0.134 0.0373 - 0.0113 0.0067 eleven 20 97.13 1.14 - 0.175 0.181 0.567 0.0244 0.0152 12 thirty 95.36 2.05 - 0.176 0.426 1.84 0.0251 0.0373

Claims (1)

A method of obtaining microsilica from natural diatomite, including preliminary grinding and processing of crushed diatomite with a solution of sodium hydroxide, characterized in that it includes preliminary calcination of diatomite at a temperature of 500 ° C for 30-120 min, after which the crushed and calcined diatomite is processed using 30% - sodium hydroxide solution, where the ratio of liquid and solid phases is 14: 1, at a temperature of 90 ° C for 2 h, then the formed precipitate is separated and silicon dioxide is precipitated with a solution of concentrated nitric acid until the acidic reaction of the pH 1-2 solution is carried out. washing and drying the filter cake, which is then transferred to a Petri dish and dried at 100-160 ° C in an oven to constant weight.