RU2601608C1 - Method for complex processing boric plaster - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing of calcium-containing industrial wastes of boric production. Method involves treatment of wastes of boric production with alkali metal hydroxide solution with calcium hydrosilicate formation. Treatment is carried out at ratio of solid and liquid phases 1: (7-10), in autoclave at temperature of 110-120 °C, obtained product is washed with water, filtered and dried. Then product is subjected to thermal treatment. Thermal treatment at 850-1,000 °C provides production of wollastonite. Calcination at temperature above 1,150-1,200 °C provides production of hardening additives in concrete.

EFFECT: technical result is increase of target product yield and expanded range of commercial products.

3 cl, 2 dwg, 2 ex

Description

The invention relates to a technology for processing calcium and silica-containing industrial wastes of boron production (borogypsum) and can be used in the production of calcium hydrosilicates, wollastonite, additives in building materials, sorbents and potash fertilizers.

The urgency of the problem of integrated processing of gypsum with obtaining various functional materials is due to the fact that over the years of work of the mining and chemical industries in our country, due to the lack of effective technologies for processing mineral raw materials, millions of tons of technogenic waste have been accumulated that are not currently being processed. In particular, in the Far East of Russia, which has reserves of unique mineral raw materials, the total amount of boric acid production waste - borogypsum - is more than 50 million tons with an annual replenishment of sludge storages of up to 800 thousand tons with the existing volumes of processing of datolithic ores at the existing enterprise of MCC Boron".

A known method of processing gypsum-containing raw materials, which use waste boron production - borogypsum [US Pat. RF №2324654, publ. 2008.05.20], including its repulpation, extraction of calcium sulfate dihydrate into the foam product by flotation using flotation reagents, dehydration of gypsum to calcium sulfate hemihydrate, its drying and grinding. Calcium sulfate dihydrate is selectively extracted by flotation using flotation reagents (a mixture of sodium salts of fatty acids - oleate, stearate, palmetate - in an amount of 0.1-0.3 kg per ton of borogypsum sludge with a weight ratio of 2: 1.5: 0.5 respectively, and liquid sodium glass in an amount of 0.02-0.05 kg / t of sludge borogypsum). Post-treatment and conversion of calcium salts contained in the sludge of borogypsum to calcium sulfate is carried out by treating the pulp with sulfuric acid and calcium hydroxide in the range of pH 2-7; this operation allows you to bleach gypsum. Obtaining a marketable product - calcium sulfate hemihydrate - is carried out by dehydration of calcium sulfate dihydrate and drying of the product in a steamer - damper - followed by grinding. The disadvantages of this method are: multi-stage process; the use of additional flotation reagents; the need for additional treatment of borogypsum pulp with sulfuric acid and calcium hydroxide, which entails additional costs and leads to equipment wear due to the use of aggressive reagents. In addition, there is no acute need for gypsum according to this scheme, since there is a fairly large number of both natural and man-made sources of its production.

A known method of producing gypsum binder from borogypsum with increased strength [US Pat. RF №2036178, publ. 1995.05.27], which consists in the introduction of a suspension of silicate bacteria containing about (4-6) · 10 ⁸ cells / ml of "Bacillus mucilaginocus" in an amount of 10-40 ml per 1 liter of suspension of borogypsum with T: W = 1: (15- 20) before autoclaving the latter. Microbiological treatment of borogypsum is carried out for 2-5 days with sparging with compressed air. After completion of the process, the precipitate of borogypsum is dehydrated on vacuum filters and dried at 50 ° C to a moisture content of 5-7%. The dried borogypsum is briquetted on a hydraulic press at a specific pressure of 120 kgf / cm ² . Borogypsum is cooked with saturated steam in an autoclave according to the following regime: pressure increase to 1.3 atm 0.5 h, isothermal exposure at 1.3 atm 3 h, pressure relief 0.5 h. After heat treatment and drying, the gypsum binder is ground in a two-chamber mill. The disadvantages of this method are multi-stage and the duration of the process; the need for the use of silicate bacteria that require long preparation, as well as high energy consumption and the production of single products - gypsum binder. In addition, the known method does not allow to process significant volumes of borogypsum.

The known technology of processing borogypsum with the production of wollastonite and sulfur dioxide [and.with. USSR 1446129, publ. 1987.05.23], which includes the heat treatment of gypsum by direct electric heating at 1250-1300 ° C for 25-30 minutes, cooling the melt at a speed of 3-5 deg / min and collecting sulfur dioxide. The disadvantages of the known technology are the multi-stage process (preliminary granulation and dehydration of borogypsum), high dehydration temperatures (220 ° C) and heat treatment of borogypsum (1250-1300 ° C) associated with significant energy consumption.

Known described in the patent of the Russian Federation No. 2090501, publ. 1997.09.20 a method for processing calcium-containing wastes for the production of phosphorus fertilizers (phosphogypsum) to produce finely dispersed wollastonite by hydrochemical interaction of calcium-containing wastes with silica-containing wastes from the production of aluminum fluoride in the presence of metal hydroxides of groups I and II, ammonium or mixtures thereof and sodium chloride at a molar ratio of CaO / SiOO in the CaO / SiO molar ratio ₂ , equal to (0.8-1.0): 1, CaO / OH ^- , equal to (0.5-2.0): 1, OH ^- / NaCl, equal to (0.5-2.0): 1 , at a temperature of 70-100 ° C for 1-3 hours with a ratio of solid and liquid phases equal to 1: (3-5), with a floor cheniem calcium silicate, which is filtered, washed, dried and calcined at 950-1050 ° C for 40-60 min. The method allows to obtain wollastonite of a high degree of purity, whiteness and uniformity in particle size. The disadvantages of this method include the need to use two types of feedstock, taken from two different man-made sources, and two reagents, which complicates the method and increases the cost of the finished product due to transportation costs, moreover, it is polluted during transportation, loading and unloading of man-made materials Environment.

Closest to the claimed is the method described in RF patent No. 2550188 for processing borogypsum by treating the feedstock with a stoichiometric amount of sodium hydroxide or potassium hydroxide with a ratio of solid and liquid phases 1: (19-20) for 1-3 hours at room temperature to obtain hydrosilicate calcium (CSH), exhibiting sorption properties in relation to heavy metals.

The known method provides for the possibility of obtaining only one marketable product, and with insufficiently high yield, which is 60-67%.

The objective of the invention is to create an effective method for processing borogypsum with the possibility of obtaining several commercial products

The technical result, the invention is aimed at, is to increase the yield of the main target product while expanding the range of marketable products.

The specified technical result is achieved by the method of processing borogypsum by processing it for 1-3 hours with a stoichiometric amount of alkali metal hydroxide according to the equation for the synthesis of calcium hydrosilicate: followed by isolation of the obtained solid product, washing it with water at 60-70 ° C and drying at a temperature of 80- 85 ° C for several hours, in which, in contrast to the known reaction is carried out at a ratio of solid and liquid phases T: W = 1: (7-10) in an autoclave at a temperature of 110-120 ° C and a pressure of 1.5-2 , 0 atm, with this floor enny product is subjected to further heat treatment.

In one embodiment of the method, the heat treatment of the resulting product is carried out at 850-1000 ° C for 1-2 hours to obtain wollastonite.

In another embodiment of the method, the resulting product is subjected to heat treatment at a temperature of 1150-1200 ° C for 1-2 hours and crushed to obtain a finely divided reinforcing additive in concrete.

The method is as follows.

Wastes from the production of boric acid (borogypsum) containing calcium sulfate dihydrate CaSO ₄ · 2H ₂ O (up to 70 wt.%) And amorphous silica SiO ₂ · nH ₂ O (up to 30 wt.%), Or, in terms of CaO and SiO ₂ , in a ratio of 0.81: 1, is mixed with a solution of alkali, mainly KOH or NaOH. The starting components are taken in the stoichiometric ratio necessary for the formation of calcium hydrosilicate, according to equations (1) and (2):

where k, m, n, q are stoichiometric coefficients in the given chemical equations of this process.

The process is carried out at a ratio of solid and liquid phases T: L = 1: (7-10), adjusting the concentration of alkali (KOH, NaOH) so that the concentration in the solution of alkali metal sulfate (K ₂ SO ₄ or Na ₂ SO ₄ ), formed as a by-product, did not exceed its ultimate solubility.

Since the efficiency of the synthesis carried out at room temperature is low, to activate the process and increase the yield of the target product, the process is carried out in an autoclave at a temperature of 110-120 ° C and a pressure of 1.5-2.0 atm, while the output of calcium hydrosilicate as the main target product reaches 95%. Processing time 1-3 hours.

The reaction conditions also significantly affect the structure and properties of the products obtained, the modification of which determines their purpose and possible scope.

The calcium hydrosilicate formed as a result of autoclave synthesis is separated by filtration, washed with water heated to 60-70 ° C, filtered and dried at a temperature of 80-85 ° C for several hours.

Depending on the composition of the hydroxide used, potassium sulfate, which can be used as a fertilizer in metallurgy and glass production, or sodium sulfate used in the manufacture of synthetic detergents, in the production of cellulose, in textile, leather, is isolated from the filtrate as a by-product. , glass industry and non-ferrous metallurgy.

Alkaline treatment of borogypsum in an autoclave at 110-120 ° C allows to obtain a product with pronounced sorption activity with respect to heavy metal ions, which can be used as a sorbent.

The dried calcium hydrosilicate is calcined at 850-1000 ° C for 1-2 hours to obtain wollastonite. The yield of wollastonite as the target product in this case is 85-95%.

By calcining the obtained calcium hydrosilicate at a temperature of 1150-1200 ° C for 1-2 hours, followed by grinding, finely dispersed powder is obtained on the basis of wollastonite and pseudowollastonite (high-temperature modification of wollastonite), which can be used as an additive in concrete, which increases the tensile strength of concrete when it is compressed and bent.

Thus, the proposed method allows a high yield to be obtained from industrial wastes of boron production for a number of products, including wollastonite, hydrosilicate sorbent, a reinforcing additive in concrete, as well as potassium fertilizer or an additive used in the manufacture of synthetic detergents in the production of cellulose , in the textile, leather, glass industry and in non-ferrous metallurgy.

The proposed method is illustrated by the following examples of specific implementation.

Wastes of boron production (borogypsum) of the composition (wt.%) Were taken as feedstock: SiO ₂ 32.2; CaO 28.4; SO ₃ 31.3; Fe ₂ O ₃ 2.7.

The synthesis was carried out in an autoclave Parr Instrument 4848 (USA).

X-ray diffraction patterns of the obtained products were recorded on a D8 ADVANCE automatic diffractometer with rotation of the sample in Cu K _α radiation. X-ray phase analysis (XRD) was performed using an EVA search program with a PDF-2 powder data bank.

The morphological characteristics of the samples were studied using a Hitachi S5500 high resolution scanning electron microscope equipped with an attachment for scanning transmission microscopy and an Thermo Scientific energy dispersive spectrometer.

When calculating the sorption capacity of the synthesized product (calcium hydrosilicate), we used the results obtained by atomic absorption spectrometry (AAS) on a SOLAAR Mb double-beam spectrometer (Thermo, USA).

Specially prepared samples of fine-grained concrete with the finely dispersed admixture obtained by the proposed method were tested for compression and bending using a combination machine type 1.0244 from Testing (Germany).

Example 1

A 200 g sample of borogypsum was introduced into a plastic reaction vessel and 2000 ml of a potassium hydroxide solution with a concentration of 40 g / l was added (T: W = 1: 10). The synthesis was carried out at a temperature of 110 ° C, a pressure of 1.5 atm for 3 hours. The resulting reaction product was washed (70 ° C), filtered and dried at a temperature of 85 ° C for 4 hours. The yield of calcium hydrosilicate under these conditions is 88.9%. The resulting product with a specific surface area of 46.0 m ² · g ^{-1 was} used as a silicate sorbent for the extraction of Cu ²⁺ , Mn ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ^{2+ ions} (sorption conditions: sorbate - chloride salts of the corresponding metal with an initial ion concentration of 200 μg · ml ^-1 , the ratio of solid and liquid phases T: W = 1: 400, temperature 20 ° C, sorption time 3 hours). The values of the sorption capacity of the silicate sorbent with respect to ions of Cu ²⁺ , Mn ²⁺ , Zn ²⁺ , Ni ²⁺ , Cd ²⁺ are 1.2, 0.4, 0.6, 1.35 and 0.63 mmol · g ^-1 (degree recoveries 97.8, 28.6, 55.6, 99.3, 87.8%).

To obtain wollastonite, the synthesis product was calcined at a temperature of 850 ° C for 2 h.

To obtain an additive in concrete, the synthesis product was calcined at a temperature of 1200 ° C for 2 hours and ground. The result of introducing the obtained additive into fine-grained concrete in an amount of 3.5% is an increase in the tensile strength of concrete in compression to 35% and in bending to 50%.

Example 2

A 200 g sample of borogypsum was introduced into a plastic reaction vessel and 1400 ml of a potassium hydroxide solution with a concentration of 40 g / l was added (T: W = 1: 7). The synthesis was carried out at a temperature of 120 ° C (pressure 2.0 atm) for 1 h. The resulting reaction product was washed (70 ° C), filtered and dried in accordance with Example 1. The yield of calcium hydrosilicate under these conditions was 90.0%. The specific surface of the obtained product is 45.0 m ² · g ^-1 .

To obtain wollastonite, the synthesis product was calcined at a temperature of 1000 ° C for 1 h.

In FIG. 1-2 shows the SEM images of microparticles of wollastonite obtained in Example 2 taken at various magnifications.

As can be seen in the images presented, the wollastonite obtained consists of agglomerates of particles with a size of 20-30 microns, having a different shape. Single needle crystals from 5 to 30 microns in size are found. In addition, in the composition of the sample there are intergrowths of particles with pronounced faces close to the lamellar shape, and massive intergrowths of particles (Fig. 2) with a developed porous surface of 20-30 microns in size.

Claims (3)

1. A method of processing borogypsum by treating it for 1-3 hours with a stoichiometric amount of alkali metal hydroxide according to the equation for the synthesis of calcium hydrosilicate, followed by isolation of the resulting solid product, washing it with water at 60-70 ° C and drying at a temperature of 80-85 ° C , characterized in that the reaction is carried out at a ratio of solid and liquid phases equal to 1: (7-10), in an autoclave at a temperature of 110-120 ° C and a pressure of 1.5-2.0 atm, while the resulting product is subjected to further thermal processing. 2. The method according to p. 1, characterized in that the resulting product is subjected to heat treatment at 850-1000 ° C for 1-2 hours to obtain wollastonite. 3. The method according to p. 1, characterized in that the resulting product is subjected to heat treatment at a temperature of 1150-1200 ° C for 1-2 hours and crushed to obtain a hardening additive in concrete.

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