WO2007030029A1 - Method for desilicifying mineral raw material - Google Patents

Abstract

The invention relates to a method for desilicifying mineral raw material consisting in separating a high-purity amorphous fine silicon dioxide from a large number of silicium-containing minerals and ores with a high degree of extraction and low energy and labour costs by carrying out said method on the base of a chemical transport gas-phase reaction. In addition the process low temperatures make it possible to use process equipment made of conventional construction materials, i.e. stainless steel and fluoroplastic. The inventive method consists in fluorinating a heated initial raw material by means of ammonia hydrobifluoride taken in a quantity which provides, in the reaction mixture, a molar ratio between the obtained ammonia hexafluorosilcate and an unreacted or additionaly introduced silicon dioxide equal to (0.5-5.0):1 and in subsequently carrying out a heat treatment at a temperature ranging from 220 to 320 °C in such a way that a sublimate is produced.

Description

 Method for desiliconization of mineral raw materials

1. The technical field

The invention relates to the chemical industry and can be used in the field of processing various minerals and ores during their desiliconization to produce amorphous silicon dioxide.

2. The prior art

Existing methods of desiliconization of natural minerals and ores can be conditionally divided into liquid-phase, solid-phase and mixed. The most common are liquid-phase methods based on the chemical resistance of silica to the action of acids, usually sulfuric (U.S. N ° 4401638, publ. 30.08.1983; U.S. JNs 4542003 publ. 09/17/1985; Z. Japan Ne 62- 153111, publ. 1987).

A significant drawback of such methods is the formation of large volumes of acidic waters, which further require disposal, as well as the special requirements for the hardware design of the processes.

A known method of desiliconization, including autoclaving in a solution of concentrated sulfuric acid a mixture of solid silicon-containing materials and fluorine-containing compounds selected from the group: sodium fluoroaluminate, cryolite, aluminum fluorosilicate, ammonium hydrodifluoride, sodium aluminum silicon fluoride, sodium fluorosilicate, sodium aluminate and trihydrate om ammonium or sodium fluorosilicate or a mixture thereof. Gaseous products released by this method: silicon tetrafluoride, hydrogen fluoride and water vapor are heated to 600-1020 ⁰ C in the presence of oxygen to form finely divided silica (US Pat. No. 6217840, publ. 04.17.2001).

However, the known method is technologically complicated, as it requires appropriate hardware design and increased safety measures due to the use of concentrated sulfuric acid and the process under high pressure. Way energy-consuming and associated with the need to utilize fluorinated gases ..

Known methods of desiliconization, based on the property of silicon dioxide to dissolve in alkali with the formation of silicates. For example, a method for desiliconizing clay ores is known, including fine grinding and agglomeration of ores; the interaction of the obtained granules with NaOH at a temperature of 100 ⁰ C to form a product containing sodium silicate; separating soluble silicates from the solid residue; carbonization of silicates by passing CO ₂ into a liquid product to form SiO ₂ .nH ₂ O and sodium carbonate; washing the residual silica with separation of it from soluble sodium carbonate (US Pat. Na 5302364, publ. 04/12/1994; US Pat. No. 5445804, publ. 08/29/1995).

The disadvantages of the methods include pollution of the obtained silicon dioxide with sodium due to the use of alkali during processing .. alkali, which leads to a limitation of its scope; high, energy consumption for carbon dioxide thermal decomposition. calcium carbonate; the complexity of the method due to the disposal of the resulting. salt solutions; low yield (not more than 80%) and purity (not more than 90%) of the obtained silicon dioxide. A known method for the separation of silica from its compounds, including the interaction of the starting materials with fluoride, ammonium hydrodifluoride or a mixture thereof in an aqueous medium in the presence of hydrofluoric acid or a cation exchange resin to form ammonium silicofluoride, separating it from unreacted silica and impurities by settling, recrystallization of the formed silicon fluoride its subsequent ^'with ammonia in an aqueous medium to precipitate silica (n. NQ US 5,458,864, publ. 17.10.1995).

The known method is time-consuming, based on the use of aggressive substances and requires high-purity silicon dioxide to obtain recrystallization of ammonium silicofluoride from siavic acid solutions.

A known method for the separation of silica from phosphorus-containing ores, including the separation of silicon tetrafluoride during acidification of ores, absorption of the obtained gaseous product with water or a solution of ammonium fluoride to obtain silicofluoric acid or ammonium fluorosilicate, and subsequent separation of silica from them by known methods (p. EP Ns 337712, publ. .1989). However, due to the complex chemical composition of phosphorus-containing ores, the processing of which, along with silicon tetrafluoride, produces a large number of volatile compounds of impurity elements, the method is characterized by a low yield and low purity of the resulting silicon dioxide.

Mechanical methods of desiliconization of ores include, as a rule, grinding, removal of clay components and subsequent flotation, but they are suitable for rock-forming minerals, such as carbonates, sulfates and clays (U.S. JVs 5334364, publ. 2.08.1994).

Dry heterophasic methods of desiliconization include the sublimation of silicon from ores in the form of tetrachloride at high temperature using oxygen and hydrogen to convert silicon tetrachloride to solid silicon dioxide (Chemistry and Technology of Rare and Scattered Elements, Vol. 2, ed. Higher School, M., 1976, 263-264). The disadvantages of the chlorine method include high energy intensity, high cost, environmental insecurity of the use of gaseous chlorine, hydrolytic instability of silicon tetrachloride, which requires sealing equipment.

A known method of desiliconization of titanium-containing raw materials by two-stage heating of raw materials with ammonium hydrodifluoride, first at a temperature of 50-190 ⁰ C for 2-72 hours, and then at 350-650 ⁰ C for 0.5-10 hours. The resulting condensate of fluoroammonium salts of titanium and silicon is then further heated to 500-800 ⁰ C in the presence of water vapor and silicon is separated from titanium in the form of sublimate ammonium hexafluorosilicate (HFSA) (Cl. RF JVs 2058408, publ. 04/20/1996).

However, due to the non-selectivity of the condensation of fluoroammonium salts of titanium and silicon, their subsequent pyrohydrolytic separation is required, which increases energy consumption and leads to the need for disposal of solutions of ammonium fluorides, which is released from solutions of ammonium hexafluorosilicate.

Closest to the claimed is a method of desiliconization of natural minerals and ores, including crushing the raw material, mixing it in a predetermined ratio with a fluorinating agent, which is used as fluoride - ammonium hydrodifluoride, which is a mixture of ammonium fluoride and hydrodifluoride, and subsequent heating at a speed of 5-10 ° C / min up to 500 ⁰ C (p. RF Ш 2226500, publ. 2004.04.10).

The disadvantage of this method is the high energy intensity of the process, the applicability of the method for a limited range of raw materials, specifically shungite, and the low purity of the obtained silicon dioxide, which according to our data does not exceed 90%.

3. Disclosure of invention

The objective of the invention is to reduce the energy consumption of the process and provide a high degree of desiliconization for a wide range of mineral objects, as well as to increase the purity and dispersion obtained by desilicon silicon dioxide.

The problem is solved by the method of desiliconization of mineral raw materials, including grinding of raw materials, fluorination during heating by mixing with ammonium hydrodifluoride in an amount that provides in the reaction mixture a molar ratio between ammonium hexafluorosilicate formed during fluorination and unreacted or additionally introduced silicon dioxide equal to (0.5-5-5 ): 1, and subsequent heating at a temperature of 220-320 ⁰ C. To implement the method, the mineral raw material and ammonium hydrodifluoride are mixed and heated to a temperature not exceeding 200 ⁰ C in an amount that ensures that the reaction mixture after fluorination obtains a predetermined molar ratio of ammonium hexafluorosilicate (HFSA) and silicon dioxide formed during fluorination, equal to (0.5 - 5): 1. In the case of a shortage in the initial ore, mainly silicate, of silicon dioxide, silicon dioxide is additionally introduced to create a given molar ratio. Then the fluorinated mixture is heated in the reactor at a temperature of 220 - 320 ⁰ C and the resulting sublimation is collected in the form of a white finely divided mass. Amorphous silicon dioxide is isolated from the resulting sublimation by known methods, based, for example, on the different solubility of the subliminal components, or by fractional condensation in water vapor and / or ammonia, followed by chemical decomposition of HPSA with ammonia. As shown by the experiments, the proposed method is based on the reaction of gas-phase chemical transport for the first time discovered by the applicant between HFSA and silicon dioxide, proceeding in a narrow temperature range of 220-320 ⁰ C: (NH ₄ ) ₂ SiF ₆ + SiO ₂ о (NH ₄ ^ Si ₂ O ₂ F ₆ t, which is the technical result of the invention, which provides a reduction in the energy intensity of the process of desiliconization, a high degree of desiliconization, and the purity and dispersion of the resulting silicon dioxide.

The volatile compound formed (NBLOGgSiGOgF _b is the fluoroammonium salt of metadisilicic acid - H ₂ Si ₂ O ₅ and can be represented as doubled ammonium oxotrifluorosilicate 2NH ₄ SiOF ₃ , which is the carrier of silicon dioxide in the sublimation, which is confirmed by physical and chemical studies.

To establish a molar ratio in which the components are connected to each other with the formation of ammonium oxofluorosilicate, we calculated the yield of silica in the gas phase on a model mixtures of HFSA and quartz at a temperature of 280 ⁰ C, in which the fractions of HFSA were taken into account, which sublimated independently (34.64%) and remained in the crucible, i.e. excluded (NH ₄ ) ₂ SiF ₆ not bound to quartz (table). According to the results of these calculations, for the ratios of the starting components 3: 1, 4: 1 and 5: 1, molar ratios of 1.1 were obtained; 1.0 and 0.9, respectively (on average 1.0), which makes it possible to reliably establish the formula of the volatile ammonium oxofluorosilicate - (NH ₄ ) ₂ SiF ₆ -SiO ₂ or NH ₄ SiOF ₃ .

Table

At temperatures above the sublimation point of (NH ₄ ) ₂ SiF ₆ (319 ⁰ C), the maximum evaporation of a mixture of (NH ₄ ) ₂ SiF ₆ with SiO ₂ is observed at a molar ratio of 1: 1, which also confirms the composition of the volatile compound (NH ₄ ) ₂ SiF ₆ -SY ₂ .

According to x-ray phase analysis, only the cubic phase (NH ₄ ) ₂ SiF _{6 is} detected in the sublimation and there is no crystalline SiO ₂ . At the same time in the IR-spectra is observed as (NH _{4) 2} SiF ₆ (fluctuation band ion • SiF ₆ ^{2 "at} 710 ^{cm" ₁₎} and SiO ₂ (strong band oscillations communication with 1100sm SiO ^"1) The absence of SiO ₂ in the X-ray diffraction patterns is explained by the presence of SiO ₂ in the sublimate in an amorphous form. The derivatographic method established that the gas-phase transport reaction proceeds in the temperature range 220 - 320 ⁰ C with a maximum speed at 245 ⁰ C, which is recorded as a deep effect on the curves of differential mass loss (DTG) and differential thermal analysis (DTA).

Under isothermal conditions, the effect of adding a silica-containing product to HFSA for a mixture of components in a 1: 1 molar ratio is already noticeable at 220 ⁰ C - the mass of the evaporated substance increases by 4 times compared to the evaporation of pure (NH ₄ ) ₂ SiF ₆ , and at 280- 300 ⁰ C is already 5 times.

The optimal molar ratio between HPSA and SiO ₂ , providing 100% extraction of SiO ₂ in the gas phase, is (1-2): 1, which is confirmed by calculations based on the mass loss

(table). Sublimated excess (NEL _t ) ₂ SiF ₆ affects the chemical composition of the resulting sublimates, which are fine powders of gross composition and (NH ₄ ) ₂ SiF ₆ -Si0 ₂ , where n takes values greater than or equal to 1.

A study of the kinetics of evaporation of a mixture of HPSA with SiO ₂ showed that the addition of silicon dioxide leads to an increase in the reaction rate constants. So, in comparison with pure (NBL _t ) ₂ SiF ₆ with a HFSA: SiO ₂ ratio of 2: 1 and a temperature of 260 ⁰ C, the evaporation rate of the mixture increases by 4.3 times, and at 280 ⁰ C - by 4.9 time. With the introduction of SiO ₂ , the mechanism of HFSA evaporation changes: a volatile complex forms, as a result of which the crystalline form of SiO ₂ becomes amorphous with additional purification, and the rate increases several times, which implies that the inventive method of desiliconization, as an important process for chemical technology, in the presence of SiO ₂ can be carried out under mild conditions at significantly lower temperatures, and if necessary accelerated many times. The method is carried out in the range of molar ratios of HFSA to silicon dioxide in a fluorinated feedstock equal to (0.5 - 5): 1, while

- the maximum reaction rate of gas-phase chemical transport is observed with small amounts of HPSA, specifically, with a ratio of 0.5: 1. The content of SiO ₂ in the gas phase is maximum

(20%), because it contains the minimum amount of sublimated GFSA. At a ratio of 2: 1 due to the dilution of the sublimation with ammonium hexafluorosilicate, the SiO ₂ content in the sublimation does not exceed 14.4%, but it is possible to achieve almost complete desiliconization of the feedstock. An increase in the ratio in excess of 5: 1 is not technologically justified, since the bulk of the sublimation will be

GFSA and the reaction time will not differ much from the time of evaporation

_. pure HFSA (including due to diffusion inhibition).

Obtained by the present method as a result of the reaction of gas-phase chemical transport, amorphous dioxide is the decomposition product of (NH ₄ ) ₂ Si ₂ O ₂ F ₆ and is released from the gas phase in the condenser with decreasing temperature. Due to the difference in physicochemical properties with the carrier - HFSA, amorphous dioxide is easily separated from the carrier to obtain a white fine powder with a particle size of 5-10 μm, a low bulk density of 0.10 g / cm ³ or less, which is significantly lower than, for example, in soot or quartz, and the content of the main substance is 98.0-99.99 wt.%. 4. Embodiments of the Invention The invention is illustrated by the following examples. Example 1

1 kg of ore with a quartz content of 89.64%, obtained from kaolin - quartz of feldspar sands of the Chalgan deposit (Russia) by separation of mineral components in the water stream by their size, and

2.0 kg of ammonium hydrodifluoride is heated in a steel cuvette placed in a quartz tube for 6 hours at t = 200 ⁰ C with periodic by stirring. The amount of hydrodifluoride was calculated so that the formed HFSA with respect to unreacted quartz amounted to a molar ratio of 2: 1. With this ratio, 596 g of quartz reacted with the formation of 1769 g of (NH ₄ ) ₂ SiF _b , which corresponds to a given molar ratio in the mixture. Then the temperature in the furnace is increased to 290 ⁰ C and incubated for 16 hours. Silicon is distilled off predominantly in the form of NH ₄ SiOF ₃ . The result is 1.9 kg of sublimation in the form of a mixture of SiO ₂ and (NH ₄ ) ₂ SiF ₆ . The silicon yield was 91.8%. After processing the resulting sublimation with water, 144 g of finely dispersed amorphous silicon dioxide are obtained with a purity of 99.97% and a fineness of 5-10 microns. From the HFSA solution, the remaining 678 g of SiO ₂ (“white soot”) is deposited with ammonia with the same purity. In the non-volatile residue, the complex fluorides of aluminum, iron, potassium fluoride and α-quartz (charge impurities) in the amount of 0.115 kg were detected by XRD. Example 2

As the initial ore, quartz-containing zirconium ore of the Algaminsk deposit (Russia) containing 52% ZrO ₂ and 45% SiO _{2 was used} . The latter is distributed between the gelcircon mineral

((Ca ₅ Fe) Zr ₅ Si ₄ O ₁₉ ^ H ₂ O) (8.9%) and quartz (91.1%). The proportion of gelcircon in the concentrate is 16.8%. Since the ore has an extremely small natural particle size of 0.001 - 0.002 mm, and gelzircon is also a cryptocrystalline structure, it is the first of the components to enter the fluorination reaction with ammonium hydrodifluoride. The interaction between the components begins at room temperature and passes with subsequent self-heating in 7.5 hours. Reaction equations:

(Ca ₅ Fe) Zr ₅ Si ₄ O ₁₉ • 2H ₂ O + 31 NH ₄ HF ₂ = 5 (NH4) ₂ ZrF ₆ + 4 (NH4) 2SiF6 +

CaF ₂ + (NH ₄ ) ₃ FeF ₆ + 21H ₂ O + 20 NH ₃ ; ZrO ₂ + 3 NH ₄ HF ₂ - (NH ₄ ) ₂ ZrF ₆ + 2H ₂ O + NH ₃ ; SiO ₂ + 3 NH ₄ HF ₂ = (NH ₄ ) ₂ SiF ₆ + 2H ₂ O + NH ₃ .

Since the ore taken has a complex mineralogical and chemical composition and, in addition to gel zircon and quartz, contains baddeleyite, baddeleyite and approximately half of the quartz, which was previously established from a separate sample, enter the reaction simultaneously with gel zircon.

Therefore, to ensure a molar ratio of HFSA and SiO ₂ equal to 1:

1, 1.4 kg of ammonium hydrodifluoride are added to 1 kg of ore. After fluorination of the resulting mixture at a temperature of 190 ⁰ C for 3 hours

^• in addition to (NH ₄ ) ₂ SiF ₆ (670 g), another 225 g of SiO ₂ , which is in a molar ratio of 1: 1, is present in the fluorinated product. When the reaction mass is heated above 250 ⁰ C (NH ₄ ) ₂ SiF ₆ begins to interact with the remaining quartz and at 260-290 ⁰ C it passes into the gas phase in the form of NH ₄ SiOF ₃ vapor. Desiliconization ends at 300 ⁰ C after 5 hours, which is judged by the cessation of vapor emission. From the resulting mixture (NBLi) ₂ SiF ₆ and SiO _2, after dissolving it in water, SiO _{2 is} isolated on the filter, and the filtrate is treated with ammonia to precipitate SiO ₂ • and H ₂ O, the content of the main substance of which is 99.7%. The output of silicon in the gas phase was 96.4%.

Example 3. As the source of ore using silicate ore kaolinite

Al ₄ Si ₄ O ₁₀ (OH) ₈ or Al ₂ O ₃ • 2SiO ₂ • 2H ₂ O (94.6%), which is a promising raw material for the aluminum industry. Fluorination is carried out with ammonium hydrodifluoride to produce HFSA. Reaction equation: Al ₄ Si ₄ O ₁₀ (OH) ₈ + 24NH ₄ HF ₂ = 4 (NH ₄ ) ₃ A1F ₆ + 4 (NH ₄ ) ₂ SiF ₆ + 18 H ₂ O + 4NH ₃

Since kaolinite ore does not contain free quartz, to carry out low-temperature desiliconization, the latter is introduced into the profiled mass in an amount of 220 g (with 1 kg of kaolinite) to provide a molar ratio of HPSA to SiO ₂ equal to 2: 1, and heat to a temperature of 290-300 ⁰ C for 12 hours. Obtained 1.4 kg of sublimation, consisting of amorphous silicon dioxide, HPSA and an admixture of ammonium hydrogen chloride. The silicon yield was 95%. The purity of the obtained silicon dioxide after its separation from the carrier is 99.8%.

Thus, the inventive method of desiliconization allows you to select with the degree of extraction of 90-99.9% from a wide range of silicon-containing minerals and ores amorphous finely divided silica of high purity with minimal energy and labor costs due to the implementation of the method based on the low-temperature gas-phase chemical transport reaction. At the same time, low temperatures (not higher than 320 ⁰ C) of the process allow the use of technological equipment made of ordinary structural materials - stainless steel and fluoroplastic, which leads to a cheaper method.

Claims

CLAIM 1. The method of desiliconization of mineral raw materials, including grinding the raw materials, fluorination with a fluoronammonium compound during heating and subsequent temperature treatment of the profiled product, characterized in that the fluorination is carried out with ammonium hydrodifluoride in an amount that provides a molar ratio between the formed ammonium hexafluorosilicate and the unreacted or additionally reacted silicon dioxide, equal to (0.5 - 5.0): 1, and subsequent heat treatment is carried out at temperatures e 220 -320 ⁰ C. 2. The method according to claim 1, characterized in that the fluorination is carried out up to a molar ratio of 0.5: 1.