RU2717418C1 - Method of processing titanium-containing mineral raw materials - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to a hydrofluoride technology of processing titanium-containing mineral raw material, mainly ilmenite concentrate, and can be used in production of titanium dioxide with pigment purity, as well as iron oxide pigments. Method involves treatment of initial concentrate with solution of ammonium fluoride and/or ammonium hydrogen fluoride with heating, separation of obtained in solution fluoroammonium titanium salts from suspension of insoluble fluorine-ammonium iron salts, crystallization from ammonium hexafluorotitanate solution, its mixing with fine silicon dioxide of SiO₂ in stoichiometric ratio and subsequent pyrodihydrolysis of mixture in reactor with inner lining completely made of pressed silicon dioxide or fused quartz. Pyrodihydrolysis is carried out at stepped increase of temperature to 850–900 °C in steps of 50–100 °C and holding at each step for 20–60 minutes to obtain titanium dioxide.

EFFECT: obtaining titanium dioxide with purity of 99,5 % and whiteness of 93 standard units, as well as increasing service life of equipment with simultaneous reduction of contamination of obtained titanium dioxide by products of corrosion of reactor material.

3 cl, 2 ex

Description

The invention relates to the processing of titanium-containing mineral raw materials, mainly ilmenite concentrates, which are based on ilmenite FeTiCb, and can find application in the production of titanium dioxide, pigments based on it, as well as iron oxide pigments.

The sulfuric acid and chloride methods of processing titanium-containing raw materials that are widely used today in the industry are multistage, complex, and require significant investment in implementation. They use chemicals with high corrosive activity, which in the course of technological processes produce a large amount of waste, the volume of which exceeds the volume of the target products that pollute the environment and are difficult to process.

Hydrofluoride technology using ammonium fluoride NH ₄ F and / or ammonium hydrodifluoride NH ₄ HF ₂ as fluorinating reagents is waste-free, and due to the closure of the technological cycle and the return of all reagents involved in the process, it is environmentally acceptable. However, it has its own drawbacks, which are crucial in large-scale industrial applications.

In the general case, when the hydrofluoride technology is implemented, after the fluorinating agent is treated with the initial titanium-containing raw material, in particular ilmenite concentrate, the obtained fluorination products are separated: fluorinated ammonium salts of titanium and insoluble fluoro ammonium salts of iron are dissolved in the solution. In the next step, oxides are obtained from the isolated salts by pyrohydrolysis. The gaseous reaction products liberated in this case, mainly ammonia NH ₃ and hydrogen fluoride HF, in contact with water vapor inevitably present during processing become highly aggressive reagents. Actively interacting with many structural materials, primarily with the material of the inner lining of working reactors, these reagents cause their corrosion and destruction, which creates the risk of contamination of the target product with elements of the facing material and leads to a reduction in the life of the equipment.

Known (RU 2136771, publ. 1999.09.10) is a method for processing titanium-containing mineral raw materials to produce high-purity titanium dioxide used as a pigment in paints, enamels, etc., according to which the initial titanium-containing raw material is subjected to fluorination with ammonium hydrodifluoride at a molar ratio of 1 : (4-5) at a temperature of 50-190 ° C in a fluoroplastic reactor, then the profiled product is heated at a temperature of 350-650 ° C in a nickel reactor to separate sublimated volatile fluoroammonium complex compounds of titanium from volatile iron compounds, followed by condensation of titanium fluoro ammonium compounds in the temperature range from 230 ° C to room temperature. The heat treatment of condensed fluoroammonium complex salts to produce titanium dioxide is carried out in a glassy carbon reactor in air in two stages: with heating in the first stage from room temperature to 370-400 ° C, and in the second stage, the product formed is annealed to a temperature of 750 ° C. The disadvantage of this method is the dust extraction of finely divided fractions of iron fluoride, accompanying the process of sublimation, which leads to contamination of the equipment and after several work cycles makes it impossible to obtain titanium dioxide of pigment purity, given that after the conversion of titanium and iron into the oxide form, their purification is associated with significant difficulties. In addition, its disadvantages include a limited choice of lining materials, reduced equipment life, additional contamination of the products obtained by the lining elements of the working reactors, which is associated with the extreme aggressiveness released during the HF treatment in the presence of water vapor.

Known (RU 2623974, publ. 2017.06.29) is a method for processing titanium-containing mineral raw materials, including placer titanium ores containing leukoxenized forms of ilmenite, providing for their fluorination with a saturated aqueous solution of hydrodifluoride and / or ammonium fluoride (T: W = 1: 8- 10) at a boiling point for 40-60 minutes, followed by separation of the precipitate of fluoroammonium salts of iron from a solution containing a fluoroammonium salt of titanium. The latter is further purified from manganese by precipitation with metallic iron powder. The filtrate obtained after separation of the precipitated precipitate is purified from iron by precipitation with a 30% hydrogen peroxide solution. Ammonium oxopentafluorotitanate (NH ₄ ) ₃ TiOF ₅ , deprived of coloring impurities, is precipitated from the purified filtrate using a 25% ammonia solution, which is sent to obtain titanium dioxide by a known method - step pyrohydrolysis with maximum heating to a temperature of 850-950 ° С. The known technology justifies itself in the processing of ilmenite concentrate with a high manganese content, however, released during the pyrohydrolysis of HF, in the presence of water vapor it interacts with the material of the reactor lining, which causes its corrosion and destruction, shorten the life of the equipment as a whole and reduce the purity of the product products.

Closest to the claimed is a method of processing ilmenite concentrate to produce titanium dioxide, described together with the installation for its implementation in the Russian patent RU 2377183, publ. 12/27/2009, which provides for the treatment of ilmenite concentrate with an aqueous solution of ammonium fluoride with a concentration of about 45 weight. % when heated to 100-120 ° C at a pressure of 1-2 bar and a pH value of 6.5-7.0, filtering the resulting aqueous suspension with its separation into a precipitate fraction, which includes ammonium fluoroferrates, and a filtrate fraction, which includes ammonium fluorotitanates ; subsequent hydrolysis of the filtrate fraction to obtain a solid component, which is ammonium oxofluorotitanate; pyrohydrolysis of the latter, carried out in series in two reactors: in the first, with an internal lining of magnesium or a graphite-reinforced polymer, or glassy carbon at a temperature not exceeding 300-350 ° C, in the second, made with a lining of silicon, at a temperature of up to 850-900 ° WITH.

Ammonia NH ₄ and hydrogen fluoride HF, released during the treatment, in the presence of water vapor interact with the facing materials. It should be noted that the use of extremely flammable magnesium as a facing material, taking into account the necessary safety measures and its high cost, is impractical. Silicon dioxide SiO ₂ from the reactor lining, which has a high affinity for HF, reacts with it with the formation of volatile silicon tetrafluoride SiF ₄ by the reaction:

The resulting silicon tetrafluoride, interacting with the ammonia present, forms ammonium hexafluorosilicate (NH ₄ ) ₂ SiF ₆ , which condenses at a temperature below 350 ° C.

This process leads to a continuous loss of silicon dioxide from the reactor lining, and over time, the walls of the reactor inevitably appear - premature wear of equipment, contamination of the resulting titanium dioxide with corrosion products. As a result, the lining of a high-temperature reactor made of silicon dioxide only partially and for some time solves the problem of eliminating the above drawbacks, although it does not pollute titanium dioxide with chromophore impurities upon destruction.

The objective of the invention is to provide a method for processing titanium-containing mineral raw materials, ensuring the safety of the inner lining of the pyrohydrolysis reactor and a high service life of the equipment while obtaining targeted products of high purity.

The technical result of the method is to increase the service life of the equipment, as well as to reduce the contamination of the resulting titanium dioxide and other target products by elements from the inner lining and walls of the pyrohydrolysis reactor by increasing the safety of the said lining.

The specified technical result is achieved by a method of processing titanium-containing mineral raw materials, which involves treating it with an aqueous solution of ammonium fluoride and / or hydrodifluoride when heated to a temperature of 105-120 ° C with continuous stirring, separating a solution of titanium fluoro ammonium salts from a precipitate of insoluble iron fluor ammonium salts, and separating solid ammonium fluoro ammonium salts titanium from a solution containing them followed by pyrohydrolysis of them in the presence of finely divided silica with increasing temperature up to 850-900 ° С to obtain titanium dioxide, in which, unlike the known one, titanium ammonium hexafluorotitanate is removed from the solution and pyrohydrolyzed as titanium ammonium salt, which is mixed with finely divided silicon dioxide SiO ₂ in a stoichiometric ratio according to the equation:

(NH ₄ ) ₂ TiF ₆ + SiO ₂ → (NH ₄ ) ₂ SiF ₆ + TiO ₂ ,

wherein pyrohydrolysis is carried out in a reactor with a liner made entirely of pressed silica or fused silica, the processing temperature is increased stepwise with a step of 50-100 ° C and the exposure at each step for 20-60 minutes with a total pyrohydrolysis time of 4-8 hours.

In an advantageous embodiment of the method for increasing the purity of titanium dioxide before pyrohydrolysis of ammonium hexafluorotitanate, an additional purification of the solution containing it is carried out from microimpurity of ammonium fluoro ammonium salts by partial hydrolysis with 25% ammonia solution to pH 7.0-7.5 with precipitation of ammonium oxopentafluorotitanate, which is dissolved in hydrodifluoride fluoride ammonium and in the form of fluoroammonium salt are returned to the technological cycle.

The iron oxide red pigment is obtained by pyrohydrolysis at a temperature of 450-50 ° C obtained as a result of the separation of ammonium fluoride salts of titanium slurry fraction containing ammonium fluoroferrates.

The method is as follows.

An ilmenite concentrate containing ilmenite FeTiO ₃ is fluorinated with an aqueous solution of ammonium fluoride and / or hydrodifluoride, taken in an amount sufficient to ensure complete opening and minimize the amount of unreacted concentrate returned to the feedstock.

Fluorination is carried out at an initial temperature of the reaction mixture of 105 ° C, which, as it is removed through the gas outlet of the azeotropic mixture, water-ammonia rises to 120 ° C, and heating is continued at the temperature reached with continuous stirring for 40-60 minutes. The temperature regime at the stage of fluorination is continuously monitored, maintaining the highest possible temperature of the reaction mixture, providing a sufficiently high speed of the fluorination process, but within the specified limits, without bringing the temperature to the start of decomposition of the fluorinating reagent (140 ° C).

For effective separation of fluoro ammonium salts of titanium and fluoro ammonium salts of iron, a 15% solution of ammonium fluoride in an amount that ensures the complete dissolution of fluoro ammonium salts of titanium against the indicated concentration background of ammonium fluoride is added to the fluorinated mass (Bakeeva N.G., Gordienko P.S., Pashnina E. B. Investigation of solubility in the systems NH ₄ F- (NH ₄ ) ₂ TiF ₆ -H ₂ O and NH ₄ F- (NH ₄ ) ₃ FeF ₆ - (NH ₄ ) ₂ TiF ₆ -H ₂ O // Chemical technology, 2007.S. 389-391). Stirred and by filtration of the resulting suspension, a precipitate containing insoluble complex fluoro-ammonium salts of iron is separated from the filtrate containing complex fluoro-ammonium salts of titanium. The precipitate obtained is further washed with a solution of ammonium fluoride to remove possible filtrate residues.

This solution is added to the main filtrate and partial hydrolysis is carried out to a pH of 7.0-7.5 with an ammonia solution with a concentration of 25 weight. %, which allows you to finally clean the resulting filtrate from impurities of the complex salt of iron, which in this case is precipitated together with ammonium oxopentafluorotitanate due to their isostructurality. The obtained precipitate of ammonium oxopentafluorotitanate is treated in a solution of fluoride / and or ammonium hydrodifluoride and returned to the cycle.

The purified filtrate was evaporated before crystallization of ammonium hexafluorotitanate began.

The crystalline precipitate of ammonium hexafluorotitanate is thoroughly mixed with finely divided silica SiO ₂ according to the stoichiometry of equation (2), i.e. in a molar ratio of 1: 1, and subjected to stepwise pyrolysis in a reactor with a housing made of a corrosion-resistant structural alloy and an inner lining of pressed silicon dioxide or fused silica.

According to thermogravimetric analysis, it was found that the decomposition of ammonium hexafluorotitanate begins at a temperature of 220 ° C with the formation of NH ₄ TiOF ₃ and is accompanied by the release of ammonia and three moles of hydrogen fluoride. As the temperature rises from 350 to 550 ° C, (NH ₄ ) ₃ TiOF ₃ decomposes to form TiO ₂ . When finely dispersed silicon dioxide is added to ammonium hexafluorotitanate, decomposition of the mixture begins at a temperature of 50 ° С with the removal of water molecules from SiO ₂ ⋅nH ₂ O, which creates conditions for pyrohydrolysis of ammonium hexafluorotitanate. Further, at 220-400 ° C, an endoeffect is observed with several maxima: at 276-280, 318-320, 380-400 ° C. With a further increase in temperature, the structure of titanium dioxide is improved without loss of mass.

Pyrohydrolysis is carried out with a stepwise temperature increase, carried out using one of the known means, up to 850-900 ° C in increments of 50-100 ° C and holding at each step for 20-60 minutes with a total pyrohydrolysis time of 4-6 hours.

As a result, anatase modification titanium dioxide containing, by weight, is obtained as the target product. %: TiO ₂ - 99.5 and SiO ₂ - 0.5, whiteness 92-94 c.u. (white pigment).

After separating the solution of fluoroammonium salts of titanium and washing the remaining precipitate of fluoroammonium salts of iron with a solution of ammonium fluoride, the resulting suspension of fluoroammonium salts of iron is decanted from the heavier precipitate of unreacted particles of the feed, filtered off and subjected to pyrohydrolysis, raising the temperature to 450-500 ° С red. pigment.

Thus, due to the introduction of finely dispersed silicon dioxide at the stage of pyrohydrolysis in the reaction mixture, the proposed method almost completely eliminates the possibility of the interaction of aggressive reagents released during processing with the material of the inner lining of the reactor and its destruction and thereby completely prevents corrosion of the structural material of the reactor and pollution of the resulting titanium dioxide corrosion products. The safety of the inner lining is also an important condition for increasing the service life of all equipment.

Examples of specific implementation of the method.

Processing was subjected to ilmenite concentrate (Irshansk deposit, Zhytomyr region, Ukraine), containing, mass. %: TiO ₂ - 59.3; Fe ₂ O ₃ - 34.3; Al ₂ O ₃ - 0.42; SiO ₂ - 1.95; ZrO ₂ - 0.08; Cr ₂ O ₃ - 0.05; MnO — 0.47; P ₂ O ₅ - 0.18; CaO - 0.47; MgO - 0.04; SO ₃ - 0.15).

The whiteness of TiO ₂ samples compressed in the form of tablets was calculated based on the reflection coefficients ρ _λ measured on a Spekol 221 spectrophotometer relative to the MgO standard (100%). The composition of mineral raw materials was determined by atomic emission spectroscopy with inductively coupled argon plasma on a Plasmoguant 110 instrument and mass spectrometry with inductively coupled plasma on an Agilent 7700 s spectrometer.

For pyrohydrolysis, a reactor was used with a casing made of corrosion-resistant chromium-nickel alloy 06KHN28MDT and made of pressed dispersed silicon dioxide by facing its inner surface and other parts in contact with the reactants located inside the reactor.

Example 1

A sample of ilmenite concentrate weighing 102 g was placed in a reactor, an aqueous solution containing 238 g of ammonium hydro difluoride was added, the resulting mass was heated with an electric heater to 120 ° C and kept under stirring for 40 minutes. This dark brown mass was mixed with 950 ml of a 15% solution of ammonium fluoride; by filtration a solution of titanium fluoro ammonium salts was separated from a precipitate of insoluble iron fluoro ammonium salts. The volume of the filtrate with a density of 1.104 g / cm3 was 910 ml.

The precipitate of fluoro ammonium salts of iron was additionally washed with a 10% solution of ammonium fluoride in an amount of 150 ml to remove residual filtrate from it and this solution was attached to the main filtrate. The suspension of fluoroammonium salts of iron was decanted from the heavier precipitate of unreacted particles of raw materials (13 g), filtered through a blue ribbon filter and subjected to pyrohydrolysis in the form of a wet cake weighing 90.5 g, raising the temperature to 450-500 ° С, to obtain finely dispersed brown iron oxide (III) weighing 32.3 g

The combined filtrate containing titanium fluoroammonium salt was subjected to additional purification from impurity fluoroammonium salts of iron by partial hydrolysis with 25% ammonia solution to pH 7.0-7.5 to obtain a precipitate of ammonium oxopentafluorotitanate (weighing 31 g) containing up to 3% chromophore iron impurity which, after dissolution in ammonium hydrodifluoride, was returned to the cycle. The purified filtrate was evaporated to crystallize ammonium hexafluorotitanate weighing 98 g, which was mixed with 32 g of finely divided silica and subjected to stepwise pyrohydrolysis, raising the temperature to 850 ° C in steps of 50 ° C and holding at each step for 20 minutes with a total duration of pyrohydrolysis up to 6 o'clock. The resulting titanium dioxide weighing 36.2 g detects anatase modification, whiteness 92 c.u. (white pigment) and dispersion less than 1 micron. The composition of the mass. %: TiO ₂ - 99.7; SiO ₂ - 0.3.

Example 2

A weighed portion of ilmenite concentrate weighing 50 g was mixed with 150 g of ammonium fluoride in the form of an aqueous solution and subjected to further processing according to Example 1. In this case, fluorination was carried out at a temperature of 110 ° C for 60 minutes. After adding 400 ml of a hot 15% solution of ammonium fluoride to the resulting mass and filtering a solution of titanium fluoro ammonium salts from a precipitate of insoluble iron fluoro ammonium salts, 310 ml of a filtrate and 40.5 g of a precipitate of fluoro ammonium salts of iron were obtained.

After washing the precipitate with a 10% solution of ammonium fluoride, it was treated according to Example 1 to obtain 12.3 g of iron (III) oxide.

A washing solution was added in the same way to the main filtrate, ammonium hexafluorotitanate in the amount of 62 g was isolated from the latter, which was subjected to pyrohydrolysis by heating to 900 ° C in increments of 100 ° C and holding at each stage for 20 minutes with a total duration of pyrohydrolysis of 4.5 hours.

The composition of the obtained product, mass. %: TiO ₂ - 99.4; SiO2 0.6. Whiteness 93 c.u .; dispersion less than 1 micron.

Claims (5)

1. A method of processing titanium-containing mineral raw materials, including fluorination of titanium-containing mineral raw materials with a solution of ammonium fluoride and / or hydrodifluoride when heated to a temperature of 105-120 ° C with continuous stirring, the subsequent separation of the solution of fluoroammonium salts of titanium from the precipitate of insoluble fluoroammonium salts of iron and sludge fraction, separation solid fluoroammonium salts of titanium from a solution containing them, followed by pyrohydrolysis in the presence of silicon dioxide with increasing temperature to 850-900 ° C obtaining titanium dioxide, characterized in that the titanium fluoroammonium salt is isolated from the solution and subjected to pyrohydrolysis of ammonium hexafluorotitanate, which is mixed with finely divided silicon dioxide SiO ₂ in a stoichiometric ratio according to the equation: (NH ₄ ) ₂ TiF ₆ + SiO ₂ → (NH ₄ ) ₂ SiF ₆ + TiO ₂ , wherein pyrohydrolysis is carried out in a reactor with a liner made entirely of pressed silica or fused silica, the processing temperature is increased stepwise with a step of 50-100 ° C and the exposure at each step for 20-60 minutes with a total pyrohydrolysis time of 4-6 hours. 2. The method according to p. 1, characterized in that prior to the pyrohydrolysis of ammonium hexafluorotitanate, an additional purification of the solution of titanium fluoro ammonium salts is carried out from microimpurity of iron flu ammonium salts by partial hydrolysis to a pH of 7.0-7.5, and the resulting ammonium oxopentafluorotitanate is dissolved in hydrodifluoride ammonium and in the form of fluoroammonium salt are returned to the technological cycle. 3. The method according to p. 1, characterized in that the slurry fraction containing ammonium fluoroferrates obtained after separation of the fluoroammonium salts of iron and titanium is subjected to pyrohydrolysis at a temperature of 450-500 ° C to obtain an iron oxide red pigment.