Red iron oxide pigment preparation method

FIELD: pigment technologies.

SUBSTANCE: invention is intended for use in varnish-and-paint industry and in rubber and plastics production. Red iron oxide pigment preparation comprises: oxidation of aqueous solutions of ferric sulfate or suspensions of ferric hydroxide with air oxygen at quasi stationary temperature and pH values of reaction medium; hydrothermal heat treatment of suspension of ferric oxyhydroxides in periodical or continuous regimes in autoclaves; washing-out of pigment from water-soluble salts; drying and grinding of the pigment. During hydrothermal heat treatment FeOOH suspension is affected by nanosecond electromagnetic pulses having following characteristics: pulse duration 0.5-5 ns, pulse amplitude 4-10 kv, pulse repetition frequency 200-1000 Hz. Process is carried out at 130-200°С.

EFFECT: lowered FeOOH suspension hydrothermal heat treatment temperature and increased pigment preparation productivity.

1 tbl, 12 ex

 

The invention relates to the technology of pigments, namely the method of production of red iron oxide pigment used in paint, printing and ceramic industry, rubber, paper, plastics and other

Known Prokhladny a method of obtaining a red iron oxide pigment, comprising a stage of two-stage calcination of ferrous sulfate, wet grinding, classifying and washing from water-soluble salts calcined product, drying and grinding of the pigment (see: white E.F., Riskin IV Chemistry and technology of pigments. L.: Chemistry, 1974, s-393). The disadvantages of this method are low quality indices of the pigment due to sintering of the individual crystals in the process of calcination, and the presence of troublesome liquid (washing water) and gaseous (sulfur-containing gases) waste production.

Known sedimentary method for the synthesis of red iron oxide pigment, which includes stages of oxidation of a solution of iron sulphate (including in the presence of metallic iron) when the pH of the reaction medium 3.5 to 4.5 and a temperature of 85-100°in the presence of a specially prepared germs, washing from water-soluble salts, drying and grinding of the pigment (see: Ermilov P.I., Indacin E.A., Tolmachev I.A. Pigments and pigmented coating materials. L.: Chemistry, 1987, s-100). The drawback is this method are the low rate of synthesis of the pigment (the oxidation process are within 50-100 h) and associated high metal and energy intensity of production, as well as additional costs for preparation of embryos pigment mass fraction of up to 10 wt.%.

Closest to the proposed method is autoclave method for the synthesis of red iron oxide pigment (see Agafonov GI, Kleschev became popular, Tonchev AV, Pervushin V.Y., Schneerson AM Universal hydrothermal synthesis technology of red iron oxide pigments // Paint-and-lacquer materials and their application. 1999, No. 7-8. P.41-46)with the following main stages: a) oxidation of highly concentrated (concentration of iron (II) not less than 1 mol·l-1) aqueous sulphate solutions or suspensions hydroxide iron (II) oxygen at steady-state values of temperature and pH of the reaction medium; b) hydrothermal heat treatment (TRP) formed during the oxidation of a suspension of oxyhydroxide iron (III) α, or γ, or δ, or α- + γ, or α- + δ-modifications in batch or continuous mode in autoclaves at a temperature of 160-200°in the process of which is formed by phase α-Fe2O3; C) washing the pigment from the water-soluble salts, drying and grinding of the pigment.

The main disadvantage of the autoclave method of producing red iron oxide pigment is low, the speed of chemical transformations FeOOH→α-Fe2About3that way aprototype is solved by increasing the temperature of the stage TRP. In turn, this leads to higher energy costs and the need to use more complex autoclave equipment.

The technical result of the invention is to reduce the temperature stage of hydrothermal treatment FeOOH suspension and increase the performance of the process.

The technical result is achieved in that in a method of producing red iron oxide pigment, which includes stages of oxidation of aqueous sulphate solutions or suspensions hydroxide iron (II) oxygen at steady-state values of temperature and pH of the reaction medium, hydrothermal heat treatment of the suspension of oxyhydroxide iron (III) in batch or continuous mode in autoclaves, washing of the pigment from the water-soluble solai and drying, according to the invention in the process of hydrothermal treatment on the FeOOH suspension effect of nanosecond electromagnetic pulses with the following characteristics: pulse duration of 0.5-1 NS; pulse amplitude 6-8 kV; pulse repetition rate of 500-1000 Hz, and the hydrothermal process heat treatment is performed at a temperature of 130-200°C, after drying, carry out the grinding of the pigment.

Initiating the influence of Nemi on the process of chemical transformation FeOOH→α-Fe2O3is the following. As shown in numerous works (see, the example: Kleschev became popular Preparation of nanocrystalline oxides of Ti, Mn, Co, Fe and Zn in aqueous solutions during thermal treatment // Inorganic materials. 2005. V.41. No. 1. P.46-53) phase and chemical transformations of non-equilibrium hydrated oxides numerous hydrated oxides of p - and 3d - elements during thermal treatment solutions are carried out by the mechanism of the dissolution - precipitation" (RUM), by dissolving crystals of non-equilibrium phase formation of nuclei and growth (through the solution) crystals equilibrium phase. At relatively low temperature heat treatment limiting stage of these transformations is the process of dissolution of crystals nonequilibrium phase associated with the rupture of high powered links between kristalloobrazuyushchikh complexes of the surface layer of crystals. When exposed to NAMI with high electric field strength (up to 109V/m) is the deformation of the valence orbitals of crystalloblastic complexes, which leads to lower energy relations. Manifestation of this is the acceleration of the process of phase and chemical transformations of nonequilibrium FeOOH, the temperature decrease of the macroscopic manifestations of the transformation.

The lower limit for the pulse duration of 0.5 NS is due to the fact that generators with smaller pulse duration have a very high cost. When the pulse duration of more than 5 n is (upper limit), the impact of name drops sharply due to the reduction of the electric field strength inside the autoclave at the further increase of the pulse duration by decreasing the rate of change voltage and current.

The lower limit value of the amplitude of the pulse is due to the fact that when the amplitude is less than 4 kV decreases the rate of change of voltage and current, and thus decreases the electric field strength inside the autoclave. The upper limit on the amplitude of 10 kV pulses is limited by the technical capabilities of the generator.

The lower limit of the pulse repetition rate of 200 Hz is associated with a minimum value of the average values of energy that is fed into the autoclave during the synthesis, is required to initiate the process of transformation of FeOOH. The upper limit of the repetition frequency of 1000 Hz is limited by the technical capabilities of the generator.

The lower temperature limit of 130°stage hydrothermal treatment due to the fact that at lower temperatures the duration of the process of transformation FeOOH sharply increases, which leads to reduced performance of the process; conducting heat treatment at temperatures above 200°impractical due to the increasing intensity of this stage.

The invention is illustrated by the following examples.

Example 1 (prototype). Take 0.5 liters cleaned from mechanical impurities solution of iron sulfate (II), obtained by dissolving steel iron sulphate with a concentration of 1.3 mol/l and placed in a sealed vessel with a volume of 1 sup> 3equipped with self-priming with an aerator for mixing and oxidation of solutions (suspensions) iron(II) air, devices dispensing gas and a solution of alkali, heat and temperature, measurement of pH and temperature of the reaction medium. The oxidation is carried out at a quasi-permanent values of temperature (45±2° (C) and the pH of the reaction medium (5,5±0,5) oxygen at a pressure of 0.2 MPa. PH support dosing in the vessel an aqueous solution of sodium hydroxide (qualification "h") with a concentration of 10.3±0.1 mol/l Duration of the oxidation process was 20 minutes Received of 0.625 l suspensions of single-phase α-FeOOH concentration 93±1 g/l

Take 7 ml of the resulting suspension and placed in an autoclave with a volume of 10 cm3equipped with a feeding device of nanosecond electromagnetic pulses. The autoclave is first rapidly (within 15 min) heated in a muffle furnace, oven controlled at a temperature of 350°C, to a temperature of 180±5°C, then placed in a second furnace with a temperature of 180±2°and subjected to isothermal heat treatment in the absence of name within 2 hours after the heat treatment, the autoclave is cooled under running water to room temperature and rethermalized. The solid phase with a Buechner funnel is separated from the mother liquor, washed with water until no leachate quality the Oh reaction of sulfate ions, dried at 70°C to constant weight and powdered in an agate mortar. The phase composition of the obtained sample is examined by the method of quantitative x-ray phase analysis and its dispersion composition by scanning and transmission microscopy.

Obtained under these conditions the sample is a mixture of two phases (α-FeOOH and α-Fe2O3): mass fraction α-Fe2About345 wt.%; crystals α-Fe2About3they have isometric shape with signs of cut, their average size is 150 nm.

Example 2 (prototype). Take 7 ml suspension α-FeOOH obtained in the first experiment. Other operations are carried out analogously to example 1, except modes stage isothermal heat treatment which is performed at a temperature of 200±2°C for 2 hours

The obtained single-phase sample α-Fe2About3with an average crystal size of 170 nm.

Examples 3 and 4 (prototype). The oxidation of the ferric sulfate solution (II) is carried out analogously to example 1, except modes stage of oxidation, which is carried out at a temperature of 35±2°and the pH of the reaction medium is 6.5±0.5 in. The duration of the oxidation process was 10 minutes the resulting suspension mixture of phases γ- + α-FeOOH with a mass fraction α-FeOOH in washed from impurities and dried to a constant weight of the sample 55 wt.%.

Hydrothermal thermo is the processing of the resulting suspension was carried out similarly to example 1, by varying the temperature and duration of the process. Specific modes of heat treatment parameters, the phase composition of the samples and the average size of crystals α-Fe2About3presented in the table.

Example 5 (the proposed method). The oxidation of the ferric sulfate solution (II) is carried out analogously to example 1. The process of heat treatment of the suspension α-FeOOH similar to example 1, except that immediately after the autoclave in the second furnace, temperature-controlled at 180±2°include feeder in the reaction medium of nanosecond electromagnetic pulses with the following characteristics: pulse width of 0.5 NS, the amplitude of 6 kV, repetition rate of 500 Hz. The heat treatment are within 1 o'clock Gain-phase sample α-Fe2About3with an average crystal size of 150 nm.

Examples 6-8 (the proposed method) is carried out analogously to example 5, by varying the parameters of name, temperature and duration of heat treatment. The phase composition of the red iron oxide pigment and the average size of crystals α-Fe2About3presented in the table.

Example 9 (the proposed method). The oxidation of the ferric sulfate solution (II) is carried out analogously to examples 3 and 4. The process of heat treatment of the suspension γ- + α-FeOOH is similar to example 3, except that immediately after the SIP is the same autoclave in the second furnace, temperature-controlled at 130±2°include feeder in the reaction medium of nanosecond electromagnetic pulses with the following characteristics: pulse width of 0.5 NS, the amplitude of 8 kV, repetition rate of 1000 Hz. The heat treatment are within 2 hours Receive a single-phase sample α-Fe2About3with an average crystal size of 90 nm.

Examples 10-12 (the proposed method) is carried out analogously to example 5, by varying the parameters of name, temperature and duration of heat treatment. The phase composition of the red iron oxide pigment and the average size of crystals α-Fe2O3presented in the table.

The table shows that, compared with the reference temperature stage of hydrothermal heat treatment of the suspension FeOOH is reduced by 30°and the duration of this stage is reduced by 2-4 times.

Table
The parameters of the synthesis of red iron oxide pigment, the phase composition of the samples and the average size of crystals α-Fe2About3
No.Parameters and valuesThe way the prototypeExamples of the proposed method
123 56789101112
1.The temperature oxidation steps, °454535354545454535353535
2.the pH of the reaction medium, a unit5,55,56,56,55,55,55,55,56,56,56,56,5
3.Mass fraction α-FeOOH, wt.%100100555510010010010055555555
4.The temperature of the hydrothermal treatment, °180200130160180200160130130160180200
5The duration of the TRP, h224210,53 20,50,30,1
6.Pulse duration, NS----0,50,50,50,510,50,55
7.Pulse amplitude, kV----684886610
8.Repetition frequency, Hz----5002001000100010001000500500
9.Mass fraction α-Fe2About3in pigment, wt.%451000100100100100100100100100100
10.The average size of crystals α-Fe2About3nm150170-9017020015013090110120 130

A method of obtaining a red iron oxide pigment, which includes stages of oxidation of aqueous sulphate solutions or suspensions hydroxide iron (II) oxygen at steady-state values of temperature and pH of the reaction medium, hydrothermal heat treatment of the suspension of oxyhydroxide iron (III) in batch or continuous mode in autoclaves, washing of the pigment from the water-soluble salts and drying, characterized in that in the process of hydrothermal treatment on the FeOOH suspension effect of nanosecond electromagnetic pulses with the following characteristics: pulse duration from 0.5 to 5, the amplitude of the pulses 4-10 kV, pulse repetition rate of 200-1000 Hz, and the process of hydrothermal treatment is carried out at a temperature of 130-200°With, in addition, after drying, carry out the grinding of the pigment.



 

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