Environment-friendly high-color saturation iron oxide red pigment and preparation method thereof

Abstract

The invention discloses an environment-friendly high-color saturation iron oxide red pigment and a preparation method thereof. The preparation method comprises the following preparation steps: (1) preparing a delta-FeOOH seed crystal; and (2) second-step oxidation. According to the method disclosed by the invention, ferrous sulfate and liquid caustic soda are uniformly mixed to instantly form Fe (OH) 2 in the step (1), a strong oxidant ferrate is dropwise added in a limited manner, and a trace amount of air is supplemented for oxidization, so that Fe < 2 + > in the solution can be quickly and uniformly oxidized into delta-FeOOH seed crystals, and generation of impure-phase alpha-FeOOH and gamma-FeOOH caused by slow oxidization rate is avoided; according to the method, the condition that the seed crystal is irregular in shape and low in purity due to the fact that the oxidation rate is too high is avoided, a foundation is laid for complete phase conversion of the delta-FeOOH seed crystal into alpha-Fe2O3 in the subsequent iron sheet oxidation stage, the generated iron oxide red pigment is bright in hue and free of impurity phases and has high color saturation, and the hue standard is similar to that of iron oxide red obtained through a mixed acid method.

Description

Technical Field

[0001] The present invention relates to the technical field of iron oxide red pigments, and particularly relates to an environmentally friendly iron oxide red pigment with high color saturation and a preparation method thereof. Background Art

[0002] Iron oxide red pigments are very important inorganic color pigments, which have high chemical and physical stability, as well as good properties such as color diversity, high covering power, and non-toxicity. They are widely used as colorants for rubber, paint, artificial marble, as well as in industries such as ceramics, papermaking, ink, and art pigments.

[0003] The process routes for producing iron oxide red pigments are mainly divided into two major processes: wet process and dry process. The wet preparation technology of iron red can be divided into nitric acid method, sulfuric acid method, and mixed acid method. Among them, the product obtained by the nitric acid method has the best pigment performance, but the pollution is the most serious, and few enterprises use it. Currently, iron oxide red pigments mainly use the mixed acid method, that is, nitric acid and iron sheet are used to prepare iron red crystal seeds under high temperature and high pressure conditions, and then ferrous nitrate and ferrous sulfate are used as the driving force for crystal growth during the two-step oxidation process to obtain iron oxide red products. The iron oxide red pigments obtained by this method have relatively good quality performance, but there are also major disadvantages, that is, a large amount of wastewater and waste gas with excessive ammonia nitrogen will be generated during the preparation process, which will not only have a certain impact on the health of workers, but also need to carry out environmental protection treatment on the wastewater in the follow-up, which will greatly increase the production cost of enterprises. Although the sulfuric acid method production process has less pollution and lower cost, the quality performance of the obtained iron oxide red pigments is far inferior to that of the mixed acid method, and the product color is dull and the pigment performance is relatively poor.

[0004] The patent application with the publication number CN102557226A discloses a production method for preparing iron oxide red crystal seeds by using wastewater containing ferrous salts. This technology uses iron oxide red wastewater to carry out aeration reaction, concentrate the generated iron red sludge, and then continue the oxidation reaction to prepare α-FeOOH iron oxide red crystal seeds. Although this process is pollution-free, however, the conversion efficiency of α-FeOOH iron oxide red crystal seeds into α-Fe2O3 is relatively low during subsequent conversion, the purity is general, and the converted α-Fe2O3 may be affected to a certain extent in terms of color and stability, and the performance of the prepared α-Fe2O3 pigments is not good and cannot replace traditional mixed acid method iron oxide red pigments; the patent application with the publication number CN112875762A discloses a method for preparing iron oxide red by using pickling waste liquid, including process steps such as generating ferrous hydroxide, generating crystal seeds δ-FeOOH, generating a-Fe2O3 crystal nuclei, carrying out in-situ reaction, preparing solid iron oxide red and calcium chloride, etc. Although the conversion efficiency is improved during subsequent conversion into α-Fe2O3, the finally obtained α-Fe2O3 has general purity and cannot meet the market demand for high-purity α-Fe2O3. Summary of the Invention

[0005] To this end, the object of the present invention is to provide an environmentally friendly iron oxide red pigment with high color saturation, mild synthesis conditions, low production cost and high purity, and a preparation method thereof.

[0006] In a first aspect, the present invention provides a preparation method of an environmentally friendly iron oxide red pigment with high color saturation, comprising the following preparation steps:

[0007] (1) Preparation of δ-FeOOH seeds

[0008] Completely dissolve solid ferrous sulfate in water and put it into the seed reaction barrel so that the initial concentration of ferrous sulfate in the solution is 200-300 g / L; while stirring continuously, add a liquid alkali solution to the solution system to adjust the pH of the solution to 7.0-9.0; after the pH value of the mixed system is constant, introduce compressed air and add ferrate; after the reaction of δ-FeOOH seeds is completed, stop stirring and close the compressed air, and the preparation of δ-FeOOH seeds is completed;

[0009] (2) Two-step oxidation

[0010] Adjust the pH of the δ-FeOOH seeds obtained in step (1) to 2.0-4.0 with sulfuric acid solution, put them into an oxidation barrel filled with iron sheets, and then add ferrous sulfate to the solution in the oxidation barrel; heat up and continuously introduce compressed air into the solution in the oxidation barrel for oxidation for a period of time; take samples, filter by suction, rinse, dry and pulverize to obtain iron oxide red pigment.

[0011] Preferably, in the step (1), the ferrate is sodium ferrate or potassium ferrate, and its stoichiometric molar ratio with Fe 2+ is 1:(10-30).

[0012] Preferably, in the step (1), when adding the liquid alkali solution to the solution system, it is added in large quantities and quickly, the mass concentration of the liquid alkali is 32%, and when adding the ferrate, it is added slowly and evenly and ensured to be added dropwise within 10 minutes.

[0013] Preferably, in the step (1), at the end point of the δ-FeOOH seed reaction, the feed liquid completely turns orange-red and the pH of the feed liquid is 4.5-5.0.

[0014] Preferably, in the step (1), the stirring speed is 60-200 r / min.

[0015] Preferably, in the step (1), the air volume of the introduced compressed air is 20-60 L / min.

[0016] Preferably, in the step (2), the solid content of δ-FeOOH seeds in the oxidation tank is 60-100 g / L

[0017] Preferably, in the step (2), the concentration of ferrous sulfate is 40-60 g / L.

[0018] Preferably, in the step (2), the steam in the oxidation tank is heated to 80-90 °C for the oxidation reaction. When conducting the oxidation reaction, the air volume of the compressed air introduced is 60-120 L / min, and the oxidation reaction time is 16-20 h.

[0019] In the second aspect, the present invention provides an iron oxide red pigment prepared by using the preparation method of the environmentally friendly iron oxide red pigment with high color saturation as described above.

[0020] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0021] 1. In the present invention, the process flow for preparing high-purity and high-color saturation iron oxide red pigment is simple, and the reaction conditions are mild. Using titanium white by-product solid ferrous sulfate as the iron source, there is no introduction and discharge of polluting ammonia nitrogen compounds throughout the preparation process. The process is environmentally friendly and the production cost is low, being suitable for industrial-scale production;

[0022] 2. In the present invention, Fe(OH)2 formed instantaneously by mixing ferrous sulfate and liquid alkali is oxidized by limiting the addition of a strong oxidizing agent ferrate in step (1) and supplemented with a small amount of air, so that Fe in the solution 2+ can be quickly and uniformly oxidized into δ-FeOOH seeds, avoiding the formation of heterophase α-FeOOH and γ-FeOOH due to slow oxidation rate, and also avoiding the irregular crystal form and reduced purity of the seeds due to too fast oxidation rate. This lays a foundation for the complete phase transformation of δ-FeOOH seeds into α-Fe2O3 in the subsequent iron sheet oxidation stage, making the produced iron oxide red pigment have bright color, no heterophase generation, high color saturation, and the hue standard is similar to that of iron oxide red produced by the mixed acid method, solving the problems of dull hue of iron oxide red produced without using nitric acid or ferrous nitrate, as well as high production cost of iron oxide red, serious environmental pollution and great potential safety hazards;

[0023] 3. In the present invention, it is limited that the δ-FeOOH seeds prepared in step (1) can be directly put into the iron sheet reaction tank, and the phase transformation of δ-FeOOH into α-Fe2O3 and the oxidation growth of primary particle α-Fe2O3 can be realized in the oxidation reaction tank, making the industrial operation more simple and fast. At the same time, the generation of acicular hydrated iron oxide hydroxide during the high-temperature phase transformation is avoided, and the produced iron oxide red pigment has bright color, no heterophase generation, and high color saturation;

[0024] 4. The iron oxide red pigment prepared in the present invention can meet the hue standard of iron red prepared by the mixed acid method, and is also similar in particle morphology, both having a uniform particle size distribution and a regular spherical structure, and the purity (calculated by Fe2O3 content) is about 98%, which is significantly improved compared with the iron red prepared by the mixed acid method, providing a key technical guarantee for the subsequent development of high-purity-dependent iron oxide materials.

[0025] 5. In the present invention, a dual-functional oxidation-catalysis system is constructed with ferrate, shortening the oxidation time of 40 - 50 h in the preparation of iron oxide red pigment by the traditional mixed acid method to 16 - 20 h, achieving a breakthrough reduction in kinetic efficiency, and at the same time ensuring that the iron oxide red pigment has high color saturation and bright hue. Compared with the iron oxide red prepared by the traditional mixed acid method, ΔE is stable within 1.1. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD pattern of the iron oxide red pigment sample prepared in Example 1;

[0027] Figure 2 XRD pattern of the iron oxide red pigment sample prepared in Comparative Example 2;

[0028] Figure 3 SEM image of the iron oxide red pigment sample prepared in Example 1

[0029] Figure 4 SEM image of the iron oxide red pigment sample prepared in Example 2;

[0030] Figure 5 SEM image of the iron oxide red pigment sample prepared in Comparative Example 1;

[0031] Figure 6 SEM image of the iron oxide red pigment sample prepared in Comparative Example 2;

[0032] Figure 7 SEM image of the iron oxide red pigment sample prepared in Comparative Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Example 1:

[0035] A preparation method of an environmentally friendly iron oxide red pigment with high color saturation, comprising the following preparation steps:

[0036] (1) Preparation of δ-FeOOH seeds:

[0037] Take 2.3 kg of solid ferrous sulfate as a by-product of titanium dioxide production, dissolve it in 10 L of water to obtain a solution with a concentration of 200 g / L, and put it into a 30-L reaction barrel. While continuously stirring, rapidly add 1.3 L of 32% liquid caustic soda solution to the solution system to adjust the pH to 7.8. After the pH value of the mixed system becomes constant, introduce compressed air at a rate of 30 L / min, and slowly and evenly add an aqueous solution containing 54.4 g of sodium ferrate while stirring at a speed of 90 r / min, ensuring that the addition is completed within 10 min. When the feed liquid completely turns orange-red and the pH is 4.5, stop stirring and close the air supply, and the preparation of δ-FeOOH seeds is completed.

[0038] (2) Secondary oxidation:

[0039] Adjust the pH of the 10 L of δ-FeOOH seeds obtained in step (1) to 2.8 using 50% sulfuric acid, put it into an oxidation barrel filled with iron sheets, and add 2 L of water. At this time, the solid content in the oxidation barrel is 63 g / L. Add a 400 g / L ferrous sulfate solution to the solution in the oxidation barrel, and control the content of ferrous sulfate in the solution to be 40 g / L. Then use steam to heat up to 85°C, and continuously introduce compressed air into the solution in the oxidation barrel at a rate of 100 L / min for oxidation. After the oxidation reaction reaches 16 h, take samples, perform suction filtration, rinsing, drying, and pulverization to obtain the iron oxide red pigment sample.

[0040] Example 2:

[0041] A preparation method of an environmentally friendly iron oxide red pigment with high color saturation, comprising the following preparation steps:

[0042] (1) Preparation of δ-FeOOH seeds:

[0043] Take 3.5 kg of solid ferrous sulfate as a by-product of titanium dioxide production, dissolve it in 10 L of water to obtain a solution with a concentration of 300 g / L, and put it into a 30-L reaction barrel. While continuously stirring, rapidly add 1.8 L of 32% liquid caustic soda solution to the solution system to adjust the pH to 7.8. After the pH value of the mixed system becomes constant, introduce compressed air at a rate of 30 L / min, and slowly and evenly add an aqueous solution containing 54.4 g of sodium ferrate while stirring at a speed of 60 r / min, ensuring that the addition is completed within 10 min. When the feed liquid completely turns orange-red and the pH is 4.6, stop stirring and close the air supply, and the preparation of δ-FeOOH seeds is completed.

[0044] (2) Secondary oxidation:

[0045] Adjust the pH of the 10 L of δ-FeOOH seeds obtained in step (1) to 2.9 using 50% sulfuric acid, put them into an oxidation barrel filled with iron sheets, add 2 L of water. At this time, the solid content in the oxidation barrel is 94.5 g / L. Add a 400 g / L ferrous sulfate solution to the solution in the oxidation barrel, and control the content of ferrous sulfate to be 40 g / L. Then use steam to heat up to 90 °C, and continuously introduce compressed air into the solution in the oxidation barrel at a speed of 120 L / min for oxidation. After the oxidation reaction reaches 20 h, take samples, perform suction filtration, rinsing, drying, and pulverization to obtain an iron oxide red pigment sample.

[0046] Example 3:

[0047] A preparation method of an environmentally friendly iron oxide red pigment with high color saturation, comprising the following preparation steps:

[0048] (1) Preparation of δ-FeOOH seeds:

[0049] Take 3.5 kg of titanium white by-product solid ferrous sulfate and dissolve it in 10 L of water, with a concentration of 300 g / L, and put it into a 30 L reaction barrel. Under continuous stirring, rapidly add 1.3 L of 32% liquid alkali solution to the solution system to adjust the pH to 7.0. After the pH value of the mixed system is constant, introduce compressed air at a speed of 20 L / min, and slowly and evenly add an aqueous solution containing 71.2 g of potassium ferrate under a stirring speed of 90 r / min, ensuring that the addition is completed within 10 min. When the feed liquid completely turns orange-red and the pH is 4.5, stop stirring and close the air, and the preparation of δ-FeOOH seeds is completed;

[0050] (2) Two-step oxidation:

[0051] Adjust the pH of the 10 L of δ-FeOOH seeds obtained in step one to 3.0 using 50% sulfuric acid, put them into an oxidation barrel filled with iron sheets, add 2 L of water. At this time, the solid content in the oxidation barrel is 94.5 g / L. Then add a 400 g / L ferrous sulfate solution to the solution in the oxidation barrel, and control the content of ferrous sulfate to be 42 g / L. Then use steam to heat up to 90 °C, and continuously introduce compressed air into the solution in the oxidation barrel at a speed of 100 L / min for oxidation. After the oxidation reaction reaches 18 h, take samples, perform suction filtration, rinsing, drying, and pulverization to obtain an iron oxide red pigment sample.

[0052] Example 4:

[0053] A preparation method of an environmentally friendly iron oxide red pigment with high color saturation, comprising the following preparation steps:

[0054] (1) Preparation of δ-FeOOH seeds:

[0055] 3.5 kg of solid ferrous sulfate, a byproduct of titanium dioxide, was dissolved in 10 L of water to a concentration of 300 g / L, and was put into a 30 L reaction barrel. Under constant stirring, 2.5 L of 32% liquid alkali solution was added to the solution system in large quantities and quickly to adjust the pH to 9.0. After the pH value of the mixed system became constant, compressed air was introduced at a speed of 20 L / min, and an aqueous solution containing 59.35 g of sodium ferrate was slowly and evenly added at a stirring speed of 90 r / min, ensuring that the addition was completed within 10 min. When the feed liquid completely turned orange-red and the pH was 4.7, stirring was stopped, the air was turned off, and the preparation of δ-FeOOH seed crystals was completed.

[0056] (2) Two-step oxidation:

[0057] The 10L δ-FeOOH seed crystals obtained in step (1) are adjusted to pH 2.8 using 50% sulfuric acid, and are put into an oxidation barrel filled with iron sheets, and 2L of water is added. At this time, the solid content in the oxidation barrel is 94.5g / L, and then 400g / L of ferrous sulfate solution is added to the solution in the oxidation barrel to control the content of ferrous sulfate to 45g / L; then, steam is used to heat the solution to 90°C, and compressed air is continuously introduced into the solution in the oxidation barrel at a rate of 100L / min for oxidation; after the oxidation reaction reaches 16h, sampling, suction filtration, rinsing, drying, and crushing are performed to obtain an iron oxide red pigment sample.

[0058] Comparative Example 1:

[0059] In this comparative example, the conventional mixed acid method is used to prepare the iron oxide red pigment, which specifically includes the following steps:

[0060] (1) Preparation of α-Fe2O3 seed crystals:

[0061] Put 70kg of iron sheet into a high-pressure reaction barrel, add an appropriate amount of water, and heat the steam to 75°C; add 120kg of dilute nitric acid with a content of 45% at one time; react at a pressure of 0.45MPa, maintain the pressure for 30 minutes, open the vent valve, and when the pressure drops to 0.1-0.2MPa, the preparation of α-Fe2O3 seed crystals is completed;

[0062] (2) Two-step oxidation:

[0063] Put the prepared α-Fe2O3 seed crystals into the reaction barrel, add iron sheet, ferrous nitrate solution and appropriate amount of water, control the content of ferrous nitrate to 45g / L, heat the steam to 75℃, and control the air volume to 80m 3 / h, and maintain the whole reaction process until the ferrous nitrate content in the reaction barrel is reduced to 5g / L, and the oxidation reaction with ferrous nitrate as the medium is completed.

[0064] Transfer the above-mentioned liquid material into another reaction barrel, add iron sheet, ferrous sulfate and appropriate amount of water, control the content of ferrous sulfate to be 35 g / L, heat up with steam to 85 °C, control the air volume to be 100 m 3 / h, and maintain the reaction throughout the process. The content of ferrous sulfate during the reaction is maintained at 30 - 40 g / L. When the reaction reaches 30 - 40 h, take samples, perform suction filtration, rinsing, drying, and crushing to obtain the iron oxide red pigment sample.

[0065] Comparative Example 2:

[0066] In this comparative example, a preparation method of iron oxide red includes the following preparation steps:

[0067] (1) Preparation of δ-FeOOH seeds:

[0068] Take 3.5 kg of titanium white by-product solid ferrous sulfate and dissolve it in 10 L of water, with a concentration of 300 g / L, and put it into a 30 L reaction barrel. While continuously stirring, add 1.8 L of 32% liquid caustic soda solution to the solution system in a large amount and quickly, and adjust the pH to 7.8; after the pH value of the mixed system is constant, introduce compressed air at a speed of 20 L / min, and slowly and evenly add 123 g of 30% hydrogen peroxide solution by mass while stirring at a speed of 60 r / min, ensuring that the addition is completed within 10 min; when the liquid material completely turns orange-red and the pH is 4.56, stop stirring, close the air, and the preparation of δ-FeOOH seeds ends;

[0069] (2) Two-step oxidation:

[0070] Adjust the pH of the 10 L of δ-FeOOH seeds obtained in step (1) to 2.8 using 50% sulfuric acid, put it into an oxidation barrel filled with iron sheet, and add 2 L of water. At this time, the solid content in the oxidation barrel is 94.5 g / L. Then add a 400 g / L ferrous sulfate solution to the solution in the oxidation barrel, and control the content of ferrous sulfate to be 40 g / L; then heat up to 90 °C using steam, and continuously introduce compressed air into the solution in the oxidation barrel at a speed of 100 L / min for oxidation; after the oxidation reaction reaches 16 h, take samples, perform suction filtration, rinsing, drying, and crushing to obtain the iron oxide red pigment sample.

[0071] Comparative Example 3:

[0072] In this comparative example, a preparation method of iron oxide red includes the following preparation steps:

[0073] (1) Preparation of α-Fe2O3 seeds:

[0074] Take 3.5 kg of solid ferrous sulfate as a by-product of titanium dioxide production, dissolve it in 10 L of water to obtain a solution with a concentration of 300 g / L, and put it into a 30-L reaction barrel. While continuously stirring, add 1.8 L of 32% liquid caustic soda solution to the solution system in a large amount and quickly to adjust the pH to 7.8. After the pH value of the mixed system becomes constant, introduce compressed air at a rate of 30 L / min, and slowly and uniformly add an aqueous solution containing 54.4 g of sodium ferrate while stirring at a speed of 60 r / min, ensuring that the addition is completed within 10 min. When the feed liquid completely turns orange-red and the pH is 4.5 - 5.0, stop stirring and turn off the air, and the preparation of δ-FeOOH seeds is completed. Adjust the pH of the δ-FeOOH seeds to 2.8 with 50% sulfuric acid, raise the temperature to 100 °C by steam, then add 0.2 L of ferrous sulfate with a concentration of 400 g / L, and maintain the temperature at about 100 °C for 10 min - 30 min. After that, the color of the feed liquid changes from orange-red to bright red, and the phase transformation of δ-FeOOH seeds to α-Fe2O3 is completed.

[0075] (2) Two-step oxidation:

[0076] Put the 10-L α-Fe2O3 feed liquid obtained in step (1) into an oxidation barrel filled with iron sheets, add 2 L of water, and then add 1.2 L of ferrous sulfate with a concentration of 400 g / L to the solution in the oxidation barrel. Then use steam to raise the temperature to 90 °C, and continuously introduce compressed air into the solution in the oxidation barrel for oxidation, with the air volume being 120 L / min. After the oxidation reaction reaches 16 h, take samples, perform suction filtration, rinsing, drying, and pulverization to obtain iron oxide red pigment samples.

[0077] Comparative Example 4:

[0078] In this comparative example, a method for preparing iron oxide red includes the following preparation steps:

[0079] (1) Preparation of δ-FeOOH seeds:

[0080] Take 3.5 kg of solid ferrous sulfate as a by-product of titanium dioxide production, dissolve it in 10 L of water to obtain a solution with a concentration of 300 g / L, and put it into a 30-L reaction barrel. While continuously stirring, add 1.8 L of 32% liquid caustic soda solution to the solution system in a large amount and quickly to adjust the pH to 7.8. After the pH value of the mixed system becomes constant, while stirring at a speed of 60 r / min, slowly and uniformly add an aqueous solution containing 54.4 g of sodium ferrate, ensuring that the addition is completed within 10 min. When the feed liquid completely turns orange-red and the pH is 4.7, stop stirring and turn off the air, and the preparation of δ-FeOOH seeds is completed.

[0081] (2) Two-step oxidation:

[0082] Adjust the pH of the 10 L δ-FeOOH seeds obtained in step (1) to 2.8 using 50% sulfuric acid, put them into an oxidation barrel filled with iron sheets, add 2 L of water, then add a 400 g / L ferrous sulfate solution to the solution in the oxidation barrel, and control the ferrous sulfate content to be 40 g / L; then use steam to raise the temperature to 90 °C, and continuously introduce compressed air into the solution in the oxidation barrel for oxidation, with the air volume being 120 L / min; after the oxidation reaction reaches 16 h, take a sample, perform suction filtration, rinsing, drying, and pulverization to obtain an iron oxide red pigment sample.

[0083] Detection of sample morphology and crystal structure:

[0084] Use a MiniFlex 600 X-ray diffractometer (XRD) (Cu Kα radiation, voltage 40 kV, current 30 mA) from Rigaku Corporation, Japan to test the crystal structure of the iron oxide red pigment samples prepared in Example 1 and Comparative Example 2; use an S4800 scanning electron microscope (SEM: Scanning Electron Micrographs) produced by Hitachi, Japan to observe the surface morphology of the iron oxide red pigment samples prepared in Example 1, Example 2, and Comparative Examples 1 to 3; use a datacolor Spectro 700 color measurement instrument to analyze the hue of the iron oxide red pigment samples prepared in Examples 1 to 4 and Comparative Examples 1 to 4.

[0085] Figure 1 XRD pattern of the iron oxide red pigment sample prepared in Example 1; Figure 2 XRD pattern of the iron oxide red pigment sample prepared in Comparative Example 2; Figure 3 SEM image of the iron oxide red pigment sample prepared in Example 1; Figure 4 SEM image of the iron oxide red pigment sample prepared in Example 2; Figure 5 SEM image of the iron oxide red pigment sample prepared in Comparative Example 1; Figure 6 SEM image of the iron oxide red pigment sample prepared in Comparative Example 2; Figure 7 SEM image of the iron oxide red pigment sample prepared in Comparative Example 3.

[0086] As Figure 1 shown, the crystal structure of the iron oxide red pigment sample prepared in Example 1 of the present invention is a pure phase of α-Fe2O3, and no other impurity phases appear. As Figure 2 shown, the crystal structure of the iron oxide red pigment sample prepared in Comparative Example 2 not only has α-Fe2O3, but also has an α-FeOOH impurity phase.

[0087] As Figures 3 - 5As shown, the iron oxide red pigment samples prepared in Examples 1 and 2 of the present invention and the iron oxide red pigment sample prepared by the mixed acid method in Comparative Example 1 are similar in appearance, both of which are regular spherical structures. Figure 6 As shown in the comparative example 2, the iron oxide red pigment sample prepared using hydrogen peroxide as an oxidant contains needle-shaped impurities, namely α-FeOOH, which cannot be completely transformed into α-Fe2O3. Figure 7 As shown, in Comparative Example 3, the iron oxide red pigment sample prepared by firstly performing phase transition from δ-FeOOH to α-Fe2O3 and then adding iron sheet for oxidation also has needle-shaped impurities.

[0088] Table 1 is the CIE hue analysis of the iron oxide red pigment samples prepared in Examples 1-4 and Comparative Examples 1-4

[0089]

[0090] From the data in Table 1, it can be seen that the hue of the iron oxide red pigment samples prepared in Examples 1-3 is relatively bright, reaching the hue standard of the iron oxide red pigment samples prepared by the mixed acid method; and the particle size is close to that of the iron oxide red pigment prepared by the mixed acid method, especially in terms of purity, which is more than 1.5% higher than that of the iron oxide red prepared by the mixed acid method. This achievement provides a key technical guarantee for the subsequent development of high-purity dependent iron oxide materials in the fields of energy storage batteries and functional magnetic materials. The hue of the iron oxide red pigment sample obtained in Example 4 is slightly inferior to that of Examples 1-3. The reason is that when preparing the seed crystals in Example 4, the pH reaches 9.0, which causes the slurry to be in a state of micro-hair spray, thereby making the seed crystals and the iron oxide red finished product particle size slightly larger, but the purity is still more than 1.5% higher than that of the iron oxide red prepared by the mixed acid method.

[0091] The iron oxide red pigment sample obtained in Comparative Example 2 has a relatively large particle size, and its L* and b* values ​​are relatively high, and its hue is bright and yellowish. SEM and XRD results show that it contains needle-shaped impurities, namely α-FeOOH. The presence of impurities causes the obtained iron oxide red pigment sample to have low purity and poor hue, and will cause undesirable phenomena such as yellowing of the coating film when it is subsequently used in a coating system.

[0092] The iron oxide red pigment sample obtained in Comparative Example 3 was firstly subjected to a high temperature phase conversion to α-Fe2O3 at 100°C, and then put into iron sheet for oxidation and growth of particles into iron oxide red with pigment properties. However, when the phase conversion was performed first and then the oxidation was performed, Fe 3+ Under high temperature and no iron sheet conditions, there will be problems such as uncontrolled hydrolysis, leading to the formation of α-FeOOH impure crystals. Once the impure crystals are formed, it is difficult to convert them into α-Fe2O3 in the oxidation barrel, which will eventually affect the hue of the iron oxide red pigment sample and its subsequent application in related fields.

[0093] The particle size of the iron oxide red pigment sample obtained in Comparative Example 4 is relatively large, the size distribution is uneven, and the hue is not good. This is mainly because during the preparation of the seed crystal, the addition of ferrate is not accompanied by the introduction of air volume, that is, the gas-liquid mass transfer enhancement is not implemented in this process, resulting in a decrease in the oxidation rate.

[0094] In the present invention, the preparation method of the environmentally friendly iron oxide red pigment with high color saturation has mild reaction conditions, no special requirements for pressure and temperature, a simple process flow, low production costs, and the whole production process is non-toxic and pollution-free. By adding ferrate, pure-phase δ-FeOOH is obtained at the seed crystal preparation stage, and the phase transformation from δ-FeOOH to pure-phase α-Fe2O3 and the growth of particles are realized during the iron sheet oxidation stage, obtaining an iron oxide red pigment with excellent dispersion performance, good pigment performance and high purity, which can be preferably applied in fields such as coatings, construction, and batteries.

[0095] In the present invention, the experimental conditions of the exemplified examples are not limited to this. The above-exemplified values are the values referred to during the experiment, and are only the preferred embodiments of the present invention, and are not used to limit the present invention. Any modifications, substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of an environmentally friendly iron oxide red pigment with high color saturation, characterized in that, It includes the following preparation steps: (1) Preparation of δ-FeOOH seeds Completely dissolve solid ferrous sulfate in water and put it into the seed reaction tank, so that the initial concentration of ferrous sulfate in the solution is 200 - 300 g / L; while continuously stirring, add liquid caustic solution to the solution system to adjust the solution pH to 7.0 - 9.0; after the pH value of the mixed system is constant, introduce compressed air and add ferrate; after the reaction of δ-FeOOH seeds ends, stop stirring and close the compressed air, and the preparation of δ-FeOOH seeds is completed; (2) Two-step oxidation Adjust the pH of the δ-FeOOH seeds obtained in step (1) to 2.0 - 4.0 using sulfuric acid solution, put them into the oxidation tank filled with iron sheets, and then add ferrous sulfate to the solution in the oxidation tank; Heat up and continuously introduce compressed air into the solution in the oxidation tank for oxidation for a period of time; take samples, filter by suction, rinse, dry, and pulverize to obtain iron oxide red pigment.

2. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, wherein, In the step (1), the ferrate is sodium ferrate or potassium ferrate, and its stoichiometric molar ratio with Fe 2+ is 1:(10 - 30).

3. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (1), when adding the liquid caustic solution to the solution system, it is added in large quantities and quickly, the mass concentration of the liquid caustic is 32%, and when adding ferrate, it is added slowly and evenly and ensured to be added dropwise within 10 minutes.

4. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (1), at the end point of the δ-FeOOH seed reaction, the feed liquid completely turns orange-red, and the pH of the feed liquid is 4.5 - 5.

0.

5. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (1), the stirring speed is 60 - 200 r / min.

6. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (1), the air volume of the introduced compressed air is 20 - 60 L / min.

7. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (2), the solid content of the δ-FeOOH seeds in the oxidation tank is 60 - 100 g / L.

8. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (2), the concentration of ferrous sulfate is 40 - 60 g / L.

9. The preparation method of an environmentally friendly iron oxide red pigment with high color saturation according to claim 1, characterized in that, In the said step (2), heat up the vapor in the oxidation tank to 80 - 90 °C for the oxidation reaction. When carrying out the oxidation reaction, the air volume of the introduced compressed air is 60 - 120 L / min, and the oxidation reaction time is 16 - 20 h.

10. An iron oxide red pigment prepared by using the preparation method of the environmentally friendly high color saturation iron oxide red pigment according to any one of claims 1 - 9.

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