Method for improving performance of dry-process iron oxide red pigment

Abstract

The invention discloses a method for improving the performance of a dry-process iron oxide red pigment, which comprises the following steps: dissolving fine particles and aggregates of dry-process iron oxide red with an inorganic acid, and adding dissolved ferric iron and an alkaline precipitator into ferric oxide in a parallel flow manner, so that ferric iron is precipitated to form ferric hydroxide colloid again, and the ferric hydroxide colloid is uniformly coated on primary particles of ferric hydroxide; and the iron oxide red is converted into the iron oxide red through calcination, so that the pigment properties such as dispersity and uniformity of the dry-process iron oxide red are improved.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of iron oxide, and in particular to a method for improving the performance of dry-process iron oxide red pigment. Background Art

[0002] Iron oxide pigment is the second largest inorganic pigment after titanium dioxide and the largest colored inorganic pigment. It has a wide color range, is inexpensive and non-toxic, and is weather-resistant and rust-proof. It can be used in building materials, coatings, inks, rubber, plastics, ceramics, enamel, food and other industrial fields. At present, the global total annual production capacity of iron oxide pigment is about 1 million tons.

[0003] Among them, red iron oxide is the largest and most complete variety of iron oxide pigments, accounting for about 70% of the total amount of iron oxide pigments. There are many process routes for producing red iron oxide. According to the state of the reaction raw materials, it is generally divided into two major processes: dry process and wet process. Among them, the dry calcination process includes green vitriol calcination method (including ferrous chloride), iron yellow calcination method, and iron black calcination method. Although the iron yellow and iron black calcination methods have better product quality, the cost is high; the green vitriol calcination method has quality disadvantages such as poor coloring power; the wet process includes iron sheet nitric acid method, iron sheet sulfuric acid method, iron sheet nitric acid-sulfuric acid mixed acid method, also known as iron sheet method, the main advantages are easy control of components, simple equipment, and low production cost; the red iron oxide particles prepared by the iron sheet method are easy to form pseudo-particles of aggregates, with poor uniformity, low coloring power, and difficult to disperse.

[0004] At present, the red iron oxide produced by domestic steel enterprises is processed by the Roots roasting method, which is essentially a ferrous chloride spray calcination method. The original intention is to recover acid. Iron oxide is only a by-product. The particle size uniformity is poor and agglomeration is serious, so it cannot be used as a pigment.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The object of the present invention is to provide a method for improving the performance of dry-process iron oxide red pigment. The iron oxide red obtained by the preparation method of the present invention has good dispersibility and high uniformity.

[0007] The present invention is achieved in that:

[0008] On the one hand, the present invention provides a method for improving the performance of dry-process iron oxide red pigment, which comprises: adding an inorganic acid to an iron oxide red slurry until the iron oxide red is partially dissolved, and then separating the dissolved trivalent iron solution from the undissolved iron oxide; preparing the undissolved iron oxide into a second slurry, heating it, and adding the dissolved trivalent iron solution and an alkaline precipitant to the second slurry in parallel, and obtaining the dry-process iron oxide red pigment after washing, calcining, and crushing after the reaction.

[0009] In some embodiments, the concentration of red iron oxide in the slurry is 100-500 g / L.

[0010] In some embodiments, the inorganic acid includes hydrochloric acid and sulfuric acid.

[0011] In some embodiments, the dissolution rate of red iron oxide in the slurry is controlled at 1-50%.

[0012] In some embodiments, the concentration of iron oxide in the second slurry is 100-300 g / L.

[0013] In some embodiments, the second slurry is heated to 70-90°C.

[0014] In some embodiments, the alkaline precipitating agent is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, calcium oxide, calcium hydroxide, potassium carbonate, and potassium bicarbonate.

[0015] In some embodiments, the pH of the reaction system is controlled to be between 3-5 when the ferric iron solution and the alkaline precipitant are added.

[0016] In some embodiments, after the inorganic acid is added to the slurry, the temperature is raised to 90-100°C.

[0017] On the other hand, the present invention also provides a dry-process iron oxide red pigment obtained by the above preparation method.

[0018] The present invention has the following beneficial effects:

[0019] The present invention dissolves fine particles and agglomerates of dry-process iron oxide red with an inorganic acid, and adds the dissolved trivalent iron and an alkaline precipitant to the iron oxide in parallel, so that the trivalent iron precipitates to reform iron hydroxide colloid, which is evenly coated on the primary particles of iron hydroxide, and then converted into iron oxide red through calcination, thereby improving the pigment properties of the dry-process iron oxide red, such as dispersibility and uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 This is the test result diagram of original sample 1 in the experimental example;

[0022] Figure 2 This is a test result diagram of red iron oxide obtained in Example 1. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0024] In dry iron oxide red, due to process reasons, the particle uniformity is poor and agglomeration is serious. In order to overcome the above problems, the present invention proposes a method for improving the performance of dry iron oxide red pigment, which comprises the following steps:

[0025] (1) Add an inorganic acid capable of dissolving 1-50% of the red iron oxide equivalent to the red iron oxide slurry, raise the temperature to dissolve part of the red iron oxide, and separate the dissolved trivalent iron from the undissolved iron oxide.

[0026] Wherein, the concentration of red iron oxide in the red iron oxide slurry is 100-500 g / L. Optionally, the concentration of red iron oxide in the red iron oxide slurry can be 100 g / L, 110 g / L, 120 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L or 500 g / L, or any value between 100-500 g / L.

[0027] In the present invention, the amount of inorganic acid added is an amount capable of dissolving 1-50% by mass of red iron oxide in the slurry.

[0028] When inorganic acid is added to the slurry, the fine particles in the red iron oxide primary particles will be preferentially dissolved by the inorganic acid due to their large specific surface area. In addition, the soft agglomerates between the primary particles are mainly formed by cross-linking of iron hydroxide, which has an amorphous structure and will also be preferentially dissolved by the inorganic acid. Therefore, the fine particles and soft agglomerates in the red iron oxide primary particles can be dissolved by the inorganic acid. The primary particles after acid hydrolysis have good dispersion and improved uniformity.

[0029] The role of the inorganic acid in the present invention is to dissolve red iron oxide. All inorganic acids that can dissolve red iron oxide fall within the protection scope of the present invention, such as hydrochloric acid and sulfuric acid.

[0030] In order to accelerate the dissolution of red iron oxide, the temperature of the slurry is raised to 90-100°C after adding the inorganic acid. Optionally, the temperature of the slurry can be raised to 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C or 100°C, or any value between 90-100°C.

[0031] For the separation of ferric iron and iron oxide, conventional separation means in the art can be used as long as the separation effect can be achieved. In some optional embodiments, the separation method is suction filtration, and the dissolved ferric iron and undissolved iron oxide are separated by suction filtration, and the separated iron oxide is prepared as a filter cake.

[0032] (2) The iron oxide separated in step (1) is prepared into a second slurry, i.e., iron oxide slurry, and heated to 70-90°C.

[0033] Wherein, the concentration of iron oxide in the iron oxide slurry is 100-300 g / L. Optionally, the concentration of iron oxide in the iron oxide slurry can be 100 g / L, 110 g / L, 120 g / L, 150 g / L, 200 g / L, 250 g / L or 300 g / L, or any value between 100-300 g / L.

[0034] In order to avoid the formation of new seeds at low temperature, the temperature of the iron oxide slurry is raised to 90-100°C in the present invention. Optionally, the temperature of the slurry can be raised to 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C or 100°C, or any value between 90-100°C.

[0035] (3) The dissolved trivalent iron solution and the alkaline precipitant are added to the iron oxide slurry in parallel, and after the reaction, the dry iron oxide red pigment is obtained after washing, calcining and crushing.

[0036] The alkaline precipitant is used to precipitate the trivalent iron ions and reform the iron hydroxide colloid. The iron oxide slurry is added in parallel so that the formed iron hydroxide colloid is evenly coated on the primary particles.

[0037] In the present invention, the alkaline precipitant is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, calcium oxide, calcium hydroxide, potassium carbonate and potassium bicarbonate.

[0038] When the dissolved ferric iron solution and the alkaline precipitant are added to the iron oxide slurry in parallel, the pH of the reaction system of the ferric iron and the alkaline precipitant is controlled at 3-5 because within this pH range, the ferric hydroxide formed by the reaction of the ferric iron and the alkaline precipitant can be evenly coated on the surface of the iron oxide.

[0039] In the present invention, the dissolved ferric iron and the undissolved iron oxide are separated and the iron oxide is re-prepared into a slurry because the pH can be controlled in this way so that it grows on the original particles. If they are not separated, the pH can only gradually increase, and new crystal seeds will be formed.

[0040] The dry iron oxide red obtained by the above preparation method has pigment properties such as high uniformity and high dispersibility.

[0041] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0042] Example 1

[0043] This embodiment provides a method for improving the performance of dry-process iron oxide red pigment, and the steps are as follows:

[0044] S1. Add the dry iron oxide red raw material to water and stir evenly to obtain a slurry with a concentration of 300 g / L of iron oxide red raw material, add hydrochloric acid that can dissolve 20% of the iron oxide red equivalent, and heat it to 95 ° C to dissolve the iron oxide red into trivalent iron ions; filter the slurry to obtain a trivalent iron solution and an iron oxide red filter cake;

[0045] S2. Slurry the iron red filter cake to 200 g / L and heat to 80°C;

[0046] S3. Control the pH to 4 and add the trivalent iron solution and calcium carbonate in parallel, and finally wash, calcine at 500°C and crush to obtain red iron oxide.

[0047] Example 2

[0048] This embodiment provides a method for improving the performance of dry-process iron oxide red pigment, and the steps are as follows:

[0049] S1. Add the red iron oxide raw material to water and stir evenly to obtain a slurry with a red iron oxide raw material concentration of 500 g / L, add sulfuric acid that can dissolve 50% of the red iron oxide equivalent, heat it to 100 ° C, dissolve the red iron oxide into trivalent iron ions, and separate the slurry by suction filtration to obtain a trivalent iron solution and a red iron filter cake;

[0050] S2. Slurry the iron red filter cake to 100 g / L and heat to 70°C;

[0051] S3. Control pH=3, add trivalent iron solution and liquid alkali in parallel, and finally wash, calcine at 500°C, and crush to obtain red iron oxide.

[0052] Example 3

[0053] This embodiment provides a method for improving the performance of dry-process iron oxide red pigment, and the steps are as follows:

[0054] S1. Add the red iron oxide raw material into water and stir evenly to obtain a slurry with a red iron oxide raw material concentration of 100 g / L, add hydrochloric acid capable of dissolving 10% red iron oxide equivalent, heat it to 90 ° C, dissolve the red iron oxide into trivalent iron ions, and separate the slurry by suction filtration to obtain a trivalent iron solution and a red iron filter cake;

[0055] S2. Slurry the iron red filter cake to 300 g / L and heat to 90°C;

[0056] S3. Control the pH to 5, add the trivalent iron solution and potassium carbonate in parallel, and finally wash, calcine at 500°C, and crush to obtain red iron oxide.

[0057] Comparative Example 1

[0058] The dry iron oxide red raw material is slurried to 300g / L, and hydrochloric acid that can dissolve 20% of the iron oxide red equivalent is added, and the temperature is raised to 95°C to dissolve the iron oxide red into trivalent iron ions; the slurry is filtered and separated to obtain a trivalent iron solution and an iron oxide red filter cake; the iron oxide red filter cake is slurried to 200g / L, heated to 60°C, the pH is controlled to be 4, and the trivalent iron solution and calcium carbonate are added in parallel, and finally the iron oxide red is obtained by washing, calcining at 500°C, and crushing.

[0059] Comparative Example 2

[0060] The dry iron oxide red raw material is slurried to 300g / L, and hydrochloric acid that can dissolve 20% of the iron oxide red equivalent is added, and the temperature is raised to 95°C to dissolve the iron oxide red into trivalent iron ions; the slurry is filtered and separated to obtain a trivalent iron solution and an iron oxide red filter cake; the iron oxide red filter cake is slurried to 200g / L, heated to 60°C, the pH is controlled to be 6, and the trivalent iron solution and calcium carbonate are added in parallel, and finally the iron oxide red is obtained by washing, calcining at 500°C, and crushing.

[0061] Experimental example

[0062] The red iron oxide obtained in Example 1-3 and Comparative Example 1-2 was subjected to red phase detection and relative tinting strength detection. The detection results are shown in Table 1:

[0063] Table 1 Redness and relative tinting strength test results

[0064]

[0065] Note: Sample 1 is purchased dry iron red, and sample 2 is LANXESS 4140. Δa represents the redness. The larger the value, the redder it is and the better the quality.

[0066] According to the test results in Table 1, it can be concluded that compared with original sample 2 and comparative example 1, the iron oxide red prepared in Examples 1-3 is significantly better in red phase and relative tinting strength. Compared with original sample 1, the iron oxide red obtained in Example 1 is slightly lower in red phase, but the relative tinting strength is basically the same.

[0067] At the same time, the red iron oxide obtained by original sample 1 and Example 1 was tested by scanning electron microscope. The test results are as follows Figure 1-2 As shown, Figure 1 This is the test result diagram of sample 1. Figure 2 The test result diagram of iron oxide red obtained in Example 1 shows that, by comparison, Figure 1 , Figure 2 The red iron oxide in the coating is more uniform.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for improving the performance of dry iron oxide red pigment, characterized in that: include: Adding inorganic acid to the red iron oxide slurry until the red iron oxide is partially dissolved, and then separating the dissolved trivalent iron solution from the undissolved iron oxide; The undissolved iron oxide is prepared as a second slurry, which is heated, and the dissolved trivalent iron solution and the alkaline precipitant are added to the second slurry in parallel. After the reaction, the dry iron oxide red pigment is obtained after washing, calcining and crushing.

2. The preparation method according to claim 1, characterized in that: The concentration of red iron oxide in the slurry is 100-500 g / L.

3. The preparation method according to claim 1, characterized in that: The inorganic acid includes hydrochloric acid and sulfuric acid.

4. The preparation method according to claim 1, characterized in that: The dissolution rate of red iron oxide in the slurry is controlled at 1-50%.

5. The preparation method according to claim 1, characterized in that: The concentration of iron oxide in the second slurry is 100-300 g / L.

6. The preparation method according to claim 1, characterized in that: The second slurry was heated to 70-90°C.

7. The preparation method according to claim 1, characterized in that: The alkaline precipitant is selected from at least one of sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium carbonate, calcium oxide, calcium hydroxide, potassium carbonate and potassium bicarbonate.

8. The preparation method according to claim 1, characterized in that: When the ferric iron solution and the alkaline precipitant are added, the pH of the reaction system is controlled to be between 3 and 5.

9. The preparation method according to claim 1, characterized in that: After adding inorganic acid into the slurry, the slurry is heated to 90-100°C.

10. The dry-process iron oxide red pigment obtained by the preparation method according to any one of claims 1 to 9.

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