Method for preparing iron oxide red pigment with high tinting strength

Abstract

The invention provides a method for preparing a high-tinting-strength iron oxide red pigment, which comprises the following steps: 1, carrying out first reaction on oxidizing gas and a first reaction mixture containing ferrite under an alkaline condition to form a seed crystal; 2, oxidizing gas, zero-valent iron and a second reaction mixture containing the seed crystal and second ferrite are subjected to a second reaction under the acidic condition, and the iron oxide red pigment is prepared, the method does not use a nitrogen-containing reagent. The method has the advantages of being simple in process, low in cost, high in product yield and environmentally friendly, and the product with excellent colored light performance and improved coloring strength can be prepared.

Description

Technical Field

[0001] The present application relates to the field of inorganic pigments, and more specifically to an iron oxide red pigment and a preparation method thereof. Background Art

[0002] Iron oxide pigments are the most important type of colored inorganic pigments. They have a wide color range, are inexpensive and non-toxic, are weather-resistant and rust-proof, and are widely used in building materials, coatings, inks, rubber, plastics, ceramics, enamel and other industrial fields. The global total production capacity of iron oxide pigments is about 1 million tons / year, among which red iron oxide is the largest and most complete variety of iron oxide pigments, accounting for about 50% of the total iron oxide pigments.

[0003] The production process of red iron oxide is mainly divided into two major process routes: dry process and wet process. Among them, the dry calcination process has high energy consumption, poor hue, and poor pigment performance, and has been gradually eliminated. The wet process currently used is the nitric acid method / mixed acid method. Although the performance of the red iron oxide pigment prepared by these methods can meet the relevant requirements of industrial production, these processes will inevitably produce a large amount of nitrogen-containing wastewater, waste residue and waste gas during the production process. With the increasingly stringent relevant environmental protection laws and regulations around the world, these process methods are facing increasing pressure. In addition, the cost of treating the three wastes of this process is also very high, and its industrial prospects are bleak.

[0004] In order to overcome the above problems, people have been working hard to develop a production process for red iron oxide that does not use nitrogen-containing reagents, but these nitrogen-free processes always have insurmountable defects. For example, these processes can often only use solutions with very low ferrous ion concentrations (usually below 2g / L, for example, less than 1g / L) to prepare pigments, which results in a very low yield per unit volume of product, resulting in its low industrial value. In addition, compared with the nitrogen-containing synthesis process described above, the red iron oxide pigment prepared by these nitrogen-free processes often has insufficient tinting strength. Furthermore, these nitrogen-free processes often have very complex step designs, and may require multi-step oxidation-crystallization operations, and colloids may be formed during the process, resulting in a linear increase in process complexity and related costs; and these processes also often have to use dispersants such as propylene glycol, which further brings about problems such as increased costs, increased environmental risks, and difficulty in material handling, which is industrialized.

[0005] Therefore, the art is eager to develop a new process for synthesizing iron oxide red pigment, which does not use nitrogen-containing raw materials, and the prepared iron oxide red pigment can have performance that is not inferior to that of products synthesized by nitrogen-containing methods, and preferably can overcome the other defects mentioned above at the same time.

[0006] In view of the above-mentioned problems of the prior art, the inventors of the present application have conducted a lot of in-depth research and developed a novel method, which can adopt a simple, low-cost and green and environmentally friendly process to achieve the synthesis of high-performance iron oxide red pigment and can effectively overcome the above-mentioned defects of the prior art. Summary of the invention

[0007] A first aspect of the present invention provides a method for preparing an iron oxide red pigment, the method comprising:

[0008] Step 1: allowing an oxidizing gas to react with a first reaction mixture containing a first ferrous salt under alkaline conditions to form seed crystals;

[0009] Step 2: allowing the oxidizing gas, zero-valent iron and a second reaction mixture containing the seed crystal and a second ferrous salt to undergo a second reaction under acidic conditions to obtain the iron oxide red pigment;

[0010] The method does not use nitrogen containing reagents.

[0011] According to an embodiment of the first aspect of the present application, in the step 1, the pH value of the alkaline condition is 11-13. According to another embodiment of the first aspect of the present application, in the step 2, the pH value of the acidic condition is 2-4.

[0012] According to another embodiment of the first aspect of the present application, the first reaction mixture is an aqueous solution or slurry comprising ferrous sulfate, wherein the content of ferrous sulfate is 5-60 g / L.

[0013] According to another embodiment of the first aspect of the present application, the second reaction mixture is an aqueous solution or slurry comprising ferrous sulfate and the seed crystals, wherein the content of ferrous sulfate is 10-50 g / L.

[0014] According to another embodiment of the first aspect of the present application, in step one and step two, the oxidizing gas is selected from one or more of the following: air, oxygen, and ozone.

[0015] According to another embodiment of the first aspect of the present application, the zero-valent iron is selected from one or more of the following: iron powder, iron sheet, iron filings, iron particles, and iron slag.

[0016] According to another embodiment of the first aspect of the present application, both step one and step two are performed without stirring.

[0017] According to another embodiment of the first aspect of the present application, no colloid is formed in step one and step two.

[0018] According to another embodiment of the first aspect of the present application, in step 1, the oxidizing gas is heated at 0.03-0.3 m 3 / hour·L flow rate is provided to the first reaction, and the duration of the first reaction is 20-120 minutes. According to another embodiment of the first aspect of the present application, in the step 2, the reaction temperature is 85-95°C. According to another embodiment of the first aspect of the present application, in the step 2, the amount of the seed crystal in the second reaction mixture is 0.1-0.4 mol / L.

[0019] The second aspect of the present application provides an iron oxide red pigment, which is prepared by the method of the present invention.

[0020] According to one embodiment of the second aspect of the present application, the tinting strength of the iron oxide red pigment is greater than 102% of commercial iron oxide red 110.

[0021] In the specific implementation section below, the method and prepared product of the present application are further introduced in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The XRD pattern of the seed crystal synthesized in one embodiment of the present application is shown;

[0023] Figure 2 The SEM image of the seed crystal synthesized in one embodiment of the present application is shown;

[0024] Figure 3 The XRD diagram of the iron oxide red synthesized in one embodiment of the present application is shown;

[0025] Figure 4 The SEM image of the red iron oxide synthesized in one example of the present application is shown. DETAILED DESCRIPTION

[0026] "Range" disclosed herein is in the form of lower limit and upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges that can be defined in this way are inclusive and combinable, i.e. any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.

[0027] In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.

[0028] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0029] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0030] In this application, if there is no special explanation, the "including" mentioned herein means open or closed. For example, the "including" may mean that other components not listed may also be included, or only the listed components may be included.

[0031] The overall technical concept of the present invention is to develop a simple and low-cost two-step method for synthesizing iron oxide red pigment. In step one, ferrous salt is oxidized with an oxidizing gas under controlled alkaline pH conditions to form seed crystals; then in step two, the seed crystals are mixed with ferrous salt and zero-valent iron under controlled acidic pH conditions, and then an oxidizing gas is provided to obtain an iron oxide red product.

[0032] According to one embodiment of the present application, no nitrogen-containing reagent is used in the method of the present invention. The nitrogen-containing reagent refers to a compound whose chemical composition contains nitrogen, such as nitric acid, nitrous acid, nitrates, nitrites, ammonia, organic amines, organic compounds containing nitro or nitroso, organic metal complexes containing ammonia ligands and / or organic amine ligands, etc. These compounds will not be used in the method of the present application. Therefore, the method of the present invention can avoid the three industrial wastes generated by the use of these nitrogen-containing reagents, as well as the environmental pollution pressure and cost problems caused thereby.

[0033] According to one embodiment of the present application, for the step 1, the ferrous salt aqueous solution is first mixed with the alkaline aqueous solution, and water is added as needed, and then the pH value of the formed first reaction mixture (for example, in the form of a solution or slurry) is adjusted to an alkaline range, for example, 11-13, preferably 11.5-12.5. And in the entire step 1, the pH value of the reaction mixture is monitored at any time and acid (preferably sulfuric acid solution) or alkali solution is added as needed at any time to keep the pH of the reaction mixture within the above range.

[0034] According to one embodiment of the application, the alkaline aqueous solution is an aqueous solution of an inorganic base, such as sodium hydroxide, potassium hydroxide, or a mixture thereof, preferably an aqueous sodium hydroxide solution. The concentration of the alkaline aqueous solution can be 2-40 weight %, such as 5-38 weight %, or 10-35 weight %, preferably 20-32 weight %. The concentration of the basic compound (such as an inorganic base) in the final first reaction mixture can be 0.1-10 weight %, such as 0.5-5 weight %, or 1-3 weight %.

[0035] According to one embodiment of the present application, the ferrous salt is a water-soluble salt of ferrous iron, preferably ferrous sulfate. The ferrous salt used to prepare the ferrous salt aqueous solution in the present application can be a ferrous salt containing crystal water, such as ferrous sulfate heptahydrate.

[0036] In the present invention, there is no particularly strict requirement for the concentration of the ferrous salt aqueous solution used as a raw material to prepare the first reaction mixture, wherein the ferrous salt concentration should not be too high (do not exceed its solubility in water to produce insoluble matter) nor too low (which will lead to a serious decrease in production efficiency and a surge in the workload of operators).

[0037] According to one embodiment of the present application, the concentration of ferrous salt (eg ferrous sulfate) in the final first reaction mixture may be 0.1-6 wt %, such as 0.5-5 wt %, or 1-4.5 wt %, or 1.5-4 wt %, preferably 2-3.8 wt %.

[0038] In another calculation method (based on the ratio of the weight of ferrous salt to the volume of the first reaction mixture), the content of ferrous salt in the first reaction mixture is 5-60 g / L, which is much higher than the 1-2 g / L concentration commonly used in the prior art. For example, according to a specific embodiment of the present invention, the content of ferrous salt in the first reaction mixture is 5-60 g / L, preferably 20-60 g / L.

[0039] According to one embodiment of the present application, after the first reaction mixture (e.g., in the form of a solution or slurry) is prepared, stirring is stopped and an oxidizing gas is introduced into the first reaction mixture. The oxidizing gas may include one or more of the following: air, oxygen, ozone, etc., preferably air.

[0040] According to a preferred embodiment of the present application, the oxidizing gas is delivered from a gas distributor located below the first reaction mixture. The gas distributor has a large number of openings to distribute the oxidizing gas in the first reaction mixture as evenly as possible.

[0041] According to one embodiment of the present application, the oxidizing gas used is air, and the flow rate of the air is 0.01-0.3 m / s. 3 / hour·L, preferably 0.06-0.2 m 3 / hour·liter. The above units represent that the air is supplied to the first reaction mixture per unit volume (per liter) at a flow rate of several cubic meters per hour. According to another embodiment of the present application, the oxidizing gas used is oxygen (pure oxygen) or ozone, and the flow rate of oxygen or ozone is 0.002-0.15 m 3 / hour·L, preferably 0.01-0.1 m 3 The above units represent that the oxygen (pure oxygen) or ozone is supplied to the first reaction mixture per unit volume (per liter) at a flow rate of several cubic meters per hour.

[0042] According to a specific embodiment of the present application, in step one, after the oxidizing gas starts to be provided, except for the impact and stirring effect of the gas flow of the oxidizing gas itself on the first reaction mixture, no other stirring (such as mechanical stirring and magnetic stirring) is performed on the first reaction mixture.

[0043] According to one embodiment of the present application, the step 1 is performed at a temperature of 5° C. to 50° C., preferably at 10-30° C. According to another embodiment of the present application, the step 1 is performed for 20-120 minutes, preferably 30-55 minutes.

[0044] According to one embodiment of the present application, brown-red iron oxide seed crystals are prepared in step one, and no colloid (also referred to herein as "hair gel") is formed during the entire process of step one.

[0045] After the step 1 is completed, the seed crystals are collected for the reaction in the step 2.

[0046] According to one embodiment of the present application, the seeds prepared in step 1 are in the form of a water suspension (fine iron red seeds suspended in water), more preferably a suspension of iron red seeds in alkaline water.

[0047] Before preparing the second reaction mixture, the pH value of the seed suspension is first adjusted to an acidic range, preferably 2-4, more preferably 3-4, with dilute sulfuric acid. According to a specific embodiment of the present application, in step 2, the seed suspension adjusted to acidity, the aqueous solution of the second ferrous salt and optional additional water are added to the reactor and mixed thoroughly to form a second reaction mixture. Zero-valent iron is added to the second reaction mixture, and a second oxidizing gas is introduced into the second reaction mixture to react to prepare red iron oxide.

[0048] According to one embodiment of the present application, in the second reaction mixture, the amount of the seed crystals (the seed crystals prepared in step 1) is 0.1-0.4 mol / L, preferably 0.12-0.32 mol / L.

[0049] According to one embodiment of the present application, in the second reaction mixture, the second ferrous salt is a water-soluble salt of ferrous iron, preferably ferrous sulfate. The ferrous salt used in the present application to prepare the ferrous salt aqueous solution can be a ferrous salt containing crystal water, such as ferrous sulfate heptahydrate. According to a preferred embodiment of the present application, the content of the second ferrous salt in the second reaction mixture is 10-50 g / L, preferably 15-45 g / L, and more preferably 25-40 g / L.

[0050] According to one embodiment of the present application, the zero-valent iron includes various iron raw materials of small size, such as iron powder, iron sheet, iron filings, iron particles, and iron slag. In the case of using iron sheet, the iron sheet can be cut or sheared into suitable sizes (such as small pieces or thin strips) according to the size of the reactor used, so as to facilitate adding to the reactor. The scrap iron sheet can be used as the raw material of the present invention after simply removing the dirt and oxides on the surface of the scrap iron sheet. In the prior art, it is often necessary to use ferrous salts with higher purity as raw materials to obtain high-quality iron oxide red pigments, while the present invention can relax the above requirements for raw materials.

[0051] In addition, in the prior art method using ferrite as raw material, ferrite will inevitably produce by-products in the process of synthesizing red iron oxide under alkaline conditions, which seriously affects the quality of red iron oxide pigment. The present invention uses zero-valent iron as raw material, which can simply and effectively overcome the above problem.

[0052] During step 2, sufficient amount of zero-valent iron is maintained in the reactor at all times. A specific amount of zero-valent iron raw material can be added at appropriate intervals based on experience. The presence of zero-valent iron in the reactor can also be observed to ensure that sufficient amount of zero-valent iron is always present in the reactor.

[0053] According to one embodiment of the present application, after the second reaction mixture (e.g., in the form of a solution or slurry) is prepared, stirring is stopped and an oxidizing gas is introduced into the second reaction mixture. The oxidizing gas may include one or more of the following: air, oxygen, ozone, etc., preferably air.

[0054] According to a preferred embodiment of the present application, the oxidizing gas is delivered from a gas distributor located below the second reaction mixture. The gas distributor has a large number of openings to distribute the oxidizing gas in the second reaction mixture as evenly as possible.

[0055] According to one embodiment of the present application, the oxidizing gas flow rate of step 2 is significantly less than the oxidizing gas flow rate of step 1. According to an exemplary embodiment of the present application, in step 2, the oxidizing gas used is air, and the air flow rate is 0.25-2 liters / minute / liter, that is, 0.25-2 liters / minute of air (equivalent to 0.015-0.12 m 3 / hour / liter, preferably 0.6-1 liter / minute / liter (0.036-0.06 m 3 / hour / liter).

[0056] According to another exemplary embodiment of the present application, in step 2, the oxidizing gas used is oxygen (pure oxygen) or ozone, and its flow rate is 0.05-0.4 liters / minute / liter, that is, 0.05-0.4 liters / minute of air (equivalent to 0.003-0.024 m 3 / hour / liter, preferably 0.12-0.2 liters / minute / liter (0.0072-0.012 m 3 / hour / liter).

[0057] According to one embodiment of the present application, the oxidizing gas used in step one and step two may be at normal pressure or pressurized.

[0058] According to one embodiment of the present application, during the reaction process of step 2, hydrogen ions are generated during the oxidation of ferrous ions, and the reaction of zero-valent iron (such as iron sheet) with acid consumes hydrogen ions. Therefore, during the entire reaction process of step 2, the second reaction mixture is always kept within the acidic range with little fluctuation. In addition, during the entire reaction process of step 2, zero-valent iron is supplemented as needed to ensure that zero-valent iron is sufficient.

[0059] According to a specific embodiment of the present application, in step 2, after the oxidizing gas starts to be provided, except for the impact and stirring effect of the gas flow of the oxidizing gas itself on the second reaction mixture, no other stirring (such as mechanical stirring and magnetic stirring) is performed on the second reaction mixture.

[0060] According to another embodiment of the present application, in step 2, in addition to the impact and stirring of the oxidizing gas, the second reaction mixture is also mechanically stirred or magnetically stirred. For experiments using iron sheets as raw materials, the sheet or strip iron sheets can be fixed to the stirring shaft, the grid plate in the reactor, the support plate, etc. to prevent the iron sheets from colliding or interfering with the stirring device.

[0061] According to one embodiment of the present application, the step 2 is carried out at a temperature of 85-95° C., preferably at 90-95° C. According to another embodiment of the present application, the reaction of step 2 is continued for 16-150 hours.

[0062] According to one embodiment of the present application, red iron oxide precipitate is formed in the step 2.

[0063] According to one embodiment of the present application, no colloid will be formed during the entire process of step 2 (ie, no "gel" will be formed).

[0064] The red iron oxide precipitate obtained in the above step 2 can be sold and used as red iron oxide pigment after undergoing one or more conventional treatments selected from the following: filtering, washing and drying, grinding, sieving, blending, etc.

[0065] Without wishing to be bound by theory, the inventors believe that in the above step 1, the ferrous salt (e.g., ferrous sulfate) is oxidized by an oxidizing gas (e.g., air) under alkaline conditions to form α-FeOOH seed crystals; then in the above step 2, the zero-valent iron (e.g., iron sheet) is etched by acid under acidic conditions and enters the second reaction mixture, where it is oxidized by air and participates in crystal growth. The high temperature-induced deformation causes the seed crystal particles to transform into α-FeOOH during the crystal growth process. 2 O 3 , and finally iron oxide red pigment was prepared.

[0066] The method of the present invention can achieve the following advantages:

[0067] A. In the prior art, the process using nitric acid or mixed acid must consume more than 300 kg of nitric acid for each ton of iron oxide red pigment produced, and will produce a large amount of pollutants such as ammonia nitrogen, nitric nitrogen wastewater and nitrogen oxide waste gas. The treatment of these nitrogen-containing three wastes requires complex processes and a large amount of cost. In contrast, the method of the present invention does not require the use of any nitrogen-containing reagents (such as but not limited to nitric acid and ammonia raw materials), avoids the generation of the above-mentioned nitrogen-containing three wastes, and has good economic and environmental benefits.

[0068] B. The red iron oxide produced by the method of the present invention has good light performance and sufficient red color, which can match the color performance of the products of the mixed acid method (i.e., the industrialized prior art using nitric acid) in the prior art; and the red iron oxide produced by the method of the present invention has improved excellent tinting strength. Compared with the existing main industrial products (iron oxide red pigments produced by using nitric acid or mixed acid method), the product of the present invention has higher tinting strength. For example, compared with industrial red iron oxide products produced by nitric acid method (such as red iron oxide 110 and red iron oxide 130-1 produced by Jiangsu Yuxing), the tinting strength of the red iron oxide produced by the method of the present invention is higher than 102%, and can reach up to 105%. Compared with the nitrogen-free synthesis method recorded in the prior art, the color performance and tinting strength of the red iron oxide product obtained by the method of the present invention are significantly improved.

[0069] C. The nitrogen-free synthesis method recorded in the prior art has to use a lower ferrous salt concentration, otherwise the reaction system and product properties will be unstable. However, the method of the present invention can use a much higher ferrous salt concentration for pigment synthesis through process design, achieving a higher unit volume product yield.

[0070] D. The nitrogen-free synthesis methods recorded in the prior art all include specially designed complex processes, such as multi-stage temperature curves, multi-step crystallization and other operations, while the method of the present invention adopts simple and easy-to-implement steps, and the design of process conditions is also quite convenient, and has good industrial application value.

[0071] E. The present invention uses zero-valent iron as a raw material to carry out a reaction under acidic conditions, thereby effectively avoiding the defect of ferrous salts in the prior art that side reactions occur under alkaline conditions, thereby simply and effectively improving the quality of the product, red iron oxide.

[0072] In the following examples, the method of the present application is specifically described with specific examples, the purpose of which is to better understand the content of the present application. It should be understood that these examples are merely illustrative and not restrictive.

[0073] Example

[0074] All reagents used in the following examples are commercially available analytical reagents, so the water used is deionized water. In the following examples, a glass reactor with an effective volume of 10 liters (13 liters when fully filled) was used for the reaction, and the reactor was equipped with a stirring device and a heating-temperature control device, and an air inlet and a gas distributor were provided at the bottom of the reactor.

[0075] Example 1

[0076] In this Example 1, the method of oxidizing red iron was carried out by the method according to the present invention.

[0077] First, in step 1, a seed crystal is prepared by the following method: 8.5 liters of water are added to the reactor, the pH value of which is adjusted to 12 with a 32% mass concentration of NaOH aqueous solution, 1 liter of an aqueous solution containing 450 grams of ferrous sulfate heptahydrate and 405 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10L of slurry (first reaction mixture). After the above slurry is prepared, the stirrer stops rotating, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 0.6 m 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 55 minutes to generate brown-red iron red seeds. During the entire process of preparing the seeds, no gel phenomenon was observed. The seeds were collected and used directly in step 2.

[0078] In a separate reactor, all the seed suspension obtained in step 1 above is added to the reactor, and then allowed to stand for a period of time. After the seed is settled at the bottom of the reactor, an appropriate volume of clarified liquid is drawn from the upper part of the reactor, and its pH value is adjusted to about 3 with dilute sulfuric acid, and then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor. Water is then added to the reactor to adjust the volume of the reaction mass (second reaction mixture) therein to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction process. Air is introduced through a gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor is detected to be close to the color of the corresponding standard sample. During the entire reaction process, ensure that the reactor contains sufficient iron scale. After the reaction is completed, filter, wash and dry the red iron oxide precipitate formed in the reactor.

[0079] Example 2

[0080] In this Example 2, the method of red iron oxide was carried out by the method according to the present invention.

[0081] First, in step 1, seed crystals are prepared in the following manner: 8.5 liters of water are added to the reactor, the pH value thereof is adjusted to 12 with a mass concentration of 32%, 1 liter of an aqueous solution containing 450 grams of ferrous sulfate heptahydrate and 405 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10 liters of slurry (first reaction mixture). After the above slurry is prepared, the stirrer is stopped, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters. 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 30 minutes to generate brown-red iron red seeds. During the entire process of preparing the seeds, no gel phenomenon was observed. The seeds were collected and used directly in step 2.

[0082] The XRD and SEM images of the seeds synthesized in the above steps are shown in Figure 1 and Figure 2 As can be seen from the figure, the seed crystals obtained in the above steps are small particles of needle-shaped α-FeOOH.

[0083] In a separate reactor, all the seed suspension obtained in step 1 above is added to the reactor, and then allowed to stand for a period of time. After the seed is settled at the bottom of the reactor, an appropriate volume of clarified liquid is drawn from the upper part of the reactor, and its pH value is adjusted to about 3 with dilute sulfuric acid. Then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) therein to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction process. Air is introduced through the gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor is detected to be close to the color of the corresponding standard sample. During the entire reaction process, ensure that the reactor contains sufficient iron scale. After the reaction is completed, filter, wash and dry the red iron oxide precipitate formed in the reactor.

[0084] The XRD and SEM images of the final product obtained in this example are shown in Figure 3 and Figure 4 .Depend on Figure 3 It can be seen that the iron oxide red prepared in this embodiment is similar to the standard card Hematite-Fe 2 O3 The diffraction peaks are consistent, sharp and symmetrical, and no impurity peaks appear, indicating that the prepared sample is α-Fe with good crystallinity. 2 O 3 Crystal. Figure 4 It can be seen that the red iron oxide sample prepared in this embodiment is uniform in size, has clear edges, and is a relatively regular granular crystal.

[0085] Example 3

[0086] In this Example 3, the method of iron red oxidation was carried out by the method according to the present invention.

[0087] First, in step 1, a seed crystal is prepared by the following method: 7.5 liters of water is added to the reactor, the pH value thereof is adjusted to 12 with a 32% by mass NaOH aqueous solution, 2 liters of an aqueous solution containing 600 grams of ferrous sulfate heptahydrate and 540 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10 liters of slurry (first reaction mixture). After the above slurry is prepared, the stirrer is stopped, and air is introduced through a gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters. 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 50 minutes to generate brown-red iron red seeds. During the whole process of preparing the seeds, no gel phenomenon was observed. The seeds were collected and used directly in step 2.

[0088] In a separate reactor, all the seed suspension obtained in step 1 above is added to the reactor, and then allowed to stand for a period of time. After the seed is settled at the bottom of the reactor, an appropriate volume of clarified liquid is drawn from the upper part of the reactor, and its pH value is adjusted to about 3 with dilute sulfuric acid, and then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction material (second reaction mixture) therein to 10 liters, and then the stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction materials evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction process. Air is introduced through the gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles to move the slurry upward, and the air flux is 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the material in the reactor detects that it is close to the color of the corresponding standard sample and stops the reaction. During the entire reaction process, ensure that the reactor contains sufficient iron scale. After the reaction is completed, filter, wash and dry the red iron oxide precipitate formed in the reactor.

[0089] Example 4

[0090] In this Example 4, the method of oxidizing red iron was carried out by the method according to the present invention.

[0091] First, in step 1, a seed crystal is prepared by the following method: 8.5 liters of water are added to the reactor, the pH value of which is adjusted to 12 with a 32% mass concentration of NaOH aqueous solution, 1 liter of an aqueous solution containing 450 grams of ferrous sulfate heptahydrate and 405 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10L of slurry (first reaction mixture). After the above slurry is prepared, the stirrer stops rotating, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 30 minutes to generate brown-red iron red seeds. During the entire process of preparing the seeds, no gelling phenomenon was observed. Collect the seeds. The above steps were repeated once again. The seed suspensions obtained twice were combined, allowed to stand in a barrel for a period of time, and then an appropriate volume of clarified liquid was drawn from the top for step 2.

[0092] In a separate reactor, all the seed suspension after the above volume concentration is added to the reactor. The pH value is adjusted to about 3 with dilute sulfuric acid, and then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) to 10 liters, and then the stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction. Air is introduced through a gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 10 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor detects a color close to the corresponding standard sample. During the entire reaction process, the naked eye is observed to ensure that there is sufficient iron sheet in the reactor. After the reaction is completed, the iron oxide red precipitate formed in the reactor is filtered, washed and dried.

[0093] Example 5

[0094] In this Example 5, the method of red iron oxide was carried out by the method according to the present invention.

[0095] First, in step 1, a seed crystal is prepared by the following method: 8.5 liters of water are added to the reactor, the pH value of which is adjusted to 12 with a 32% mass concentration of NaOH aqueous solution, 1 liter of an aqueous solution containing 450 grams of ferrous sulfate heptahydrate and 405 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10L of slurry (first reaction mixture). After the above slurry is prepared, the stirrer stops rotating, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 30 minutes to generate brown-red iron red seeds. During the entire process of preparing the seeds, no gelling phenomenon was observed. Collect the seeds. The above steps were repeated once again. The seed suspensions obtained twice were combined, allowed to stand in a barrel for a period of time, and then an appropriate volume of clarified liquid was drawn from the top for step 2.

[0096] In a separate reactor, all the concentrated seed suspension is added to the reactor. The pH value is adjusted to about 3 with dilute sulfuric acid, and then 1250 ml of a solution containing 500 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir thoroughly to mix the reaction mass. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction. Air is introduced through a gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 10 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor is detected to be close to the color of the corresponding standard sample. During the entire reaction process, the naked eye is observed to ensure that there is sufficient iron sheet in the reactor. After the reaction is completed, the iron oxide red precipitate formed in the reactor is filtered, washed and dried.

[0097] In addition, the inventors of the present application have also found that the process parameter design in the method of the present invention will also have a significant impact on the performance of the iron oxide red pigment product.

[0098] Example 6

[0099] In this Example 6, the effect of air flow rate on the performance of the iron oxide red product was investigated.

[0100] First, in step 1, a seed crystal is prepared by the following method: 8.5 liters of water are added to the reactor, the pH value of which is adjusted to 12 with a 32% by mass NaOH aqueous solution, 1 liter of an aqueous solution containing 300 grams of ferrous sulfate heptahydrate and 270 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to form a slurry of about 10 liters (the first reaction mixture). After the above slurry is prepared, the stirrer stops rotating, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 6 meters 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 30 minutes to generate brown-red iron red seeds. During the whole process of preparing the seeds, no gelling phenomenon was observed. The seeds were collected and used directly in step 2. The above steps were repeated once again. The seed suspensions obtained twice were combined, allowed to stand in a barrel for a period of time, and then an appropriate volume of clarified liquid was drawn from the top for step 2.

[0101] In a separate reactor, all the seed suspension after the above volume concentration is added to the reactor. The pH value is adjusted to about 3 with dilute sulfuric acid, and then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and then water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction. Air is introduced through a gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor detects a color close to the corresponding standard sample. During the entire reaction process, the naked eye is observed to ensure that there is sufficient iron sheet in the reactor. After the reaction is completed, the iron oxide red precipitate formed in the reactor is filtered, washed and dried.

[0102] Example 7

[0103] In this Example 7, the effect of the reaction temperature in step 2 on the performance of the iron oxide red product was investigated.

[0104] First, in step 1, a seed crystal is prepared by the following method: 8.5 liters of water are added to the reactor, the pH value of which is adjusted to 12 with a 32% mass concentration of NaOH aqueous solution, 1 liter of an aqueous solution containing 450 grams of ferrous sulfate heptahydrate and 405 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10L of slurry (first reaction mixture). After the above slurry is prepared, the stirrer stops rotating, and air is introduced through the gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 30 minutes to generate brown-red iron red seeds. During the entire process of preparing the seeds, no gel phenomenon was observed. The seeds were collected and used directly in step 2.

[0105] In a separate reactor, all the seed suspension obtained in step 1 above is added to the reactor, and then allowed to stand for a period of time. After the seed is settled at the bottom of the reactor, an appropriate volume of clarified liquid is drawn from the upper part of the reactor, and its pH value is adjusted to about 3 with dilute sulfuric acid, and then 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) therein to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 80-85°C during the subsequent reaction process. Air is introduced through the gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles to move the slurry upward, and the air flux is 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the material in the reactor detects that it is close to the color of the corresponding standard sample and stops the reaction. During the whole reaction process, the reactor was visually inspected to ensure that there was sufficient iron scale in the reactor. After the reaction was completed, the red iron oxide precipitate formed in the reactor was filtered, washed and dried.

[0106] Example 8

[0107] In this Example 8, the effect of the ferrous salt concentration in step one on the performance of the iron oxide red product was investigated.

[0108] First, in step 1, a seed crystal is prepared by the following method: 7.5 liters of water is added to the reactor, the pH value thereof is adjusted to 12 with a 32% by mass NaOH aqueous solution, 2 liters of an aqueous solution containing 700 grams of ferrous sulfate heptahydrate and 630 grams of a 32% by weight NaOH aqueous solution are simultaneously added to the reactor under stirring, and mixed evenly to prepare about 10 liters of slurry (first reaction mixture). After the above slurry is prepared, the stirrer is stopped, and air is introduced through a gas distributor. After the air leaves the gas distributor, it is dispersed into small bubbles and moves upward to the slurry. The air flux is 2 meters. 3 / hour. During the entire reaction process, the pH value of the slurry was monitored in real time and NaOH aqueous solution was added dropwise at any time to keep the pH value of the slurry at 11.5-12.5. The reaction lasted for 45 minutes to generate brown-red iron red seeds. During the whole process of preparing the seeds, no gel phenomenon was observed. The seeds were collected and used directly in step 2.

[0109] In a separate reactor, all the seed suspension obtained in step 1 above is added to the reactor, and then allowed to stand for a period of time. After the seed is settled at the bottom of the reactor, an appropriate volume of clarified liquid is drawn from the upper part of the reactor, and its pH value is adjusted to about 3 with dilute sulfuric acid. 750 ml of a solution containing 300 g of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) therein to 10 liters, and then stirring is stopped, and sufficient iron sheet is added to the reactor. Stir well to mix the reaction mass evenly. The temperature of the reactor is heated to above 90°C, and the reaction temperature is controlled at 90-95°C during the subsequent reaction. Air is introduced through a gas distributor, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, with an air flux of 6 liters / minute. The reaction is continued, and a small amount of sample is taken out from the reactor every few hours, and the sample is prepared on the color card as described below, and the color is measured until the reaction is stopped when the material in the reactor is detected to be close to the color of the corresponding standard sample. During the whole reaction process, the reactor was visually inspected to ensure that there was sufficient iron scale in the reactor. After the reaction was completed, the red iron oxide precipitate formed in the reactor was filtered, washed and dried.

[0110] Comparative Example 1

[0111] In this comparative example, iron sheet was not used in step 2. Instead, ferrous oxide solution was used to prepare red iron oxide, and the red iron oxide product was characterized.

[0112] Step 1 in this comparative example is exactly the same as Example 2, and seed is prepared. In an independent reactor, the seed suspension obtained in step 1 is all added to the reactor, then left to stand for a period of time, after the seed is settled at the bottom of the reactor, the clarified liquid of appropriate volume is extracted from the upper part of the reactor, its pH value is adjusted to about 3 with dilute sulfuric acid, 750 milliliters of solution containing 300 grams of ferrous sulfate heptahydrate is added to the reactor, and water is added to the reactor to adjust the volume of the reaction mass (second reaction mixture) to 10 liters. Stir well so that the reaction mass is mixed evenly. The temperature of the reactor is heated to more than 90 ° C, and the reaction temperature is controlled at 90-95 ° C in the subsequent reaction process, and stirring is carried out all the time. Air is introduced through a gas distributor at the beginning, and after the air leaves the gas distributor, it is dispersed into small bubbles and moves the slurry upward, and the air flux is 10 liters / minute. The NaOH aqueous solution with a concentration of 32% by weight was dripped into the reactor at a uniform rate, and the heptahydrate ferrous sulfate solution with a concentration of 40 g / 100 ml was dripped at the same time, and sampling was performed regularly to ensure that the pH value of the reaction material and the ferrous ion concentration remained substantially unchanged. The reaction was continued, and a small amount of sample was taken out from the reactor every few hours, and sample preparation was performed on the color card as described below, and color measurement was performed until the material in the reactor detected a color close to the corresponding standard sample and stopped the reaction. After the reaction was completed, the iron oxide red precipitate formed in the reactor was filtered, washed and dried.

[0113] Next, the properties of the iron oxide red products obtained in the above Examples 1-8 and Comparative Example 1 were characterized by the following techniques, and the characterization results are summarized in Table 1:

[0114] The standard samples used in the characterization of tinting strength performance are industrial products iron oxide red 110 and 130-1 (purchased from Jiangsu Yuxing Company, synthesized by industrial mixed acid method). The sampled or finally obtained pigments in the reaction process of each embodiment of the present invention and comparative example 1 are uniformly mixed with titanium dioxide in a weight ratio of 1:2 to form a diluted pigment sample. 20g of butyl acetate, 7g of ATU, and 45g of P104 are added to 10 liters of silicone acrylic resin (R-05 type), mixed evenly, and a mixed resin is obtained.

[0115] Weigh 10.00 g of glass beads (2-3 mm in diameter) and add them to a 50 ml plastic bottle. Then weigh 0.7500 g of the diluted pigment sample and pour it into the plastic bottle. Add 5.00 g of mixed resin into the plastic bottle. Then place the plastic bottle in a SpeedMixer DAC 150Z oscillator and oscillate for 3 minutes. After the oscillation, use an SZQ preparation device to prepare a sample on a color card to form a wet film with a thickness of 200 μm. After placing it at room temperature for about 10 minutes, place it on a heating plate and heat it for about 45 minutes. After cooling to room temperature, use Datacolor to measure and compare the color.

[0116] The slurry obtained from the second step reaction of each embodiment and comparative example 1 was uniformly mixed, and 100 ml of sample was taken, filtered, washed, dried, and then weighed to calculate the yield, which was expressed in g / 100 ml.

[0117] Table 1 Characterization results of iron oxide red of Examples 1-8 and Comparative Example 1

[0118]

[0119] From the characterization results shown in Table 1, it can be seen that the tinting strength and red phase data of Comparative Example 1 are quite poor, while the above Examples 1-8 all achieve the preparation of iron oxide red pigment without using nitrogen-containing reagents.

[0120] The iron oxide red products prepared in Examples 1 to 5 of the present invention have excellent red phase data compared with industrial iron oxide red, and the tinting strength is also better than the iron oxide red in the prior art.

[0121] In Examples 6-8, one of the air flux, oxidation reaction temperature and ferrous salt concentration is outside the preferred range of the present invention. Although the iron oxide red product can be synthesized, the seed crystals prepared in Example 6 are amorphous iron oxide hydrates. Although iron oxide crystals are finally obtained, the crystal particle size is uneven, resulting in low tinting power and poor color light performance of the sample; in Example 7, it is difficult to dehydrate the seed crystals to complete the crystal transformation at a relatively low temperature, resulting in a large amount of impurities in the product, yellowish color, insufficient tinting power, orange appearance, and poor quality of the prepared iron oxide red product; in Example 8, the ferrous salt concentration is too high in the seed crystal preparation stage, the prepared seed crystal particles are relatively large, and it is difficult for the seed crystal particles to complete the crystal transformation in the crystal growth stage, resulting in impurities in the product, insufficient red color, low tinting power, and poor quality of the prepared iron oxide red product.

Claims

1. A method for preparing iron oxide red pigment, the method comprising: Step 1: allowing a first reaction mixture containing a first ferrous salt to react with an oxidizing gas under alkaline conditions to form seed crystals; Step 2: allowing the second reaction mixture containing the seed crystal and the second ferrous salt to undergo a second reaction with an oxidizing gas and zero-valent iron under acidic conditions to obtain the iron oxide red pigment; The method does not use nitrogen containing reagents.

2. The method according to claim 1, characterized in that In the step 1, the pH value of the alkaline condition is 11-13; in the step 2, the pH value of the acidic condition is 2-4.

3. The method according to claim 1, characterized in that The first reaction mixture is an aqueous solution or slurry containing ferrous sulfate, wherein the content of ferrous sulfate is 5-60 g / L; The second reaction mixture is an aqueous solution or slurry comprising ferrous sulfate and the seed crystals, wherein the content of ferrous sulfate is 10-50 g / L.

4. The method according to claim 1, characterized in that In step 1 and step 2, the oxidizing gas is selected from one or more of the following: air, oxygen, and ozone.

5. The method according to claim 1, characterized in that The zero-valent iron is selected from one or more of the following: iron powder, iron sheet, iron filings, iron particles, and iron slag.

6. The method according to claim 1, characterized in that The step 1 and the step 2 are both carried out without stirring.

7. The method according to claim 1, characterized in that No colloid is formed in the steps 1 and 2.

8. The method according to claim 1, characterized in that In step 1, the oxidizing gas is heated at 0.03-0.3 m 3 / hour·L flow rate is provided to the first reaction, and the duration of the first reaction is 20-120 minutes; In the step 2, the reaction temperature is 85-95°C; In the step 2, the amount of the seed crystal in the second reaction mixture is 0.1-0.4 mol / L.

9. An iron oxide red pigment prepared by the method according to any one of claims 1 to 8.

10. The iron oxide red pigment according to claim 9, characterized in that The tinting strength of the iron oxide red pigment is greater than 102% of the benchmark commercial iron oxide red 110.

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