Method for preparing high-grade iron oxide red by taking ferrous chloride tetrahydrate as raw material

Abstract

The invention discloses a method for preparing high-grade iron oxide red by taking ferrous chloride tetrahydrate as a raw material, which sequentially comprises the following three steps: dehydrating the ferrous chloride tetrahydrate, calcining the ferrous chloride and preparing the iron oxide red, and mainly comprises the following steps: drying the ferrous chloride tetrahydrate to prepare ferrous chloride powder; the ferrous chloride powder is ferrous chloride monohydrate powder or ferrous chloride dehydrate powder or mixed powder containing ferrous chloride monohydrate and ferrous chloride dehydrate, calcining the powder to prepare iron oxide red, crushing the calcined iron oxide red, feeding the crushed iron oxide red into a slurry pool, dissolving, carrying out filter pressing, and cleaning to obtain an iron oxide red filter cake; and drying and crushing the iron oxide red filter cake to obtain a high-grade iron oxide red finished product. The finished product prepared by the method meets the requirements of high-grade iron oxide red parameters on various indexes such as relative color difference value, strength difference value, iron content, 105 DEG C volatile matter mass fraction, water soluble matter mass fraction, screen residue (greater than or equal to 45 microns) mass fraction, water suspension pH value, oil absorption, product particle size and the like.

Description

Technical Field

[0001] The invention relates to a method for preparing red iron oxide, in particular to a method for preparing high-grade red iron oxide by using high-purity ferrous chloride tetrahydrate as a raw material. Background Art

[0002] Red iron oxide, also known as iron oxide red or iron red, is a dark red or red powder. It is the world's largest inorganic dye pigment with a chemical formula of α-Fe2O3 and a melting point of 1565°C. It is non-toxic and insoluble in water. It is currently the largest inorganic pigment in terms of production and usage except for titanium dioxide. It is also the largest product in terms of production and usage among the iron oxide series pigments (iron red, iron yellow, iron black, etc.). It has good light resistance, weather resistance, hiding power, high wear resistance and corrosion resistance, and is widely used in building materials, coatings, plastics, rubber, ceramics, glass, inks, lithium batteries and other industries. At present, the traditional preparation methods of red iron oxide include dry process and wet process. The dry process includes green vitriol calcination method, iron yellow calcination method, iron black calcination method, ferrous sulfate-soda ash calcination method, and the wet process includes sulfate method, nitrate method, and mixed acid salt method.

[0003] There are also some reports on the preparation of red iron oxide using ferrous chloride as raw material. The preparation method disclosed in the Chinese patent CN101898800A is to add alkali solution to neutralize the ferrous chloride solution obtained by reducing the nickel-containing ferric chloride etching waste liquid with iron powder and removing nickel, and obtain a mixture of ferrous hydroxide and ferrous carbonate precipitate, which is then filtered, washed, dried, and calcined to prepare red iron oxide. The preparation method disclosed in the Chinese patent CN103818968B is to first remove impurities and purify the gallium-extracting resin eluate to obtain a ferrous chloride solution; then concentrate and crystallize the ferrous chloride solution to obtain ferrous chloride crystals; then dissolve the ferrous chloride crystals to obtain a ferrous chloride solution, adjust the pH of the ferrous chloride solution to 5-7, filter, obtain ferrous carbonate precipitate, and then dry and calcine the ferrous carbonate precipitate to prepare red iron oxide. Obviously, the above two patents prepare red iron oxide after modifying ferrous chloride, that is, the object of calcination is not ferrous chloride, but ferrous hydroxide or ferrous carbonate.

[0004] Chinese patent CN103771537B directly calcined ferrous chloride to prepare red iron oxide. This process is a method for preparing ferrous chloride tetrahydrate, red iron oxide and sulfuric acid using byproducts of the titanium dioxide industry. The byproduct contains ferrous sulfate heptahydrate. A certain amount of byproducts of the titanium dioxide industry is dissolved in concentrated hydrochloric acid, and then ferrous chloride tetrahydrate crystals are precipitated under stirring conditions. After filtering, ferrous chloride tetrahydrate is directly calcined to obtain red iron oxide and produce HCl; wherein the calcination temperature of ferrous chloride tetrahydrate is 400-800°C, and the calcination time is 0.5-3h. This process directly calcined ferrous chloride tetrahydrate to prepare red iron oxide. Unfortunately, the technical parameters of the prepared red iron oxide are not disclosed, which makes it impossible to evaluate the quality of the prepared red iron oxide. Directly calcining ferrous chloride tetrahydrate will easily lead to the precipitation of crystal water due to its excessive water content, which will redissolve FeCl2 and cause the calcined iron red to become lumpy, resulting in uneven oxidation. In addition, if the calcination time is too short, it will easily lead to incomplete calcination and high salt content; if the calcination time is too long, it will easily cause the product color to turn black.

[0005] In May 2015, the 5th issue of Volume 47 of Inorganic Salt Industry (domestic publication number: CN: 12-1069 / TQ) published "Research on the process of producing high-quality red iron oxide from ferrous chloride", published by Xie Xiaocui, Hu Yangdong, Zhang Weitao and Li Hua, which disclosed a method for preparing red iron oxide from ferrous chloride tetrahydrate crystal raw material. The specific reaction process is: Pretreatment of FeCl2·4H2O crystals: First, weigh a certain amount of FeCl2·4H2O crystals, crush and sieve to a particle size of ≤70μm for standby use; Reaction process: After the compressed air is stabilized, it enters the washing bottle for humidification through a rotor flowmeter, and the wet air enters from the bottom of the reactor and is heated in the quartz particle bed. The temperature of the reaction area is controlled by adjusting the power of the electric furnace heater. When the temperature of the reaction area rises to the set temperature, the raw materials are added from the top of the reactor at one time. The small amount of solid powder brought out during the reaction is separated from the main airflow in the solid collection bottle, and the gas is washed by the alkali absorption tower and discharged.

[0006] This paper studies the effects of oxidation temperature and reaction time on the physical phase, purity, hue, oil absorption and particle size of the product, and discusses the relationship between oxidation temperature and oxidation time. The optimal process conditions for preparing high-quality iron oxide red were obtained through experiments: oxidation temperature of 400℃ and oxidation time of 60min. Under these conditions, the product obtained has a purity of 99.5%, a pure and bright hue, a particle size of 100-150nm, and an oil absorption of 0.241g / g. By studying the relationship between oxidation temperature and reaction time, it is proved that the reaction time required for temperature increase is correspondingly shortened, that is, the reaction process has time-temperature equivalence. However, it can be seen that this study is based on laboratory rather than large-scale production. The object of oxidation is still FeCl2·4H2O, and the compressed air introduced is humidified wet air. Obviously, because it is a laboratory dosage, and the FeCl2·4H2O crystals are crushed and sieved to a particle size of ≤70μm, although there will be no uneven oxidation caused by the accumulation of raw materials, it is necessary to add a crushing and screening step, which makes the entire preparation process more complicated and increases the difficulty of control. In the large-scale production process, excessive water content in ferrous chloride during the calcination step can easily lead to the precipitation of crystal water, which can easily redissolve FeCl2, causing the calcined iron red to become lumpy. Uneven oxidation still objectively exists.

[0007] In summary, finding a method suitable for large-scale production of high-grade red iron oxide to avoid uneven oxidation during the calcination process has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0008] Obviously, in the process of preparing high-grade red iron oxide with ferrous chloride tetrahydrate as raw material, the water content of ferrous chloride tetrahydrate as the calcination object has not been studied, and this has a corresponding impact on the calcination process conditions, such as temperature and time, and further affects the subsequent preparation processes such as slurrying, color matching and red iron oxide filter cake. Therefore, the purpose of the present invention is to provide a method for preparing red iron oxide that can effectively avoid uneven oxidation during the calcination process; in order to meet the needs of large-scale production, the source of raw materials should also be diversified. Another purpose of the present invention is to directly use the by-product ferrous chloride tetrahydrate crystals in the titanium dioxide production process as the raw material for ferrous oxide production, so as to realize the integration of the titanium dioxide production line and the red iron oxide production line.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] A method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as a raw material is to calcine ferrous chloride powder under oxygen-rich conditions, wherein the ferrous chloride powder is ferrous chloride monohydrate powder or / and ferrous chloride dihydrate powder. That is, the ferrous chloride powder is ferrous chloride monohydrate powder, or ferrous chloride dihydrate powder, or a mixed powder containing ferrous chloride monohydrate and ferrous chloride dihydrate.

[0011] The chemical formula of ferrous chloride tetrahydrate is FeCl2·4H2O, its molecular weight is 198.81, and the theoretical water content of ferrous chloride tetrahydrate is 36.26Wt%. The water in ferrous chloride tetrahydrate is crystal water, which is a water molecule bound to a compound. They are combined with other components in the compound in a certain proportion to form crystalline hydrates. These crystal waters have specific positions and functions in the crystal structure. When heated or other conditions change, the crystal water will be lost. Ferrous chloride tetrahydrate is usually transparent blue-green monoclinic crystals or gray-green monoclinic crystals or crystalline powders. The ferrous chloride monohydrate formed after drying ferrous chloride tetrahydrate is generally yellow-green powder; the ferrous chloride dihydrate formed after drying ferrous chloride tetrahydrate is usually green powder, and its color is slightly darker than that of ferrous chloride tetrahydrate.

[0012] Ferrous chloride tetrahydrate generally exists in the form of crystals, and is formed into a powdery substance by crushing or drying. In the prior art, ferrous chloride tetrahydrate is crushed to form a powdery substance and then calcined. The present invention is different from the prior art in that, in order to adapt to large-scale production and simplify the production process, ferrous chloride tetrahydrate is dried to remove part of the water to form a powdery substance, and then the powdery substance is directly used as a calcination object.

[0013] Therefore, the calcination object used in the present invention is the dried ferrous chloride powder, and its water content range is 12.15Wt%-21.67Wt%, based on the total weight of the ferrous chloride powder. The reason for considering the range of water content is that as the calcination object, the ferrous chloride powder with too high or too low water content has a great influence on the calcination process conditions and effects.

[0014] Specifically, if the ferrous chloride used as the calcination object has a large water content, it may first lead to obstruction of temperature transfer. For example, the vaporization of water absorbs heat, which slows down the oxidation reaction rate. Water has a large specific heat capacity. During the calcination process, the vaporization of a large amount of water will absorb a large amount of heat, causing the system temperature to rise slowly, making it difficult to reach the ideal temperature required for the oxidation reaction of ferrous chloride. For example, the calcination temperature was originally set to 600°C, but due to the heat absorption of water vaporization, the actual material temperature may only reach about 400°C; another phenomenon that leads to obstruction of temperature transfer is uneven heat distribution. Excessive water will form a local water phase in the material, resulting in uneven heat transfer inside the material. Some areas may have a low temperature due to excessive water, and the oxidation reaction cannot be fully carried out; while other areas may have relatively high temperatures, but due to the incoordination of the overall reaction system, they cannot effectively promote the complete oxidation reaction.

[0015] More seriously, the high water content of ferrous chloride powder can easily lead to particle agglomeration. During high-temperature calcination, excessive water content may cause ferrous chloride to react with water to generate some sticky intermediates. These sticky substances will bind the particles together to form larger agglomerates, further hindering the diffusion of oxygen and the oxidation reaction. In addition, the liquid film formed by water on the surface of ferrous chloride particles will cause the particles to agglomerate with each other due to the effect of surface tension. The specific surface area of ​​the agglomerated particles is reduced, and the contact area with oxygen is also reduced accordingly, which is not conducive to the full progress of the oxidation reaction and leads to incomplete oxidation.

[0016] The high water content of ferrous chloride powder can easily lead to the hydrolysis of ferrous chloride. Ferrous chloride will undergo hydrolysis reaction in water to generate ferrous hydroxide. When the water content is too high, the hydrolysis reaction will intensify, and the generated ferrous hydroxide will cover the surface of ferrous chloride particles, preventing further contact between oxygen and ferrous chloride, affecting the oxidation reaction. These side reactions will consume oxygen, reduce the amount of oxygen used for ferrous chloride oxidation, and also lead to incomplete oxidation.

[0017] In addition, if the water content of ferrous chloride, which is the object of calcination, is too low, incomplete oxidation will also occur. The first is the existence of crystal structure defects. Reaction water contributes to the formation and growth of red iron oxide crystals during the calcination process. In the absence of reaction water, the growth of crystals may be restricted, resulting in imperfect crystal structures and defects. This will affect the physical and chemical properties of the product, such as hardness, density, magnetism, etc., making its performance unstable or failing to meet the expected requirements in the application. Secondly, it causes color changes. The color of red iron oxide is related to factors such as its crystal structure and particle size. Lack of reaction water may cause uneven crystal growth and a wider distribution of particle size, thereby changing the color of the product, such as lighter color or color difference, affecting its coloring effect and color consistency as a pigment. In addition, it will also lead to incomplete reactions. During the calcination of red iron oxide, reaction water may participate in some chemical reactions to promote the conversion of raw materials and the reaction. Lack of reaction water may lead to incomplete reaction, and some components in the raw materials cannot fully react to form red iron oxide, thereby reducing the yield of the product and increasing production costs. Due to incomplete reaction or difficulty in crystal growth, higher temperature and longer calcination time may be required to achieve the desired product quality, but there is a great possibility that red iron oxide will not be obtained but black iron oxide will be obtained.

[0018] Therefore, the present invention selects the water content of the ferrous chloride powder as the calcination object to be within the range of 12.15wt%-21.67wt% in order to avoid incomplete oxidation caused by excessive or insufficient water content, thereby ensuring the acquisition of high-grade red iron oxide products.

[0019] A specific method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as a raw material comprises the following steps:

[0020] S1: Dehydration of ferrous chloride tetrahydrate: drying ferrous chloride tetrahydrate to prepare ferrous chloride powder, wherein the ferrous chloride powder is ferrous chloride monohydrate powder or ferrous chloride dihydrate powder or a mixed powder containing ferrous chloride monohydrate and ferrous chloride dihydrate, wherein the drying temperature is 140-180°C;

[0021] S2: Calcination of ferrous chloride: Calcination of ferrous chloride powder to produce red iron oxide, wherein the calcination is carried out under oxygen-rich conditions, wherein the calcination temperature is 400-600°C, and the calcination time is 1-2 hours;

[0022] S3: Preparation of red iron oxide product: The calcined red iron oxide is sent to the slurry pool to form a primary slurry, and then the primary slurry is ground, dissolved, color matched, filtered, and cleaned to obtain a red iron oxide filter cake, and then the red iron oxide filter cake is dried and crushed to obtain a high-grade red iron oxide finished product.

[0023] Preferably, the drying temperature required for preparing ferrous chloride monohydrate powder is 170-180°C, the drying time is 2-5s, the calcination temperature is 400°C-450°C, the calcination time is 1.7-2h, wherein the drying is performed using a flash dryer; the best is that the drying temperature required for preparing ferrous chloride monohydrate powder is 180°C, the drying time is 3s, the calcination temperature is 410°C, the calcination time is 1.8h, and the prepared high-grade iron oxide red The relative color difference value ΔE is 0.97, the intensity difference value is 96.38%, the iron content (expressed as Fe2O3) is 96.25%, the mass fraction of volatile matter at 105°C is 0.92%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 0.67%, the mass fraction of the residue (≥45μm) is 0.21%, the pH value of the aqueous suspension is 4.82, the oil absorption is 21.32g / 100g, and the product particle size (D50) is 0.95μm.

[0024] Preferably, the drying temperature required for preparing ferrous chloride dihydrate powder is 140-160°C, the drying time is 2-5s, the calcination temperature is 500°C-600°C, the calcination time is 1.5-1.7h, wherein the drying is performed using a flash dryer; the best is that the drying temperature required for preparing ferrous chloride dihydrate powder is 145°C, the drying time is 2.3s, the calcination temperature is 600°C, the calcination time is 1.6h, and the prepared high-grade iron oxide The relative color difference value ΔE of red is 0.84, the intensity difference value is 98.27%, the iron content (expressed as Fe2O3) is 97.01%, the mass fraction of volatile matter at 105°C is 0.21%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 0.54%, the mass fraction of the residue (≥45μm) is 0.19%, the pH value of the aqueous suspension is 5.15, the oil absorption is 18.27g / 100g, and the product particle size (D50) is 1.03μm.

[0025] Preferably, the drying temperature required for preparing the mixed powder of ferrous chloride monohydrate and ferrous chloride dihydrate is 150-170°C, the drying time is 2-5s, the calcination temperature is 450°C-500°C, the calcination time is 1-1.5h, wherein the drying is performed using a flash dryer. The best is that the drying temperature required for preparing the powders of ferrous chloride monohydrate and ferrous chloride dihydrate is 160°C, the drying time is 2.6s, the calcination temperature is 480°C, the calcination time is 1.3h, the relative color difference value ΔE of the prepared high-grade iron oxide red is 0.72, the intensity difference value is 100.75%, the iron content (expressed as Fe2O3) is 96.71%, the mass fraction of volatile matter at 105°C is 0.38%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 0.43%, the mass fraction of the residue (≥45μm) is 0.17%, the pH value of the aqueous suspension is 5.53, the oil absorption is 20.75g / 100g, and the product particle size (D50) is 1.11μm.

[0026] Furthermore, the equipment used for drying in S1 is a flash dryer, and the ferrous chloride powder produced after drying is collected by a cyclone dust collector. The ferrous chloride powder is the raw material for the subsequent calcination process. Of course, other drying equipment, such as a drying box, can also be used, but the drying time is longer. In order to shorten the time required for the process, the present invention uses a flash dryer; the dehydrated flue gas generated by the drying in S1 passes through a bag filter and then enters a water curtain washing device, and is discharged after being washed to the standard.

[0027] Furthermore, ferrous chloride tetrahydrate is dried after metering. The metering can be carried out in a variety of ways, mainly to calculate the total amount of water in ferrous chloride tetrahydrate. The reason for metering is that in large-scale production, the drying time and temperature can be better controlled to control the water content in the ferrous chloride powder within an appropriate range.

[0028] Furthermore, in the ferrous chloride calcining step S2, the ferrous chloride powder collected by the cyclone dust collector is added into the calcining rotary kiln through the calcining spiral for calcining, and the tail gas generated during the calcining process is collected by the cyclone dust collector for large particles, and then enters the bag filter through the air supply and cooling device, and the HCl-containing tail gas after dust removal is sprayed and absorbed to prepare hydrochloric acid; the oxygen-rich condition is formed by blowing air into the calcining rotary kiln, and the air blowing conditions can be adjusted to maintain the oxygen-rich condition in the combustion rotary kiln; the calcining rotary kiln is heated by natural gas, and the inner wall of the calcining rotary kiln is equipped with an anti-sticking chain to prevent the calcined object from forming agglomerates during the calcining process.

[0029] Furthermore, in the step S3 of preparing the red iron oxide product, the red iron oxide is sent to a slurry pool for slurrying to form a primary slurry, and then the primary slurry is ground to 4.1-8.7 μm by a sand mill, and then maintained at 50-70°C to dissolve to form a red iron oxide slurry, and then the color of the red iron oxide slurry is matched by the slurry pool so that the color of the red iron oxide slurry reaches or approaches the color of the standard sample, and then the red iron oxide slurry is filtered by a filter press to form a filter cake and a filtered mother liquor, and the filter cake is washed with industrial water to obtain a red iron oxide filter cake, and then the red iron oxide filter cake is dried and crushed to 4.1-8.7 μm to make a high-grade red iron oxide product. The dried red iron oxide filter cake is crushed not to further obtain smaller particles, but only to break the lumps into powder.

[0030] Furthermore, in order to be suitable for industrialized large-scale production, it should also be considered that the ferrous chloride raw material may contain certain impurities. In the case of large-scale production, the use of pure ferrous chloride tetrahydrate may not be the most economical and appropriate, and the source of ferrous chloride tetrahydrate should be diversified; the ferrous chloride tetrahydrate used can be derived from the by-products in the preparation process of titanium dioxide by hydrochloric acid method, thereby integrating the titanium dioxide production line and the red iron oxide production line. In the preparation process of titanium dioxide by hydrochloric acid method, hydrochloric acid is mainly used to acid-leach titanium concentrate or titanium slag. There are a large number of ferrous ions in the waste liquid after acid leaching of titanium concentrate or titanium slag. The ferrous ions in the waste liquid are separated to obtain ferrous chloride tetrahydrate crystals, which are used as raw materials to prepare red iron oxide.

[0031] The ferrous chloride tetrahydrate is prepared by the following method:

[0032] Titanium concentrate is leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I. Hydrogen chloride gas is introduced into mother liquor I. When the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped to obtain mother liquor II. Mother liquor II is then cooled to 10-15°C to crystallize ferrous chloride. Finally, centrifugal filtration is performed to obtain filtrate and ferrous chloride tetrahydrate crystals.

[0033] The weight percentage of metallic iron in the ferrous chloride tetrahydrate is greater than 96%, the total weight percentage of impurities is less than or equal to 4%, and the weight percentage of metallic manganese is less than or equal to 0.5%, all based on the total weight of metals in the ferrous chloride tetrahydrate.

[0034] The best is that the mass concentration of hydrogen chloride in the mother liquor I is 8-12%, the mass concentration of ferrous ions in the mother liquor I is 120-170g / L, the mass concentration of manganese ions is 1-5g / L, the mass concentration of calcium ions is 1-5%, and the mass concentration of magnesium ions is 5-15g / L. In the process of mother liquor I absorbing hydrogen chloride gas to obtain mother liquor II, the solution temperature is maintained at 40-60°C. The purity of ferrous chloride crystals is ≥99%, the content of Mn element is ≤0.06wt%, and the total content of other impurity elements is ≤0.04wt%.

[0035] The beneficial effects of the present invention are:

[0036] The invention adopts the by-product in the titanium dioxide production process, i.e., high-purity ferrous chloride tetrahydrate crystals as a raw material to prepare a high-grade iron oxide red product, realizes a perfect coupling between the titanium dioxide production line and the iron oxide red production line, and satisfies the diversified sources of ferrous chloride tetrahydrate raw materials; at the same time, the impurity ion content of ferrous chloride tetrahydrate is controlled, which is more conducive to the preparation of a high-grade iron oxide red product.

[0037] The ferrous chloride tetrahydrate crystals are dried, and part of the crystal water is evaporated, so that the calcined object becomes a ferrous chloride monohydrate powder or a ferrous chloride dihydrate powder or a mixed powder containing ferrous chloride monohydrate and ferrous chloride dihydrate, which can effectively prevent the material entering the calcination rotary kiln from being in a block shape, and then the adverse consequences of incomplete oxidation occur. Unlike the prior art, before entering the calcination rotary kiln, the ferrous chloride powder does not need to be crushed again, and its particle size range does not need to be limited. The ferrous chloride powder obtained by flash drying can meet the calcination conditions, and a stirring knife can be used in the flash evaporation device to prevent the ferrous chloride powder from agglomerating. Control the water content range in the ferrous chloride powder to avoid incomplete oxidation of the ferrous chloride powder, because the water content is large, it is easy to cause the ferrous chloride to agglomerate, and some materials lack oxygen and cannot react, which leads to incomplete oxidation; low water content leads to lack of reaction water, which cannot react and also leads to incomplete oxidation. The high-grade iron oxide red prepared by the present invention meets the requirements of high-grade iron oxide red parameters in terms of various indicators such as relative color difference value, strength difference value, iron content, mass fraction of volatile matter at 105°C, mass fraction of water-soluble matter, mass fraction of sieve residue (≥45μm), pH value of water suspension, oil absorption, product particle size, etc. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with embodiments.

[0039] Raw material preparation: hydrogen chloride gas is introduced into the mother liquor after titanium dioxide is filtered from the titanium concentrate through acid leaching, so that the mass concentration of hydrogen chloride in the mother liquor reaches 26-28%, and then the temperature is lowered to 10-15°C, and high-purity ferrous chloride tetrahydrate crystals are precipitated and filtered to obtain the ferrous chloride tetrahydrate crystals, the purity of which is ≥99%, the content of Mn element is ≤0.06wt%, and the total content of other impurity elements is ≤0.04wt%.

[0040] Example 1: A red iron oxide product close to the standard chromaticity Y101 was prepared by calcining FeCl2·H20 powder.

[0041] S1: Dehydration of ferrous chloride tetrahydrate: FeCl2·4H20 crystals are fed into the flash dryer through the flash dryer feeding screw, and heat is exchanged with the hot flue gas generated by natural gas combustion at 180°C for 3s in the flash dryer. At a relatively high temperature, FeCl2·4H20 undergoes a dehydration reaction, and the obtained FeCl2·H20 powder is collected in a cyclone dust collector, wherein the water content of the FeCl2·H20 powder is 12.15wt%. The dehydrated flue gas passes through a bag filter and enters a water curtain washing device, and is discharged after washing. In order to prevent the FeCl2·H20 powder entering the flash dryer from dissolving and agglomerating, the FeCl2·H20 powder can be crushed by a stirring blade provided in the flash dryer;

[0042] S2: Calcination of ferrous chloride: The FeCl2·H2O powder collected by the cyclone dust collector is added to the calcination kiln through the calcination screw, and heated to 410°C in the kiln. At the same time, air is blown into the kiln through the blower. Under oxygen-rich conditions, the FeCl2·H2O powder is calcined for 1.8 hours to become red iron oxide. The calcination kiln is heated by natural gas, and the inner wall of the kiln is equipped with an anti-sticking chain to prevent the FeCl2·H2O powder from sticking. The tail gas generated by the calcination is collected by the cyclone dust collector to collect large particles, and then enters the bag filter through the air supply and cooling device. The HCl-containing tail gas after dust removal is sprayed and absorbed to make hydrochloric acid, which is recycled and reused in the acid leaching of titanium concentrate, or the HCl tail gas is directly passed into the mother liquor after the titanium dioxide is filtered out by the acid leaching of titanium concentrate;

[0043] S3: Preparation of red iron oxide product: The calcined red iron oxide is sent to a slurry pool for slurrying to form a primary slurry, which is then crushed to 4.1 μm by a sand mill and dissolved at 50°C to allow the salt in the particles to fully dissolve into the solution to form red iron oxide slurry. The slurry is then passed through a slurry pool for color matching to make the color of the red iron oxide slurry reach or approach the color of the standard sample Y101, and the red iron oxide slurry is filtered through a filter press to form a filter cake and a filtered mother liquor. The filter cake is washed with industrial water to obtain a red iron oxide filter cake, which is then dried in a belt dryer and crushed to 4.1 μm to produce a high-grade red iron oxide product. The various indicators of the obtained high-grade red iron oxide are shown in Table 2.

[0044] The following Examples 2 to 4 are all prepared according to the method in Example 1, except that the process conditions in the preparation process are different, see Table 1; in addition, Example 2 uses FeCl2·2H20 powder as the calcination object to prepare a red iron oxide product with a chromaticity close to the standard sample H130, and Examples 3 and 4 use a mixed powder containing FeCl2·H20 powder and FeCl2·2H20 powder as the calcination object to prepare red iron oxide products with chromaticities close to the standard sample 130S and 130A, respectively. The various indicators of the red iron oxide prepared in Examples 2 to 4 are shown in Table 2.

[0045] Table 1: Process conditions of Examples 2-4

[0046]

[0047] Table 2: Various indicators of red iron oxide products

[0048]

[0049]

[0050] It can be seen from Table 2 that the various indicators of the red iron oxide in Examples 1-4 all meet the requirements of the national standard (GB / T1863-2008 Iron Oxide Pigments), and all are high-grade red iron oxide products.

[0051] Comparative Example 1: Preparation of iron oxide red product close to standard chromaticity Y101 using FeCl2·4H20 crystal as calcination object

[0052] The FeCl2·4H2O powder is added into the calcining rotary kiln through the calcining screw, and heated to 450°C in the rotary kiln, and air is blown into the rotary kiln through the blower. After calcining for 1 hour under oxygen-rich conditions, the FeCl2·4H2O powder is calcined into red iron oxide, and the diameter of the red iron oxide particles is measured to be D50 = 6.5μm. The calcined red iron oxide is then sent to a slurry pool for slurrying to form a primary slurry, and then the primary slurry is crushed to 1.0μm by a sand mill and maintained at 50-70°C for a period of time to allow the salt in the particles to fully dissolve into the solution to form red iron slurry. The color of the red iron slurry is then matched in the slurry pool so that the chromaticity of the red iron slurry reaches or approaches the chromaticity of the standard sample Y101. The red iron slurry is then filtered through a filter press to form a filter cake and a filtered mother liquor. After the filter cake is washed with industrial water, a red iron oxide filter cake is obtained. The red iron oxide filter cake is then sent to a belt dryer for drying, and then crushed to 1.0μm by a pulverizer to make a red iron oxide finished product.

[0053] The obtained red iron oxide is compared with the standard sample Y101, and the indicators are as follows:

[0054] The relative color difference value ΔE is 2.34, the intensity difference value is 89.27%, the iron content (expressed as Fe2O3) is 95.01%, the mass fraction of volatile matter at 105°C is 0.21%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 1.64%, the mass fraction of the residue (≥45μm) is 0.19%, the pH value of the aqueous suspension is 4.75, the oil absorption is 18.27g / 100g, and the product particle size (D50) is 1.23μm.

[0055] From the above indicators, it can be seen that because comparative example 1 did not adopt drying technology to remove the crystal water, the water content of ferrous chloride entering the calcining rotary kiln was too high, resulting in rapid dissolution after entering the rotary kiln, and material agglomeration, resulting in incomplete oxidation at the end. The iron red salt content was high, the particle diameter was large, the product color was larger than the standard sample 101ΔE, and the strength difference value was relatively small.

[0056] Comparative Example 2: Preparation of iron oxide red product close to standard chromaticity Y101 using FeCl2·3H20 as calcination object

[0057] The FeCl2·3H2O powder is added into the calcining rotary kiln through the calcining screw, and heated to 400°C in the rotary kiln, and air is blown into the rotary kiln through the blower. After calcining for 1 hour under oxygen-rich conditions, the FeCl2·3H2O powder is calcined into red iron oxide, and the diameter of the red iron oxide particles is measured to be D50 = 4.3μm. The calcined red iron oxide is then sent to a slurry pool for slurrying to form a primary slurry, and then the primary slurry is crushed to 1.0μm by a sand mill and maintained at 50-70°C for a period of time to allow the salt in the particles to fully dissolve into the solution to form red iron slurry. The color of the red iron slurry is then matched in the slurry pool so that the chromaticity of the red iron slurry reaches or approaches the chromaticity of the standard sample Y101. The red iron slurry is then filtered through a filter press to form a filter cake and a filtered mother liquor. After the filter cake is washed with industrial water, a red iron oxide filter cake is obtained. The red iron oxide filter cake is then sent to a belt dryer for drying, and then crushed to 1.0μm by a pulverizer to make a red iron oxide finished product.

[0058] The obtained red iron oxide is compared with the standard sample Y101, and the indicators are as follows:

[0059] The relative color difference value ΔE is 1.27, the intensity difference value is 92.93%, the iron content (expressed as Fe2O3) is 96.35%, the mass fraction of volatile matter at 105°C is 0.26%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 1.13%, the mass fraction of the residue (≥45μm) is 0.25%, the pH value of the aqueous suspension is 5.15, the oil absorption is 20.31g / 100g, and the product particle size (D50) is 1.18μm.

[0060] From the above indicators, it can be seen that compared with comparative example 1, comparative example 2 has reduced the moisture content of raw materials because one crystal water is dried, the agglomeration inside the rotary kiln is improved, the calcination is more complete, the final iron red salt content is lower, the particle diameter is smaller, the product color is smaller than the standard sample 101ΔE, and the strength difference value is larger. However, it still does not meet the requirements of the national standard GB / T 1863-2008.

[0061] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in this application, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing high-grade red iron oxide using ferrous chloride tetrahydrate as raw material, which is prepared by calcining ferrous chloride powder under oxygen-rich conditions, characterized in that The ferrous chloride powder is ferrous chloride monohydrate powder and / or ferrous chloride dihydrate powder.

2. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 1, characterized in that The water content in the ferrous chloride powder is 12.15wt%-21.67wt%, based on the total weight of the ferrous chloride powder.

3. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 1 or 2, characterized in that The steps include: S1: Dehydration of ferrous chloride tetrahydrate: drying ferrous chloride tetrahydrate to prepare ferrous chloride powder, wherein the ferrous chloride powder is ferrous chloride monohydrate powder or ferrous chloride dihydrate powder or a mixed powder containing ferrous chloride monohydrate and ferrous chloride dihydrate, wherein the drying temperature is 140-180°C; S2: Calcination of ferrous chloride: Calcination of ferrous chloride powder to produce red iron oxide, wherein the calcination is carried out under oxygen-rich conditions, wherein the calcination temperature is 400-600°C, and the calcination time is 1-2 hours; S3: Preparation of red iron oxide product: The calcined red iron oxide is sent to the slurry pool to form a primary slurry, and then the primary slurry is ground, dissolved, color matched, filtered, and cleaned to obtain a red iron oxide filter cake, and then the red iron oxide filter cake is dried and crushed to obtain a high-grade red iron oxide finished product.

4. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The ferrous chloride powder is ferrous chloride monohydrate powder, the required drying temperature is 170-180°C, the drying time is 2-5s, the calcination temperature is 400°C-450°C, the calcination time is 1.7-2h, wherein the drying adopts a flash drier.

5. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The ferrous chloride powder is ferrous chloride dihydrate powder, the required drying temperature is 140-160°C, the drying time is 2-5s, the calcination temperature is 500°C-600°C, the calcination time is 1.5-1.7h, wherein the drying adopts a flash drier.

6. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The ferrous chloride powder is a mixed powder of ferrous chloride monohydrate and ferrous chloride dihydrate, the required drying temperature is 150-170°C, the drying time is 2-5s, the calcination temperature is 450-500°C, the calcination time is 1-1.5h, wherein the drying adopts a flash dryer.

7. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The ferrous chloride powder produced after drying in S1 is collected by a cyclone dust collector.

8. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The dehydrated flue gas generated by drying in S1 passes through the bag filter and then enters the water curtain washing device, and is discharged after being washed to the required standard.

9. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The ferrous chloride tetrahydrate is dried after being measured.

10. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 4, characterized in that The drying temperature is 180° C., the drying time is 3 seconds, the calcination temperature is 410° C., and the calcination time is 1.8 hours.

11. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 10, characterized in that The high-grade iron oxide red has a relative color difference value ΔE of 0.97, a strength difference value of 96.38%, an iron content (expressed as Fe2O3) of 96.25%, a mass fraction of volatile matter at 105°C of 0.92%, a mass fraction of water-soluble matter (measured after drying at 105°C) of 0.67%, a mass fraction of sieve residue (≥45μm) of 0.21%, a pH value of the aqueous suspension of 4.82, an oil absorption of 21.32g / 100g, and a product particle size (D50) of 0.95μm.

12. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 5, characterized in that The drying temperature is 145° C., the drying time is 2.3 seconds, the calcination temperature is 600° C., and the calcination time is 1.6 hours.

13. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 12, characterized in that The high-grade iron oxide red has a relative color difference value ΔE of 0.84, a strength difference value of 98.27%, an iron content (expressed as Fe2O3) of 97.01%, a mass fraction of volatile matter at 105°C of 0.21%, a mass fraction of water-soluble matter (measured after drying at 105°C) of 0.54%, a mass fraction of sieve residue (≥45μm) of 0.19%, a pH value of the aqueous suspension of 5.15, an oil absorption of 18.27g / 100g, and a product particle size (D50) of 1.03μm.

14. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 6, characterized in that The drying temperature is 160° C., the drying time is 2.6 seconds, the calcination temperature is 480° C., and the calcination time is 1.3 hours.

15. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 14, characterized in that The relative color difference value ΔE of the high-grade iron oxide red is 0.72, the intensity difference value is 100.75%, the iron content (expressed as Fe2O3) is 96.71%, the mass fraction of volatile matter at 105°C is 0.38%, the mass fraction of water-soluble matter (measured after drying at 105°C) is 0.43%, the mass fraction of the residue (≥45μm) is 0.17%, the pH value of the aqueous suspension is 5.53, the oil absorption is 20.75g / 100g, and the product particle size (D50) is 1.11μm.

16. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that In the ferrous chloride calcining step S2, the ferrous chloride powder collected by the cyclone dust collector is added into the calcining rotary kiln through the calcining screw for calcination. The tail gas generated during the calcination process is passed through the cyclone dust collector to collect large particles, and then enters the bag filter through the air supply and cooling device. The HCl-containing tail gas after dust removal is sprayed and absorbed to produce hydrochloric acid.

17. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The oxygen-rich condition in the ferrous chloride calcining step S2 is formed by blowing air into the calcining rotary kiln.

18. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that In the ferrous chloride calcining step S2, the calcining rotary kiln is heated by natural gas, and the inner wall of the calcining rotary kiln is equipped with an anti-sticking chain.

19. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that In the red iron oxide product preparation step S3, the red iron oxide is sent to a slurry pool for slurrying to form a primary slurry, and then the primary slurry is ground to 4.1-8.7 μm by a sand mill, and then maintained at 50-70° C. to dissolve to form red iron oxide slurry, and then the slurry pool is used for color matching so that the chromaticity of the red iron oxide slurry reaches or approaches the chromaticity of the standard sample, and then the red iron oxide slurry is filtered by a filter press to form a filter cake and a filtered mother liquor, and the filter cake is washed with industrial water to obtain a red iron oxide filter cake, and then the red iron oxide filter cake is dried and crushed to 4.1-8.7 μm to prepare a high-grade red iron oxide finished product.

20. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 1 or 2, characterized in that The weight percentage of metallic iron in the ferrous chloride tetrahydrate is greater than 96%, the total weight percentage of impurities is less than or equal to 4%, and the weight percentage of metallic manganese is less than or equal to 0.5%, all based on the total weight of metals in the ferrous chloride tetrahydrate.

21. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 3, characterized in that The weight percentage of metallic iron in the ferrous chloride tetrahydrate is greater than 96%, the total weight percentage of impurities is less than or equal to 4%, and the weight percentage of metallic manganese is less than or equal to 0.5%, all based on the total weight of metals in the ferrous chloride tetrahydrate.

22. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 1 or 2, characterized in that The ferrous chloride tetrahydrate is prepared by the following method: titanium concentrate is acid-leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I, hydrogen chloride gas is introduced into the mother liquor I, when the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped to obtain mother liquor II, and then the mother liquor II is cooled to 10-15°C to crystallize ferrous chloride, and finally centrifugally filtered to obtain filtrate and ferrous chloride tetrahydrate crystals.

23. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 22, characterized in that The mass concentration of hydrogen chloride in the mother liquor I is 8-12%.

24. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 22, characterized in that The mass concentration of ferrous ions in the mother solution I is 120-170 g / L, the mass concentration of manganese ions is 1-5 g / L, the mass concentration of calcium ions is 1-5%, and the mass concentration of magnesium ions is 5-15 g / L.

25. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 22, characterized in that During the process in which mother liquor I absorbs hydrogen chloride gas to obtain mother liquor II, the solution temperature is maintained at 40-60°C.

26. The method for preparing high-grade iron oxide red using ferrous chloride tetrahydrate as raw material according to claim 22, characterized in that The purity of the ferrous chloride crystals is ≥99%, the content of Mn element is ≤0.06wt%, and the total content of other impurity elements is ≤0.04wt%.

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