Water-saving method in red iron oxide preparation process

Abstract

The application discloses a water-saving method in the preparation process of iron oxide red, which is characterized by washing the filter cake formed after pressure filtration in the process of pressure filtration and washing of iron oxide red slurry, wherein the washing comprises: first washing the iron oxide red filter cake with secondary washing water, and the water after washing the filter cake forms primary washing water; second washing the iron oxide red filter cake with tertiary washing water, and the water after washing the filter cake forms secondary washing water; third washing the iron oxide red filter cake with clean water, and the water after washing the filter cake forms tertiary washing water; and the total amount of clean water used for washing each batch of iron oxide red filter cake is: when the conductivity of the primary washing water exceeds the rated value, the primary washing water is used for slaking the calcined iron oxide red, and the application fully utilizes the washing water at each stage and maximally saves the amount of clean water.

Description

Technical Field

[0001] This invention relates to a method for preparing iron oxide red, and particularly to a method for saving washing water during the washing process of iron oxide red filter cake. Background Technology

[0002] Iron oxide red, also known as ferric oxide red or iron red, is a deep red or red powder. It is currently the most widely used inorganic dyeing pigment in the world. Its chemical formula is α-Fe₂O₃, its melting point is 1565℃, it is non-toxic, and insoluble in water. It is currently the inorganic pigment with the second largest production and usage after titanium dioxide, and it is also the product with the largest production and usage among iron oxide pigments (iron red, iron yellow, iron black, etc.). It has good lightfastness, weather resistance, hiding power, and high abrasion resistance and corrosion resistance, and is widely used in building materials, coatings, plastics, rubber, ceramics, glass, inks, and lithium battery industries. Currently, the traditional preparation methods for iron oxide red include dry processes and wet processes. Dry processes include the calcination method of ferrous sulfate, the calcination method of iron yellow, the calcination method of iron black, and the calcination method of ferrous sulfate-soda ash. Wet processes include the sulfate method, the nitrate method, and the mixed acid salt method.

[0003] In the wet process of producing iron oxide red, the calcined iron oxide red is fed into a slurry tank to form a primary slurry. The primary slurry is then ground, dissolved, mixed, filtered, and washed to obtain an iron oxide red filter cake. The iron oxide red filter cake is then dried and pulverized to obtain the finished iron oxide red product.

[0004] After the initial slurry is filtered, the mother liquor is discharged from the filter press. This mother liquor contains certain water-soluble substances, and the filter cake formed after filtration also contains water-soluble substances. These water-soluble substances significantly affect the quality of the iron oxide red product. Therefore, the filter cake needs to be washed to dissolve as much of the water-soluble substances as possible, significantly reducing their content to meet the standard requirements for iron oxide red products. According to GB / T 1863-2008 Iron Oxide Pigments, the purity of iron oxide red products is expressed by the content of ferric oxide, with specific requirements: Class A not less than 95%, Class B not less than 70%, Class C not less than 40%, and Class D not less than 10%. Regarding the water-soluble content, the standard for higher-quality Type I red and brown products stipulates that the mass fraction of water-soluble substances (measured after drying at 105℃) ≤ 0.3%, and the total mass fraction of water-soluble oxides and sulfates (expressed as Cl) ≤ 0.3%. - and SO4 -2 (Indicates) ≤0.1%.

[0005] There are many documents on washing iron oxide red filter cakes. Chinese patent "A Method for Water Washing and Separation of High-Purity Iron Oxide Red" (publication number CN104445434B) discloses a method for water washing and separation of high-purity iron oxide red. First, iron oxide red is mixed with water and ground. Then, an iron-containing electrolyte solution is added to the water-washed iron oxide red slurry and stirred. After the slurry is allowed to stand, the lower layer of settled iron oxide red material and the upper layer of water washing liquid are separated. The filter cake after pressing the lower layer of settled iron oxide red material is dried. The upper layer of water washing liquid is separated into filtrate and solid iron oxide red material using a filtration device, and the filtrate is discharged. At the same time, the liquid and solid iron oxide red material separated by the filter press are recovered and reused. This method can reduce the loss rate of iron oxide red to less than 1% and solve the environmental problem of wastewater discharge.

[0006] The invention, published under CN202322365650.1, provides a method for manufacturing an iron oxide red washing device. The device involves adding an iron oxide red solution and a chloride ion removal agent to a stirring tank via a dosing pipe. Then, an electric motor and an electromagnetic rod are used to adsorb and remove impurities from the iron oxide red. Finally, the electromagnetic rod, after adsorbing impurities, is transferred to a washing tank for further cleaning, thus achieving both water washing and impurity separation of the iron oxide red.

[0007] The utility model relates to a filter cake washing system, with application number CN202320128275.8. The system includes a filtration system, an atomization system, and a positive pressure system. The atomization system can atomize and transfer the washing liquid to the filtration system, and the positive pressure system can inject the atomized washing liquid into the filter cake. This system can achieve uniform washing of the filter cake. The system is also detachable and can provide all-round spraying and washing.

[0008] In Chinese patent CN116216680B, "A Method for Preparing Lithium Iron Phosphate Cathode Material Using Industrial Waste Iron Sludge", paragraphs

[0049] and

[0050] of its specification disclose S4, the filtration and washing process: the above-mentioned iron slurry is filtered and the filter cake is washed with pure water. The washing endpoint is that the conductivity of the rinsing water is ≤300μs / cm (the actual measurement in this case was 285μs / cm). Obviously, pure water is used to ensure the washing effect. However, such a low conductivity of the rinsing water is suspicious, because the conductivity of ordinary tap water is also higher than 1000μs / cm.

[0009] Some technologies for the comprehensive utilization of wastewater generated during the washing of iron oxide red filter cake have also been reported. For example, the paper "Research on Wastewater Treatment and Resource Utilization of Iron Oxide Red Plant" by Ge Qilong focuses on the optimal process parameters for treating acidic wastewater from an iron oxide red plant, demonstrating the feasibility of using the wastewater to produce iron oxide red pigment and determining the optimal reaction conditions. Experimental results show that after treatment with NaOH solution, the precipitated iron-containing sludge can be used as iron oxide red seed crystals for the production of iron oxide red pigment, achieving a certain degree of resource utilization of the wastewater.

[0010] "Treatment and Utilization of Wastewater from Iron Oxide Production" by Wang Handong mentions that solids, ammonia nitrogen, sulfate, etc., in washing wastewater can be separated and recovered. The treated water can be recycled in the iron oxide production process without affecting the quality of the iron oxide product. The remaining washing wastewater can be used to recover iron oxide through fine filtration, drying, and roasting. After a series of treatments such as neutralization and precipitation with lime milk to remove sulfate, the filtrate can also obtain ammonia water with a mass fraction of about 15%, which can be sold as a product or used in iron oxide production.

[0011] In summary, the existing technology mentions washing the iron oxide red filter cake with pure water or clean water, which leads to a large amount of pure water and clean water being used. Furthermore, the comprehensive utilization of the washing water for the iron oxide red filter cake is not addressed in the washing process itself. Summary of the Invention

[0012] Obviously, the amount of water used for washing the iron oxide red filter cake is a core issue directly related to production costs. There is no research on how to minimize the use of water while ensuring the washing effect of the iron oxide red filter cake. Therefore, the purpose of this invention is to provide a method that can effectively remove water-soluble substances by utilizing the washing water of the iron oxide red filter cake, while minimizing the use of water.

[0013] The technical solution adopted by this invention to solve its technical problem is:

[0014] The inventors discovered that the relationship between conductivity and water-soluble content is not a fixed value; it is influenced by various factors such as the type of salt and temperature. For the washing solution of iron oxide red filter cake, at the same temperature, there is a corresponding relationship between conductivity and water-soluble content. Conductivity is an indicator of the electrolyte content in water; the more dissolved impurity ions in the water, the higher the conductivity. During the washing process of iron oxide red, as the number of washes increases, the impurity content in the washing water gradually decreases, and the conductivity also decreases accordingly. Therefore, by monitoring the conductivity changes of the first, second, and third washes, the working conditions and washing effect of the washing water can be determined. This invention designs a three-stage washing process for iron oxide red filter cake and establishes an optimal model for the amount of clean water used by utilizing the conductivity differences between different washes, thus maximizing the conservation of clean water consumption.

[0015] A water-saving method in the preparation of iron oxide red involves washing the filter cake formed after pressure filtration during the pressure filtration and washing process of the iron oxide red slurry. The washing includes:

[0016] The iron oxide red filter cake is washed for the first time with secondary wash water, and the water after washing the filter cake is called primary wash water.

[0017] The iron oxide red filter cake is washed a second time with three washes of water, and the water used to wash the filter cake is called secondary wash water.

[0018] The iron oxide red filter cake is washed a third time with clean water, and the water after washing the filter cake is called the third wash water.

[0019] The total amount of clean water used for washing each batch of iron oxide red filter cake is:

[0020]

[0021] In the formula, M is the initial total amount of water-soluble matter in the iron oxide red filter cake. std This refers to the total amount of water-soluble matter that can remain in the washed iron oxide red filter cake.

[0022] The conductivity of the secondary wash water is C2, and the amount of secondary wash water used is V2;

[0023] The conductivity of the three washes is C3, and the amount of water used in the three washes is V3.

[0024] The amount of clean water used is V0, and the conductivity of the clean water is C0;

[0025] This formula is derived based on the principles of water-soluble migration and mass conservation. It is used to calculate the amount of washing water required to achieve water conservation and meet the water-soluble content requirements of the product. The derivation process is as follows:

[0026] 1. First wash (use two rinses)

[0027] According to the law of conservation of mass, the decrease in water-soluble matter in the filter cake during the first wash is equal to the increase in water-soluble matter in the second wash water. Therefore, we can obtain: M - M1 = k1C2V2, where M1 is the water-soluble matter content in the filter cake after the first wash.

[0028] 2. Second wash (use three washes)

[0029] Similarly, during the second wash, M1-M2=k2C3V3, where M2 is the water-soluble content in the filter cake after the second wash.

[0030] 3. Third wash (using clean water)

[0031] During the third wash, M2-M std =k3C0V0

[0032] Based on the final washing requirements, we know that when the conductivity of the water after three washes reaches the rated conductivity C... rated At that time, the washing is complete, that is, C3 = C rated

[0033] By combining the above three equations, we can obtain:

[0034]

[0035] k1 represents the migration coefficient of water-soluble substances during the first wash, k2 during the second wash, and k3 during the third wash. Simply put, it indicates the proportion of water-soluble substances that can migrate from the filter cake during the washing process, given a unit conductivity of wash water and a unit volume. For example, k1, representing the migration coefficient of water-soluble substances during the first wash, reflects the migration of water-soluble substances in the filter cake under the influence of the second wash water. Similarly, k2, representing the migration coefficient of water-soluble substances during the second wash, reflects the migration of water-soluble substances in the filter cake under the influence of the third wash water; and similarly, k3, representing the migration coefficient of water-soluble substances during the third wash, reflects the migration of water-soluble substances in the filter cake under the influence of clean water.

[0036] From the formula derivation process, the unit of the water-soluble matter migration coefficient is... From a mass transfer perspective, the washing process is a process of mass transfer between phases, namely the filter cake and the wash water (or purified water). When the wash water (or purified water) comes into contact with the filter cake, water-soluble substances are transferred from the filter cake phase and the residual mother liquor in the filter cake to the wash water (or purified water) phase. The rate of this process is affected by factors such as the interfacial area, concentration difference, and mass transfer coefficient. The water-soluble substance migration coefficient can be understood as a coefficient that integrates these mass transfer factors. It reflects the efficiency of water-soluble substances being transferred from the filter cake to the washing liquid under specific washing conditions, such as the properties of the wash water (or purified water) and the state of the filter cake. Through numerous experiments and explorations, the inventors obtained the water-soluble substance migration coefficient k1 for the first wash as follows: The migration coefficient k2 of water-soluble substances during the second wash is The migration coefficient k3 of water-soluble substances during the third wash is

[0037] To more accurately adjust the amounts of secondary, tertiary, and clean water while simultaneously achieving the desired washing effect—that is, minimizing the water-soluble content in the filter cake after washing—it is necessary to consider the conductivity differences between the primary and secondary wash water, and between the secondary and tertiary wash water. Only when these two differences meet certain conditions can the tertiary wash water be used for the second wash of the filter cake, or vice versa. If the conductivity differences do not meet the requirements, clean water should be added to the tertiary or secondary wash water to adjust their conductivity, ensuring the conductivity differences meet the requirements and achieving full utilization of the tertiary and secondary wash water. Furthermore, the amounts of tertiary and secondary wash water should be carefully considered to minimize the total amount of clean water used for the third wash of the filter cake and the amount added to the secondary and tertiary wash water.

[0038] Therefore, after adding clean water to the secondary and / or tertiary rinse water, the total amount of clean water used is:

[0039] V total =V add2 +V add3 +V0

[0040] It should also satisfy:

[0041]

[0042] In the formula, V total V is the total amount of clean water used. add2 V is the amount of clean water added during the second rinse. add3 To replenish the amount of clean water added during the three rinses, This represents the minimum permissible difference in conductivity between the primary and secondary wash water. This represents the minimum permissible difference in conductivity between the secondary and tertiary washes.

[0043] The derivation of this formula is as follows:

[0044] 4. Define the conductivity difference.

[0045] Let the difference in conductivity between the primary and secondary wash water be ΔC. 1-2 =C1-C2

[0046] Let the difference in conductivity between the secondary and tertiary wash water be ΔC. 2-3 =C2-C3

[0047] 5. Set the difference requirement

[0048] Assume there exists a minimum permissible difference in conductivity between the primary and secondary wash water. And a minimum permissible difference in conductivity between the secondary and tertiary wash water.

[0049] when and Only then can the previous washing process be carried out, that is, the filter cake is washed for the first time with secondary wash water and for the second time with tertiary wash water.

[0050] 6. Consider adding clean water to adjust conductivity.

[0051] like Let V be the volume of clean water that needs to be added to the secondary wash water. add2 Then we have:

[0052]

[0053] The final solution yields:

[0054]

[0055] Similarly, if Let V be the volume of clean water that needs to be added to the secondary wash water. add3 Then we have:

[0056]

[0057] The final solution yields:

[0058]

[0059] The total amount of clean water used, including the water added for the second and third rinses, and the clean water used for the final third rinse, is V. total =V add2 +V add3 +V0, to make V total Minimum, V needs to be considered comprehensively. add2 Vadd3 The relationship between V0 and V0 is optimized and adjusted based on actual conductivity and factors such as water-soluble matter migration.

[0060] The conductivity of the purified water is C0, which is 1250 μs / cm. The conductivity of the three-wash water is C3 ≤ 9800 μs / cm, which is also the rated conductivity of the three-wash water. A conductivity less than or equal to this rated conductivity indicates that the iron oxide red filter cake meets the quality requirements after washing. The conductivity of the secondary wash water is C2 ≤ 16000 μs / cm. A conductivity less than or equal to this can be used to perform the first washing of the iron oxide red filter cake.

[0061] The minimum permissible difference in conductivity between the primary and secondary wash water. The minimum permissible difference in conductivity between the secondary and tertiary wash water.

[0062] When the conductivity of the primary wash water exceeds 32000 μs / cm, the primary wash water is introduced into the slurry tank to slurry the calcined iron oxide red.

[0063] The primary wash water, secondary wash water, and tertiary wash water are stored in primary wash water tank, secondary wash water tank, and tertiary wash water tank, respectively, while clean water is stored in a clean water tank. In the initial stage of washing the iron oxide red filter cake, i.e., when there is no primary wash water in the primary wash water tank, the iron oxide red filter cake is washed with clean water for the first time to form primary wash water, which is then stored in the primary wash water tank. In the initial stage of washing the iron oxide red filter cake, i.e., when there is no secondary wash water in the secondary wash water tank, the iron oxide red filter cake is washed with clean water for the second time to form secondary wash water, which is then stored in the secondary wash water tank. In the initial stage of washing the iron oxide red filter cake, i.e., when there is no tertiary wash water in the tertiary wash water tank, the iron oxide red filter cake is washed with clean water for the third time to form tertiary wash water, which is then stored in the tertiary wash water tank.

[0064] When the conductivity of the secondary wash water in the secondary wash water tank exceeds the rated value of 16000 μs / cm, clean water is introduced from the clean water tank into the secondary wash water tank until the conductivity is lower than the rated value of 16000 μs / cm.

[0065] When the conductivity of the third wash water in the third wash tank exceeds the rated value of 9800 μs / cm, clean water is introduced from the clean water tank into the third wash tank until the conductivity is lower than the rated value of 9800 μs / cm.

[0066] An apparatus for implementing a water-saving method in the preparation process of iron oxide red includes a filter press, a slurry tank, a mother liquor tank, a clean water tank, a primary wash water tank, a secondary wash water tank, and a tertiary wash water tank. The outlet of the slurry tank is connected to the inlet of the filter press via an inlet manifold equipped with a slurry pump and a control valve. The outlet of the filter press is connected to an outlet manifold. The outlets of the clean water tank, the primary wash water tank, and the secondary wash water tank are each connected to a wash water inlet manifold via pipes equipped with control valves and wash water pumps. The outlet of the tertiary wash water tank is connected to the inlet of the slurry tank via a return pipe equipped with a return pump. The wash water inlet manifold is connected to the inlet manifold of the filter press, and the outlet manifold is connected to the wash water outlet manifold. The wash water outlet manifold is connected to the inlets of the primary wash water tank, the secondary wash water tank, the tertiary wash water tank, and the mother liquor tank via pipes equipped with independent control valves.

[0067] The beneficial effects of this invention are:

[0068] First, this invention scientifically sets up a three-stage washing process for the iron oxide red filter cake, and makes full use of the washing water from each stage. Specifically, the iron oxide red filter cake is washed for the first time with the second wash water, and the water after washing the filter cake forms the first wash water; the iron oxide red filter cake is washed for the second time with the third wash water, and the water after washing the filter cake forms the second wash water; the iron oxide red filter cake is washed for the third time with clean water, and the water after washing the filter cake forms the third wash water; and the first wash water is reused in the slurry tank to slurry the calcined iron oxide red.

[0069] Secondly, by controlling parameters such as the total amount of water-soluble matter in the initial iron oxide red filter cake, the residual amount of water-soluble matter in the iron oxide red filter cake after washing, the conductivity of each wash water, the conductivity difference between the first and second wash water, and the conductivity difference between the second and third wash water, as well as setting the migration coefficient of water-soluble matter in each wash, a mathematical model was established to minimize the total amount of clean water used. This allows the present invention to save the maximum amount of clean water used while effectively removing water-soluble matter from the iron oxide red filter cake. Attached Figure Description

[0070] Figure 1 This is a diagram of a filter press apparatus for implementing the method of the present invention.

[0071] 1-Slurry tank, 2-Filter press, 3-Mother liquor tank, 4-Clear water tank, 5-Primary wash water tank, 6-Secondary wash water tank, 7-Tertiary wash water tank, 8-Inlet manifold, 9-Outlet manifold, 10-Return pipe, 11-Wash water inlet manifold, 12-Slurry pump, 13-Wash water outlet manifold, 14-Wash water pump, 15-Return pump, 20-Feed control valve, 21-First control valve, 22-Second control valve, 23-Third control valve, 24-Fourth control valve, 25-Fifth control valve, 26-Sixth control valve, 27-Seventh control valve. Detailed Implementation

[0072] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0073] A filter press apparatus implementing the water-saving method of the present invention includes a slurry tank 1, a filter press 2, a mother liquor tank 3, a clean water tank 4, a primary wash water tank 5, a secondary wash water tank 6, and a tertiary wash water tank 7. The filter press 2 is equipped with an inlet manifold 8, an outlet manifold 9, a wash water inlet manifold 11, and a wash water outlet manifold 13. The outlet of the slurry tank 1 is connected to the inlet of the filter press 2 via the inlet manifold 8, which is equipped with a slurry pump 12 and a feed control valve 20. The outlet of the filter press 2 is connected to the outlet manifold 9. The wash water inlet manifold 11 is connected to the inlet manifold 8 of the filter press 1. The outlet manifold 9 is connected to the wash water outlet manifold 13. The wash water outlet manifold 13 is connected to the inlet of the mother liquor tank 3 via a pipe equipped with a first control valve 21. The outlet of the clean water tank 4 is connected via a pipe equipped with a second control valve. Pipes 22 and 14 are connected to the main inlet pipe 11 of the wash water. The outlet of the tertiary wash tank 7 is connected to the main inlet pipe 11 of the wash water through a pipe equipped with a third control valve 23 and another wash water pump 14. The outlet of the secondary wash tank 6 is connected to the main inlet pipe 11 of the wash water through a pipe equipped with a fourth control valve 24 and another wash water pump 14. The main outlet pipe 13 of the wash water is connected to the inlet of the primary wash tank 5 through a pipe equipped with a fifth control valve 25. The main outlet pipe 13 of the wash water is connected to the inlet of the secondary wash tank 6 through a pipe equipped with a sixth control valve 26. The main outlet pipe 13 of the wash water is connected to the inlet of the tertiary wash tank 7 through a pipe equipped with a seventh control valve 27. The outlet of the primary wash tank 5 is connected to the inlet of the slurry tank 2 through a return pipe 10 equipped with a return pump 15.

[0074] In the initial stage of washing the iron oxide red filter cake, when there is no primary wash water in the primary wash tank 5, the iron oxide red filter cake is washed with clean water for the first time, and the resulting primary wash water is stored in the primary wash tank 5. Similarly, in the initial stage of washing the iron oxide red filter cake, when there is no secondary wash water in the secondary wash tank 6, the iron oxide red filter cake is washed with clean water for the second time, and the resulting secondary wash water is stored in the secondary wash tank 6. Finally, in the initial stage of washing the iron oxide red filter cake, when there is no tertiary wash water in the tertiary wash tank 7, the iron oxide red filter cake is washed with clean water for the third time, and the resulting tertiary wash water is stored in the tertiary wash tank 7. After the initial stage, when washing the iron oxide red filter cake again, the iron oxide red filter cake is washed with the secondary wash water for the first time, and the water remaining after washing the filter cake is the primary wash water. The iron oxide red filter cake is then washed with the tertiary wash water for the second time, and the water remaining after washing the filter cake is the secondary wash water. Finally, the iron oxide red filter cake is washed with clean water for the third time, and the water remaining after washing the filter cake is the tertiary wash water.

[0075] The total amount of clean water used for washing each batch of iron oxide red filter cake is:

[0076]

[0077] In the formula, M is the initial total amount of water-soluble matter in the iron oxide red filter cake. std This refers to the total amount of water-soluble matter that can remain in the washed iron oxide red filter cake.

[0078] The conductivity of the secondary wash water is C2, and the amount of secondary wash water used is V2;

[0079] The conductivity of the three washes is C3, and the amount of water used in the three washes is V3.

[0080] The amount of clean water used is V0, and the conductivity of the clean water is C0;

[0081] Based on the above, three embodiments and one comparative example were designed. It is assumed that the amount of iron oxide red slurry requiring filtration and washing in each embodiment and comparative example is 1 m³. 3 After the slurry was filtered and the mother liquor was discharged, the iron oxide red filter cake contained 269 kg of solution and 500 kg of iron oxide red. The total amount of water-soluble matter in the 269 kg of solution was 7.42 kg. The conductivity of the clean water was 1250 μs / cm. The highest conductivity of the three washes after the third wash, i.e., the rated conductivity of the three washes, was 9800 μs / cm.

[0082] Example 1: Conventional three-stage washing

[0083] A water-saving method in the preparation of iron oxide red involves washing the filter cake formed after pressure filtration during the pressure filtration and washing process of the iron oxide red slurry. The washing includes:

[0084] The secondary wash water from the secondary wash tank 6 is fed into the filter press 2 for the first washing of the iron oxide red filter cake. Once the wash water enters the filter cake, it begins to penetrate the pores under pressure difference. Due to the porous structure of the filter cake, the wash water flows along the pores, resulting in diffusion. At a microscopic level, the wash water comes into contact with the mother liquor in the filter cake pores and impurities on the solid surface. For soluble substances in the filter cake, due to the concentration difference, the soluble substances diffuse from the high-concentration area (the mother liquor portion of the filter cake) to the low-concentration area (the wash water). This is a spontaneous process based on physicochemical principles, conforming to the law of diffusion. During this process, the wash water gradually replaces the mother liquor in the filter cake pores, while simultaneously dissolving and carrying away soluble impurities. For iron oxide red filter cake, impurities may include some water-soluble substances such as salts, acids, and alkalis remaining from the production process. These substances will dissolve in the wash water and be gradually carried out of the filter cake as the wash water flows. Then, the water is discharged through the outlet manifold 9 to form primary wash water, which is stored in the primary wash water tank 5.

[0085] Similarly, the iron oxide red filter cake is washed a second time with the third wash water in the third wash water tank 7. The water after washing the filter cake forms the secondary wash water, which is stored in the secondary wash water tank 6.

[0086] Similarly, the iron oxide red filter cake is washed a third time with clean water from the clean water tank 4. The water after washing the filter cake forms the third wash water, which is stored in the third wash water tank 7.

[0087] In this embodiment, the initial total amount of water-soluble matter in the iron oxide red filter cake is M = 7.42 kg, and the allowable residual total amount of water-soluble matter in the iron oxide red filter cake after washing is M std =0.68kg, the conductivity of the clean water C0 = 1250μs / cm, the conductivity of the second wash water C2 = 15423μs / cm, and the conductivity of the third wash water C3 = 9753μs / cm. Secondary wash water usage V2 = 1.5 × 10 6 cm 3 The amount of water used for three washes, V3, is 1.5 × 10⁻⁶. 6 cm 3 According to the following formula,

[0088]

[0089] We obtain V0≈1.5×10 6 cm 3 .

[0090] The parameters for the three washings of the iron oxide red filter cake are shown in Table 1, and the washing effect after the three washings is shown in Table 2. The total amount of clean water used for washing was 1.5 m³. 3 The conductivity of the primary wash water is C1 = 24903 μs / cm, which does not meet the condition for reusing the primary wash water in slurry tank 1.

[0091] Example 2: Replenishing the secondary wash water with clean water (the difference in conductivity between the primary and secondary wash water)

[0092] The iron oxide red filter cake was washed according to the method in Example 1. The measured conductivity of the secondary wash water in secondary wash tank 6 was C2 = 17327 μs / cm, exceeding the rated value of 16000 μs / cm. The conductivity of the primary wash water in primary wash tank 5 was C1 = 24859 μs / cm and C0 = 1250 μs / cm. Therefore, ΔC... 1-2 =7532 μs / cm, while the minimum permissible difference in conductivity between primary and secondary wash water is... Obviously, 0.2 × 10⁻⁶ units of clean water from clean water tank 4 are added to secondary wash water tank 6. 6 cm3 After rinsing with clean water, the conductivity of the secondary wash water is C2 = 15184 μs / cm, thus causing ΔC 1-2 =9675μs / cm, which meets the conditions for reuse of secondary wash water.

[0093] In this embodiment, the initial total amount of water-soluble matter in the iron oxide red filter cake is M = 7.42 kg, and the allowable residual total amount of water-soluble matter in the iron oxide red filter cake after washing is M std =0.66kg, the conductivity of the clean water C0 = 1250μs / cm, the conductivity of the second wash water C2 = 15184μs / cm, and the conductivity of the third wash water C3 = 9700μs / cm. Secondary wash water usage V2 = 1.5 × 10 6 cm 3 The amount of water used for three washes, V3, is 1.5 × 10⁻⁶. 6 cm 3 V add2 =0.2×10 6 cm 3 According to the following formula,

[0094]

[0095] We obtain V0≈1.5×10 6 cm 3 According to V total =V add2 +V add3 +V0 yields V total =1.7×10 6 cm 3 .

[0096] Clean water was added to the secondary washing tank 6. The parameters for the three washings of the iron oxide red filter cake are shown in Table 1, and the washing results are shown in Table 2. The total amount of clean water used for washing was 1.7 m³. 3 The conductivity of the primary wash water is C1 = 24859 μs / cm, which does not yet meet the condition for reusing the primary wash water in slurry tank 1.

[0097] Example 3: Replenishing the three rinses with clean water (the difference in conductivity between the second and third rinses)

[0098] The iron oxide red filter cake was washed according to the method in Example 1. The measured conductivity of the third wash water in the third wash tank 6 was C3 = 12675 μs / cm, the conductivity of the third wash water in the third wash tank 7 exceeded the rated value of 9800 μs / cm, and the conductivity of the second wash water in the second wash tank 5 was C2 = 15078 μs / cm and C0 = 1250 μs / cm. Therefore, ΔC... 2-3=2403 μs / cm, while the minimum permissible difference in conductivity between the second and third wash water is... Obviously, 0.4 × 10⁻⁶ water was added to the third-stage washing tank 7 using clean water from tank 4. 6 cm 3 After rinsing with clean water, the conductivity of the three rinses, C3 = 9629 μs / cm, thus causing ΔC 2-3 =5449μs / cm, which meets the conditions for reuse of three wash waters.

[0099] In this embodiment, the initial total amount of water-soluble matter in the iron oxide red filter cake is M = 7.42 kg, and the allowable residual total amount of water-soluble matter in the iron oxide red filter cake after washing is M std =0.63kg, the conductivity of the clean water C0 = 1250μs / cm, the conductivity of the second wash water C2 = 15078μs / cm, and the conductivity of the third wash water C3 = 9629μs / cm. Secondary wash water usage V2 = 1.5 × 10 6 cm 3 The amount of water used for three washes, V3, is 1.5 × 10⁻⁶. 6 cm 3 V add3 =0.4×10 6 cm 3 According to the following formula

[0100]

[0101] We obtain V0≈1.5×10 6 cm 3 According to V total =V add2 +V add3 +V0 yields V total =1.9×10 6 cm 3 .

[0102] Clean water was added to the three-stage washing tank 7. The parameters for the three-stage washing of the iron oxide red filter cake are shown in Table 1, and the washing effect after washing is shown in Table 2. The total amount of clean water used for washing was 1.9 m³. 3 The conductivity of the primary wash water is C1 = 24744 μs / cm, which does not yet meet the conditions for reusing the primary wash water in slurry tank 1.

[0103] Comparative example: all three washes were done with clean water.

[0104] The iron oxide red filter cake was washed according to the method in Example 1.

[0105] In this embodiment, the initial total amount of water-soluble matter in the iron oxide red filter cake is M = 7.42 kg, and the allowable residual total amount of water-soluble matter in the iron oxide red filter cake after washing is M std =0.44kg, the conductivity of the clean water C0 = 1250μs / cm, the conductivity of the first wash water C1 = 21182μs / cm, the conductivity of the second wash water C2 = 12765μs / cm, and the conductivity of the third wash water C3 = 8982μs / cm. All three washes use a 1.5m... 3 The parameters for three washings of the iron oxide red filter cake with clean water are shown in Table 1, and the washing results are shown in Table 2. The total amount of clean water used for washing was 4.5 m³. 3 .

[0106] Table 1: Parameters of Examples 1-3 and Comparative Examples

[0107]

[0108] As can be seen from Table 1, when processing the same volume of iron oxide red slurry, the total amount of clean water used in Example 1 is equivalent to 33.3% of that in the comparative example, the total amount of clean water used in Example 2 is equivalent to 37.8% of that in the comparative example, and the total amount of clean water used in Example 3 is equivalent to 42.2% of that in the comparative example.

[0109] Table 2: Washing Effects of Examples 1-3 and Comparative Examples

[0110]

[0111] As shown in Table 2, according to GB / T 1863-2008 Iron Oxide Pigments, the washing effects of Examples 1, 2, 3, and the comparative examples, where the purity of the iron oxide red product is expressed as ferric oxide content, all reached Class A purity of not less than 95%. Regarding the water-soluble content, the standard for higher-quality Type I red and brown products specifies a water-soluble content (measured after drying at 105℃) of ≤0.3%. The total mass fraction of water-soluble oxides and sulfates (expressed as Cl- and SO42-) in Examples 1, 2, 3, and the comparative examples is also shown in the washing effects. 2- (Indicated) Only the comparative example is ≤0.1%, while Examples 1, 2, and 3 are slightly greater than 0.1%; The washing effect of Examples 1, 2, 3 and the comparative example, wherein the mass fraction of the residue (45μm) on the sieve is >0.1% and ≤1%, which meets the Type 3 standard.

Claims

1. A water-saving method in the preparation process of iron oxide red, wherein the filter cake formed after pressure filtration is washed during the pressure filtration and washing process of iron oxide red slurry, characterized in that... The washing process includes: The iron oxide red filter cake is washed for the first time with secondary wash water, and the water after washing the filter cake is called primary wash water. The iron oxide red filter cake is washed a second time with three washes of water, and the water used to wash the filter cake is called secondary wash water. The iron oxide red filter cake is washed a third time with clean water, and the water after washing the filter cake is called the third wash water. The amount of clean water used for washing each batch of iron oxide red filter cake is as follows: ； In the formula, The total amount of water-soluble matter in the initial iron oxide red filter cake is expressed in kg. The total amount of water-soluble matter allowed to remain in the washed iron oxide red filter cake, in kg; The conductivity of the secondary wash water is The unit is μs / cm; the amount of water used for the second wash is... The unit is cm³; The conductivity of the three washes is The unit is μs / cm; the amount of water used for three washes is The unit is cm³; The amount of clean water used for washing each batch of iron oxide red filter cake is: The unit is cm. 3 The electrical conductivity of pure water is The unit is μs / cm; This represents the migration coefficient of water-soluble substances during the first wash. This represents the migration coefficient of water-soluble substances during the second wash. This is the migration coefficient of water-soluble substances during the third wash; Among them, the migration coefficient of water-soluble substances during the first wash 92-96 The migration coefficient of water-soluble substances during the second wash 196–204 The migration coefficient of water-soluble substances during the third wash 885-915 ; Furthermore, the secondary and tertiary rinse water includes replenished clean water; after replenishing the secondary and / or tertiary rinse water with clean water, the total amount of clean water used is: ； It should also satisfy: ； ； In the formula, This refers to the total amount of clean water used after adding clean water to the secondary and / or tertiary rinses, expressed in cm³. 3 ; The amount of clean water added during the second rinse, expressed in cm³. 3 ; The amount of clean water added during the three rinses, expressed in cm. 3 ; The minimum permissible difference in conductivity between primary and secondary wash water, expressed in μs / cm; The minimum permissible difference in conductivity between the secondary and tertiary washes, expressed in μs / cm.

2. The water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The conductivity of the water is 1250 .

3. The water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The conductivity of the three washes ≤9800 .

4. The water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The conductivity of the secondary wash water ≤16000 .

5. A water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The minimum permissible difference in conductivity between the primary and secondary wash water. =9400 .

6. The water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The minimum permissible difference in conductivity between the secondary and tertiary wash water. =5400 .

7. A water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The conductivity of the primary wash water exceeds 32000. At that time, the washing water is introduced into the pulping tank to pulp the calcined iron oxide red.

8. A water-saving method in the preparation process of iron oxide red according to claim 1, characterized in that... The primary wash water, secondary wash water, and tertiary wash water are stored in primary wash water tank, secondary wash water tank, and tertiary wash water tank, respectively, while the clean water is stored in a clean water tank.

9. A water-saving method in the preparation process of iron oxide red according to claim 8, characterized in that... When the conductivity of the secondary wash water in the secondary wash tank exceeds the rated value of 16000 Clean water is introduced from the clean water tank into the secondary wash water tank until the conductivity drops below the rated value of 16000. .

10. A water-saving method in the preparation process of iron oxide red according to claim 8, characterized in that... When the conductivity of the third rinse water in the third rinse tank exceeds the rated value of 9800 Clean water is passed from the clean water tank into the tertiary wash tank until the conductivity drops below the rated value of 9800. .

11. A water-saving method in the preparation process of iron oxide red according to claim 8, characterized in that... In the initial stage of washing the iron oxide red filter cake, that is, when there is no primary wash water in the primary wash tank, the iron oxide red filter cake is washed with clean water for the first time to form primary wash water, which is then stored in the primary wash tank.

12. A water-saving method in the preparation process of iron oxide red according to claim 8, characterized in that... In the initial stage of washing the iron oxide red filter cake, when there is no secondary wash water in the secondary wash water tank, the iron oxide red filter cake is washed a second time with clean water to form secondary wash water, which is then stored in the secondary wash water tank.

13. A water-saving method in the preparation process of iron oxide red according to claim 8, characterized in that... In the initial stage of washing the iron oxide red filter cake, when there is no third wash water in the third wash water tank, the iron oxide red filter cake is washed a third time with clean water to form the third wash water, which is then stored in the third wash water tank.

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