Method for recovering valuable components from hydrolysis mother liquor of titanium dioxide prepared by chlorination leaching method

Abstract

The present invention discloses a method for recovering valuable components in a hydrolysis mother liquor prepared by a chlorination leaching process for titanium dioxide. The method heats and concentrates the titanium hydrolysis mother liquor obtained by filtering hydrated titanium dioxide prepared by a titanium liquid hydrolysis process. 4+ Completely hydrolyze and add a certain amount of sulfuric acid to precipitate calcium ions in the form of calcium sulfate, condense and recover hydrochloric acid, filter to obtain the perovskite composite material and concentrated mother liquor. 2+ Oxidized to Fe 3+ The valuable component Fe in the concentrated mother liquor was concentrated by step precipitation method with pH adjustment. 3+ 、Al 3+ 、Mn 2+ Mg 2+ The invention realizes the recycling and utilization of hydrochloric acid and aluminum compound, and the production process is environmentally friendly. Iron oxide powder, manganese hydroxide, magnesium hydroxide and sodium chloride by-products are produced, and the added value of the products is increased.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide production, and in particular to a green and high value-added method for preparing titanium dioxide by using a chlorination leaching method of titanium concentrate or titanium middlings. Background Art

[0002] Titanium dioxide refers to a white powder product with excellent pigment properties, whose main chemical component is titanium dioxide (TiO2) and particle size is 200-350nm. It is obtained by post-treatment with organic, inorganic or composite coatings. It is one of the most important inorganic chemical raw materials and is widely used in industrial fields such as coatings, plastics, papermaking, catalysis, rubber, ink, chemical fiber, and ceramics.

[0003] Wet-process titanium dioxide production technologies include sulfuric acid and hydrochloric acid (chloride leaching). Sulfuric acid is a mature technology with decades of experience, while chloride leaching is currently under development and is beginning to gain application. The primary titanium raw material for chloride leaching is titanium concentrate. One method involves using hydrochloric acid to decompose the titanium concentrate and iron powder to produce an acid-dissolved slurry. Titanium exists in the solution as titanium oxychloride, while other hydrochloric acid-soluble impurities decompose into soluble chloride salts, primarily ferrous, calcium, magnesium, manganese, and trivalent aluminum salts. Undecomposed minerals remain in the solution as solid impurities and are removed by filtration. The filtrate is then finely filtered to produce a titanium solution. The titanium solution undergoes freeze crystallization to separate ferrous chloride tetrahydrate to remove the majority of the ferrous iron, concentrate the titanium solution, hydrolyze the concentrated titanium solution to produce hydrated titanium dioxide, filter, wash, calcine, and perform post-processing to produce pigment-grade titanium dioxide. The filtrate obtained after filtering the concentrated titanium liquid hydrolysis slurry is called titanium hydrolysis mother liquor. The currently available method is to prepare low-grade ferric oxide powder that absorbs hydrochloric acid and contains oxides such as calcium, magnesium, manganese, and aluminum through spray roasting and absorption. The ferric oxide powder has a high impurity content and is difficult to be used directly as an ironmaking raw material. Alternatively, the titanium hydrolysis mother liquor can be treated by addition and subtraction neutralization precipitation method. Hydrochloric acid cannot be recovered, resulting in a large amount of waste residue and a large amount of waste salt solution that is difficult to handle. The second method for producing titanium dioxide is to extract and separate the titanium liquid obtained by acid decomposition and filtration of titanium concentrate. 4+ and Fe 2+ 、Fe 3+ , Ca 2+ Mg 2+ 、Al 3+The refined titanium liquid is treated with hydrolysis or spray heating hydrolysis, filtration and washing, drying, calcination and post-treatment to obtain titanium dioxide powder by hydrochloric acid method. The typical process is the American ANI method (patents such as US6440383), with the extraction of titanium element as the first step. The Canadian CTL method (patents such as CA2513309) takes the extraction of iron element as the first step. There are also some literature reports on the effective separation of various metal elements from titanium element by extraction. However, the stability of titanium liquid is low and the extraction efficiency is low, the separation effect of the extractant is poor, the process flow is long, the recovery rate of hydrochloric acid is low, and the solid waste and environmental protection problems have not been completely solved, making it difficult to achieve industrialization. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to provide a method for separately recovering the valuable components contained in the titanium hydrolysis mother liquor during the production process of titanium dioxide prepared by the chloride leaching method of titanium concentrate. The method can utilize step-by-step hydrolysis, spray roasting, absorption and evaporation methods to separately recover the valuable components Ti, Ca, Cl, Fe, Al, Mn, Mg and Na contained in the titanium hydrolysis mother liquor. The products can replace part of the production raw materials and serve as by-products, thereby increasing the added value of the products and making the process environmentally friendly.

[0005] The technical solution of the present invention is: a method for recovering valuable components in a hydrolysis mother liquor prepared by a chlorination leaching method of titanium dioxide, comprising the following steps:

[0006] (1) adding sulfuric acid to the hydrolysis mother liquor under stirring, heating and concentrating, condensing and recovering hydrochloric acid, and filtering after the concentration is completed to obtain a concentrated mother liquor and a perovskite composite material;

[0007] (2) heating and stirring the concentrated mother liquor of (1) obtained in the step of stirring, introducing compressed air, adding NaOH solution, controlling the pH to be ≤3, and conducting an oxidative hydrolysis reaction at 70-95° C., filtering after completion of the reaction to obtain an iron hydroxide filter cake and an iron precipitation filtrate, dissolving the iron hydroxide filter cake and spray roasting to obtain iron oxide powder and recovering hydrochloric acid;

[0008] (3) heating and stirring the iron precipitation filtrate obtained in step (2), adding NaOH solution, controlling the pH to ≤ 4.2, and performing a hydrolysis reaction at 70-95° C., filtering after the hydrolysis is completed to obtain an aluminum hydroxide filter cake and an aluminum precipitation filtrate, and dissolving the aluminum hydroxide filter cake to produce a sodium tetrahydroxyaluminate solution;

[0009] (4) heating and stirring the aluminum precipitation filtrate obtained in step (3), adding NaOH solution, controlling the pH to ≤8.6, and performing a hydrolysis reaction at 70-95° C., filtering after the reaction is completed to obtain a manganese hydroxide filter cake and a manganese precipitation filtrate; the manganese hydroxide filter cake is dried and crushed to obtain manganese hydroxide powder;

[0010] (5) heating and stirring the manganese precipitation filtrate obtained in step (4), adding NaOH solution, controlling the pH value to ≤ 10.7, and performing a hydrolysis reaction at 70-95° C., filtering after the hydrolysis is completed to obtain a magnesium hydroxide filter cake and a magnesium precipitation filtrate, and drying and crushing the magnesium hydroxide filter cake to obtain magnesium hydroxide powder;

[0011] (6) heating and evaporating the magnesium precipitation filtrate obtained in step (5) to crystallize sodium chloride, and centrifuging to obtain sodium chloride crystals.

[0012] Furthermore, in step (1), the sulfuric acid added reacts with the Ca 2+ The molar ratio is 1:1.

[0013] Furthermore, in step (2), the oxidative hydrolysis reaction time is 15-18 hours, and in steps (3), (4) and (5), the hydrolysis reaction time is 1.5-2 hours.

[0014] Furthermore, in step (4), the method for producing sodium tetrahydroxyaluminate solution after the aluminum hydroxide filter cake is dissolved is as follows: the aluminum hydroxide filter cake is stirred and slurried with water and heated to adjust the solid content to 20%, steam is introduced into the aluminum hydroxide slurry for heating, a 15% sodium hydroxide solution is added, and the solution is stirred and dissolved to prepare a sodium tetrahydroxyaluminate solution for post-treatment of the aluminum coating of the primary titanium dioxide product, the dissolution temperature is 40-60°C, the pH is controlled to be ≥12.5 during the process and at the end point, and the reaction time is 1-1.5 hours.

[0015] Furthermore, in step (6), the method for heating and evaporating the magnesium precipitation filtrate is: pumping the magnesium precipitation filtrate into a triple-effect evaporation system, performing triple-effect evaporation using superheated steam, and transporting the supersaturated sodium chloride crystal liquid to a centrifugal separation device for separation to obtain sodium chloride crystals, and returning the filtrate to the triple-effect evaporation system through a filtrate pump.

[0016] The present invention heats and concentrates the titanium hydrolysis mother liquor obtained by filtering the titanium hydrolysis process to prepare hydrated titanium dioxide. 4+ Completely hydrolyze and add a certain amount of sulfuric acid to precipitate calcium ions in the form of calcium sulfate, condense and recover hydrochloric acid, filter to obtain the perovskite composite material and concentrated mother liquor. 2+ Oxidized to Fe 3+ The valuable component Fe in the concentrated mother liquor was concentrated by step precipitation method with pH adjustment. 3+ 、Al 3+ 、Mn 2+ Mg 2+The hydrolysis and precipitation are carried out in sequence. When the hydrolysis and precipitation of each element ion is complete and the other element ions have not yet been hydrolyzed and precipitated, the filtration and separation are carried out, and the filtrate is used for the hydrolysis and precipitation of the next element ion. The iron hydroxide filter cake obtained by filtering in the iron precipitation process is dissolved online in a plate and frame filter press using the leaching mother liquor produced in the porous silicon-titanium composite material preparation station of the previous process. The prepared ferric chloride solution is subjected to spray roasting and acid absorption processes to prepare iron oxide powder and iron salt roasting to absorb hydrochloric acid, and the absorbed hydrochloric acid is used as a leaching acid or analytical acid. The aluminum hydroxide filter cake is added with sodium hydroxide solution and stirred and dissolved to prepare a tetrahydroxyaluminate sodium solution for aluminum coating post-treatment, which replaces the sodium aluminate raw material. The manganese hydroxide and magnesium hydroxide filter cakes are dried and crushed as by-products. The magnesium precipitation filtrate is a sodium chloride solution, which is evaporated to prepare a sodium chloride product by triple effect evaporation.

[0017] Titanium hydrolysis mother liquor is obtained by leaching titanium concentrate and titanium middlings with hydrochloric acid and HCl, filtering the leaching slurry, filtering the leachate, freezing crystallizing and separating ferrous chloride, concentrating the clear titanium liquid, hydrolyzing the concentrated titanium liquid to prepare hydrated titanium dioxide, filtering and washing, and contains free hydrochloric acid, incompletely hydrolyzed Ti 4+ And dissolved chloride salts of Ca, Fe, Al, Mn, Mg, and Na. According to the calcium ion concentration in the hydrolysis mother liquor, Ca is added to the titanium hydrolysis mother liquor. 2+ / SO4 2- The molar ratio of 1:1 is stoichiometric sulfuric acid solution, the titanium hydrolysis mother liquor is heated and concentrated in a concentration kettle, the mother liquor is concentrated to 12-18% of the original volume, the gas phase is condensed and absorbed to obtain condensed absorption acid, Ti 4+ Completely hydrolyzed to hydrated titanium dioxide, Ca 2+ The solution is precipitated with CaSO4 and filtered to obtain a calcium titanium composite and a concentrated mother liquor for iron precipitation. The calcium titanium composite can be used as a filler in the plastics, rubber and other industries after drying and calcining at 650±50℃.

[0018] The concentrated mother liquor of iron precipitation is heated and stirred in the iron precipitation reactor, and compressed air is introduced through the high-efficiency bubble distributor in the reactor. First, the oxygen in the compressed air is used to separate the Fe 2+ Partially oxidized to Fe 3+ :4FeCl2+O2+4HCl=4FeCl3+2H2O; the free HCl and Fe in the concentrated mother liquor 3+ Hydrolysis produces Fe 2+ The oxidation process requires the addition of excess HCl to neutralize the NaOH solution and precipitate iron hydroxide: FeCl3+3H2O=Fe(OH)3+3HCl, HCl+NaOH=NaCl+H2O. The hydrolysis temperature is 70-95℃, and the pH is controlled to be ≤3 during the process and at the end point. 3+Metal ions other than those in the original material remain unhydrolyzed. After hydrolysis, the slurry is filtered in a modified plate-and-frame filter press, where the ferric hydroxide filter cake is dissolved online using a mother liquor. This mother liquor is derived from the primary acid leaching residue of titanium concentrate, which is then leached with hydrochloric acid and HCl to produce a porous silicon-titanium composite. This mother liquor contains free acid and ferrous chloride. The ferric chloride solution used to dissolve the ferric hydroxide online undergoes a spray roasting and acid absorption process to produce iron oxide powder and iron salts, which are then roasted and absorbed with hydrochloric acid.

[0019] After iron precipitation, the filtrate is stirred and heated in the aluminum precipitation reactor. 3+ The HCl generated by hydrolysis is simultaneously added into NaOH solution to neutralize and precipitate aluminum hydroxide. The hydrolysis temperature is 70-95℃, and the pH is controlled to be ≤4.2 during the process and at the end point. 3+ The aluminum hydroxide filter cake and the filtrate after aluminum precipitation are obtained by filtration. The aluminum hydroxide filter cake is stirred and slurried in an aluminum dissolving reactor with water. Utilizing the amphoteric properties of aluminum hydroxide, the aluminum dissolving reactor is heated and stirred and dissolved with sodium hydroxide solution to prepare a sodium tetrahydroxyaluminate solution for the post-treatment of the aluminum coating of the primary titanium dioxide product. The dissolution temperature is 40-60°C, and the pH is controlled to be ≥12.5 during the process and at the end point.

[0020] The filtrate after aluminum precipitation is stirred and heated in the manganese precipitation reactor. 2+ The HCl generated by hydrolysis is simultaneously neutralized by adding a NaOH solution to precipitate manganese hydroxide. The hydrolysis temperature is 70-95°C, and the pH is controlled to be ≤8.6 during the process and at the end point. The manganese hydroxide filter cake and the filtrate after precipitation are obtained by filtration. The manganese hydroxide filter cake is dried and crushed to obtain manganese hydroxide powder.

[0021] The filtrate after manganese precipitation is stirred and heated in the magnesium precipitation reactor. 2+ The HCl generated by hydrolysis is simultaneously neutralized by the addition of a NaOH solution to precipitate magnesium hydroxide. The hydrolysis temperature is 70-95°C, and the pH is controlled to be ≤10.7 during the process and at the end point. The hydrolysis slurry is filtered to obtain a magnesium hydroxide filter cake and a sodium chloride salt solution. The magnesium hydroxide filter cake is dried and pulverized to obtain magnesium hydroxide powder.

[0022] The magnesium precipitation filtrate is crystallized into sodium chloride product through a triple-effect evaporation device, and the evaporated condensed water is used in the production system.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention realizes the comprehensive utilization of vanadium-titanium magnetite resources, develops methods for separately recovering the valuable components Ti, Ca, Cl, Fe, Al, Mn, Mg and Na contained in the titanium hydrolysis mother liquor, and cyclically recovers hydrochloric acid and aluminum compounds. The production process is environmentally friendly, and iron oxide powder, manganese hydroxide, magnesium hydroxide and sodium chloride by-products are produced, thereby increasing the added value of the products. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0026] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0027] Example 1

[0028] The contents of the components in the titanium hydrolysis mother liquor in this embodiment are as follows:

[0029] Free HCl: 165.66 g / L, TiO2: 4.34 g / L, Fe 2+ :15.09g / L,Ca 2+ :2.18g / L,Al 3+ :1.18g / L,Mg 2+ :4.22g / L,Mn 2+ :1.33g / L,Na + :1.67g / L, total Cl - :206.01g / L.

[0030] The titanium hydrolysis mother liquor from the titanium hydrolysis mother liquor storage tank is metered into the hydrolysis mother liquor concentration reactor through the mother liquor feed pump, with a feed rate of 17.41m 3 / hr, start stirring and add 70% mass concentration sulfuric acid, the feed rate is 74L / hr. Turn on the steam, use the jacket indirect heat exchange method to heat the titanium hydrolysis mother liquor to boiling, condense and recover the hydrolysis mother liquor condensed acid, about 14.70m 3 / hr, pumped to the hydrated titanium dioxide secondary wash acid storage tank, with a free HCl concentration of 192.68 g / L, for washing the hydrated titanium dioxide filter cake.

[0031] The concentrated mother liquor flows into the concentrated mother liquor storage tank, and the discharge volume is 2.68m 3 / hr. The concentrated mother liquor in the concentrated mother liquor storage tank is pumped to the diaphragm filter press for filtration, and the filtrate is pumped to the iron precipitation liquid storage tank. The filter residue is a calcium titanium composite material, which can be used as a filler in the plastics, rubber and other industries after drying and calcining at 650±50℃. The content of each component in the concentrated mother liquor clear liquid is: free HCl: 15.51g / L, Fe 2+ :98.05g / L,Al 3+ :7.67g / L,Mg 2+ :27.45g / L,Mn 2+ :8.62g / L,Na + :10.64g / L, total Cl - :272.37g / L.

[0032] The 2.6m3 in the iron precipitation liquid storage tank 3 The concentrated mother liquor for iron precipitation is pumped into the iron precipitation reactor, stirred and heated, and compressed air is introduced through the high-efficiency bubble distributor in the reactor. First, the oxygen in the compressed air is used to precipitate Fe under the acidic conditions of the concentrated mother liquor itself. 2+ Partially oxidized to Fe 3+ , free HCl and Fe 3+ Hydrolysis produces Fe 2+ The excess HCl in the oxidation reaction is neutralized by adding 15% NaOH solution to precipitate ferric hydroxide. The hydrolysis temperature is 70-95℃, and the oxidation-hydrolysis reaction time is 15-18 hours. The pH is controlled to be ≤3 during the process and at the end point. 3+ Other metal ions are not hydrolyzed.

[0033] After the hydrolysis is completed, the slurry is pumped to the modified plate and frame filter press for filtration. The filtrate is pumped to the aluminum precipitation liquid storage tank, about 2.75m 3 The content of each component in the aluminum precipitation liquid is: Al 3+ :7.42g / L,Mg 2+ :26.62g / L,Mn 2+ :8.28g / L,Na + :101.39g / L, total Cl - :269.27g / L.

[0034] The iron hydroxide filter cake is dissolved online in a plate and frame filter press with a leaching mother liquor. The leaching mother liquor used is the leaching mother liquor obtained by filtering and separating the porous silicon-titanium composite prepared by acid leaching residue of titanium concentrate and chlorination leaching with hydrochloric acid and HCl. Its composition is: free HCl: 156.49 g / L, Fe 2+ : 88.35g / L, the amount of leaching mother liquor used is 2.43m 3 The acidic ferric chloride solution obtained by dissolving ferric hydroxide online is pumped to the ferric chloride solution intermediate storage tank.

[0035] The outlet valve of the intermediate storage tank for the ferric chloride solution was opened, and the ferric chloride solution was sprayed into the roasting furnace. There, it came into contact with hot air at a temperature of 750-850°C and reacted with O2 and H2O to decompose into a mixture of H2O and HCl gas and ferric oxide powder. The absorption acid storage tank was opened, and the washing acid from washing the hydrated titanium dioxide filter cake was used as the absorption liquid for the falling film absorption system in the spray roasting section to produce regenerated acid. The regenerated acid was pumped into the regenerated acid storage tank for chlorination leaching, with a regenerated acid concentration of 348.32 g / L. 718.48 kg of ferric oxide powder was obtained.

[0036] The 2.75m3 aluminum precipitate storage tank 3 After iron precipitation, the filtrate is pumped into a volume of 4m3 The aluminum precipitation reactor is stirred and heated by steam jacket, Al 3+ The HCl generated by hydrolysis is simultaneously added with 15% NaOH solution to neutralize and precipitate aluminum hydroxide. The hydrolysis temperature is 70-95°C and the hydrolysis reaction time is 1.5-2 hours. The pH is controlled to be ≤4.2 during the process and at the end point. 3+ Other metal ions are not hydrolyzed.

[0037] Al 3+ After the hydrolysis is completed, the aluminum slurry is pumped to the plate and frame filter press for filtration. The filtrate is pumped to the manganese precipitate storage tank, about 2.8m 3 The content of each component in the manganese precipitation solution is: Mg 2+ :26.12g / L,Mn 2+ :8.24g / L,Na + :120.35g / L, total Cl - :268.25g / L.

[0038] The aluminum hydroxide filter cake obtained by filtration and washing is shoveled into a 2m 3 The aluminum hydroxide filter cake obtained from the multiple reaction processes is stirred and slurried with water and heated to adjust the solid content to 20%. A steam valve is opened to introduce steam into the aluminum hydroxide slurry for heating. A sodium hydroxide feed pump is started to add a 15% sodium hydroxide solution, which is stirred and dissolved to prepare a sodium tetrahydroxyaluminate solution for post-treatment of the aluminum coating of the primary titanium dioxide product. The dissolution temperature is 40-60°C, and the pH is controlled to be ≥12.5 during the process and at the end point. The reaction time is 1-1.5 hours.

[0039] Open the manganese precipitation liquid storage tank and pour 2.8m 3 After aluminum precipitation, the filtrate is pumped into a volume of 4m 3 In the manganese precipitation reactor, start stirring, open the steam regulating valve to heat the steam jacket, Mn 2+ The HCl generated by hydrolysis is simultaneously added with a 15% NaOH solution to neutralize and precipitate manganese hydroxide. The hydrolysis temperature is 70-95° C., the pH is controlled to be ≤8.6 during the process and at the end point, and the hydrolysis reaction time is 1.5-2 hours.

[0040] Mn 2+ After the hydrolysis is completed, the manganese slurry is pumped to the plate and frame filter press for filtration. The filtrate is pumped to the magnesium precipitation liquid storage tank, about 2.82m 3 The content of each component in the manganese precipitation solution is: Mg 2+ :26.08g / L,Na + :126.43g / L, total Cl - :266.43g / L.

[0041] The manganese hydroxide filter cake obtained by filtering and washing is dried and crushed to obtain manganese hydroxide powder.

[0042] 2.82m3 of manganese precipitation solution in the storage tank 3 After manganese precipitation, the filtrate is pumped into a volume of 4m 3 In the magnesium precipitation reactor, start stirring, open the steam regulating valve to heat the steam jacket, Mg 2+ HCl generated by hydrolysis is simultaneously added with 8% NaOH solution to neutralize and precipitate magnesium hydroxide. The hydrolysis temperature is 70-95° C., the pH is controlled to be ≤10.7 during the process and at the end point, and the hydrolysis reaction time is 1.5-2 hours.

[0043] Mg 2+ After the hydrolysis is completed, the magnesium slurry is pumped to the plate and frame filter press for filtration and washing. The filtrate is pumped to the sodium chloride liquid storage tank, about 3.55m 3 The content of each component in the magnesium precipitation solution is: Na + :140.12g / L,Cl - :211.73g / L.

[0044] The magnesium hydroxide filter cake is filtered and washed, and then dried and crushed to obtain magnesium hydroxide powder.

[0045] Brine from the sodium chloride storage tank is metered into the triple-effect evaporation system via a brine feed pump, where it is evaporated using superheated steam. The supersaturated sodium chloride crystals are then transferred to a centrifugal separator for separation. The filtrate is then returned to the triple-effect evaporation system via a filtrate pump. The resulting sodium chloride crystals have a moisture content of 3-5%.

Claims

1. A method for recovering valuable components from the hydrolysis mother liquor of titanium dioxide prepared by the chlorination leaching method, characterized in that: The steps include: (1) adding sulfuric acid to the hydrolysis mother liquor under stirring, heating and concentrating, condensing and recovering hydrochloric acid, and filtering after the concentration is completed to obtain a concentrated mother liquor and a perovskite composite material; (2) heating and stirring the concentrated mother liquor of (1) obtained in the step of stirring, introducing compressed air, adding NaOH solution, controlling the pH to be ≤3, and conducting an oxidative hydrolysis reaction at 70-95° C., filtering after completion of the reaction to obtain an iron hydroxide filter cake and an iron precipitation filtrate, dissolving the iron hydroxide filter cake and spray roasting to obtain iron oxide powder and recovering hydrochloric acid; (3) heating and stirring the iron precipitation filtrate obtained in step (2), adding NaOH solution, controlling the pH to ≤ 4.2, and performing a hydrolysis reaction at 70-95° C., filtering after the hydrolysis is completed to obtain an aluminum hydroxide filter cake and an aluminum precipitation filtrate, and dissolving the aluminum hydroxide filter cake to produce a sodium tetrahydroxyaluminate solution; (4) heating and stirring the aluminum precipitation filtrate obtained in step (3), adding NaOH solution, controlling the pH to ≤8.6, and performing a hydrolysis reaction at 70-95° C., filtering after the reaction is completed to obtain a manganese hydroxide filter cake and a manganese precipitation filtrate; the manganese hydroxide filter cake is dried and crushed to obtain manganese hydroxide powder; (5) heating and stirring the manganese precipitation filtrate obtained in step (4), adding NaOH solution, controlling the pH value to ≤ 10.7, and performing a hydrolysis reaction at 70-95° C., filtering after the hydrolysis is completed to obtain a magnesium hydroxide filter cake and a magnesium precipitation filtrate, and drying and crushing the magnesium hydroxide filter cake to obtain magnesium hydroxide powder; (6) heating and evaporating the magnesium precipitation filtrate obtained in step (5) to crystallize sodium chloride, and centrifuging to obtain sodium chloride crystals.

2. The method according to claim 1, characterized in that In step (1), the added sulfuric acid reacts with the Ca in the hydrolysis mother liquor. 2 + The molar ratio is 1:

1.

3. The method according to claim 1, characterized in that In step (2), the oxidative hydrolysis reaction time is 15-18 hours, and in steps (3), (4) and (5), the hydrolysis reaction time is 1.5-2 hours.

4. The method according to claim 1, wherein In step (3), the method for producing sodium tetrahydroxyaluminate solution after the aluminum hydroxide filter cake is dissolved is as follows: the aluminum hydroxide filter cake is stirred and slurried with water and heated to adjust the solid content to 20%, steam is introduced into the aluminum hydroxide slurry for heating, a sodium hydroxide solution with a concentration of 15% is added, and the solution is stirred and dissolved to prepare a sodium tetrahydroxyaluminate solution for post-treatment of aluminum coating of titanium dioxide primary product, the dissolution temperature is 40-60°C, the pH is controlled to be ≥12.5 during the process and at the end point, and the reaction time is 1-1.5 hours.

5. The method according to claim 1, characterized in that In step (6), the method for heating and evaporating the magnesium precipitation filtrate is as follows: the magnesium precipitation filtrate is pumped into a triple-effect evaporation system, triple-effect evaporation is performed using superheated steam, the sodium chloride crystal liquid reaching a supersaturated state is transported to a centrifugal separation device for separation to obtain sodium chloride crystals, and the filtrate is returned to the triple-effect evaporation system through a filtrate pump.

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