Refining method of titanium dioxide by-product ferrous sulfate heptahydrate

Abstract

The invention relates to the technical field of titanium dioxide by-product refining, and particularly discloses a titanium dioxide by-product ferrous sulfate heptahydrate refining method, which comprises: S1, dissolving titanium dioxide by-product ferrous sulfate heptahydrate in pure water, adding an additive 1 capable of precipitating Al, Ti and Zn ions, and filtering to obtain a filtrate 1; s2, adding an additive 2 capable of precipitating Fe ions in the form of ferrous hydroxide into the filtrate 1, and filtering to obtain a filter cake; s3, washing the filter cake to remove foreign ions adsorbed on the surface of ferrous hydroxide, dissolving with a sulfuric acid solution, and filtering to obtain filtrate 2; and S4, adding a reducing agent into the filtrate 2 to reduce part of oxidized Fe < 3 + > into Fe < 2 + >, then evaporating, concentrating and crystallizing the solution, filtering, and drying to obtain high-purity ferrous sulfate heptahydrate. The technical problem that in the prior art, the refining and purifying process of the titanium dioxide by-product ferrous sulfate heptahydrate is caught in dilemma that either fluoride and sulfide which are not environmentally friendly and unsafe are used, or energy consumption and water treatment cost are increased is solved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide by-product refining, in particular to a method for refining ferrous sulfate heptahydrate, a titanium dioxide by-product. Background Art

[0002] Ferrous sulfate heptahydrate, commonly known as green vitriol, is an inorganic compound with the chemical formula FeSO₄·7H₂O. It is primarily used in the manufacture of water purifiers, disinfectants, iron catalysts, coal dyes, grass tanning agents, bleaching agents, wood preservatives, and compound fertilizer additives. It is a major raw material for the production of iron phosphate (a primary precursor of lithium iron phosphate). In the titanium dioxide production industry, ferrous sulfate heptahydrate is a byproduct of the sulfuric acid process. However, due to its high content of metallic impurities such as titanium, aluminum, manganese, magnesium, and zinc, its added value when sold directly is low.

[0003] To increase the added value of ferrous sulfate heptahydrate, a byproduct of titanium dioxide, the industry generally refines and purifies it. Existing methods for purifying ferrous sulfate heptahydrate, a byproduct of titanium dioxide, often employ a process that adds sulfides to remove Mn impurities and then adds fluorides to remove Mg impurities. This process offers excellent purification results and a short production process. For example, Patent Publication No. CN108046337A discloses a method for purifying ferrous sulfate, a byproduct of titanium dioxide. This method uses sulfides and fluorides to remove Mn and Mg impurities. While this process is effective, sulfides and fluorides are hazardous chemicals and can corrode equipment during production. Sulfides react easily with metals at high temperatures, forming sulfides that corrode metal components. The resulting hydrogen sulfide gas can corrode pipes, valves, and other components, shortening the equipment's service life. Fluorides, on the other hand, easily react with titanium alloys and have a strong blocking ability against reverse osmosis membranes, easily clogging membrane pores. Furthermore, sulfides and fluorides can be harmful to the health of operators and produce waste liquid containing sulfur and fluorine, which is less environmentally friendly and safe.

[0004] To avoid the use of hazardous chemicals such as sulfides and fluorides in the purification of ferrous sulfate heptahydrate, a byproduct of titanium dioxide, a process has emerged in the industry that only adds chemical reagents to remove impurities such as Ti and Al, while impurities such as Mn and Mg are purified through repeated crystallization. For example, patent publication number CN202311599862.6 discloses a method for removing impurities from ferrous sulfate, a byproduct of titanium dioxide, using this process to reduce the content of impurities such as Mg and Mn through multiple recrystallizations.

[0005] While the aforementioned process can remove impurities like Mg and Mn without using hazardous chemicals, the repeated dissolution and recrystallization process not only lengthens the purification process but also increases energy consumption and water treatment costs. Consequently, the purification process for ferrous sulfate heptahydrate, a byproduct of titanium dioxide, faces a dilemma: either use environmentally unsafe fluorides and sulfides, or increase energy consumption and water treatment costs. Summary of the Invention

[0006] The object of the present invention is to provide a method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, so as to solve the technical problem that the existing refining and purification process of ferrous sulfate heptahydrate, a by-product of titanium dioxide, is caught in the dilemma of either using fluorides and sulfides that are environmentally unfriendly and unsafe, or increasing energy consumption and water treatment costs.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, comprising the following steps: S1: dissolving ferrous sulfate heptahydrate, a by-product of titanium dioxide, in pure water, adding additive 1 that can precipitate Al and Ti impurities, and filtering to obtain filtrate 1; S2: Adding additive 2 that can precipitate Fe ions in the form of ferrous hydroxide to filtrate 1, and filtering to obtain a filter cake; S3: The filter cake in S2 is washed to remove impurities adsorbed on the surface of ferrous hydroxide, then dissolved with sulfuric acid solution and filtered to obtain filtrate 2; S4: Add a reducing agent to the filtrate 2 to partially oxidize the Fe 3+ Reduction to Fe 2+ The solution is then evaporated, concentrated, crystallized, filtered, and dried to finally obtain high-purity ferrous sulfate heptahydrate.

[0008] The beneficial effects of this embodiment are: 1, in the purification process of titanium dioxide by-product ferrous sulfate heptahydrate in the prior art, impurities such as Ti and Al can be precipitated and removed using general chemicals, and it is difficult to process Mn and Mg impurities. The processing of Mn and Mg impurities is usually two techniques, wherein traditional precipitation method adds sulfide to remove Mn impurity, and adds fluoride to remove Mg impurity. Although this technique utilizes the mode of precipitation to remove Mn and Mg impurity, it is simple to operate and effective. However, the sulfide and fluoride used are hazardous chemicals themselves, causing corrosion to equipment and harming the operator, and the sulfur-containing and fluorine-containing waste liquid produced after its purification is also difficult to process. And the present invention selects the mode of converting ferrous sulfate to ferrous hydroxide to directly precipitate, thereby separating with impurities such as Mg and Mn, it can be realized that the impurities such as Mg and Mn of ferrous sulfate heptahydrate can be removed without using sulfide and fluoride, which is more environmentally friendly.

[0009] 2. Another purification process for Mn and Mg impurities is the recrystallization process. By taking advantage of the solubility difference between Mn and Mg impurities and ferrous sulfate, the impurity-containing ferrous sulfate heptahydrate is dissolved in hot water (e.g., 60-80°C) at high temperature. At this point, the target substance (FeSO4) and impurities (MnSO4, MgSO4, etc.) are fully dissolved to form a nearly saturated solution. The saturated solution is then slowly cooled and crystallized at low temperature. The solubility of FeSO4·7H2O decreases significantly with decreasing temperature, and pure crystals are precipitated first; while impurity ions (such as Mg 2+ 、Mn 2+ The solubility of the sulfate salt is less affected by temperature (i.e., it maintains a high solubility at low temperatures), and some of it remains in the mother liquor. Therefore, high-purity ferrous sulfate heptahydrate can be obtained through repeated dissolution and crystallization. However, this method requires repeated high-temperature dissolution (60-80°C) and subsequent cooling and crystallization, which increases energy consumption and water treatment costs. This application, however, does not require multiple high-temperature dissolution and recrystallization steps, and therefore consumes less energy than the recrystallization process.

[0010] 3. The present invention has a significantly different method for removing Mg and Mn impurities from the prior art. The present invention innovatively utilizes the fact that different ion hydroxides precipitate in different pH ranges and separates the target ferrous sulfate heptahydrate from the impurities by converting it into ferrous hydroxide. First, impurity ions such as Al and Ti are precipitated in a low pH range (2-5). Then, the pH is adjusted to 7.5-9, and the target ferrous sulfate heptahydrate is converted into ferrous hydroxide precipitate for separation, leaving the Mg and Mn ions in the high pH solution. This achieves a process for purifying ferrous sulfate heptahydrate without using sulfides or fluorides and without multiple recrystallizations. The process is green and environmentally friendly, has low energy consumption, low impurity removal cost, does not introduce new impurities, and is easy to industrialize.

[0011] Furthermore, the additive 1 added in S1 is one or both of ammonia water and phosphoric acid, and the pH value of the S1 solution is adjusted to a range of 2-5.

[0012] Furthermore, preferably, the pH value of the solution after adding the additive 1 in S1 is 4.5.

[0013] Furthermore, the additive 2 in S2 is one or more of ammonia water, sodium hydroxide, ammonium bicarbonate, and ammonium carbonate. After adding the additive 2, the pH value of the S2 solution is adjusted to a range of 7.5-9.

[0014] Furthermore, preferably, the pH value range described in S2 is 8.5.

[0015] Furthermore, the sulfuric acid used in S3 has a mass concentration range of 10%-20%.

[0016] Furthermore, preferably, the mass concentration of sulfuric acid used in S3 is 16%.

[0017] Furthermore, the evaporation and crystallization temperature is 40-60°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0019] The following is further described in detail through specific implementation methods: Implementation example Figure 1 As shown: Overview of Methods A method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, comprises the following steps: S1: dissolving ferrous sulfate heptahydrate, a byproduct of titanium dioxide, in pure water to form a ferrous sulfate solution, adding additive 1, wherein additive 1 is a substance capable of adjusting pH and / or forming colloids, such as ammonia and / or phosphoric acid; adjusting the pH of the solution to a value between 2 and 5 so that impurities such as Al and Ti form hydroxides or colloidal precipitates, thereby separating them from the ferrous sulfate solution, removing general metal impurities such as Al and Ti, and filtering to obtain filtrate 1; S2: Add additive 2 to the filtrate 1 and adjust the pH value to be within the range of 7.5-9, so that the Fe ions are precipitated in the form of ferrous hydroxide, leaving impurity ions such as Mg and Mn in the liquid (thereby achieving the purpose of removing Mg and Mn impurities), and filtering to obtain the ferrous hydroxide filter cake; S3: The filter cake is washed with pure water and 4 times with water twice to remove the impurity ions adsorbed on the surface of ferrous hydroxide, and then dissolved with dilute sulfuric acid solution and filtered to obtain filtrate 2; S4: Add a reducing agent to the filtrate 2 to partially oxidize the Fe 3+ Reduction to Fe 2+ The solution is then evaporated, concentrated, crystallized, filtered, and dried to finally obtain high-purity ferrous sulfate heptahydrate.

[0020] Example 1 Ferrous sulfate heptahydrate, a by-product of titanium dioxide, was dissolved in pure water and stirred to dissolve. Ammonia water was added to adjust the pH of the solution to 4.5, and the filtrate was filtered to obtain the filtrate. Ammonia water was further added to the filtrate to adjust the pH to 9. After reacting for half an hour, the ferrous hydroxide filter cake was filtered to obtain the filter cake. The filter cake was washed twice with water 4 times the mass of the wet filter cake and then dissolved with 16% sulfuric acid solution. After sufficient dissolution, 1% of the mass of the wet filter cake was added with iron powder for reduction, and the ferrous sulfate solution was filtered to obtain the solution. The solution was evaporated and crystallized in an oven at 40°C, and filtered and dried to obtain high-purity ferrous sulfate heptahydrate.

[0021] Example 2 Ferrous sulfate heptahydrate, a by-product of titanium dioxide, was dissolved in pure water and stirred to dissolve. Phosphoric acid was added followed by ammonia water to adjust the pH of the solution to 3. The filtrate was filtered to obtain the filtrate. Ammonia was further added to the filtrate to adjust the pH to 8. After reacting for half an hour, the ferrous hydroxide filter cake was filtered to obtain the ferrous hydroxide filter cake. The filter cake was washed twice with water 4 times the mass of the wet filter cake and then dissolved with 16% sulfuric acid solution. After sufficient dissolution, iron powder 1% by mass of the wet filter cake was added for reduction, and the ferrous sulfate solution was filtered to obtain the solution. The solution was evaporated and crystallized in an oven at 45°C, and filtered and dried to obtain high-purity ferrous sulfate heptahydrate.

[0022] The data of ferrous sulfate heptahydrate after refinement and purification in this application are as follows:

[0023] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, characterized by: The following steps are involved: S1: dissolving ferrous sulfate heptahydrate, a by-product of titanium dioxide, in pure water, adding additive 1 that can precipitate Al and Ti impurities, and filtering to obtain filtrate 1; S2: Adding additive 2 that can precipitate Fe ions in the form of ferrous hydroxide to filtrate 1, and filtering to obtain a filter cake; S3: The filter cake in S2 is washed to remove impurities adsorbed on the surface of ferrous hydroxide, then dissolved with sulfuric acid solution and filtered to obtain filtrate 2; S4: Add a reducing agent to the filtrate 2 to partially oxidize the Fe 3+ Reduction to Fe 2+ The solution is then evaporated, concentrated, crystallized, filtered, and dried to finally obtain high-purity ferrous sulfate heptahydrate.

2. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 1, wherein: The additive 1 added in S1 is one or both of ammonia water and phosphoric acid, and the pH value of the S1 solution is adjusted to a range of 2-5.

3. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 2, wherein: The pH value of the solution after adding the additive 1 in S1 is 4.

5.

4. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 1, wherein: The additive 2 in S2 is one or more of ammonia water, sodium hydroxide, ammonium bicarbonate, and ammonium carbonate. After adding the additive 2, the pH value of the S2 solution is adjusted to a range of 7.5-9.

5. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 4, characterized in that: The pH value described in S2 is 8.

6. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 1, characterized in that: The mass concentration of sulfuric acid used in the S3 is in the range of 10% to 20%.

7. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 6, characterized in that: The mass concentration of sulfuric acid used in the S3 is 16%.

8. The method for refining ferrous sulfate heptahydrate, a by-product of titanium dioxide, according to claim 1, characterized in that: The evaporation and crystallization temperature is 40-60°C.

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