Titanium white waste acid impurity removal process

Abstract

The application provides a titanium white waste acid impurity removal process, which comprises the following steps: S1, after filtering and washing, the titanium white waste acid is concentrated and heated for a period of time, then cooled, and concentrated acid and ferrous sulfate crystals are obtained; S2, a reducing agent iron powder is added to the concentrated acid solution, and the solution is heated to above 90 DEG C, then a nano precipitant is added when the pH value of the solution reaches 3-4.5, the addition amount of the nano precipitant is 1:10-30 of the material liquid ratio (g / L) of the concentrated acid solution; S3, then a modified flocculating agent is added to the solution obtained in S2, the addition amount of the modified flocculating agent is 1:5-10 of the material liquid ratio (g / L) of the solution, and filtration separation is performed, thereby obtaining ferrous sulfate and sulfuric acid; the process can efficiently remove ferrous sulfate and heavy metal ions, so that the treated sulfuric acid can be recycled to the acidolysis titanium concentrate process.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide processing technology, and more specifically, to a process for removing impurities from titanium dioxide waste acid. Background Technology

[0002] Currently, most enterprises in my country use the sulfuric acid process to produce titanium dioxide. This process uses inexpensive and readily available ilmenite and sulfuric acid as raw materials, and the technology is relatively mature, simple to operate, and has low investment and product costs. However, the sulfuric acid process for producing titanium dioxide consumes a large amount of resources, especially water and sulfuric acid, and generates a lot of waste and byproducts. Approximately 4 tons of sulfuric acid are needed to produce 1 ton of titanium dioxide, but the final product, titanium dioxide, does not contain acid. Therefore, a large amount of ferrous sulfate and waste sulfuric acid are generated during the production process. Waste sulfuric acid is the unreacted sulfuric acid produced during the acidolysis of titanium dioxide, which is separated through water washing and filtration. Ferrous sulfate is formed by the reaction of sulfuric acid with iron elements in the ore during acidolysis, and precipitated through crystallization and filtration; industrially, it is also called ferrous sulfate helium. Approximately 8-10 tons of waste acid containing 15%-20% free H₂SO₄ and 2.5-3.5 tons of ferrous sulfate are discharged for every 1 ton of titanium dioxide produced. Of the titanium dioxide waste acid generated during the production process of titanium dioxide enterprises, 22% to 26% can be directly recycled for the acidolysis process of the titanium dioxide production line. The remaining part cannot be used directly due to its high impurity content and requires further treatment. Summary of the Invention

[0003] The purpose of this invention is to provide a waste acid removal process for titanium dioxide, which can efficiently remove ferrous sulfate and heavy metal ions, so that the treated sulfuric acid can be recycled and reused in the acidolysis of titanium concentrate.

[0004] The embodiments of the present invention are achieved through the following technical solutions:

[0005] A process for removing impurities from titanium dioxide waste acid includes the following steps:

[0006] S1. After filtering and washing, the waste acid from titanium dioxide is concentrated and heated for a period of time, and then cooled to obtain concentrated acid and ferrous sulfate crystals. In this invention, part of the ferrous sulfate in the waste acid is extracted by concentration and crystallization, and then the waste acid is further treated to remove the remaining ferrous sulfate and other heavy metals.

[0007] S2. Add reducing agent iron powder to the concentrated acid solution and heat to above 90℃. When the pH value of the solution reaches 3-4.5, add nano precipitant. The ratio of the amount of nano precipitant added to the concentrated acid solution (g / L) is 1:10-30. Stir. Use iron powder to adjust the pH of the solution to about 4.0, thereby removing titanium from the waste acid. At the same time, iron powder can also reduce ferric ions to reduce iron loss and avoid introducing other impurity elements into the waste acid solution.

[0008] S3. Then, add a modified flocculant to the solution obtained in S2. The ratio of the amount of modified flocculant added to the solution (g / L) is 1:5-10. After filtration and separation, ferrous sulfate and sulfuric acid are obtained.

[0009] Furthermore, the heating temperature in S1 is 320-350℃. The temperature is then reduced to 85-95℃.

[0010] Furthermore, the concentration heating device in S1 is equipped with at least three heating zones: a first heating zone with a steam pressure of 0.45-0.55 MPa and a temperature of 320-340℃; a second heating zone with a steam pressure of 0.3-0.4 MPa and a temperature of 340-350℃; and a third heating zone with a steam pressure of 0.08-0.1 MPa and a temperature of 320-330℃. Under negative pressure, the material is concentrated to 55%. After heat exchange, cooling, and ferrous sulfate monohydrate crystallization and ripening, a 55% acid by mass fraction is obtained through solid-liquid separation, which can be reused in acidolysis reactions.

[0011] Furthermore, the reducing agent in S2 is iron powder, and the ratio (g / L) of the amount of iron powder added to the concentrated acid solution is 1:50-80.

[0012] Furthermore, the nano-precipitant is a combination of soluble sulfate and sulfur. When the nano-precipitant of the present invention is added to waste acid, its reactivity can be improved, thereby enabling it to undergo various chemical and physical reactions such as precipitation, co-precipitation, and surface adsorption with heavy metals more efficiently, thus removing heavy metal ions more efficiently. Moreover, the nano-precipitant of the present invention can better avoid sulfur residue and reduce the loss of ferrous sulfate, so that the extracted ferrous sulfate can be efficiently recycled and reused.

[0013] Furthermore, the preparation method of the nano-active precipitant is as follows: soluble sulfate and sodium sulfide are dissolved separately in sodium chloride solution, and then the two solutions are mixed, filtered, washed and dried to obtain nano-powder material.

[0014] Furthermore, the soluble sulfate includes potassium sulfate or ammonium sulfate. In removing impurities from ferrous sulfate in waste acid, this invention avoids using solutions containing sodium ions, as this would introduce Na ions into the waste acid, causing excessive Na impurities and hindering impurity removal.

[0015] Furthermore, the modified flocculant is acrylamide grafted with hydroxyl or carboxyl groups. By introducing active groups, it has better flocculation performance and can accelerate ion sedimentation.

[0016] Further, the preparation method of the modified acrylamide involves graft copolymerization of chitosan, nano-silica, and acrylamide, specifically including the following steps: a certain mass of chitosan, nano-silica powder, and acrylamide (mass ratio 1:1-2:4-5) is fully dissolved in a 1% acetic acid solution. Under a nitrogen atmosphere, cerium ammonium nitrate initiator is added, and after stirring evenly, a reverse emulsion polymerization method is used. The reaction is carried out at 55-65℃ for 3-5 hours to obtain an emulsion. After washing repeatedly with anhydrous ethanol, the precipitate is dried to obtain the modified acrylamide. The obtained modified acrylamide exhibits more wrinkles and protrusions on its surface morphology, forming more active sites, and demonstrating good water solubility and flocculation properties. The modified flocculant of this invention can not only compensate for the shortcomings of chitosan's low molecular weight resulting in weak bridging ability, but also improve the solubility of chitosan. Moreover, the addition of acrylamide gives the polymer higher chemical activity, enhancing its adsorption performance for heavy metal ions during the treatment of waste acid.

[0017] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0018] This invention first extracts a portion of ferrous sulfate from waste acid through concentration and crystallization. Then, the waste acid is further reduced, and a highly reactive nano-precipitant is added to remove heavy metal ions while reducing the loss of ferrous sulfate, enabling the extracted ferrous sulfate to be efficiently recycled and reused. Subsequently, modified acrylamide with active groups is used as a flocculant, resulting in higher reactivity, good water solubility and flocculation properties, and enhanced adsorption performance for heavy metal ions. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0020] Example 1

[0021] 1. Preparation of nano-precipitants

[0022] Dissolve 50g of ammonium sulfate in 100ml of water, and gradually add NaCl at room temperature until saturation; dissolve 10g of sodium sulfide in 100ml of anhydrous ethanol, and gradually add NaCl at room temperature until saturation; then stir the two solutions thoroughly, filter under vacuum, wash the filter cake three times with anhydrous ethanol, and dry it under vacuum at 50℃ for 3 hours to obtain nanopowder materials.

[0023] 2. Preparation of modified flocculants

[0024] 10g of chitosan, 20g of nano-silica powder and 50g of acrylamide were fully dissolved in 1% acetic acid solution. Nitrogen was purged to remove oxygen, and cerium ammonium nitrate initiator was added under nitrogen atmosphere. The mixture was then reacted at 60℃ for 4 hours using reverse emulsion polymerization to obtain an emulsion. After washing 5 times with anhydrous ethanol, the precipitate was vacuum dried at 60℃ for 3 hours to obtain modified acrylamide.

[0025] 3. A process for removing impurities from titanium dioxide waste acid, comprising the following steps:

[0026] S1. After filtration and washing, the waste acid from titanium dioxide is concentrated in three stages: First heating zone: steam pressure 0.5 MPa, temperature 330℃; Second heating zone: steam pressure 0.35 MPa, temperature 345℃; Third heating zone: steam pressure 0.09 MPa, temperature 325℃; Then, the temperature is lowered to 90℃ to obtain concentrated acid and ferrous sulfate crystals.

[0027] S2. Add iron powder to the concentrated acid solution and heat to 95°C. The ratio of iron powder to concentrated acid solution (g / L) is 1:60. When the pH of the solution reaches 4.0, add nano precipitant. The ratio of nano precipitant to concentrated acid solution (g / L) is 1:20. Stir.

[0028] S3. Then, add a modified flocculant to the solution obtained in S2. The ratio of the amount of modified flocculant added to the solution (g / L) is 1:8. After filtration and separation, sulfuric acid and ferrous sulfate with a mass fraction of 92.6% are obtained.

[0029] Example 2

[0030] The difference between this embodiment and Embodiment 1 is that during the three-stage concentration in S1: the first heating zone has a steam pressure of 0.45 MPa and a temperature of 340°C; the second heating zone has a steam pressure of 0.3 MPa and a temperature of 350°C; the third heating zone has a steam pressure of 0.08 MPa and a temperature of 330°C; then the temperature is lowered to 85°C; finally, sulfuric acid and ferrous sulfate with a mass fraction of 91.5% are obtained.

[0031] Example 3

[0032] The difference between this embodiment and embodiment 1 is that: in S2, the ratio of iron powder added to concentrated acid solution (g / L) is 1:70, and nano-precipitant is added when the pH value of the solution reaches 4.0, with the ratio of nano-precipitant added to concentrated acid solution (g / L) being 1:15; finally, sulfuric acid and ferrous sulfate with a mass fraction of 92.5% are obtained.

[0033] Example 4

[0034] The difference between this embodiment and Example 1 is that the amount of modified flocculant added in S3 is 1:5 with the ratio of the amount of the solution to the amount of the solution (g / L); and finally, sulfuric acid and ferrous sulfate with a mass fraction of 91.9% are obtained.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that step S1 is not included; and sulfuric acid with a mass fraction of 72% is finally obtained.

[0037] Comparative Example 2

[0038] The difference between this comparative example and Example 1 is that the nano-precipitant in step S2 is replaced with sodium sulfide; and sulfuric acid with a mass fraction of 61% is finally obtained.

[0039] Comparative Example 3

[0040] The difference between this comparative example and Example 1 is that the modified flocculant in step S3 is replaced with polyacrylamide; and sulfuric acid with a mass fraction of 60% is finally obtained.

[0041] Experimental Example 1

[0042] The titanium dioxide waste acid from Examples 1-4 and Comparative Examples 1-3 after impurity removal was subjected to ICP testing, and the test results are shown in Table 1. It should be noted that before impurity removal, the waste acid contained the following concentrations: Ti 850 ppm, Zn 68 ppm, Mn 1340 ppm, Mg 5100 ppm, and Ca 320 ppm.

[0043] Table 1. Detection results of waste acid from titanium dioxide after impurity removal.

[0044] Ti Zn Mn Mg Ca Example 1 12 11 76 30 36 Example 2 14 13 75 31 34 Example 3 11 12 78 33 37 Example 4 12 13 77 32 35 Comparative Example 1 392 34 625 2100 185 Comparative Example 2 435 45 821 3500 260 Comparative Example 3 418 41 816 3450 245

[0045] As shown in Table 1, the impurity removal process of this invention can obtain high-quality concentrated sulfuric acid that can be returned to the acidolysis titanium concentrate process for continued use, thereby realizing the recycling of sulfuric acid and bringing greater economic benefits to enterprises.

[0046] Comparative Example 1 shows that the lack of concentration pretreatment of titanium dioxide waste acid resulted in a higher amount of impurities in the waste acid, which reduced the extraction efficiency of ferrous sulfate.

[0047] Comparative Example 2 shows that replacing the nano-precipitant with sodium sulfide has a poor effect on removing impurities and is not conducive to the extraction of ferrous sulfate.

[0048] Comparative Example 3 shows that the flocculation effect of traditional flocculants is generally poor, while the modified acrylamide flocculant has a prominent flocculation effect, which can effectively enhance the adsorption performance of heavy metal ions in titanium dioxide waste acid and improve the recovery quality of sulfuric acid.

[0049] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for removing impurities from titanium dioxide waste acid, characterized in that, Includes the following steps: S1. After filtering and washing, the waste acid from titanium dioxide is concentrated and heated for a period of time, and then cooled to obtain a concentrated acid solution and ferrous sulfate crystals. S2. Add a reducing agent to the concentrated acid solution and heat to above 90°C. When the pH value of the solution reaches 3~4.5, add the nano precipitant and stir. S3. Then, add the modified flocculant to the solution obtained in S2, filter and separate to obtain ferrous sulfate and sulfuric acid; the modified flocculant is acrylamide grafted with hydroxyl or carboxyl groups, and the modified acrylamide is prepared by graft copolymerizing chitosan, nano silica powder and acrylamide.

2. The titanium dioxide waste acid removal process according to claim 1, characterized in that, The heating temperature in S1 is 320-350℃; the temperature is then reduced to 85-95℃.

3. The titanium dioxide waste acid removal process according to claim 2, characterized in that, The device used for concentration heating in S1 has at least three heating zones: the first heating zone has a steam pressure of 0.45-0.55 MPa and a temperature of 320-340℃; the second heating zone has a steam pressure of 0.3-0.4 MPa and a temperature of 340-350℃; and the third heating zone has a steam pressure of 0.08-0.1 MPa and a temperature of 320-330℃.

4. The titanium dioxide waste acid removal process according to claim 1, characterized in that, The reducing agent mentioned in S2 is iron powder, and the ratio of the amount of iron powder added to the concentrated acid solution is 1g:50-80L.

5. The titanium dioxide waste acid removal process according to claim 1, characterized in that, The nano-precipitant mentioned in S2 is a combination of soluble sulfate and sodium sulfide.

6. The titanium dioxide waste acid removal process according to claim 5, characterized in that, The preparation method of the nano-precipitant is as follows: soluble sulfate and sodium sulfide are dissolved separately in sodium chloride solution, and then the two solutions are mixed, filtered, washed and dried to obtain nano-powder material.

7. The titanium dioxide waste acid removal process according to claim 6, characterized in that, The soluble sulfates include potassium sulfate or ammonium sulfate.

8. The titanium dioxide waste acid removal process according to claim 1, characterized in that, The method for preparing the modified acrylamide, The process includes the following steps: a certain mass of chitosan, nano-silica powder and acrylamide are fully dissolved in acetic acid solution, an initiator is added under a nitrogen atmosphere and heated; after reacting for a period of time using reverse emulsion polymerization, an emulsion is obtained, which is then washed and dried to obtain modified acrylamide.