Method for preparing iron phosphate by comprehensively utilizing titanium dioxide by-product

Abstract

The invention relates to the technical field of titanium dioxide production waste recycling, and particularly discloses a method for preparing iron phosphate by comprehensively utilizing titanium dioxide by-products, which takes waste acid and solid waste ferrous sulfate heptahydrate generated in a process of producing titanium dioxide by a sulfuric acid method as raw materials, and comprises the following steps: S1, mixing and stirring titanium dioxide waste acid and ferrous sulfate heptahydrate, pre-mixed acid liquid is obtained; s2, hydrogen peroxide is added into the premixed acid liquid for oxidation, and then a complexing agent and an extracting agent are added for extraction; s3, water is added for reverse extraction, then iron powder is added, filtering is conducted, and a ferrous solution is obtained; s4, nitrite and dilute sulphuric acid are added into the ferrous solution for a polymerization reaction, and a polymeric ferric sulfate solution is obtained; and S5, adding phosphate into the polyferric sulfate solution, and reacting at high temperature to obtain the high-purity iron phosphate. According to the method, recycling of waste acid and solid waste in the process of preparing titanium dioxide through a sulfuric acid method is integrated, the waste disposal cost is reduced, the waste recycling process is simplified, and the effect of preparing high-purity iron phosphate is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling of titanium dioxide production waste, and particularly relates to a method for preparing iron phosphate by comprehensively utilizing titanium dioxide by-products. BACKGROUND

[0002] The sulfuric acid method is a mature process for preparing titanium dioxide, and the process flow is as follows: ilmenite or acid-soluble titanium slag is crushed into ore powder, concentrated sulfuric acid is added, and acidolysis is performed at high temperature to generate titanium oxysulfate (TiOSO4) solution. In the acidolysis process, in addition to titanium elements, various impurity metal elements in the ore powder will also be acidolysed to form soluble sulfate. Since the solution contains high-iron sulfate, iron filings need to be added for reduction.

[0003] Next, a flocculating agent is added to the solution to precipitate various impurities, preliminary impurity removal is performed, and then cooling crystallization is performed. This step can make most of the ferrous sulfate crystallize and precipitate, and then the solution is concentrated and hydrolyzed (at 90°C) to generate water-insoluble titanium dioxide hydrate precipitate (metatitanic acid). The hydrolysis precipitate slurry is filtered and preliminarily washed to remove most of the soluble impurities, and then secondary water washing is performed under reducing conditions, sulfuric acid is used for acid immersion, and a reducing agent is added to reduce the trace amount of adsorbed metal impurities (mainly high-iron) in a rinsing manner. This step is also the main reason for the generation of waste acid in the sulfuric acid method.

[0004] The chemical reactions involved in the sulfuric acid method are as follows: FeTiO3+2H2SO4+5H2O=FeSO47H2O+TiOSO4; TiOSO4+2H2O=TiO(OH)2+H2SO4; TiO(OH)2=TiO2+H2O.

[0005] Ferrous sulfate heptahydrate (green vitriol) is the main solid by-product of the preparation of titanium dioxide by the sulfuric acid method. 3.5-4 t of ferrous sulfate heptahydrate by-product is generated per ton of titanium dioxide product, and the purity of ferrous sulfate is generally less than 90%, and it also contains Fe (III), Mg, Ti, Mn and other impurities. The waste acid generated in the water washing step is the main liquid by-product of the sulfuric acid method. 6-7 t of titanium dioxide waste acid is generated per ton of titanium dioxide product, and the main components are H2SO4 (20-25%), FeSO4 and H2TiO3, and it also contains trace amounts of V, Mg, Mn, Sc and other metal elements.

[0006] The exploration of the treatment method of these solid waste, waste liquid by-products has been accompanied by the development of the sulfuric acid method process. For example, for waste acid, Shandong Dongjia Company combines waste acid with coking enterprise waste ammonia water to produce ammonium sulfate, Sichuan Longma Company uses waste acid to produce phosphate, and waste acid is recycled as a resource, which not only avoids pollution but also creates benefits. For green vitriol, it is usually purified by recrystallization method, colloidal adsorption method, chemical precipitation method and other methods to produce ferrous sulfate product. However, due to the difference in treatment method of solid waste and waste liquid, the recovery of the two by-products is usually recovered and treated separately, which undoubtedly increases the treatment cost.

[0007] Phosphorus iron plays an extremely important role in catalysis, wastewater treatment and lithium battery fields, and is an important precursor for preparing lithium iron phosphate positive materials. Compared with other ferrous salts, it has the advantages of low cost, good oxidation stability and good cycle performance, and is increasingly valued today with the rapid development of lithium batteries. In existing research, there is a process for producing phosphorus iron from titanium white powder by-products, but all of them are prepared from green vitriol, a sulfuric acid method solid waste. In contrast, waste acid is usually used to recover sulfuric acid due to its low iron content and more complex impurities.

[0008] In summary, there is an urgent need for a process that can comprehensively recover and utilize sulfuric acid method by-products and prepare phosphorus iron to reduce waste recovery process, reduce recovery cost and improve economic benefit. SUMMARY

[0009] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method for preparing phosphorus iron by comprehensively utilizing titanium white by-products, so as to at least achieve the effects of reducing waste disposal cost, simplifying waste recovery process and preparing high-purity phosphorus iron.

[0010] The purpose of the present application is achieved by the following technical solutions: A method for preparing phosphorus iron by comprehensively utilizing titanium white by-products, using waste acid and solid waste ferrous sulfate heptahydrate generated in the process of producing titanium dioxide by the sulfuric acid method as raw materials, comprising the following steps: S1: mixing and stirring titanium white waste acid and ferrous sulfate heptahydrate to dissolve the ferrous sulfate heptahydrate, and obtaining a premixed acid solution; S2: adding hydrogen peroxide to the premixed acid solution for oxidation, then adding a complexing agent and an extractant for extraction, and obtaining an iron extraction solution; S3: adding water to the iron extraction solution for back extraction, then adding iron powder to the back extraction solution, filtering, and obtaining a ferrous solution; S4: adding nitrite and dilute sulfuric acid to the ferrous solution in an oxygen environment for polymerization reaction, and obtaining a polymerized ferric sulfate solution; S5: adding the polymeric ferric sulfate solution into phosphate, adjusting pH, reacting at high temperature, neutralizing pH, and obtaining high-purity ferric phosphate.

[0011] Further, in step S1, the titanium white waste acid and the ferrous sulfate heptahydrate do not have strict proportion limits, as long as the ferrous sulfate heptahydrate can be completely dissolved in the titanium white waste acid.

[0012] Further, in step S2, the complexing agent includes concentrated hydrochloric acid.

[0013] Further, in step S2, the extractant includes one of methyl isobutyl ketone, tributyl phosphate or isopropyl ether; preferably, the extractant is methyl isobutyl ketone.

[0014] Further, in step S2, the complexing agent and the extractant can be added in excess.

[0015] Further, in step S3, the volume ratio of the water to the extractant is 3-4:1.

[0016] Further, in step S3, the iron powder is added in excess.

[0017] Notably, the present application adopts an oxidation-complexation-extraction-reverse extraction-reduction method, first, Fe 2+ and Fe 3+ in solid waste and waste liquid are oxidized into Fe 3+ which is easy to complex, then the complexing agent of concentrated hydrochloric acid is used, and then the complex trace metal elements in the original impurities are effectively removed through the extraction and reverse extraction process, and finally, high-purity ferrous solution is obtained after reduction, so as to prepare high-purity ferric phosphate subsequently. Moreover, the extractant used in the present application can be recycled, the reverse extraction agent is deionized water, and the concentrated hydrochloric acid is low in price, so the whole process cost is extremely low.

[0018] Further, in step S4, the molar ratio of ferrous ions, nitrite and sulfate ions in the sulfurous acid solution is 1:1:2-3.

[0019] Further, in step S4, the temperature of the polymerization reaction is 55-65℃; preferably, the temperature of the polymerization reaction is 60℃.

[0020] Further, in step S5, the phosphate includes one of ammonium phosphate, sodium phosphate and potassium phosphate; preferably, the phosphate is sodium phosphate or potassium phosphate, although sodium element is introduced, but the influence on the solution pH is small and no waste gas is generated.

[0021] Further, in step S5, the molar ratio of iron ions in the polymeric ferric sulfate to phosphate ions in the phosphate is 2:3-5.

[0022] Further, in step S5, the pH is 1.5-1.8.

[0023] Further, in step S5, the reaction temperature is 70-80℃.

[0024] The beneficial effects of the present application are: 1. The present application integrates the recycling method of waste acid and solid waste generated in the process of producing titanium dioxide by sulfuric acid method, and simplifies the by-product treatment process.

[0025] 2. The present application adopts the method of oxidation-complexation-extraction-stripping-reduction, which effectively removes the metal impurities in waste acid and solid waste that are difficult to remove, and is beneficial to the preparation of high-purity iron phosphate product.

[0026] 3. The extractant used in the process of the present application can be recycled repeatedly, the stripping agent is deionized water, and the concentrated hydrochloric acid is low in price. The overall process is low in cost and has a large-scale promotion prospect. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The process flow chart of the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described in further detail below, but the protection scope of the present application is not limited to the following.

[0029] Example 1 The present embodiment provides a method for preparing iron phosphate product by comprehensively utilizing the by-products of titanium dioxide production by sulfuric acid method, and the specific method is as follows: 1) Take 20L titanium dioxide waste liquid produced by sulfuric acid method and 500g iron sulfate heptahydrate into a reaction kettle and stir for 30min to make the iron sulfate heptahydrate completely dissolved.

[0030] 2) Excess hydrogen peroxide is added to the reaction kettle for oxidation, and the stirring is continued during the reaction, until the acid solution is red-brown and no bubbles are generated, then an equal volume of concentrated hydrochloric acid is added, and after shaking, it is placed for 2h to generate flocculent precipitate.

[0031] 3) Methyl isobutyl ketone is used as an extractant, and an equal volume of extractant is added to the hydrochloric acid, and after extraction is completed, the extractant is used for stripping with four times the volume of deionized water to obtain a ferric chloride solution.

[0032] 4) The concentration of iron ions in the ferric chloride solution is 0.26mol / L, and a slight excess of iron filings is added for reduction, and after complete reaction, the excess iron powder is filtered out.

[0033] 5) Add 0.26 mol / L of sodium nitrite and 0.52 mol / L of dilute sulfuric acid into the solution, and carry out polymerization reaction under the condition of sealing environment at 60°C by introducing high-purity oxygen, with the reaction pressure being half of the standard atmospheric pressure, until oxygen is no longer consumed, i.e. the reaction is stopped.

[0034] 6) Add sodium phosphate into the reaction kettle to control the pH to be 2.5, and then react at 70°C for 2 h, neutralize the pH, and filter to obtain iron phosphate, which is then washed, dried, calcined, and thus iron phosphate product is obtained.

[0035] The obtained iron phosphate product is sampled, redissolved in a quantitative amount of hydrochloric acid, and the iron content is detected by titanium trichloride reduction-potassium dichromate titration method, the phosphorus content is detected by quinoline molybdenum citrone weight method, and then the iron-phosphorus ratio is calculated. The detection results are: iron content 29.3%, phosphorus content 16.8%, and iron-phosphorus ratio 0.967.

[0036] Example 2 The present example provides a method for comprehensively utilizing the by-products of sulfuric acid method for producing titanium dioxide to prepare iron phosphate product, and the specific method is as follows: 1) Take 20 L of titanium dioxide waste liquid produced by the sulfuric acid method and 1 kg of iron sulfate heptahydrate into a reaction kettle, and stir for 30 min to make the iron sulfate heptahydrate completely dissolved.

[0037] 2) Add excess hydrogen peroxide into the reaction kettle for oxidation, and continuously stir during the reaction process, until the acid solution is red-brown and no gas bubbles are generated, then add concentrated hydrochloric acid with the same volume as the solution, shake, and then stand for 2 h to generate flocculent precipitate.

[0038] 3) Use methyl isobutyl ketone as an extractant, and add an extractant with the same volume as the hydrochloric acid. After extraction is completed, use four times the volume of deionized water of the extractant for back extraction to obtain a ferric chloride solution.

[0039] 4) The concentration of iron ions in the ferric chloride solution is 0.34 mol / L, and a slight excess of iron filings is added for reduction. After complete reaction, the excess iron powder is filtered out.

[0040] 5) Add 0.34 mol / L of sodium nitrite and 0.68 mol / L of dilute sulfuric acid into the solution, and carry out polymerization reaction under the condition of sealing environment at 60°C by introducing high-purity oxygen, with the reaction pressure being half of the standard atmospheric pressure, until oxygen is no longer consumed, i.e. the reaction is stopped.

[0041] 6) Add sodium phosphate into the reaction kettle to control the pH to be 2.5, and then react at 70°C for 2 h, neutralize the pH, and filter to obtain iron phosphate, which is then washed, dried, calcined, and thus iron phosphate product is obtained.

[0042] The obtained iron phosphate product was sampled and redissolved in a quantitative hydrochloric acid, the iron content was detected by titanium trichloride reduction-potassium dichromate titration method, the phosphorus content was detected by quinoline molybdenum citrone weight method, and then the iron phosphorus ratio was calculated. The detection results are: iron content 29.8%, phosphorus content 16.3%, iron phosphorus ratio 1.01.

[0043] Example 3 The present embodiment provides a method for comprehensively utilizing the by-products of titanium dioxide production by sulfuric acid method to prepare iron phosphate products, and the specific method is as follows: 1) 25L titanium dioxide waste liquid produced by sulfuric acid method and 1kg iron sulfate heptahydrate were taken into a reaction kettle and stirred for 30min to make the iron sulfate heptahydrate completely dissolved.

[0044] 2) Excess hydrogen peroxide was added to the reaction kettle for oxidation, and the stirring was continued during the reaction, until the acid solution was red-brown and no bubbles were generated, then an equal volume of concentrated hydrochloric acid was added, and after shaking, it was placed for 2h to generate flocculent precipitate.

[0045] 3) Methyl isobutyl ketone was used as an extractant, and an equal volume of extractant was added to the hydrochloric acid, and after the extraction was completed, the extractant was back-extracted with four times the volume of deionized water to obtain an iron chloride solution.

[0046] 4) The concentration of iron ions in the iron chloride solution was 0.31mol / L, and a slight excess of iron filings was added for reduction, and after complete reaction, the excess iron powder was filtered out.

[0047] 5) 0.31mol / L of sodium nitrite and 0.62mol / L of dilute sulfuric acid were added to the solution, and in a sealed environment at 60℃, high-purity oxygen was introduced, and the reaction pressure was half of the standard atmospheric pressure, until the oxygen was no longer consumed, i.e. the reaction was stopped.

[0048] 6) Sodium phosphate was added to the reaction kettle to control the pH to 2.5, and then reacted at 80℃ for 2h, and then neutralized and filtered to obtain iron phosphate, which was then washed, dried, and calcined to obtain the iron phosphate product.

[0049] The obtained iron phosphate product was sampled and redissolved in a quantitative hydrochloric acid, the iron content was detected by titanium trichloride reduction-potassium dichromate titration method, the phosphorus content was detected by quinoline molybdenum citrone weight method, and then the iron phosphorus ratio was calculated. The detection results are: iron content 29.5%, phosphorus content 16.6%, iron phosphorus ratio 0.985.

[0050] Comparative Example The present embodiment provides a method for comprehensively utilizing the by-products of titanium dioxide production by sulfuric acid method to prepare iron phosphate products, and the specific method is as follows: 1) 20L titanium dioxide waste liquid produced by sulfuric acid method and 500g iron sulfate heptahydrate were added into a reaction kettle and stirred for 30min to make the iron sulfate heptahydrate completely dissolved, and the concentration of Fe 2+ in the solution was detected as 3.08mol / L.

[0051] 2) 3.08mol / L of sodium nitrite and 6.16mol / L of dilute sulfuric acid were added into the solution, and high-purity oxygen was introduced under a sealed environment at 60℃ to carry out polymerization reaction, the reaction pressure was half of the standard atmospheric pressure, and the reaction was stopped until the oxygen was no longer consumed.

[0052] 3) Excessive sodium phosphate was added into the reaction kettle to control the pH to be 2.5, and then the reaction was carried out at 70℃ for 2h, and the pH was neutralized and filtered to obtain iron phosphate, which was then washed, dried, and calcined to obtain the iron phosphate product.

[0053] The obtained iron phosphate product was sampled and dissolved in a quantitative hydrochloric acid, the iron content was detected by titanium trichloride reduction-potassium dichromate titration method, the phosphorus content was detected by quinoline molybdenum citrone weight method, and then the iron-phosphorus ratio was calculated. The detection results were: iron content 25.4%, phosphorus content 17.0%, and iron-phosphorus ratio 0.828. Compared with examples 1-3, the purity of the comparative example was obviously lower, and there should be calcium phosphate or aluminum phosphate impurities in the product.

[0054] The above only describes the preferred embodiments of the present application, and it should be understood that the present application is not limited to the forms disclosed herein, and should not be considered as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concepts described herein by the above teachings or related art or knowledge. Any modification and change made by those skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the appended claims of the present application.

Claims

1. A method for preparing ferric phosphate by comprehensively utilizing titanium dioxide by-products, using waste acid and solid waste ferrous sulfate heptahydrate generated in the sulfuric acid process for producing titanium dioxide as raw materials, characterized in that, The method comprises the following steps: S1: mixing and stirring titanium white waste acid and ferrous sulfate heptahydrate to dissolve the ferrous sulfate heptahydrate, and obtaining a premixed acid solution; S2: adding the premixed acid solution into hydrogen peroxide to perform oxidation, and then adding a complexing agent and an extractant to perform extraction, and obtaining an iron extraction solution; S3: adding water into the iron extraction solution to perform back extraction, and then adding iron powder into the back extraction solution, and filtering to obtain a ferrous solution; S4: adding the ferrous solution into a nitrite and dilute sulfuric acid in an oxygen environment to perform a polymerization reaction, and obtaining a polymerized ferric sulfate solution; S5: adding the polymerized ferric sulfate solution into a phosphate, adjusting pH, and reacting at high temperature, and neutralizing pH to obtain high-purity ferric phosphate.

2. The method of claim 1, wherein the method further comprises: In step S2, the complexing agent comprises concentrated hydrochloric acid.

3. The method of producing iron phosphate according to claim 2, characterized by: In step S2, the extractant comprises one of methyl isobutyl ketone, tributyl phosphate or isopropyl ether.

4. The method of producing iron phosphate according to claim 2, characterized by: In step S3, the volume ratio of the water to the extractant is 3-4:

1.

5. The method of producing iron phosphate according to claim 2, characterized by: In step S4, the molar ratio of ferrous ions, nitrite and sulfate ions in the dilute sulfuric acid in the ferrous solution is 1:1:2-3.

6. The method of producing iron phosphate according to claim 2, characterized by: In step S4, the temperature of the polymerization reaction is 55-65℃.

7. The method of producing iron phosphate according to claim 2, characterized by: In step S5, the phosphate comprises one of ammonium phosphate, sodium phosphate and potassium phosphate.

8. The method of producing iron phosphate according to claim 2, characterized by: In step S5, the molar ratio of iron ions in the polymerized ferric sulfate to phosphate ions in the phosphate is 2:3-5.

9. The method of producing iron phosphate according to claim 2, characterized by: In step S5, the pH is 1.5-1.

8.

10. The method of producing iron phosphate according to claim 2, characterized by: In step S5, the temperature of the reaction is 70-80℃.

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