Method for recycling titanium from titanium waste residues and preparation methods of titanium dioxide and SCR denitration catalyst

Abstract

The invention relates to the field of titanium recovery, and discloses a method for recovering titanium from titanium waste residues and a preparation method of titanium dioxide and an SCR denitration catalyst. The method for recycling the titanium from the titanium waste residues comprises the following steps: 1) adding a buffering agent in the presence of water to obtain a solution A; 2) carrying out first contact on the solution A and titanium waste residues to obtain a solution B; 3) carrying out second contact on the solution B and alkali to obtain a solution C; and 4) carrying out centrifugal separation on the solution C, and drying to obtain titanium dioxide. According to the method disclosed by the invention, the effects of environment-friendly cost reduction, low cost, simple operation and simple equipment are achieved, titanium compounds in the waste residues can be completely converted into anatase titanium dioxide, and the product can be reused for preparing the SCR denitration catalyst.

Description

Technical Field

[0001] The invention relates to titanium recovery, and in particular to a method for recovering titanium from titanium waste slag, and a method for preparing titanium dioxide and an SCR denitration catalyst. Background Art

[0002] Titanium dioxide is a well-known material with various uses, including cosmetics, personal care products, plastics, surface coatings, catalyst support materials, etc. As for the crystal form of titanium dioxide, three types are available, rutile, anatase and brookite, among which anatase is widely used in catalysts and solar cells.

[0003] Organic titanium and titanium tetrachloride are common titanium industrial raw materials, often used in high-purity titanium industry, catalyst field and other industries. Such industries often produce titanium-containing byproducts or wastes. Such raw materials are prone to hydrolysis and often contain organic matter, which are generally hazardous solid wastes. Usually, such wastes are treated by hydrolysis. The resulting residues are difficult to use in the coating field due to their low purity and insufficient whiteness. Moreover, they are often not used in the cosmetics field due to the impurities they contain, so they are often landfilled. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem of difficulty in treating titanium waste slag in the prior art and to provide a method for recovering titanium from titanium waste slag. The method has the effects of reducing environmental protection cost expenditure, low cost, simple operation, and simple equipment, and can convert all titanium compounds in the waste slag into anatase titanium dioxide, and the product can be reused in the preparation of SCR denitrification catalyst.

[0005] In order to achieve the above object, the present invention provides a method for recovering titanium from titanium waste slag in a first aspect, wherein the method comprises the following steps:

[0006] 1) adding a buffer in the presence of water to obtain solution A;

[0007] 2) bringing solution A into first contact with titanium waste slag to obtain solution B;

[0008] 3) contacting solution B with a base for a second time to obtain solution C;

[0009] 4) Centrifuge and dry solution C to obtain titanium dioxide.

[0010] The buffer is one or more of a mixture of acetic acid and sodium acetate, a mixture of ammonia water and ammonium chloride, ammonium carbonate and ammonium bicarbonate.

[0011] The amount of the buffer is such that the pH value of the solution A is 7.1-11.

[0012] The amount of the titanium waste slag is such that the pH value of the solution B is 4-7.

[0013] The amount of the alkali is such that the pH value of the solution C is 7.1-11,

[0014] In the mixture of acetic acid and sodium acetate, the mass ratio of acetic acid to sodium acetate is 1:10-1000.

[0015] In the mixture of ammonia water and ammonium chloride, NH 3 ·H 2 The mass dosage ratio of aqueous ammonia to ammonium chloride is 1:25-3000.

[0016] Preferably, the amount of the buffer is such that the pH value of the solution A is 7.1-9.5;

[0017] Preferably, the amount of the titanium waste slag is such that the pH value of the solution B is 4.5-6.5;

[0018] Preferably, the amount of the base is such that the pH value of the solution C is 7.1-9.5;

[0019] Preferably, the amount of the base used is such that the pH value of solution C is restored to the pH value of solution A.

[0020] Preferably, the titanium waste slag contains one or more of titanium tetrachloride, titanium alkoxide and chlorine-substituted titanium alkoxide.

[0021] Preferably, the base is a base with a pK b Bases with values ​​of 3-12;

[0022] Preferably, the base is one or more of ammonium carbonate, ammonium bicarbonate, ammonia water, ammonium acetate and ammonium citrate.

[0023] Preferably, the method further comprises the step of repeating step 2) and step 3).

[0024] Preferably, the centrifugal separation conditions include: temperature of 1-40°C, rotation speed of 500-10000 rpm, and time of 3-180 min.

[0025] Preferably, the drying conditions include: temperature of 40-150° C., time of 1-48 h; preferably, the drying conditions include: temperature of 70-100° C., time of 1-12 h.

[0026] The second aspect of the present invention provides titanium dioxide, which is prepared by the method for recovering titanium from titanium waste slag as described in any one of the first aspects of the present invention.

[0027] Preferably, the crystalline phase of the titanium dioxide is anatase phase.

[0028] The third aspect of the present invention provides a method for preparing an SCR denitration catalyst, wherein the method comprises the steps of preparing titanium dioxide by the method for recovering titanium from titanium waste slag as described in any one of the first aspects of the present invention, and the step of preparing the SCR denitration catalyst using the titanium dioxide as a raw material.

[0029] The method for recovering titanium from titanium waste slag provided by the present invention reduces the cost of hazardous waste treatment and the purchase of titanium dioxide in the production of SCR denitration catalysts. The equipment is easily available, the operation steps are simple, and there is no risk of liquid splashing during the operation. It is easy to realize industrialized large-scale production and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a graph showing the nitrogen oxide conversion rate at different temperatures. DETAILED DESCRIPTION

[0031] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0032] According to a first aspect of the present invention, a method for recovering titanium from titanium waste slag is provided, characterized in that the method comprises the following steps:

[0033] 1) adding a buffer in the presence of water to obtain solution A;

[0034] 2) bringing solution A into first contact with titanium waste slag to obtain solution B;

[0035] 3) contacting solution B with a base for a second time to obtain solution C;

[0036] 4) Centrifuge and dry solution C to obtain titanium dioxide.

[0037] The buffer is one or more of a mixture of acetic acid and sodium acetate, a mixture of ammonia water and ammonium chloride, ammonium carbonate and ammonium bicarbonate.

[0038] The amount of the buffer is such that the pH value of the solution A is 7.1-11.

[0039] The amount of the titanium waste slag is such that the pH value of the solution B is 4-7.

[0040] The amount of the alkali is such that the pH value of the solution C is 7.1-11,

[0041] In the mixture of acetic acid and sodium acetate, the mass ratio of acetic acid to sodium acetate is 1:10-1000.

[0042] In the mixture of ammonia water and ammonium chloride, NH 3 ·H 2 The mass dosage ratio of aqueous ammonia to ammonium chloride is 1:25-3000.

[0043] According to the present invention, preferably, in the mixture of acetic acid and sodium acetate, the mass ratio of acetic acid to sodium acetate is 1:50-150; more preferably, in the mixture of acetic acid and sodium acetate, the mass ratio of acetic acid to sodium acetate is 1:80-100.

[0044] According to the present invention, preferably, in the mixture of ammonia water and ammonium chloride, NH 3 ·H 2 The mass ratio of ammonia water to ammonium chloride is 1:200-400. More preferably, NH 3 ·H 2 The mass ratio of ammonia water to ammonium chloride is 1:200-300. 3 ·H 2 The mass ratio of aqueous ammonia to ammonium chloride is 1:250-300.

[0045] According to the present invention, in order to ensure that the final product is anatase titanium dioxide and that the titanium compounds in the titanium waste slag can be completely converted into titanium dioxide, preferably, the amount of the buffer is such that the pH value of the solution A is 7.1-9.5.

[0046] Specific examples of the amount of the buffer used to achieve a pH value of the solution A include 7.1, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.3, 9.4, 9.5, 9.6, 9.8, 10, 10.5, 11, etc., and ranges formed by any two of the above.

[0047] According to the present invention, preferably, the amount of the titanium waste slag is such that the pH value of the solution B is 4.5-6.5.

[0048] Specific examples of the amount of the titanium waste slag used to make the pH value of the solution B include: 4, 4.2, 4.4, 4.6, 4.2, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.5, 6.6, 6.8, 7, etc., and the range formed by any two of the above.

[0049] According to the present invention, preferably, the amount of the base used is such that the pH value of the solution C is 5-10.

[0050] Specific examples of the amount of the buffer used to achieve a pH value of the solution A include 7.1, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.3, 9.4, 9.5, 9.6, 9.8, 10, 10.5, 11, etc., and ranges formed by any two of the above.

[0051] In a particularly preferred embodiment of the present invention, the amount of the base used is such that the pH value of solution C is restored to the pH value of solution A.

[0052] In the present invention, first, water and a buffer are mixed to obtain a solution A.

[0053] In the present invention, by using a buffer and an alkali to adjust the pH value, it can be ensured that the final product obtained is titanium dioxide, thereby improving the recycling rate and reducing costs while protecting the environment.

[0054] According to the present invention, in order to make the operation simpler, preferably, the buffer is ammonium carbonate and / or ammonium bicarbonate; more preferably, the buffer is ammonium bicarbonate. When ammonium carbonate and / or ammonium bicarbonate are used, since ammonium carbonate and ammonium bicarbonate are buffers themselves and can also act as a base, the operation is simpler.

[0055] In the present invention, solution A is first contacted with titanium waste slag, and there is no particular limitation on the first contact, and the reaction can be carried out under normal conditions (such as room temperature 5-40°C, and there is no particular limitation on the time). In step 2), titanium waste slag is slowly added to solution A to obtain solution B.

[0056] According to the present invention, the titanium waste slag is titanium-containing waste slag commonly produced in the art, without special limitation, such as organic titanium process waste slag, titanium tetrachloride, etc. Preferably, the titanium waste slag contains one or more of titanium tetrachloride, alkoxy titanium and chlorine-substituted alkoxy titanium.

[0057] In the present invention, solution B is brought into second contact with a base. There is no particular limitation on the second contact, and the reaction can be carried out under normal conditions (such as room temperature 5-40° C., and there is no particular limitation on the time). In step 3), a base is added to solution B to obtain solution C.

[0058] According to the present invention, in order to be able to more effectively control the pH value, preferably, the base is a base with a pK b Preferably, the base is one or more of ammonium carbonate, ammonium bicarbonate, ammonia, ammonium acetate and ammonium citrate.b When the pH value of the solution is a strong base with a pK value below 3, the pH value of the solution rises too fast and the pH value cannot be effectively controlled. Therefore, in the present invention, the pH value of the solution with a pK value of 0.04 is used. b Bases with values ​​of 3-12.

[0059] According to the present invention, in order to further stabilize the pH of the hydrolysis system, step 2) and step 3) can be repeated. Preferably, the number of repetitions is 1-7 times, for example, 1 time, 2 times, 3 times, 4 times, 5 times, 6 times or 7 times.

[0060] Specifically, repeat step 2) and step 3) once for explanation, and the specific steps are as follows:

[0061] 1) adding a buffer in the presence of water to obtain solution A;

[0062] 2) bringing solution A into first contact with organic titanium waste residue to obtain solution B;

[0063] 3) contacting solution B with a base for a second time to obtain solution C;

[0064] 3-1) bringing solution C into first contact with organic titanium waste residue to obtain solution B 1 ;

[0065] 3-2) Solution B 1 A second contact with a base is performed to obtain a solution C 1 ;

[0066] 4) Solution C 1 The product was centrifuged and dried to obtain titanium dioxide.

[0067] In the present invention, before step 4), a step of stirring solution C may be further included. There is no particular limitation on the stirring operation. It is only necessary to stir the mixture in solution C until it is uniformly mixed. Preferably, the stirring time is 0.2-1 h.

[0068] Next, the solution C was centrifuged and dried to obtain anatase titanium dioxide.

[0069] According to the present invention, there is no particular limitation on the centrifugal separation operation, and various conventional centrifugal separation methods in the art can be used. Preferably, in step 4), the centrifugal separation conditions include: temperature of 1-40°C, rotation speed of 500-10000rpm, and time of 3-180min.

[0070] According to the present invention, there is no particular limitation on the drying operation, and various conventional drying methods in the art can be used. Preferably, the drying conditions include: a temperature of 40-150°C and a time of 1-48h; more preferably, the drying conditions include: a temperature of 70-100°C and a time of 1-12h.

[0071] According to a second aspect of the present invention, there is provided titanium dioxide, which is prepared by the method for recovering titanium from titanium waste slag according to the first aspect of the present invention.

[0072] According to the present invention, preferably, the crystal phase of the titanium dioxide is anatase phase.

[0073] According to a third aspect of the present invention, a method for preparing an SCR denitration catalyst is provided, the method comprising the steps of preparing titanium dioxide by the method for recovering titanium from titanium waste slag as described in the first aspect of the present invention, and preparing the SCR denitration catalyst using the titanium dioxide as a raw material.

[0074] The present invention will be described in detail below by way of examples, but the present invention is not limited to the following examples.

[0075] XRD testing equipment: purchased from Rigaku, Japan, model SmartLab.

[0076] Example 1

[0077] 1) At 25°C, 0.6 g of ammonium carbonate was mixed with 7.5 ml of water to obtain a solution A with a pH of 9.4;

[0078] 2) Slowly add titanium waste slag to solution A until pH = 5.1 to obtain solution B, in which white precipitate can be seen;

[0079] 3) adding ammonium carbonate to solution B so that the pH value of the solution is 9.4 to obtain solution C;

[0080] 4) Stirring solution C for 0.5 h, centrifuging (temperature 25° C., speed 6000 rpm, 5 min), and drying at 80° C. for 12 h to obtain titanium dioxide S1.

[0081] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0082] Example 2

[0083] 1) At 25°C, 0.7 g of ammonium carbonate was mixed with 7.5 ml of water to obtain a solution A with a pH of 9.1;

[0084] 2) Slowly add titanium waste slag to solution A until pH = 5.3 to obtain solution B, in which white precipitate can be seen;

[0085] 3) adding ammonium carbonate to solution B so that the pH value of the solution is 9.1 to obtain solution C;

[0086] 3-1) Slowly add titanium waste slag to solution C until pH = 5.3 to obtain solution B 1 ;

[0087] 3-2) In solution B 1 Ammonium carbonate was added to make the pH value of the solution 9.1 to obtain solution C 1 ;

[0088] 3-3) In solution C 1 Slowly add titanium waste to pH = 5.3 to obtain solution B 2 ;

[0089] 3-4) In solution B 2 Ammonium carbonate was added to make the pH value of the solution 9.1 to obtain solution C 2 ;

[0090] 8) Stir solution C 2 After 0.5 h, centrifugation was performed (temperature 25°C, rotation speed 6000 rpm, 6 min) and then dried at 80°C for 12 hours to obtain titanium dioxide S2.

[0091] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0092] Example 3

[0093] 1) At 25°C, 1.25 g of ammonium carbonate was mixed with 15 ml of water to obtain a solution A with a pH of 9.3;

[0094] 2) Slowly add titanium waste slag to solution A until the pH is 4.8 to obtain solution B, in which white precipitate can be seen;

[0095] 3) adding ammonium carbonate to solution B so that the pH value of the solution is 9.3 to obtain solution C;

[0096] 3-1) Slowly add titanium waste slag to solution C until pH = 4.8 to obtain solution B 1 ;

[0097] 3-2) In solution B 1 Ammonium carbonate was added to make the pH value of the solution 9.3 to obtain solution C 1 ;

[0098] 3-3) In solution C 1 Slowly add titanium waste to pH = 4.8 to obtain solution B 2 ;

[0099] 3-4) In solution B 2Ammonium carbonate was added to make the pH value of the solution 9.3 to obtain solution C 2 ;

[0100] 8) Stir solution C 2 After 0.5 h, centrifugation was performed (temperature 25° C., rotation speed 6000 rpm, 5 min) and then dried at 80° C. for 12 hours to obtain titanium dioxide S3.

[0101] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0102] Example 4

[0103] 1) At 25°C, 7.906 g of ammonium carbonate was mixed with 50 ml of water to obtain a solution A with a pH of 7.1;

[0104] 2) Slowly add titanium waste slag to solution A until pH = 6.0 to obtain solution B, in which white precipitate can be seen;

[0105] 3) adding ammonium carbonate to solution B so that the pH value of the solution is 7.1 to obtain solution C;

[0106] 3-1) Slowly add titanium waste slag to solution C until pH = 6.0 to obtain solution B 1 ;

[0107] 3-2) In solution B 1 Ammonium carbonate was added to the solution to make the pH value of the solution 7.1 to obtain solution C 1 ;

[0108] 3-3) In solution C 1 Slowly add titanium waste slag to pH = 6.0 to obtain solution B 2 ;

[0109] 3-4) In solution B 2 Ammonium carbonate was added to the solution to make the pH value of the solution 7.1 to obtain solution C 2 ;

[0110] 3-5) In solution C 2 Slowly add titanium waste slag to pH = 6.0 to obtain solution B 3 ;

[0111] 3-6) In solution B 3 Ammonium carbonate was added to the solution to make the pH value of the solution 7.1 to obtain solution C 3 ;

[0112] 10) Stir solution C 3 After 0.5 h, centrifugation was performed (temperature 25°C, rotation speed 6000 rpm, 6 min) and then dried at 80°C for 12 hours to obtain titanium dioxide S4.

[0113] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0114] Example 5

[0115] 1) At 25° C., a mixture of 0.9 g of aqueous ammonia and ammonium chloride (the weight ratio of aqueous ammonia to ammonium chloride is 1:100) and 7.5 ml of water were mixed to obtain a solution A with a pH of 8.9;

[0116] 2) Slowly add titanium waste slag to solution A until pH = 6.1 to obtain solution B, in which white precipitate can be seen;

[0117] 3) adding ammonia water to solution B so that the pH value of the solution is 8.9 to obtain solution C;

[0118] 3-1) Slowly add titanium waste slag to solution C until pH = 6.1 to obtain solution B 1 ;

[0119] 3-2) In solution B 1 Ammonia water was added to make the pH value of the solution 8.9 to obtain solution C 1 ;

[0120] 3-3) In solution C 1 Slowly add titanium waste to pH = 6.1 to obtain solution B 2 ;

[0121] 3-4) In solution B 2 Ammonia water was added to make the pH value of the solution 8.9 to obtain solution C 2 ;

[0122] 8) Stir solution C 2 After 0.5 h, the mixture was centrifuged (temperature 25 ° C, rotation speed 6000 rpm, 6 min) and dried at 80 ° C for 12 hours to obtain titanium dioxide S5.

[0123] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0124] Example 6

[0125] 1) At 25° C., a mixture of 0.7 g of acetic acid and sodium acetate (the weight ratio of acetic acid to sodium acetate is 1:275) and 7.5 ml of water are mixed to obtain a solution A with a pH of 9.0;

[0126] 2) Slowly add titanium waste slag to solution A until the pH is 6.5 to obtain solution B, in which white precipitate can be seen;

[0127] 3) adding ammonia water to solution B so that the pH value of the solution is 9.0 to obtain solution C;

[0128] 3-1) Slowly add titanium waste slag to solution C until pH = 6.5 to obtain solution B 1 ;

[0129] 3-2) In solution B 1 Ammonia water was added to make the pH value of the solution 9.0 to obtain solution C 1 ;

[0130] 3-3) In solution C 1 Slowly add titanium waste slag to pH = 6.5 to obtain solution B 2 ;

[0131] 3-4) In solution B 2 Ammonia water was added to make the pH value of the solution 9.0 to obtain solution C 2 ;

[0132] 8) Stir solution C 2 After 0.5 h, the mixture was centrifuged (temperature 25 ° C, speed 6000 rpm, 6 min) and dried at 80 ° C for 12 hours to obtain titanium dioxide S6.

[0133] XRD analysis confirmed that it was pure anatase titanium dioxide.

[0134] Comparative Example 1

[0135] 1) At 25°C, 5 g of ammonium carbonate was mixed with 15 ml of water to obtain a solution A with a pH of 12.1;

[0136] 2) Slowly add titanium waste slag to solution A until pH = 7.2 to obtain solution B. White precipitate can be seen in solution B, and during the addition of titanium waste slag, the liquid has obvious splashing phenomenon;

[0137] 3) adding ammonium carbonate to solution B so that the pH value of the solution is 12.1 to obtain solution C;

[0138] 4) Stirring solution C for 0.5 h, centrifuging (temperature 25° C., speed 6000 rpm, 5 min), and drying at 80° C. for 12 h to obtain titanium dioxide D1.

[0139] XRD analysis confirmed that the crystal phase contained anatase and rutile.

[0140] Comparative Example 2

[0141] 1) At 25°C, 1.25 g of ammonium carbonate was mixed with 15 ml of water to obtain a solution A with a pH of 9.3;

[0142] 2) Slowly add titanium waste slag to solution A until pH = 0.3 to obtain solution B,

[0143] At this point the titanium slag is completely dissolved and the solution is clear.

[0144] Test Example 1

[0145] The titanium dioxide obtained in Example 1 or commercial anatase titanium dioxide and ammonium metavanadate were mixed in proportion (the dosage ratio was 1 wt % V in terms of oxide). 2 O 5 :99wt%V 2 O 5 ), add water and heat to dissolve, stir evenly and heat to evaporate to dryness. The obtained solid is dried at 100°C overnight and calcined at 550°C for 2h to obtain a catalyst.

[0146] Take 100 mg of catalyst and heat it for 60000 h -1 Catalyst activity was evaluated at a space velocity of 500 ppm NO + 550 ppm NH 3 +2vol.%O 2 +N 2 , the nitrogen oxide conversion rate was tested at different temperatures, and the results are as follows Figure 1 shown.

[0147] Figure 1 It is a graph showing the nitrogen oxide conversion rate at different temperatures. It can be seen from the graph that the denitrification efficiency of Example 1 (the triangle mark in the graph, or Example-1) in the entire temperature range is similar to or slightly higher than that of the reference sample (the circle mark in the graph, or Reference) made from rutile raw material.

[0148] Table 1

[0149]

[0150] It can be seen from the results in Table 1 that anatase phase titanium dioxide can be obtained by using the method of the present invention, and the titanium compound in the waste slag can be completely converted into titanium dioxide.

[0151] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for recovering titanium from titanium waste slag, characterized in that: The method comprises the following steps: 1) adding a buffer in the presence of water to obtain solution A; 2) bringing solution A into first contact with titanium waste slag to obtain solution B; 3) contacting solution B with a base for a second time to obtain solution C; 4) Centrifuge and dry solution C to obtain titanium dioxide. Wherein, the buffer is one or more of a mixture of acetic acid and sodium acetate, a mixture of ammonia water and ammonium chloride, ammonium carbonate and ammonium bicarbonate. The amount of the buffer is such that the pH value of the solution A is 7.1-11. The amount of the titanium waste slag is such that the pH value of the solution B is 4-7. The amount of the alkali is such that the pH value of the solution C is 7.1-11, In the mixture of acetic acid and sodium acetate, the mass ratio of acetic acid to sodium acetate is 1:10-1000. In the mixture of ammonia water and ammonium chloride, the mass ratio of ammonia water to ammonium chloride calculated as NH3·H2O is 1:25-3000.

2. The method according to claim 1, wherein: The amount of the buffer is such that the pH value of the solution A is 7.1-9.5; Preferably, the amount of the titanium waste slag is such that the pH value of the solution B is 4.5-6.5; Preferably, the amount of the base is such that the pH value of the solution C is 7.1-9.5; Preferably, the amount of the base used is such that the pH value of solution C is restored to the pH value of solution A.

3. The method according to claim 1, wherein: In step 2), the titanium waste slag contains one or more of titanium tetrachloride, titanium alkoxide and chlorine-substituted titanium alkoxide.

4. The method according to claim 1, wherein: In step 3), the base is b Bases with values ​​of 3-12; Preferably, the base is one or more of ammonium carbonate, ammonium bicarbonate, ammonia water, ammonium acetate and ammonium citrate.

5. The method according to claim 1, wherein: Before performing step 4), the method further comprises the steps of repeating steps 2) and 3).

6. The method according to claim 1, wherein: In step 4), the centrifugal separation conditions include: temperature of 1-40°C, rotation speed of 500-10000 rpm, and time of 3-180 min.

7. The method according to claim 1, wherein: In step 4), the drying conditions include: temperature of 40-150° C., time of 1-48 h; preferably, the drying conditions include: temperature of 70-100° C., time of 1-12 h.

8. A titanium dioxide, characterized in that The titanium is prepared by the method for recovering titanium from titanium waste slag as described in any one of claims 1 to 7.

9. The titanium dioxide according to claim 8, wherein The crystalline phase of the titanium dioxide is anatase phase.

10. A method for preparing a SCR denitration catalyst, characterized in that: The method comprises the steps of preparing titanium dioxide by the method for recovering titanium from titanium waste slag as claimed in any one of claims 1 to 7, and preparing an SCR denitration catalyst by using the titanium dioxide as a raw material.

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