A method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum

Abstract

The invention discloses a method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum. The wastewater treatment comprises the following steps: adding acidic wastewater to limestone slurry, performing a first neutralization reaction, generating a primary precipitated white gypsum and a supernatant; then performing acid leaching to remove iron, and then washing, dehydrating, drying, and calcining the precipitate to obtain gypsum powder; adding limestone slurry to the supernatant, and continuously stirring, performing a second neutralization reaction, generating a secondary precipitate and a supernatant, and the secondary precipitate is dehydrated to serve as a raw material for recovering vanadium and titanium; adding alkali residue slurry to the supernatant generated by the second neutralization reaction, performing a third neutralization reaction, generating a tertiary precipitate, and the tertiary precipitate is dehydrated to serve as a raw material for recovering iron. The present invention realizes the effective separation of gypsum and valuable metals (iron, vanadium, and titanium), greatly reduces the moisture content of gypsum, and simultaneously promotes the comprehensive utilization of gypsum and the recycling of valuable metals (iron, vanadium, and titanium).

Description

Technical Field

[0001] The invention relates to the technical field of acidic wastewater treatment, and in particular to a method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum. Background Art

[0002] Currently, acidic wastewater generated by the sulfuric acid process titanium dioxide industry, both domestically and internationally, is mostly treated using either a one-step or two-step neutralization process. The one-step neutralization process involves adding carbide slag or slaked lime powder to the acidic wastewater, adjusting the pH to approximately 7. This produces titanium gypsum, primarily composed of calcium sulfate and ferric (or ferrous) hydroxide. However, due to its high impurity content, high water content, high viscosity, and poor color, building materials produced directly from this gypsum have low flexural and compressive strengths, failing to meet building material standards. Furthermore, the valuable metals in the gypsum, such as vanadium, titanium, and iron, cannot be recycled. The two-step neutralization process typically involves adding limestone slurry to the acidic wastewater for neutralization. The pH typically rises slowly after reaching 4. In the second step, carbide slag or slaked lime powder is added to adjust the pH to approximately 7. This two-step neutralization process also produces only one precipitate, namely titanium gypsum. This gypsum, similar to the one-step process, has properties that make it virtually unusable and its valuable metals unrecoverable. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present invention is to provide a method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum, so as to solve the problems that the gypsum produced by the existing method for treating titanium dioxide acidic wastewater has many impurities, high water content, low strength, and valuable metals such as vanadium, titanium and iron in the gypsum cannot be recycled.

[0004] The present invention solves the above technical problems with the following technical solutions: Provided is a method for treating titanium dioxide acid wastewater and comprehensively utilizing titanium gypsum, comprising the following steps:

[0005] (1) filtering and removing slag from the titanium dioxide acid wastewater, adding the deslagging acid wastewater to a continuously stirred limestone slurry to carry out the first step of neutralization reaction, and generating a primary precipitated white gypsum when the pH value is reduced to 1.8-2.2;

[0006] (2) acid leaching the primary precipitated white gypsum to remove iron, then washing and dehydrating the precipitate after iron removal to obtain white gypsum, which is then dried and calcined to obtain gypsum powder;

[0007] (3) adding limestone slurry to the supernatant generated by the first neutralization reaction, and continuously stirring to carry out the second neutralization reaction. When the pH value is 3.8-4, a secondary precipitate and a supernatant are generated;

[0008] (4) Alkali residue slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. When the pH is greater than 7, three precipitations are generated.

[0009] The beneficial effects of the present invention are as follows: after removing impurities from titanium dioxide acidic wastewater, the present invention uses a three-step neutralization method, and the secondary precipitation is dehydrated to serve as a raw material for recovering vanadium and titanium, and the tertiary precipitation is dehydrated to serve as a raw material for recovering iron, thereby achieving effective separation of white gypsum (calcium sulfate) and valuable metals (iron, vanadium and titanium), greatly reducing the water content of white gypsum, and promoting the comprehensive utilization of white gypsum and the recovery and utilization of valuable metals (iron, vanadium and titanium).

[0010] The reaction process of the present invention is as follows:

[0011] 1. The first step of neutralization reaction (pH value drops from 7 to 1.8-2.2) is mainly divided into two steps:

[0012] S1: pH drops from 7 to around 5:

[0013] CaCO3+2H + →Ca 2+ +H2O+CO2↑

[0014] Ca 2+ +SO4 2- →CaSO4↓

[0015] Fe 2- +2H2O→Fe(OH)2↓+2H + (pH>4)

[0016] A small amount of 4Fe(OH)2↓+O2+2H2O→4Fe(OH)3↓

[0017] TiO 2+ +2H2O→TiO(OH)2↓+2H + (pH ≥ 4)

[0018] 2VO2 + +3H2O→V2O5↓+6H + (pH ≥ 4)

[0019] This step mainly produces three kinds of precipitation mixtures, the first is calcium sulfate precipitate, the second is ferrous hydroxide precipitate and ferric hydroxide precipitate, and the third is titanium precipitate and vanadium precipitate; among them, the second ferrous hydroxide precipitate is mainly in the form of colloidal precipitate, and some of it is converted into ferric hydroxide precipitate due to air oxidation. The third is unstable metatitanic acid precipitate and vanadium pentoxide precipitate.

[0020] S2: pH value drops from 5 to 1.8-2.2:

[0021] Fe(OH)2+2H + →Fe 2+ +2H2O

[0022] 2Fe(OH)3+6H + →2Fe 3+ +6H2O

[0023] TiO(OH)2+2H + →TiO 2+ +2H2O

[0024] V2O5+2H + →2VO2 + +H2O

[0025] This step re-dissolves the iron precipitate, titanium precipitate and vanadium precipitate generated in step S1, and finally only white calcium sulfate precipitate remains.

[0026] In the first neutralization reaction, calcium carbonate finally only reacts with sulfuric acid, and the neutralization reaction completes more than 90mt% of the sulfuric acid. After the first neutralization reaction, the mass fraction of sulfuric acid in the supernatant of the acidic wastewater decreases from the initial 1.5-3% to 0.1-0.5%, and the mass fractions of other components do not change much. The precipitate produced in this step is the largest among the precipitates produced by the three-step neutralization reaction, and the precipitate amount accounts for more than 70mt%.

[0027] In the first neutralization reaction, the pH value is maintained above 5 for most of the reaction process, which can ensure that the generated CaSO4 is in the form of granular or flaky crystals with a moisture content of less than 12%. As a result, the subsequently prepared building gypsum powder has high strength and good quality. Therefore, the building gypsum powder produced by the present invention has high compressive and flexural strengths and meets the requirements of grade 2.0 and above of the "Building Gypsum" standard.

[0028] 2. The second step of neutralization reaction (pH value rises from 1.8-2.2 to 3.8-4) main chemical reactions:

[0029] H2SO4+CaCO3→CaSO4↓+H2O+CO2↑

[0030] FeSO4+CaCO3+2H2O→CaSO4↓+Fe(OH)2↓+H2CO3(H2CO3→H2O+CO2↑)

[0031] A small amount of 4Fe(OH)2↓+O2+2H2O→4Fe(OH)3↓

[0032] TiOSO4+CaCO3→CaSO4↓+TiO(OH)2↓+H2CO3

[0033] TiO 2+ +2H2O→TiO(OH)2↓+2H + (at pH 4)

[0034] 2VO2 + +3H2O→V2O5↓+6H + (at pH 4)

[0035] This step mainly produces a mixture of three precipitates, the first of which is a calcium sulfate precipitate, the second of which is a ferrous hydroxide precipitate and a small amount of ferric hydroxide precipitate, and the third of which is a metatitanic acid precipitate and a vanadium precipitate. In the mixed precipitate, calcium sulfate accounts for 45-55mt%, ferrous hydroxide precipitate (containing a small amount of ferric hydroxide) precipitate accounts for 20-25mt%, metatitanic acid precipitate accounts for 9-12mt%, and other substances account for 10-20mt% (of which vanadium precipitate accounts for 0.5-1mt%). After the second step of neutralization reaction, almost all of the vanadium and titanium in the acidic wastewater react to form precipitates. This is because vanadium and titanium produce the most precipitates at a pH between 3.8 and 4. In acidic wastewater with a pH of 4, 90mt% of vanadium and titanium form precipitates, and in acidic wastewater with a pH of 4.5, more than 99mt% of vanadium and titanium form precipitates. The reason why the present invention determines the pH value to be 3.8-4 is that when the pH value is greater than 4, the iron content in the precipitate also increases significantly. Therefore, the pH value is determined to be 3.8-4 to separate the vanadium and titanium.

[0036] 3. The third step of neutralization reaction (pH = 3.8-4 rises to above 7) main chemical reactions:

[0037] FeSO4+Ca(OH)2→CaSO4↓+Fe(OH)2↓

[0038] 4Fe(OH)2↓+O2+2H2O→4Fe(OH)3↓

[0039] H2SO4+Ca(OH)2→CaSO4↓+2H2O

[0040] This step mainly produces a mixture of two precipitates, the first is calcium sulfate precipitate, and the second is ferrous hydroxide precipitate and a small amount of ferric hydroxide precipitate; in the mixed precipitate, calcium sulfate accounts for 61-65mt%, ferrous hydroxide precipitate (containing a small amount of ferric hydroxide) accounts for 30-32mt%, and other substances account for 3-8mt%. The precipitate produced by this precipitation reaction has the highest iron content.

[0041] On the basis of the above technical solution, the present invention can also be improved as follows:

[0042] Furthermore, calcium sulfate seeds are added to the limestone slurry in step (1).

[0043] The beneficial effect of adopting the above further technical solution is: because calcium sulfate seeds are added to the limestone slurry, the subsequently generated calcium sulfate precipitate will adhere to the seeds and grow into plate-like calcium sulfate crystals, and the subsequently prepared building gypsum powder has high strength and good quality.

[0044] Furthermore, the mass ratio of the calcium sulfate seed crystals to the limestone in the limestone slurry is 1:20-100.

[0045] Furthermore, the calcium sulfate seed crystals are selected from the white gypsum dehydrated in step (2).

[0046] Furthermore, in step (2), the white gypsum is acid-leached to remove iron by reacting an acid solution having a pH value of 0.8-1.2 with the white gypsum to remove iron; wherein the volume ratio of the white gypsum to the acid solution is 1:5-10.

[0047] Furthermore, when the acid solution reacts with the white gypsum, the stirring speed is 200-300 r / min and the reaction time is 10-20 min.

[0048] Furthermore, the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron is removed.

[0049] Furthermore, in step (2), the drying step is to steam the precipitate with gas at 500-1000° C. for 5-10 seconds.

[0050] Furthermore, the calcination temperature in step (2) is 160-180°C.

[0051] Furthermore, the secondary precipitate generated in step (3) is returned to the acidic wastewater in step (1), and steps (1) to (3) are continued. After 3-5 cycles, a secondary precipitate is generated.

[0052] The beneficial effects of adopting the above-mentioned further technical solution are: the secondary precipitate is returned to the acidic wastewater for neutralization reaction to continue to purify the white gypsum, and the content of iron, vanadium, titanium and other substances in the supernatant of the first neutralization reaction will be continuously enriched. The secondary precipitate after multiple cycles of enrichment can be used as a raw material for extracting vanadium and titanium.

[0053] Furthermore, the slurry in step (4) is prepared by adding water to carbide slag, slaked lime powder or steel slag.

[0054] The present invention has the following beneficial effects: white gypsum crystals generated by the first neutralization reaction are in the form of flakes or particles, with large crystal particles and low water content, and the subsequently produced building gypsum powder has high compressive and flexural strengths, meeting the requirements of grade 2.0 and above of the "Building Gypsum" standard; the secondary precipitate generated by the second neutralization reaction has a titanium content of 5-7 mt% and a vanadium content of 0.4-0.6 mt%, and the secondary precipitate is returned to the first neutralization reaction for multiple cycles, so that the titanium content in the secondary precipitate is enriched to 14-20 mt%, and the vanadium content is enriched to 1-2.5 mt%, and the secondary precipitate can be used as a high-quality mineral raw material for extracting vanadium and titanium and producing titanium dioxide; and the tertiary precipitate generated by the third neutralization reaction has an iron content of more than 20 mt%, and can be directly used as a raw material for ironmaking. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is an optical microscope image of the white gypsum prepared in Example 1;

[0056] Figure 2 This is an optical microscope image of the white gypsum prepared in Example 2;

[0057] Figure 3 This is an optical microscope image of the white gypsum prepared in Example 3;

[0058] Figure 4 This is an optical microscope image of the white gypsum prepared in Comparative Example 1;

[0059] Figure 5 This is a technical process flow chart of Example 1;

[0060] Figure 6 This is a physical picture of the one- to three-time precipitation obtained in Example 1;

[0061] Figure 7 This is a microscopic morphology of the primary precipitate obtained in Example 1;

[0062] Figure 8 This is a microscopic morphology of the secondary precipitate obtained in Example 1;

[0063] Figure 9 The microscopic morphology of the three precipitations prepared in Example 1;

[0064] Figure 10 This is a microscopic morphology of the mixed precipitate obtained in Comparative Example 4;

[0065] Figure 11 This is a microscopic element analysis diagram of the primary precipitate obtained in Example 1;

[0066] Figure 12 This is a microscopic element analysis diagram of the secondary precipitate obtained in Example 1;

[0067] Figure 13 The microscopic element analysis diagram of the three precipitates prepared in Example 1;

[0068] Figure 14 The microscopic element analysis diagram of the mixed precipitate prepared for Comparative Example 4; DETAILED DESCRIPTION

[0069] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0070] Example 1:

[0071] A method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum (see the process flow chart) Figure 5 ), including the following steps:

[0072] (1) Grind limestone (calcium carbonate) into 200 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:50;

[0073] (2) filtering the titanium dioxide acid wastewater to remove residue, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding the acid wastewater after deslagging to a continuously and fully stirred limestone slurry to perform the first neutralization reaction, and using a pH tester to monitor the pH value in real time. When the pH value drops to 2, a primary precipitated white gypsum is generated. During the reaction process, the pH value is maintained above 5 for most of the time and eventually drops to 2;

[0074] (3) After the primary precipitated white gypsum is filtered and dehydrated, it is introduced into a decontamination tank containing an acid solution with a pH value of 1 to dissolve and remove iron. The stirring is maintained at a low speed of 250 r / min and the reaction time is 15 min. The precipitate is then washed and dehydrated to obtain white gypsum, which is then steamed at 800°C for 8 seconds and then enters a hammer multi-stage calcination system and calcined at 170°C to obtain gypsum powder. The volume ratio of white gypsum to acid solution is 1:8, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed.

[0075] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 4, a secondary precipitate and a supernatant with high vanadium and titanium contents are generated;

[0076] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued. After four cycles, a secondary precipitate enriched in vanadium and titanium is generated, and the secondary precipitate is dehydrated and used as a raw material for recovering vanadium and titanium;

[0077] (6) Carbide slag slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 7.5, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0078] Example 2:

[0079] A method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum comprises the following steps:

[0080] (1) Grind limestone (calcium carbonate) into 180 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:20;

[0081] (2) filtering the titanium dioxide acid wastewater to remove residue, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding the acid wastewater after deslagging to a continuously and fully stirred limestone slurry to perform the first neutralization reaction, and monitoring the pH value in real time with a pH tester. When the pH value drops to 1.8, a primary precipitated white gypsum is generated, and the pH value is maintained above 5 for most of the reaction process;

[0082] (3) The primary precipitated white gypsum is filtered and dehydrated, and then introduced into a de-impurity tank containing an acid solution with a pH value of 0.8 for dissolution and iron removal, while maintaining low-speed stirring, the rotation speed is maintained at 200 r / min, and the reaction time is 20 min. The precipitate is then washed and dehydrated to obtain white gypsum, which is then steamed at 500°C for 10 seconds and then enters a hammer-type multi-stage calcination system and calcined at 160°C to obtain gypsum powder; wherein the volume ratio of white gypsum to acid solution is 1:5, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed;

[0083] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 3.8, a secondary precipitate and a supernatant with high vanadium and titanium contents are generated;

[0084] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued for three cycles to generate a secondary precipitate enriched in vanadium and titanium. The secondary precipitate is dehydrated and used as a raw material for recovering vanadium and titanium;

[0085] (6) Add slaked lime powder slurry to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 8, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0086] Example 3:

[0087] A method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum comprises the following steps:

[0088] (1) Grind limestone (calcium carbonate) into 190 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:100;

[0089] (2) filtering the titanium dioxide acid wastewater to remove residue, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding the acid wastewater after deslagging to a continuously and fully stirred limestone slurry to perform the first neutralization reaction, and monitoring the pH value in real time with a pH tester. When the pH value drops to 2.2, a primary precipitated white gypsum is generated, and the pH value is maintained above 5 for most of the reaction process;

[0090] (3) After the primary precipitated white gypsum is filtered and dehydrated, it is introduced into a decontamination tank containing an acid solution with a pH value of 1.2 to dissolve and remove iron, while maintaining low-speed stirring, the rotation speed is maintained at 300 r / min, and the reaction time is 10 min. Then, the precipitate is washed and dehydrated to obtain white gypsum, which is steamed at 1000°C for 5 seconds and then enters a hammer-type multi-stage calcination system and calcined at 160-180°C to obtain gypsum powder; wherein the volume ratio of white gypsum to acid solution is 1:10, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed;

[0091] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 3.9, a secondary precipitate and a supernatant with high vanadium and titanium contents are generated;

[0092] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued. After 5 cycles, a secondary precipitate enriched in vanadium and titanium is generated, and the secondary precipitate is dehydrated and used as a raw material for recovering vanadium and titanium;

[0093] (6) Steel slag slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 8.5, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0094] Comparative Example 1:

[0095] A method for treating titanium dioxide acidic wastewater comprises the following steps:

[0096] (1) Grind limestone (calcium carbonate) into 200 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:50;

[0097] (2) filtering the titanium dioxide acid wastewater to remove slag, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding limestone slurry to the acid wastewater after the slag removal, stirring, and performing the first step of neutralization reaction, and monitoring the pH value in real time with a pH tester. When the pH value rises from 2 to 7, a primary precipitated white gypsum is generated;

[0098] (3) After the primary precipitated white gypsum is filtered and dehydrated, it is introduced into a decontamination tank containing an acid solution with a pH value of 1 to dissolve and remove iron. The stirring is maintained at a low speed of 250 r / min and the reaction time is 15 min. The precipitate is then washed and dehydrated to obtain white gypsum, which is then steamed at 800°C for 8 seconds and then enters a hammer multi-stage calcination system and calcined at 170°C to obtain gypsum powder. The volume ratio of white gypsum to acid solution is 1:8, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed.

[0099] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 4, a secondary precipitate and a supernatant with high vanadium and titanium contents are generated;

[0100] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued. After four cycles, a secondary precipitate enriched in vanadium and titanium is generated, and the secondary precipitate is dehydrated and used as a raw material for recovering vanadium and titanium;

[0101] (6) Carbide slag slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 7.5, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0102] Comparative Example 2:

[0103] A method for treating titanium dioxide acidic wastewater comprises the following steps:

[0104] (1) Grind limestone (calcium carbonate) into 200 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:50;

[0105] (2) filtering the titanium dioxide acid wastewater to remove residue, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding the acid wastewater after deslagging to a continuously and fully stirred limestone slurry to perform the first neutralization reaction, and monitoring the pH value in real time with a pH tester. When the pH value drops to 2, a primary precipitated white gypsum is generated, and the pH value is maintained above 5 for most of the reaction process;

[0106] (3) After the primary precipitated white gypsum is filtered and dehydrated, it is introduced into a decontamination tank containing an acid solution with a pH value of 1 to dissolve and remove iron. The stirring is maintained at a low speed of 250 r / min and the reaction time is 15 min. The precipitate is then washed and dehydrated to obtain white gypsum, which is then steamed at 800°C for 8 seconds and then enters a hammer multi-stage calcination system and calcined at 170°C to obtain gypsum powder. The volume ratio of white gypsum to acid solution is 1:8, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed.

[0107] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 3, a secondary precipitate and a supernatant are generated;

[0108] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued for 4 cycles to generate a secondary precipitate, which is then dehydrated and used as a raw material for recovering vanadium and titanium;

[0109] (6) Carbide slag slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 7.5, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0110] Comparative Example 3:

[0111] A method for treating titanium dioxide acidic wastewater comprises the following steps:

[0112] (1) Grind limestone (calcium carbonate) into 200 mesh fine powder, add water, and then add calcium sulfate seeds to prepare limestone slurry; wherein the mass ratio of calcium sulfate seeds to limestone in the limestone slurry is 1:50;

[0113] (2) filtering the titanium dioxide acid wastewater to remove residue, using the filter residue as a raw material to recover vanadium, titanium, and iron, adding the acid wastewater after deslagging to a continuously and fully stirred limestone slurry to perform the first neutralization reaction, and monitoring the pH value in real time with a pH tester. When the pH value drops to 2, a primary precipitated white gypsum is generated, and the pH value is maintained above 5 for most of the reaction process;

[0114] (3) After the primary precipitated white gypsum is filtered and dehydrated, it is introduced into a decontamination tank containing an acid solution with a pH value of 1 to dissolve and remove iron. The stirring is maintained at a low speed of 250 r / min and the reaction time is 15 min. The precipitate is then washed and dehydrated to obtain white gypsum, which is then steamed at 800°C for 8 seconds and then enters a hammer multi-stage calcination system and calcined at 170°C to obtain gypsum powder. The volume ratio of white gypsum to acid solution is 1:8, and the acid solution comes from the recovered acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron removed.

[0115] (4) adding limestone slurry to the supernatant generated by the first neutralization reaction, performing a second neutralization reaction, and continuously stirring to release carbon dioxide in the water. The pH value is monitored in real time by a pH online detector. When the pH value is 6, a secondary precipitate and a supernatant are generated;

[0116] (5) The secondary precipitate generated in step (4) is returned to the acidic wastewater of step (2), and steps (2) to (4) are continued for 4 cycles to generate a secondary precipitate, which is then dehydrated and used as a raw material for recovering vanadium and titanium;

[0117] (6) Carbide slag slurry is added to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. The pH value is monitored in real time by a pH online detector. When the pH value is 7.5, three precipitations are generated. The three precipitations are dehydrated and used as raw materials for recovering iron. The water after the third step neutralization reaction can be used as recycled water in the plant after passing the test.

[0118] Comparative Example 4:

[0119] A method for treating traditional titanium dioxide acidic wastewater comprises the following steps:

[0120] (1) Limestone powder (calcium carbonate) and quicklime (calcium oxide) are ball-milled into fine powders of 200 mesh or larger, and water is added to prepare limestone slurry (calcium carbonate slurry) and lime slurry (calcium hydroxide slurry);

[0121] (2) Limestone slurry is added to the acidic wastewater and stirred continuously to carry out the first step of neutralization reaction, and the pH value is monitored in real time with a pH tester. When the pH value is 4, lime slurry is added. When the pH is ≥ 7, a traditional mixed precipitate (titanium gypsum) is generated. After dehydration by filter pressing and exposure to air, red titanium gypsum is generated.

[0122] Test example

[0123] 1. Detection of white gypsum crystal form and moisture content

[0124] The white gypsum prepared in Examples 1-3 and Comparative Example 1 was analyzed by optical microscope. Figure 1-4 ,Depend on Figure 1-4 It can be seen that the white gypsum crystals prepared in Examples 1-3 are larger and fuller, while the white gypsum crystals prepared in Comparative Example 1 are generally needle-shaped with an aspect ratio of 20-30.

[0125] The water content of the white gypsum prepared in Examples 1-3 and Comparative Example 1 was measured using an automatic water content meter. The results are shown in Table 1. As can be seen from Table 1, the water content of the white gypsum prepared in Examples 1-3 was reduced to below 12% after centrifugal dehydration, while the water content of the white gypsum prepared in Comparative Example 1 was 42% after centrifugal dehydration.

[0126] From the above results, it can be seen that the white gypsum prepared by the present invention has larger and fuller crystals and better dehydration performance. Therefore, the bulk density of the gypsum powder prepared subsequently becomes larger and the strength of the gypsum products becomes stronger.

[0127] Table 1 White gypsum moisture content

[0128]

[0129]

[0130] 2. Compressive and flexural strength test of white gypsum powder

[0131] The white gypsum powder prepared in Examples 1-3 and Comparative Example 1, and the traditional titanium gypsum prepared in Comparative Example 4 were prepared into building gypsum powder test blocks, and the compressive and flexural strength were tested using an integrated flexural and compressive strength tester. The test results are shown in Table 2. As can be seen from Table 2, the gypsum powder prepared in Examples 1-3 has high flexural and compressive strength, meeting the requirements of grade 2.0 and above in "Building Gypsum" (GB / T 9776-2008).

[0132] Table 2 Compression and flexural strength of white gypsum powder

[0133]

[0134] 3. Detection of titanium and vanadium content in secondary precipitation

[0135] The titanium and vanadium contents in the secondary precipitates prepared in Examples 1-3 and Comparative Examples 2-3 were detected by XRF. The test results are shown in Table 3. As can be seen from Table 3, the titanium content in the secondary precipitates of the present invention is enriched to 14-20 mt%, and the vanadium content is enriched to 1-2.5 mt%. They can be used as high-quality mineral raw materials for extracting vanadium and titanium and producing titanium dioxide, and achieve effective separation of gypsum (calcium sulfate) and valuable metals.

[0136] Table 3 Titanium and vanadium content in secondary precipitation

[0137]

[0138]

[0139] 4. Detection of iron content in tertiary precipitation

[0140] The iron content in the tertiary precipitates prepared in Examples 1-3 and Comparative Examples 2-3 was detected by XRF. The test results are shown in Table 4. As can be seen from Table 4, the tertiary precipitates generated by the neutralization reaction in the third step of the present invention have an iron content of more than 20 mt%, which can be directly used as a raw material for ironmaking, thereby achieving effective separation of gypsum (calcium sulfate) and valuable metals.

[0141] Table 4 Iron content in three precipitations

[0142] Iron content (mt%) Example 1 22.5 Example 2 21.8 Example 3 23.1 Comparative Example 2 12.7 Comparative Example 3 18.5

[0143] 5. Take photos of the first, second and third precipitates obtained in Example 1. Figure 6 .Depend on Figure 6 It can be seen that the first precipitation obtained by the present invention is white gypsum, the second precipitation is vanadium-titanium gypsum, and the third precipitation is iron gypsum.

[0144] 6. The primary precipitate, secondary precipitate and tertiary precipitate obtained in Example 1 and the mixed precipitate obtained in Comparative Example 4 were analyzed by scanning electron microscopy (magnification 500-2000 times). Figure 7-10 .Depend on Figure 7-10 It can be seen that in Example 1, the primary precipitate is mainly flaky or columnar crystals (mainly gypsum), the secondary precipitate is a mixture of small particles (mainly titanium precipitate), and the tertiary precipitate is mainly flocculent precipitate (mainly iron precipitate). The mixed precipitate obtained in Comparative Example 4 is a mixed state in which block crystals (gypsum) are wrapped by flocculent matter (ferric hydroxide) and small particles (vanadium titanium precipitate).

[0145] VII. The primary precipitate, secondary precipitate and tertiary precipitate obtained in Example 1 and the mixed precipitate obtained in Comparative Example 4 were subjected to element distribution analysis using a scanning electron microscope and an energy spectrum analyzer (magnification 500-2000 times). The results are shown in FIG. Figure 11-14 .Depend on Figure 11-14It can be seen that in Example 1, the primary precipitate is mainly flaky or columnar crystals, and the elements are mainly calcium, sulfur, and oxygen coexisting simultaneously (calcium sulfate); the secondary precipitate is a mixture of small particles, and the elements are mainly titanium; the tertiary precipitate is mainly a flocculent precipitate mainly composed of iron and calcium elements; while in Comparative Example 4, the mixed precipitate elements calcium, iron, vanadium and titanium are evenly distributed.

[0146] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum, characterized in that: The following steps are involved: (1) Filter and remove the slag from the titanium dioxide acid wastewater, and add the deslagging acid wastewater into the continuously stirred limestone slurry to carry out the first step of neutralization reaction. When the pH value drops to 1.8-2.2, a primary precipitated white gypsum and a supernatant are generated; (2) The primary precipitated white gypsum is subjected to acid leaching to remove iron, and the precipitate after iron removal is washed and dehydrated to obtain white gypsum, which is then dried and calcined to obtain gypsum powder; (3) Add limestone slurry to the supernatant generated by the first neutralization reaction and continue stirring to carry out the second neutralization reaction. When the pH value is 3.8-4, a secondary precipitate and supernatant are generated; (4) Adding alkali residue slurry to the supernatant generated by the second step neutralization reaction to carry out the third step neutralization reaction. When the pH is greater than 7, three precipitations are generated; In step (1), calcium sulfate seeds are added to the limestone slurry; The mass ratio of calcium sulfate seed crystals to limestone in the limestone slurry is 1:20-100; The calcium sulfate seed crystals are selected from the white gypsum dehydrated in step (2); In step (2), the white gypsum is dissolved and iron is removed by reacting the white gypsum with an acid solution having a pH of 0.8-1.2; wherein the volume ratio of the white gypsum to the acid solution is 1:5-10; The acid solution comes from the recycled acid in the titanium dioxide production process and the recycled acid solution after the white gypsum is dissolved and iron is removed; The secondary precipitate generated in step (3) is returned to the acidic wastewater in step (1), and steps (1) to (3) are continued. After 3-5 cycles, a secondary precipitate is generated.

2. The method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum according to claim 1, characterized in that: The drying in step (2) is to steam the precipitate with gas at 500-1000°C for 5-10s.

3. The method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum according to claim 1, characterized in that: The calcination temperature in step (2) is 160-180°C.

4. The method for treating titanium dioxide acidic wastewater and comprehensively utilizing titanium gypsum according to claim 1, characterized in that: In step (4), the alkali slag slurry is prepared by adding water to carbide slag, slaked lime powder or steel slag.

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