Method for treating acidic wastewater in production of titanium dioxide by sulfuric acid method

Abstract

The invention relates to the technical field of a sulfuric acid method titanium dioxide production process, and discloses a method for treating acidic wastewater in sulfuric acid method titanium dioxide production, which comprises the following steps: feeding acidic wastewater in sulfuric acid method titanium dioxide production into a first-stage neutralization reaction tank, introducing a neutralizer, and carrying out a first-stage neutralization precipitation reaction; carrying out solid-liquid separation on the reacted slurry; the separated filter cake is recovered and sent to a titanium dioxide production process, the filtrate is sent to a second-stage neutralization reaction tank, a neutralizer is introduced, a second-stage neutralization precipitation reaction is carried out, the reacted slurry is subjected to solid-liquid separation, and the obtained filter cake is dried to obtain iron oxide; and carrying out membrane separation treatment on the filtrate after secondary separation, sending the separated dilute phase back to the titanium dioxide production process as purified water, and carrying out evaporation concentration crystallization on the separated concentrated phase solution to obtain ammonium sulfate. According to the method, resources in the acid wastewater can be fully recycled and recycled, generation of solid waste is avoided, the economic effect is improved, and green development is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of sulfuric acid process titanium dioxide production technology, and in particular to a method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process. Background Art

[0002] The sulfuric acid method is a common titanium dioxide production process, which involves acid-hydrolyzing titanium raw materials with sulfuric acid to generate titanyl sulfate, which is then hydrolyzed to generate metatitanic acid, which is then processed by calcination to produce titanium dioxide products. The sulfuric acid method uses low-cost and readily available ilmenite and sulfuric acid as raw materials, and has mature technology and simple equipment. It is currently the main production method in industrial production.

[0003] In the process of producing titanium dioxide by sulfuric acid method, a large amount of acidic wastewater such as dilute sulfuric acid is generated. The recovery, treatment and utilization of acidic wastewater are important issues in the production process of titanium dioxide by sulfuric acid method. Among them, acidic wastewater mainly comes from the first washing liquid of metatitanic acid, the filtrate and washing liquid of the second washing, the acidic wastewater of gas washing produced by acid decomposition, and the absorption water of calcination tail gas spray, etc., and metatitanic acid washing is the main source of acidic wastewater.

[0004] At present, the acidic wastewater produced by the sulfuric acid process of titanium dioxide is mainly neutralized with lime, and the chemical reaction process involved is as follows:

[0005] CaO + H2O → Ca(OH)2 (1);

[0006] H2SO4+Ca(OH)2→CaSO4·2H2O↓(2);

[0007] TiOSO4+Ca(OH)2+3H2O→Ti(OH)4↓+CaSO4·2H2O↓(3);

[0008] FeSO4+Ca(OH)2+2H2O→CaSO4·2H2O↓+Fe(OH)2↓(4);

[0009] 2FeSO4+2Ca(OH)2+4H2O+O2→2Fe(OH)3↓+2CaSO4·2H2O↓(5).

[0010] First, the acidic wastewater from each process of the production process is recovered and buffered, then air is introduced and lime is added for neutralization reaction and oxidative aeration to generate a mixed precipitate of calcium sulfate dihydrate, iron hydroxide and titanium hydroxide; then, the slurry after the reaction is separated into solid and liquid, and the resulting filter cake is gypsum calcium sulfate containing iron oxide and a small amount of titanium oxide, commonly known as titanium gypsum or red mud, which is sent out for utilization or stockpiling; the filtrate and a small amount of solids that pass through the filter are further treated by clarification, fiber filtration, etc. until the industrial treated acidic wastewater that meets the national emission standards is discharged into natural water bodies.

[0011] Since the treated water in the acid wastewater recycling treatment cannot be recycled, the entry conditions of the titanium dioxide industry stipulate that the discharge of acid wastewater from sulfuric acid process titanium dioxide treatment must be less than 80m3 per ton. 3 The existing treatment technology and means can achieve an ideal acid wastewater discharge of about 60m3 per ton of sulfuric acid titanium dioxide. 3 At the same time, the impurity elements in the lime and enriched sewage are sent out as titanium gypsum solid waste, which not only produces huge solid waste and requires a large area of ​​land for storage, but also consumes a large amount of lime, increases carbon emissions, and reduces the utilization rate of titanium and iron resources. Summary of the invention

[0012] The technical problems to be solved by the present invention are:

[0013] At present, in the process of producing titanium dioxide by sulfuric acid method, although the acidic wastewater can be made to meet the national emission standards through lime neutralization and other methods, the treatment of acidic wastewater generated in the production of titanium dioxide will still cause a large amount of waste and resource consumption, with low economic benefits and contrary to the concept of green and environmentally friendly sustainable development.

[0014] The technical solution adopted by the present invention is:

[0015] In order to treat the acidic wastewater generated in the production of titanium dioxide by the sulfuric acid process in a greener way, the present invention provides a method for treating the acidic wastewater in the production of titanium dioxide by the sulfuric acid process, comprising the following steps:

[0016] S1: The acidic wastewater generated in the production of titanium dioxide by sulfuric acid method is sent to the first stage neutralization reaction tank, and a neutralizing agent is introduced to carry out the first stage neutralization precipitation reaction, and the slurry is separated into solid and liquid after the reaction;

[0017] The filter cake after S2 separation is recovered and sent to the titanium dioxide production process, and the filtrate is sent to the second stage neutralization reaction tank, and a neutralizing agent is introduced to carry out the second stage neutralization precipitation reaction. After the reaction, the slurry is solid-liquid separated, and the obtained filter cake is dried to obtain an iron hydroxide product;

[0018] S3 performs membrane separation on the filtrate after the secondary separation, and the separated dilute phase is sent back to the titanium dioxide production process as purified water. The separated concentrated phase solution is evaporated, concentrated and crystallized to obtain ammonium sulfate product.

[0019] Preferably, the neutralizing agent is selected from one or more of ammonia gas, ammonia water, new energy green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt.

[0020] Preferably, in step S1, in the first stage of neutralization precipitation reaction, the reaction pH is controlled to be 1.0-4.0, and the reaction residence time is 0.5-2.5h.

[0021] Preferably, in step S2, in the second stage of neutralization precipitation reaction, the reaction pH is controlled to be 6.0-8.0, and the reaction residence time is 1-3 hours.

[0022] Preferably, in step S1 and step S2, after the neutralization precipitation reaction, the slurry is first thickened and then washed and separated.

[0023] Preferably, in step S3, a multi-stage reverse osmosis membrane filtration separator is used for membrane separation treatment, and the concentration multiple of the treated acidic wastewater is 1-4 times.

[0024] Preferably, the dilute phase conductivity in the membrane separation process is 10-30 μs / cm.

[0025] The treatment principle of the present invention for the acidic wastewater in the production of titanium dioxide by sulfuric acid method is as follows:

[0026] H2SO4+2NH4OH→(NH4)2SO4+2H2O(6);

[0027] TiOSO4+2(NH)4OH+H2O→TiO2·2H2O↓+(NH4)2SO4(7);

[0028] FeSO4+(NH)4OH→Fe(OH)2↓+(NH4)2SO4(8);

[0029] MSO4+(NH)4OH→M(OH)2↓+(NH4)2SO4(9);

[0030] That is, first, the sulfuric acid in the acidic wastewater produced by the sulfuric acid process titanium dioxide is neutralized with ammonia to generate ammonium sulfate. As the acidity of the wastewater gradually decreases, the soluble titanium therein begins to be precipitated. The solution after the titanium precipitation is separated and the sulfates of ferrous sulfate, iron and other trace metals M therein are further neutralized and precipitated with ammonia to precipitate iron and trace metal hydroxides, which are then precipitated and separated to obtain a dilute ammonium sulfate solution generated by all the reactions. After membrane separation and concentration, the concentrated solution is evaporated, concentrated and crystallized to produce ammonium sulfate products. The dilute phase water and concentrated evaporated condensed water obtained by membrane separation are returned to the titanium dioxide production process together to replace the original process water and realize the recycling of water resources.

[0031] The beneficial effects of the present invention are as follows:

[0032] The present invention adopts an ammonia neutralizing agent to recover the iron and titanium resources in the acidic wastewater produced by the sulfuric acid process titanium dioxide through step-by-step neutralization precipitation. The neutralizing agent reacts with sulfuric acid and sulfate in the acidic wastewater to form an ammonium sulfate solution, and the iron and titanium elements can be recovered separately, thereby realizing the effective recovery and utilization of resources in the acidic wastewater, solving the problem that the existing treatment technology will generate a large amount of treated water and solid waste titanium gypsum and is difficult to recycle, and alleviating the impact of a large amount of wastewater discharged to the outside and the like on natural water bodies.

[0033] Specifically, since the alkaline chemical energy of the ammonia neutralizer is utilized in the present invention, the sulfuric acid in the acidic wastewater can be neutralized and the sulfate ions in the metal sulfate can be replaced. Before and after the neutralization precipitation treatment, the chemical properties of the ammonia neutralizer as a nitrogen fertilizer resource have unchanged characteristics, avoiding the generation of more waste gas or solid waste due to the neutralization precipitation treatment, etc., and reducing the subsequent further treatment, discharge or stacking problems. Therefore, the method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid method of the present invention can not only recycle and reuse almost all resources in the acidic wastewater, but also avoid the generation of solid waste in the treatment process, improve the economic effect of production, and promote green and sustainable production development. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the acidic wastewater treatment method of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0036] The present invention provides a method for treating acidic wastewater in the production of titanium dioxide by a sulfuric acid process, comprising the following steps: (1)

[0038] The acidic wastewater generated in the production process of titanium dioxide by sulfuric acid method is passed into the first stage neutralization reaction tank, and a neutralizing agent is added to adjust the pH value to 1.0-4.0 (preferably 2.0-3.0) to carry out the first stage neutralization precipitation reaction; the slurry after reaction and precipitation is sent to a thickener for the first stage thickening treatment, and the thickened slurry is separated and washed, and the separated filter cake is sent back to the titanium dioxide production process as a recovered titanic acid precipitate, and the filtrate and washing liquid are combined into the thickener clear liquid and sent to the second stage neutralization reaction tank. (2)

[0040] A neutralizing agent is added to the second-stage neutralization reaction tank, and the pH value is adjusted to 6.0-8.0 (preferably 6.5-7.5) to carry out a second-stage neutralization precipitation reaction; the slurry after the reaction precipitation is sent to a thickener for a second-stage thickening treatment, and after the thickened slurry is separated and washed, the secondary filter cake is dried and dehydrated to obtain a ferric hydroxide product; the secondary filtrate and the secondary washing liquid are combined into the thickener clear liquid, and sent to a membrane filter for membrane separation treatment, and the dilute phase after membrane separation is used as purified water and returned to the titanium dioxide production process for use, which can replace the original process water and realize the recycling of water resources; the concentrated phase solution after membrane separation is evaporated, concentrated and crystallized to obtain an ammonium sulfate product.

[0041] In the present invention, the neutralizing agent can be selected from ammonia gas, ammonia water, new energy green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt, etc., and the alkaline ammonium salt can be selected from ammonium carbonate, ammonium bicarbonate, etc.; the neutralizing agent is preferably a mixture of gas ammonia and ammonia water.

[0042] In the present invention, in the membrane separation treatment after the second stage neutralization reaction, a single-stage or multi-stage reverse osmosis membrane filter separator can be used, preferably a multi-stage reverse osmosis membrane system composed of low pressure, medium pressure and high pressure, and the concentration multiple of the treated acidic wastewater is 1-4 times, preferably 2-3 times.

[0043] That is, the separated filtrate after the second stage neutralization and precipitation reaction is sent to a reverse osmosis membrane multi-stage separation device system including a pretreatment system, an osmosis and reverse osmosis system, and auxiliary dosing, cleaning, backwashing, etc. The membrane separation system is composed of high, medium and low pressure reverse osmosis membranes.

[0044] In the present invention, the concentrated phase solution after membrane separation treatment can be concentrated by multi-stage evaporation, heat pump and mechanical compression MVR, preferably MVR concentration; the dilute phase conductivity of membrane separation is 10-30μs / cm, preferably 15-25μs / cm.

[0045] Compared with the existing acid wastewater neutralization treatment method, the method for treating acid wastewater in the production of titanium dioxide by sulfuric acid method of the present invention can effectively realize the efficient resource utilization and recycling of the acid wastewater in the production of titanium dioxide. The ammonia neutralizer is used to reduce the emission of waste gas and waste byproducts in the process of acid wastewater treatment through the alkaline chemical energy of ammonia and the chemical characteristics of unchanged nitrogen resource properties, so as to realize sustainable production with carbon reduction and environmental protection to a greater extent; and the treated water can be used for the production of titanium dioxide, reducing the large demand for raw water in the production stage, realizing the recycling and repeated utilization of water resources, and improving the economic benefits of the production process.

[0046] Example 1

[0047] The sulfuric acid process for producing titanium dioxide generates 16m3 of 3 The acidic wastewater was sampled and the main components and their contents in the acidic wastewater were determined. The results are shown in Table 1:

[0048] Table 1 Composition of acidic wastewater from the production of titanium dioxide by sulfuric acid process

[0049] Components Content (g / L) Components Content (g / L) <![CDATA[H2SO4]]> 36.96 <![CDATA[MgSO4]]> 2.40 <![CDATA[FeSO4]]> 16.18 <![CDATA[Al2(SO4)3]]> 1.55 <![CDATA[TiOSO4]]> 3.12 <![CDATA[CaSO4]]> 0.25

[0050] The acid wastewater is continuously sent into the 50m 3 In the first-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the first-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the first-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1 hour. The pH value of the slurry is maintained at about 2.5 to neutralize and precipitate titanium sulfate in the acidic wastewater.

[0051] After the first stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 4m 3 The filter cake was washed with purified water from a low-pressure reverse osmosis membrane separation system, and about 71.35 kg of filter cake with a water content of about 65% was obtained per hour. The filtrate and washing liquid after filtration were added to the overflow clear liquid of the thickener to obtain 16.58 m 3 The first stage neutralizes the separation liquid.

[0052] The first stage of neutralization separation liquid is continuously fed into the 50m 3 In the second-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the second-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the second-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1.5 hours. The pH value of the slurry is maintained at about 6.5 to neutralize the ferrous sulfate and other metal sulfates in the precipitation separation liquid.

[0053] After the second stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 1m 3 The purified water of the low-pressure reverse osmosis membrane separation system is used for washing, and about 339.08 kg of filter cake with a water content of about 55% is obtained per hour. The filtrate and washing liquid after the filter press are combined with the overflow clear liquid of the thickener to obtain 17.39m 3 The second stage neutralizes the separation liquid.

[0054] The second stage of neutralization separation liquid is heated at 17.39m / h 3 , the total salt concentration is 6.55%, together with the concentrated salt solution returned from the secondary reverse osmosis cycle, it is sent to the medium-pressure reverse osmosis system of the membrane separation device, and the initial filtration pressure is controlled at 1.5MPa. After reaching the filtration pressure of 4.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 10%, it is continuously passed into the high-pressure reverse osmosis system, and the initial filtration pressure is controlled at 4.5MPa. After reaching the filtration pressure of 8.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 15%, it is passed into the MVR concentration evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation is performed to obtain 1.27t of ammonium sulfate with a water content of about 10% per hour.

[0055] The dilute phase separated by the medium-pressure reverse osmosis system and the dilute phase separated by the high-pressure reverse osmosis system are mixed with the condensed water produced by MVR evaporation and introduced into the low-pressure reverse osmosis system together. The initial filtration pressure is controlled at 0.5MPa. After reaching the filtration pressure of 2MPa, backwashing circulation filtration is carried out; the concentrated phase of the low-pressure reverse osmosis system is sent to the medium-pressure reverse osmosis system to obtain 14.8m 3 The dilute phase purified water, with an electrical conductivity of 20μs / cm, is returned to the titanium dioxide production process to replace desalted water.

[0056] Example 2

[0057] The sulfuric acid process for producing titanium dioxide generates 240m3 of 3 The acidic wastewater was sampled and the main components and their contents in the acidic wastewater were determined. The results are shown in Table 1:

[0058] Table 1 Composition of acidic wastewater from the production of titanium dioxide by sulfuric acid process

[0059]

[0060]

[0061] The acid wastewater is continuously fed into three 100m 3In the first-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the first-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the first-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1 hour. The pH value of the slurry is maintained at about 3.0 to neutralize and precipitate titanyl sulfate in the acidic wastewater.

[0062] After the first stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 4m 3 The filter cake is washed with purified water from a low-pressure reverse osmosis membrane separation system, and about 1.22 tons of filter cake with a water content of about 65% is obtained per hour. The filtrate and washing liquid after filtration are combined with the overflow clear liquid of the thickener to obtain 247.5m 3 The first stage neutralizes the separation liquid.

[0063] The first stage of neutralization separation liquid is continuously fed into three 100m 3 In the second-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the second-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the second-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1.5 hours. The pH value of the slurry is maintained at about 7.0 to neutralize the ferrous sulfate and other metal sulfates in the precipitation separation liquid.

[0064] After the second stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 20m 3 The purified water of the low-pressure reverse osmosis membrane separation system is washed several times, and about 5.866 tons of filter cake with a water content of about 55% is obtained per hour. The filtrate and washing liquid after filtration are combined with the overflow clear liquid of the thickener to obtain 264.4m 3 The second stage neutralizes the separation liquid.

[0065] The second stage neutralization separation liquid is heated at 264.4m / h 3 , the total salt concentration is 5.35%, together with the concentrated salt solution returned from the secondary reverse osmosis cycle, it is sent to the medium-pressure reverse osmosis system of the membrane separation device, and the initial filtration pressure is controlled at 1.5MPa. After reaching the filtration pressure of 4.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 10%, it is continuously passed into the high-pressure reverse osmosis system, and the initial filtration pressure is controlled at 4.5MPa. After reaching the filtration pressure of 8.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 13%, it is passed into the MVR concentration evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation is performed to obtain 14.55t of ammonium sulfate with a water content of about 2% per hour.

[0066] The dilute phase separated by the medium-pressure reverse osmosis system and the dilute phase separated by the high-pressure reverse osmosis system are mixed with the condensed water produced by MVR evaporation and introduced into the low-pressure reverse osmosis system together. The initial filtration pressure is controlled at 0.5MPa. After reaching the filtration pressure of 2MPa, backwashing circulation filtration is carried out; the concentrated phase of the low-pressure reverse osmosis system is sent to the medium-pressure reverse osmosis system to obtain 236m 3 The dilute phase purified water, with an electrical conductivity of 10μs / cm, is returned to the titanium dioxide production process to replace desalted water.

[0067] Example 3

[0068] The sulfuric acid process for producing titanium dioxide generates 1022 m3 of 3 The acidic wastewater was sampled and the main components and their contents in the acidic wastewater were determined. The results are shown in Table 1:

[0069] Table 1 Composition of acidic wastewater from the production of titanium dioxide by sulfuric acid process

[0070] Components Content (g / L) Components Content (g / L) <![CDATA[H2SO4]]> 43.72 <![CDATA[MgSO4]]> 2.69 <![CDATA[FeSO4]]> 18.91 <![CDATA[Al2(SO4)3]]> 1.74 <![CDATA[TiOSO4]]> 3.60 <![CDATA[CaSO4]]> 0.31

[0071] The acid wastewater is continuously fed into five 100m 3 In the first-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the first-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the first-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1 hour. The pH value of the slurry is maintained at about 2.2 to neutralize and precipitate titanium sulfate in the acidic wastewater.

[0072] After the first stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 4m 3 The purified water from the low-pressure reverse osmosis membrane separation system is used for washing, and about 2.82 tons of filter cake with a water content of about 65% is obtained per hour. The filtrate and washing liquid after filtration are combined with the overflow clear liquid of the thickener to obtain 1037.2m 3 The first stage neutralizes the separation liquid.

[0073] The first stage of neutralization separation liquid is continuously fed into five 100m 3 In the second-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the second-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the second-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1.5 hours. The pH value of the slurry is maintained at about 6.5 to neutralize the ferrous sulfate and other metal sulfates in the precipitation separation liquid.

[0074] After the second stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and filtered with 100m 3 The filter cake is washed with purified water from a low-pressure reverse osmosis membrane separation system, and about 16.099 tons of filter cake with a water content of about 55% is obtained per hour. The filtrate and washing liquid after filtration are added to the overflow clear liquid of the thickener to obtain 1093.5m 3 The second stage neutralizes the separation liquid.

[0075] The second stage of neutralization separation liquid is heated at 1093.5m / h 3 , the total salt concentration is 5.08%, together with the concentrated salt solution returned from the secondary reverse osmosis cycle, it is sent to the medium-pressure reverse osmosis system of the membrane separation device, and the initial filtration pressure is controlled at 1.5MPa. After reaching the filtration pressure of 4.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 10%, it is continuously passed into the high-pressure reverse osmosis system, and the initial filtration pressure is controlled at 4.5MPa. After reaching the filtration pressure of 8.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 12%, it is passed into the MVR concentration evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation is performed to obtain 56.15t of ammonium sulfate with a water content of about 0.4% per hour.

[0076] The dilute phase separated by the medium-pressure reverse osmosis system and the dilute phase separated by the high-pressure reverse osmosis system are mixed with the condensed water produced by MVR evaporation and introduced into the low-pressure reverse osmosis system together. The initial filtration pressure is controlled at 0.5MPa. After reaching the filtration pressure of 2MPa, backwashing circulation filtration is carried out; the concentrated phase of the low-pressure reverse osmosis system is sent to the medium-pressure reverse osmosis system to obtain 1010m 3 The dilute phase purified water, with an electrical conductivity of 10μs / cm, is returned to the titanium dioxide production process to replace desalted water.

[0077] Example 4

[0078] The sulfuric acid process for producing titanium dioxide generates 40.5 m3 of 3 The acidic wastewater was sampled and the main components and their contents in the acidic wastewater were determined. The results are shown in Table 1:

[0079] Table 1 Composition of acidic wastewater from the production of titanium dioxide by sulfuric acid process

[0080] Components Content (g / L) Components Content (g / L) <![CDATA[H2SO4]]> 37.25 <![CDATA[MgSO4]]> 2.42 <![CDATA[FeSO4]]> 16.33 <![CDATA[Al2(SO4)3]]> 1.60 <![CDATA[TiOSO4]]> 3.17 <![CDATA[CaSO4]]> 0.27

[0081] The acid wastewater is continuously sent into the 50m 3In the first-stage neutralization reaction tank of the volume, a stirring mechanism is arranged in the first-stage neutralization reaction tank, and an ammonia distribution pipe is arranged at the bottom of the tank. Ammonia is blown into the first-stage neutralization reaction tank, and the residence time of the reaction materials is controlled to be 1.2 hours. The pH value of the slurry is maintained at about 2.7 to neutralize and precipitate titanyl sulfate in the acidic wastewater.

[0082] After the first stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 4m 3 The purified water of the low-pressure reverse osmosis membrane separation system is used for washing, and about 200.9 kg of filter cake with a water content of about 65% is obtained per hour. The filtrate and washing liquid after the filter press are combined with the overflow clear liquid of the thickener to obtain 43.0 m 3 The first stage neutralizes the separation liquid.

[0083] The first stage of neutralization separation liquid is continuously fed into the 50m 3 The second stage neutralization reaction tank has a capacity of 2000 tons. The second stage neutralization reaction tank is equipped with a stirring mechanism and an ammonia distribution pipe is provided at the bottom of the tank. Ammonia is blown into the second stage neutralization reaction tank and 30% ammonium bicarbonate is added. The residence time of the reaction materials is controlled to be 1.75 hours and the pH value of the slurry is maintained at about 6.6 to neutralize the ferrous sulfate and other metal sulfates in the precipitation separation liquid.

[0084] After the second stage of neutralization and sedimentation, the slurry overflows into the thickener, and a small amount of flocculant is added for sedimentation and thickening. The slurry at the bottom of the thickener is continuously sent to the filter press through the filter press pump tank for filter separation and is filtered with 1m 3 The filter cake is washed with purified water from a low-pressure reverse osmosis membrane separation system, and about 752.4 kg of filter cake with a water content of about 55% is obtained per hour. The filtrate and washing liquid after filtration are added to the overflow clear liquid of the thickener to obtain 47.3 m 3 The second stage neutralizes the separation liquid.

[0085] The second stage neutralization separation liquid is heated at 47.3m / h 3 , the total salt concentration is 6.31%, together with the concentrated salt solution returned from the secondary reverse osmosis cycle, it is sent to the medium-pressure reverse osmosis system of the membrane separation device, and the initial filtration pressure is controlled at 1.5MPa. After reaching the filtration pressure of 4.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 10%, it is continuously passed into the high-pressure reverse osmosis system, and the initial filtration pressure is controlled at 4.5MPa. After reaching the filtration pressure of 8.5MPa, backwashing circulation filtration is carried out; when the total salt ion concentration of the concentrated phase solution is increased to 15%, it is passed into the MVR concentration evaporation system for evaporation, concentration and crystallization treatment, and centrifugal separation is performed to obtain 2.44t of ammonium sulfate with a water content of about 6.5% per hour.

[0086] The dilute phase separated by the medium-pressure reverse osmosis system and the dilute phase separated by the high-pressure reverse osmosis system are mixed with the condensed water produced by MVR evaporation and introduced into the low-pressure reverse osmosis system together. The initial filtration pressure is controlled at 0.5MPa. After reaching the filtration pressure of 2MPa, backwashing circulation filtration is carried out; the concentrated phase of the low-pressure reverse osmosis system is sent to the medium-pressure reverse osmosis system to obtain 55.3m 3 The dilute phase purified water, with a conductivity of 15μs / cm, is returned to the titanium dioxide production process to replace desalted water.

[0087] Through the records and verification of the above embodiments, the method for treating acidic wastewater in the production of titanium dioxide by the sulfuric acid method proposed in the invention can effectively prevent a large amount of waste gas and solid waste from being discharged into natural water bodies and the environment, and realize the recycling and reuse of resources such as water to a greater extent, bringing significant economic benefits to producers and promoting the green and sustainable development of titanium dioxide production technology.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid method, characterized in that: The steps include: S1: The acidic wastewater generated in the production of titanium dioxide by sulfuric acid method is sent to the first stage neutralization reaction tank, and a neutralizing agent is introduced to carry out the first stage neutralization precipitation reaction, and the slurry is separated into solid and liquid after the reaction; The filter cake after S2 separation is recovered and sent to the titanium dioxide production process, and the filtrate is sent to the second stage neutralization reaction tank, and a neutralizing agent is introduced to carry out the second stage neutralization precipitation reaction. After the reaction, the slurry is solid-liquid separated, and the obtained filter cake is dried to obtain an iron hydroxide product; S3 performs membrane separation on the filtrate after the secondary separation, and the separated dilute phase is sent back to the titanium dioxide production process as purified water. The separated concentrated phase solution is evaporated, concentrated and crystallized to obtain ammonium sulfate product.

2. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: The neutralizing agent is selected from one or more of ammonia gas, ammonia water, new energy green ammonia, chemical gray ammonia, natural gas, coal black ammonia and alkaline ammonium salt.

3. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S1, in the first stage of neutralization precipitation reaction, the reaction pH is controlled to be 1.0-4.0, and the reaction residence time is 0.5-2.5h.

4. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S2, in the second stage of neutralization precipitation reaction, the reaction pH is controlled to be 6.0-8.0, and the reaction residence time is 1-3 hours.

5. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 1, characterized in that: In step S1 and step S2, after the neutralization precipitation reaction, the slurry is first thickened and then washed and separated.

6. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 5, characterized in that: In step S3, a multi-stage reverse osmosis membrane filtration separator is used for membrane separation treatment, and the concentration multiple of the treated acidic wastewater is 1-4 times.

7. The method for treating acidic wastewater in the production of titanium dioxide by sulfuric acid process according to claim 6, characterized in that: The dilute phase conductivity in membrane separation treatment is 10-30μs / cm.

Images