WO2022104737A1 - Production method for full resource recycling of wastewater from sulfuric-acid-method-based titanium dioxide production - Google Patents

Abstract

A production method for the full resource recycling of wastewater from sulfuric-acid-method-based titanium dioxide production. The method involves neutralizing the wastewater from sulfuric-acid-method-based titanium dioxide production with lime, separating the wastewater from gypsum by means of a filter press (2), adding a sodium carbonate solution from a carbonization tower to the wastewater for a precipitation treatment for saturated calcium sulfate in the wastewater, clarifying and separating the slurry to obtain a calcium carbonate precipitate and a sodium sulfate solution, subjecting the separated dilute sodium sulfate solution to membrane separation by means of a membrane filter, adding lime to a concentrated phase sodium sulfate solution resulting from the membrane separation for a causticization reaction, obtaining a sodium hydroxide solution as a filtrate, subjecting same to carbonization with a carbon dioxide-containing tail gas generated during the titanium dioxide production process to obtain a sodium carbonate solution, and then returning the sodium carbonate solution to the step of precipitating saturated calcium sulfate in the wastewater treatment process. By means of the method, the technical difficulty of being incapable of economically recycling wastewater neutralized with lime during sulfuric-acid-method-based titanium dioxide production is solved, influencing factors of the external discharge of existing neutralized wastewater on an environmental water body are eliminated, and a large amount of raw water resources used for production are saved.

Description

A production method for recycling all resources of waste water from titanium dioxide production by sulfuric acid method technical field

The invention relates to a production method for the treatment and recycling of production wastewater, in particular to a resource-based production method for the treatment and recycling of titanium dioxide production wastewater by sulfuric acid method and the recycling of wastewater containing calcium sulfate.

Background technique

The wastewater produced by sulfuric acid method titanium dioxide mainly comes from the metatitanic acid in the production process, the first washing liquid, the second washing filtrate and the washing liquid, the acid waste water produced by acid hydrolysis, the spray absorption water of the calcining tail gas, the sewage circulating drainage, and the floor washing. , Equipment flushing, desalination station regeneration wastewater and sporadic wastewater. The main pollutants in the waste water are H ₂ SO ₄ , TiO ₂ , Fe ²⁺ , Fe ³⁺ , Na ⁺ and small and trace amounts of HSO ₃ ^- , F ^- and Cl ^- and other harmful substances. The chemical reaction principle of the existing wastewater treatment method is as follows:

CaO+H ₂ O→Ca(OH) ₂ (1)

H ₂ SO ₄ +Ca(OH) ₂ →CaSO ₄ ·2H ₂ O↓ (2)

FeSO ₄ +Ca(OH) ₂ +2H ₂ O→CaSO ₄ ·2H ₂ O↓+Fe(OH) ₂ ↓ (3)

FeSO ₄ +Ca(OH) ₂ +2H ₂ O+1/2O ₂ →Fe(OH) ₃ ↓+CaSO ₄ ·2H ₂ O↓ (4)

As shown in Figure 1, different types of acidic waste water from various production processes enter the adjustment tank for buffer adjustment, and are pumped to the neutralization reaction tank for air bubbling stirring and oxidation, and lime slurry is added to carry out neutralization and oxidation aeration. A mixed precipitate of calcium sulfate dihydrate and ferric hydroxide is formed; the neutralized and oxidized slurry is sent to a filter press for solid-liquid separation, and the separated filter cake is gypsum calcium sulfate containing iron oxide and a small amount of titanium oxide. It is accustomed to call it "titanium gypsum" or "red mud", which is sent for external use or storage for disposal; the pressure filtration filtrate is filtered by a clarifier or fiber filter due to the initial filtrate and filtered and a small amount of solids during filtration. Industrial wastewater that meets the national discharge standard is discharged to natural water bodies. Since the treated water cannot be recycled, the entry conditions for the titanium dioxide industry stipulate that the discharge amount of wastewater from titanium dioxide treated by sulfuric acid method must be less than 80 cubic meters. Applying and so on, the most effective production unit ton of titanium dioxide discharge and treatment wastewater is still about 60 cubic meters.

Such a large amount of treated wastewater cannot be reused. The reason is that the sulfuric acid method titanium dioxide wastewater adopts the above-mentioned reaction principle in lime, and the generated gypsum calcium sulfate is used as a precipitate with relatively large solubility, and the gypsum treated wastewater is separated. The saturated concentration of calcium sulfate is larger. The solubility product Ksp of calcium sulfate is 4.93×10 ^-5 at 25℃. Due to the influence of the "salt effect" caused by the temperature and the salt content, the treated wastewater after separation of gypsum still contains about 2-4kg per cubic meter. of saturated calcium sulfate solution. Except for a small amount of lime, the existing treatment methods are almost directly discharged into public water bodies, which not only wastes a lot of water resources, but also affects the water environment. However, the reason for not carrying out reuse and reuse is that direct reuse is very unfavorable to the production of titanium dioxide, and the traditional water treatment, purification and reuse technology and economy cannot pass the test. Its core reasons are as follows:

(1) If it is directly reused for titanium dioxide production, two unfavorable conditions will occur

First, it is used for spraying cooling circulating water. As the concentration of evaporation cycle increases, exceeding the saturated concentration and the absorption of sulfur oxides in acid gas, a large amount of calcium sulfate will be precipitated, which will block the pipeline and system, resulting in unsustainable production and cannot be used at all. .

Second, it is used as metatitanic acid washing, which consumes the most water in the production of titanium dioxide by sulfuric acid method. Also, due to the high concentration of sulfuric acid in metatitanic acid, the "same ion effect" exceeds the saturated concentration of calcium sulfate, and a large amount of calcium sulfate is precipitated. It is adsorbed on metatitanic acid and brought into the calcined product, which not only affects the content of titanium dioxide, but also seriously affects the pigment performance of titanium dioxide; at the same time, it causes the filter cloth of the filter medium to be fouled. Calcium sulfate scaling cannot be removed; therefore, cannot be used at all.

(2) If it is reused after the treatment of soft water purification, it is equally unacceptable economically and technically.

The first is to use the ion exchange method to treat the usual raw water. The ton of titanium dioxide is calculated as 60 cubic meters, of which about 240 kg of saturated calcium sulfate needs to be removed, plus the soluble sulfates brought in due to the manufacture of rutile crystal seeds and post-treatment coating. , it is necessary to use hundreds of kilograms of raw materials of anion and cation exchangers such as table salt, hydrochloric acid and sodium hydroxide, and at the same time, a large amount of concentrated brine containing calcium chloride is still discharged after the exchange, which is not only expensive, but also doubled. The quality of the effluent salt solution is unacceptable to the environment, and a lot of chemical resources are wasted.

The second is to directly use reverse osmosis membrane to separate and treat wastewater according to the usual raw water treatment. When the concentration of the concentrated brine side of the membrane separation exceeds the saturated concentration of calcium sulfate, calcium sulfate is precipitated; due to the high concentration of the membrane surface and its surface energy The surface energy of the crystal nucleus (precursor) precipitated by supersaturated calcium sulfate is large, which rapidly deposits and scales on the membrane, preventing the passage of water molecules and reducing the separation efficiency of the membrane. During the cycle, the reverse osmosis membrane will be fouled and scrapped, and the required investment is large and the operating cost is high. As described in Chinese Patent Publication No. CN106315910A, "a treatment method for titanium dioxide wastewater" not only needs to add flocculant aluminum trichloride to the treated wastewater to flocculate the ultrafine suspended solids and then perform ultrafiltration, but also to prevent saturated calcium sulfate When other substances are crystallized and deposited on the reverse osmosis membrane, scale inhibitors need to be added; since the calcium sulfate content in the treated wastewater is as high as 4000mg/L, the converted calcium ion concentration is nearly 1200mg/L, a large and expensive scale inhibitor is required, which not only increases wastewater treatment Recycling costs, due to the presence of scale inhibitors in water, affects the use of circulating water, and even affects the quality of titanium dioxide production products, such as phosphorus-based scale inhibitors and aluminum trichloride flocculants, enter titanium dioxide from recycled water. The produced metatitanic acid is enriched, and the titanium dioxide microcrystalline particles with pigment properties cannot be calcined in the rotary kiln. Because phosphorus and aluminum are both control agents for controlling the particle size and crystal form of titanium dioxide production, the amount and instability will cause The quality of titanium dioxide is inferior; if an organic complexing agent is used, the molecular weight of the complexing agent is much larger than the molecular weight of the water molecular weight and the pore size of the membrane separation, which will block the membrane pores, also reduce the separation efficiency, and even cause the membrane material to be scrapped in a short time. In addition, the dense phase brine produced by it has a low concentration and has not been used yet. It is also discharged out, which does not reduce the absolute amount of solute discharge to the water body, and enters the water body and affects the environment.

The third is to use ultrafiltration before membrane separation. Ultrafiltration is only effective for ultrafine solid particles, but is meaningless for saturated solutions or even supersaturated solutions; because the saturated concentration of calcium sulfate in the treated wastewater after separation of gypsum is relatively high Once the ultrafiltration and membrane separation is microscopically subjected to changes in pressure, temperature, fluid convection, surface friction, and surface energy, it will cause precipitation and block the water molecules and ion channels of the ultrafiltration medium and membrane, making separation difficult. .

Fourth, US patents US4966710 and US6086842, the former US4966710 uses sodium hydroxide to adjust the pH of the sodium sulfate solution to be magnesium and calcium in the precipitation solution, which is used to purify the sodium sulfate solution and reduce the chemical regenerant used for ion exchange regeneration, instead of using Impurities in the sodium carbonate precipitation solution; the latter US6086842 produces high-quality desulfurized gypsum without calcium sulfite for desulfurization tail gas, adopts sodium sulfate causticization cycle absorption, and does not use carbon dioxide in production to produce sodium carbonate.

Therefore, this is also the "crux" of the existing global sulfuric acid method titanium dioxide wastewater treatment that cannot be recycled economically, and can only be treated by the negative method of external drainage. Therefore, the consumption of raw water for production is large, the utilization rate of water resources is low, and the external drainage is astonishing, which affects the environment and does not meet the requirements of green and sustainable development. And the sulfuric acid method titanium dioxide production wastewater, using the carbon dioxide resources in the existing sulfuric acid method titanium dioxide production and the coupled production of lime raw material caustic solution and wastewater treatment, to remove the calcium ion content in the saturated calcium sulfate solution in the wastewater after separation of gypsum, It is returned to the gypsum, and the production coupling and its own waste and auxiliary resources are used, which is conducive to the recycling of all resources of the membrane separation treatment wastewater, and reduces the purchase cost of commercial chemicals; it solves the technology that the sulfuric acid method titanium dioxide neutralization treatment wastewater is difficult to recycle. The difficulty is to save the consumption of raw water resources in production, and eliminate the influence factors of the existing neutralization treatment wastewater on the environmental water body; The production process and technology production method of fully coupling and recycling its wastewater resources have not been reported.

SUMMARY OF THE INVENTION

In order to solve the technical and economic difficulties that the existing waste water of titanium dioxide production by sulfuric acid method cannot be recycled and reused, the carbon dioxide resources in the exhaust gas of titanium dioxide production by sulfuric acid method, lime caustic solution and wastewater treatment device are used for mass flow and chemical energy flow. The coupled production technology overcomes the problems and deficiencies of difficult recycling and economical utilization of titanium dioxide wastewater by sulfuric acid method after neutralization and treatment, eliminates the influence factors of the existing treatment wastewater discharge on the environmental water body, and saves the production of a large amount of raw water resources used for production as the goal. The object of the present invention is to provide a production method for the full resource recycling of waste water produced by sulfuric acid method titanium dioxide. The method is to treat the wastewater after the titanium dioxide production wastewater of the sulfuric acid method is neutralized and precipitated with limestone and lime to separate gypsum, and add the sodium carbonate solution prepared by recycling itself to precipitate, wherein the concentration of saturated calcium sulfate left in the wastewater due to the separation of gypsum is carbonic acid. Calcium and sodium sulfate slurry; precipitation reaction slurry solution is clarified to separate calcium carbonate slurry and sodium sulfate solution. The clarified and separated calcium carbonate thick slurry is recycled back to the titanium dioxide wastewater to be used as calcium carbonate resources, and the separated sodium sulfate solution is subjected to membrane separation by reverse osmosis membrane. The dilute phase liquid (purified water) obtained by membrane separation is returned to titanium dioxide production as process water, replacing the externally supplied raw water resources used in production. The concentrated salt solution containing sodium sulfate obtained by membrane separation is added with lime for causticization reaction to generate calcium sulfate precipitation and sodium hydroxide solution slurry, and the slurry is separated by pressure filtration; the separated calcium sulfate filter cake is recycled back to titanium dioxide wastewater In the slurry of neutralized and precipitated calcium sulfate, it is separated as the neutralized and precipitated wastewater gypsum; a part of the separated sodium hydroxide solution is returned to titanium dioxide as an alkali absorption liquid for acid hydrolysis and calcined acid tail gas washing, and a part is produced by titanium dioxide Carbon dioxide in the tail gas is carbonized, and sodium hydroxide is carbonized into sodium carbonate solution, which is used to remove saturated calcium sulfate in the treatment wastewater to become calcium carbonate precipitation to provide carbonate ion substances, which are recycled and returned to the treatment wastewater for precipitation in saturated calcium sulfate solution. Calcium ions; achieve the coupled recycling of all resources of titanium dioxide wastewater by sulfuric acid method. Compared with the existing technology of directly discharging waste water after neutralization treatment, the production method for the coupled utilization of total resources of titanium dioxide production waste water by sulfuric acid method protected by the present invention not only solves the full recycling utilization of titanium dioxide production waste water, but also saves money. It meets the need for a large amount of raw water in titanium dioxide production, and achieves the reuse of production water and a large number of waste water reduction; and not only optimizes the production process of waste water treatment, but also makes full use of waste secondary resources carbon dioxide from the production of titanium dioxide drying tail gas, saving waste water treatment. It also reduces the demand for sodium hydroxide in the production of titanium dioxide and maximizes the utilization of resources because of the low-cost chemical energy causticization recovery membrane of lime to separate concentrated brine. The utilization rate and reuse rate of resources are improved, the economic benefits of producers are increased, and the technical and economic goals of coupling full-cycle reuse of wastewater produced by sulfuric acid method titanium dioxide are achieved.

The production principle of the present invention is as follows:

H ₂ SO ₄ +CaCO ₃ +H ₂ O→CaSO ₄ ·2H ₂ O↓+CO ₂ ↑ (5)

H ₂ SO ₄ +Ca(OH) ₂ →CaSO ₄ ·2H ₂ O↓ (6)

CaSO ₄ ·2H ₂ O→Ca ⁺² +SO4 ^-2 +2H ₂ O (7)

Na ₂ CO ₃ +CaSO ₄ →Na ₂ SO ₄ +CaCO ₃ ↓ (8)

Na ₂ SO ₄ +Ca(OH) ₂ +2H ₂ O→2NaOH+CaSO ₄ ·2H ₂ O↓ (9)

2NaOH+CO ₂ →Na ₂ CO ₃ +H ₂ O (10)

As shown in reaction equations (5) and (6), the calcium sulfate produced by the neutralization of titanium dioxide production wastewater by sulfuric acid method and limestone and lime milk has a solubility product of Ksp=4.93×10 ^-5 , which is separated by pressure filtration as gypsum dihydrate After the calcium sulfate solid filter cake, there are still saturated calcium sulfate ions in the solution, as shown in the ionization equation (7), calcium ions and sulfate ions. Once the solution concentration changes and the sulfate concentration increases, calcium sulfate dihydrate solids will be precipitated, and direct production, recycling and utilization cannot be adopted. According to the reaction equation (8), as long as there is sodium carbonate in the solution, saturated calcium sulfate will generate sodium sulfate solution and calcium carbonate precipitation, and the resulting calcium carbonate precipitate has a solubility product Ksp=4.8×10 ^–9 , that is, a difference of 10 ^‐4 times four orders of magnitude, where the calcium ion concentration is far away from the calcium sulfate saturation concentration. The solution after the separation of the precipitated calcium carbonate is subjected to membrane separation through a reverse osmosis membrane, and the membrane separation dilute phase is returned to the production of titanium dioxide as purified process water. Precipitation of sodium solution and calcium sulfate dihydrate; carbon dioxide of reaction formula (5) is generated when the sodium hydroxide solution after separating calcium sulfate dihydrate is used to absorb titanium dioxide and post-processing the tail gas or limestone produced by drying combustion fuel and neutralize the precipitated calcium sulfate. The gas is carbonized according to the reaction equation (10) to obtain a sodium carbonate solution, and the obtained sodium carbonate solution is circulated back to the reaction equation (8) for removing the saturated calcium sulfate in the waste water and the filtrate.

The technical scheme of the present invention is:

The waste water from titanium dioxide production by sulfuric acid method is added into the neutralization reaction tank, limestone, lime milk and air are added in sections to carry out neutralization, precipitation and oxidation reaction, and the slurry after the reaction and precipitation is sent to the filter press (1) for pressure filtration separation. The filter cake separated by pressure filtration is discharged as titanium gypsum and sent to cement and other building materials for use; the separated filtrate is sent to the sedimentation tank as treated wastewater, and the sodium carbonate solution sent by the carbonization tower and the carbonic acid after precipitating saturated calcium sulfate are added. Calcium is recycled back to the slurry, along with precipitation of calcium saturated calcium sulfate in solution. The material of precipitation calcium carbonate is sent to the clarification tank (1) for clarification; part of the clarified thick slurry is returned to the sedimentation tank as a circulating seed, and the saturated calcium sulfate is precipitated as calcium carbonate, and the rest is returned to the neutralization reaction tank to replace part of the lime milk for neutralization Waste water, clarified clear liquid is sent to membrane filter for membrane separation; dilute phase of membrane separation is returned to titanium dioxide production as purified water to replace the original process water; dense phase solution of membrane separation is sent to causticizing tank and lime milk is added for further purification. stage causticization; the causticized material is sent to the filter press (2) for pressure filtration, the separated filter cake is returned to the wastewater neutralization reaction tank and is incorporated into the neutralization slurry; the separated filtrate is used as a sodium hydroxide solution, and part of it is sent to the In the carbonization tower, carbon dioxide in the production tail gas is used for carbonization, and the carbonized solution is sent to the precipitation tank to precipitate calcium carbonate; part of it is returned to titanium dioxide to replace the purchased lye raw material.

Compared with the existing sulfuric acid method titanium dioxide wastewater treatment production technology, a production method for the coupled utilization of total resources of sulfuric acid method titanium dioxide production wastewater protected by the present invention not only solves the complete recycling utilization of titanium dioxide production wastewater, but also saves titanium dioxide. The production of white powder requires a large amount of raw water, which has achieved the reuse of production water and a large amount of emission reduction of waste water. It not only optimizes the production process of waste water treatment, but also makes full use of the waste secondary resource carbon dioxide of titanium dioxide production tail gas, which saves the production cost of waste water treatment. The demand for sodium hydroxide in the production of white powder maximizes the utilization of resources. The utilization and reuse rate of resources are improved, the economic benefit of the producer is increased, and the technical and economic purpose of coupling the waste water of titanium dioxide production by sulfuric acid method to recycle and reuse all resources is achieved.

Preferably, the waste water is titanium dioxide production waste water by sulfuric acid method and waste water containing calcium sulfate.

Preferably, the neutralizing agent includes lime, limestone and acetylene to produce calcium carbide slag and other basic calcium raw materials, preferably limestone and lime.

Preferably, the neutralization reaction tank can be a single reactor with stirring, or a plurality of reactors with stirring in series.

Preferably, the neutralization reaction tank is preferably connected in series with a plurality of reaction tanks with agitators, and the neutralization pH is controlled according to different levels. 7.0-7.5.

Preferably, the filter press for separating gypsum is a common commercially available filter press with a diaphragm press, preferably provided with a back-blowing central hole system and a compressed air central filter cake drying system.

Preferably, the precipitation tank can be a single reactor with stirring, or a plurality of reactors with stirring in series; preferably more than two.

Preferably, the carbonization solution is added to the precipitation tank to precipitate calcium carbonate, and the thick slurry of the clarification tank can be added as crystal seed, or not; it is best to add thick slurry as crystal seed.

Preferably, the sodium carbonate added to the precipitation is that the molar ratio of saturated calcium sulfate (M _Na2CO3 /M _CaSO4 ) is 1.0-1.2, preferably 1.05-1.10, and thick slurry seeds are added to generate the calcium carbonate ratio ( M _crystal /M _raw ) is 1-3, preferably 1.5-2.

Preferably, the clarification tank (1) can be a continuous clarification tank and an alternately used parallel semi-continuous clarification tank, and the clarification residence time is 1-3 hours, preferably 1.0-1.5 hours.

Preferably, the membrane filter adopts a reverse osmosis membrane filtration separator, which can be single-stage or multi-stage, and the multi-stage is used for the post-treatment of titanium dioxide for the third washing water, and the rest are preferably single-stage, and the initial pressure of membrane filtration It is 1-2MPa, preferably 1.5MPa, the final pressure is 4-5MPa, preferably 4.5MPa, and the concentration ratio of the treated wastewater is 6-15 times, preferably 8-10 times.

Preferably, the conductivity of the membrane separation dilute phase (purified water) is 60-120us/cm, preferably 80-100us/cm, which is directly returned to the titanium dioxide production process water.

Preferably, the causticizing tank adopts a series of multi-stage causticizing, and the number of stages is 2-5, preferably more than 3. The molar ratio (M _Ca(OH)2 /M _Na2SO4 ) of lime milk and sodium sulfate added to causticization is 1.1-1.4, preferably 1.15-1.25.

Preferably, the filter cake separated by the filter press (2) is returned to the neutralization reaction tank to react with the neutralization slurry; the filtrate is used as caustic lye, and part of the filtrate is returned to the production of titanium dioxide, and part is sent to the carbonization tower for carbonization ; The distribution ratio is determined according to the amount of saturated sulfuric acid that needs to be eliminated in the wastewater treatment.

As preferably, the carbon dioxide gas used in the carbonization of the carbonization tower can be the carbon dioxide gas produced by the use of calcium carbonate (limestone) in the post-processing dry tail gas of titanium dioxide production, rotary kiln calcination tail gas and waste water neutralization reaction; The value is controlled at 11.5-12.5, preferably at 12.

Compared with the prior art, the principle and beneficial effects of the present invention:

In the present invention, the waste water produced by the sulfuric acid method titanium dioxide is subjected to lime neutralization reaction precipitation, and the gypsum is separated by a filter press. The treated wastewater solution mainly composed of sodium sulfate is obtained. The treated wastewater solution is filtered and purified by a membrane filter. The purified water obtained by membrane filtration is returned to titanium dioxide production and recycled as process water, and the treated wastewater is not discharged; the concentrated sodium sulfate solution obtained by membrane filtration and separation is added with lime for multi-stage causticization to obtain sodium hydroxide solution; sodium hydroxide solution Carbon dioxide in waste gas produced by titanium dioxide is carbonized to obtain sodium carbonate solution, which is returned to the precipitation tank for precipitation and treatment of saturated calcium sulfate in wastewater, so as to achieve the purpose of coupling and recycling all resources of titanium dioxide wastewater by sulfuric acid method.

The method of the invention solves the problem of long-term difficulty in recycling caused by the concentration of saturated calcium sulfate in the neutralization of sulfuric acid method titanium dioxide and the concentration of saturated calcium sulfate in the wastewater due to the use of carbon dioxide resources in the existing sulfuric acid method titanium dioxide production and the coupled production of lime causticizing solution and wastewater treatment. The technical difficulty eliminates the influence factors of the existing neutralization treatment wastewater on the environmental water body, saves a large amount of raw water used in production, and saves water resources.

Due to the use of all element resources in wastewater and wastewater treatment, titanium dioxide production mass flow and chemical energy flow for coupled production and treatment, the invention adopts a large cycle of titanium dioxide production and wastewater treatment and a small cycle in wastewater treatment, which not only solves the problem of sulfuric acid method The technical problem of recycling waste water from titanium dioxide production, and the water consumption per unit of titanium dioxide production has been greatly reduced. It not only realizes the coupled utilization and reuse of all resources in wastewater, saves the use of resources, but also increases the economic benefits of producers. Not only significant energy saving and consumption reduction, but also significant economic benefits. Therefore, the present invention not only innovates the utilization of resources by cyclically coupling the waste water of titanium dioxide production by the sulfuric acid method, but also greatly reduces the resource cost and the waste water discharge water cost, improves the economic and social benefits of production, and solves the problem that the traditional process cannot be recycled and the economic exploited technical difficulties.

Description of drawings

Figure 1. Process flow chart of the traditional sulfuric acid method for titanium dioxide production wastewater treatment.

Fig. 2. A production method process flow diagram of the present invention for the full resource recycling of titanium dioxide waste water by sulfuric acid method.

Detailed ways

Example 1

As shown in Figure 2, 1600L per hour (specific gravity 1.05, containing sulfuric acid 36.96g/L, ferrous sulfate 16.80g/L, titanium sulfate 0.525g/L, see Table 1) and 29.0L of lime milk containing 170g/L calcium oxide per hour is neutralized in three series-connected 2000L bottoms with an air distribution pipe in a stirring neutralization reaction tank, and air is blown in for aeration oxidation to control the stay of the reaction material. The time was 1 hour, the pH value of the slurry was 7.5, and the slurry overflowed from the top of the third-stage neutralization reaction tank and entered the filter press pump tank and then continuously sent it to the filter press for pressure filter separation, obtaining 27.4 kg of water content 45% per hour. The filter cake and 1685L treated wastewater (specific gravity 1.005 and its composition are shown in Table 2).

Table 1 Composition of titanium dioxide production wastewater

component	Concentration (g/L)	component	content(%)
H 2 SO 4	36.96	MgSO 4	2.10
FeSO4	16.80	Al 2 (SO 4 ) 3	1.05
Na 2 SO 4	1.30	CaSO4	1.05

Table 2 Composition of treated wastewater

component	Concentration (g/L)	component	Concentration (g/L)
pH	7.2	MgSO 4	0.010
FeSO4	0.001	Al 2 (SO 4 ) 3	0.010
Na 2 SO 4	1.25	CaSO4	3.35

1685L per hour of treated wastewater is continuously fed into the 5500Ld saturated calcium sulfate precipitation tank, and 146L of carbonized sodium carbonate solution with a concentration of 30g/L and 33L of clarified thick slurry with a concentration of 250g/L calcium carbonate are added every hour, and the precipitation reaction The material has a residence time of 1 hour, and is continuously sent to the clarification tank (1) for clarification to obtain 50L of calcium carbonate thick slurry with a concentration of 250g/L, 33L is circulated back to the sedimentation tank to provide crystal seeds, and 17L is circulated back to the acid waste water neutralization reaction tank.

The clarified liquid from the clarification tank (1) is sent to the membrane separation device at 1814.2L per hour for separation. The initial filtration pressure is 1.5MPa, and after reaching the filtration pressure of 4.5MPa, backwashing and circulating filtration are performed. The purified water separated from the membrane filter is 1636L per hour, and the concentrated brine is 178L. The composition of the membrane separation influent, the separation purified water and the concentrated brine is shown in Table 3. The sodium sulfate concentration in the influent is 3.49g/L. It is only 16mg/L, the conductivity is 107us/cm, the concentration of sodium sulfate in concentrated brine increases to 34.72g/L, and the conductivity is 98000us/cm. The water recovery cycle returns titanium dioxide productivity at 90%.

Table 3 Membrane separation in and out water composition

component	Influent concentration (g/L)	Purified water concentration (g/L)	Concentration of brine (g/L)
pH	7.6	7.2	7.8
Na 2 SO 4	4.66	0.016	42.60
MgSO 4	0.005	‐‐
CaSO4	‐‐	‐‐	‐‐

Conductivity (us/cm)

9000

107

98000

The concentrated brine separated by the membrane is 178L per hour, sent to the causticizing tank with stirring in 3 stages, and 4.3L lime milk containing CaO of 170g/L is added to each of the 3 stages, totaling 13.1L, for causticization, the material residence time 30 minutes each for a total residence time of 1.5 hours. The causticized slurry was sent to the filter press (2) for pressure filtration, and 16.80 kg of filter cake with a water content of 45% and 178.6 L of filtrate containing 20.1 g/L of sodium hydroxide were separated. The filtrate was carbonized with titanium dioxide dried tail gas to obtain 180L of a solution containing 26.43g/L of sodium carbonate, and 166L was separated and returned to the precipitation tank to precipitate saturated calcium sulfate solution, and the remaining 14L was used for other acidic tail gas washing instead of the original commercial hydroxide Sodium solution.

Example 2

As shown in Figure 2, the acid wastewater from the production of titanium dioxide by the sulfuric acid method is 240m3 per hour, and the main composition is shown in Table 4. It is neutralized with 36.5m3 of lime milk containing 200g/L calcium oxide per hour in four series of 180m3 with stirring. The neutralization reaction is carried out in the reaction tank. The bottom of the two-stage neutralization reaction tank is equipped with an air distribution pipe, and air is blown into the reaction tank for aeration oxidation. The residence time of the reaction material is controlled for 1.5 hours, and the pH value of the slurry is 7.5. The top of the four-stage neutralization reaction tank overflowed into the filter press pump tank and then was continuously sent to the filter press for pressure filter separation. 45.5 tons of filter cake with a water content of 45% and 253 tons of treated wastewater were obtained per hour. The composition is shown in Table 5.

Table 4 Composition of titanium dioxide production wastewater

component	Concentration (g/L)	component	content(%)
H 2 SO 4	41.06	MgSO 4	1.10
FeSO4	18.66	Al 2 (SO 4 ) 3	0.95
Na 2 SO 4	1.54	CaSO4	1.55

Table 5 Composition of treated wastewater

component	Concentration (g/L)	component	Concentration (g/L)
pH	7.0	MgSO 4	0.010
FeSO4	0.001	Al 2 (SO 4 ) 3	0.010
Na 2 SO 4	1.46	CaSO4	3.65

253 tons of treated wastewater per hour are continuously fed into three saturated calcium sulfate precipitation tanks of 110m3 in series, and 4.6m3 of clarified thick slurry with a concentration of 300g/L calcium carbonate and 22m3 of carbonized slurry with a concentration of 35.6g/L are added every hour. The sodium carbonate solution and the precipitation reaction material have a residence time of 1 hour, and are continuously sent to the clarification tank (1) for clarification to obtain 6.8m3 of calcium carbonate thick slurry with a concentration of 300g/L, 4.6m3 of which are circulated back to the precipitation tank to provide crystal seeds, 2.2m3 It is recycled back to the wastewater neutralization reaction tank.

The clarified liquid from the clarification tank ( ¹ ) is 278m3 per hour and sent to the membrane separation device with a membrane separation area of 5000m2 for separation. The separated purified water is 255m3 per hour, and the concentrated brine is 23m3. The composition of brine is shown in Table 3. The concentration of sodium sulfate in the influent water is 4.80g/L, the purified water is only 20mg/L, and the conductivity is 113us/cm. The concentration of sodium sulfate in the concentrated brine increases to 57.98g/L, and the conductivity is 98000us/cm. The water recovery cycle returns titanium dioxide productivity at 90%.

Table 3 Membrane separation in and out water composition

component	Influent concentration (g/L)	Purified water concentration (g/L)	Concentration of brine (g/L)
pH	7.5	7.2	7.6
Na 2 SO 4	4.80	0.016	57.98
MgSO 4	0.005	‐‐
CaSO4	‐‐	‐‐	‐‐
Conductivity (us/cm)	10000	113	98000

The concentrated brine separated by the membrane is 23m3 per hour, sent to the causticizing tank of 15m3 with stirring in 5-stage series, and 0.63m3 of lime milk containing CaO of 200g/L is added to each of the 5-stages, for a total of 3.16m3, for causticization, The material residence time is 30 minutes each, and the total residence time is 2.5 hours. The causticized slurry is sent to the filter press (2) for pressure filtration, and 3.5 tons of filter cake with 50% water content and 21m3 of filtrate containing 29.4g/L sodium hydroxide are separated. 2.6m3 of the filtrate was separated and returned to the production of titanium dioxide, and the remaining 18.4m3 was carbonized with the titanium dioxide dried tail gas to obtain a solution containing 35.60g/L of sodium carbonate.

Claims (10)

1. A production method for recycling all resources of waste water from titanium dioxide production by sulfuric acid method, comprising:

   The sulfuric acid method titanium dioxide production wastewater, limestone and lime are added to the neutralization reaction tank for precipitation reaction, and the reaction material with complete precipitation reaction is sent to the filter press for filtration and separation; the separated filter cake is used as titanium gypsum to send gypsum building materials and cement building materials. , the separation filtrate is used as the treated wastewater for full recycling processing and production;

   The waste water after separation and treatment by the filter press is added to the sedimentation tank, and at the same time, the sodium carbonate solution from the carbonization tower is added, and the reaction is controlled to precipitate the saturated calcium sulfate in the waste water, so that the calcium carbonate precipitation material with lower solubility is formed, and the precipitation material It is sent to the clarification tank for clarification; the calcium carbonate slurry of the heavy phase bottom material in the clarification tank is returned to the neutralization reaction tank for neutralization reaction with the wastewater sent from the production of titanium dioxide; the light phase clear liquid of the clarification tank is sent to the membrane for separation Membrane separation of salt liquid is carried out by the device, and the dilute phase (purified water) of the membrane separation is returned to the titanium dioxide production process as process water, which saves the external supply of raw water and water resources, and fully utilizes the waste water;

   Membrane separation concentrated phase sodium sulfate solution is sent to causticizing tank, lime milk is added for causticizing reaction, resulting in precipitated calcium sulfate and sodium hydroxide solution, causticizing slurry is sent to filter press for separation, and the separated filter cake is returned to lime Neutralize with the reaction tank and the titanium dioxide wastewater; the separated filtrate is sent to the carbonization tower as sodium hydroxide solution, and carbon dioxide-containing tail gas generated in the titanium dioxide production process is carbonized, converted into sodium carbonate solution, and recycled to the sedimentation tank Calcium ions of saturated calcium sulfate in the precipitation treatment wastewater;

   Depending on the mass flow of the causticized separation solution, part of the filtrate can be returned to titanium dioxide production as dilute alkali solution.
2. The production method of full resource recycling utilization of a kind of sulfuric acid method titanium dioxide production waste water according to claim 1, it is characterized in that: described production waste water is the production waste water of sulfuric acid method titanium dioxide production and the need to carry out neutralization treatment; The pH of the neutralization reaction is 6-8, preferably 7.0-7.5.
3. A production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid method according to claim 1-2, characterized in that: the treatment wastewater is titanium dioxide production wastewater that is neutralized by limestone and lime, and filtered by a filter press (1 ) Treatment wastewater after separation of gypsum filter cake, which contains saturated calcium sulfate solution and a small amount of soluble sulfate impurity solution, and the concentration range of saturated calcium sulfate is 1-5g/L, that is, 1-5Kg/m3.
4. According to any one of claims 1-3, a production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid method is characterized in that: the sodium carbonate solution from the carbonization tower is added to the sedimentation tank, and the addition amount is the same as that of saturated sulfuric acid. The molar ratio of calcium (M _Na2CO3 /M _CaSO4 ) is 1.0-1.2, preferably 1.05-1.10, and the resulting calcium carbonate ratio (M _crystal /M _raw ) is 1-3, preferably 1.5 by adding thick slurry seeds -2.
5. A production method for the utilization of all resources of titanium dioxide production wastewater by sulfuric acid method according to claim 1 or 4, characterized in that: the clarification time of the clarification tank (1) is 1-3 hours, preferably 1.5-2.0 hours; Clarifier tank (1) The amount of thick slurry circulating back to the sedimentation tank is 2/3 of the total amount, which is used as the crystal seed for precipitation calcium carbonate; 1/3 of the total amount is circulated back to the reaction neutralization tank to react with the titanium dioxide production wastewater; The liquid part is sent to the membrane separation filter.
6. A production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid method according to any one of claims 1-5, characterized in that: the clear liquid separated from the clarification tank (1) is fed into a system containing a pretreatment system. , reverse osmosis system and reverse osmosis membrane separation device composed of auxiliary dosing, cleaning, backwashing, etc. to carry out membrane separation; the initial pressure of membrane filtration is 1.5MPa, the final pressure is 4-5MPa, preferably 4.5MPa, and then reverse osmosis is carried out. The concentration ratio of rinsing and treating wastewater is 6-15 times, preferably 8-10 times. Membrane separation purified water is directly returned to titanium dioxide production and recycled as process water; membrane separation concentrated brine is sodium sulfate solution, which can be used as causticization to prepare sodium hydroxide and sodium carbonate solution to eliminate saturated calcium sulfate in wastewater treatment, and can also be concentrated again enrichment.
7. According to any one of claims 1 and 5-6, a production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid method is characterized in that: the method of membrane separation and filtration can adopt multi-stage and single-stage separation; The separated water can be used in the titanium dioxide post-treatment process; preferably, the conductivity of the membrane separation dilute phase (purified water) is 60-120us/cm, preferably 80-100us/cm; the purified water is directly returned to the titanium dioxide production Process water; Membrane separation dense phase is sodium sulfate salt solution sent to causticizing tank for reaction.
8. A production method for utilizing the full resource utilization of titanium dioxide production wastewater by sulfuric acid process according to any one of claims 1-6, characterized in that: the causticizing tank adopts multi-stage causticizing in series, and the number of stages is between 2- Grade 5, preferably above Grade 3; the molar ratio of lime milk to sodium sulfate (M _Ca(OH)2 /M _Na2SO4 ) for causticization is 1.1-1.4, preferably 1.15-1.25; Dosing the milk of lime dosing.
9. A production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid process according to claims 1 and 6-7, characterized in that: the causticized material comprises calcium sulfate generated by causticization and hydroxide that does not participate in the reaction Calcium is fed into the filter press (2) for pressure filtration, and the filter cake is beaten and recycled back to the neutralization reaction tank. The filtrate is divided according to the total amount of sodium hydroxide and the amount of saturated calcium sulfate that needs to be precipitated, and part of the filtrate is sent to the carbonization tower for carbonization. , and part of it is returned to the production of titanium dioxide to replace the amount of lye required for production.
10. A production method for full resource utilization of titanium dioxide production wastewater by sulfuric acid method according to claims 1 and 6-8, characterized in that: the carbon dioxide gas used in the carbonization of the carbonization tower can be dried after the production of titanium dioxide. Exhaust gas, exhaust gas of metatitanic acid rotary kiln calcination, carbon dioxide gas generated during the neutralization reaction of waste water with calcium carbonate (limestone), combustion fuel and exhaust gas of boiler; .

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