CN112499813A - Production method for full resource recycling of waste water in titanium dioxide production by sulfuric acid process - Google Patents
Production method for full resource recycling of waste water in titanium dioxide production by sulfuric acid process Download PDFInfo
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Abstract
The invention discloses a production method for full resource recycling of wastewater produced by sulfuric acid process titanium dioxide, which comprises the steps of neutralizing the wastewater produced by sulfuric acid process titanium dioxide with lime and treating the wastewater after gypsum is separated from a filter press, adding recycled sodium carbonate solution to precipitate saturated calcium sulfate in the wastewater, clarifying and separating slurry to obtain calcium carbonate precipitate and sodium sulfate solution, and performing membrane separation on the separated dilute sodium sulfate solution through a membrane filter; adding lime into the concentrated sodium sulfate solution subjected to membrane separation for causticization reaction, taking the filtrate as a sodium hydroxide solution, carbonizing carbon dioxide-containing tail gas generated in the production process of titanium dioxide to obtain a sodium carbonate solution, and returning to the treatment of wastewater to precipitate saturated calcium sulfate. The invention economically solves the technical difficulty that the waste water from lime neutralization treatment in the production process of titanium dioxide by a sulfuric acid method cannot be economically recycled, eliminates the influence factors of the outward discharge of the waste water from the prior neutralization treatment on the environmental water body, and saves a large amount of raw water resources for production and use.
Description
Technical Field
The invention relates to a production method for treating and recycling production wastewater, in particular to a resource production method for treating and recycling production wastewater of titanium dioxide by a sulfuric acid method and recycling treatment wastewater containing calcium sulfate.
Background
The wastewater generated by the sulfate process titanium dioxide mainly comes from metatitanic acid primary washing liquid, secondary washing filtrate, washing liquid and acidolysis in the production processGenerated gas washes acidic waste water, calcined tail gas sprays absorption water, sewage circulating drainage, terrace flushing, equipment flushing, desalted water station regeneration waste water and sporadic waste water. The main pollutant in the produced wastewater is H2SO4、TiO2、Fe2+、Fe3+、Na+And small and trace amounts of HSO3 －、F-And Cl-And the like. The chemical reaction principle of the existing wastewater treatment method is as follows:
CaO+H2O→Ca(OH)2 (1)
H2SO4+Ca(OH)2→CaSO4·2H2O↓ (2)
FeSO4+Ca(OH)2+2H2O→CaSO4·2H2O↓+Fe(OH)2↓ (3)
FeSO4+Ca(OH)2+2H2O+1/2O2→Fe(OH)3↓+CaSO4·2H2O↓ (4)
as shown in figure 1, acid wastewater from different production processes enters a regulating tank for buffering and conditioning, is pumped into a neutralization reaction tank for bubbling stirring and oxidation by air, and is added with lime slurry for neutralization and oxidation aeration to generate mixed precipitate of calcium sulfate dihydrate and ferric hydroxide; the neutralized and oxidized slurry is sent into a filter press for solid-liquid separation, the separated filter cake is gypsum calcium sulfate containing ferric oxide and a small amount of titanium oxide, the production habit is called titanium gypsum or red mud, and the titanium gypsum or red mud is sent out for utilization or stockpiling for disposal; the initial stage filtrate and the penetrated and small amount of solid are filtered by a clarifying pool or a fiber filter, and then the filter-pressing filtrate is discharged to natural water as industrial wastewater meeting the national discharge standard. Because the treated water can not be recycled, the admission conditions of the titanium dioxide industry stipulate that the discharge amount of the titanium dioxide treated wastewater per ton of sulfuric acid process is less than 80 cubic meters, and the most effective production device still has about 60 cubic meters of the discharge amount of the titanium dioxide treated wastewater per ton of sulfuric acid process despite the adoption of a plurality of innovative means such as intermediate recycling, reuse and reuse, and reuse of washing water.
So large treated wastewaterThe reason why the discharge amount cannot be recycled is that the sulfuric acid method titanium dioxide wastewater adopts the reaction principle in the lime, the generated gypsum calcium sulfate is used as a precipitate with relatively high solubility, and the saturated concentration of calcium sulfate in the wastewater treated after the gypsum is separated is high. The solubility product Ksp of the calcium sulfate is 4.93 multiplied by 10 at 25 DEG C–5Because of the influence of the temperature and the salt effect degree caused by the salt content, the treated wastewater after gypsum separation per cubic meter also contains about 2-4 kg of saturated calcium sulfate solution. Except for a small amount of lime dissolving, the existing treatment method almost directly discharges the lime into public water, thereby not only wasting a large amount of water resources, but also influencing the water environment. However, the reason why reuse and multiplexing are not performed is that: the direct reuse is very unfavorable for the production of titanium dioxide, and the technology and the economy can not be over-closed according to the traditional water treatment, re-purification and reuse technology. The core of the method is as follows:
(1) if the titanium dioxide is directly recycled to the production of titanium dioxide, two adverse conditions are generated
Firstly, be used for spraying cooling circulation water, along with evaporation cycle concentration increases, surpasss saturated concentration and the absorption of sulfur oxide in the acid gas and gets into, then separate out a large amount of calcium sulfate, blocks up pipeline and system, causes production to be unable to last, can not use at all.
Secondly, the titanium dioxide is used for washing metatitanic acid with the largest water consumption in the production of titanium dioxide by a sulfuric acid method, and the sulfuric acid concentration of the liquid holdup in the metatitanic acid is higher, so that the same ion effect exceeds the saturated concentration of calcium sulfate, a large amount of calcium sulfate is separated out and adsorbed on the metatitanic acid and is brought into a calcined product, the content of titanium dioxide is influenced, and the pigment performance of the titanium dioxide is seriously influenced; meanwhile, the filter cloth of the filter medium is scaled, and the existing filter cloth adopts a hydrofluoric acid soaking, cleaning and regenerating mode, so that calcium sulfate scaling cannot be removed; therefore, it cannot be used at all.
(2) If the soft water is recycled after being purified, the method is also economically and technically unacceptable
Firstly, the ion exchange method is adopted to treat according to the common raw water, the ton titanium dioxide is calculated according to 60 cubic meters, wherein about 240kg of saturated calcium sulfate which needs to be removed is added with soluble sulfate brought by manufacturing rutile crystal seeds and post-treatment envelopes, the raw materials of anion and cation exchangers of salt, hydrochloric acid, sodium hydroxide and the like with corresponding equivalent weight need to be used for hundreds of kilograms, and simultaneously, a large amount of concentrated saline containing calcium chloride is still discharged after the exchange, so that the economic cost is high, the quality of discharged saline solution is doubled, the environment is not acceptable, and a large amount of chemical substance resources are wasted.
Secondly, the reverse osmosis membrane is directly adopted for separating and treating the wastewater according to the common raw water treatment, and when the concentration of the concentrated brine separated by the membrane is increased to exceed the saturated concentration of calcium sulfate, calcium sulfate is precipitated; because the concentration of the surface of the membrane is high and the surface energy of the membrane is low, the surface energy of a crystal nucleus (precursor) precipitated by supersaturated calcium sulfate is large, the crystal nucleus (precursor) is rapidly deposited and scaled on the membrane, water molecules are prevented from passing through, the membrane separation efficiency is reduced, the cleaning is frequent, the regeneration is difficult, the reverse osmosis membrane is polluted, blocked and scrapped almost in a short operation period, and the required investment is large and the operation cost is high. For example, the Chinese patent publication No. CN106315910A discloses a method for treating titanium dioxide wastewater, which comprises adding a flocculating agent aluminum trichloride into the wastewater to flocculate ultrafine suspended solids and then carrying out ultrafiltration, and adding a scale inhibitor to prevent saturated calcium sulfate and other substances from crystallizing and depositing on a reverse osmosis membrane; because the content of calcium sulfate in the treated wastewater reaches 4000mg/L, the equivalent concentration of calcium ions is nearly 1200mg/L, and a large and expensive scale inhibitor is needed, the wastewater treatment recycling cost is increased, the use of circulating water is influenced due to the existence of the scale inhibitor in water, and even the quality influence of titanium dioxide production products is brought, such as a phosphorus scale inhibitor and an aluminum trichloride flocculating agent, the phosphorus scale inhibitor and the aluminum trichloride flocculating agent enter metatitanic acid produced by titanium dioxide from recycled water to be enriched, titanium dioxide microcrystal particle particles with pigment performance can not be calcined in a rotary kiln, and the quality of the titanium dioxide is poor due to the fact that phosphorus and aluminum are both control agents for controlling the production granularity and crystal form of the titanium dioxide; if the organic complexing agent is adopted, the molecular weight of the complexing agent is far larger than the aperture of the water molecular weight separated from the membrane, so that the membrane aperture is blocked, the separation efficiency is also reduced, and even the membrane material is scrapped in a short period. In addition, the concentration of the generated concentrated phase brine is low, the concentrated phase brine is still not utilized and is also discharged outside, the absolute discharge amount of solutes to a water body is not reduced, and the solutes enter the water body to influence the environment.
Performing ultrafiltration before membrane separation, wherein the ultrafiltration is only effective on ultrafine solid particles and has no significance on saturated solution and even supersaturated solution; because the saturated concentration of calcium sulfate in the treated wastewater after gypsum separation is relatively high, once the micro-scale changes of pressure, temperature, fluid convection, surface friction and surface energy are applied to ultrafiltration and membrane separation, precipitation is caused to separate out, and water molecules and ion channels of an ultrafiltration medium and a membrane are blocked, so that the separation is difficult to carry out.
Fourthly, US patent US4966710 and US6086842, the former US4966710 uses sodium hydroxide to adjust the pH value of the sodium sulfate solution to magnesium and calcium in the precipitation solution, and is used for purifying the sodium sulfate solution to reduce the chemical regenerant used in ion exchange regeneration, but not to use the impurities in the sodium carbonate precipitation solution; the latter US6086842 produces high quality desulfurized gypsum without calcium sulfite from the desulfurized tail gas, and uses sodium sulfate to causticize, circulate and absorb, and does not use carbon dioxide in the production to produce sodium carbonate.
Therefore, the method is also a 'symptom complex' where the existing global sulfuric acid method titanium dioxide wastewater treatment cannot be economically recycled, and only adopts a negative method of discharging water outside to treat. Therefore, the consumption of raw water for production is large, the utilization rate of water resources is low, the discharged water amount is remarkable, the environment is influenced, and the requirements of green sustainable development are not met. The waste water produced by the sulfuric acid method titanium dioxide is coupled with the lime raw material causticizing solution and waste water treatment by utilizing the carbon dioxide resource in the existing sulfuric acid method titanium dioxide production, the calcium ion content in the saturated calcium sulfate solution in the waste water after gypsum separation is removed, the calcium ion content is returned to the gypsum, and the production coupling and the waste and side resources of the production coupling and the waste and side resources are utilized, so that the full resource recycling of the waste water after membrane separation treatment is facilitated, and the purchase cost of commodity medicaments is reduced; the technical difficulty that the wastewater generated by the neutralization treatment of titanium dioxide by the sulfuric acid method is difficult to recycle is solved, the raw water resource consumption in production is saved, and the influence factors of the outward discharge of the existing neutralization treatment wastewater on the environmental water body are eliminated; the membrane separation concentrated brine is causticized by lime, sodium resources and low-price alkaline chemical energy in the concentrated brine are recovered, and the production process and the production method of the technology are fully coupled and recycled, and are not reported.
Disclosure of Invention
In order to solve the technical and economic difficulties that the existing sulfuric acid method titanium dioxide production wastewater can not be recycled, the coupling production technology of mass flow and chemical energy source flow is carried out by utilizing the carbon dioxide resource in the tail gas discharged in the sulfuric acid method titanium dioxide production, lime causticizing solution and a wastewater treatment device, the problem and the defect that the sulfuric acid method titanium dioxide wastewater is difficult to be recycled after neutralization treatment are overcome, the influence factors of the outward discharge of the existing treatment wastewater on the environmental water body are eliminated, and the production of a large amount of raw water resources used for production is saved; the invention aims to provide a production method for recycling the full resources of the wastewater generated in the production of titanium dioxide by a sulfuric acid method. The method comprises the steps of adding a sodium carbonate solution prepared by recycling the waste water generated in the production of titanium dioxide by a sulfuric acid method and limestone and lime to neutralize and precipitate the waste water and separate gypsum, wherein the saturated calcium sulfate concentration left in the waste water due to the separated gypsum is calcium carbonate and sodium sulfate slurry; and clarifying the precipitation reaction slurry solution to separate calcium carbonate slurry and sodium sulfate solution. The calcium carbonate thick slurry after clarification and separation is circularly returned to the titanium dioxide wastewater to be neutralized and used as calcium carbonate resources, and the separated sodium sulfate solution is subjected to membrane separation through a reverse osmosis membrane. The dilute phase liquid (purified water) obtained by membrane separation is used as process water to return to the production of titanium dioxide, so as to replace external raw water resources used in production. Adding lime into concentrated salt solution containing sodium sulfate obtained by membrane separation to perform causticization reaction to generate slurry of calcium sulfate precipitate and sodium hydroxide solution, and performing filter pressing separation on the slurry; the separated calcium sulfate filter cake is circularly returned to the titanium dioxide waste water and the slurry of the precipitated calcium sulfate to be used as the neutralized precipitated waste water and the gypsum to be separated together; one part of the separated sodium hydroxide solution is used as alkali absorption liquid to return to acidolysis in titanium dioxide production and washing of calcined acidic tail gas, one part of the separated sodium hydroxide solution is carbonized by carbon dioxide in the tail gas in titanium dioxide production, sodium hydroxide is carbonized into sodium carbonate solution, the sodium carbonate solution is used for removing saturated calcium sulfate in the treatment wastewater to form calcium carbonate precipitate to provide carbonate ion substances, and the carbonate ion substances are used for recycling calcium ions in the saturated calcium sulfate solution which is used for precipitating in the treatment wastewater; the full resource coupling cyclic utilization of the titanium dioxide wastewater by the sulfuric acid method is achieved. Compared with the prior art of directly discharging and treating wastewater after neutralization treatment, the production method for the full resource coupling utilization of the titanium dioxide production wastewater by the sulfuric acid method, disclosed by the invention, not only solves the full recycling utilization of the titanium dioxide production wastewater, but also saves the requirement of titanium dioxide production on a large amount of raw water, and realizes the reutilization of production water and the large emission reduction of the wastewater; the wastewater treatment production process is optimized, the waste byproduct carbon dioxide of the titanium dioxide production drying tail gas is fully utilized, and the production cost of wastewater treatment is saved; and the lime is used for causticizing the chemical energy with low price to recover the membrane for separating the strong brine, so that the required amount of the sodium hydroxide in the production of the titanium dioxide is reduced, and the resource utilization is maximized. The utilization rate and the reuse rate of resources are improved, the economic benefit of producers is increased, and the technical and economic purposes of the coupling full-cycle recycle of the wastewater generated in the titanium dioxide production by the sulfuric acid method are achieved.
The production principle of the invention is as follows:
H2SO4+CaCO3+H2O→CaSO4·2H2O↓+CO2↑ (5)
H2SO4+Ca(OH)2→CaSO4·2H2O↓ (6)
CaSO4·2H2O→Ca+2+SO4-2+2H2O (7)
Na2CO3+CaSO4→Na2SO4+CaCO3↓ (8)
Na2SO4+Ca(OH)2+2H2O→2NaOH+CaSO4·2H2O↓ (9)
2NaOH+CO2→Na2CO3+H2O (10)
as shown in reaction equations (5) and (6), the solubility product Ksp of calcium sulfate generated by neutralizing the sulfuric acid method titanium dioxide production wastewater with limestone and lime milk is 4.93 × 10–5After being filter-pressed and separated as a solid filter cake of calcium sulfate dihydrate of gypsum, saturated calcium sulfate ions also exist in the solution, as shown by the ionization equation (7)Calcium and sulfate ions. Once the concentration of the solution is changed and the concentration of sulfate radical is increased, calcium sulfate dihydrate solid can be separated out, and direct production, reuse and utilization cannot be adopted. As shown in the reaction equation (8), saturated calcium sulfate in the solution generates sodium sulfate solution and calcium carbonate precipitate as long as sodium carbonate exists, and the solubility product Ksp of the generated calcium carbonate precipitate is 4.8 × 10–9I.e. by 10-4Four orders of magnitude, with calcium ion concentrations far from calcium sulfate saturation concentrations. Carrying out membrane separation on the solution after the precipitated calcium carbonate is separated through a reverse osmosis membrane, taking a membrane separation dilute phase as purified process water to return to the production and use of titanium dioxide, and adding lime into a concentrated phase of the membrane separation according to a reaction equation (9) to causticize to obtain a sodium hydroxide solution and a dihydrate calcium sulfate precipitate; after absorbing titanium dioxide, treating tail gas generated by drying combustion fuel or limestone by using the sodium hydroxide solution after separating the calcium sulfate dihydrate to neutralize and precipitate calcium sulfate, generating carbon dioxide gas in a reaction formula (5), carrying out carbonization reaction according to a reaction formula (10) to obtain a sodium carbonate solution, and circularly returning the obtained sodium carbonate solution to the reaction formula (8) for removing saturated calcium sulfate in wastewater neutralization filtrate.
The technical scheme of the invention is as follows:
adding the sulfuric acid method titanium dioxide production wastewater into a neutralization reaction tank, adding limestone and lime milk in sections and introducing air to perform neutralization, precipitation and oxidation reaction, and sending the slurry subjected to reaction and precipitation into a filter press (1) for filter pressing and separation. Filter cakes separated by filter pressing are discharged as titanium gypsum to be conveyed out to cement and other building materials for utilization; and (3) sending the separated filtrate serving as treatment wastewater into a precipitation tank, adding a sodium carbonate solution sent by a carbonization tower in a circulating manner and calcium carbonate obtained after the saturated calcium sulfate is precipitated in a circulating manner to return slurry, and precipitating the calcium of the saturated calcium sulfate in the solution. The material of precipitated calcium carbonate is sent into a clarifying tank (1) for clarification; returning the clarified thick slurry part to a precipitation tank to be used as circulating crystal seeds to precipitate saturated calcium sulfate into calcium carbonate precipitate, returning the rest part to a neutralization reaction tank to replace partial lime milk to neutralize wastewater, and sending clarified clear liquid into a membrane filter to carry out membrane separation; the dilute phase of the membrane separation is used as purified water to return to the production of titanium dioxide to replace the original process water; feeding the concentrated phase solution subjected to membrane separation into a causticizing tank, and adding lime milk to carry out multistage causticization; the causticized material is sent into a filter press (2) for filter pressing, and a filter cake is separated and returned to the wastewater neutralization reaction tank to be merged into the neutralized slurry; separating the filtrate as sodium hydroxide solution, partially sending into a carbonization tower, carbonizing with carbon dioxide in the production tail gas, and sending the carbonized solution into a precipitation tank to precipitate calcium carbonate; and part of the titanium dioxide is returned to the production of titanium dioxide to replace the purchased alkali liquor raw material.
Compared with the existing sulfuric acid process titanium dioxide wastewater treatment production technology, the production method for full resource coupling utilization of sulfuric acid process titanium dioxide production wastewater, which is protected by the invention, not only solves the full recycling utilization of titanium dioxide production wastewater, but also saves a large amount of raw water requirements for titanium dioxide production, and realizes the reutilization of production water and the large amount of emission reduction of wastewater. The wastewater treatment production process is optimized, the waste and side resources of the tail gas in the titanium dioxide production are fully utilized, and the production cost of wastewater treatment is saved; and the lime is used for causticizing the chemical energy with low price to recover the membrane for separating the strong brine, so that the required amount of the sodium hydroxide in the production of the titanium dioxide is reduced, and the resource utilization is maximized. Improves the utilization and reuse rate of resources, increases the economic benefit of producers, and achieves the technical and economic purpose of coupling full resource recycling of the wastewater generated in the titanium dioxide production by the sulfuric acid method.
Preferably, the wastewater is sulfuric acid method titanium dioxide production wastewater and calcium sulfate-containing treatment wastewater.
Preferably, the neutralizing agent comprises alkaline calcium raw materials such as lime, limestone and acetylene production carbide slag, and preferably limestone and lime.
Preferably, the neutralization reaction tank may be a single stirred reactor or a plurality of stirred reactors connected in series.
Preferably, the neutralization reaction tank is a reaction tank with a plurality of stirrers connected in series, and neutralization pH control is carried out according to different grades, from the low stage to the last stage, and the pH is controlled between 6.0 and 8.0, preferably between 7.0 and 7.5.
Preferably, the filter press for separating gypsum is a common commercially available filter press with diaphragm press, and is preferably provided with a back-blowing central hole system and a compressed air central filter cake blow-drying system.
Preferably, the precipitation tank can be a single stirred reactor or a plurality of stirred reactors connected in series; preferably two or more.
Preferably, the carbonized solution is added into the precipitation tank to precipitate the calcium carbonate, and the precipitation tank can be added with the thick slurry of the clarification tank as seed crystal or not; it is preferable to add the thick paste as seed crystals.
Preferably, the precipitation is carried out by adding sodium carbonate in a molar ratio (M) of saturated calcium sulfateNa2CO3/MCaSO4) 1.0-1.2, preferably 1.05-1.10, and adding seed crystals of the thick paste to produce a proportion of calcium carbonate (M)Crystal grain/MRaw material) Is 1-3, preferably 1.5-2.
Preferably, the clarifying tank (1) can adopt a continuous clarifying tank and a parallel semi-continuous clarifying tank which are alternately used, and the clarifying residence time is 1 to 3 hours, preferably 1.0 to 1.5 hours.
Preferably, the membrane filter adopts a reverse osmosis membrane filtration separator, can adopt a single stage or multiple stages, the multiple stages are used for treating the three washing water after titanium dioxide, the rest is preferably a single stage, the initial pressure of the membrane filtration is 1-2MPa, preferably 1.5MPa, the final pressure is 4-5MPa, preferably 4.5MPa, and the concentration multiple of the treated wastewater is 6-15 times, preferably 8-10 times.
Preferably, the electric conductivity of the membrane separation dilute phase (purified water) is 60-120us/cm, preferably 80-100us/cm, and the dilute phase is directly returned to the water for the titanium dioxide production process.
Preferably, the causticizing tank adopts multistage causticization in series, and the stage number is 2-5 stages, preferably more than 3 stages. Causticizing and adding the molar ratio (M) of lime milk to sodium sulfateCa(OH)2/MNa2SO4) Is 1.1-1.4, preferably 1.15-1.25.
Preferably, the filter cake separated by the filter press (2) returns to the neutralization reaction tank to react with the neutralized slurry; the filtrate is used as causticized alkali liquor, part of the filtrate is returned to the production and use of titanium dioxide, and part of the filtrate is sent to a carbonization tower for carbonization; the distribution ratio is determined by the amount of saturated sulfuric acid to be eliminated to the extent necessary in the treatment of wastewater.
Preferably, the carbon dioxide gas used for the carbonization of the carbonization tower can be the carbon dioxide gas generated by the neutralization reaction of the tail gas generated by drying after the production of titanium dioxide, the tail gas generated by calcining in a rotary kiln and waste water by using calcium carbonate (limestone); the carbonization degree is controlled at pH value of 11.5-12.5, preferably 12.
Compared with the prior art, the invention has the following principle and beneficial effects:
the invention adds the recycled sodium carbonate solution to precipitate calcium ions in the saturated calcium sulfate concentration in the wastewater after the wastewater produced by the titanium dioxide by the sulfuric acid method is subjected to lime neutralization reaction and precipitation and gypsum separation by a filter press, and replaces and obtains the wastewater treatment solution mainly containing sodium sulfate. The wastewater solution is filtered and purified by a membrane filter. Purified water obtained by membrane filtration is used as process water and returned to the production of titanium dioxide for recycling, and treated wastewater is not discharged; adding lime into concentrated sodium sulfate solution obtained by membrane filtration and separation for multistage causticization to obtain sodium hydroxide solution; the sodium hydroxide solution is carbonized by carbon dioxide in the waste gas generated in the production of titanium dioxide to obtain a sodium carbonate solution, and then the sodium carbonate solution returns to a precipitation tank to precipitate saturated calcium sulfate in the wastewater, so that the aim of full resource coupling recycling of the titanium dioxide wastewater in the sulfuric acid process is fulfilled.
The method of the invention utilizes the coupling production of carbon dioxide resource, lime causticization solution and wastewater treatment in the existing sulfuric acid method titanium dioxide production, solves the technical difficulty of long-term difficult recycling caused by saturated calcium sulfate concentration in the sulfuric acid method titanium dioxide neutralization treatment wastewater, eliminates the influence factor of the outward discharge 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.
The invention utilizes the whole element resource in the wastewater and the wastewater treatment as well as the titanium dioxide production mass flow and the chemical energy flow to carry out the coupling production and treatment, and adopts the titanium dioxide production and wastewater treatment major cycle and the minor cycle in the wastewater treatment, thereby not only solving the technical problem of recycling the wastewater in the titanium dioxide production by the sulfuric acid process, but also greatly reducing the water consumption of the titanium dioxide production unit. Not only coupling utilization and reuse of the whole resources in the wastewater are realized, the use amount of the resources is saved, but also the economic benefit of a producer is increased. Not only the energy saving and consumption reduction are obvious, but also the economic benefit is obvious. Therefore, the invention not only innovatively utilizes resources coupling the wastewater generated in the titanium dioxide production by the sulfuric acid process in a circulating manner, greatly reduces the resource cost and the wastewater discharge water cost, improves the economic and social benefits of production, and solves the technical problem that the traditional process cannot realize the recycling and economic utilization.
Drawings
FIG. 1 is a flow chart of a traditional sulfuric acid method titanium dioxide production wastewater treatment process.
FIG. 2 is a process flow chart of the production method for full resource recycling of titanium dioxide wastewater by a sulfuric acid process.
Detailed Description
Example 1
As shown in figure 2, 1600L of acidic wastewater (specific gravity of 1.05, wherein the sulfur acid is 36.96g/L, the ferrous sulfate is 16.80g/L, and the titanium sulfate is 0.525g/L, see table 1) from the production of titanium dioxide by a sulfuric acid method and 29.0L of lime milk containing 170g/L calcium oxide per hour are subjected to neutralization reaction in three 2000L stirring neutralization reaction tanks with air distribution pipes at the bottoms, air is blown in for aeration oxidation, the retention time of reaction materials is controlled to be 1 hour, the pH value of slurry is 7.5, the slurry overflows from the tops of the third-stage neutralization reaction tanks and enters a filter press pump tank, and then is continuously sent to a filter press for filter press separation, 27.4 kg of filter cakes with the water content of 45 percent and 1685L of treated wastewater per hour are obtained (the specific gravity of 1.005 and the composition is shown in table 2).
TABLE 1 titanium dioxide production wastewater composition
| Components | Concentration (g/L) | Components | Content (%) |
| H2SO4 | 36.96 | MgSO4 | 2.10 |
| FeSO4 | 16.80 | Al2(SO4)3 | 1.05 |
| Na2SO4 | 1.30 | CaSO4 | 1.05 |
TABLE 2 composition of the treated wastewater
| Components | Concentration (g/L) | Components | Concentration (g/L) |
| pH | 7.2 | MgSO4 | 0.010 |
| FeSO4 | 0.001 | Al2(SO4)3 | 0.010 |
| Na2SO4 | 1.25 | CaSO4 | 3.35 |
1685L of treated wastewater is continuously fed into a 5500Ld saturated calcium sulfate precipitation tank per hour, 146L of carbonized sodium carbonate solution with the concentration of 30g/L and 33L of recycled clear thick slurry of calcium carbonate with the concentration of 250g/L are simultaneously added per hour, the residence time of the precipitated reaction materials is 1 hour, the reaction materials are continuously fed into a clarification tank (1) for clarification to obtain 50L of calcium carbonate thick slurry with the concentration of 250g/L, 33L of calcium carbonate thick slurry is circularly returned to the precipitation tank to provide seed crystals, and 17L of calcium carbonate thick slurry is circularly returned to an acidic wastewater neutralization reaction tank.
1814.2L of clarified liquid from the clarifying tank (1) per hour is sent to a membrane separation device for separation, the initial filtering pressure is 1.5MPa, and the backwashing circulation filtration is carried out after the filtering pressure reaches 4.5 MPa. 1636L of purified water separated from the membrane filter per hour, 178L of concentrated brine enriched, and the compositions of the membrane separated feed water, the separated purified water and the concentrated brine are shown in Table 3, wherein the concentration of sodium sulfate in the feed water is 3.49g/L, the purified water is only 16mg/L, the conductivity is 107us/cm, the concentration of sodium sulfate in the concentrated brine is increased to 34.72g/L, and the conductivity is 98000 us/cm. The productivity of titanium dioxide returned by water recovery and circulation is 90%.
TABLE 3 Membrane separation Water in and out composition
178L of strong brine obtained by membrane separation per hour is fed into a 3-level causticizing tank with stirring, 4.3L of lime milk containing 170g/L of CaO is respectively added into 3 levels, the total amount is 13.1L, causticization is carried out, the material retention time is respectively 30 minutes, and the total retention time is 1.5 hours. The causticized slurry is sent to a filter press (2) for filter pressing, and 16.80 kg of filter cake containing 45 percent of water and 178.6L of filtrate containing 20.1g/L of sodium hydroxide are separated. Carbonizing the filtrate by using titanium dioxide dry tail gas to obtain 180L of solution containing 26.43g/L of sodium carbonate, separating 166L, circularly returning to the precipitation tank to precipitate saturated calcium sulfate solution, and using the rest 14L of solution to wash other acidic tail gas to replace the original commercial sodium hydroxide solution.
Example 2
As shown in figure 2, 240m3 per hour of acidic wastewater from titanium dioxide production by a sulfuric acid method mainly comprises the following components shown in Table 4, lime cream 36.5m3 containing 200g/L calcium oxide per hour is subjected to neutralization reaction in four serially-connected neutralization reaction tanks with stirring of 180m3, the bottoms of the two subsequent stages of neutralization reaction tanks are provided with air distribution pipes, air is blown into the neutralization reaction tanks for aeration oxidation, the retention time of reaction materials is controlled to be 1.5 hours, the pH value of slurry is 7.5, the slurry overflows from the tops of the fourth stage neutralization reaction tanks, enters a filter press pump tank and is continuously conveyed into a filter press for filter press separation, and 45.5 tons of filter cakes with the water content of 45 percent and 253 tons of treated wastewater are obtained per hour, and the composition of the acidic wastewater is shown in Table 5.
TABLE 4 titanium dioxide production wastewater composition
| Components | Concentration (g/L) | Components | Content (%) |
| H2SO4 | 41.06 | MgSO4 | 1.10 |
| FeSO4 | 18.66 | Al2(SO4)3 | 0.95 |
| Na2SO4 | 1.54 | CaSO4 | 1.55 |
TABLE 5 composition of the treated wastewater
| Components | Concentration (g/L) | Components | Concentration (g/L) |
| pH | 7.0 | MgSO4 | 0.010 |
| FeSO4 | 0.001 | Al2(SO4)3 | 0.010 |
| Na2SO4 | 1.46 | CaSO4 | 3.65 |
253 tons of treated wastewater are continuously fed into three saturated calcium sulfate precipitation tanks connected in series at 110m3 per hour, simultaneously 4.6m3 of clear thick slurry circularly returned by calcium carbonate with the concentration of 300g/L and 22m3 of carbonized sodium carbonate solution with the concentration of 35.6g/L are added per hour, the mixture stays for 1 hour, the mixture is continuously fed into a clarification tank (1) for clarification to obtain calcium carbonate thick slurry with the concentration of 6.8m3 of 300g/L, 4.6m3 is circularly returned to the precipitation tank to provide seed crystals, and 2.2m3 is circularly returned to the wastewater neutralization reaction tank.
The clear liquid from the clarifying tank (1) is sent into a tank with 278m 3m per hour and 5000m per hour2The membrane separation device with the membrane separation area is used for separation, the separated purified water is 255m3 per hour, the concentrated brine is 23m3, the compositions of the membrane separation inlet water, the separated purified water and the concentrated brine are shown in table 3, the concentration of sodium sulfate in the inlet water is 4.80g/L, the purified water is only 20mg/L, the conductivity is 113us/cm, the concentration of sodium sulfate in the concentrated brine is increased to 57.98g/L, and the conductivity is 98000 us/cm. The productivity of titanium dioxide returned by water recovery and circulation is 90%.
TABLE 3 Membrane separation Water in and out composition
| Components | Feed water concentration (g/L) | Concentration of purified Water (g/L) | Concentration of concentrated brine (g/L) |
| pH | 7.5 | 7.2 | 7.6 |
| Na2SO4 | 4.80 | 0.016 | 57.98 |
| MgSO4 | 0.005 | -- | |
| CaSO4 | -- | -- | -- |
| Conductivity (us/cm) | 10000 | 113 | 98000 |
23m3 of concentrated brine separated by the membrane per hour is sent into 5-stage causticizing tanks which are connected in series and are provided with 15m3 and stirring, lime milk with CaO of 200g/L is respectively added into 5 stages, 0.63m3 is added, the total amount is 3.16m3, causticization is carried out, the material residence time is respectively 30 minutes, and the total residence time is 2.5 hours. The causticized slurry was sent to a filter press (2) for press filtration to separate 3.5 tons of filter cake containing 50% water and 21m3 filtrate containing 29.4g/L sodium hydroxide. 2.6m3 of filtrate is separated and returned to the titanium dioxide production, the rest 18.4m3 is carbonized by titanium dioxide drying tail gas, and 20.1m3 of solution containing 35.60g/L of sodium carbonate is obtained and circularly returned to the precipitation tank to precipitate saturated calcium sulfate solution.
Claims (10)
1. A production method for full resource recycling of wastewater generated in titanium dioxide production by a sulfuric acid method comprises the following steps:
adding the sulfuric acid method titanium dioxide production wastewater, limestone and lime into a neutralization reaction tank for precipitation reaction, and feeding the reaction material with complete precipitation reaction into a filter press for filtration and separation; the separated filter cake is used as titanium gypsum to be sent to gypsum building materials and cement building materials, and the separated filtrate is used as treated wastewater to be processed and produced by full recycling;
adding the wastewater separated by the filter press into a precipitation tank, simultaneously adding a sodium carbonate solution from a carbonization tower, controlling the reaction to precipitate saturated calcium sulfate in the wastewater to generate a calcium carbonate precipitation material with lower solubility, and sending the precipitation material into a clarifying tank for clarification; returning the heavy-phase bed charge calcium carbonate slurry of the clarifying tank to the neutralization reaction tank, and carrying out neutralization reaction with wastewater sent from titanium dioxide production; the light phase clear liquid of the clarifying tank is sent into a membrane separator for membrane separation of salt liquid, and the dilute phase (purified water) of the membrane separation is taken as process water and returned to the titanium dioxide production process, so that external raw water resources are saved, and the wastewater is fully utilized;
membrane separation concentrated phase sodium sulfate solution is sent into a causticizing tank, lime milk is added for causticizing reaction to generate precipitated calcium sulfate and sodium hydroxide solution, causticized slurry is sent into a filter press for separation, and separated filter cake is returned to a lime neutralization reaction tank for neutralization with titanium dioxide wastewater; sending the separated filtrate serving as a sodium hydroxide solution into a carbonization tower, carbonizing tail gas containing carbon dioxide generated in the production process of titanium dioxide to convert the tail gas into a sodium carbonate solution, and recycling the sodium carbonate solution into a precipitation tank to precipitate calcium ions of saturated calcium sulfate in the wastewater;
the solution after causticizing separation can be returned to titanium dioxide production to be used as dilute alkali liquor according to the mass flow condition.
2. The production method of the full resource recycling of the wastewater in the sulfuric acid process titanium dioxide production according to claim 1, characterized in that: the production wastewater is the production wastewater produced by the titanium dioxide by the sulfuric acid process and required to be neutralized; the pH value of the neutralization reaction with lime is 6-8, preferably 7.0-7.5.
3. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to claims 1-2, characterized in that: the wastewater is obtained by neutralizing the titanium dioxide production wastewater with limestone and lime and separating a gypsum filter cake by a filter press (1), and the wastewater contains saturated calcium sulfate solution and a small amount of soluble sulfate impurity solution, wherein the concentration range of the saturated calcium sulfate is 1-5g/L, namely 1-5Kg/m 3.
4. The production method of full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to any one of claims 1 to 3, characterized in that: the precipitation tank is added with sodium carbonate solution from a carbonization tower, and the molar ratio of the added amount of the sodium carbonate solution to the amount of saturated calcium sulfate (M)Na2CO3/MCaSO4) 1.0-1.2, preferably 1.05-1.10, and adding seed crystals of the thick paste to produce a proportion of calcium carbonate (M)Crystal grain/MRaw material) Is 1-3, preferably 1.5-2.
5. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to claim 1 or 4, characterized in that: the clarifying time of the clarifying tank (1) is 1-3 hours, preferably 1.5-2.0 hours; the thick slurry in the clarifying tank (1) is circularly returned to the precipitating tank, and the amount of the thick slurry is 2/3 of the total amount, and the thick slurry is used as the seed crystal of precipitated calcium carbonate; 1/3 of the total amount is circularly returned to the reaction neutralization tank to react with the titanium dioxide production wastewater; the clear liquid fraction was sent to a membrane separation filter.
6. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to any one of claims 1 to 5, characterized in that: clear liquid separated by the clarifying tank (1) is sent into a reverse osmosis membrane separation device comprising a pretreatment system, a reverse osmosis system and auxiliary medicine adding, cleaning, backwashing and the like for membrane separation; the membrane filtration is performed at an initial pressure of 1.5MPa and a final pressure of 4-5MPa, preferably 4.5MPa, and then the backwashing is performed, and the concentration of the treated wastewater is 6-15 times, preferably 8-10 times. The membrane separation purified water is directly returned to the titanium dioxide production and is recycled as process water; the membrane separation concentrated brine is a sodium sulfate solution, can be used for preparing sodium hydroxide and sodium carbonate solution by causticization for eliminating saturated calcium sulfate in wastewater treatment, and can also be concentrated and enriched.
7. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to any one of claims 1 and 5-6, characterized in that: the membrane separation filtration can adopt multi-stage and single-stage separation; the multistage separated water can be used in the post-treatment process of titanium dioxide; preferably, the conductivity of the membrane separation dilute phase (purified water) is 60-120us/cm, preferably 80-100 us/cm; the purified water directly returns to the water used in the titanium dioxide production process; the concentrated phase of membrane separation is sodium sulfate solution which is sent to a causticization tank for reaction.
8. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to any one of claims 1 to 6, characterized in that: the causticizing tank adopts multistage causticization in series, the stage number is 2-5 stages, preferably more than 3 stages; causticizing and adding the molar ratio (M) of lime milk to sodium sulfateCa(OH)2/MNa2SO4) 1.1-1.4, preferably 1.15-1.25; and the lime milk adding amount is distributed according to the causticization level.
9. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to claims 1 and 6-7, characterized in that: the causticized material comprises calcium sulfate generated by causticization and calcium hydroxide which does not participate in the reaction, the calcium sulfate and the calcium hydroxide are sent to a filter press (2) for filter pressing, the filter cake is beaten and circularly returned to a neutralization reaction tank, the filtrate is divided according to the total amount of the sodium hydroxide and the amount of saturated calcium sulfate required to be precipitated, part of the filtrate is sent to a carbonization tower for carbonization, and part of the filtrate is returned to titanium dioxide production to replace the alkali lye required for production.
10. The production method for full resource utilization of wastewater in titanium dioxide production by sulfuric acid process according to claims 1 and 6-8, characterized in that: the carbon dioxide gas adopted by the carbonization of the carbonization tower can be dry tail gas after the production of titanium dioxide, tail gas generated by calcining a metatitanic acid rotary kiln, carbon dioxide gas generated by neutralizing waste water by using calcium carbonate (limestone), combustion fuel and tail gas generated by a boiler; the carbonization degree is controlled at pH value of 11.5-12.5, preferably 12.
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