1. Patent Search
  2. Details

PRODUCTION METHOD FOR FULL RESOURCE RECYCLING OF SULPHATE-PROCESS TITANIUM DIOXIDE PRODUCTION WASTEWATER

20220402786 · 2022-12-22

    Inventors

    Cpc classification

    International classification

    Abstract

    The disclosure discloses a production method for full resource recycling of sulphate-process titanium dioxide production wastewater. The method comprises the steps: adding sulphate-process titanium dioxide production wastewater neutralized with lime and treatment wastewater obtained by separating gypsum in a filter press into a recycled sodium carbonate solution to precipitate saturated calcium sulfate in the treatment wastewater, clarifying slurry to separate a calcium carbonate precipitate from a sodium sulfate solution, and performing membrane separation on the separated sodium sulfate solution in a membrane filter; and adding lime into the concentrated phase sodium sulfate solution for causticizing reaction, wherein the filtrate is used as a sodium hydroxide solution, carbonizing using a carbon dioxide-containing tail gas produced in the production process of titanium dioxide to obtain a sodium carbonate solution, and then precipitating saturated calcium sulfate in the treatment wastewater again.

    Claims

    1. A production method for full resource recycling of sulphate-process titanium dioxide production wastewater, comprising: adding sulphate-process titanium dioxide production wastewater together with limestone and lime into a neutralization reaction tank for precipitation reaction, and feeding completely precipitated reaction materials into a filter press for filtration and separation; and feeding a separated filter cake as titanium gypsum into a gypsum building material and a cement building material to be used, and performing processing production of full recycling of a separated filtrate as treated wastewater; adding wastewater after being separated in the filter press into a precipitation tank and meanwhile adding a sodium carbonate solution from a carbonizing tower, controlling the reaction to precipitate saturated calcium sulfate in the treatment wastewater so that a calcium carbonate precipitate material with a smaller solubility is generated, and then feeding the precipitate material into a clarifying tank to be clarified; turning a heavy phase substrate calcium carbonate slurry back to the neutralization reaction tank to undergo neutralization reaction with wastewater fed in titanium dioxide production; and feeding a light phase clear liquid from the clarifying tank into a membrane separator for membrane separation of a saline solution, turning a diluted phase (purified water) generated after membrane separation as process water back to a titanium dioxide production procedure, thereby saving externally supplied raw water resources and achieving full utilization of wastewater; feeding a concentrated phase sodium sulfate solution generated after membrane separation into a causticizing tank, then adding lime milk, allowing the above materials to undergo causticizing reaction to generate a precipitate calcium sulfate and a sodium hydroxide solution, feeding causticized slurry into the filter press for separation, and returning a separated filter cake back to the lime neutralization reaction tank to be neutralized together with titanium dioxide wastewater; and feeding a separated filtrate as the sodium hydroxide solution into the carbonizing tower to be carbonized with a carbon dioxide-containing tail gas generated in the titanium dioxide production process so that the sodium hydroxide solution is converted into a sodium carbonate solution, and then recycling the sodium carbonate solution to the precipitation tank to precipitate calcium ions of saturated calcium sulfate in treatment wastewater; and returning a part of filtrate back to the titanium dioxide production to serve as a diluted alkaline solution, depending on the mass flow of the causticized and separated solution.

    2. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the production wastewater is production wastewater which is used for sulphate-process titanium dioxide production and needs neutralization treatment; and the pH value of lime neutralization reaction is 6-8, preferably 7.0-7.5.

    3. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the treatment wastewater is treatment wastewater produced after titanium dioxide production wastewater is neutralized with limestone and lime and a gypsum filter cake is separated via the filter press (1), wherein the treatment wastewater contains a saturated calcium sulfate solution and a few amount of soluble sulfate impurity solution, and the concentration range of saturated calcium sulfate is 1-5 g/L, namely, 1-5 Kg/m.sup.3.

    4. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the sodium carbonate solution from the carbonizing tower is added into the precipitation tank, and a molar ratio (M.sub.Na2CO3/M.sub.CaSO4) of the addition amount of the sodium carbonate solution to the amount of saturated calcium sulfate is 1.0-1.2, preferably 1.05-1.10, and a ratio (M.sub.crystal/M.sub.generated) of added thick slurry crystal seeds to generated calcium carbonate is 1-3, preferably 1.5-2.

    5. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the clarifying time of the clarifying tank (1) is 1-3 h, preferably 1.5-2.0; the amount of the thick slurry recycling and returning back to the precipitation tank is ⅔ of the total amount, which serves as crystal seeds for precipitating calcium carbonate; the thick slurry whose amount is ⅓ of the total amount is recycled and returns back to the neutralization reaction tank to react with titanium dioxide production wastewater; and the clear liquid part is fed to a membrane separation filter.

    6. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the clear liquid separated via the clarifying tank (1) is fed to a reverse osmosis membrane separation device containing a pretreatment system and a reverse osmosis system supplemented with dosing, washing, back washing and the like for membrane separation; after a starting pressure for membrane filtration is 1.5 MPa, a final pressure is 4-5 MPa, preferably 4.5 MPa, back washing is performed, and the concentration multiple of the treatment wastewater is 6-15 folds, preferably 8-10 folds; the purified water produced after membrane separation directly returns back to titanium dioxide production for recycling as process water; and strong brine produced after membrane separation is a sodium sulfate solution, which is used for eliminating saturated calcium sulfate in treatment wastewater as causticized sodium hydroxide and sodium carbonate solutions, or is concentrated for enrichment again.

    7. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the membrane separation and filtration can adopt multi-stage and single-stage separation; multi-stage separation water can be used in titanium dioxide posttreatment process; preferably, the conductivity of the diluted phase (purified water) generated after membrane separation is 60-120 us/cm, preferably 80-100 us/cm; the purified water directly returns back to titanium dioxide production process water; and the concentrated phase generated after membrane separation is the sodium sulfate solution, which is fed to the causticizing tank for reaction.

    8. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the causticizing tank adopts tandem multi-stage causticizing with the number of stages being 2-5, preferably more than 3; a molar ratio (M.sub.Ca(OH)2/M.sub.Na2SO4) of lime milk to sodium sulfate added for causticizing is 1.1-1.4, preferably 1.15-1.25; and dosing distribution of line milk is performed based on the number of stages for causticizing.

    9. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the causticizing materials comprise calcium sulfate generated by causticizing and calcium hydroxide which does not involve in reaction, which are fed into a filter press (2) for filter pressing, the filter cake is pulped and recycled to return back to the neutralization reaction tank, the filtrate is shunt depending on the total amount of sodium hydroxide and the amount of saturated calcium sulfate needing to be precipitated, a part of filtrate is fed to the carbonizing tower to be carbonized, and the other part of filtrate returns back to titanium dioxide production to replace the amount of an alkaline solution required for production.

    10. The production method for full resource recycling of sulphate-process titanium dioxide production wastewater according to claim 1, wherein the carbon dioxide gas adopted for carbonizing in the carbonizing tower can be a tail gas dried after titanium dioxide production, a metatitanic acid rotary kiln calcining tail gas and a carbon dioxide gas produced when wastewater is neutralized with calcium carbonate (limestone), a tail gas produced when fuel is combusted and a boiler tail gas produced in a boiler; and a carbonizing degree is controlled at the pH of 11.5-12.5, preferably 12.

    Description

    DESCRIPTION OF THE DRAWINGS

    [0040] FIG. 1 is a process flowchart of traditional sulphate-process titanium dioxide production wastewater.

    [0041] FIG. 2 is a process flowchart of full resource recycling of sulphate-process titanium dioxide production wastewater of the disclosure.

    DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

    Example 1

    [0042] As shown in FIG. 2, 1600 L per hour of acidic wastewater (specific gravity of 1.05, containing 36.96 g/L of sulfuric acid, 16.80 g/L of ferrous sulfate, 0.525 g/L of titanium sulfate, see Table 1) and 29.0 L per hour of lime milk containing 179 g/L calcium oxide were neutralized in three tandem 2000 L neutralization tanks with stirrers and equipped with air distribution tubes at the bottoms in which air was blown for aerated oxidation, the retention time of reaction materials was controlled for 1 h, the pH value of slurry was controlled to 7.5, the slurry overflew from the top of the third-stage neutralization reaction tank to enter a filter press pump tank and then was continuously fed into the filter press for filtration and separation, so as to obtain 27.4 kg of filter cake containing 45% water and 1658 L of treatment wastewater (specific gravity of 1.005, its compositions are seen in Table 2) in each hour.

    TABLE-US-00001 TABLE 1 Compositions of titanium dioxide production wastewater Component Concentration (g/L) Component Content (%) H.sub.2SO.sub.4 36.96 MgSO.sub.4 2.10 FeSO.sub.4 16.80 Al.sub.2(SO.sub.4).sub.3 1.05 Na.sub.2SO.sub.4 1.30 CaSO.sub.4 1.05

    TABLE-US-00002 TABLE 2 Compositions of treatment wastewater Component Concentration (g/L) Component Content (%) pH 7.2 MgSO.sub.4 0.010 FeSO.sub.4 0.001 Al.sub.2(SO.sub.4).sub.3 0.010 Na.sub.2SO.sub.4 1.25 CaSO.sub.4 3.35

    [0043] 1658 L per hour of treatment wastewater was continuously fed into a 5500 Ld saturated calcium sulfate precipitation tank, and meanwhile 146 L of 30 g/L carbonized sodium carbonate solution and 33 L of 250 g/L clarified calcium carbonate thick slurry that was recycled and returned back were added in each hour, the precipitation reaction material was stayed for 1 h and then continuously fed into a clarifying tank (1) for clarification to obtain 50 L of 250 g/L calcium carbonate thick slurry, 33 L of calcium carbonate thick slurry was returned back into the precipitation tank, crystal seeds were provided, 17 L of calcium carbonate thick slurry was recycled and returned back to an acidic wastewater neutralization reaction tank.

    [0044] The clear solution from the clarifying tank (1) was fed into a 1814.2 L membrane separation device in each hour to be separated, an initial filtration pressure was 1.5 MPa, and reverse rinsing cyclic filtration was performed after 4.5 MPa of filtration pressure was reached. 1636 L of purified water and 178 L of enriched strong brine were separated from the membrane filter. The compositions of feed water, purified water and strong brine after membrane separation are seen in Table 3. The concentration of sodium sulfate in the feed water is 3.49 g/L, the concentration of the purified water is only 16 mg/L, the conductivity is 107 us/cm, the concentration of sodium sulfate in the strong brine is increased to 34.72 g/L, and the conductivity is 98000 us/cm. The rate of water recycling and returning back to titanium dioxide production is 90%.

    TABLE-US-00003 TABLE 3 Compositions of feed water after membrane separation Concentration Concentration Concentration of feed of purified of strong Component water (g/L) water (g/L) brine (g/L) pH 7.6 7.2 7.8 Na.sub.2SO.sub.4 4.66 0.016 42.60 MgSO.sub.4 0.005 — CaSO.sub.4 — — — Conductivity (us/cm) 9000 107 98000

    [0045] 178 L per hour of strong brine after membrane separation was fed into 3-stage causticizing tank with a stirrer, 4.3 L of 170 g/L lime milk was added into each of 3 stages for causticizing for 13.1 L in total, each of the materials was stayed for 30 min respectively for 1.5 h in total. The causticized slurry was fed into the filter press (2) to undergo filter press, so as to separate 16.80 kg of filter cake containing 45% water and 178.6 L of filtrate containing 20/l g/L sodium hydroxide. The filtrate was carbonized with the titanium dioxide dry tail gas to obtain 180 L of solution containing 26.43 g/L sodium carbonate, wherein 166 L of solution was recycled and returned back to the precipitation tank to precipitate a saturated calcium sulfate solution, the rest 14 L of solution was used for washing of other acidic gases to replace the original commercial sodium hydroxide solution.

    Example 2

    [0046] As shown in FIG. 2, 240 m.sup.3 per hour of acidic wastewater (main compositions are seen in Table 4) from sulphate-process titanium dioxide production and 36.5 m.sup.3 per hour of lime milk containing 200 g/L calcium oxide were neutralized in four tandem 180 m.sup.3 neutralization tanks with stirrers, the bottoms of the last two stages of neutralization reaction tanks were provided with air distribution tubes and blown with air for aerated oxidation, the retention time of reaction materials was controlled for 1.5 h, the pH value of slurry was controlled to 7.5, the slurry overflew from the top of the four-stage neutralization reaction tank to enter a filter press pump tank and then was continuously fed into the filter press for filtration and separation, so as to obtain 45.5 t of filter cake containing 45% water and 253 t of treatment wastewater in each hour. The compositions are seen in Table 5.

    TABLE-US-00004 TABLE 4 Compositions of titanium dioxide production wastewater Component Concentration (g/L) Component Content (%) H.sub.2SO.sub.4 41.06 MgSO.sub.4 1.10 FeSO.sub.4 18.66 Al.sub.2(SO.sub.4).sub.3 0.95 Na.sub.2SO.sub.4 1.54 CaSO.sub.4 1.55

    TABLE-US-00005 TABLE 5 Compositions of treatment wastewater Component Concentration (g/L) Component Content (%) pH 7.0 MgSO.sub.4 0.010 FeSO.sub.4 0.001 Al.sub.2(SO.sub.4).sub.3 0.010 Na.sub.2SO.sub.4 1.46 CaSO.sub.4 3.65

    [0047] 253 t per hour of treatment wastewater was continuously fed into 3 tandem 110 m.sup.3 saturated calcium sulfate precipitation tank, and meanwhile 4.6 m.sup.3 of 300 g/L clarified slurry returned back by circulating calcium carbonate and 22 m.sup.3 of 35.6 g/L carbonized sodium carbonate solution, the precipitation reaction material was stayed for 1 h and then continuously fed into a clarifying tank (1) for clarification to obtain 6.8 m.sup.3 of 300 g/L calcium carbonate thick slurry, 4.6 m.sup.3 of calcium carbonate thick slurry was returned back into the precipitation tank, crystal seeds were provided, 2.2 m.sup.3 of calcium carbonate thick slurry was recycled and returned back to a wastewater neutralization reaction tank.

    [0048] 278 m.sup.3 per hour of clarified solution from the clarifying tank (1) was fed into a membrane separation device with a membrane separation area of 5000 m.sup.2. The volume of the separated purified water is 255 m.sup.3 in each hour, and the volume of the enriched strong brine is 23 m.sup.3. Compositions of membrane separation feed water, separated and purified water and strong brine are seen in Table 3. The concentration of sodium sulfate in the feed water is 4.80 g/L, the concentration of the purified water is only 20 mg/L, the conductivity is 113 us/cm, the concentration of the strong brine is increased to 57.98 g/L, and the conductivity is 98000 us/cm. The rate of water recovered and returned back to titanium dioxide production is 90%.

    TABLE-US-00006 TABLE 3 Compositions of membrane separation feed water Concentration Concentration Concentration of feed of purified of strong Component water (g/L) water (g/L) brine (g/L) pH 7.5 7.2 7.6 Na.sub.2SO.sub.4 4.80 0.016 57.98 MgSO.sub.4 0.005 — CaSO.sub.4 — — — Conductivity 10000 113 98000 (us/cm) Conductivity 9000 107 98000 (us/cm)

    [0049] 23 m.sup.3 of strong brine after membrane separation was fed into 5-stage tandem 15 m.sup.3 causticizing tank with a stirrer, 0.63 m.sup.3 of 200 g/L lime milk containing CaO was added into each of 5 stages for causticizing for 3.16 L in total, each of the materials stayed for 30 min respectively for 2.5 h in total. The causticized slurry was fed into the filter press (2) to undergo filter press, so as to separate 3.5 t of filter cake containing 50% water and 21 m.sup.3 of filtrate containing 29.4 g/L sodium hydroxide. 2.6 m.sup.3 of filtrate was returned back for titanium dioxide production, the rest 18.4 m.sup.3 of filtrate was carbonized with titanium dioxide dry tail gas to obtain 20.1 m.sup.3 of 35.60 g/L solution which was recycled and returned back to the precipitation tank to precipitate the calcium sulfate solution.