High-fluorine sewage treatment method and application

Abstract

The invention provides a high-fluorine sewage treatment method and application, and relates to the technical field of crossing of sewage treatment and waste recycling. Specifically, low-concentration waste acid water generated in titanium dioxide production through a sulfuric acid method is used as an acidic medium, phosphorite is used as a calcium and phosphorus source, an acidic reaction solution containing soluble phosphate is prepared through a dissolution reaction, then the acidic reaction solution is mixed with high-fluorine sewage, then two-stage pH regulation and control are carried out to realize re-precipitation of calcium fluorophosphate, and the calcium fluorophosphate is obtained. And finally, high-fluorine sewage removal and waste acid water resource utilization are completed. According to the method, the circular economy target of treating waste with waste is achieved through calcium fluorophosphate dissolution-reprecipitation balance and accurate control over technological parameters, the fluorine removal efficiency is stabilized to be 94% or above, the concentration of fluorine in effluent is smaller than or equal to 10 mg / L, remarkable economic and environmental benefits are achieved, and the method is suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention relates to the field of interdisciplinary technology of wastewater treatment and waste resource utilization, and more specifically, to a method for treating high-fluoride wastewater and its application. Background Technology

[0002] In the sulfuric acid process for producing titanium dioxide, ilmenite reacts with sulfuric acid to produce titanium oxysulfate, which is then hydrolyzed and calcined to obtain titanium dioxide. This process requires the addition of a large amount of sulfuric acid, and the remaining sulfuric acid and byproducts after the reaction form a large amount of low-concentration wastewater, typically with a sulfuric acid concentration of 40-80 g / L. Current processes require neutralization of this wastewater before discharge. Existing neutralization processes consume large amounts of alkaline agents such as lime and carbide slag, resulting in high neutralization costs and requiring additional disposal of the resulting solid waste residue. This solid waste residue contains heavy metals and can easily cause secondary pollution to soil and groundwater.

[0003] In industries such as electronics and photovoltaics, the production of semiconductor etching and photovoltaic cells requires the use of hydrofluoric acid or fluoride-containing compounds, resulting in high-fluoride wastewater with fluoride concentrations typically ranging from 50 to 1500 ppm. Because fluoride ions are highly toxic to organisms, emissions must be strictly controlled to meet standards. Existing defluorination processes include: adding lime to generate calcium fluoride precipitate, but this lime method still results in effluent fluoride concentrations of 15-30 ppm; another method involves adding polyaluminum chloride or activated alumina to adsorb fluoride ions, followed by solid-liquid separation to remove the fluoride precipitate, but this aluminum salt adsorption method costs as much as 15-25 yuan per ton of water, exhibiting low efficiency and high cost.

[0004] Furthermore, while existing technologies utilize phosphate for fluoride removal, they largely rely on industrial-grade phosphate reagents. Some technologies attempt to treat phosphate rock by mixing waste acid with fluoride-containing wastewater, but these only focus on phosphate rock pretreatment and fail to address the deep removal of high-fluoride wastewater. Moreover, they lack tailored solutions for wastewater with varying fluoride concentrations and initial pH levels. Enhancing the synergistic reaction between titanium dioxide waste acid and phosphate rock, and developing a highly efficient and low-cost high-fluoride wastewater treatment technology, would yield significant economic and environmental benefits.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a method for treating high-fluoride wastewater, aiming to address the shortcomings of existing methods for treating high-fluoride wastewater, including high costs and poor adaptability. This invention provides a method for co-treating high-fluoride wastewater with titanium dioxide wastewater and phosphate rock, achieving "waste treatment and resource recycling." It is also suitable for high-fluoride wastewater with fluoride concentrations of 50ppm to 1500ppm and initial pH values ​​of <2.0 to >3.0, exhibiting high fluoride removal efficiency and low treatment costs.

[0007] The second objective of this invention is to provide a method for treating wastewater from the sulfuric acid process for producing titanium dioxide.

[0008] A third objective of this invention is to provide a wastewater treatment device.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for treating high-fluoride wastewater includes the following steps: (1) The waste acid solution from the sulfuric acid process for producing titanium dioxide is mixed with phosphate rock to obtain a high-phosphorus reaction solution; (2) Detect the fluoride concentration and pH value of the high-fluoride wastewater feed liquid, adjust it to obtain high-fluoride wastewater with fluoride concentration ≤500ppm and pH ≤3.0, and then mix the high-fluoride wastewater and the high-phosphorus reaction liquid to obtain a mixture; (3) Adjust the pH of the mixture to 3.5~4.0 and carry out the first defluorination reaction; then adjust the pH to 4.5~5.5 and carry out the second defluorination reaction; stop the reaction when the fluoride concentration of the reaction solution is <20ppm, stir and mature, and then separate the solid and liquid to obtain the defluorinated liquid and the calcium fluorophosphate solid phase.

[0010] Preferably, the liquid-to-solid ratio of the waste acid solution to the phosphate rock in step (1) is 3.5~6:1, in m³. 3 / t.

[0011] Preferably, the temperature of the mixing reaction in step (1) is 40℃~50℃ and the duration is 60min~90min.

[0012] Preferably, the sulfuric acid concentration of the waste acid solution from the sulfuric acid process for producing titanium dioxide is 40 g / L to 80 g / L.

[0013] Preferably, the high-phosphorus reaction solution has a pH of 1.8 to 2.2 and a phosphorus content of ≥10 g / L.

[0014] Preferably, the adjustment of the high-fluoride wastewater feed liquid in step (2) includes at least one of the following features: (a) When the initial fluoride concentration is >500 ppm, dilute with water to a fluoride concentration of 300 ppm to 500 ppm; (b) When pH > 3, add the waste acid solution from the sulfuric acid process for titanium dioxide production until the pH is 2-3; (c) When pH < 2, add the phosphate rock and stir to react, and the amount of phosphate rock added is 1 wt.% to 2 wt.%; preferably, if pH < 2 after adding the phosphate rock, add calcium hydroxide emulsion until pH is 2 to 3.

[0015] Preferably, in step (2): when the fluoride concentration of the high-fluoride wastewater is 200ppm~500ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:5~8; When the fluoride concentration of the high-fluoride wastewater is <200ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:9~12.

[0016] Preferably, the first defluorination reaction in step (3) includes: The pH adjuster is added at a rate of 5 L / h to 10 L / h, and the mixture is stirred and reacted for 15 min to 25 min. More preferably, when the pH of the reaction solution is less than 1.8 after the addition time is over, the pH adjuster is added at a rate of 8 L / h to 12 L / h until the pH of the reaction solution is 3.5 to 4.0.

[0017] Preferably, the second defluorination reaction in step (3) includes: The pH adjuster is added at a rate of 3 L / h to 7 L / h to obtain a reaction system with a pH of 4.5 to 5.5. The fluorine concentration is sampled every 5 minutes, and the addition is stopped when the fluorine concentration is <20 ppm.

[0018] Preferably, in step (3), the first defluorination reaction and the second defluorination reaction are carried out under stirring, and the stirring frequency is independently selected from 150 rpm to 200 rpm.

[0019] A method for treating wastewater from the sulfuric acid process for producing titanium dioxide, including the aforementioned method for treating high-fluoride wastewater.

[0020] A wastewater treatment device is used for the treatment method of the high-fluoride wastewater or the waste liquid treatment method of the sulfuric acid process for producing titanium dioxide. The wastewater treatment device includes a titanium dioxide wastewater storage tank, a dissolving reaction vessel, a filtration device, an acidic reaction liquid transfer tank, a mixing reaction tank, a maturation tank, and a pressure filter connected in sequence. The wastewater treatment device further includes: a high-fluoride wastewater conditioning tank and a calcium hydroxide emulsion storage tank, which are respectively connected to the mixing reaction tank; The wastewater treatment device further includes a phosphate rock crushing device, which is connected to the solid discharge port of the filter press, the solid discharge port of the filter, and the feed port of the dissolution reactor.

[0021] Preferably, the wastewater treatment device further includes: a clean water storage tank, a filter cake collection device, and a flushing water circulation tank, all connected to the filter press device. More preferably, the rinsing water circulation tank is connected to the dissolution reaction vessel.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Resource recycling: The present invention uses titanium dioxide waste acid water as the reaction medium, and the sulfuric acid digestion rate reaches more than 90%; after the phosphate rock is reacted, the filter cake can be returned to the phosphate rock processing process, realizing a closed loop of "waste acid-phosphate rock-fluorine removal-phosphate rock reuse" and reducing waste emissions.

[0023] (2) High and stable defluorination efficiency: Through phased pH control and fluoride concentration adaptation adjustment, the defluorination efficiency is stable at over 94%, and the effluent fluoride concentration is ≤10ppm, which is better than the traditional lime method (effluent fluoride content is 15~30ppm) and meets the first-class standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996).

[0024] (3) Wide range of applicability: The process of the present invention can treat high fluoride wastewater with fluoride concentration of 50~1500ppm and initial pH <1.0 to >3.0. By adjusting the parameters, it can be adapted to different water qualities, thus solving the problem of limited applicability of the existing technology.

[0025] (4) Significant economic benefits: This invention does not require the purchase of industrial-grade phosphate, calcium salt and other defluorination agents. After optimizing the parameters for different fluoride concentrations and pH values, the cost per ton of water treated is reduced by more than 60% compared with the aluminum salt method; the sludge production is reduced by 40% compared with the lime method, thus reducing the cost of sludge disposal. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 A schematic diagram of the apparatus of the present invention is provided. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0029] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] The first aspect of this invention is to provide a method for treating high-fluoride wastewater, which mainly includes the following steps: (1) The waste acid solution from the sulfuric acid process for producing titanium dioxide is mixed with phosphate rock to obtain a high-phosphorus reaction solution; (2) Detect the fluoride concentration and pH value of the high-fluoride wastewater feed liquid, adjust it to obtain high-fluoride wastewater with fluoride concentration ≤500ppm and pH ≤3.0, and then mix the high-fluoride wastewater and the high-phosphorus reaction liquid to obtain a mixture; (3) Adjust the pH of the mixture to 3.5~4.0 and carry out the first defluorination reaction; then adjust the pH to 4.5~5.5 and carry out the second defluorination reaction; stop the reaction when the fluoride concentration of the reaction solution is <20ppm, stir and mature, and then separate the solid and liquid to obtain the defluorinated liquid and the calcium fluorophosphate solid phase.

[0032] In a preferred embodiment, the sulfuric acid concentration of the waste acid solution from the sulfuric acid process for producing titanium dioxide is 40 g / L to 80 g / L, including but not limited to any one or any two of the following values: 40, 45, 50, 55, 60, 65, 70, 75, and 80 (g / L).

[0033] It is understood that the acidic wastewater from the sulfuric acid process for titanium dioxide production used in this invention mainly originates from the metatitanic acid washing process, acidolysis and calcination exhaust gas cooling and washing process, and concentrated steam condenser discharge process. The core components of the acidic wastewater from the sulfuric acid process for titanium dioxide production include, but are not limited to, free sulfuric acid and ferrous sulfate, and also contain metatitanic acid and sulfates of ferrous or iron ions, titanium ions, chromium ions, magnesium ions and other metal ions introduced from the mineral powder.

[0034] In a preferred embodiment, the phosphate rock is obtained by crushing and screening, and the screening screen is 80 mesh to 100 mesh.

[0035] It is understood that the phosphate rock used in this invention can be any ore raw material with a certain phosphorus content, including but not limited to apatite (such as fluorapatite, carboflupatite, chlorapatite), collophane, phosphate rock, phosphogypsum, struvite, etc. The core elements of the phosphate rock include but are not limited to phosphorus (P), calcium (Ca), and oxygen (O), and it is often accompanied by elements such as fluorine (F), chlorine (Cl), silicon (Si), magnesium (Mg), iron (Fe), and aluminum (Al).

[0036] In a preferred embodiment, the phosphate rock has a calcium fluorophosphate content of ≥85% by mass, meaning that the phosphate rock used in this invention is a high-grade phosphate rock with a high concentration of effective phosphate minerals. Furthermore, using a more common industry standard for phosphate rock grade, after converting all phosphorus elements (mainly from calcium fluorophosphate) in the phosphate rock to phosphorus pentoxide by stoichiometry, the phosphorus pentoxide content is ≥28% by mass.

[0037] In a preferred embodiment, the liquid-to-solid ratio of the waste acid solution to the phosphate rock in step (1) is 3.5~6:1, in m³. 3 / t; In some embodiments, when the impurity content of the phosphate rock is >10% (in this invention, the impurities in the phosphate rock specifically refer to the SiO2 content), the liquid-to-solid ratio of the waste acid to the phosphate rock is 3.5~4.5:1 to avoid excessive consumption of hydrogen ions by impurities, resulting in insufficient phosphorus dissolution. In this invention, the above liquid-to-solid ratio needs to be controlled to ensure that the phosphate rock is fully dissolved and the phosphorus content is stable at ≥10g / L, avoiding insufficient subsequent fluoride ion removal.

[0038] In one preferred embodiment, the temperature of the mixing reaction in step (1) is 40℃~50℃ and the duration is 60min~90min; in some embodiments, the mixing reaction is carried out under stirring, and the stirring frequency is 200rpm~300rpm.

[0039] In a preferred embodiment, during the mixing reaction in step (1), the phosphorus content in the reaction solution is sampled and tested every 15 min to 30 min; when the phosphorus content is <10 g / L, the waste acid solution is added; in some embodiments, the mass fraction of sulfuric acid in the waste acid solution is 5 wt.% to 10 wt.%.

[0040] In a preferred embodiment, step (1) further includes: performing solid-liquid separation after the mixing reaction to obtain phosphate rock residue with a water content ≤15wt.% and the high-phosphorus reaction solution; in some embodiments, the phosphate rock residue is returned to the phosphate rock for reuse; the pH of the high-phosphorus reaction solution is 1.8~2.2 and the phosphorus content is ≥10g / L.

[0041] In step (1) of this invention, the sulfuric acid in the waste acid solution provides hydrogen ions, which destroy the crystal lattice of calcium fluorophosphate in the phosphate rock. The reaction equation is as follows; wherein the generated phosphoric acid further dissociates into H2PO4. - This provides soluble phosphate and calcium sources for subsequent fluoride removal; Ca5(PO4)3F + 5H2SO4 → 3H3PO4 + 5CaSO4 (precipitate) + HF.

[0042] As a preferred embodiment, step (2) includes: the high-fluoride wastewater feed liquid is filtered through a grid to remove large impurities.

[0043] In a preferred embodiment, the adjustment of the high-fluoride wastewater feed liquid in step (2) includes at least one of the following features: (a) When the initial fluoride concentration is >500 ppm, dilute with water to a fluoride concentration of 300 ppm to 500 ppm; (b) When pH > 3, add the waste acid solution from the sulfuric acid process for titanium dioxide production until the pH is 2-3; (c) When pH < 2, add the phosphate rock and stir the reaction, with the amount of phosphate rock added being 1 wt.% to 2 wt.%; further, if pH < 2 after adding the phosphate rock, add calcium hydroxide emulsion to bring the pH to 2 to 3. In some embodiments, the concentration of the calcium hydroxide emulsion is 8 wt.% to 20 wt.%, and the addition rate of the calcium hydroxide emulsion is 2 L / h to 3 L / h. Further, if pH < 1 after adding the phosphate rock and cannot be raised to pH ≥ 1.5 by adding calcium hydroxide emulsion, proceed directly to the subsequent mixing reaction step.

[0044] It is understood that, through the above-mentioned diverse adjustment routes, relying on the adjustment of fluoride concentration and pH, this invention can adapt to wastewater with fluoride concentration of 50~1500ppm and initial pH <1.0 or >3.0, and has a very wide range of adaptability, thus solving the limitations of the adaptability of existing technologies.

[0045] In a preferred embodiment, in step (2), when the fluoride concentration of the high-fluoride wastewater is 200ppm to 500ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:5 to 8; when the fluoride concentration of the high-fluoride wastewater is <200ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:9 to 12.

[0046] As an optional implementation, if the fluoride concentration of the high-fluoride wastewater is 500±20ppm (i.e., close to the boundary of 500ppm) or the fluoride concentration is >500ppm (i.e., the fluoride concentration cannot be reduced to below the preset 500ppm) based on the adjustment in step (2), the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:4~6, that is, the amount of the high-fluoride wastewater after adjustment is adaptively reduced.

[0047] As a preferred embodiment, the mixing in step (2) is carried out under stirring conditions, with a stirring frequency of 150 rpm to 200 rpm and a stirring time of 10 min to 15 min.

[0048] In a preferred embodiment, each pH adjustment in step (3) is performed using calcium hydroxide emulsion (or understood as using calcium hydroxide emulsion as a pH adjuster), wherein the concentration of calcium hydroxide is 8 wt.%~20 wt.%.

[0049] In a preferred embodiment, for the first defluorination reaction: the pH adjuster is added at a rate of 5 L / h to 10 L / h, and the reaction is carried out under stirring for 15 min to 25 min; if the pH of the reaction solution is <1.8 after the addition time is completed, the pH adjuster is added at a rate of 8 L / h to 12 L / h, and the reaction is carried out under stirring for 5 min to 10 min, until a reaction system with a pH of 3.5 to 4.0 is obtained.

[0050] In this invention, the first defluorination reaction requires ensuring the system pH is between 3.5 and 4.0, and is H2PO4. - The stable presence of the solution provides a basis for the subsequent formation of calcium fluorophosphate precipitation. As in the above embodiment, the dosing rate needs to be adjusted in real time when the pH deviates. In some optional embodiments, the pH of the mixture in the first defluorination reaction includes, but is not limited to, any one or any two of the values ​​formed by 3.5, 3.6, 3.7, 3.8, 3.9, and 4.0.

[0051] As a preferred embodiment, the first defluorination reaction and the second defluorination reaction in step (3) are carried out under stirring, and the stirring frequency is independently selected from 150 rpm to 200 rpm to ensure that the pH adjuster is evenly dispersed and reacts fully with the ions.

[0052] In a preferred embodiment, for the second defluorination reaction: the pH adjuster is added at a rate of 3 L / h to 5 L / h to obtain a reaction system with a pH of 4.5 to 5.5; the fluoride concentration is sampled and tested every 5 minutes, and the addition is stopped when the fluoride concentration is <20 ppm. In an alternative embodiment, if the fluoride concentration of the high-fluoride wastewater is >500 ppm, the pH adjuster is added at a rate of 5 L / h to 7 L / h.

[0053] In this invention, the second defluorination reaction requires the system pH to be maintained between 4.5 and 5.5. This pH range is the optimal range for the formation of calcium fluorophosphate precipitate, and within this range, Ca... 2+ H2PO4 - With F - The reaction proceeds to the highest degree of forward propagation, with a fluoride removal rate of over 94%. In some optional embodiments, the pH of the mixture in the second defluorination reaction includes, but is not limited to, any one or any two of the following values: 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, and 5.5.

[0054] The reaction equation for the two-stage defluorination reaction in this invention is as follows. It can be understood that the reaction proceeds in the forward direction by staged pH control, thereby achieving stable removal of fluoride ions. 5Ca 2+ +3H2PO4 - +F - —Ca5(PO4)3F (precipitate) + 6H + .

[0055] In a preferred embodiment, the stirring frequency for maturation in step (3) is 50 rpm to 100 rpm, and the maturation time is 20 min to 40 min. In some embodiments, when the fluoride concentration after the second defluorination reaction is <20 ppm and ≥10 ppm, the maturation time is 20 min to 25 min. When the fluoride concentration after the second defluorination reaction is <10 ppm, the maturation time is shortened adaptively based on the initial time. In other embodiments, if the fluoride concentration of the reaction solution after the two-stage defluorination reaction is still ≥20 ppm (i.e., it is impossible to reduce the fluoride concentration to below 20 ppm), the maturation time is increased adaptively based on the initial time, i.e., the maturation time is 25 min to 40 min.

[0056] In a preferred embodiment, the solid-liquid separation in step (3) is performed by pressure filtration; the pressure of the pressure filtration is 0.6 MPa to 0.8 MPa, and the pore size of the filter cloth is 0.1 μm to 0.2 μm. In some optional embodiments, the wash water from the pressure filtration is collected and reused; at the same time, the fluoride concentration of the wash water from the pressure filtration is periodically tested to ensure that its fluoride concentration is ≤20 ppm. If it exceeds the standard, it needs to be partially discharged or pretreated (such as by adding a small amount of phosphate rock powder for adsorption) before reuse to avoid the accumulation of fluoride in the system and its negative impact.

[0057] In a preferred embodiment, the fluoride concentration of the defluorinating liquid obtained in step (3) is ≤10ppm, and the water content of the calcium fluorophosphate solid phase is ≤20wt.%. It is understood that those skilled in the art can treat the defluorinating liquid with any post-treatment to obtain pure water, or directly collect the defluorinating liquid and discharge or reuse it. In addition, the calcium fluorophosphate solid phase can be treated with dehydration and other methods to obtain industrial-grade calcium fluorophosphate products, or the calcium fluorophosphate solid phase can be directly collected and combined with the phosphate rock to achieve phosphate rock powder reuse. In this embodiment, the mixing mass ratio of the calcium fluorophosphate solid phase and fresh phosphate rock is 1:5~10, and after mixing, it is crushed to 80 mesh~100 mesh to ensure that the calcium fluorophosphate content is still ≥85%.

[0058] A second aspect of the present invention provides a method for treating wastewater from the sulfuric acid process for producing titanium dioxide, including the method for treating high-fluoride wastewater as described in the first aspect. It is understood that the method for treating wastewater from the sulfuric acid process for producing titanium dioxide can be completely equivalent to the method for treating high-fluoride wastewater without additional operations, or it can include any other conventional or unconventional steps; there are no limitations in this invention.

[0059] A third aspect of the present invention is to provide a wastewater treatment apparatus for performing the high-fluoride wastewater treatment method as described in the first aspect, or the wastewater treatment method for titanium dioxide production using the sulfuric acid process as described in the second aspect.

[0060] Specifically, the wastewater treatment device includes a titanium dioxide wastewater storage tank, a dissolving reactor, a filtration device, an acidic reaction liquid transfer tank, a mixing reaction tank, a maturation tank, and a pressure filter connected in sequence; further, the wastewater treatment device also includes a high-fluoride wastewater conditioning tank and a calcium hydroxide emulsion storage tank, which are respectively connected to the mixing reaction tank; further, the wastewater treatment device also includes a phosphate rock crushing device, which is respectively connected to the solid phase outlet of the pressure filter, the solid phase outlet of the filtration device, and the inlet of the dissolving reactor.

[0061] In a preferred embodiment, the wastewater treatment device further includes: a clean water storage tank, a filter cake collection device, and a flushing water circulation tank, all connected to the filter press device; in some embodiments, the flushing water circulation tank is connected to the dissolving reactor for circulating water. Figure 1 The diagram shown is a connection diagram of the present invention in this embodiment.

[0062] It is understandable that the following characteristics exist in this aspect: In one embodiment, the titanium dioxide waste liquid storage tank is connected to the dissolution reactor via a pipeline for transporting waste acid water into the reactor for reaction.

[0063] In one embodiment, the phosphate rock crushing device is connected to the feed inlet of the dissolving reactor via a conveyor belt for outputting crushed phosphate rock raw materials.

[0064] In one embodiment, the outlet of the dissolving reactor is connected to the filtration device, the residue outlet of the filtration device is connected to the phosphate rock crushing device, and the filtrate outlet of the filtration device is connected to the acidic reaction liquid transfer tank.

[0065] In one embodiment, the high-fluoride wastewater conditioning tank and the acidic reaction solution transfer tank are respectively connected to the mixing reaction tank via pipelines to supply the high-fluoride wastewater and high-phosphorus reaction solution for the mixed reaction; at the same time, the calcium hydroxide emulsion storage tank is connected to the mixing reaction tank via a metering pump to supply calcium hydroxide emulsion.

[0066] In one embodiment, the outlet of the mixing reaction tank is connected to the maturation tank, and the outlet of the maturation tank is connected to the filter press device, for realizing the processes of stirring maturation and solid-liquid separation.

[0067] In one embodiment, the filtrate outlet of the filter press is connected to the clean water storage tank, the filter cake outlet of the filter press is connected to the filter cake collection device, and the flushing water outlet of the filter press is connected to the flushing water circulation tank.

[0068] Example 1 Raw material parameters: Sulfuric acid concentration of titanium dioxide waste water is 60g / L; phosphate rock has a calcium fluorophosphate content of 88% and a P2O5 content of 30%, and is crushed to 90 mesh; high-fluoride wastewater has an initial fluoride concentration of 400ppm and a pH of 2.5.

[0069] This embodiment is performed using the following processing method: S1. Dissolution reaction: Mix the waste acid water from titanium dioxide with phosphate rock, controlling the liquid-to-solid ratio at 4m. 31 ton, stirring rate 250 r / min, temperature 45℃, reaction time 75 min; after reaction, the phosphorus content in the reaction solution is 10.5 g / L, filtered and the residue has a moisture content of 14%.

[0070] S2, Mixing stage: The high-fluoride wastewater does not need to be diluted. The reaction solution obtained in S1 is mixed with the high-fluoride wastewater at a volume ratio of 1:6. The mixture is stirred for 12 minutes. After mixing, the pH is 2.4.

[0071] S3. Defluoridation reaction: In the first stage, calcium hydroxide emulsion was added at a rate of 8 L / h, the pH was raised to 3.8, and the reaction was carried out for 20 min; in the second stage, the chemical was added at a rate of 4 L / h, the pH was raised to 5.0, and the fluoride concentration was reduced to 18 ppm; after aging for 30 min, the fluoride concentration was reduced to 8 ppm.

[0072] S4. Solid-liquid separation: The reaction solution after S3 reaction is subjected to plate and frame filter press at a pressure of 0.7 MPa. The fluoride concentration of the filtrate is 7.5 ppm, the moisture content of the filter cake is 18%, and the fluoride concentration of the rinsing water is 15 ppm.

[0073] In this embodiment: the defluorination efficiency is 98.1%, the digestion rate of titanium dioxide waste acid water is 92%, and the cost per ton of water treatment is 8.5 yuan (62% lower than that of the aluminum salt method).

[0074] Example 2 Raw material parameters: Sulfuric acid concentration of titanium dioxide wastewater is 45g / L; phosphate rock has a calcium fluorophosphate content of 86% and a P2O5 content of 29%, and is crushed to 80 mesh; high-fluoride wastewater has an initial fluoride concentration of 600ppm and a pH of 1.2.

[0075] The processing method in this embodiment is basically the same as that in embodiment 1, but the operations or parameters of each step are different as follows: S1, Dissolution reaction: Liquid-to-solid ratio 5m 3 1 ton, stirring rate 220 r / min, temperature 42℃, reaction time 80 min; in addition, 8 wt.% waste acid water was added and reacted for 15 min. The phosphorus content in the reaction solution after the reaction was 10.2 g / L. After filtration, the residue had a water content of 15%.

[0076] S2, Mixing stage: The high-fluoride wastewater needs to be diluted to a fluoride concentration of 400 ppm. After adding 1.5 wt.% phosphate rock residue, the pH of the high-fluoride wastewater rises to 1.7. Control the volume ratio of the reaction solution obtained in S1 to the high-fluoride wastewater to 1:5, stir for 15 min, and the pH after mixing is 1.75.

[0077] S3. Defluoridation reaction: In the first stage, calcium hydroxide emulsion was added at a rate of 10 L / h, the pH was raised to 3.6, and the reaction was carried out for 28 min. In the second stage, the chemical was added at a rate of 6 L / h, the pH was raised to 4.8, and the fluoride concentration was reduced to 16 ppm. After aging for 30 min, the fluoride concentration was reduced to 7 ppm.

[0078] S4. Solid-liquid separation: Plate and frame filter press pressure 0.65MPa, filtrate fluoride concentration 6.8ppm, filter cake moisture content 19%.

[0079] In this embodiment: the defluorination efficiency is 98.9%, the digestion rate of titanium dioxide waste acid water is 91%, and the cost per ton of water treated is 9.2 yuan (55% lower than the lime method).

[0080] Example 3 Raw material parameters: Sulfuric acid concentration of titanium dioxide wastewater is 50g / L; phosphate rock has a calcium fluorophosphate content of 90% and a P2O5 content of 32%, and is crushed to 100 mesh; high-fluoride wastewater has an initial fluoride concentration of 150ppm and a pH of 3.5.

[0081] The processing method in this embodiment is basically the same as that in embodiment 1, but the operations or parameters of each step are different as follows: S1, Dissolution reaction: Liquid-to-solid ratio 4.5m 3 1 ton, stirring rate 280 r / min, temperature 48℃, reaction time 70 min; after reaction, the phosphorus content in the reaction solution was 10.3 g / L, and the residue obtained after filtration had a moisture content of 13%.

[0082] S2, Mixing stage: Waste acid water needs to be added to the high-fluoride wastewater to bring the pH to 2.5; control the volume ratio of the reaction solution obtained in S1 to the high-fluoride wastewater to 1:10, stir for 13 minutes, and the pH after mixing is 2.6.

[0083] S3. Defluoridation reaction: In the first stage, calcium hydroxide emulsion was added at a rate of 6 L / h, the pH was raised to 3.7, and the reaction was carried out for 20 min; in the second stage, the chemical was added at a rate of 3 L / h, the pH was raised to 5.2, and the fluoride concentration was reduced to 12 ppm; after aging for 22 min, the fluoride concentration was reduced to 6 ppm.

[0084] S4. Solid-liquid separation: Plate and frame filter press pressure 0.7MPa, filtrate fluoride concentration 5.8ppm, filter cake moisture content 17%.

[0085] In this embodiment: the defluorination efficiency is 96.1%, the digestion rate of titanium dioxide waste acid water is 93%, and the cost per ton of water is 7.8 yuan (65% lower than the aluminum salt method).

[0086] Example 4 A comprehensive processing apparatus for performing the above embodiments is shown in the schematic diagram below. Figure 1 As shown, it specifically includes the following process units and equipment components: (1) Raw material storage and pretreatment unit Titanium dioxide waste acid water storage tank: The core function is to store titanium dioxide waste acid water. It is equipped with an online concentration monitor and a transfer pump. If the waste acid concentration is less than 40g / L, it must be filtered through a plate and frame filter to remove suspended solids before being sent to the storage tank. The storage tank volume is designed according to the daily processing capacity and is usually equipped with a stirring device to prevent ferrous sulfate from settling.

[0087] Phosphate ore crushing device: includes a jaw crusher, ball mill and screening module; crushes the raw phosphate ore to 80~100 mesh, and unqualified coarse particles after screening are returned to the ball mill for re-crushing; at the same time, it receives the phosphate ore residue from the filtration device and the calcium fluorophosphate filter cake from the filter cake collection device, mixes them and crushes them again to realize the recycling of phosphate ore.

[0088] (2) Dissolution reaction and separation unit Dissolution reactor: A sealed container equipped with jacketed heating and mechanical stirring. On the one hand, it is used to receive waste acid water from the titanium dioxide waste liquid storage tank and phosphate rock from the phosphate rock crushing device and react them; on the other hand, it is used to receive circulating water from the rinsing water circulation tank to reduce the consumption of fresh water.

[0089] Filtration device: A plate and frame filter press is used with a filter cloth pore size of 0.1μm~0.2μm to separate the slurry after dissolution reaction, and obtain phosphate rock residue (returned to the phosphate rock crushing device) and acidic reaction liquid (sent to the acidic reaction liquid transfer tank).

[0090] (3) Wastewater conditioning and mixing unit High-fluoride wastewater equalization tank: It is divided into a bar screen filtration zone, a fluoride concentration equalization zone, and a pH equalization zone. The bar screen filtration zone is used to remove large impurities from the wastewater. The fluoride concentration equalization zone adds qualified effluent from the clean water storage tank and can optionally dilute the high-fluoride wastewater. The pH equalization zone adds one or more of titanium dioxide waste acid water, phosphate rock residue, and calcium hydroxide emulsion to stabilize the pH reaction. The high-fluoride wastewater equalization tank is equipped with a pH meter, a fluoride ion concentration meter, and a stirring device.

[0091] Acidic reaction solution transfer tank: Temporarily stores the acidic reaction solution output from the filtration device. Equipped with a level sensor and a metering pump, it delivers the reaction solution according to the wastewater volume and fluoride concentration in the mixing reaction tank at a preset volume ratio, avoiding fluctuations in the mixing ratio that could affect the defluorination effect.

[0092] (4) Defluorination reaction and aging unit Mixing reaction tank: It receives pretreated wastewater from the high-fluoride wastewater equalization tank and acidic reaction liquid from the acidic reaction liquid transfer tank, and is equipped with a stirring component to achieve uniform mixing; at the same time, emulsion is added from the calcium hydroxide emulsion storage tank through a metering pump; the tank is equipped with an online pH monitoring and automatic dosing system to ensure stable reaction conditions.

[0093] Maturation tank: A container equipped with a low-speed stirring component is used to fully mature the slurry output from the mixing reaction tank and promote the precipitation and growth of calcium fluorophosphate.

[0094] (5) Solid-liquid separation and circulation unit Filter press unit: The core equipment for solid-liquid separation, using a plate and frame filter press; used to separate the slurry from the maturation tank into filtrate (sent to a clean water storage tank) and calcium fluorophosphate filter cake (sent to a filter cake collection device); after filtration, the filter cloth is rinsed with clean water, and the rinsing water is collected in a rinsing water circulation tank; the equipment is equipped with an automatic plate pulling and filter cake unloading device, suitable for continuous industrial production.

[0095] Clear water storage tank: Used to store the qualified filtrate output from the filter press. The filtrate can be directly discharged or reused (such as as dilution water in the high-fluoride wastewater equalization tank or workshop flushing water). The storage tank is equipped with a liquid level control and water quality monitoring module. If the fluoride concentration of the filtrate occasionally exceeds the standard, it will be returned to the mixing reaction tank for reprocessing.

[0096] Filter cake collection device: used to temporarily store calcium fluorophosphate filter cake, which is periodically transported to the phosphate rock crushing device, mixed with fresh phosphate rock, and then re-participated in the dissolution reaction to realize the recycling of phosphorus resources; the device is equipped with a weighing module to record the amount of filter cake reused, which facilitates the optimization of process parameters.

[0097] Rinse water circulation tank: collects the filter cloth rinsing water from the filter press and returns it to the dissolution reactor through pipeline to participate in the dissolution reaction again, reducing the consumption of fresh water; the tank is equipped with a water quality monitor, and if the suspended solids content of the rinsing water is too high, it will be pre-treated and filtered before reuse.

[0098] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for treating high-fluoride wastewater, characterized in that, Includes the following steps: (1) The waste acid solution from the sulfuric acid process for producing titanium dioxide is mixed with phosphate rock to obtain a high-phosphorus reaction solution; (2) Detect the fluoride concentration and pH value of the high-fluoride wastewater feed liquid, adjust it to obtain high-fluoride wastewater with fluoride concentration ≤500ppm and pH ≤3.0, and then mix the high-fluoride wastewater and the high-phosphorus reaction liquid to obtain a mixture; (3) Adjust the pH of the mixture to 3.5~4.0 and carry out the first defluorination reaction; then adjust the pH to 4.5~5.5 and carry out the second defluorination reaction; stop the reaction when the fluoride concentration of the reaction solution is <20ppm, stir and mature, and then separate the solid and liquid to obtain the defluorinated liquid and the calcium fluorophosphate solid phase.

2. The method for treating high-fluoride wastewater according to claim 1, characterized in that, The liquid-to-solid ratio of the waste acid solution to the phosphate rock in step (1) is 3.5~6:1, in m³. 3 / t; And / or, the temperature of the mixing reaction in step (1) is 40℃~50℃ and the duration is 60min~90min.

3. The method for treating high-fluoride wastewater according to claim 1, characterized in that, The sulfuric acid concentration of the waste acid solution from the sulfuric acid process for producing titanium dioxide is 40 g / L to 80 g / L. And / or, the pH of the high-phosphorus reaction solution is 1.8~2.2, and the phosphorus content is ≥10g / L.

4. The method for treating high-fluoride wastewater according to claim 1, characterized in that, The adjustment of the high-fluoride wastewater feed liquid in step (2) includes at least one of the following features: (a) When the initial fluoride concentration is >500 ppm, dilute with water to a fluoride concentration of 300 ppm to 500 ppm; (b) When pH > 3, add the waste acid solution from the sulfuric acid process for titanium dioxide production until the pH is 2-3; (c) When pH < 2, add the phosphate rock and stir to react, and the amount of phosphate rock added is 1 wt.% to 2 wt.%; preferably, if pH < 2 after adding the phosphate rock, add calcium hydroxide emulsion until pH is 2 to 3.

5. The method for treating high-fluoride wastewater according to claim 1, characterized in that, In step (2): when the fluoride concentration of the high-fluoride wastewater is 200ppm~500ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:5~8; When the fluoride concentration of the high-fluoride wastewater is <200ppm, the volume ratio of the high-phosphorus reaction solution to the high-fluoride wastewater is 1:9~12.

6. The method for treating high-fluoride wastewater according to claim 1, characterized in that, The first defluorination reaction in step (3) includes: The pH adjuster is added at a rate of 5 L / h to 10 L / h, and the mixture is stirred and reacted for 15 min to 25 min. Preferably, when the pH of the reaction solution is less than 1.8 after the addition time is over, the pH adjuster is added at a rate of 8 L / h to 12 L / h until the pH of the reaction solution is 3.5 to 4.

0.

7. The method for treating high-fluoride wastewater according to claim 1, characterized in that, The second defluorination reaction in step (3) includes: The pH adjuster is added at a rate of 3 L / h to 7 L / h to obtain a reaction system with a pH of 4.5 to 5.

5. The fluorine concentration is sampled every 5 minutes, and the addition is stopped when the fluorine concentration is <20 ppm.

8. A method for treating wastewater from the sulfuric acid process for producing titanium dioxide, characterized in that, This includes the method for treating high-fluoride wastewater as described in any one of claims 1 to 7.

9. A wastewater treatment device, characterized in that, Used for the treatment of high-fluoride wastewater as described in any one of claims 1 to 7, or the wastewater treatment method for titanium dioxide production by the sulfuric acid process as described in claim 8; The wastewater treatment device includes a titanium dioxide wastewater storage tank, a dissolving reaction vessel, a filtration device, an acidic reaction liquid transfer tank, a mixing reaction tank, a maturation tank, and a pressure filter connected in sequence. The wastewater treatment device further includes: a high-fluoride wastewater conditioning tank and a calcium hydroxide emulsion storage tank, which are respectively connected to the mixing reaction tank; The wastewater treatment device further includes a phosphate rock crushing device, which is connected to the solid discharge port of the filter press, the solid discharge port of the filter, and the feed port of the dissolution reactor.

10. The wastewater treatment apparatus according to claim 9, characterized in that, The wastewater treatment device further includes: a clean water storage tank, a filter cake collection device, and a flushing water circulation tank, all connected to the filter press device. Preferably, the rinsing water circulation tank is connected to the dissolution reaction vessel.

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