Recycling treatment method and system for industrial wastewater containing fluorine and heavy metal ions

Abstract

The invention belongs to the field of pickling wastewater treatment in the iron and steel industry, and discloses a method and a system for resourceful treatment of industrial wastewater containing fluorine and heavy metal ions. The method comprises the following steps: converting heavy metal ions and fluorine ions in wastewater into hydroxide and fluorine-containing complex co-precipitation by using sodium hydroxide, separating the hydroxide and fluorine-containing complex co-precipitation from a water phase, and converting the heavy metal fluorine-containing complex in the co-precipitation into water-insoluble heavy metal hydroxide and water-soluble sodium fluoride by using sodium hydroxide; sodium fluoride in the water is converted into calcium fluoride precipitate and water-soluble sodium hydroxide by using calcium hydroxide, the obtained NaOH aqueous solution is reused as a part of the sodium hydroxide in the previous step, a small amount of residual heavy metal ions and fluorine ions in the wastewater are completely precipitated by using calcium hydroxide, and the generated wastewater enters a biochemical system for denitration treatment. The method greatly reduces the consumption of sodium hydroxide and the output of solid hazardous wastes, relieves the burden of biochemical treatment, and reduces the cost of whole wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the technical field of pickling wastewater treatment in the steel industry, and in particular relates to a method and system for resource treatment of industrial wastewater containing fluorine and heavy metal ions. Background Art

[0002] In stainless steel manufacturing, in order to remove the scale on the surface of steel after annealing, a mixed acid composed of nitric acid and hydrofluoric acid is generally used for surface cleaning. This process is called pickling or acid leaching. Because of its good cleaning effect, it has been widely used at home and abroad. This mixed acid (pickling solution) used for cleaning can be used repeatedly. After the pickling effect decreases, the pickling solution is treated as pickling wastewater and discharged. At present, the most commonly used method in China is to use lime milk as a neutralizing precipitant to treat stainless steel wastewater under strong alkaline conditions. This is mainly because lime is widely available, the cost of lime milk is very cheap, and it has a good precipitation and removal effect on heavy metal ions such as chromium and fluoride ions in waste acid water. This process is stable, the water quality can be stably up to standard, and the operation control is simple. However, in the daily operation of wastewater stations of various enterprises, in order to ensure that the effluent meets the standard, lime milk is often added in excess, resulting in a large increase in the amount of sludge residue (more than 1.5 times the theoretical amount). Since this sludge residue is a solid hazardous waste, it is difficult to recycle and treat it, resulting in high subsequent disposal costs. Chinese patent CN200710067749.8 discloses a method of using sodium hydroxide instead of lime as a neutralizing precipitant. First, sodium hydroxide is added to the wastewater to adjust the pH value to 9.0-9.5. After heavy metal elements are precipitated, lime and other agents are added to remove a large amount of fluoride ions in the water. This method can, to a certain extent, play a role in the quality reduction of sludge residue compared with the lime treatment process, so that the generated heavy metal sludge and calcium fluoride are collected and treated separately, and the generated heavy metal sludge has the conditions for recycling. However, this method also has certain disadvantages, namely: the cost of the NaOH agent used is much more expensive than the price of lime, and the amount added is also relatively large, resulting in the comprehensive cost of the final wastewater treatment being higher than the process cost of using lime neutralizing precipitant; in addition, the large amount of NaOH added will lead to excessive salt (Na+ salt) content in the effluent after physical and chemical treatment, affecting the activity of microorganisms, thereby increasing the difficulty of removing NO3- ions in the effluent by subsequent biochemical treatment. Chinese patent CN200910101868.X discloses a method, firstly adding lime milk to adjust the pH value of wastewater to 5-6, then adding liquid alkali to adjust the pH value to 9.0-9.5, forming heavy metal hydroxide precipitation to remove heavy metal ions in wastewater, and then adding hydrochloric acid, polyaluminium chloride and lime milk to precipitate and remove fluoride ions under the condition of pH=8-9. Finally, the wastewater is adjusted to neutral by adding hydrochloric acid and then enters the biochemical system for NO3- removal treatment and then discharged. The main disadvantage of this method is that although a large amount of heavy metal ions can be precipitated in the form of hydroxides under the condition of pH=5-6 by adding lime milk first, it will also be accompanied by the generation of a certain amount of calcium fluoride precipitation. At this time, the wastewater still contains a certain amount of unprecipitated heavy metal ions and calcium ions and fluoride ions generated by partial dissolution of calcium fluoride; after further adding liquid alkali to adjust the pH value to 9.0-9.5, while generating heavy metal hydroxide precipitation, the dissolved calcium ions and fluoride ions are inevitably precipitated in the form of calcium fluoride.Therefore, the precipitation products of the above two-stage precipitation process are a mixture of heavy metal hydroxides and calcium fluoride, which are actually still hazardous solid wastes. These fluorine-containing and heavy metal-containing mixed sludge residues are difficult to process and recycle. Chinese patent CN201711277304.2 discloses a method in which NaOH is added to the primary and secondary neutralization tanks to adjust the waste acid water to pH = 5-6 and pH to 7.5-8.5, respectively, so as to better control the pH value, and then an ultrafine separator is used to separate the solid and liquid to obtain heavy metal sludge, and the separation liquid uses CaCl2, PAC, and PAM to remove fluorine. The purpose of this method is to achieve the separation and recycling of pure metal sludge and calcium fluoride sludge, and to achieve zero discharge of hazardous solid waste. However, when conducting a verification experiment according to the method described in Chinese patent CN201711277304.2, it was found that when the mixed acid was adjusted to pH 5-8.5 with NaOH, colloidal precipitates such as Fe(OH)3 and Cr(OH)3 were easily generated, and it was difficult to achieve solid-liquid separation using general methods (in Chinese patent CN201711277304.2, it was achieved by using an ultrafine separator), and the colloidal precipitate contained a large amount of fluoride ions that could not be removed by washing with water. These fluoride ions were mainly in the form of fluorine-containing complexes of heavy metal ions (for example, Na3FeF6, Na3CrF6) that were encapsulated and adsorbed in the heavy metal hydroxide colloidal precipitate, which actually made it impossible to obtain relatively pure heavy metal sludge residue. In addition, all the alkali used in the neutralization precipitation is NaOH, which has the disadvantages of high reagent cost due to the large amount of NaOH used and increased difficulty in biochemical treatment of the final process wastewater due to the high Na salt content. CaCl2 is used for fluoride removal, but the cost of CaCl2 is more than twice that of calcium hydroxide, which further increases the cost of fluoride removal reagents, and a large amount of chloride ions will be introduced into the water, which will increase the burden of removing NO3- on the final biochemical system.

[0003] In view of the above analysis, the technical problems that need to be solved urgently in the prior art are:

[0004] (1) In the prior art, Ca(OH)2 is directly used to neutralize and precipitate wastewater under strong alkaline conditions. In order to ensure the treatment effect, excessive Ca(OH)2 needs to be added to remove heavy metal ions and fluoride ions in the wastewater. However, the amount of solid residue formed far exceeds the theoretical amount, and the solid residue is a mixture of heavy metal hydroxides and fluorides, calcium hydroxide and calcium fluoride, which is a solid hazardous waste that is difficult to further treat.

[0005] (2) In the existing patents, NaOH is directly used to neutralize and precipitate the wastewater under the condition of pH = 9.0-9.5 to remove heavy metal ions, and then Ca(OH)2 is used to remove fluoride ions in the wastewater. Although the amount of solid waste residue generated is reduced, the amount of NaOH used is too large, and the price of NaOH is significantly higher than that of Ca(OH)2, resulting in too high a cost of treatment agents. In addition, the large amount of NaOH added results in an excessively high Na+ (salt) content in the separated liquid after solid-liquid separation, which significantly increases the burden and difficulty of further biochemical denitrification (NO3-) treatment of the wastewater.

[0006] (3) In the existing patents, Ca(OH)2 is first added to adjust the pH value of the wastewater to pH = 5.0-6.0, and then NaOH is added to adjust the pH value of the wastewater to pH = 9.0-9.5, so as to precipitate the heavy metal ions and fluoride ions in the wastewater in stages, and then Ca(OH)2 is added to remove the fluoride ions. Although the amount of NaOH used and the amount of solid slag generated are reduced, the solid slag formed in the two stages is a mixture of heavy metal hydroxides and calcium fluoride, which is a solid hazardous waste that is difficult to further treat.

[0007] (4) In the existing patents, NaOH is first used to adjust the wastewater pH to pH = 8.5 to remove heavy metal ions, and then CaCl2 is used to remove fluoride ions. On the one hand, the heavy metal hydroxide precipitate obtained contains heavy metal fluorine-containing complexes (Na3FeF6, Na3CrF6, etc.) that are difficult to remove by washing, so solid hazardous waste is actually still formed; on the other hand, the price of CaCl2 as a fluorine precipitation agent is significantly higher than that of Ca(OH)2, and the amount of NaOH used to adjust the pH is still large, which increases the cost of wastewater treatment agents, and the Cl- and Na+ contents in the final process wastewater are very high, which increases the burden of further biochemical treatment.

[0008] In summary, the existing technologies and patents for treating acidic wastewater containing heavy metal ions and fluoride ions all have at least one of the following deficiencies, for example, the amount of waste residue formed after treatment is large, the waste residue is a mixture of heavy metal hydroxides and calcium fluoride and becomes solid hazardous waste, the price of NaOH used to neutralize the acidity of the wastewater is high and the amount used is too large, the price of CaCl2 used to precipitate fluoride ions is relatively high, and the salt (Na+ and Cl-) content in the wastewater after removing heavy metal ions and fluoride ions is too high, which increases the burden and difficulty of further biochemical treatment. Summary of the invention

[0009] In view of the problems existing in the prior art, the present invention provides a method and system for resource treatment of industrial wastewater containing fluorine and heavy metal ions.

[0010] The present invention is achieved by a method for resource treatment of industrial wastewater containing fluorine and heavy metal ions, the method specifically comprising:

[0011] S1: In the primary neutralization sedimentation tank, NaOH is added to the industrial wastewater containing fluoride ions and heavy metal ions, the pH is adjusted to pH = 5.3-5.8, the reaction is stirred for 15-30 minutes, and the obtained precipitate is subjected to solid-liquid separation;

[0012] S2: adding clean water to the solid residue obtained in step S1 at a ratio of solid residue dry weight to water weight = 1:1-1:10 to make a slurry, then adding NaOH to adjust the pH of the slurry to pH = 10-11, stirring the reaction for 3-5 hours, and then performing solid-liquid separation;

[0013] S3: Add lime Ca(OH)2 to the separated liquid obtained in step S2, stir and react for 15-30 minutes, and then separate the solid and liquid. The obtained solid is CaF2 containing only a small amount of incompletely reacted Ca(OH)2 (<1Wt%). The obtained separated liquid is NaOH solution, which is reused in step S1 or step S2 as part of the alkali used to adjust the pH.

[0014] S4: washing the solid residue obtained in step S2 with clean water at least twice and performing solid-liquid separation, the obtained heavy metal (mainly Cr, Fe, etc.) hydroxide mixture has a low impurity content, and the separated liquid after washing the solid residue contains a certain amount of NaOH. The separated liquid after the first washing of the solid residue is recycled into the primary neutralization sedimentation tank, and the separated liquid after the second and multiple washings of the solid residue is recycled into the secondary neutralization sedimentation tank, all of which are used as part of the alkali used to adjust the pH;

[0015] S5: The separated liquid obtained in step S1 and the separated liquid after the second and multiple washing of the solid residue in step S4 are introduced into a secondary neutralization sedimentation tank, and Ca(OH)2 is added thereto to adjust the pH to pH=9.0-9.5, and 0.02‰ of flocculant and 2‰ of coagulant calculated by the mass of the separated liquid are added, and the reaction is stirred for 15-30 minutes, and then solid-liquid separation is performed to obtain lime slag mainly containing Ca(OH)2 and a small amount of CaF2. The separated liquid is adjusted to pH=7-9 with hydrochloric acid and then introduced into the biochemical system for denitrification (NO3 - )deal with.

[0016] Furthermore, in said S4, the solid residue is washed with clean water, and the pH of the solid-liquid separation liquid after the first washing of the solid residue is ≥10, and the pH of the solid-liquid separation liquid after the second or multiple washings of the solid residue is 7.0-9.0.

[0017] Furthermore, the specific amount of clean water used in the second or multiple washings of the solid slag or the specific pH control value of the separation liquid after washing the solid slag is based on the fact that the fluorine and sodium impurities in the final solid slag after washing are completely removed, that is, here it means that the final heavy metal hydroxide slag can meet the requirements for the minimum impurity limit in the slag for resource recycling.

[0018] Furthermore, the weight ratio of the amount of Ca(OH)2 added to S3 to the fluorine contained in the separated liquid is generally 1:1.0 to 1:3.0, so that the F in the separated liquid obtained by solid-liquid separation after the reaction is - The ion content is preferably less than 200 mg / L. The coagulant is one or more of polyaluminium ferric chloride, polyferric chloride, polyferric sulfate and polyaluminium chloride. The flocculant is polyacrylamide (PAM).

[0019] Furthermore, if the fluorine- and heavy metal ion-containing industrial wastewater contains hexavalent chromium (Cr 6+ ), you need to add a small amount of reducing agent (such as zero-valent iron powder, ferrous sulfate, etc.) to reduce hexavalent chromium to trivalent chromium.

[0020] Another object of the present invention is to provide a resource treatment system for industrial wastewater containing fluorine and heavy metal ions, the system specifically comprising:

[0021] The precipitation and separation module is used to precipitate and separate heavy metal ions and fluoride ions in wastewater;

[0022] The impurity removal and purification module is used to treat the mixture of heavy metal hydroxide and its fluorine-containing complex to achieve impurity removal and purification of heavy metal hydroxide;

[0023] Complete precipitation module, used to completely precipitate the small amount of heavy metal ions and fluoride ions remaining in the wastewater with calcium hydroxide;

[0024] The denitrification treatment module is used to send the generated wastewater into the biochemical system for denitrification (NO3 - )deal with.

[0025] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0026] First, the present invention can precipitate more than 90% of heavy metal (chromium, iron, etc.) ions in wastewater mainly in the form of heavy metal hydroxides and their fluorine-containing complexes (Na3FeF6, Na3CrF6) by adding sodium hydroxide under the condition of pH=5.3-5.8. Compared with the process of precipitating all heavy metal ions in wastewater with NaOH under the condition of pH>9.0, the consumption and cost of NaOH reagent are effectively reduced.

[0027] The invention treats the obtained heavy metal hydroxide and its fluorine-containing complex precipitate with NaOH under the condition of pH=10-11, converts the fluorine ions in the precipitate into water-soluble sodium fluoride, thereby obtaining the heavy metal hydroxide with high purity that can be recycled as a resource.

[0028] The present invention adds Ca(OH)2 to the obtained NaF solution to convert it into calcium fluoride with high purity that can be recycled and NaOH solution that can be recycled, thereby greatly reducing the usage amount of NaOH and the cost of reagents in the entire wastewater treatment process.

[0029] The present invention converts the remaining small amount of heavy metal ions and fluoride ions in the wastewater from which most of the heavy metal ions and fluoride ions have been removed into lime slag (mainly containing Ca(OH)2, CaF2 and heavy metal hydroxides) by adding Ca(OH)2, thereby significantly reducing the generation of solid hazardous waste and the salt content in the wastewater that eventually enters the biochemical treatment system.

[0030] The invention significantly reduces the amount of NaOH added when treating wastewater, greatly reduces the amount of solid hazardous waste generated, effectively reduces the load of biochemical treatment of wastewater, and realizes resource treatment of wastewater at a relatively low cost.

[0031] Second, the economic benefits of industrializing the treatment of chromium-containing industrial sludge

[0032] The present invention aims at the treatment demand of chromium-containing industrial sludge, optimizes the wastewater treatment process of the stainless steel industry, and realizes the resource utilization of sludge. In the annual 500,000 tons of stainless steel wastewater treatment project, through the technical transformation of the present invention, the sludge volume is reduced to 8706.08 tons / year, of which 4880.84 tons of sludge can be recycled, and the total treatment cost is reduced from 20.6272 million yuan of traditional technology to 17.788 million yuan, saving 2.8392 million yuan for the waste-producing unit every year. Charging a technical service fee of 10% of the saved cost can achieve an annual net profit of 283,900 yuan, while promoting the industrialization of supporting services for waste disposal projects.

[0033] The present invention realizes the resource utilization of sludge in ceramic pigments and coating pigments, greatly reduces the purchase of traditional raw materials (such as iron oxide red and chromium oxide green), and significantly reduces production costs. Taking black pigment per ton as an example, the traditional process cost is 4,940 yuan, while through the technology of the present invention, the production cost can be reduced to 2,760 yuan, saving 44.12% of the cost per ton, while solving the problem of harmless treatment of sludge, providing a more competitive solution for pigment production companies.

[0034] The high-fluorine sludge produced by traditional treatment processes causes serious corrosion to ceramic kilns and related equipment, with annual maintenance costs as high as 40 million yuan. The technology of the present invention reduces the fluorine content in the sludge to less than 3%, significantly reducing the corrosion of kiln bricks, smoke exhaust pipes and waste heat boilers, thereby extending the equipment maintenance cycle from 3 months to about 2 years, reducing equipment maintenance costs to a normal range, significantly reducing production costs and increasing equipment life, and solving the technical bottleneck of high-fluorine sludge being difficult to apply to production.

[0035] Thirdly, the prior art CN 117964162 A discloses a method for treating low-concentration fluoride-containing wastewater. Through multiple water washes, the fluoride content in the precipitate residue can be effectively removed (dry basis F < 5%). However, for high-concentration fluoride-containing wastewater (F > 5000 mg / L), the fluoride content in the generated precipitate residue increases significantly (15% < F < 30%), and the effect of water wash treatment is limited, unable to effectively reduce the fluoride content in the residue. The high-fluoride precipitate residue has special physical and chemical properties during the treatment process, especially showing significant corrosiveness under high-temperature conditions, which may cause serious damage to high-temperature kiln bricks and flue gas pipelines. This corrosiveness limits the applicability of existing high-temperature treatment technologies and also poses higher requirements for the safe treatment of high-fluoride materials. The resource utilization of high-fluoride precipitate residue is an important research direction in the field of wastewater treatment. However, the high fluoride content not only affects the processability of the material but also may lead to equipment loss and environmental risks, becoming the main obstacle in the process of resource utilization. Therefore, the prior art lacks an effective treatment method for high-fluoride materials. With the increasing concentration of fluoride in industrial wastewater, the existing low-concentration wastewater treatment technologies are difficult to meet the requirements. Especially when treating high-concentration fluoride-containing wastewater, the high fluoride content in the residue poses a threat to the safety of treatment equipment and subsequent processes. There is an urgent need for an innovative treatment method for high-fluoride precipitate residue to effectively control its fluoride content.

[0036] To address the above challenges, it is urgent to develop a treatment technology specifically for high-fluoride materials. This technology should be able to reduce the fluoride content of the material while reducing its corrosiveness and ensuring the safety and sustainability of the subsequent resource utilization process. This will provide reliable technical support for the treatment and resource utilization of high-concentration fluoride-containing wastewater and promote the development of the wastewater treatment field. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flowchart of the resource treatment method for industrial wastewater containing fluoride and heavy metal ions provided by an embodiment of the present invention;

[0038] Figure 2 is a basic process route diagram provided by an embodiment of the present invention;

[0039] Figure 3 is a module diagram of the resource treatment system for industrial wastewater containing fluoride and heavy metal ions provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Such as Figure 1 、 Figure 2 As shown, an embodiment of the present invention provides a method for resource treatment of industrial wastewater containing fluorine and heavy metal ions, the method specifically comprising:

[0042] S1: In the primary neutralization sedimentation tank, NaOH is added to the industrial wastewater containing fluoride ions and heavy metal ions, the pH is adjusted to pH = 5.3-5.8, the reaction is stirred for 15-30 minutes, and the obtained precipitate is subjected to solid-liquid separation;

[0043] S2: adding clean water to the solid residue obtained in step S1 at a ratio of solid residue dry weight to water weight = 1:1-1:10 to make a slurry, then adding NaOH to adjust the pH of the slurry to pH = 10-11, stirring the reaction for 3-5 hours, and then performing solid-liquid separation;

[0044] S3: Add lime Ca(OH)2 to the separated liquid obtained in step S2, stir and react for 15-30 minutes, and then separate the solid and liquid. The obtained solid is CaF2 containing only a small amount of incompletely reacted Ca(OH)2 (<1Wt%), which can be widely used in cement, ceramics, glass, steel and other industries. The obtained separated liquid is NaOH solution, which is reused in step S1 or step S2 as part of the alkali used to adjust the pH;

[0045] S4: washing the solid residue obtained in step S2 with clean water at least twice and performing solid-liquid separation. The obtained heavy metal (mainly Cr, Fe, etc.) hydroxide mixture has a low impurity content (F content <2.0Wt%, Na <1.0Wt%) and can be used as a raw material for ceramic glaze and metal smelting. The separated liquid after washing the solid residue contains a certain amount of NaOH. The separated liquid after the first washing of the solid residue is recycled into the primary neutralization sedimentation tank, and the separated liquid after the second and multiple washings of the solid residue is recycled into the secondary neutralization sedimentation tank, all of which are used as part of the alkali used to adjust the pH;

[0046] S5: The separated liquid obtained in step S1 and the separated liquid after the second and multiple washing of the solid residue in step S4 are introduced into a secondary neutralization sedimentation tank, and Ca(OH)2 is added thereto to adjust the pH to pH=9.0-9.5, and 0.02‰ of flocculant and 2‰ of coagulant calculated by the mass of the separated liquid are added, and the reaction is stirred for 15-30 minutes, and then solid-liquid separation is performed to obtain lime slag mainly containing Ca(OH)2 and a small amount of CaF2. The separated liquid is adjusted to pH=7-9 with hydrochloric acid and then introduced into the biochemical system for denitrification (NO3 - )deal with.

[0047] Working principle of resource recovery treatment method for industrial wastewater containing fluoride and heavy metal ions.

[0048] 1. Primary neutralization precipitation: initial precipitation and separation

[0049] In the primary neutralization sedimentation tank, sodium hydroxide (NaOH) is added to the industrial wastewater containing fluoride ions and heavy metal ions to adjust the pH of the wastewater to 5.3-5.8. This pH range is the pH range for heavy metal ions (such as Cr 3 +, Fe 3 +) to form the best conditions for hydroxide precipitation. Stir for 15-30 minutes to ensure complete reaction and separate heavy metals and fluoride ions in wastewater in the form of precipitation. Solid-liquid separation is used to obtain solid residue and preliminarily treated separated liquid. The solid residue contains fluoride and heavy metal hydroxide and enters the subsequent treatment step.

[0050] 2. Solid slag purification: secondary slurry preparation and deep separation

[0051] After adding water to the solid slag obtained in step S1 to make a slurry, the pH of the slurry is adjusted to 10-11 with NaOH again. Under this alkaline condition, the impurities in the fluoride ions and heavy metal hydroxides are further released and form new precipitates, and the reaction is stirred for 3-5 hours to ensure complete reaction. Subsequently, solid-liquid separation is performed to obtain high-purity heavy metal hydroxides and a separated liquid containing fluoride. The heavy metal precipitate is further purified by subsequent washing, and its impurity content (such as fluorine and sodium) is greatly reduced, which can be used for ceramic glazes or metal smelting.

[0052] 3. Fluorine resource utilization: extraction and recycling of calcium fluoride

[0053] The separated liquid obtained in step S2 is further reacted by adding lime (Ca(OH)2) to promote the combination of fluoride ions and calcium ions to generate high-purity calcium fluoride (CaF2). The calcium fluoride precipitate is collected by solid-liquid separation, and its impurity content is low (the content of incompletely reacted Ca(OH)2 is <1%), and can be directly applied to the cement, ceramic, glass and steel industries as a resource product. The obtained separated liquid is a NaOH solution, which can be recycled and reused in step S1 or S2 as an alkali source for adjusting the pH value, thereby reducing the consumption of chemicals.

[0054] 4. Secondary neutralization and denitrification: final purification and safe discharge

[0055] The separated liquid after washing in step S1 and step S4 is introduced into a secondary neutralization sedimentation tank. The pH is adjusted to 9.0-9.5 by adding lime, and flocculants and coagulants are added to promote the precipitation of impurities, thereby generating lime slag mainly containing Ca(OH)2 and a small amount of CaF2. The lime slag is collected and processed after solid-liquid separation. The obtained separated liquid is adjusted to neutrality (pH 7-9) with hydrochloric acid to ensure that it meets the requirements of biochemical treatment, and then enters the biochemical system for denitrification treatment. The denitrification process removes residual nitrate (NO3 - ) is converted into nitrogen, achieving deep purification of nitrogen pollutants and ultimately achieving wastewater discharge that meets standards.

[0056] 5. System closed loop and resource utilization

[0057] This method minimizes fluoride ion and heavy metal pollution in wastewater through multi-stage precipitation, separation and resource utilization, and converts by-products (such as calcium fluoride and heavy metal hydroxides) into high-value-added industrial raw materials. The NaOH solution and clean water in the separation liquid are recycled and reused within the system, reducing the consumption of fresh chemicals and water resources, forming an environmentally friendly, efficient and economical closed-loop system for industrial wastewater resource treatment.

[0058] S1, using a relatively low amount of NaOH under relatively low pH conditions (5.3-5.8), precipitates and separates the precipitated heavy metal ions in the wastewater in the form of heavy metal hydroxides, and further purifies the obtained heavy metal hydroxides with NaOH to remove the fluoride ions carried therein. This is because in the wastewater containing heavy metal ions (mainly Fe 3+ and Cr 3+ ) and fluoride ion solution, the following series of reactions will occur after adding NaOH:

[0059] Fe 3+ +3OH - →Fe(OH)3↓

[0060] Cr 3+ +3OH - →Cr(OH)3↓

[0061] Fe 3+ +3F - +xFe(OH)3→FeF3·xFe(OH)3↓

[0062] Cr 3+ +3F - +yCr(OH)3→CrF3·yCr(OH)3↓

[0063] 3Na + +3F - +FeF3·xFe(OH)3→Na3FeF6·xFe(OH)3↓

[0064] 3Na + +3F - +CrF3·xCr(OH)3→Na3CrF6·xCr(OH)3↓

[0065] Therefore, the heavy metal hydroxide precipitate obtained after adding NaOH contains fluoride ions in the form of heavy metal fluorine-containing complexes. If not treated, the heavy metal hydroxide will become solid hazardous waste. After the heavy metal hydroxide containing fluoride ions is separated from the solid and liquid and washed, the solid residue is treated with NaOH under high alkalinity (pH = 10-11), and the following reaction will occur:

[0066] 3NaOH+Na3FeF6→6NaF+Fe(OH)3↓

[0067] 3NaOH+Na3CrF6→6NaF+Cr(OH)3↓

[0068] Since the generated NaF is soluble in water, the fluoride ions contained in the heavy metal hydroxide can be removed, thereby converting it from solid hazardous waste into valuable raw materials that can be recycled.

[0069] In S3, Ca(OH)2 is added to the separated liquid obtained by solid-liquid separation after treating the heavy metal hydroxide with NaOH, so as to convert the NaF dissolved in the separated liquid into NaOH and calcium fluoride. This is because after adding Ca(OH)2, the following reaction occurs between NaF and Ca(OH)2:

[0070] 2NaF+Ca(OH)2→2NaOH+CaF2↓

[0071] Since heavy metal hydroxides do not dissolve in a strong alkaline environment (pH = 10-11) when treated with NaOH, the resulting solid-liquid separation liquid contains only NaF and almost no heavy metal ions. Therefore, the CaF2 precipitate obtained by the above reaction has a high purity (does not contain heavy metal ions) and can be used as a resource. The liquid phase after separating the CaF2 precipitate contains only NaOH, which can be reused as an alkali solution to neutralize and adjust the pH value of the initial waste acid water stock solution. Therefore, the above-mentioned alkaline treatment and defluorination process of the heavy metal hydroxide does not increase the amount of NaOH used in the entire wastewater treatment process.

[0072] In the step S5, Ca(OH)2 is further added to the separated liquid obtained by adding NaOH to precipitate the heavy metal hydroxide, so that the heavy metal ions and fluoride ions remaining in the wastewater are completely precipitated by generating lime slag (mainly containing Ca(OH)2, heavy metal hydroxide, and calcium fluoride) under the condition of pH=9.0-9.5. Since more than 90% of the heavy metal ions and fluoride have been removed in the form of precipitation during the neutralization and precipitation with NaOH, the amount of the lime slag obtained when further treating the wastewater with Ca(OH)2 has been greatly reduced compared with the existing technical patents, and the Na salt content in the wastewater after the lime slag is separated is greatly reduced, so it can be conveniently further subjected to biochemical treatment.

[0073] The heavy metal hydroxides (without fluoride ions and sodium ions) and calcium fluoride (without heavy metal ions) obtained from the treatment of wastewater have high purity and can be recycled. For example, the former can be used as raw materials for ceramic glazes or steelmaking recycled materials, and the latter can be widely used as raw materials for the production of glass, ceramics and cement.

[0074] In said S4, the solid residue is washed with clean water, the pH of the solid-liquid separation liquid after the first washing of the solid residue is ≥10, and the pH of the solid-liquid separation liquid after the second or multiple washings of the solid residue is 7.0-9.0.

[0075] The specific amount of clean water used in the second or multiple washings of the solid slag or the specific pH control value of the separation liquid after washing the solid slag is based on the fact that the fluorine and sodium impurities in the final solid slag after washing are completely removed, that is, here it means that the final heavy metal hydroxide slag can meet the requirements for the minimum impurity limit in the slag for resource recycling.

[0076] The weight ratio of the amount of Ca(OH)2 added to S3 to the fluorine contained in the separated liquid is generally 1:1.0 to 1:3.0, so that the F in the separated liquid obtained by solid-liquid separation after the reaction is - The ion content is preferably less than 200 mg / L. The coagulant is one or more of polyaluminium ferric chloride, polyferric chloride, polyferric sulfate and polyaluminium chloride. The flocculant is polyacrylamide (PAM).

[0077] If the industrial wastewater containing fluorine and heavy metal ions (such as stainless steel mixed acid pickling wastewater) contains hexavalent chromium (Cr 6+ ), you need to add a small amount of reducing agent (such as zero-valent iron powder, ferrous sulfate, etc.) to reduce hexavalent chromium to trivalent chromium.

[0078] like Figure 3 As shown, an embodiment of the present invention provides a system for resource treatment of industrial wastewater containing fluorine and heavy metal ions, which specifically includes:

[0079] The precipitation and separation module is used to precipitate and separate heavy metal ions and fluoride ions in wastewater;

[0080] The impurity removal and purification module is used to treat the mixture of heavy metal hydroxide and its fluorine-containing complex to achieve impurity removal and purification of heavy metal hydroxide;

[0081] Complete precipitation module, used to completely precipitate the small amount of heavy metal ions and fluoride ions remaining in the wastewater with calcium hydroxide;

[0082] The denitrification treatment module is used to send the generated wastewater into the biochemical system for denitrification (NO3 - )deal with.

[0083] (1) Sedimentation and separation module: efficient removal of heavy metals and fluoride ions

[0084] This system uses a precipitation separation module and a chemical precipitation method to separate heavy metal ions and fluoride ions in wastewater in the form of precipitation. By adding an appropriate amount of precipitant (such as sodium hydroxide or lime milk), heavy metal ions in wastewater form hydroxide precipitates, and fluoride ions form insoluble fluoride precipitates. This module can effectively reduce the concentration of heavy metals and fluoride ions in wastewater, provide stable water quality conditions for subsequent treatment, and ensure the basis for treatment efficiency and resource utilization.

[0085] (2) Impurity removal and purification module: optimization of purification of heavy metal hydroxides

[0086] On the basis of precipitation separation, the impurity removal and purification module further refines the mixture of heavy metal hydroxides and their fluorine-containing complexes. Impurities in the mixture are removed by means of multi-stage filtration and chemical cleaning to obtain high-purity heavy metal hydroxides. The purified heavy metal precipitate can be used for subsequent resource utilization, such as the preparation of pigments or other industrial raw materials, while significantly reducing the amount of waste residue and improving economic benefits and environmental value.

[0087] (3) Complete precipitation and denitrification treatment module: achieving comprehensive purification

[0088] For the small amount of heavy metal ions and fluoride ions remaining in the wastewater, the complete precipitation module uses calcium hydroxide for further treatment to ensure that the residual pollutants in the wastewater are completely precipitated and the concentration of heavy metals and fluoride ions in the effluent is significantly reduced. Subsequently, the wastewater enters the denitrification treatment module, where the nitrate (NO3 - ) is converted into nitrogen or other harmless substances to further purify the effluent. This dual treatment mode ensures that wastewater discharge meets environmental protection standards and achieves harmless and resourceful treatment of industrial wastewater.

[0089] 1. Specific application fields or related products of the present invention.

[0090] The waste acid water used in each embodiment comes from a pickling wastewater sample containing heavy metal ions, hydrofluoric acid and nitric acid from a large stainless steel enterprise in Guangdong Province. The water quality is shown in Table 1.

[0091] Table 1: Water quality of pickling waste acid samples Unit (mg / L)

[0092]

[0093] *The sample is an average mixed sample taken from a stainless steel enterprise for 3 times

[0094] Example 1 (Comparative Example 1)

[0095] In the neutralization sedimentation tank, 59.4 kg of lime Ca(OH)2 was added to 2000 L of waste acid water under stirring conditions, and the pH of the slurry was measured to be 9.0, and then 1.8 kg of polyaluminium chloride and 0.02 kg of polyacrylamide (PAM) were added. The slurry was subjected to solid-liquid separation to obtain 114.8 kg of solid slag cake containing 50% water. 1.5 L of 6 mol / L hydrochloric acid was added to the obtained separated liquid to adjust the pH of the separated liquid to 7.0, and the components of the separated liquid and the solid slag were respectively detected. The test results are shown in Table 2:

[0096] Table 2

[0097]

[0098] Comparing the data in Table 2 and Table 1, it can be seen that after adding lime, heavy metal ions and fluoride ions in wastewater can be effectively removed, and the removal rates of Fe, Cr and F are 99.69%, 99.97% and 99.85% respectively; the obtained solid slag contains a large amount of heavy metal ions (Fe, Cr), Ca and F, and the solid slag yield is 0.0574kg 固渣 / L 废水 , this solid residue belongs to solid hazardous waste.

[0099] Example 2 (Comparative Example 2)

[0100] In the neutralization sedimentation tank, 41.36 kg of solid NaOH was added to 2000 L of waste acid water under stirring conditions, and the pH of the slurry was measured to be 9.5. Then 1.8 kg of polyaluminium chloride and 0.02 kg of polyacrylamide were added. The slurry was subjected to solid-liquid separation to obtain 30.17 kg of metal cake containing 50% water, and the solid and liquid components were detected. 32.37 kg of lime was added to the obtained 1980 kg separated liquid to remove F -, add 0.02kg of polyacrylamide while stirring, separate the slurry into solid and liquid, and obtain 47.6kg of calcium fluoride cake containing 50% water. Add 13L of 6mol / L hydrochloric acid to the separated liquid to adjust the pH of the separated liquid to 7.0. Detect the components of the separated liquid and the solid residue respectively. The test results are shown in Table 3:

[0101] Table 3

[0102]

[0103] Comparing the data in Table 3 with Table 2, it can be seen that adding NaOH to adjust the pH of the waste acid to 9.5 can basically remove the heavy metal ions in the wastewater, and can obtain metal slag with relatively low impurities of sodium and fluorine that can be utilized as a resource. The calcium fluoride slag obtained by removing the fluorine in the separation liquid with lime also has a low content of heavy metals and a high content of calcium fluoride, which has resource utilization value. Therefore, the advantage of using NaOH to neutralize the waste acid is that the generated sludge residue can be greatly separated and reduced in quantity. However, it can be seen from Table 3 that the Na 2+ introduced into the final effluent after solid-liquid separation of the wastewater treated with NaOH + Very high, which will remove NO3 from the subsequent biochemical system - The comparison of reagent and disposal costs between Example 2 and Example 1 is shown in Table 4 below:

[0104] Table 4

[0105]

[0106] As shown in Table 4, adding NaOH to treat waste acid water to neutralize acid and precipitate heavy metal ions requires a large amount of NaOH reagents, and since the unit cost of NaOH reagents is much higher than the unit cost of lime reagents, although adding NaOH can greatly reduce or even fully utilize the sludge residue, it also consumes and greatly increases the cost of NaOH reagents. The comprehensive cost may be slightly higher than the comprehensive cost of lime treatment process.

[0107] Example 3

[0108] Step 1

[0109] 2000L of waste acid water was introduced into the primary neutralization sedimentation tank, 34.36kg of solid NaOH was added, and the mixture was stirred and mixed evenly. The pH value of the waste acid water was measured to be 5.51. After 20 minutes of reaction, the reaction liquid was subjected to solid-liquid separation to obtain 26.9kg of mud cake containing 50% water. The test results are shown in Table 5 and Table 6.

[0110] Table 5

[0111]

[0112] The data in Table 5 are compared with those in Example 2. The addition of NaOH in the present invention reduces the amount of NaOH used because the pH of the waste acid water is only adjusted to 5.5. At the same time, more than 90% of the heavy metal ions (Fe, Cr) and more than 85% of the F can be removed at pH = 5.5. - It is separated from the wastewater in the form of precipitation, and the Na ions in the filtrate are greatly reduced.

[0113] Table 6

[0114]

[0115] From the data analysis of Table 6, by using the patented technology of the present invention, by adding NaOH under the condition of pH = 5.5, the precipitate obtained mainly contains Fe, Cr, F, and Na, among which the molar ratio of F / Na is about 2.5, while the molar ratio of F / Na in the known heavy metal fluorine-containing complex Na3MF6 (M = Fe, Cr, etc.) is 2.0, and the molar ratio of F / Na in the heavy metal fluoride MF3 (M = Fe, Cr, etc.) is 3.0. Therefore, the precipitate is composed of heavy metal hydroxides, fluorides and fluorine-containing complexes.

[0116] Step 2

[0117] In the alkali-washed slag stirring tank, first add 26.9 kg of mud cake (13.45 kg of dry slag) obtained after solid-liquid separation at pH = 5.5 in step 1 and 135 kg of water (tap water), and start stirring. Then add 1.3 kg of NaOH (solid), and the slurry pH is measured at 10.7. Continue stirring for 4.0 hours, perform solid-liquid separation on the slurry, and test the components of the obtained separation liquid (NaF liquid) and solid slag (primary alkali-washed slag). The results are shown in Table 7.

[0118] Table 7

[0119]

[0120] According to the data in Table 7 and the comparative analysis with the data in Table 5 and Table 6, after the slag is washed with alkali once, the ratio of Fe and Cr content in the solid slag does not change much, while the ratio of the sum of Fe and Cr content to Na content and F content increases significantly, and there are a large amount of F and Na and only a small amount of Fe and Cr in the separation liquid. This shows that after the slag is washed with alkali once, F and Na are well eluted from the solid slag and enter the eluent.

[0121] Step 3

[0122] 127.5 kg (NaF liquid) of the primary alkali-washed residue filtrate obtained in step 2 was added with 3.5 kg of lime Ca(OH)2 and stirred in a stirring tank (NaF replacement reaction tank) for 20 minutes, and solid-liquid separation was performed using a filtering device. The components of the separated liquid were detected as shown in Table 8. The separated liquid (NaOH alkali liquid) was added to the solid residue after primary alkali washing obtained in step 2, and the alkali-washed residue was washed for the second time in the alkali-washed residue stirring tank, and then solid-liquid separation was performed. The components of the solid residue after alkali washing (secondary alkali-washed residue) and the separated liquid were analyzed, and the results are shown in Table 9. 126 kg of the separated liquid (NaOH) was refluxed into the primary neutralization sedimentation tank to neutralize the waste acid.

[0123] Table 8

[0124]

[0125]

[0126] According to the data in Table 8 and the comparative analysis with the data in Table 7, after the second alkali washing of the slag with the recycled NaOH alkali solution, the obtained separated liquid contains a large amount of F - and Na + Therefore, the separation liquid is still essentially a NaF solution. The fluoride ions in the obtained solid slag (secondary alkali washing slag) are basically removed, and the sodium ion content is also greatly reduced to a lower value level (at this time, the sodium and fluoride in the solid slag mainly exist in the form of NaOH and NaF).

[0127] In a stirring tank, 7.2 kg of lime Ca(OH)2 was added to 151 kg of NaF solution obtained in step 3, and the mixture was stirred for 20 minutes to separate the solid and liquid. The separated liquid was sent to a primary neutralization sedimentation tank to neutralize the waste acid. The obtained separated liquid was subjected to component composition detection and analysis, and the results are shown in Table 9.

[0128] Table 9

[0129]

[0130] From the data analysis in Table 9, the separation liquid contains high concentration of Na ions, while F - , heavy metal ions, etc. The pH of the primary and secondary separation liquids (recycled alkali solution) were measured to be 12.7 and 13.6 respectively. Therefore, the above separation liquid is actually a NaOH solution, which can be added to the primary neutralization sedimentation tank as recycled alkali solution to neutralize the waste acid.

[0131] The solid slag obtained by adding lime Ca(OH)2 to the NaF solution in the above step 3 was analyzed for component composition. The results are shown in Table 10.

[0132] Table 10

[0133]

[0134]

[0135] From the data in Table 10, it can be seen that the solid slag mainly contains Ca and F, wherein the molar ratio of Ca / F is greater than the theoretical value of CaF2=0.5 in CaF2, indicating that the solid slag is mainly composed of CaF2 and Ca(OH)2.

[0136] The solid slag composed of CaF2 and Ca(OH)2 was further purified to remove impurities such as unreacted lime Ca(OH)2. 0.3L of 6mol / L dilute hydrochloric acid was added to 24.3kg of solid slag (water content 50%), and 25kg of water was added. After stirring evenly, the pH of the slurry was measured to be 7.9. The slurry was separated into solid and liquid, and the separated liquid entered the secondary neutralization sedimentation tank for treatment. The composition of the obtained solid slag was analyzed, and the results are shown in Table 11.

[0137] Table 11

[0138]

[0139] From the data in Table 11, it can be seen that the solid slag obtained after purification mainly contains Ca and F, and other impurities are very small, and the Ca / F molar ratio is close to 0.5, indicating that the solid slag is CaF2. The purity of the CaF2 is >95%, and the content of heavy metal elements [Cr, Ni, Mn] is less than 0.01%, and the resource recovery value is high.

[0140] Step 4

[0141] In a stirring tank, 200 kg of tap water was added to the 31.1 kg solid residue (mud cake) obtained after the second alkali washing in step 3. After stirring, the pH of the mud was tested to be 10.5. After stirring for 20 minutes, solid-liquid separation was performed, wherein a portion of the 201 kg separation liquid (NaOH) was used as the alkali (NaOH) used for the alkali washing of the residue in step 2, and the remaining portion entered the primary neutralization sedimentation tank to neutralize the waste acid. The component composition of the separation liquid obtained after washing the solid residue was analyzed, and the results are shown in Table 12.

[0142] Table 12

[0143]

[0144] From the data in Table 12, it can be seen that the Na in the separated liquid after washing the solid residue is + The content of F -The content is relatively small, while the content of other impurities such as heavy metals is very low. After testing, the separated liquid after washing the solid residue has a strong alkalinity (pH ≥ 10.0). Therefore, the separated liquid after washing the solid residue can also be used as NaOH recycling alkali liquid and enter the primary neutralization sedimentation tank for use as a neutralization precipitation agent for treating waste acid.

[0145] In the stirring tank, 200 kg of clean water was further added to the solid-liquid separation residue (28.5 kg), and after stirring and washing for 20 minutes, the mud pH was tested to be 7.7. The mud was separated into solid and liquid, and the separated liquid entered the secondary neutralization sedimentation tank. The components of the obtained separated solid residue and separated liquid were analyzed, and the results are shown in Table 13.

[0146] Table 13

[0147]

[0148] From the data analysis in Table 13, the solid slag obtained after the secondary slag washing (final washing slag, metal hydroxide slag) mainly contains Fe and Cr, and the contents of the main impurities fluorine and sodium are reduced to less than 1%, and the contents of other impurities are also very low, which can meet the requirements of recycling resources for ceramic color glaze raw materials or other industries. The Na content in the separated liquid after the secondary slag washing is low, and its pH value is less than 8.0. Due to the low alkalinity, it is not necessary to reuse the alkali solution. It can enter the secondary neutralization sedimentation tank and be subsequently treated with the intermediate wastewater to remove a small amount of heavy metal impurities and fluoride ions in the wastewater.

[0149] Step 5

[0150] Combine the solid-liquid separation liquid obtained in step 1 and the separation liquid obtained after the secondary slag washing in step 4, and enter the secondary neutralization sedimentation tank together, add lime Ca(OH)2 and flocculant 0.04kg (PAM), coagulant polyaluminium ferric chloride 4kg (PAFC), stir and mix evenly, and measure the pH of the mixed liquid to 9.5. After standing for 1h, solid-liquid separation is then performed. The filtered filtrate is adjusted to pH = 7.0 with 6mol / L hydrochloric acid (2L) and introduced into the biochemical system for NO3 removal. - The obtained solid slag (slag from the secondary neutralization sedimentation tank) and separated liquid (water from the secondary neutralization sedimentation tank) were analyzed for component composition. The results are shown in Table 14.

[0151] Table 14

[0152]

[0153]

[0154] From the data analysis in Table 14, the slag from the secondary neutralization sedimentation tank mainly contains Ca and F as well as a small amount of heavy metals, while the content of Ca and F as well as a small amount of heavy metals in the effluent from the secondary neutralization sedimentation tank is very low. - Except for the relatively high content of NO3 in the effluent from the secondary neutralization sedimentation tank, the indicators of the other components all meet the requirements of the relevant national standards "Iron and Steel Industry Water Pollutant Discharge Standard: GB13456-2012". - It is further processed through the biochemical system.

[0155] Embodiment 4

[0156] Step 1

[0157] The waste acid water (2000L) was put into the primary neutralization sedimentation tank, and 126kg of the recycled alkali solution (NaOH) in step 3 of Example 3 and 47kg of the recycled alkali solution (NaOH) in step 4 of Example 3 were first added, and then 21.17kg of solid NaOH was added, and the mixture was stirred and mixed evenly. The pH value of the waste acid water was measured to be 5.51. After stirring and reacting for 20 minutes, the reaction liquid was subjected to solid-liquid separation to obtain 26.2kg of mud cake containing 50% water. The components of the separated liquid and solid residue were tested respectively. The test results are shown in Table 15 and Table 16.

[0158] Table 15

[0159]

[0160] The data in Table 15 are compared with those in Example 2. The use of the present invention further reduces the amount of NaOH used in the primary sedimentation tank after the reuse alkali solution (NaOH) in Example 3. The amount of NaOH added is reduced by 48.8% compared with Example 2. At the same time, more than 90% of the heavy metal ions (Fe, Cr) and more than 86% of the F are removed at pH = 5.5. - It is separated from the wastewater in the form of precipitation, and the Na ions in the filtrate are greatly reduced.

[0161] Table 16

[0162]

[0163] From the data analysis of Table 16, by using the patented technology of the present invention, by adding NaOH at pH = 5.5, the precipitate obtained is close to the data in Table 6 of Example 3, and it is also judged that the precipitate is composed of heavy metal hydroxides, fluorides and fluorine-containing complexes.

[0164] Step 2

[0165] In the alkali-washed slag stirring tank, first add 26.2 kg of mud cake (13.1 kg of dry slag) obtained after solid-liquid separation at pH = 5.5 in step 1, then add 154 kg of recycled alkali solution (NaOH) in step 4 of Example 3, start stirring, and then measure the slurry pH = 10.9, and continue stirring for 4.0 hours. The slurry is subjected to solid-liquid separation, and the components of the obtained separation liquid (NaF liquid) and solid slag (primary alkali-washed slag) are tested, and the results are shown in Table 17.

[0166] Table 17

[0167]

[0168] According to the data in Table 17 and the comparative analysis with the data in Table 16 and Table 15, after the slag is washed with alkali once, the ratio of Fe and Cr content in the solid slag does not change much, while the ratio of the sum of Fe and Cr content to Na content and F content increases significantly, and there are a large amount of F and Na and only a small amount of Fe and Cr in the separation liquid. This shows that after the slag is washed with alkali once, F and Na are well eluted from the solid slag and enter the eluent.

[0169] Step 3

[0170] 153kg (NaF liquid) of the primary alkali-washed slag filtrate obtained in step 2 was added with 4.2kg of lime Ca(OH)2 and stirred in a stirring tank (NaF replacement reaction tank) for 20 minutes, and solid-liquid separation was performed using a filtering device, and the separation liquid (NaOH alkali liquid) was added to the primary alkali-washed solid slag obtained in step 2, and the alkali-washed slag was washed for the second time in the alkali-washed slag stirring tank, and then solid-liquid separation was performed. The components of the alkali-washed solid slag (secondary alkali-washed slag) and the separation liquid obtained were analyzed, and the results are shown in Table 18.

[0171] Table 18

[0172]

[0173] According to the data in Table 18 and the comparative analysis with the data in Table 17, after the second alkali washing of the slag with the recycled NaOH alkali solution, the obtained separated liquid contains a large amount of F - and Na + Therefore, the separation liquid is still essentially a NaF solution. The fluoride ions in the obtained solid slag (secondary alkali washing slag) are basically removed, and the sodium ion content is also greatly reduced to a lower value level (at this time, the sodium and fluoride in the solid slag mainly exist in the form of NaOH and NaF).

[0174] In a stirring tank, 7.2 kg of lime Ca(OH)2 was added to 151 kg of NaF solution obtained in step 3, and the mixture was stirred for 20 minutes to separate the solid and liquid. The separated liquid was sent to a primary neutralization sedimentation tank to neutralize the waste acid. The obtained separated liquid was analyzed for its composition, and the results are shown in Table 5, Table 19 and Table 20.

[0175] Table 19

[0176]

[0177] From the data in Table 19, it can be seen that the separation liquid contains a high concentration of Na ions, while F - , heavy metal ions, etc. In addition, the pH of the separated liquid was tested to be 13.52. Therefore, the separated liquid is essentially a NaOH solution, which can be added to the primary neutralization sedimentation tank as a recycled alkali solution to neutralize the waste acid.

[0178] The solid slag obtained by adding lime Ca(OH)2 to the NaF solution in the above step 3 was analyzed for component composition. The results are shown in Table 20.

[0179] Table 20

[0180]

[0181] From the data in Table 20, it can be seen that the solid slag mainly contains Ca and F, wherein the molar ratio of Ca / F is greater than the theoretical value of CaF2=0.5 in CaF2, indicating that the solid slag is mainly composed of CaF2 and Ca(OH)2.

[0182] The solid slag composed of CaF2 and Ca(OH)2 was further purified to remove impurities such as unreacted lime Ca(OH)2. 0.3 kg of 1:1 dilute hydrochloric acid was added to 23.4 kg of solid slag (water content 50%), and 25 kg of water was added. After stirring evenly, the pH of the slurry was measured to be 8.0. The slurry was separated into solid and liquid, and the separated liquid entered the secondary neutralization sedimentation tank for treatment. The component composition of the obtained solid slag was analyzed, and the results are shown in Table 21.

[0183] Table 21

[0184]

[0185] From the data in Table 21, it can be seen that the solid slag obtained after purification mainly contains Ca and F, and other impurities are very small, and the Ca / F molar ratio is close to 0.5, indicating that the solid slag is CaF2. The purity of the CaF2 is >95%, and the content of heavy metal elements [Cr, Ni, Mn] is less than 0.01%, and the resource recovery value is high.

[0186] Step 4

[0187] In a stirring tank, 200 kg of clean water was added to 30.1 kg of solid residue (mud cake) obtained after the second alkali washing in step 3. After stirring, the pH value of the mud was tested to be 10.2. After continuous stirring for 20 minutes, solid-liquid separation was performed, wherein a part of the separation liquid (NaOH) 201.5 kg was used as the alkali (NaOH) used for the alkali washing residue in step 2, and the remaining part entered the primary neutralization sedimentation tank to neutralize the waste acid. The component composition of the separation liquid obtained after the water-washed solid residue was analyzed, and the results are shown in Table 22.

[0188] Table 22

[0189]

[0190] From the data in Table 22, it can be seen that Na in the separated liquid after washing the solid residue is + The content of F - The content is relatively small, while the content of other impurities such as heavy metals is very low. After testing, the separated liquid after washing the solid residue has a strong alkalinity (pH ≥ 10.0). Therefore, the separated liquid after washing the solid residue can also be used as NaOH recycling alkali liquid and enter the primary neutralization sedimentation tank for use as a neutralization precipitation agent for treating waste acid.

[0191] In a stirring tank, 200 kg of clean water was further added to the solid-liquid separation residue (28.3 kg) obtained in step 4. After stirring and washing for 20 minutes, the pH of the mud was tested to be 7.8. After the mud was separated from the solid and liquid, the components of the separated solid residue and the separated liquid were analyzed. The results are shown in Table 23.

[0192] Table 23

[0193]

[0194] From the data analysis in Table 23, it can be seen that the solid slag obtained after the secondary slag washing (final washing slag, metal hydroxide slag) mainly contains Fe and Cr, and the contents of the main impurities fluorine and sodium are reduced to less than 1%, and the contents of other impurities are also very low, which can meet the requirements of recycling resources for ceramic color glaze raw materials or other industries. The Na content in the separated liquid after the secondary slag washing is low, and its pH value is less than 8.0. Due to the low alkalinity, it is not necessary to reuse the alkali solution. It can enter the secondary neutralization sedimentation tank and be subsequently treated with the intermediate wastewater to remove a small amount of heavy metal impurities and fluoride ions in the wastewater.

[0195] Step 5

[0196] The solid-liquid separation liquid obtained in step 1 and the separation liquid obtained after the secondary slag washing in step 4 are combined and enter the secondary neutralization sedimentation tank together. Lime Ca(OH)2 and flocculant 0.04kg (PAM) and coagulant polyaluminum ferric chloride 4kg (PAFC) are added thereto. After stirring and mixing evenly, the pH value of the mixed liquid is measured to be 9.6. After standing for 1 hour, solid-liquid separation is then carried out. The filtrate after filtration is adjusted to pH = 7.0 with 6mol / L hydrochloric acid (2L). The components of the obtained solid slag (slag from the secondary neutralization sedimentation tank) and the separation liquid (water from the secondary neutralization sedimentation tank) are analyzed. The results are shown in Table 24

[0197] Table 24

[0198]

[0199] From the data in Table 24, it can be seen that the slag from the secondary neutralization sedimentation tank mainly contains Ca and F as well as a small amount of heavy metals, while the content of Ca and F as well as a small amount of heavy metals in the effluent from the secondary neutralization sedimentation tank is very low. - Except for the relatively high content of NO3 in the effluent from the secondary neutralization sedimentation tank, the indicators of the other components all meet the requirements of the relevant national standards "Iron and Steel Industry Water Pollutant Discharge Standard: GB13456-2012". - It is further processed through the biochemical system.

[0200] Comparison of the cost of treating one ton of reagent by this embodiment and the traditional lime method

[0201] For the same batch of stainless steel pickling wastewater in the example, the direct lime Ca(OH)2 treatment process commonly used by stainless steel enterprises was adopted to treat the waste acid water, and the cost and economic benefit advantages of the technology of the present invention compared with the traditional lime treatment process were mainly compared. The main comparison was made on the cost of the consumed dosage of the reagents, the amount of sludge residue produced and the disposal cost for the same batch of pickling wastewater of more than 2 tons, and the result data is shown in Table 25:

[0202] Table 25

[0203]

[0204]

[0205] From the above analysis, the amount of hazardous solid slag required for disposal is reduced by more than 95% when the technology of the present invention is used compared with the traditional lime neutralization process for treating wastewater. The technology of the present invention treats fluorine-containing wastewater and cleverly utilizes the alkali washing slag process to convert the fluorine-containing and sodium-containing impurities (hexafluoro compounds) in the slag into NaF first, and then converts them into NaOH with low-cost lime, thereby greatly reducing the consumption of NaOH reagents, which also compensates for and solves the problem of high cost of NaOH reagents for treating wastewater. Its more important significance is that the solid waste slag recovery rate reaches more than 90%, and the original chromium-containing and fluorine-containing hazardous compound mixed slag is separated and converted into valuable metal oxide slag and higher-purity valuable calcium fluoride inorganic slag, which not only "reduces costs and increases efficiency, saves energy and reduces emissions, and sustainably utilizes and develops resources", but also better conforms to the national development principles and requirements of "reduction, resource utilization, and harmlessness".

[0206] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for resource treatment of industrial wastewater containing fluorine and heavy metal ions, characterized in that: The method specifically includes: S1: In the primary neutralization sedimentation tank, NaOH is added to the industrial wastewater containing fluoride ions and heavy metal ions, the pH is adjusted to pH = 5.3-5.8, the reaction is stirred for 15-30 minutes, and the obtained precipitate is subjected to solid-liquid separation; S2: adding clean water to the solid residue obtained in step S1 at a ratio of solid residue dry weight to water weight = 1:1-1:10 to make a slurry, then adding NaOH to adjust the pH of the slurry to pH = 10-11, stirring the reaction for 3-5 hours, and then performing solid-liquid separation; S3: Add lime Ca(OH)2 to the separated liquid obtained in step S2, stir and react for 15-30 minutes, and then separate the solid and liquid. The obtained solid is CaF2 containing only a small amount of incompletely reacted Ca(OH)2 (<1Wt%). The obtained separated liquid is NaOH solution, which is reused in step S1 or step S2 as part of the alkali used to adjust the pH. S4: washing the solid residue obtained in step S2 with clean water at least twice and performing solid-liquid separation, the obtained heavy metal hydroxide mixture has a low impurity content, and the separated liquid after washing the solid residue contains a certain amount of NaOH, the separated liquid after the first washing of the solid residue is recycled into the primary neutralization sedimentation tank, and the separated liquid after the second and multiple washings of the solid residue is recycled into the secondary neutralization sedimentation tank, all of which are used as part of the alkali used to adjust the pH; S5: The separated liquid obtained in step S1 and the separated liquid after the second and multiple washing of the solid residue in step S4 are introduced into a secondary neutralization sedimentation tank, and Ca(OH)2 is added thereto to adjust the pH to pH=9.0-9.5, and 0.02‰ of flocculant and 2‰ of coagulant calculated by the mass of the separated liquid are added, and the reaction is stirred for 15-30 minutes, and then solid-liquid separation is performed to obtain lime slag mainly containing Ca(OH)2 and a small amount of CaF2. The separated liquid is adjusted to pH=7-9 with hydrochloric acid and then introduced into the biochemical system for denitrification (NO3 - )deal with.

2. The method for resource treatment of industrial wastewater containing fluorine and heavy metal ions according to claim 1, characterized in that: In said S4, the solid residue is washed with clean water, the pH of the solid-liquid separation liquid after the first washing of the solid residue is ≥10, and the pH of the solid-liquid separation liquid after the second or multiple washings of the solid residue is 7.0-9.

0.

3. The method for resource treatment of industrial wastewater containing fluorine and heavy metal ions according to claim 1, characterized in that: The specific amount of clean water used in the second or multiple washings of the solid slag or the specific pH control value of the separation liquid after washing the solid slag is based on the fact that the fluorine and sodium impurities in the final solid slag after washing are completely removed, that is, here it means that the final heavy metal hydroxide slag can meet the requirements for the minimum impurity limit in the slag for resource recycling.

4. The method for resource treatment of industrial wastewater containing fluorine and heavy metal ions according to claim 1, characterized in that: The weight ratio of the amount of Ca(OH)2 added to S3 to the fluorine contained in the separated liquid is generally 1:1.0 to 1:3.0, so that the F in the separated liquid obtained by solid-liquid separation after the reaction is - The ion content is preferably less than 200 mg / L. The coagulant is one or more of polyaluminium ferric chloride, polyferric chloride, polyferric sulfate and polyaluminium chloride. The flocculant is polyacrylamide (PAM).

5. The method for resource treatment of industrial wastewater containing fluorine and heavy metal ions according to claim 1, characterized in that: If the industrial wastewater containing fluorine and heavy metal ions contains hexavalent chromium (Cr 6+ ), then it is necessary to add a small amount of reducing agent to reduce hexavalent chromium to trivalent chromium.

6. A resource treatment system for industrial wastewater containing fluorine and heavy metal ions according to claims 1-5, characterized in that: The system specifically includes: The precipitation and separation module is used to precipitate and separate heavy metal ions and fluoride ions in wastewater; The impurity removal and purification module is used to treat the mixture of heavy metal hydroxide and its fluorine-containing complex to achieve impurity removal and purification of heavy metal hydroxide; Complete precipitation module, used to completely precipitate the small amount of heavy metal ions and fluoride ions remaining in the wastewater with calcium hydroxide; The denitrification treatment module is used to send the generated wastewater into the biochemical system for denitrification (NO3 - )deal with.

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