Method and system for recovering potassium sulfate and sodium chloride from dust collected during smelting of blast furnace ferromanganese

Abstract

The application discloses a method and system for recovering potassium sulfate and sodium chloride from dust removal ash in blast furnace ferromanganese smelting, and first proposes a technical route for recovering high-purity potassium sulfate and sodium chloride by washing dust removal ash in blast furnace ferromanganese smelting. According to the characteristics of impurities contained in the waste water obtained by washing and leaching the dust removal ash in blast furnace ferromanganese smelting, one or more of the pretreatment methods such as oxidation, reduction, electrolysis, salt precipitation, precipitation and flocculation adsorption are used for impurity removal. In the case that no impurities are introduced and no secondary pollution is caused, the purity of potassium salt and sodium salt is improved at low cost. The whole process does not discharge waste water and waste gas, has high economic value, and meets the green and environmental protection production requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the treatment of solid waste ash in the steel industry, in particular to a method and system for recovering potassium sulfate and sodium chloride from blast furnace manganese iron smelting dust removal ash, belonging to the field of resource treatment technology of blast furnace manganese iron smelting dust removal ash in the steel industry. BACKGROUND

[0002] High-carbon ferromanganese is an iron alloy material with wide application. The current production process includes blast furnace method and electric furnace method. Among them, the blast furnace method is the earliest to be applied, and is still widely used in China at present. A large amount of dust removal ash is generated in the production process of blast furnace ferromanganese, which mainly contains iron, manganese, fluorine, alkali metals, etc.

[0003] At present, there is no specific disposal technology for such blast furnace manganese iron smelting dust removal ash. Some domestic steel plants use manganese iron dust removal ash to produce cold solidified briquettes and then re-enter the furnace for utilization. Although such disposal method has simple process and low cost, it will lead to the problems of reducing the final product ore grade, enriching fluorine ions and chlorine ions, equipment corrosion, and nodulation, etc.

[0004] At present, there are few reported disposal technologies for manganese iron smelting dust removal ash. Chinese patent CN105905925B "Method for comprehensive recovery of valuable metals from smelting manganese iron dust removal ash and waste slag" is a disposal object for electric furnace manganese iron smelting dust removal ash. It uses water washing, and the water washing liquid is concentrated and crystallized to obtain potassium hydroxide product. The water washing residue is leached with concentrated sulfuric acid, an oxidizing agent is added to the leaching liquid, and the pH is adjusted, a heavy metal removal agent is added, and then the product is obtained by filtration, concentration and crystallization, and drying to obtain manganese sulfate product. In the whole process, potassium hydroxide, zinc slag and manganese sulfate are recovered. This method uses the idea of hydrometallurgy to recover multiple metals. However, this method deals with dust removal ash generated by electric furnace, which is different from blast furnace manganese iron smelting dust removal ash. Research shows that blast furnace manganese iron smelting dust removal ash contains a large amount of carbonate and fluorine ions, in addition to sulfate ions, and also contains a high content of sulfite ions. SUMMARY

[0005] In view of the shortcomings of the prior art, the present application provides a method and system for recovering potassium sulfate and sodium chloride from blast furnace manganese iron smelting dust removal ash. According to the characteristics of the impurities contained in the water washing wastewater of blast furnace manganese iron smelting dust removal ash, one or more of oxidation, reduction, electrolysis, salt precipitation, precipitation and flocculation adsorption are used for impurity removal. The purity of the target product can be improved at low cost without introducing impurities and causing secondary pollution. The whole process does not discharge wastewater and waste gas, has high economic value, and meets the requirements of green and environmentally friendly production.

[0006] To achieve the above technical purposes, the technical solutions adopted by the present application are as follows:

[0007] According to a first embodiment of the present application, a method for recovering potassium sulfate and sodium chloride from dust removal ash of blast furnace ferromanganese smelting is provided.

[0008] A method for recovering potassium sulfate and sodium chloride from dust removal ash of blast furnace ferromanganese smelting, the method comprising the following steps:

[0009] 1) Water washing leaching is performed on the dust removal ash of blast furnace ferromanganese smelting to obtain leaching wastewater.

[0010] 2) One or more of oxidation, reduction, electrolysis, salt precipitation, precipitation, and flocculation adsorption are used to pretreat the leaching wastewater to obtain pretreated wastewater.

[0011] 3) Acid is added to the pretreated wastewater to adjust the wastewater to neutral, and then high-purity potassium sulfate and sodium chloride are recovered by temperature-variable evaporation desalination.

[0012] As a preferred, step 2) specifically comprises the following steps:

[0013] 201a) Carbon dioxide is introduced into the leaching wastewater to precipitate impurity salts, and after solid-liquid separation, wastewater supernatant is obtained, part of which is recycled to the water washing section to enrich salt content.

[0014] 201b) First, potassium permanganate solution is added to the wastewater supernatant obtained in 201a) to perform oxidation treatment. Then soluble ferrous salt solution is added to the oxidized wastewater to perform reduction treatment. Finally, acid is added to the reduced wastewater to adjust the wastewater to weak alkaline for precipitation reaction, and after the reaction is completed, the pretreated wastewater is obtained.

[0015] In the present application, the supernatant recycled to the water washing section is 10% to 90% of the entire wastewater supernatant, preferably 20% to 80%, and more preferably 30% to 60%. By recycling the supernatant, the salt content is increased.

[0016] As a preferred, step 2) specifically comprises the following steps:

[0017] 202a) Potassium permanganate solution is added to the leaching wastewater to perform oxidation treatment. Then acid is added to the oxidized wastewater to adjust the wastewater to weak alkaline for zinc removal by precipitation, and after solid-liquid separation, zinc-removed wastewater is obtained.

[0018] 202b) After the zinc-removed wastewater obtained in 202a) is adjusted to acidic by adding acid, iron-carbon micro-electrolysis treatment is performed. Then the wastewater after micro-electrolysis is adjusted to alkaline by adding alkali to perform precipitation treatment, and after solid-liquid separation, the pretreated wastewater is obtained.

[0019] As a preferred, step 2) specifically comprises the following steps:

[0020] 203a) adding activated carbon method acid washing wastewater to the leaching wastewater to make the mixed wastewater weakly alkaline. Then adding aluminum sulfate solution to the mixed wastewater to carry out defluorination treatment. Finally adding sulfide to the defluorinated wastewater to carry out heavy metal removal treatment, and obtaining heavy metal removal and defluorination wastewater after solid-liquid separation.

[0021] 203b) adding sodium hypochlorite solution to the heavy metal removal and defluorination wastewater obtained in 203a) to carry out oxidation treatment, thereby obtaining pretreated wastewater.

[0022] Preferably, in step 201b), the soluble ferrous salt is ferrous sulfate and / or ferrous chloride, preferably ferrous sulfate.

[0023] Preferably, in step 201b), the pH of the wastewater is adjusted to weak alkalinity by using sulfuric acid to adjust the pH of the wastewater to 7.5-9, preferably using dilute sulfuric acid to adjust the pH of the wastewater to 8-8.5.

[0024] Preferably, in step 201b), the mass concentration of the potassium permanganate solution is 15-30%, preferably 20-25%. The amount of potassium permanganate solution used is 2-7% of the total mass of the wastewater, preferably 3-5%. The oxidation treatment time is 5-40 min, preferably 10-30 min. And / or

[0025] Preferably, in step 201b), the mass concentration of the soluble ferrous salt solution is 10-30%, preferably 15-25%. The amount of soluble ferrous salt solution used is 3-8% of the total mass of the wastewater, preferably 4-6%. The reduction treatment time is 5-40 min, preferably 10-30 min.

[0026] Preferably, in step 202a), the pH of the wastewater is adjusted to weak alkalinity by using sulfuric acid to adjust the pH of the wastewater to 7.5-9, preferably using dilute sulfuric acid to adjust the pH of the wastewater to 8-8.5.

[0027] Preferably, in step 202b), the pH of the wastewater is adjusted to acidity by using sulfuric acid to adjust the pH of the wastewater to 1-4, preferably using dilute sulfuric acid to adjust the pH of the wastewater to 2-3.

[0028] Preferably, in step 202b), the pH of the wastewater is adjusted to alkalinity by using sodium hydroxide solution to adjust the pH of the wastewater to 8-10, preferably to 8.5-9.5.

[0029] Preferably, in step 202a), the mass concentration of the potassium permanganate solution is 15-30%, preferably 20-25%. The amount of potassium permanganate solution used is 2-7% of the total mass of the wastewater, preferably 3-5%. The oxidation treatment time is 5-40 min, preferably 10-30 min.

[0030] As preferred, in step 202b), the time of the iron-carbon micro-electrolysis treatment is not less than 20 min, preferably 30-60 min. The time of the precipitation treatment is not less than 10 min, preferably 15-30 min.

[0031] As preferred, in step 203a), the pH of the mixed wastewater is 7.5-9, preferably pH is 8-8.5.

[0032] As preferred, in step 203a), the mass concentration of the aluminum sulfate solution is 20-35%, preferably 25-30%. The addition amount of the aluminum sulfate solution is 0.1-0.8% of the total mass of the wastewater, preferably 0.3-0.6%. The time of the defluorination treatment is 0.3-2h, preferably 0.5-1.5h.

[0033] As preferred, in step 203a), the sulfide is one or more of barium sulfide, sodium sulfide, hydrogen sulfide, preferably barium sulfide, and the addition amount is 0.2-0.8% of the mass of the wastewater, preferably 0.3-0.5%.

[0034] As preferred, in step 203b), the mass concentration of the sodium hypochlorite solution is 0.5-5%, preferably 0.8-4%, and the addition amount is 0.01-3% of the mass of the wastewater, preferably 0.05-2%.

[0035] As preferred, in step 1), the dust of the blast furnace manganese iron smelting is the dust containing iron, manganese, fluorine, alkali metal, carbonate and sulfite generated during the manganese iron smelting by the blast furnace method. The water washing is a three-stage countercurrent water washing, and the water-cement ratio during the water washing is 1-7:1, preferably 2-5:1.

[0036] As preferred, in step 3), the adjustment of the wastewater to neutral by adding acid is to adjust the pH of the wastewater to 6-7 by adding sulfuric acid, preferably to adjust the pH of the wastewater to 6.5-7 by adding dilute sulfuric acid.

[0037] According to the second embodiment of the present application, a system for recovering potassium sulfate and sodium chloride from the dust of the blast furnace manganese iron smelting is provided.

[0038] A method for recovering potassium sulfate and sodium chloride from the dust of the blast furnace manganese iron smelting or a system for the method of the first embodiment, the system comprising a three-stage countercurrent water washing device, a filter pressing device, a pretreatment impurity removal unit, a readjustment pool and an evaporation and salt separation device arranged in series. The three-stage countercurrent water washing device is connected with a manganese iron dust conveying mechanism at the dust inlet, and is communicated with an industrial water conveying pipeline at the water inlet. The readjustment pool is provided with an acid adding pipeline, and a pH probe is arranged inside. The potassium salt outlet of the evaporation and salt separation device is connected with a potassium salt conveying mechanism, and the sodium salt outlet is connected with a sodium salt conveying mechanism.

[0039] As preferred, the pretreatment and impurity removal unit comprises a mixed salt precipitation tank, a redox tank and a precipitation tank arranged in series. The water inlet of the mixed salt precipitation tank is connected to the water outlet of the filter press device through a water pipeline. The water outlet of the precipitation tank is connected to the water inlet of the readjustment tank through a water pipeline. The mixed salt precipitation tank is also connected to a carbon dioxide gas inlet pipeline. The redox tank is also provided with an oxidizing agent adding mechanism and a reducing agent adding mechanism. The precipitation tank is also provided with a dilute sulfuric acid adding pipeline, which is provided with a pH probe inside. The exhaust outlet of the readjustment tank and the exhaust outlet of the precipitation tank are both connected to the carbon dioxide gas inlet pipeline through a gas pipeline.

[0040] As preferred, the pretreatment and impurity removal unit comprises an oxidation tank, a readjustment precipitation tank, a transition tank, an iron-carbon micro-electrolysis reactor and a neutralization precipitation tank arranged in series. The water inlet of the oxidation readjustment tank is connected to the water outlet of the filter press device through a water pipeline. The water outlet of the neutralization precipitation tank is connected to the water inlet of the readjustment tank through a water pipeline. The oxidation tank is also provided with a potassium permanganate adding pipeline. The readjustment precipitation tank is also provided with a first acid liquid adding pipeline. The transition tank is also provided with a second acid liquid adding pipeline. The neutralization precipitation tank is also provided with a liquid alkali adding pipeline. The readjustment precipitation tank, the transition tank and the neutralization precipitation tank are all provided with a pH probe inside.

[0041] As preferred, the pretreatment and impurity removal unit comprises a mixed water tank, a fluorine removal tank, a neutralization and heavy metal removal tank and a transition oxidation tank arranged in series. The water inlet of the mixed water tank is connected to the water outlet of the filter press device. The water outlet of the transition oxidation tank is connected to the water inlet of the readjustment tank through a water pipeline. The water inlet of the mixed water tank is also connected to an acidic washing wastewater inlet pipeline. The fluorine removal tank is also provided with an aluminum sulfate solution adding pipeline. The neutralization and heavy metal removal tank is also provided with a sulfide adding mechanism. The transition oxidation tank is also provided with a sodium hypochlorite adding pipeline. The mixed water tank is also provided with a pH probe.

[0042] In the prior art, the composition of the blast furnace manganese iron smelting dust produced during the smelting of manganese iron by the blast furnace method is complex, directly discharging into the environment pollutes the environment and also causes waste of valuable resources, but the treatment of the blast furnace manganese iron smelting dust in the prior art is not satisfactory, and there is no perfect treatment process. How to realize the high resource treatment of the blast furnace manganese iron smelting dust has been a big problem that has plagued scholars in the field for a long time.

[0043] In the present application, the technical concept of using blast furnace ferromanganese smelting dust to recycle high-purity potassium sulfate and sodium chloride is proposed for the first time: through three-stage countercurrent water washing, blast furnace ferromanganese smelting dust is water-washed and leached to obtain filter cake (external disposal) and leaching wastewater; for the impurity ions such as iron, manganese, zinc, fluorine, carbonate, sulfite and hydroxide contained in the leaching wastewater, one or more of oxidation, reduction, electrolysis, salt precipitation, precipitation and flocculation adsorption are used for pretreatment and impurity removal; finally, the wastewater after impurity removal is adjusted to neutral by acid, further removing residual carbonate, reducing the difficulty of subsequent evaporation and separation of potassium sulfate and sodium chloride, and improving the quality of potassium salt and sodium salt.

[0044] In the present application, three pretreatment process routes are designed for the pretreatment and impurity removal process of leaching wastewater:

[0045] Route one mainly includes three stages of carbonation and impurity salt precipitation, oxidation, reduction and adjustment. ① Carbonation and impurity salt precipitation: Since the leaching wastewater contains a large amount of carbonate, carbon dioxide (preferably from the carbon dioxide generated in the subsequent pH adjustment process) is introduced into the leaching wastewater to react with potassium carbonate and sodium hydroxide in the leaching wastewater, so that potassium carbonate is converted into potassium bicarbonate with low solubility and precipitates. In addition, with the increase of potassium carbonate concentration in the solution (potassium ions are continuously enriched by water washing and leaching), a common ion effect will occur, causing potassium fluoride in the solution to precipitate. The precipitated potassium bicarbonate and potassium fluoride are discharged from the system. The impurity salts are reduced at the source of the wastewater. At the same time, a large amount of carbon dioxide generated in the subsequent pH adjustment process can be recycled for carbonation reaction, improving the resource utilization efficiency, reducing the production cost and achieving zero emission of waste gas. ② Oxidation: analysis shows that the leaching wastewater contains a large amount of sulfite ions, which will reduce the purity of recovered potassium sulfate if not removed. The sulfite ions are oxidized to sulfate ions by using high-oxidizing potassium permanganate. The potassium brought in by potassium permanganate will not affect the water quality, and the manganese brought in will be removed in the subsequent process. ③ Reduction: research shows that the wastewater contains high-valence manganese and iron, which can exist stably in a high-alkaline solution. The high-valence manganese and iron ions are reduced to divalent manganese ions and trivalent iron ions by using a reducing ferrous salt, and then the high-alkaline wastewater is used to achieve deep purification of manganese and iron in the wastewater. ④ Adjustment: a large amount of zinc metal exists in the wastewater, and at the same time, combined with the ion fraction analysis of potassium sulfate, the solution can be adjusted to pH 8 or so to remove zinc metal and purify potassium salt at the same time.

[0046] Route two mainly includes four stages of oxidation, two-stage pH adjustment, iron-carbon micro-electrolysis, and precipitation for heavy metal and fluorine removal. ① Oxidation: analysis shows that the wastewater contains a large amount of sulfite ions, which will reduce the purity of recovered potassium sulfate if not removed. The sulfite ions are oxidized to sulfate ions by using high-oxidizing potassium permanganate, and the potassium introduced by potassium permanganate will not affect the water quality, and the manganese introduced will be removed in the subsequent process. ② Two-stage pH adjustment: research shows that a large amount of zinc metal also exists in the water, and the removal of zinc metal can be achieved by adjusting the pH of the wastewater after oxidation to about 8. In addition, at this time, iron and manganese in the wastewater exist in high valence state and will not precipitate. Thus, the purity of the obtained zinc precipitate is high. Then the pH of the wastewater is adjusted to about 1-4, which is more conducive to the iron-carbon micro-electrolysis treatment of the wastewater under acidic conditions. ③ Iron-carbon micro-electrolysis: research shows that the wastewater contains high-valence manganese and iron, which can exist stably in a high-alkaline solution. The high-valence manganese and iron ions are reduced to divalent manganese ions and trivalent iron ions by using the reducing property of iron-carbon micro-electrolysis under acidic conditions. ④ Precipitation for heavy metal and fluorine removal: the wastewater after iron-carbon micro-electrolysis is adjusted to alkalinity by using liquid alkali, so that the metals such as manganese and iron in the wastewater are changed into precipitates for removal. In addition, research shows that under alkaline conditions, iron precipitate will adsorb fluorine, and manganese will form manganese fluoride. Thus, the removal of heavy metals and fluorine is achieved at this stage.

[0047] Route three mainly includes four stages of water mixing, defluorination, heavy metal removal, and oxidation. ① Water mixing: generally, the leaching wastewater is strongly alkaline (pH is generally > 10), and the active carbon method flue gas scrubbing wastewater is acidic. The pH of the mixed wastewater is adjusted to about 8 by using the acidity of the flue gas scrubbing wastewater, and the high-valence manganese and iron ions in the wastewater are reduced to divalent manganese ions and trivalent iron ions by using the reducing property of the flue gas scrubbing wastewater. Then, the high alkalinity of the wastewater is used to achieve deep purification of zinc, manganese, and iron in the wastewater. ② Defluorination: the wastewater after mixing and alkali adjustment contains high-concentration fluorine ions, which will affect the quality of salt products and corrode equipment if not removed. Aluminum sulfate is used to remove fluorine ions. Aluminum sulfate will hydrolyze to form aluminum hydroxide colloid in water with pH of 8, adsorb fluorine ions, and thus remove them without introducing impurity ions. ③ Heavy metal removal: sulfide is added to the wastewater after defluorination to further remove calcium, magnesium, and residual heavy metal ions in the wastewater by sulfidation. ④ Oxidation: since the leaching wastewater contains sulfite ions and the flue gas scrubbing wastewater contains thiosulfate ions, the sulfite and thiosulfate ions are oxidized to sulfate ions by using sodium hypochlorite, thereby improving the quality of potassium salt and sodium salt.

[0048] In the present application, the blast furnace ferromanganese smelting dust is the dust generated during the smelting of ferromanganese by the blast furnace method, which is mixed and stirred with industrial water and the blast furnace ferromanganese smelting dust at a certain ratio (for example, the water-cement ratio is 1-7:1) for water washing treatment. After the blast furnace ferromanganese smelting dust is fully water washed and leached, the easily soluble substances in the blast furnace ferromanganese smelting dust enter the water. The filtered residue after water washing is returned to sintering or is disposed of externally. The obtained leaching wastewater is strongly alkaline (generally pH>11). The cations contained in the leaching wastewater mainly include iron, manganese, potassium, sodium, zinc, etc., and the anions contained mainly include carbonate, sulfite, sulfate, chloride, fluoride, hydroxide, etc.

[0049] In the present application, in the pretreated wastewater, a large amount of carbonate, sulfate and chloride are contained simultaneously, which is a quinary phase diagram, and the salt separation is difficult. Therefore, by adding dilute sulfuric acid to adjust the pH of the wastewater to 6-7, the carbonate is acidified. Thus, the anions in the wastewater are changed into sulfate and chloride, and the difficulty of evaporation and salt separation is reduced. At the same time, the purity of potassium sulfate and sodium chloride is further improved.

[0050] In the present application, the sulfuric acid and dilute sulfuric acid used are aqueous solutions of sulfuric acid with a solute mass fraction of less than or equal to 70%.

[0051] Compared with the prior art, the present application has the following beneficial technical effects:

[0052] 1: Based on the characteristics of the blast furnace ferromanganese smelting dust, the present application first proposes the technical concept of recovering high-purity potassium sulfate and sodium chloride by water washing of the blast furnace ferromanganese smelting dust. The purification and impurity removal of the wastewater are realized by water washing, oxidation, reduction, electrolysis, salt separation, precipitation, flocculation and adsorption, etc., which promotes the recycling of high-purity potassium sulfate and sodium chloride and greatly guarantees the recovery of high-value potassium sulfate and sodium chloride products by temperature swing evaporation separation.

[0053] 2: The present application is designed according to the water quality of the washed dust wastewater, which can remove the key pollutants affecting the quality of by-products at low cost without introducing impurities and causing secondary pollution. At the same time, the separation and precipitation process of carbonate, sulfate, fluoride, heavy metals such as high-valence iron and manganese is optimized, which simplifies the complex multi-component phase diagram and greatly reduces the difficulty of salt separation. At the same time of recovering a variety of high-value salt products, the wastewater and waste gas are also realized zero emission. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The process flow diagram of the method for recovering potassium sulfate and sodium chloride from the blast furnace ferromanganese smelting dust according to the present application.

[0055] Figure 2 The pretreatment process flow diagram of the leaching wastewater according to the present application Figure One .

[0056] Figure 3 A flow chart of the pretreatment process of leaching wastewater of the present application Figure Two .

[0057] Figure 4 A flow chart of the pretreatment process of leaching wastewater of the present application Figure Three .

[0058] Figure 5 A structural diagram of the system for recovering potassium sulfate and sodium chloride from dust ash of blast furnace manganese iron smelting according to the present application.

[0059] Figure 6 A structural diagram of the pretreatment impurity removal unit according to the present application.

[0060] The figure mark: 1: three-stage countercurrent water washing device; 101: manganese iron ash conveying mechanism; 102: industrial water conveying pipeline; 2: filter pressing device; 3: pretreatment impurity removal unit; 301: salt precipitation pool; 3011: carbon dioxide inlet pipeline; 302: oxidation-reduction pool; 3021: oxidant adding mechanism; 3022: reducing agent adding mechanism; 303: sedimentation pool; 3031: dilute sulfuric acid adding pipeline; 304: oxidation pool; 3041: potassium permanganate adding pipeline; 305: readjustment sedimentation pool; 3051: first acid liquid adding pipeline; 306: transition pool; 3061: second acid liquid adding pipeline; 307: iron-carbon micro-electrolysis reactor; 308: neutralization sedimentation pool; 3081: liquid alkali adding pipeline; 309: water mixing pool; 3091: acidic washing wastewater inlet pipeline; 310: defluorination pool; 3101: aluminum sulfate solution adding pipeline; 311: neutralization and heavy metal removal pool; 3111: sulfide adding mechanism; 312: transition oxidation pool; 3121: sodium hypochlorite adding pipeline; 4: readjustment pool; 401: acid adding pipeline; 5: evaporation and salt separation device; 501: potassium salt conveying mechanism; 502: sodium salt conveying mechanism; 6: pH probe. DETAILED DESCRIPTION

[0061] The technical solutions of the present application are illustrated below, and the scope of protection claimed by the present application includes but is not limited to the following embodiments.

[0062] A system for recovering potassium sulfate and sodium chloride from dust ash of blast furnace manganese iron smelting, which comprises three-stage countercurrent water washing device 1, filter pressing device 2, pretreatment impurity removal unit 3, readjustment pool 4 and evaporation and salt separation device 5 arranged in series. The manganese iron ash conveying mechanism 101 is connected to the ash inlet of the three-stage countercurrent water washing device 1, and the industrial water conveying pipeline 102 is communicated to the water inlet thereof. The acid adding pipeline 401 is arranged on the readjustment pool 4, and the pH probe 6 is arranged inside. The potassium salt conveying mechanism 501 is connected to the potassium salt outlet of the evaporation and salt separation device 5, and the sodium salt conveying mechanism 502 is connected to the sodium salt outlet thereof.

[0063] As preferred, the pretreatment and impurity removal unit 3 comprises a mixed salt precipitation tank 301, a redox tank 302 and a precipitation tank 303 arranged in series. The water inlet of the mixed salt precipitation tank 301 is connected to the water outlet of the filter press 2 through a water pipeline. The water outlet of the precipitation tank 303 is connected to the water inlet of the readjustment tank 4 through a water pipeline. The mixed salt precipitation tank 301 is also connected to a carbon dioxide inlet pipeline 3011. The redox tank 302 is also provided with an oxidant adding mechanism 3021 and a reducing agent adding mechanism 3022. The precipitation tank 303 is also provided with a dilute sulfuric acid adding pipeline 3031, and a pH probe 6 is arranged inside the pipeline. The exhaust outlet of the readjustment tank 4 and the exhaust outlet of the precipitation tank 303 are both connected to the carbon dioxide inlet pipeline 3011 through a gas pipeline.

[0064] As preferred, the pretreatment and impurity removal unit 3 comprises an oxidation tank 304, a readjustment precipitation tank 305, a transition tank 306, an iron-carbon micro-electrolysis reactor 307 and a neutralization precipitation tank 308 arranged in series. The water inlet of the oxidation readjustment tank 304 is connected to the water outlet of the filter press 2 through a water pipeline. The water outlet of the neutralization precipitation tank 308 is connected to the water inlet of the readjustment tank 4 through a water pipeline. The oxidation tank 304 is also provided with a potassium permanganate adding pipeline 3041. The readjustment precipitation tank 305 is also provided with a first acid liquid adding pipeline 3051. The transition tank 306 is also provided with a second acid liquid adding pipeline 3061. The neutralization precipitation tank 308 is also provided with a liquid alkali adding pipeline 3081. The readjustment precipitation tank 305, the transition tank 306 and the neutralization precipitation tank 308 are all provided with a pH probe 6.

[0065] As preferred, the pretreatment and impurity removal unit 3 comprises a mixed water tank 309, a defluorination tank 310, a neutralization and heavy metal removal tank 311 and a transition oxidation tank 312 arranged in series. The water inlet of the mixed water tank 309 is connected to the water outlet of the filter press 2. The water outlet of the transition oxidation tank 312 is connected to the water inlet of the readjustment tank 4 through a water pipeline. The water inlet of the mixed water tank 309 is also connected to an acidic washing wastewater inlet pipeline 3091. The defluorination tank 310 is also provided with an aluminum sulfate solution adding pipeline 3101. The neutralization and heavy metal removal tank 311 is also provided with a sulfide adding mechanism 3111. The transition oxidation tank 312 is also provided with a sodium hypochlorite adding pipeline 3121. The mixed water tank 309 is also provided with a pH probe 6.

[0066] Example 1

[0067] As Figures 5-6As shown, a system for recovering potassium sulfate and sodium chloride from dust ash smelted by a blast furnace manganese iron includes three-stage countercurrent water washing device 1, filter pressing device 2, pretreatment impurity removal unit 3, readjustment pool 4 and evaporation and salt separation device 5 arranged in series. The ash inlet of the three-stage countercurrent water washing device 1 is connected with a manganese iron ash conveying mechanism 101, and the water inlet is communicated with an industrial water conveying pipeline 102. The readjustment pool 4 is provided with an acid adding pipeline 401, and a pH probe 6 is arranged in the readjustment pool 4. The potassium salt outlet of the evaporation and salt separation device 5 is connected with a potassium salt conveying mechanism 501, and the sodium salt outlet is connected with a sodium salt conveying mechanism 502.

[0068] Example 2

[0069] Example 1 is repeated, except that the pretreatment impurity removal unit 3 includes a mixed salt precipitation pool 301, an oxidation-reduction pool 302 and a sedimentation pool 303 arranged in series. The water inlet of the mixed salt precipitation pool 301 is communicated with the water outlet of the filter pressing device 2 through a water conveying pipeline. The water outlet of the sedimentation pool 303 is communicated with the water inlet of the readjustment pool 4 through a water conveying pipeline. The mixed salt precipitation pool 301 is also communicated with a carbon dioxide gas inlet pipeline 3011. The oxidation-reduction pool 302 is also provided with an oxidizing agent adding mechanism 3021 and a reducing agent adding mechanism 3022. The sedimentation pool 303 is also provided with a dilute sulfuric acid adding pipeline 3031, and a pH probe 6 is arranged in the sedimentation pool 303. The exhaust outlet of the readjustment pool 4 and the exhaust outlet of the sedimentation pool 303 are both communicated with the carbon dioxide gas inlet pipeline 3011 through a gas conveying pipeline.

[0070] Example 3

[0071] Example 1 is repeated, except that the pretreatment impurity removal unit 3 includes an oxidation pool 304, a readjustment sedimentation pool 305, a transition pool 306, an iron-carbon micro-electrolysis reactor 307 and a neutralization sedimentation pool 308 arranged in series. The water inlet of the oxidation readjustment pool 304 is communicated with the water outlet of the filter pressing device 2 through a water conveying pipeline. The water outlet of the neutralization sedimentation pool 308 is communicated with the water inlet of the readjustment pool 4 through a water conveying pipeline. The oxidation pool 304 is also provided with a potassium permanganate adding pipeline 3041. The readjustment sedimentation pool 305 is also provided with a first acid liquid adding pipeline 3051. The transition pool 306 is also provided with a second acid liquid adding pipeline 3061. The neutralization sedimentation pool 308 is also provided with a liquid alkali adding pipeline 3081. The readjustment sedimentation pool 305, the transition pool 306 and the neutralization sedimentation pool 308 are all provided with a pH probe 6.

[0072] Example 4

[0073] Example 1 is repeated, except that the pre-treatment impurity removal unit 3 comprises a water mixing tank 309, a fluoride removal tank 310, a heavy metal removal and neutralization tank 311, and a transition oxidation tank 312 arranged in series. The water inlet of the water mixing tank 309 is connected to the water outlet of the pressure filtration device 2. The water outlet of the transition oxidation tank 312 is connected to the water inlet of the backwashing tank 4 through a water pipeline. The water inlet of the water mixing tank 309 is also connected to an acidic washing wastewater inlet pipeline 3091. The fluoride removal tank 310 is also provided with an aluminum sulfate solution adding pipeline 3101. The heavy metal removal and neutralization tank 311 is also provided with a sulfide adding mechanism 3111. The transition oxidation tank 312 is also provided with a sodium hypochlorite adding pipeline 3121. The water mixing tank 309 is also provided with a pH probe 6.

[0074] Example 5

[0075] A method for recovering potassium sulfate and sodium chloride from blast furnace ferromanganese smelting dust, comprising the following steps:

[0076] 1) Water washing leaching of blast furnace ferromanganese smelting dust is performed to obtain leaching wastewater.

[0077] 2) Pretreatment of the leaching wastewater: 201a) carbon dioxide is introduced into the leaching wastewater to precipitate impurity salts, and after solid-liquid separation, wastewater clear liquid is obtained, part of which is recycled to the water washing section for salt enrichment. 201b) First, a potassium permanganate solution is added to the wastewater clear liquid obtained in 201a) for oxidation treatment. Then a soluble ferrous salt solution is added to the oxidized wastewater for reduction treatment. Finally, acid is added to the reduced wastewater to adjust the wastewater to weak alkaline for precipitation reaction, and pretreated wastewater is obtained after the reaction is completed.

[0078] 3) Acid is added to the pretreated wastewater to adjust the wastewater to neutral, and then high-purity potassium sulfate and sodium chloride are recovered by temperature-variable evaporation desalination.

[0079] Example 6

[0080] A method for recovering potassium sulfate and sodium chloride from blast furnace ferromanganese smelting dust, comprising the following steps:

[0081] 1) Water washing leaching of blast furnace ferromanganese smelting dust is performed to obtain leaching wastewater.

[0082] 2) Pretreatment of the leaching wastewater: 202a) a potassium permanganate solution is added to the leaching wastewater for oxidation treatment. Then acid is added to the oxidized wastewater to adjust the wastewater to weak alkaline for zinc removal by precipitation, and zinc-removed wastewater is obtained after solid-liquid separation.

[0083] 202b) After the zinc removal wastewater obtained in 202a) is adjusted to be acidic by adding acid, iron-carbon micro-electrolysis treatment is performed. Then, after the wastewater after micro-electrolysis is adjusted to be alkaline by adding alkali, precipitation treatment is performed, and after solid-liquid separation, pretreated wastewater is obtained.

[0084] 3) Acid is added to the pretreated wastewater to adjust the wastewater to be neutral, and then high-purity potassium sulfate and sodium chloride are obtained by temperature-variable evaporation desalination recovery.

[0085] Example 7

[0086] A method for recovering potassium sulfate and sodium chloride from blast furnace manganese iron smelting dust removal ash, comprising the following steps:

[0087] 1) The blast furnace manganese iron smelting dust removal ash is water-washed and leached to obtain leaching wastewater.

[0088] 2) Pretreatment of leaching wastewater: 203a) Add acid washing wastewater by activated carbon method to the leaching wastewater to make the mixed wastewater weakly alkaline. Then add aluminum sulfate solution to the mixed wastewater for defluorination treatment. Finally, add sulfide to the defluorinated wastewater for heavy metal removal treatment, and after solid-liquid separation, heavy metal removal and defluorination wastewater is obtained.

[0089] 203b) Add sodium hypochlorite solution to the heavy metal removal and defluorination wastewater obtained in 203a) for oxidation treatment to obtain pretreated wastewater.

[0090] 3) Acid is added to the pretreated wastewater to adjust the wastewater to be neutral, and then high-purity potassium sulfate and sodium chloride are obtained by temperature-variable evaporation desalination recovery.

[0091] Application Example 1

[0092] The blast furnace manganese iron smelting dust removal ash generated when the system described in Example 2 and the method described in Example 5 are used for blast furnace manganese iron smelting can be used to prepare high-purity potassium sulfate and sodium chloride from raw materials. The specific process is as follows:

[0093] The blast furnace manganese iron smelting dust removal ash is water-washed and leached by three-stage water washing with industrial water at a water / ash ratio of 1:6, and then pressure filtration treatment is performed to obtain filter cake (external disposal) and leaching wastewater (pH>11). Then, carbon dioxide is introduced into the obtained leaching wastewater for carbonation reaction treatment for 60 min. Solid-liquid separation is performed to obtain wastewater clear liquid, and 6% of the total wastewater mass, with a mass concentration of 25%, of potassium permanganate solution is added to the wastewater clear liquid, and stirring is performed for oxidation treatment for 40 min. Then, 5% of the total wastewater mass, with a mass concentration of 25%, of ferrous sulfate solution is added to the wastewater after oxidation, and stirring is performed for reduction treatment for 40 min. Then, dilute sulfuric acid is added to the wastewater after reduction treatment to adjust the pH of the wastewater to 8 for precipitation reaction for 30 min, and finally, pretreated wastewater is obtained by solid-liquid separation.

[0094] The pH of the pretreated wastewater is adjusted to 6.5 by adding dilute sulfuric acid to the pretreated wastewater; then the pretreated wastewater with neutral pH is subjected to evaporation and salt separation to obtain high-purity potassium sulfate (purity 95.53%) and sodium chloride (purity 96.87%) respectively. The carbon dioxide produced in the process of adjusting the wastewater to alkaline and the process of adjusting the wastewater to neutral is used for the carbonation reaction of the wastewater. No wastewater and waste gas are discharged in the whole process of the embodiment.

[0095] Application Example 2

[0096] The blast furnace manganese iron smelting dust produced in the process of manganese iron smelting by the blast furnace method is used as raw material to prepare high-purity potassium sulfate and sodium chloride by using the system described in Embodiment 3 and the method described in Embodiment 6. The specific process is as follows:

[0097] The blast furnace manganese iron smelting dust is subjected to three-stage water leaching by using industrial water with a water-cement ratio of 1:6, and then is subjected to pressure filtration treatment to obtain filter cake (external disposal) and leaching wastewater (pH>11). A potassium permanganate solution with a mass concentration of 25% and a total mass of 5.5% of the wastewater is added to the leaching wastewater, and the wastewater is stirred and subjected to oxidation treatment for 40 min. Then dilute sulfuric acid is added to the oxidized wastewater to adjust the pH of the wastewater to 8 for precipitation reaction for 30 min, and finally solid-liquid separation is performed to obtain zinc-removed wastewater. Then dilute sulfuric acid is used to adjust the pH of the zinc-removed wastewater to 3, and the wastewater is transported into an iron-carbon micro-electrolysis reactor for treatment for 45 min; finally, the wastewater after micro-electrolysis is adjusted to pH 9 by using liquid alkali for neutralization and precipitation treatment for 30 min. After solid-liquid separation, pretreated wastewater is obtained.

[0098] The pH of the pretreated wastewater is adjusted to 6.5 by adding dilute sulfuric acid to the pretreated wastewater; then the pretreated wastewater with neutral pH is subjected to evaporation and salt separation to obtain high-purity potassium sulfate (purity 96.27%) and sodium chloride (purity 95.66%) respectively. No wastewater and waste gas are discharged in the whole process of the embodiment.

[0099] Application Example 3

[0100] The blast furnace manganese iron smelting dust produced in the process of manganese iron smelting by the blast furnace method is used as raw material to prepare high-purity potassium sulfate and sodium chloride by using the system described in Embodiment 4 and the method described in Embodiment 7. The specific process is as follows

[0101] The dust of blast furnace manganese iron smelting is washed by water with water-cement ratio of 1:5.5, and then is treated by three-stage water leaching and pressure filtration to obtain filter cake (external disposal) and leaching wastewater (pH>11). The activated carbon method is used to add acid washing wastewater to the leaching wastewater, and the pH of the mixed wastewater is 8. Then, 0.65% of the total wastewater mass and 30% of the mass concentration of aluminum sulfate solution are added to the mixed wastewater for defluorination treatment for 45 min. Then, 0.5% of the total wastewater mass of barium sulfide is added to the defluorinated wastewater for heavy metal removal reaction for 30 min, and heavy metal removal and defluorinated wastewater is obtained by solid-liquid separation. Finally, 0.3% of the total wastewater mass and 1% of the mass concentration of sodium hypochlorite solution are added to the heavy metal removal and defluorinated wastewater for oxidation treatment for 30 min. The pretreated wastewater is obtained after the treatment is completed.

[0102] Dilute sulfuric acid is added to the pretreated wastewater to adjust the pH of the pretreated wastewater to 6.5. Then, the neutralized pretreated wastewater is treated by evaporation and salt separation to obtain high-purity potassium sulfate (purity of 96.07%) and sodium chloride (purity of 94.81%). The whole process of this embodiment does not discharge wastewater and waste gas.

Claims

1. A method for recovering potassium sulfate and sodium chloride from dust collected during blast furnace ferromanganese smelting, characterized in that: The method includes the following steps: 1) The dust from the blast furnace ferromanganese smelting process is washed and leached with water to obtain leaching wastewater; 2) The leachate wastewater is pretreated by one or more of the following methods: oxidation, reduction, electrolysis, salt precipitation, precipitation, flocculation and adsorption, to obtain pretreated wastewater; Step 2) specifically includes the following steps: 201a) Carbon dioxide is introduced into the leachate wastewater to precipitate impurities. After solid-liquid separation, a clear wastewater is obtained, and part of the clear wastewater is recycled to the washing section for salt enrichment. 201b) First, add potassium permanganate solution to the wastewater clear liquid obtained in 201a) for oxidation treatment; then add soluble ferrous salt solution to the oxidized wastewater for reduction treatment; finally, add acid to the reduced wastewater to adjust the wastewater to weak alkalinity for precipitation reaction. After the reaction is completed, pretreated wastewater is obtained. or Step 2) specifically includes the following steps: 202a) Add potassium permanganate solution to the leaching wastewater for oxidation treatment; then add acid to the oxidized wastewater to adjust the wastewater to weak alkalinity for precipitation and zinc removal, and obtain zinc-removed wastewater after solid-liquid separation; 202b) Add acid to the zinc-removed wastewater obtained in 202a) to adjust the wastewater to acidity and then perform iron-carbon micro-electrolysis treatment; then add alkali to the micro-electrolysis wastewater to adjust the wastewater to alkalinity for precipitation treatment, and obtain pretreated wastewater after solid-liquid separation; or Step 2) specifically includes the following steps: 203a) Add activated carbon acid washing wastewater to the leaching wastewater to make the mixed wastewater weakly alkaline; then add aluminum sulfate solution to the mixed wastewater for defluorination treatment; finally add sulfide to the defluorinated wastewater for gravimetric removal treatment, and obtain gravimetric defluorinated wastewater after solid-liquid separation; 203b) Add sodium hypochlorite solution to the gravimetric defluorinated wastewater obtained in 203a) for oxidation treatment to obtain pretreated wastewater; 3) Add acid to the pretreated wastewater to adjust it to neutral, and then recover high-purity potassium sulfate and sodium chloride by temperature-variable evaporation.

2. The method according to claim 1, characterized in that: In step 201b), the soluble ferrous salt is ferrous sulfate and / or ferrous chloride; and / or In step 201b), the addition of acid to adjust the wastewater to a weakly alkaline state means adjusting the pH of the wastewater to 7.5-9 using sulfuric acid.

3. The method according to claim 2, characterized in that: In step 201b), the addition of acid to adjust the wastewater to a weakly alkaline state means adjusting the pH of the wastewater to 8-8.5 using dilute sulfuric acid.

4. The method according to claim 1, characterized in that: In step 201b), the mass concentration of the potassium permanganate solution is 15-30%; the amount of potassium permanganate solution used is 2-7% of the total mass of wastewater; and the oxidation treatment time is 5-40 min.

5. The method according to claim 4, characterized in that: In step 201b), the mass concentration of the potassium permanganate solution is 20-25%; the amount of potassium permanganate solution used is 3-5% of the total mass of wastewater; and the oxidation treatment time is 10-30 min.

6. The method according to claim 1, characterized in that: In step 201b), the mass concentration of the soluble ferrous salt solution is 10-30%; the amount of soluble ferrous salt solution used is 3-8% of the total mass of wastewater; and the reduction treatment time is 5-40 min.

7. The method according to claim 6, characterized in that: In step 201b), the mass concentration of the soluble ferrous salt solution is 15-25%; the amount of soluble ferrous salt solution used is 4-6% of the total mass of wastewater; and the reduction treatment time is 10-30 min.

8. The method according to claim 1, characterized in that: In step 202a), the addition of acid to adjust the wastewater to a weakly alkaline state means adjusting the pH of the wastewater to 7.5-9 using sulfuric acid; and / or In step 202b), the addition of acid to adjust the wastewater to an acidic level is achieved by using sulfuric acid to adjust the pH of the wastewater to 1-4; and / or In step 202b), the addition of alkali to adjust the wastewater to alkalinity means adjusting the pH of the wastewater to 8-10 using sodium hydroxide solution.

9. The method according to claim 8, characterized in that: In step 202a), the addition of acid to adjust the wastewater to a weakly alkaline state means adjusting the pH of the wastewater to 8-8.5 using dilute sulfuric acid; and / or In step 202b), the addition of acid to adjust the wastewater to acidity involves using dilute sulfuric acid to adjust the pH of the wastewater to 2-3; and / or In step 202b), the addition of alkali to adjust the wastewater to alkalinity means adjusting the pH of the wastewater to 8.5-9.5 using sodium hydroxide solution.

10. The method according to claim 1, characterized in that: In step 202a), the mass concentration of the potassium permanganate solution is 15-30%; the amount of potassium permanganate solution used is 2-7% of the total mass of the wastewater; the oxidation treatment time is 5-40 min; and / or In step 202b), the iron-carbon micro-electrolysis treatment time is not less than 20 min; the precipitation treatment time is not less than 10 min.

11. The method according to claim 10, characterized in that: In step 202a), the mass concentration of the potassium permanganate solution is 20-25%; the amount of potassium permanganate solution used is 3-5% of the total mass of the wastewater; the oxidation treatment time is 10-30 min; and / or In step 202b), the iron-carbon micro-electrolysis treatment time is 30-60 min; the precipitation treatment time is 15-30 min.

12. The method according to claim 1, characterized in that: In step 203a), the pH of the mixed wastewater is 7.5-9; and / or In step 203a), the mass concentration of the aluminum sulfate solution is 20-35%; the amount of aluminum sulfate solution added is 0.1-0.8% of the total mass of the wastewater; the defluorination treatment time is 0.3-2 hours; and / or In step 203a), the sulfide is one or more of barium sulfide, sodium sulfide, and hydrogen sulfide, and its dosage is 0.2-0.8% of the wastewater mass; and / or In step 203b), the sodium hypochlorite solution has a mass concentration of 0.5-5% and is added in an amount of 0.01-3% of the wastewater mass.

13. The method according to claim 12, characterized in that: In step 203a), the pH of the mixed wastewater is 8-8.5; and / or In step 203a), the mass concentration of the aluminum sulfate solution is 25-30%; the amount of aluminum sulfate solution added is 0.3-0.6% of the total mass of the wastewater; the defluorination treatment time is 0.5-1.5 hours; and / or In step 203a), the amount of sulfide added is 0.3-0.5% of the wastewater mass; and / or In step 203b), the sodium hypochlorite solution has a mass concentration of 0.8-4% and is added in an amount of 0.05-2% of the wastewater mass.

14. The method according to any one of claims 1-13, characterized in that: In step 1), the dust from blast furnace ferromanganese smelting is dust containing iron, manganese, fluorine, alkali metals, carbonate, and sulfite generated during blast furnace ferromanganese smelting; the water washing is a three-stage countercurrent water washing process, with a water-to-ash ratio of 1-7:1; and / or In step 3), adding acid to adjust the wastewater to neutral means adding sulfuric acid to adjust the pH of the wastewater to 6-7.

15. The method according to claim 14, characterized in that: In step 1), the water-to-cement ratio during washing is 2-5:1; and / or In step 3), the addition of acid to adjust the wastewater to neutral means adding dilute sulfuric acid to adjust the pH of the wastewater to 6.5-7.

16. A system for use in the method of any one of claims 1-15, characterized in that: The system includes a three-stage countercurrent water washing device (1), a filter press (2), a pretreatment and impurity removal unit (3), a return tank (4), and an evaporation and salt separation device (5) arranged in series. The ash inlet of the three-stage countercurrent water washing device (1) is connected to a manganese iron ash conveying mechanism (101), and its water inlet is connected to an industrial water conveying pipeline (102). The return tank (4) is equipped with an acid addition pipeline (401), and a pH probe (6) is installed inside it. The potassium salt outlet of the evaporation and salt separation device (5) is connected to a potassium salt conveying mechanism (501), and its sodium salt outlet is connected to a sodium salt conveying mechanism (502). The pretreatment and impurity removal unit (3) includes a mixed salt precipitation tank (301), an oxidation-reduction tank (302), and a sedimentation tank (303) arranged in series. The inlet of the mixed salt precipitation tank (301) is connected to the outlet of the filter press (2) through a water supply pipe. The outlet of the sedimentation tank (303) is connected to the inlet of the return tank (4) through a water supply pipe. A carbon dioxide inlet pipe (3011) is also connected inside the mixed salt precipitation tank (301). An oxidant addition mechanism (3021) and a reducing agent addition mechanism (3022) are also provided on the oxidation-reduction tank (302). A dilute sulfuric acid addition pipe (3031) is also provided on the sedimentation tank (303), and a pH probe (6) is installed inside it. The exhaust ports of the return tank (4) and the sedimentation tank (303) are both connected to the carbon dioxide inlet pipe (3011) through a gas supply pipe. The pretreatment and impurity removal unit (3) includes an oxidation tank (304), a settling tank (305), a transition tank (306), an iron-carbon micro-electrolysis reactor (307), and a neutralization sedimentation tank (308) arranged in series. The inlet of the oxidation tank (304) is connected to the outlet of the filter press (2) via a water supply pipe. The outlet of the neutralization sedimentation tank (308) is connected to the inlet of the settling tank (4) via a water supply pipe. The oxidation tank (304) also has... A potassium permanganate addition pipe (3041) is provided; a first acid addition pipe (3051) is also provided on the settling tank (305); a second acid addition pipe (3061) is also provided on the transition tank (306); a liquid alkali addition pipe (3081) is also provided on the neutralization sedimentation tank (308); pH probes (6) are also provided in the settling tank (305), the transition tank (306), and the neutralization sedimentation tank (308); or The pretreatment and impurity removal unit (3) includes a mixing tank (309), a defluorination tank (310), a neutralization and deweighting tank (311), and a transition oxidation tank (312) arranged in series. The inlet of the mixing tank (309) is connected to the outlet of the filter press (2). The outlet of the transition oxidation tank (312) is connected to the inlet of the return tank (4) through a water supply pipe. The inlet of the mixing tank (309) is also connected to an acidic washing wastewater inlet pipe (3091). An aluminum sulfate solution addition pipe (3101) is also provided on the defluorination tank (310). A sulfide addition mechanism (3111) is also provided on the neutralization and deweighting tank (311). A sodium hypochlorite addition pipe (3121) is also provided on the transition oxidation tank (312). A pH probe (6) is also provided in the mixing tank (309).

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