A process for resource utilization of waste acid from sulfuric acid pickling

Abstract

The invention discloses a process for resource utilization of waste acid from sulfuric acid pickling, wherein the waste acid from pickling is pretreated, and particles are removed by filtration; the pretreated water is lifted to an acid-resistant nanofiltration system, and the concentrated waste acid on the concentrated water side flows through a filter column; in a filter column with a height-to-diameter ratio of 5 to 8, three layers of particles are arranged from top to bottom according to specific gravity from small to large, and the middle layer is 1 to 5 mm blast furnace slag particles; after the blast furnace slag is washed with pure water, the sodium hydroxide solution and the blast furnace slag are reacted, and the reaction liquid is removed and filtered to obtain liquid sodium silicate; the pH is adjusted to 3 to 5 to form a polysodium silicate solution; a mixed solution of ferric sulfate, magnesium sulfate and aluminum sulfate is slowly added to the polysodium silicate solution, reacted, placed, and matured to form a polysilicate ferromagnesium-aluminum coagulant. The concentrated solution produced by nanofiltration and blast furnace slag are used to produce the polysilicate ferromagnesium-aluminum coagulant, thereby realizing the resource utilization of waste acid from sulfuric acid pickling and blast furnace slag, and no waste is generated.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a process for resource utilization of waste acid from sulfuric acid pickling. Background Art

[0002] Pickling is one of the indispensable processes in cold rolling mills. In the process of production, cold rolled steel needs to be pickled to remove the iron oxide scale on the surface of the steel. According to the process requirements, pickling can be hydrochloric acid pickling or sulfuric acid pickling.

[0003] Hydrochloric acid pickling is widely used. There is a relatively mature acid regeneration process for the waste acid discharged during the pickling process. The waste acid is recycled after being treated by the acid regeneration process. Sulfuric acid pickling is mainly used in electrogalvanizing, electrotinning, silicon steel hot stretching and leveling units. Compared with the hydrochloric acid pickling process, the amount of waste acid discharged is relatively small. Most sulfuric acid does not have an acid regeneration process, and the high-concentration waste acid discharged is directly transported to the wastewater treatment station for treatment.

[0004] The treatment processes for acid wastewater from cold rolling mills are basically the same. Figure 1 The acidic wastewater from different units first enters the regulating tank for water quality balance, and aeration is performed in the regulating tank to prevent precipitation. At the same time, some Fe 2+ Oxidized to Fe 3+ ; Then it enters the primary and secondary neutralization tanks, and lime is added to adjust the pH roughly and finely. The pH of the secondary neutralization tank is controlled at around 8-9. Aeration is continued in the neutralization tank to remove the remaining Fe 2+ Oxidized to Fe 3+ ; After neutralization, it enters the clarification tank for mud-water separation. The effluent from the clarification tank enters the final neutralization tank for fine-tuning by adding acid or alkali according to the actual pH, and finally is discharged after filtration; the precipitated sludge produced in the clarification tank enters the concentration tank for concentration and then is dehydrated by the sludge dewatering machine. The dehydrated sludge is transported out for treatment, and the supernatant produced by the concentration tank and the sludge dewatering machine is returned to the regulating tank for further treatment.

[0005] Liu Qin and others used sulfuric acid pickling waste liquid to prepare polyferric sulfate chloride. Add excess scrap iron and a certain amount of hydrochloric acid waste liquid to a certain amount of sulfuric acid pickling waste liquid, heat in a 70°C water bath for 3 hours, and filter to obtain a green transparent liquid. The pH value of the filtrate was measured to be between 3.2 and 4.0, and the iron content was 90 to 130 g / L. Add ferrous sulfate to the filtrate to adjust its iron ion concentration and the ratio of sulfate and chloride; add stabilizer and waste hydrochloric acid (to adjust acidity); heat to about 50°C and stir to fully dissolve ferrous sulfate and stabilizer. Add oxidant in batches within 0.5 hours, and then react for 1 hour to obtain reddish-brown composite polyferric sulfate chloride.

[0006] Wan Jinbao and others from Nanchang University used a single tube packing rising film concentration crystallization method to treat sulfuric acid pickling wastewater. Waste acid content: H2SO4 is 5% to 7%, FeSO4 is 200 to 230g / L; waste acid quantity: 7000m 3 / a; inlet and outlet temperatures of frozen brine: -15~-10℃; content of concentrated liquid: H2SO4 is 7.24%, FeSO4 is 26.9%; content of crystallization mother liquor: H2SO4 is 12.5%, FeSO4 is 6.75%; content of regenerated acid: H2SO4 is 12%~15%, FeSO4 is less than or equal to 6.75%; content of ferrous sulfate: FeSO4·7H2O is greater than or equal to 95%.

[0007] Zhang Tao and others used the diffusion dialysis process to recover the waste sulfuric acid produced in the copper smelting process. Generally, the flow ratio of the waste acid raw liquid to the water flow was controlled to be 1:1. After the diffusion dialysis process, 80-90% of the sulfuric acid can be recycled, and 10-20% of the sulfuric acid still remains in the waste liquid, which is generally neutralized. After the process is used, the amount of waste liquid to be treated does not decrease, but the concentration is reduced; the concentration of the recovered sulfuric acid is lower than that of the raw liquid, and it needs to be mixed with new acid before recycling. Summary of the invention

[0008] Therefore, the technical problem to be solved by the present invention is to provide a method for treating sulfuric acid pickling waste liquid and provide a way to utilize it as a resource.

[0009] The technical solution of the present invention is a process for resource utilization of waste acid from sulfuric acid pickling, comprising the following steps:

[0010] (1) The pickling waste liquid discharged from the cold rolling sulfuric acid pickling unit is lifted to the pretreatment filtration system to filter and remove particulate matter in the pickling waste acid; the facilities and pipelines in contact with the pickling waste liquid in the filtration system are made of acid-resistant materials; the pretreated produced water enters the pretreatment produced water pool;

[0011] (2) The pre-treated water is lifted to the acid-resistant nanofiltration system, and the flux of the nanofiltration membrane is controlled at 5-25L / m 2 ·h, the recovery rate is controlled at 50-95%; SO4 in the produced water side after nanofiltration process 2- The concentration is 3-10%, the TFe concentration is 0.1-1g / L, and it can be returned to the pickling unit for recycling; the concentrated water side concentrates the waste acid SO4 2- Concentration 3-10%, TFe concentration 10-30 g / L;

[0012] (3) The concentrated waste acid on the concentrated water side flows through a filter column; in a filter column with a height-to-diameter ratio of 5 to 8, three layers of particles are arranged from top to bottom in descending order of specific gravity, with the middle layer being 1 to 5 mm blast furnace slag particles; the height of the upper and lower particles is 5 to 10 cm, and the particle diameter is 1 to 3 cm;

[0013] (4) Continue filtering the water from the filter column, add aluminum sulfate to the filtrate, control the molar ratio of (Fe+Mg):Al to be 1:1-1:2, and form a mixed solution of iron sulfate, magnesium sulfate and aluminum sulfate;

[0014] (5) washing the blast furnace slag with pure water and then taking it out from the filter column, mixing the sodium hydroxide solution and the blast furnace slag in a ratio of 1:0.5 to 1:2, adding the mixture into a reaction kettle, controlling the pressure in the reaction kettle at 0.8 to 1.2 MPa, heating the mixture with steam, removing the reaction liquid after the reaction is completed, filtering out the unreacted blast furnace slag to obtain liquid sodium silicate; adjusting the pH to 3 to 5 to form a polysodium silicate solution;

[0015] (6) Slowly add the mixed solution of ferric sulfate, magnesium sulfate and aluminum sulfate into the polysodium silicate solution, control the reaction temperature at 45-55° C., react for 1-3 hours, and then place it at room temperature for aging for 12-24 hours to form a polysilicate iron magnesium aluminum coagulant.

[0016] The quality of waste acid water discharged from the cold rolling sulfuric acid pickling unit is: SO4 2- 3~10%, TFe 1~10g / L, pH 0~0.5. The pickling waste liquid discharged from the cold rolling sulfuric acid pickling unit is first discharged into the waste acid pit, and then the waste acid is lifted to the pretreatment filtration system by a primary lifting pump to remove a small amount of particulate matter in the pickling waste acid to reduce the impact on subsequent processes.

[0017] According to a process for recycling waste acid from sulfuric acid pickling of the present invention, preferably, the filtration in step (1) adopts an inorganic ceramic membrane or a sintered organic membrane. The membrane pore size ranges from 20 to 200 nm. The circulation volume is 5 to 30 times the processing volume; the membrane flux is controlled at 50 to 300 L / m 2 ·h, to ensure that the effluent silt density index (SDI) is less than 5. Since the waste acid is highly acidic, the filtration facilities and pipelines used need to be resistant to acid corrosion, and inorganic ceramic membranes or sintered organic membranes are preferably used.

[0018] According to a process for recycling waste acid from sulfuric acid pickling of the present invention, preferably, the filtration described in step (1) is cross-flow filtration. Cross-flow filtration is a preferred filtration method, and other filtration methods may also be used. In cross-flow filtration, the feed liquid flows parallel to the membrane surface, and in dead-end filtration, the feed liquid flows perpendicular to the membrane; in cross-flow filtration, the shear force generated when the feed liquid flows through the membrane surface carries away the particles retained on the membrane surface, which can reduce membrane pollution.

[0019] According to the process for recycling waste acid from sulfuric acid pickling of the present invention, preferably, the nanofiltration system in step (2) uses an acid-resistant nanofiltration membrane, which can operate stably for a long time under the condition of an acid concentration of less than 20%. The nanofiltration membrane only allows monovalent H + Passing through, into the produced water side, divalent and trivalent Fe 2+ , Fe 3+ It cannot pass through and is retained on the concentrated water side; in order to maintain charge balance, some divalent SO4 2- It will pass through the nanofiltration membrane and enter the water production side.

[0020] According to a process for resource utilization of waste acid from sulfuric acid pickling of the present invention, preferably, the upper particles in step (3) are solid PVC balls, and the lower particles are pebbles. The solid PVC balls, blast furnace slag particles, and pebbles are distributed in sequence from top to bottom. The specific gravity of pebbles is greater than that of blast furnace slag, and they play a supporting role to prevent blast furnace slag from blocking the water inlet. The specific gravity of PVC balls is less than that of blast furnace slag, and they prevent blast furnace slag from being lost. Pebbles and PVC balls can also be replaced by other materials with similar properties. The particle size of the upper and lower layer particles is greater than that of blast furnace slag. Preferably, the particle size of the upper layer particles is 1-3 cm, and the particle size of the lower layer particles is 1-3 cm. The upper and lower layer particles serve as support layers, and except for the upper and lower support layers of 5 to 10 cm, the rest are blast furnace slag.

[0021] The composition of blast furnace slag is as follows:

[0022] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO MnO <![CDATA[Fe2O3]]> S content(%) 32～49 32～41 6～17 2～13 0.1～4 0.15～4 0.2～2

[0023] According to a process for resource utilization of waste acid from sulfuric acid pickling of the present invention, preferably, the filter column in step (3) can be selected to be one or more stages.

[0024] According to a process for resource utilization of waste acid from sulfuric acid pickling of the present invention, preferably, the reaction time in step (5) is 5 to 10 hours.

[0025] According to a process for resource utilization of waste acid from sulfuric acid pickling of the present invention, preferably, the pH value is adjusted in step (5) by using sulfuric acid produced by nanofiltration.

[0026] According to a process for recycling waste acid from sulfuric acid pickling of the present invention, preferably, in step (6), the molar ratio of (Fe+Mg) to Si is controlled to be 1:2-3. Si is produced by the alkali dissolution process of blast furnace slag, and the molar ratio of (Fe+Mg) to Si is calculated according to the valence state of the ions.

[0027] According to a process for resource utilization of waste acid from sulfuric acid pickling of the present invention, preferably, in step (3), concentrated waste acid is input from the bottom of the filter column and flows out from the top, with a flow rate of 0.1 to 1 BV / h. The hydrogen ions in the concentrated waste acid can dissolve components such as CaO, MgO, and Al2O3 in blast furnace slag into the waste acid to form CaSO4, MgSO4, Al2(SO4)3, etc., while consuming hydrogen ions. The filter column can be selected to be one or more stages, and the final effluent pH is 5 to 7.

[0028] CaSO4 is dissolved at a low pH. As the dissolution reaction continues, the pH value gradually increases, the solubility of CaSO4 decreases, and precipitation is formed. Therefore, the final effluent from the filter column contains suspended matter and needs to be filtered. The filtration can be done by multi-media filtration, microfiltration or ultrafiltration to filter out particles of 5 to 50 μm.

[0029] The Fe content in the filtered water is 10-30 g / L, and the Al and Mg contents are related to the Al and Mg contents in the blast furnace slag, which are generally 2-10 g / L and 0.5-4 g / L respectively.

[0030] The SiO2 in the blast furnace slag is insoluble in acid and still exists in the blast furnace slag. It is rinsed with pure water, and then the blast furnace slag after the waste acid is filtered out is taken out from the filter column.

[0031] More preferably, solid sodium hydroxide and pure water are dissolved in a ratio of 1:1 to 1:2 to prepare the sodium hydroxide solution.

[0032] Beneficial effects:

[0033] The present invention provides a process for recycling waste acid from sulfuric acid pickling. After being treated by the invention, nanofiltration and the acid produced can be returned to the unit for recycling; the concentrated liquid produced by nanofiltration and blast furnace slag are used to produce polysilicate aluminum-magnesium-iron coagulant, realizing the recycling of waste acid from sulfuric acid pickling and blast furnace slag without generating waste. The invention has both economic and environmental effects, and has good social and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The invention is a process flow for treating acidic wastewater in the prior art.

[0035] Figure 2 The present invention discloses a process flow chart for resource utilization of waste acid from sulfuric acid pickling. DETAILED DESCRIPTION

[0036] Example 1

[0037] The quality of waste acid water discharged from the cold rolling sulfuric acid pickling unit is: SO4 2- 6%, TFe 2 g / L, pH 0.25.

[0038] Sintered organic membrane is used, the membrane pore size is 100nm, cross-flow filtration is used for filtration, the circulation volume is 20 times the processing volume, and the membrane flux is controlled at 200L / m 2 h, effluent silt density index (SDI) 2.6. The pretreated produced water enters the acid-resistant nanofiltration system. The flux of the nanofiltration membrane is 15L / m 2 ·h, the recovery rate is controlled at 90%. SO4 in the produced water after nanofiltration process 2- The concentration is 5.8%, the TFe concentration is 0.2g / L, which can be returned to the pickling unit for recycling; the concentrated water side concentrates the waste acid SO4 2- Concentration 6.1%, TFe concentration 18g / L.

[0039] Screen the blast furnace slag particles with a particle size of 1 to 5 mm and fill them into a column with a height-to-diameter ratio of 6. Fill the bottom of the column with 8 cm pebbles with a particle size of 1 to 3 cm; fill the top of the column with 8 cm PVC solid balls with a particle size of 1 to 3 cm. The composition of blast furnace slag is as follows:

[0040] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO MnO <![CDATA[Fe2O3]]> S content(%) 35 38 15 8 0.2 1.1 1.2

[0041] The concentrated waste acid is input from the bottom of the blast furnace slag column and flows out from the top at a flow rate of 0.2BV / h. The filtration is two-stage series, and the final effluent pH is 5.0. The suspended particles are removed by filtration.

[0042] The content of Fe in the filtered water is 18g / L, and the contents of Al and Mg are 7g / L and 2.5g / L respectively. Aluminum sulfate is added to the filtrate, and the molar ratio of (Fe+Mg):Al is controlled to be 1:1 to form a mixed solution of iron sulfate, magnesium sulfate and aluminum sulfate.

[0043] The blast furnace slag after the waste acid is filtered is taken out from the filter column. Solid sodium hydroxide and pure water are dissolved in a ratio of 1:1, and then sodium hydroxide and blast furnace slag are mixed in a ratio of 1:1 and added to the reactor. The pressure in the reactor is controlled at 1Mpa, and steam is used for heating. The reaction time is 8h. After the reaction is completed, the reaction liquid is removed, and the liquid sodium silicate is obtained after filtering out the unreacted blast furnace slag. The pH is adjusted to 4 with sulfuric acid produced by nanofiltration to form a polysodium silicate solution.

[0044] The molar ratio of (Fe+Mg) to Si was controlled to be 1:2, and the mixture of ferric sulfate, magnesium sulfate and aluminum sulfate was slowly added to the polysodium silicate solution. The reaction temperature was controlled at 50°C and the reaction was carried out for 2 hours. Then, the mixture was left to mature at room temperature for 15 hours to form a polysodium silicate coagulant.

[0045] Example 2

[0046] The quality of waste acid water discharged from the cold rolling sulfuric acid pickling unit is: SO42- 8%, TFe 10 g / L, pH 0.14.

[0047] Sintered organic membrane is used, the membrane pore size is 100nm, cross-flow filtration is used, the circulation volume is 5 times the processing volume, and the membrane flux is controlled at 50L / m 2 h, effluent silt density index (SDI) 1.5. The pretreated produced water enters the acid-resistant nanofiltration system. The flux of the nanofiltration membrane is 25L / m 2 ·h, the recovery rate is controlled at 50%. SO4 in the produced water after nanofiltration process 2- The concentration is 7.9%, the TFe concentration is 0.3g / L, which can be returned to the pickling unit for recycling; the concentrated water side concentrates the waste acid SO4 2- Concentration 8.3%, TFe concentration 19.3g / L.

[0048] Screen the blast furnace slag particles with a particle size of 1 to 5 mm and fill them into a column with a height-to-diameter ratio of 6. Fill the bottom of the column with 8 cm pebbles with a particle size of 1 to 3 cm; fill the top of the column with 8 cm PVC solid balls with a particle size of 1 to 3 cm. The composition of blast furnace slag is as follows:

[0049] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO MnO <![CDATA[Fe2O3]]> S content(%) 35 38 15 8 0.2 1.1 1.2

[0050] The concentrated waste acid is input from the bottom of the blast furnace slag column and flows out from the top at a flow rate of 0.5 BV / h. The filtration is five-stage series, and the final effluent pH is 5.2. The suspended particles are removed by filtration.

[0051] The content of Fe in the filtered water is 19.3g / L, and the contents of Al and Mg are 5.2g / L and 3.1g / L respectively. Aluminum sulfate is added to the filtrate, and the molar ratio of (Fe+Mg):Al is controlled to be 1:1.5 to form a mixed solution of iron sulfate, magnesium sulfate and aluminum sulfate.

[0052] The blast furnace slag after the waste acid is filtered is taken out from the filter column. Solid sodium hydroxide and pure water are dissolved in a ratio of 1:1.5, and then sodium hydroxide and blast furnace slag are mixed in a ratio of 1:0.5 and added to the reactor. The pressure in the reactor is controlled at 0.8Mpa, and steam is used for heating. The reaction time is 10h. After the reaction is completed, the reaction liquid is removed, and the unreacted blast furnace slag is filtered out to obtain liquid sodium silicate. The pH is adjusted to 3 with sulfuric acid produced by nanofiltration to form a polysodium silicate solution.

[0053] The molar ratio of (Fe+Mg) to Si was controlled to be 1:2.5, and the mixed solution of ferric sulfate, magnesium sulfate and aluminum sulfate was slowly added to the polysodium silicate solution. The reaction temperature was controlled at 45°C and the reaction was carried out for 3 hours. Then, the mixture was left to mature at room temperature for 12 hours to form a polysilicate iron magnesium aluminum coagulant.

[0054] Example 3

[0055] The quality of waste acid water discharged from the cold rolling sulfuric acid pickling unit is: SO4 2- 5%, TFe 1.6g / L, pH 0.0.3.

[0056] Sintered organic membrane is used, the membrane pore size is 100nm, cross-flow filtration is used for filtration, the circulation volume is 30 times the processing volume, and the membrane flux is controlled at 300L / m 2 h, effluent silt density index (SDI) 3.2. The pre-treated produced water enters the acid-resistant nanofiltration system. The flux of the nanofiltration membrane is 5L / m 2 ·h, the recovery rate is controlled at 95%. After the nanofiltration process, SO4 2- The concentration is 4.5%, the TFe concentration is 0.28g / L, which can be returned to the pickling unit for recycling; the concentrated water side concentrates the waste acid SO4 2- Concentration 6.0%, TFe concentration 28.9g / L.

[0057] Screen the blast furnace slag particles with a particle size of 1 to 5 mm and fill them into a column with a height-to-diameter ratio of 6. Fill the bottom of the column with 8 cm pebbles with a particle size of 1 to 3 cm; fill the top of the column with 8 cm PVC solid balls with a particle size of 1 to 3 cm. The composition of blast furnace slag is as follows:

[0058] Element CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> MgO MnO <![CDATA[Fe2O3]]> S content(%) 35 38 15 8 0.2 1.1 1.2

[0059] The concentrated waste acid is input from the bottom of the blast furnace slag column and flows out from the top at a flow rate of 0.3BV / h. The filtration is four-stage series, and the final effluent pH is 5.8. The suspended particles are removed by filtration.

[0060] The content of Fe in the filtered water is 28.9 g / L, and the contents of Al and Mg are 6.2 g / L and 3.4 g / L respectively. Aluminum sulfate is added to the filtrate, and the molar ratio of (Fe+Mg):Al is controlled to be 1:2 to form a mixed solution of iron sulfate, magnesium sulfate and aluminum sulfate.

[0061] The blast furnace slag after the waste acid is filtered is taken out from the filter column. Solid sodium hydroxide and pure water are dissolved in a ratio of 1:2, and then sodium hydroxide and blast furnace slag are mixed in a ratio of 1:2 and added to the reactor. The pressure in the reactor is controlled at 1.2Mpa, and steam is used for heating. The reaction time is 5h. After the reaction is completed, the reaction liquid is removed, and the liquid sodium silicate is obtained after filtering out the unreacted blast furnace slag. The pH is adjusted to 5 with sulfuric acid produced by nanofiltration to form a polysodium silicate solution.

[0062] The molar ratio of (Fe+Mg) to Si was controlled to be 1:3, and the mixture of ferric sulfate, magnesium sulfate and aluminum sulfate was slowly added to the polysodium silicate solution. The reaction temperature was controlled at 55°C, and the reaction was carried out for 1 hour. Then, the mixture was left to mature at room temperature for 24 hours to form a polysilicate iron magnesium aluminum coagulant.

Claims

1. A process for resource utilization of waste acid from sulfuric acid pickling, characterized in that: The steps include: (1) The pickling waste liquid discharged from the cold rolling sulfuric acid pickling unit is lifted to the pretreatment filtration system to filter and remove particulate matter in the pickling waste acid; the facilities and pipelines in the filtration system that are in contact with the pickling waste liquid are made of acid-resistant materials; The pretreated produced water enters the pretreated produced water pool; (2) The pre-treated water is lifted to the acid-resistant nanofiltration system, and the flux of the nanofiltration membrane is controlled at 5-25L / m 2 ·h, the recovery rate is controlled at 50-95%; SO4 in the produced water side after nanofiltration process 2- Concentration 3-10%, TFe concentration 0.1-1g / L; concentrated waste acid SO4 on the concentrated water side 2- Concentration 3-10%, TFe concentration 10-30 g / L; (3) The concentrated waste acid on the concentrated water side flows through a filter column; in a filter column with a height-to-diameter ratio of 5 to 8, three layers of particles are arranged from top to bottom in descending order of specific gravity, with the middle layer being 1 to 5 mm blast furnace slag particles; the height of the upper and lower particles is 5 to 10 cm, and the particle diameter is 1 to 3 cm; (4) Continue filtering the water from the filter column, add aluminum sulfate to the filtrate, control the molar ratio of (Fe+Mg):Al to be 1:1-1:2, and form a mixed solution of iron sulfate, magnesium sulfate and aluminum sulfate; (5) washing the blast furnace slag with pure water and then taking it out from the filter column, mixing the sodium hydroxide solution and the blast furnace slag in a ratio of 1:0.5 to 1:2, adding the mixture into a reaction kettle, controlling the pressure in the reaction kettle at 0.8 to 1.2 MPa, heating the mixture with steam, removing the reaction liquid after the reaction is completed, filtering out the unreacted blast furnace slag to obtain liquid sodium silicate; adjusting the pH to 3 to 5 to form a polysodium silicate solution; (6) Slowly add the mixed solution of ferric sulfate, magnesium sulfate and aluminum sulfate into the polysodium silicate solution, control the reaction temperature at 45-55° C., react for 1-3 hours, and then place it at room temperature for aging for 12-24 hours to form a polysilicate iron magnesium aluminum coagulant.

2. A process for resource utilization of waste acid from sulfuric acid pickling according to claim 1, characterized in that: The filtration in step (1) uses an inorganic ceramic membrane or a sintered organic membrane.

3. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: The filtration in step (1) is cross-flow filtration.

4. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: The nanofiltration system in step (2) uses an acid-resistant nanofiltration membrane and can operate stably for a long time under acid concentration conditions within 20%.

5. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: The upper layer particles in step (3) are PVC solid balls, and the lower layer particles are pebbles.

6. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: The filtration column in step (3) can be selected to be single-stage or multi-stage.

7. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: The reaction time of step (5) is 5 to 10 hours.

8. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: In step (5), the pH value is adjusted using sulfuric acid produced by nanofiltration.

9. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: In step (6), the molar ratio of (Fe+Mg) to Si is controlled to be 1:2-3.

10. A process for recycling waste acid from sulfuric acid pickling according to claim 1, characterized in that: In step (3), the concentrated waste acid is input from the bottom of the filter column and flows out from the top at a flow rate of 0.1 to 1 BV / h.

Images