Preparation method of modified micro-sand and hardening, TOC removal and phosphorus removal treatment method for chemical wastewater

Abstract

The application discloses a modified micro-sand preparation method and a chemical wastewater hardness reduction, TOC removal and phosphorus removal treatment method. The preparation raw materials of the modified micro-sand include fine sand, coal cinder fine material, cerium oxide and zero-valent nano-iron. The modified micro-sand has the advantages of high specific gravity, strong adsorption performance, organic matter micro-electrolysis removal, recycling and high catalytic activity under acidic and alkaline conditions. The chemical wastewater hardness reduction, TOC removal and phosphorus removal treatment method has the synergistic ability of TOC removal, hardness reduction and TP removal, is simple to operate, low in operation cost and free of secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of chemical wastewater treatment technology, specifically relating to a loading flocculant and a precipitation process for reducing hardness, removing TOC and phosphorus in chemical wastewater. Background Technology

[0002] Wastewater coagulation and sedimentation technology is mainly used to reduce hardness, such as hardness removal in circulating water effluent and gasified ash water. Currently, TOC removal technologies for wastewater mainly include oxidation processes, such as hydrogen peroxide oxidation and ozone oxidation, as well as combined processes; adsorption processes, such as activated carbon adsorption and resin adsorption; and biochemical processes, such as activated sludge processes and biofilter processes. Phosphorus removal processes mainly include biological phosphorus removal and chemical phosphorus removal. Conventional high-density sedimentation tanks have advantages over traditional coagulation and sedimentation, such as high settling efficiency, stable effluent, and small footprint. Microsand flocculation sedimentation processes typically involve adding sea sand or a high-density flocculant, or using magnetic carriers and magnetic separation technology for recycling. However, synergistic processes that reduce hardness, remove TOC, and remove phosphorus are currently almost nonexistent in the market. The challenge lies in using modified microsand with good separation effect, excellent adsorption performance, and the ability to form Fe-C-CeO3 micro-batteries with multi-valent redox interactions to load the flocculation sedimentation process, while simultaneously achieving the above effects through the screening and compounding of coagulants and flocculants.

[0003] CeO2, as a transition metal oxide, is characterized by abundant oxygen vacancy defects and Ce... 3+ and Ce 4+ Its ability to flexibly transform between states makes it a hot material in the field of catalysis. However, its poor electrical conductivity largely limits the development of single-component CeO2 in electrocatalysis.

[0004] Currently invented flocculants primarily function to increase floc settling properties. This is achieved through co-settling of the flocs with the heavier flocculant, increasing settling velocity and improving hydraulic loading, as exemplified by CN103232102A. For catalysts with organic matter degradation capabilities, conventional methods involve loading metals such as Fe / Ce / Cu, which catalyze the production of hydroxyl radicals from hydrogen peroxide to break down organic compounds, as exemplified by CN113083364A. Some flocculants are recyclable; by adding magnetic materials such as iron(III) oxide to their carriers, they achieve recycling through magnetic separation, while simultaneously contributing to settling. The agent has a large specific surface area and a porous structure, and removes organic matter through adsorption, such as CN113058555A. However, the aforementioned flocculants / catalysts cannot simultaneously degrade organic matter and improve settling properties under the same process. Therefore, this invention can combine the advantages of the above inventions into one, using coal slag as a carrier, modifying it with nano-iron, and simultaneously loading cerium oxide. This allows the carbon in the coal slag and the nano-iron to enhance the conductivity of cerium oxide, thereby degrading organic matter. At the same time, it has a large specific surface area and a large specific gravity, which can adsorb and degrade organic matter, while improving the settling speed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing modified microsand, wherein the modified microsand has the advantages of high specific gravity, strong adsorption performance, micro-electrolysis removal of organic matter, and recycling, and has high catalytic activity under both acidic and alkaline conditions.

[0006] Another objective of this invention is to provide a method for treating chemical wastewater by reducing hardness, removing TOC and phosphorus, which has the synergistic ability to remove TOC, reduce hardness and remove TP, and is simple to operate, has low operating costs and no secondary pollution.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing modified micro-sand includes the following steps:

[0009] (1) Fine sand, fine coal slag, cerium oxide, zero-valent nano iron and water are mixed evenly in a mass ratio of 5:(0.1-5):(0.01-1):(0.01-1):(50-500), heated to 40-80℃ to obtain a slurry, which is then granulated and dried to obtain granular material.

[0010] (2) Water vapor is introduced into the particulate material and reacted at 120-280℃, preferably 150-200℃ for 5-12h, preferably 6-8h. The mixture is then cooled, washed, and dried to obtain modified micro-sand.

[0011] The fine coal slag material described in this invention is obtained by crushing coal slag and filtering it through a 10-100 mesh sieve.

[0012] Preferably, in step (1) of the present invention, the mixing is performed by ultrasound for 60-120 minutes.

[0013] Preferably, in step (1) of the present invention, the heating time is 2-8 hours.

[0014] Preferably, step (1) drying is performed at 100-110℃ for 2-3 hours.

[0015] Preferably, the amount of water vapor introduced in step (2) is 5-20 mL / g, based on the mass of the particulate matter.

[0016] Preferably, the washing in step (2) includes the following steps: washing with deionized water 3-5 times, and then washing with anhydrous ethanol 3-5 times.

[0017] Preferably, the drying in step (2) is performed at 100-110°C for 2-3 hours.

[0018] Preferably, the zero-valent iron nanoparticles have an average particle size of 10-50 nm, a purity greater than 99.9%, and a specific surface area of ​​20-100 m². 2 / g, preferably spherical crystal form.

[0019] Preferably, the coal slag contains 40-50 wt% SiO2, 30-50 wt% Al2O3, 4-20 wt% Fe2O3, 1-5 wt% CaO, and 1-5 wt% C.

[0020] Preferably, the fine sand is garnet with a particle size of 80–120 mesh and a density of 3.8–4.1 g / cm³. 3 The bulk density is 2.3 to 2.4.

[0021] Preferably, the specific surface area of ​​the modified micro-sand is 50-200 m². 2 / g.

[0022] A method for treating chemical wastewater by reducing hardness, removing TOC, and dephosphorizing includes the following steps:

[0023] a) Coagulation stage: Wastewater enters the primary loading coagulation tank, where PAC (polyaluminum chloride) coagulant is added; then it enters the secondary loading coagulation tank, where sodium hydroxide solution is added at a rate gradient G = 500-800 s. -1 Stir and retain for 5-10 minutes; then enter the three-stage loading coagulation tank, add sodium carbonate to the three-stage loading coagulation tank to form calcium magnesium floc precipitate;

[0024] b) Loading flocculation stage: In step a), the product enters the loading flocculation tank, where PAM (anionic polyacrylamide) and modified micro-sand are added.

[0025] c) Sedimentation stage: The product from step b) enters the inclined plate sedimentation tank for sedimentation. The clear liquid overflows as effluent, and the sludge containing modified micro-sand flocs settles to the bottom of the inclined plate sedimentation tank.

[0026] d) Sludge centrifugation stage: Sludge containing modified micro-sand flocs is discharged from the bottom of the inclined plate sedimentation tank to the loading agent separator. After centrifugation, the modified micro-sand is separated from the floc sludge. The modified micro-sand with a higher specific gravity flows radially downward and enters the loading flocculation tank, while the floc sludge with a lower specific gravity flows radially upward and enters the sludge buffer tank. Part of the sludge is returned to the primary loading coagulation tank, and the remaining part enters the sludge storage tank.

[0027] The product of step a) of the present invention includes PAC-containing micro-organic flocs and inorganic flocs such as calcium hydroxide and calcium carbonate.

[0028] The method of this invention uses modified micro-sand loading flocculation technology to increase the specific gravity of flocs and reduce the settling time, and utilizes the porous structure of the modified carrier to improve the removal efficiency of organic matter, thereby improving the pretreatment effect on chemical wastewater.

[0029] Preferably, in step a), the PAC dosage in the primary loading coagulation tank is 10-500 mg / L, based on the wastewater volume of the primary loading coagulation tank.

[0030] Preferably, in step a), the amount of sodium hydroxide added in the primary loading coagulation tank is controlled according to pH 7.5-9.5.

[0031] Preferably, in step a), the molar ratio of sodium carbonate to the sum of calcium and magnesium in the wastewater in the three-stage loading coagulation tank is 1:(0.5-1).

[0032] Preferably, in step b), PAM is an anionic compound with a number-average molecular weight of 8-20 million and a dosage of 0.5-2 mg / L, based on the wastewater volume of the primary loading coagulation tank.

[0033] Preferably, in step b), modified micro-sand is added to make its content in the wastewater 10-500 mg / L.

[0034] Preferably, step b) uses a velocity gradient G = 500-800 s. -1 Stir and let stand for 5-10 minutes.

[0035] Preferably, the residence time of the sedimentation stage in step c) is 0.5-10h.

[0036] Preferably, in step d) the sludge centrifugation stage, the modified micro-sand flocculent sludge contains modified micro-sand and flocculent sludge, with a density of 1.1%-1.5% g / cm³. 3 .

[0037] Preferably, in step d) the sludge centrifugation stage, the proportion of sludge returned to the primary loading coagulation tank is 10%-50%.

[0038] Preferably, in step d) the sludge centrifugation stage, the loss rate of micro-sand is 0.1-0.5 g / t water.

[0039] The wastewater described in this invention mainly includes biochemical production water or circulating water discharge, with a flow rate of 1000-1500 t / h, hardness of 200-600 mg / L, TOC of 15-55 mg / L, and TP of 0.1-5.5 mg / L. Through the above process, the wastewater indicators can be reduced to hardness less than 60 mg / L, TOC less than 15 mg / L, and TP less than 0.1 mg / L. The loss and replenishment of modified loading agent are less than 0.5 g / t of wastewater, which has significant advantages.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) The modified micro-sand of the present invention has a specific gravity of 3.8-4.1 g / cm³. 3 This results in a faster settling speed, increasing the overall process load by more than 30%; it also has a large specific surface area (50-200m²). 2 / g), which greatly enhances its adsorption performance; Fe-C forms a micro galvanic cell inside the modified microsand, which can degrade organic matter by breaking down its chains;

[0042] (2) The micro-sand modified with nano-iron in this invention contains Fe / Fe 2+ / Fe 3+ Fe→Fe 2+ During the oxidation process, weak oxidants S / I2 / Cu in the water can be eliminated. 2+ Etc., Fe → Fe 3+ and Fe 2+ →Fe 3+ During oxidation, strong oxidants in water such as Cl2 / Br2 / HNO3 can be eliminated; Fe 3+ → During the reduction of Fe, reducing agents such as H2 / CO / Zn in water can be eliminated; Fe 3+ →Fe 2+ During the reduction process, reducing agent S in the water can be eliminated. 2- / HS - SO3 2- / HSO 3- wait.

[0043] (3) This invention utilizes nano-iron and carbon in coal slag to enhance the electrical conductivity of cerium oxide, while simultaneously forming Ce under high temperature conditions. 3+ and Ce 4+ This increases the number of oxygen vacancies, giving it high catalytic activity under both acidic and alkaline conditions.

[0044] (4) The modified micro-sand loading flocculation sedimentation process of the present invention has the synergistic ability to remove TOC, reduce hardness and remove TP. It is simple to operate, has low operating cost and no secondary pollution. Attached Figure Description

[0045] Figure 1 Here is a schematic diagram of the structure of an embodiment of the present invention:

[0046] The components include: 1. Wastewater pipeline; 2. PAC pipeline; 3. Sodium hydroxide pipeline; 4. Sodium carbonate pipeline; 5. PAM pipeline; 6. Additive pipeline; 7. Sediment return pipeline; 8. Sludge separation pipeline; 9. Sludge return pipeline; 10. Sludge discharge pipeline; 11. Hydrochloric acid pipeline; 12. Wastewater discharge pipeline; 13. Sludge tank discharge pipeline; 14. Primary loading coagulation tank; 15. Secondary loading coagulation tank; 16. Tertiary loading coagulation tank; 17. Loading flocculation tank; 18. Inclined plate sedimentation tank; 19. Sludge storage tank; 20. Additive separator; 21. Sludge buffer tank. Detailed Implementation

[0047] The following specific embodiments further illustrate the technical solution and effects of the present invention. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Simple modifications made to the present invention based on the concept of the present invention are all within the scope of protection claimed by the present invention.

[0048] The high-efficiency loading flocculation sedimentation pretreatment device for reclaimed water includes a reagent dosing system (PAC pipeline 2, PAM pipeline 5, sodium hydroxide pipeline 3, sodium carbonate pipeline 4, hydrochloric acid pipeline 11), a loading flocculation sedimentation system (primary loading coagulation tank 14, secondary loading coagulation tank 15, tertiary loading coagulation tank 16, loading flocculation tank 17, inclined plate sedimentation tank 18), a loading agent utilization system (loading agent pipeline 6, sludge return pipeline 7, sludge separation pipeline 8, loading agent separator 20), and a sludge treatment system (sludge return pipeline 9, sludge discharge pipeline 10, sludge buffer tank 21, sludge storage tank 19).

[0049] The reagent dosing system is as follows: PAC pipeline 2 has a reagent concentration of 10% and is added to the primary loading coagulation tank 14; sodium hydroxide pipeline 3 has a reagent concentration of 32% and is added to the secondary loading coagulation tank 15; sodium carbonate pipeline 4 has a reagent concentration of 10% and is added to the tertiary loading coagulation tank 16; PAM pipeline 5 has a reagent concentration of 0.1% and is added to the loading flocculation tank 17; HCl pipeline 11 has a reagent concentration of 30% and is added to the external drainage pipeline 12.

[0050] In the loading flocculation sedimentation system, wastewater from wastewater pipeline 1 enters the primary loading coagulation tank 14, where PAC agent is added and mixed evenly; it then enters the secondary loading coagulation tank 15 and is mixed evenly with sodium hydroxide; it enters the tertiary loading coagulation tank 16 and is mixed evenly with sodium carbonate; it then enters the loading flocculation sedimentation tank 17 and is mixed evenly with PAM to produce flocs, which then enter the inclined plate sedimentation tank 18; the flocculent sludge containing the loading agent is discharged through the sludge return pipeline 7, and the supernatant overflows through the inclined plate, mixes with HCl, and is discharged through the external water discharge pipeline 12;

[0051] In the loading agent utilization system, the flocculent sludge containing the loading agent is discharged to the loading agent separation system 20 through the sludge return pipeline 7. Under the action of centrifugal force and gravity, the supernatant and sludge are discharged from the sludge separation pipeline 8 to the sludge buffer tank 21; while the loading agent is discharged from the loading agent pipeline 6 to the loading flocculation tank 17.

[0052] In the sludge treatment system, part of the sludge in the sludge buffer tank 21 is discharged to the primary loading coagulation tank 14 through the sludge return pipeline 9, and the remaining part is discharged to the sludge storage tank 19 through the sludge discharge pipeline 10. After further sedimentation and concentration, it is discharged through the sludge tank discharge pipeline 13.

[0053] During operation, wastewater enters the primary loading coagulation tank 14 through wastewater pipeline 1. PAC concentration of 100 mg / L is added based on the water volume. In the secondary loading coagulation tank 15, sodium hydroxide is added until the pH reaches 9, causing large organic molecules, phosphate ions, and PAC to form flocs. In the tertiary loading coagulation tank 16, sodium carbonate concentration of 200 mg / L is added, causing calcium ions to form calcium carbonate precipitate. Upon entering the loading flocculation tank 17, the loading agent separated by the loading agent separator is added here to maintain a concentration of 50 mg / L. Simultaneously, PAM 2 mg / L is added, causing the small flocs to transform into heavier flocs. These flocs, along with the wastewater, enter the inclined plate sedimentation tank 18. Here, the heavier flocs settle rapidly and are discharged from the bottom for recycling; the clarified liquid overflows and is discharged externally.

[0054] The separation efficiency of the loading agent separation system is usually above 99%, but a small amount of loading agent is still discharged with the sludge. According to the loading agent concentration test at 17 locations in the loading flocculation tank, when it is below 20 mg / L, based on the system volume of 720 m³, 3 Add approximately 50 kg of loading agent, with a replenishment cycle of approximately 3-6 months;

[0055] After separation by the loading agent separator 20, the flocculent sludge is transported to the sludge buffer tank 21 through the sludge separation pipeline 8. There are still a small amount of loading agent and PAM and other agents in it. According to the flow rate of the sludge return pipeline 7, it is added to the primary loading coagulation tank 14 through the sludge return pipeline 9. This has the effect of increasing the particle size of flocculent particles and reducing the amount of agents used.

[0056] The wastewater has a TOC of 35 mg / L, TP (total phosphorus) of 1.5 mg / L, hardness of 460 mg / L, and SS (suspended solids) of 18 mg / L.

[0057] Comparative Example 1:1# Loader (Fine Sand):

[0058] Garnet, grain size: 80-120 mesh, density: 3.8-4.1 g / cm³ 3 Bulk density: 2.3 to 2.4.

[0059] Comparative Example 2: Preparation of Additive #2 (Fine Sand + Cinder + Nano Iron):

[0060] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, zero-valent nano-iron, and deionized water in a mass ratio of 5:5:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce steam at 10 mL / min, and react at 200℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified micro-sand.

[0061] Comparative Example 3: Preparation of Additive #3 (Fine Sand + Cinder + Cerium Oxide):

[0062] The coal slag was crushed and filtered through a 100-mesh sieve to obtain fine coal slag. Fine sand, fine coal slag, cerium oxide, and deionized water were mixed in a mass ratio of 5:5:1:200, sonicated for 120 min, then heated to 80℃ and stirred for 6 h to obtain a slurry. The slurry was then granulated and dried to obtain granular material. The granular material was placed in an oxidation reaction tube, and steam was introduced at a rate of 10 mL / min. The reaction was carried out at 200℃ for 6 h. After cooling to room temperature, the material was washed and dried to obtain modified micro-sand.

[0063] Example 4: Preparation of Additive #4 (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0064] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water in a mass ratio of 5:5:1:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce steam at 10 mL / min, and react at 200℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified micro-sand.

[0065] Example 5: Preparation of #5 Loader (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0066] The coal slag was crushed and filtered through a 100-mesh sieve to obtain fine coal slag. Fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water were mixed in a mass ratio of 5:5:0.01:1:200, sonicated for 120 min, then heated to 80℃ and stirred for 6 h to obtain a slurry. The slurry was then granulated and dried to obtain granular material. The granular material was placed in an oxidation reaction tube, and steam was introduced at a rate of 10 mL / min. The reaction was carried out at 200℃ for 6 h. After cooling to room temperature, the material was washed and dried to obtain modified micro-sand.

[0067] Example 6: Preparation of Additive #6 (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0068] The coal slag was crushed and filtered through a 100-mesh sieve to obtain fine coal slag. Fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water were mixed in a mass ratio of 5:5:1:0.01:200, sonicated for 120 min, then heated to 80℃ and stirred for 6 h to obtain a slurry. The slurry was then granulated and dried to obtain granular material. The granular material was placed in an oxidation reaction tube, and steam was introduced at a rate of 10 mL / min. The reaction temperature was controlled at 200℃ for 6 h. After cooling to room temperature, the material was washed and dried to obtain modified micro-sand.

[0069] Example 7: Preparation of #7 Loader (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0070] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water in a mass ratio of 5:0.1:1:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce steam at 10 mL / min, and react at 200℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified microsand.

[0071] Comparative Example 8: Preparation of 8# Loader (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0072] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water in a mass ratio of 1:5:1:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce steam at 10 mL / min, and react at 200℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified micro-sand.

[0073] Example 9: Preparation of #9 Loader (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0074] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water in a mass ratio of 5:5:1:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce steam at 10 mL / min, and react at 150℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified micro-sand.

[0075] Example 10: Preparation of 10# Loader (Fine Sand + Cinder + Nano Iron + Cerium Oxide):

[0076] Crush the coal slag and filter it through a 100-mesh sieve to obtain fine coal slag. Mix fine sand, fine coal slag, cerium oxide, zero-valent nano-iron, and deionized water in a mass ratio of 5:5:1:1:200, sonicate for 120 min, then heat to 80℃ and stir for 6 h to obtain a slurry. Pelletize and dry to obtain granular material. Place the granular material in an oxidation reaction tube, introduce water vapor at 5 mL / min, and react at 200℃ for 6 h. Cool to room temperature, wash, and dry to obtain modified micro-sand.

[0077] Table 1 Wastewater Treatment Effect

[0078]

[0079] As shown in the table above, Additive #4 exhibits the best TOC removal, phosphorus removal, hardening removal, and SS reduction effects. Through cross-verification between proportions (1 / 2 / 3) and examples (4 / 5 / 6 / 7 / 9 / 10), it is demonstrated that the additive prepared using a mixture of fine sand and coal slag as a carrier, modified with nano-iron and cerium oxide, firstly demonstrates a better sedimentation aid effect, reducing SS and TP in the permeate; secondly, it improves the conductivity of the carrier, forming Ce. 3+ and Ce4+ This increases oxygen vacancies, giving it high catalytic activity in the removal of TOC and organophosphorus compounds from wastewater; the decommissioned loading agent can be reused, achieving a recycling effect.

[0080] During continuous operation, the pH is controlled at 8.5-9, the PAC dosage is 100-150 mg / L, the PAM dosage is 1-2 mg / L, the loading agent is 30-50 mg / L, and the sodium carbonate is 350-400 mg / L. The effluent TOC removal rate is over 50%, the TP removal rate is over 90%, and the hardness removal rate is over 85%. It is suitable for pretreatment and deep treatment processes in dual-membrane systems.

Claims

1. A method for preparing modified micro-sand, comprising the following steps: (1) Fine sand, fine coal slag, cerium oxide, zero-valent nano iron and water are mixed evenly in a mass ratio of 5:(0.1-5):(0.01-1):(0.01-1):(50-500), heated to 40-80℃ to obtain a slurry, which is then granulated and dried to obtain granular material; (2) Water vapor is introduced into the particulate material and reacted at 120-280℃ for 5-12 hours. After cooling, washing and drying, modified micro-sand is obtained. The fine coal slag is obtained by crushing coal slag and filtering it through a 10-100 mesh sieve. The coal slag contains 40-50 wt% SiO2, 30-50 wt% Al2O3, 4-20 wt% Fe2O3, 1-5 wt% CaO, and 1-5 wt% C; The fine sand is garnet, with a particle size of 80-120 mesh and a density of 3.8-4.1 g / cm³. 3 The bulk density is 2.3~2.

4.

2. The method according to claim 1, characterized in that, In step (1), the heating time is 2-8 hours.

3. The method according to claim 1, characterized in that, In step (2), the amount of water vapor introduced is 5-20 mL / g, based on the mass of the particulate matter.

4. The method according to claim 1, characterized in that, The zero-valent iron nanoparticles have an average particle size of 10-50 nm, a purity greater than 99.9%, and a specific surface area of ​​20-100 m². 2 / g.

5. The method according to claim 4, characterized in that, The zero-valent nano-iron is in a spherical crystal form.

6. The method according to claim 1, characterized in that, Step (2) involves reacting at 150-200℃ for 6-8 hours.

7. A method for treating chemical wastewater by reducing hardness, removing TOC, and dephosphorizing, comprising the following steps: a) Coagulation stage: Wastewater enters the primary loading coagulation tank, where PAC coagulant is added; then it enters the secondary loading coagulation tank, where sodium hydroxide solution is added at a rate gradient G = 500-800 s. -1 Stir and retain for 5-10 minutes; then enter the three-stage loading coagulation tank, add sodium carbonate to the three-stage loading coagulation tank to form calcium magnesium floc precipitate; b) Loading flocculation stage: In step a), the product enters the loading flocculation tank, and PAM and the modified micro-sand prepared by the preparation method according to any one of claims 1-6 are added to the loading flocculation tank; c) Sedimentation stage: The product from step b) enters the inclined plate sedimentation tank for sedimentation. The clear liquid overflows as effluent, and the sludge containing modified micro-sand flocs settles to the bottom of the inclined plate sedimentation tank. d) Sludge centrifugation stage: Sludge containing modified micro-sand flocs is discharged from the bottom of the inclined plate sedimentation tank to the loading agent separator. After centrifugation, the modified micro-sand is separated from the floc sludge. The modified micro-sand with a higher specific gravity flows radially downward and enters the loading flocculation tank, while the floc sludge with a lower specific gravity flows radially upward and enters the sludge buffer tank. Part of the sludge is returned to the primary loading coagulation tank, and the remaining part enters the sludge storage tank.

8. The method for treating chemical wastewater by reducing hardness, removing TOC, and dephosphorizing according to claim 7, characterized in that, Step a) The PAC dosage in the primary loading coagulation tank is 10-500 mg / L, based on the wastewater volume of the primary loading coagulation tank; the sodium hydroxide dosage in the primary loading coagulation tank is controlled according to the pH value of 7.5-9.5; in the tertiary loading coagulation tank, the molar ratio of sodium carbonate to the sum of calcium and magnesium elements in the wastewater is 1:(0.5-1).

9. The method for treating chemical wastewater by reducing hardness, removing TOC, and dephosphorizing according to claim 7 or 8, characterized in that, In step b), modified micro-sand is added to make its content in the wastewater 10-500 mg / L.

10. The method for treating chemical wastewater by reducing hardness, removing TOC, and dephosphorizing according to claim 7, characterized in that, In step d), during the sludge centrifugation stage, the proportion of sludge returned to the primary loading coagulation tank is 10%-50%.

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