CN104230041B - A treatment method for grinding wastewater in the semiconductor industry - Google Patents

Abstract

The present invention relates to water technology, disclose the processing method of abrasive waste water in a kind of semicon industry, for solving the waste of the electric energy existed when processing abrasive waste water in prior art, the problem that processing cost is higher.The method is: first add the aqueous slkali that mass concentration is 3% 20% in the SS concentration abrasive waste water more than 50mg/l, pH value is adjusted to 10.5 11, add the high-molecular coagulant adopting that mass concentration is 3% 10% again and electrical conductivity is adjusted to 150 μ s/cm 300 μ s/cm, and the inorganic salts coagulant that mass concentration is 3% 10%, pH value is adjusted to 7 8.5；Finally, abrasive waste water is carried out settlement separate, obtain the SS concentration waste water less than 50mg/l, so, owing to said method need not use filter screen, therefore, reduce power consumption, and processing cost, meanwhile, also improve treatment effeciency.

Description

A treatment method for grinding wastewater in the semiconductor industry

technical field

The invention relates to water treatment technology, in particular to a treatment method for grinding wastewater in the semiconductor industry.

Background technique

The semiconductor device industry is an important part of the current and future electronic information industry. With the rise of the semiconductor industry, the demand for semiconductor products in the international market is increasing. Wafer manufacturing is an important process in the semiconductor manufacturing process. In wafer manufacturing, with the upgrading of manufacturing technology and the reduction of the size of wires and gates, photolithography technology has higher and higher requirements for the flatness of the wafer surface. The CMP (Chemical Mechanical Polishing) process belongs to Fundamental process in chip fabs to planarize the surface of a wafer. When the wafer is cleaned with ultrapure water in the process of wafer grinding, a large amount of grinding wastewater will be generated. Among them, the SS (Suspended Solids, suspended matter) contained in the grinding wastewater far exceeds the SS concentration specified in the national standard and is less than 50mg/ l emission standards, a large number of SS will cause serious pollution to the environment.

In the prior art, in order to avoid excessive SS contained in the generated grinding wastewater from polluting the environment, so that the discharged grinding wastewater can meet the waste discharge standards formulated by the government, ultrafiltration is mainly used to remove the SS contained in the grinding wastewater.

The ultrafiltration method is a physical method, which uses a filter to remove SS contained in the grinding wastewater. Although this method can achieve the effect of reducing the concentration of SS in the grinding wastewater, on the one hand, because the filter is easily blocked by SS, it needs to use electric energy to periodically Cleaning the filter screen, therefore, consumes a lot of electric energy; on the other hand, due to the high hardness of the abrasive particles, it is easy to cause damage to the filter screen, resulting in low treatment efficiency of the wastewater treatment system, and regular cleaning is required. The screens are maintained, therefore, increasing the cost of the wastewater treatment system.

Contents of the invention

An embodiment of the present invention provides a method for treating grinding wastewater in the semiconductor industry, which is used to solve the problems of large power consumption, low treatment efficiency and high treatment cost in the prior art.

A treatment method for grinding wastewater in the semiconductor industry, comprising:

Adding an alkali solution with a mass concentration of 3%-20% in the grinding wastewater with a suspended matter concentration greater than 50mg/l, adjusting the pH value of the hydrogen ion concentration index of the grinding wastewater to 10.5-11;

Add a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 to adjust the conductivity of the grinding wastewater to 150μs/cm-300μs/cm, and the mass concentration is 3%-10 % inorganic salt coagulant to adjust the pH value of the grinding wastewater to 7-8.5;

The grinding wastewater with a pH value of 7-8.5 is subjected to sedimentation and separation to obtain wastewater with a suspended matter concentration less than 50 mg/l.

In the embodiment of the present invention, an alkali solution with a mass concentration of 3%-20% is first added to the grinding wastewater with a suspended matter concentration greater than 50 mg/l, and the pH (Hydrogen Ion Concentration, hydrogen ion concentration index) value of the grinding wastewater is adjusted to 10.5-11, then add a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 to adjust the conductivity of the grinding wastewater to 150μs/cm-300μs/cm, and the mass concentration 3%-10% inorganic salt coagulant, adjust the pH value of the grinding wastewater to 7-8.5; finally, settle the grinding wastewater with a pH value of 7-8.5 to obtain a suspended solid concentration of less than 50mg/l In this way, since the above method does not need to use the filter screen, the power consumption caused by regular cleaning of the filter screen and the cost of regular maintenance of the filter screen are avoided. At the same time, the damage to the filter screen is also avoided. The effect of processing efficiency, therefore, also achieves the purpose of improving processing efficiency.

Description of drawings

Fig. 1 is the detailed flowchart of grinding wastewater treatment in the semiconductor industry in the embodiment of the present invention;

Fig. 2A is the schematic diagram of the color chart in the embodiment of the present invention;

Fig. 2 B is the schematic diagram of pH test paper test pH value in the embodiment of the present invention;

Fig. 3 is a schematic diagram of the treatment of grinding wastewater in the semiconductor industry in an embodiment of the present invention.

detailed description

In order to reduce the consumption of electric energy and treatment cost of the sewage treatment system, and improve the treatment efficiency, in the embodiment of the present invention, an alkali solution with a mass concentration of 3%-20% is first added to the grinding wastewater with a suspended matter concentration greater than 50mg/l, and the Adjust the pH value of the grinding wastewater to 10.5-11, and then add a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 to adjust the conductivity of the grinding wastewater to 150μs/cm- 300μs/cm, and an inorganic salt coagulant with a mass concentration of 3%-10%, adjust the pH value of the grinding wastewater to 7-8.5; finally, settle and separate the grinding wastewater with a pH value of 7-8.5 to obtain Wastewater with a suspended matter concentration less than 50mg/l. In this way, since the above method does not need to use a filter screen, the power consumption caused by regular cleaning of the filter screen and the cost of regular maintenance of the filter screen are avoided. At the same time, It also avoids the impact of filter screen damage on the processing efficiency, and therefore, also achieves the purpose of improving the processing efficiency.

Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, in the embodiment of the present invention, the detailed process of grinding wastewater treatment in the semiconductor industry is as follows:

Step 100: Add an alkali solution with a mass concentration of 3%-20% to the grinding wastewater with a SS concentration greater than 50 mg/l, and adjust the pH value of the grinding wastewater to 10.5-11.

Step 110: Add a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 to adjust the conductivity of the grinding wastewater to 150 μs/cm-300 μs/cm, and the mass concentration is 3 %-10% inorganic salt coagulant to adjust the pH value of the grinding wastewater to 7-8.5.

Step 120: Settling and separating the grinding wastewater with a pH value of 7-8.5 to obtain wastewater with a SS concentration of less than 50 mg/l.

In the prior art, there are three main methods for measuring SS in wastewater: dilution and inoculation, phenol disulfonic acid spectrophotometry and gravimetric method. Therefore, in the embodiment of the present invention, the SS concentration involved in step 110 and step 120 It can be determined by dilution and inoculation method, or by phenolic disulfonic acid spectrophotometric method, or by gravimetric method. Among the above three methods, the gravimetric method is the more commonly used determination method. The determination principle of this method is to pass the water sample through a medium-speed quantitative filter paper (a filter membrane with a pore size of 0.45 microns), and compare the filter paper before and after passing through the water sample. Weighing is carried out to calculate the mass of particulate matter in a certain amount of water sample, so as to obtain the content of SS, and then obtain the concentration of SS.

The SS in the grinding wastewater has surface hydroxyl groups in the aqueous solution. Most of these surface hydroxyl groups have Brönstedt amphiprotic properties, and will be positively charged or negatively charged with the change of pH value. Since this solution uses coagulation and precipitation methods to reduce the SS in the grinding wastewater, and the charge carried by the coagulant is a positive charge, in order to increase the force between the SS in the wastewater and the coagulant, the embodiment of the present invention In the process, before performing step 110, adjust the pH value of the grinding wastewater, that is, add an alkaline solution to the grinding wastewater whose SS concentration reaches 50 mg/l, and stop adding the alkaline solution until the pH value of the grinding wastewater is adjusted to 10.5-11, wherein , SS presents a negatively charged form when it is in a solution with a pH value of 10.5-11, and then a coagulant is added to the grinding wastewater with an alkaline solution.

In the embodiment of the present invention, in step 100, an alkali solution with a mass concentration of 3%-20% can be used to adjust the pH value of the grinding wastewater to 10.5-11, but when the same pH value is reached, the added alkali with a high mass concentration The volume of the solution is larger than that of an alkaline solution with a lower mass concentration.

In the embodiment of the present invention, there are various alkali solutions for adjusting the pH value in step 100. Preferably, KOH (Potassium hydroxide, potassium hydroxide) or NaOH (Sodium hydroxide, sodium hydroxide) can be used to adjust the pH of the grinding wastewater. value is adjusted.

In the embodiment of the present invention, the mass concentration of the alkali solution to adjust the pH value in step 100 may be 3%, may be 9%, may be 10%, may be 12%, may also be 15%, preferably, Adjust the pH value of the grinding wastewater to 10.5-11 by using an alkali solution with a mass concentration of 10%.

In practical applications, there are many methods for measuring the pH value. For example, the pH value can be measured with an acid-base indicator, the pH value can also be measured with a pH test paper, and the pH value can also be measured with a pH meter.

Acid-base indicator method: add a pH indicator to the solution to be tested, and the color of different indicators will change according to different pH values. For example, if an acidic solution is dropped into the litmus test solution, the litmus test solution will turn red ; drop the alkaline solution into the litmus test solution, then the litmus test solution will turn blue (the litmus test solution does not change color when it meets a neutral liquid), and the color presented by the solution added with the indicator is consistent with the pH indication in Table 1 The range of discoloration of the agent is matched to determine the range of PH, and it can also be compared with the color card shown in Figure 2A to determine the range of pH value, wherein there are 14 colors in the color card shown in Figure 2A, different The colors correspond to different pH values. The acid-base indicator method can roughly estimate the range of the pH value, but cannot accurately obtain the pH value.

Table 1

PH test paper (extensive test paper and precision test paper) method: use a glass rod to dip a little of the solution to be tested onto the test paper, and then the pH value of the solution can be obtained according to the color change of the test paper and compared with the color comparison card, as shown in Figure 2B for details. The test paper is made of iron hydrogen and used to measure the pH value of the solution to be tested, but the oil does not contain iron, so the pH test paper cannot show the pH value of the oil. When using the PH test paper method, in operation, it should be noted that the test paper cannot be placed in the liquid to be tested, nor can the test paper be wetted with water to measure the pH value.

PH meter method: A PH meter is an instrument for measuring the pH value of a solution. It uses a pH selective electrode (such as a glass electrode) to measure the pH value of the solution. The pH meter can be accurate to two decimal places, and can accurately measure the pH value of the solution.

In the embodiment of the present invention, when measuring the pH value in step 100 and step 110, the pH value can be measured by using an acid-base indicator, the pH value can also be measured by pH test paper, or the pH value can be measured by a pH meter. Preferably, Use a pH meter to measure the pH value.

In the embodiment of the present invention, before step 110 is performed, that is, before the coagulant is not added to the grinding wastewater, the fine suspended particles in the water are of very light weight, and undergo random Brownian motion due to the collision of the molecular thermal motion of the water. , the movement is relatively stable. The specific reason is: the particles are all charged with the same sex, and the electrostatic repulsion between them prevents the particles from approaching each other and aggregates into larger particles; secondly, the charged suspended matter can hydrate with the surrounding water molecules to form A layer of hydration shell can hinder the aggregation of suspended substances. Therefore, the more charged a suspended substance is, the greater its potential; the more counter ions in the diffusion layer, the greater the hydration effect, and the hydration layer is also The thicker, and therefore the thicker the diffusion layer, the greater the stability.

The principle of coagulation and sedimentation by adding coagulant is that, because the coagulant is an electrolyte, it will electrically neutralize the suspended matter in the wastewater, so that the fine suspended matter in the wastewater will be condensed into flocs, and then the suspended matter will be removed. After the coagulant is put into the wastewater, the suspended solids are reduced or eliminated due to the potential reduction, which destroys the stable state of the particles (this process is called destabilization), and the destabilized particles aggregate into larger particles (this process is called coagulation). , Unstabilized suspended solids can also form large particles (this process is called flocculation). Different coagulants destabilize, coagulate or flocculate suspended solids in different ways. The coagulation process can be divided into four types according to the mechanism: compression electric double layer, adsorption neutralization, adsorption bridging, and sediment net laying. Coagulation and sedimentation can not only remove fine suspended particles with a particle size of 10 ^-3 ~ 10 ^-6 mm in wastewater, but also remove color, oil, microorganisms, nitrogen and phosphorus and other nutrient-rich substances, heavy metals and organic matter.

In the embodiment of the present invention, after the pH value of the grinding wastewater is adjusted to 10.5-11, step 110 is performed, that is, a polymer coagulant with a mass concentration of 3%-10% and a mass concentration of 3%-10% are added to the grinding wastewater. 10% inorganic salt coagulant, and the amount of polymer coagulant added is controlled by the conductivity of the grinding wastewater added to the coagulant, and the added non-polar salt is controlled by the pH value of the grinding wastewater added to the coagulant The amount of coagulant, specifically: the amount of polymer coagulant added to make the conductivity of the grinding wastewater within the range of 150μs/cm-300μs/cm, the amount of inorganic salt coagulant added to adjust the pH value To 7-8.5 can be.

The polymer coagulants used in step 110 are divided into two types: inorganic polymer coagulants and organic polymer coagulants, among which PAC (Polyaluminium Chloride, polyaluminum chloride) and polymerized iron oxide are currently widely used inorganic polymer coagulant. Polyaluminum chloride is a polymer pre-formed in the optimal form under artificial control conditions. It can exert excellent coagulation effect after being put into water. It has strong adaptability to various water qualities and a wide range of applicable pH values. The effect on low-temperature water is also good, and the floc particles formed are relatively large. Therefore, it is an inorganic polymer coagulant that is often used at present.

There are natural and synthetic organic polymer coagulants. This kind of coagulant has huge linear molecules. Each macromolecule is composed of many chain links, and the chain links are combined with covalent bonds. The organic polymer coagulant has an excellent coagulation effect due to the strong adsorption between the chain links on the molecule and the suspended particles in the water. Although the organic polymer mixing agent has excellent coagulation effect, the manufacturing process is complicated and the price is relatively expensive, so it is generally not used.

There are many types of inorganic salt coagulant used in step 110, aluminum salt or iron salt can be used.

The aluminum salt coagulant mainly includes aluminum sulfate, the chemical formula is: Al ₂ (SO4) ₃ ·nH ₂ O, where n=6, 10, 14, 16, 8 and 27, that is, aluminum sulfate contains different amounts of crystal water , the commonly used aluminum sulfate is Al ₂ (SO4) ₃ ·18H ₂ O, its molecular weight is 666.41, its specific gravity is 1.61, its appearance is white, lustrous crystal. Aluminum sulfate is easily soluble in water, the aqueous solution is acidic, the solubility at room temperature is about 50%, and the solubility in boiling water increases to more than 90%. In our country, block or granular aluminum sulfate is mostly used. Block or granular aluminum sulfate is easy to use, has good coagulation effect, and will not bring adverse effects on the treated water quality. Aluminum sulfate is easily soluble in water. Therefore, when aluminum sulfate is added to wastewater, it can be added dry or wet.

Iron salt coagulants mainly include: ferric chloride and ferrous sulfate. Ferric chloride (FeCl ₃ ) is a commonly used coagulant. It is a dark brown crystal with strong water absorption and is easily soluble in water. Its solubility increases with the rise of temperature and has good sedimentation performance. The effect of low turbidity water is better than that of aluminum salt. The ferric chloride supplied by my country includes anhydrous, crystalline hydrate and liquid. Liquids, crystals or damp anhydrous substances are extremely corrosive, and corrosion-resistant equipment must be considered for preparation and dosing equipment. After ferric chloride is added to water, it reacts with the alkalinity of natural water to form ferric hydroxide colloid. The advantage of ferric chloride is that the formed alum flower has a large specificity, is easy to settle, still has a good effect at low temperature and low turbidity, and has a wide range of suitable pH values. The disadvantage is that the solution is highly corrosive, and the water after treatment The chromaticity is higher than that of aluminum salt.

Ferrous sulfate (FeSO ₄ ) is a translucent green crystal, commonly known as vitriol, which is easy to dissolve in water, with a solubility of 21% at a water temperature of 20°C. Ferrous sulfate is usually a by-product of the production of other chemical products, and the price is low, but its heavy metal content should be tested to ensure that the heavy metal content in the treated water does not exceed the limit of the relevant national water quality standards when the maximum dosage is used.

When ferrous sulfate is added to water, the dissociated Fe ²⁺ can only generate simple mononuclear complexes, so it does not have a good coagulation effect like ferric salts. The Fe ²⁺ remaining in the water will make the treated water colored. When the chroma in the water is high, the Fe ²⁺ will react with the colored substances in the water to form a darker substance that is not easy to precipitate (but Fe ³⁺ can be used to remove the color ). According to the above discussion, when using ferrous sulfate, ferrous iron should be oxidized to ferric iron first, and then coagulate. Usually, ferrous iron can be quickly oxidized by adjusting the pH value, adding chlorine, aeration and other methods. When the pH value of the water is above 8.0, the Fe ²⁺ of the added ferrous salt is easily oxidized to Fe ³⁺ by the dissolved oxygen in the water. When the pH value of the raw water is low, ferrous sulfate can be mixed with lime and alkaline conditions The use of alkaline agents such as activated silicic acid and other activated silicic acid can promote the oxidation of ferrous ions. When the pH value of the raw water is low and the dissolved oxygen is insufficient, the ferrous iron can be oxidized by adding chlorine:

6FeSO ₄ +3Cl ₂ =2Fe(SO ₄ ) ₃ +2FeCl ₃

Since the filter membrane has higher requirements on the iron salt coagulant, but relatively lower on the aluminum salt coagulant, therefore, in the embodiment of the present invention, if the treated grinding wastewater is directly discharged, then in step 110, iron Salt coagulant. If the treated grinding waste water needs to be reused after membrane filtration, aluminum salt coagulant is used in step 110.

In the embodiment of the present invention, when an aluminum salt coagulant is used in step 110, preferably, an aluminum sulfate coagulant is used as the aluminum salt coagulant; when an iron salt coagulant is used in step 110, preferably , using ferric chloride coagulant or ferrous sulfate coagulant.

In the embodiment of the present invention, the mass concentration of the polymer coagulant solution used in step 110 may be 3%, may be 4%, may be 5%, may be 5.5%, may also be 6%. Preferably, a polymer coagulant solution with a mass concentration of 5% is added to the grinding wastewater with a pH value of 10.5-11.

Similarly, in the embodiment of the present invention, the mass concentration of the inorganic salt coagulant solution used in step 110 can be 3%, 4%, 5%, 5.5%, or 6%. %. Preferably, a salt coagulant solution with a mass concentration of 5% is added to the grinding wastewater with a pH value of 10.5-11.

In practical applications, there are some factors that affect the coagulation effect, for example, (1) Water temperature: Water temperature has a significant impact on the coagulation effect. The influence of water temperature is mainly manifested in: a. It affects the speed of the chemical reaction of the chemical alkalinity in the water, because its hydrolysis is an endothermic reaction, so it has a great influence on the coagulation of metal salts; b. It affects the formation and quality of alum flowers , when the water temperature is low, the flocs form slowly, the structure is loose, and the particles are small; c, when the water temperature is low, the viscosity of the water is high, and the intensity of the Brownian motion is weakened, which is not conducive to the coagulation of destabilized colloidal particles, and the shear force of the water flow also increases, which affects the flocs growth. This factor mainly affects the coagulation of inorganic salts, and has little effect on polymer coagulants; (2) The influence of the composition, nature and concentration of impurities in water: impurities in water are like clay, if the particle size is small and uniform, The coagulation effect is poor; the concentration of particles (that is, the turbidity of water) is too low and it is not conducive to coagulation; if there is a large amount of organic matter in the water, it will be adsorbed on the surface of the colloidal particles, so that it loses the characteristics of the original colloidal particles and has the characteristics of coagulation. The high stability of organic matter will lead to poor coagulation effect; if the concentration of dissolved salts in water causes an increase in anions, it will have the same charge as colloidal particles, which will also affect the coagulation effect. In addition, it is also related to the amount of coagulant, the speed of water mixing and the uniformity of mixing when the coagulant is added; (3) hydraulic conditions, etc.

In the embodiment of the present invention, there are many ways to measure the conductivity in step 110, for example, the electrode conductivity measurement method, the electromagnetic conductivity measurement method, and the ultrasonic conductivity measurement method can also be used.

In the embodiment of the present invention, after the coagulant is added to the grinding wastewater, step 120 is performed, that is, sedimentation and separation are carried out to realize the separation of sludge and supernatant. Clear water pool, so as to achieve the purpose of removing suspended solids, in which, the supernatant can be directly discharged or recycled.

In the embodiment of the present invention, when the grinding wastewater with a pH value of 7-8.5 is settled in step 120, there are various methods adopted. Preferably, the grinding wastewater with a pH value of 7-8.5 is settled by chemical sedimentation Settled.

Further, in order to strengthen the coagulation effect of suspended matter, in the embodiment of the present invention, after adding a polymer coagulant and an inorganic salt coagulant to the grinding wastewater with a pH value of 10.5-11, before sedimentation and separation, that is The following operation is also performed between step 110 and step 120: adding a coagulant aid to the grinding wastewater until the conductivity is adjusted to 300 μs/cm-500 μs/cm.

In the embodiment of the present invention, there are various coagulation aids used above, for example, anionic polyacrylamide, activated silicic acid (or active silica), bone glue, sodium alginate and various polyelectrolytes.

In the embodiment of the present invention, the mass concentration of the coagulant aid solution may be 1‰, 1.5‰, 2‰, 2.5‰, or 3‰. Preferably, a coagulant aid with a mass concentration of 2‰ is added to the grinding wastewater.

In the embodiment of the present invention, there are many ways to add alkaline solution, coagulant, coagulant and precipitation separation in the grinding wastewater. Preferably, the method shown in Figure 3 can be used to add the alkaline solution in the The pH adjustment reaction tank is carried out, the coagulant is added in the coagulation reaction tank, the coagulant aid is added in the coagulation aid reaction tank, and then the grinding wastewater flows into the inclined tube advection sedimentation tank for precipitation and separation to obtain sludge With the supernatant, wherein, the sludge is regularly removed, and the supernatant flows into the clear water tank for direct discharge or recycling.

To sum up, in the embodiment of the present invention, an alkali solution with a mass concentration of 3%-20% is first added to the grinding wastewater with a suspended matter concentration greater than 50mg/l, and the pH value of the grinding wastewater is adjusted to 10.5-11, and then Add a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 to adjust the conductivity of the grinding wastewater to 150μs/cm-300μs/cm, and the mass concentration is 3%-10 % inorganic salt coagulant, adjust the pH value of the grinding wastewater to 7-8.5; finally, settle and separate the grinding wastewater with a pH value of 7-8.5 to obtain wastewater with a suspended solids concentration of less than 50 mg/l. In this way, Since the above method does not need to use a filter screen, it avoids the power consumption caused by regular cleaning of the filter screen and the cost of regular maintenance of the filter screen. At the same time, it also avoids the impact of filter screen damage on the processing efficiency. Therefore, the object of improving the processing efficiency is also achieved.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (9)

1. A treatment method for grinding waste water in the semiconductor industry, characterized in that, comprising: Add an alkali solution with a mass concentration of 3%-20% to the grinding wastewater with a suspended matter concentration greater than 50 mg/l, and adjust the pH value of the hydrogen ion concentration index of the grinding wastewater to 10.5-11, so that the grinding wastewater The active force of the suspended matter SS and the coagulant added in the grinding wastewater becomes larger; Adding a polymer coagulant with a mass concentration of 3%-10% to the grinding wastewater with a pH value of 10.5-11 adjusts the conductivity of the grinding wastewater to 150 μs/cm-300 μs/cm, and the mass concentration is 3%-10 % inorganic salt coagulant to adjust the pH value of the grinding wastewater to 7-8.5; Will The grinding wastewater with a pH value of 7-8.5 is subjected to sedimentation and separation to obtain wastewater with a suspended solids concentration of less than 50 mg/l; Among them, the grinding wastewater The pH value is adjusted to 10.5-11 and the mass concentration is 3%-20% alkali solution is: sodium hydroxide NaOH solution, or potassium hydroxide KOH solution. 2. The method according to claim 1, characterized in that, the mass concentration of the alkali solution is 10%. 3. The method of claim 1, wherein at The polymer coagulant with a mass concentration of 3%-10% added to the grinding wastewater with a pH value of 10.5-11 is: polyaluminum chloride or polyferric oxide. 4. The method according to claim 1 or 3, characterized in that the mass concentration of the polymer coagulant is 5%. 5. The method of claim 1, wherein at The inorganic salt coagulant with a mass concentration of 3%-10% added to the grinding wastewater with a pH value of 10.5-11 is: aluminum sulfate, ferric chloride or ferrous sulfate. 6. The method according to claim 1 or 5, characterized in that the mass concentration of the inorganic salt coagulant is 5%. 7. method as claimed in claim 1 is characterized in that, will grind waste water After the pH value is adjusted to 7-8.5, before sedimentation and separation, also include: Add a coagulant aid with a mass concentration of 1‰-3‰ to the grinding wastewater until the conductivity is adjusted to 300μs/cm-500μs/cm. 8. The method according to claim 7, wherein the coagulation aid is: anionic polyacrylamide or activated silicic acid. 9. The method according to claim 7 or 8, characterized in that the mass concentration of the coagulant aid is 2‰.