CN110407361A - A zero-discharge and resource-based treatment process for silica gel wastewater and a silica gel wastewater treatment system - Google Patents

Abstract

The invention relates to a zero-discharge and resource-based treatment process of silica gel wastewater and a silica gel wastewater treatment system, comprising the following steps: concentration of impurities, recovery of produced water, flocculation precipitation, circulation filtration, concentration of sodium sulfate, cooling crystallization and recovery of sodium sulfate solids, The filtration of the first-stage disc-tube nanofiltration membrane group can remove more than 99% of sulfate radicals from the product water, and also remove calcium and magnesium ions and some silica, so that the product water can meet the requirements of silica gel pickling process water. The concentrated water from the first-stage disc-tube nanofiltration membrane group enters the reaction sedimentation tank, and the silica crystals in the concentrated water are precipitated by adding a flocculant, and then enters the second-stage disc-tube nanofiltration membrane group to concentrate the concentrated water, and through heating, Lowering the temperature and further concentrating makes the sodium sulfate crystallize out in the crystallization tank, and removes the sodium sulfate in the treatment system. The invention solves the problems of low efficiency, high cost and poor effect of the existing silica gel wastewater treatment process, and realizes zero discharge of silica gel wastewater and resource recovery and utilization.

Description

A zero-discharge and resource-based treatment process for silica gel wastewater and silica gel wastewater treatment system

technical field

The invention relates to the technical field of wastewater treatment, in particular to a zero-discharge and resource-recycling treatment process for silica gel wastewater and a silica gel wastewater treatment system.

Background technique

China produces 240,000 tons (2018 data) of silica gel every year. According to the current requirements of resource consumption and sewage discharge conditions in the silica gel industry, each ton of product consumes 15 tons of water and produces 12 tons of waste water at the same time, producing nearly 3 million tons of waste water every year.

The main raw material for the production of silica gel is sodium silicate (commonly known as water glass, sodium silicate), which is obtained by chemical processing of silica. That is, the melt produced by calcining quartz ore powder and soda ash at a high temperature of 1100-1350°C is soaked in water to obtain a colorless and transparent viscous liquid. The production method of silica gel is mainly the sulfuric acid method, which is obtained by the reaction of sodium silicate and sulfuric acid.

The main process of silica gel production includes: rubber making, aging, acid soaking, washing, drying and other processes.

Silica gel wastewater mainly comes from the washing process of silica gel acid bubbles. The wastewater has high acidity and a pH value of about 2-3. It contains a large amount of sulfate and silicate, and the content of sodium sulfate can reach up to 4%. In addition, it also contains a small amount of chloride ions, Calcium and magnesium ions. Silica gel wastewater has the characteristics of high acidity, high salt content, high silicon content and difficult treatment.

The existing silica gel pickling wastewater treatment process generally uses quicklime to adjust the pH first, and then adds flocculants, such as polyaluminum chloride, polyferric chloride, polyacrylamide, etc., to make the silicon-containing wastewater flocculate and precipitate, and then press filter to Solid-liquid separation. This treatment process will generate a large amount of solid waste, and introduce a large amount of calcium and magnesium impurities into the wastewater, which will add too much burden to the subsequent treatment, and has problems such as low efficiency, high cost, and poor treatment effect.

There is also a silica gel wastewater treatment process that uses pH adjustment + multi-stage precipitation reaction, then concentrates with membrane technology, and then evaporates and crystallizes with MVR. This kind of process technology also adds a large amount of chemicals and produces a large amount of solid waste. Moreover, the evaporation crystallization method has a huge investment and extremely high operating costs, making it difficult to popularize and implement.

To sum up the existing treatment methods, only silica gel wastewater is treated as ordinary wastewater, which does not combine the characteristics of water quality well. Secondly, when designing the treatment process according to the recycling standard, it did not seriously combine the water requirements of the silica gel production process, and there was a phenomenon of over-treatment. In addition, from the perspective of resource utilization, the recycling value of sodium sulfate has been ignored.

In fact, if the water quality standard after treatment is used in the rubber washing process, it cannot be measured by conventional indicators. Gel washing is an indispensable process in the production of silica gel. It is to wash off the Na ₂ SO ₄ formed by the granular gel, and remove the anions and cations (mainly H ⁺ , Na ⁺ , SO ₄ ^2- and SiO ₃ ^2- etc.) are controlled within the range of process requirements. Therefore, if the quality of produced water is to meet the requirements of reuse water (gel washing process), the main consideration should be to remove sodium sulfate and achieve recycling.

According to the characteristic that the solubility of sodium sulfate changes with temperature, the method of crystallization by lowering the temperature of the saturated solution is more feasible than the evaporation crystallization process, with less equipment investment and low operating cost. Sodium sulfate is soluble in water, but its solubility varies with temperature: at 0-10°C, its solubility is 5-9%, and at 30-40°C, its solubility is 41-49%. Therefore, it is conceivable to concentrate the sodium sulfate in the solution to a high concentration, such as above 30%, when the temperature is above 30°C, and then reduce the temperature to below 10°C to saturate and crystallize the sodium sulfate and separate it.

Concentration using nanofiltration (NF) membrane technology is a more economical and effective method. Nanofiltration (NF) technology is called "loose reverse osmosis membrane", the interception rate of divalent and high-valent ions is significantly higher than that of monovalent ions, and its removal rate of sulfate radical reaches more than 99%. big. Generally, the transmembrane pressure difference required for nanofiltration (NF) separation is generally 0.5-2.0 MPa, which is 0.5-3.0 MPa lower than the pressure difference necessary to achieve the same permeation flux with reverse osmosis.

Concentrating high-concentration sodium sulfate wastewater requires a multi-stage nanofiltration (NF) membrane concentration process. The sodium sulfate content in raw waste water can reach up to 4%, and the solubility of sodium sulfate can reach more than 30 grams when it is above 30 ° C, and the saturated crystallization concentration is less than 9 grams when it is below 10 ° C. Therefore, a high concentration multiple is required to increase the concentration of sodium sulfate. concentration to meet high crystallization efficiency. In order to achieve a high concentration factor, a multi-stage concentration process is required. Among them, in the first-stage nanofiltration concentration, although there are some calcium and magnesium ions and silicon dioxide in the water, the pH is very low, about 2-3, and the scaling tendency is not serious. Combined with the addition of scale inhibitors, it is not necessary to add drugs to adjust pH precipitation treatment.

The use of disc tube nanofiltration (disc tube membrane module) technology is beneficial to reduce the harm of fouling and fouling of the membrane. Disc tube nanofiltration membrane, with its special flow channel design, special deflector plate structure, high-speed water flow to wash the surface of the membrane, can withstand the accumulation of certain colloidal particles, thus improving the anti-fouling ability. Even if the influent SDI (pollution index) reaches 15, it can still operate normally. Ordinary coiled membrane elements generally require SDI<5, so ordinary coiled membrane technology cannot be used.

After the first-stage disc-tube nanofiltration treatment, the concentration of concentrated water is reduced by more than half, the concentration of ions is more than doubled, and the hardness components and silica in the water are concentrated. Silicon treatment to prevent fouling of the nanofiltration membrane, and then it is suitable for membrane concentration treatment.

Contents of the invention

Aiming at the problems of low efficiency, high cost and poor effect of the existing silica gel wastewater treatment process, the present invention provides a zero discharge and resource recovery treatment process of silica gel waste water and a silica gel waste water treatment system, which can use the produced water in the silica gel pickling process, And sodium sulfate is recovered through cooling and crystallization, which reduces costs, saves energy and protects the environment.

The present invention is achieved through the following technical solutions:

A zero-discharge and resource-based treatment process for silica gel wastewater is provided, comprising the following steps:

The first step, impurity concentration and product water recovery: After the wastewater is pretreated to filter out suspended solids, it is passed into the first-stage disc-tubular membrane module and sulfate, calcium and magnesium ions and part of the carbon dioxide are oxidized by the first-stage disc-tubular membrane module. Silicon is concentrated on the concentrated water side, and the permeated liquid side of the first-stage disc-tube membrane module is recycled for silica gel pickling process water;

The second step, flocculation sedimentation and circulation filtration: pass the concentrated water of the first-stage disc-tube membrane module into the sedimentation tank, first adjust the pH to neutral, and then add flocculant to make the calcium magnesium ions and silicon dioxide in the water form precipitation , solid-liquid separation in the sedimentation tank, the liquid solution in the sedimentation tank is passed into the tubular membrane group, and the concentrated water of the tubular membrane group is returned to the sedimentation tank to form a circulating filter;

The third step, sodium sulfate concentration, cooling and crystallization: the product water of the tubular membrane group is passed into the second-stage disc-type membrane module to concentrate sodium sulfate, and the concentrated water of the second-stage disc-type membrane module is cooled to make the Sodium sulfate crystallizes out, and the crystallized solution is refluxed into the inlet water of the second-stage disc-tube membrane module, and the crystallized solution is heated during the reflux process to make it unsaturated with sodium sulfate. After the membrane module is further concentrated, the concentrated water is cooled and crystallized to realize multi-stage concentration and cooling crystallization of the concentrated water;

The 4th step, reclaim sodium sulfate solid.

Further, the first-stage disc-tube membrane module is a disc-tube nanofiltration membrane group; the second-stage disc-tube membrane module is a disc-tube nanofiltration membrane group or a disc-tube reverse osmosis membrane group.

Further, in the second step, when the concentration of calcium and magnesium ions in the solution in the sedimentation tank is lower than 1mmol/L, and the concentration of silicon dioxide is lower than 20mg/L, the product water of the tubular membrane group is passed into the second-stage disc tubular membrane module deal with.

Further, in the third step, the temperature of the concentrated water in the second-stage disc-tube membrane module is cooled to below 10°C; the crystallized solution is returned to the process of the second-stage disc-tube membrane module, and its temperature is heated to 30-35°C .

Sodium sulfate is soluble in water, but its solubility varies with temperature: at 0-10°C, its solubility is 5-9%, and at 30-40°C, its solubility is 41-49%. Therefore, it is conceivable to concentrate the sodium sulfate in the solution to a high concentration, such as above 30%, when the temperature is above 30°C, and then reduce the temperature to below 10°C to saturate and crystallize the sodium sulfate and separate it.

Furthermore, in the third step, the product water of the second-stage disc-tube membrane module is recycled for the silica gel pickling process water.

Further, the tubular membrane group is a tubular ultrafiltration membrane group or a tubular microfiltration membrane group.

Further, in the second step, the flocculant is one or a combination of calcium chloride, magnesium chloride, polyaluminum chloride, and PAM.

A silica gel wastewater treatment system using the treatment process, including a wastewater regulating tank, and also includes a first-stage disc-and-tube membrane module, a second-stage disc-and-tube membrane module, a sedimentation tank, and a tubular membrane group;

The water inlet end of the first-stage disc-tubular membrane module is connected to the wastewater regulating tank, the concentrated water end of the first-stage disc-tubular membrane module is connected to the water inlet end of the tubular membrane group through the sedimentation tank, and the concentrated water end of the tubular ultrafiltration membrane group is The water end is connected to the sedimentation tank through the first return pipe;

The water inlet end of the second-stage disc-tube membrane module is connected to the water-producing end of the tubular membrane group through the intermediate water tank, and the concentrated water end of the second-stage disc-tube membrane module is connected to a crystallization tank. The cooling device, the crystallization tank is also connected to the water inlet end of the second-stage disc-tube membrane module through the second return pipe, and the second return pipe is provided with a heating device that can raise the temperature of the reflux liquid.

This scheme uses the filtration of the first-stage disc-tube membrane module to remove more than 99% of sulfate radicals from the product water, and also removes calcium and magnesium ions and some silica, so that the product water can meet the requirements of silica gel pickling process water. The concentrated water of the first-stage disc-tubular membrane module enters the reaction sedimentation tank, and the silica crystals in the concentrated water are precipitated by adding chemicals. Sodium sulfate crystallizes out in the crystallization tank, removes sodium sulfate in the treatment system and recovers sodium sulfate solid.

Further, the first-stage disc-tube membrane module is a disc-tube nanofiltration membrane group; the second-stage disc-tube membrane module is a disc-tube nanofiltration membrane group or a disc-tube reverse osmosis membrane group.

Further, the water production end of the first-stage disc-tube membrane module and the water-production end of the second-stage disc-tube membrane module are both connected to the water production reuse tank.

The water produced by the first and second disc tube nanofiltration membrane groups can be recycled for the silica gel pickling process, which realizes the recycling of resources and reduces waste.

Beneficial effects of the present invention:

1. It is not necessary to adjust the pH in the front-end pretreatment, but based on DT nanofiltration, it is suitable for operation between the pH value of 2-11, and when operating between the pH value of 2-4, it can reduce the fouling tendency of the nanofiltration membrane , which is conducive to the long-term stable operation of the membrane system.

2. In the front-end pretreatment, dosing to adjust the pH and precipitation treatment is not carried out. The pH of the produced water is low, which is more suitable for reuse in the silica gel pickling process water. Only alkali is added to adjust the pH in the first-level DTNF concentrated water flocculation and precipitation treatment stage. At this stage, the amount of water has been reduced by more than half of the original water, and the pH is higher than that of the original water. The acidic medium retained in the product water is exactly what is needed for the reuse process, and the amount of acid added to the reuse water is reduced, so that the amount of alkali added to directly adjust the pH of the raw water is lower than that of the original water. More than 50%, while reducing the generation of solid waste by more than 50%, the precipitation reaction effect is better, and it also saves chemicals, equipment investment and floor space.

3. The precipitation reaction tank and tubular ultrafiltration constitute a circulating solid-liquid separation system. The quality of ultrafiltration effluent is good, so that the second-stage disc tubular membrane module can have a high concentration ratio and improve the efficiency of subsequent sodium sulfate crystallization separation. There is no need to build a large sedimentation and clarification tank, and the floor space is small; the system has a high degree of integration, good operability, and is convenient for automatic control.

4. Adopt the multi-stage recovery process of cooling crystallization, re-concentration, and re-cooling crystallization, and recover sodium sulfate as a resource. Compared with the recovery process of evaporation and crystallization, it does not require a large amount of steam and high power load, and the investment cost and operating cost are lower. Reduced by more than 80%, the energy-saving benefit is obvious.

5. It adopts disc-tube nanofiltration (disc-tube membrane module) technology, special flow channel design, special deflector plate structure, high-speed water washing the surface of the membrane, and can withstand certain colloidal particle aggregation, thus improving the anti- Fouling ability, can tolerate raw water SDI>15, so at low pH, it can prevent silica colloidal fouling in raw water from fouling nanofiltration membranes. The focus of the new process is no waste water discharge, and all produced water can be reused, which greatly saves the water replenishment of the process.

Description of drawings

Fig. 1 is the structural representation of silica gel wastewater treatment system in embodiment 1 in the present invention;

Fig. 2 is a schematic structural diagram of a silica gel wastewater treatment system in Example 2 of the present invention.

As shown in the figure:

1. Wastewater adjustment tank, 2. Pretreatment equipment, 3. First-stage disc-tube nanofiltration membrane group, 4. Sedimentation tank, 5. Tubular ultra-filtration membrane group, 6. Second-stage disc-tube nanofiltration membrane group, 7. Crystallization tank, 8. Produced water reuse tank, 9. Sludge dehydration equipment, 10. First return pipe, 11. Intermediate water tank, 12. Second return pipe, 13. Second-stage disc tube reverse osmosis membrane group .

Detailed ways

In order to clearly illustrate the technical features of the solution, the solution will be described below through specific implementation modes.

Example 1:

A zero-discharge and resource-based treatment process for silica gel wastewater, comprising the following steps:

The first step is concentration of impurities and recovery of produced water: after the wastewater is pretreated to filter out suspended solids, it is passed into the first-stage disc-type nanofiltration membrane group 3 and the sulfuric acid, calcium Magnesium ions and part of silicon dioxide are concentrated in concentrated water, and the product water from the first-stage disc-tube membrane group 3 is recycled for silica gel pickling process water.

Before the waste water is passed into the first-stage disc-tube nanofiltration membrane group 3, the waste water in different periods is homogeneously regulated and pretreated to remove suspended particles in the waste water.

The second step, flocculation sedimentation and circulation filtration: pass the concentrated water of the first-stage disc-type nanofiltration membrane group 3 into the sedimentation tank 4, first adjust the pH to neutral, and then add flocculants to make the calcium and magnesium ions in the water and Silica forms a precipitate, which separates the solid from the liquid in the sedimentation tank, and the solution in the sedimentation tank is passed into the tubular membrane group, and the concentrated water of the tubular membrane group is returned to the sedimentation tank 4 to form a circulating filter. In this embodiment, the tubular membrane group is the tubular ultrafiltration membrane group 5 .

The concentrated water of the first-stage disc-tube nanofiltration membrane group 3 is passed into the sedimentation tank 4, and alkaline substances are first added in the sedimentation tank 4 to adjust the pH. The alkali used can be caustic soda, soda ash, quicklime, magnesium oxide, etc., which can increase the pH. Agents, and then add flocculants, the flocculants used include calcium chloride, magnesium chloride, polyaluminum chloride, PAM, etc., which can convert calcium magnesium hardness and silica colloid into precipitates.

In the second step, when the concentration of calcium and magnesium ions in the solution in the sedimentation tank 4 is lower than 1mmol/L, and the concentration of silicon dioxide is lower than 20mg/L, the product water of the tubular ultrafiltration membrane group 5 is passed to the next step for processing.

The third step, sodium sulfate concentration, cooling and crystallization: the product water of the tubular ultrafiltration membrane group 5 is passed into the second disc tubular nanofiltration membrane group 6 to concentrate sodium sulfate, and the second disc tubular nanofiltration membrane group 6 The concentrated water is cooled to crystallize the sodium sulfate in it, and the concentrated water of the second-stage disc tube nanofiltration membrane group 6 is cooled to a temperature of 0-10°C, and the crystallized solution is refluxed to the second disc tube nanofiltration membrane group 6. In the filter membrane group 6, heat the solution after crystallization to 30-40°C during the reflux process, so that it is in an unsaturated state for sodium sulfate. Cooling and crystallization realizes multi-stage concentration and cooling crystallization of the concentrated water, and the water produced by the second-stage disc-tube nanofiltration membrane group 6 is recovered for silica gel pickling process water.

The 4th step, reclaim sodium sulfate solid.

This process is applied to a silica gel wastewater treatment system, including a wastewater regulating tank 1, and also includes a first-stage disc-tube nanofiltration membrane group 3, a second-stage disc-tube nanofiltration membrane group 6, a sedimentation tank 4 and a tubular membrane group ; The tubular membrane group is a tubular ultrafiltration membrane group or a tubular microfiltration membrane group. In this embodiment, a tubular ultrafiltration membrane group 5 is used.

At least one or more of multimedia filtration, microfiltration, and ultrafiltration for wastewater pretreatment are also connected between the wastewater regulating tank 1 and the water inlet of the first-stage disc-tube nanofiltration membrane group 3. its combination.

The concentrated water end of the first-stage disc tubular nanofiltration membrane group 3 is connected to the water inlet end of the tubular ultrafiltration membrane group 5 through the reaction sedimentation tank 4, and the concentrated water end of the tubular ultrafiltration membrane group 5 passes through the first return pipe 10 It is connected with the reaction sedimentation tank 4; the reaction sedimentation tank 4 is provided with a sewage outlet and is connected with a sludge dewatering device 9 through the sewage outlet.

The water inlet end of the second-stage disc-tube nanofiltration membrane group 6 is connected to the water-producing end of the tubular ultrafiltration membrane group 5 through the intermediate water tank 11, and the concentrated water end of the second-stage disc-tube nanofiltration membrane group 6 is connected to a crystallization tank 7. The crystallization tank 7 is provided with a cooling device capable of cooling concentrated water. The crystallization tank 7 is also connected to the water inlet end of the second-stage disc-tube nanofiltration membrane group 6 through the second return pipe 12, and the second return pipe 12 There is a heating device that can raise the temperature of the reflux liquid.

The water production end of the first-stage disc-tube nanofiltration membrane group 3 and the water-production end of the second-stage disc-tube nanofiltration membrane group 6 are both connected to the water production reuse pool 8 .

The implementation method is as follows:

The raw water enters the waste water regulating tank 1 to homogeneously regulate the waste water entering in different periods, and then passes through the pretreatment equipment 2 and enters the first-stage disc-tube nanofiltration membrane group 3 . For the disc-tube membrane module technology, the pretreatment equipment 2 can be multi-media filtration, microfiltration, ultrafiltration, all of which can meet the water inlet requirements.

The produced water from the first-stage disc-tube membrane module 3 enters the product water reuse tank 8. Due to the technological characteristics of the disc-tube membrane module, more than 99% of sulfate radicals are removed from the produced water, and calcium and magnesium ions and part of the carbon dioxide are also removed. Silicon, which fully meets the water requirements for silica gel pickling process.

Concentrated water from the first-stage disc-tubular membrane module 3 enters the sedimentation tank 4, and the sedimentation tank 4 and the tubular ultrafiltration membrane group 5 form a circulation separation system. Sodium hydroxide is added to the sedimentation tank 4 to adjust the pH, and sodium carbonate and magnesium are added to make the hardness in the water and silicon dioxide form crystallization precipitation; The filter membrane group 5 is separated and filtered, and the produced water enters the intermediate water tank 14 for buffering and then enters the second-stage disc-tube nanofiltration membrane group 6 . The concentrated water of the tubular ultrafiltration membrane group 5 is returned to the reaction sedimentation tank 4 through the first return pipe 10, and the lower part of the reaction sedimentation tank 4 is a sludge concentration area, and the concentrated sludge is poured into the sludge dewatering equipment 9, and the dehydrated sludge The mud is sent to landfill, and the dehydrated overflow liquid is returned to the sedimentation tank 4.

The effluent from the tubular ultrafiltration membrane group 5, the hardness and silicon dioxide and other easy-to-scale substances are removed, and then enters the second-stage disc tubular nanofiltration membrane group 6 for concentration treatment. At this time, the scaling components have been removed from the incoming water. Although the salt content is higher than that of the first-stage incoming water, after being treated by the second-stage disc-tube nanofiltration membrane group 6, the concentration ratio can still be more than doubled. The sodium sulfate content of the concentrate can be concentrated to more than 20% under the limit condition of the working pressure of the membrane module. The concentrated solution enters the crystallization tank, and the temperature is lowered to below 10°C by the cooling device, so that the sodium sulfate is crystallized and precipitated, and the finished product of sodium sulfate is obtained.

After cooling and precipitation, the supernatant after removing the sodium sulfate crystals is a saturated solution. The crystallization tank 7 is also connected with the water inlet end of the second-stage disc-tube nanofiltration membrane group 6 through the second return pipe 12, and the second return pipe 12 is provided with a heating device that can heat up the return liquid, and the return liquid passes through the second return pipe. After the return pipe 12, the temperature rises, the solubility of sodium sulfate increases, and it is in an unsaturated state again. It flows back through the second return pipe 12 to the water inlet end of the second-stage disc-tube membrane module 6, and concentrates again.

The heating device used in the present invention can be an electric heating tube, a heat exchanger and other devices, which can meet the function of raising the temperature of the treatment liquid; and the cooling device can also use other cooling equipment such as a heat exchanger to meet the cooling of the treatment liquid. function. Both the cooling device and the heating device used in the present invention are products of the prior art, and the specific structure will not be repeated.

Example 2:

A zero-discharge and resource-based treatment process for silica gel wastewater, comprising the following steps:

The first step is concentration of impurities and recovery of produced water: after the wastewater is pretreated to filter out suspended solids, it is passed into the first-stage disc-type nanofiltration membrane group 3 and the sulfuric acid, calcium Magnesium ions and part of silica are concentrated on the concentrated water side, and the product water from the disc-tube membrane module is recycled for silica gel pickling process water.

Before the waste water is passed into the first-stage disc-tube nanofiltration membrane group 3, the waste water in different periods is homogeneously regulated and pretreated.

The second step, flocculation sedimentation and circulation filtration: pass the concentrated water of the first-stage disc-type nanofiltration membrane group 3 into the sedimentation tank 4, first adjust the pH to neutral, and then add flocculants to make the calcium and magnesium ions in the water and Silica forms a precipitate, the liquid solution passes into the tubular membrane group, the concentrated water of the tubular membrane group flows back to the sedimentation tank 4, and the produced water enters the intermediate water tank 11, thereby forming a circulating filter. In this embodiment, the tubular membrane group is the tubular ultrafiltration membrane group 5 .

The concentrated water of the first-stage disc-tube nanofiltration membrane group 3 is passed into the sedimentation tank 4, and alkaline substances are first added in the sedimentation tank 4 to adjust the pH. The alkali used can be caustic soda, soda ash, quicklime, magnesium oxide, etc., which can increase the pH. Agents, and then add flocculants, the flocculants used include calcium chloride, magnesium chloride, polyaluminum chloride, PAM, etc., which can convert calcium magnesium hardness and silica colloid into precipitates.

In the second step, when the concentration of calcium and magnesium ions in the solution in the sedimentation tank 5 is lower than 1 mmol/L, and the concentration of silicon dioxide is lower than 20 mg/L, the product water of the tubular ultrafiltration membrane group 5 is passed to the next step for processing.

The third step, sodium sulfate concentration, cooling and crystallization: the product water from the tubular ultrafiltration membrane group 5 is passed into the second-stage disc-type reverse osmosis membrane group 13 to concentrate sodium sulfate, and the second-stage disc-type reverse osmosis membrane group 13 The concentrated water is cooled to crystallize the sodium sulfate in it. The temperature for cooling the concentrated water in the second-stage disc-tube reverse osmosis membrane group 13 is 0-10°C, and the crystallized solution is refluxed to the second-stage disc-tube reverse osmosis membrane group 13. In the osmotic membrane group 13, heat the crystallized solution to 30-40°C during the reflux process, so that it is in an unsaturated state for sodium sulfate. Cooling and crystallization realizes multi-stage concentration and cooling crystallization of the concentrated water, and the water produced in the two-stage disc-tube reverse osmosis membrane group 13 is recovered for silica gel pickling process water.

The 4th step, reclaim sodium sulfate solid.

A silica gel wastewater treatment system, including a wastewater regulating tank 1, and also includes a first-stage disc-tube nanofiltration membrane group 3, a second-stage disc-tube reverse osmosis membrane group 13, a sedimentation tank 4, and a tubular ultrafiltration membrane group 5;

At least one or more of multimedia filtration, microfiltration, and ultrafiltration for wastewater pretreatment are also connected between the wastewater regulating tank 1 and the water inlet of the first-stage disc-tube nanofiltration membrane group 3. its combination.

The concentrated water end of the first-stage disc tubular nanofiltration membrane group 3 is connected to the water inlet end of the tubular ultrafiltration membrane group 5 through the sedimentation tank 4, and the concentrated water end of the tubular ultrafiltration membrane group 5 is connected to the The sedimentation tank 4 is connected; the sedimentation tank 4 is provided with a sewage outlet and is connected with a sludge dehydration device 9 through the sewage outlet.

The water inlet end of the disc tube type reverse osmosis membrane group 13 is connected to the water production end of the tube type ultrafiltration membrane group 5 through the intermediate water tank 11, and the concentrated water end of the second disc tube type reverse osmosis membrane group 13 is connected to the crystallization tank 7, The crystallization tank 7 is provided with a cooling device capable of cooling concentrated water. The crystallization tank 7 is also connected to the water inlet end of the second-stage disc-tube reverse osmosis membrane group 13 through the second return pipe 12. The second return pipe 12 is provided with A heating device that can raise the temperature of the reflux liquid.

The water production end of the first-stage disc-tube nanofiltration membrane group 3 and the water-production end of the second-stage disc-tube reverse osmosis membrane group 13 are both connected to the water production reuse tank 8 .

The implementation method of the present invention is as follows:

The raw water enters the waste water regulating tank 1 to homogeneously regulate the waste water entering in different periods, and then passes through the pretreatment equipment 2 and enters the first-stage disc-tube nanofiltration membrane group 3 . For the disc-tube membrane module technology, the pretreatment equipment 2 can be multi-media filtration, microfiltration, ultrafiltration, all of which can meet the water inlet requirements.

The produced water from the first-stage disc-tube nanofiltration membrane group 3 enters the produced water reuse tank 8. Due to the technological characteristics of the disc-tube membrane module, the produced water removes more than 99% of sulfate radicals, and also removes calcium and magnesium ions and some Silica fully meets the water requirements for silica gel pickling process.

Concentrated water from the first-stage disc tubular membrane nanofiltration membrane group 3 enters the sedimentation tank 4, and the sedimentation tank 4 and the tubular ultrafiltration membrane group 5 form a circulating separation system. Sodium hydroxide is added to the sedimentation tank 4 to adjust the pH, and sodium carbonate and magnesium are added to make the hardness and silicon dioxide in the water form crystallization precipitation; The ultrafiltration membrane group 5 separates and filters, and the product water enters the disc-tube reverse osmosis membrane group 13 behind. The concentrated water of the tubular ultrafiltration membrane group 5 flows back to the sedimentation tank 4 through the first return pipe 10. The lower part of the sedimentation tank 4 is the sludge concentration area, and the concentrated sludge is poured into the sludge dewatering equipment 9, and the dehydrated sludge is discharged Send it to landfill, and the dehydrated overflow liquid is returned to the reaction sedimentation tank 4.

The effluent from the tubular ultrafiltration membrane group 5, the hardness and silicon dioxide and other easy-to-scale substances are removed, and then enters the second-stage disc tubular reverse osmosis membrane group 13 for concentration treatment. At this time, the scaling components have been removed from the influent water. Although the salt content is higher than that of the first-stage influent water, after being treated by the second-stage disc-tube reverse osmosis membrane group 13, the concentration ratio can still be more than doubled. The sodium sulfate content of the concentrate can be concentrated to more than 20% under the limit condition of the working pressure of the membrane module. The concentrated solution enters the crystallization tank, and the temperature is lowered to below 10°C by the cooling device, so that the sodium sulfate is crystallized and precipitated, and the finished product of sodium sulfate is obtained.

After cooling and precipitation, the supernatant after removing the sodium sulfate crystals is a saturated solution. The crystallization tank 7 is also connected to the water inlet end of the second-stage disc-tube reverse osmosis membrane group 13 through the second return pipe 12. The second return pipe 12 is provided with a heating device that can heat the return liquid, and the return liquid passes through the second After the return pipe 12, the temperature rises, the solubility of sodium sulfate increases, and it is in an unsaturated state. It flows back through the second return pipe 12 to the water inlet end of the second-stage disc-tube reverse osmosis membrane group 13, and concentrates again.

The heating device used in the present invention can be an electric heating tube, a heat exchanger and other devices, which can meet the function of raising the temperature of the treatment liquid; and the cooling device can also use other cooling equipment such as a heat exchanger to meet the cooling of the treatment liquid. function. The cooling device and the heating device used in the present invention are the same as those in the prior art, and the specific structure will not be repeated.

After the waste water is processed through the treatment process of embodiment 1 and embodiment 2 of the present invention, the index parameters of each item contained in it change as shown in the following table:

In addition, the difference between Example 1 and Example 2 in this program is that the second-stage disc-tube membrane group in Example 1 uses DTNF (nanofiltration), and its working pressure is lower than that of Example 2 using DTRO (reverse osmosis), which can reduce Operating energy consumption.

Of course, the above description is not limited to the above examples, and the undescribed technical features of the present invention can be realized by or using existing technologies, and will not be repeated here; the above embodiments and drawings are only used to illustrate that the technical solutions of the present invention are not is a limitation of the present invention, and the present invention has been described in detail with reference to preferred embodiments, and those of ordinary skill in the art should understand that changes, modifications, Neither addition nor replacement deviates from the gist of the present invention, and should also belong to the protection scope of the claims of the present invention.

Claims (10)

1. a kind of no pollution of silica gel waste water discharges and recycling treatment process, it is characterised in that: the following steps are included:

The first step, impurity concentration, produce water recycling: waste water is preprocessed filter out suspended matter after, be passed through level-one dish tubular membrane component And sulfate radical, calcium ions and magnesium ions and part of silica are concentrated in concentrated water side by level-one dish tubular membrane component, level-one dish tubular type The production water recycling of membrane module permeate side is used for silica gel acid cleaning process water；

Second step, flocculation sedimentation, circulating filtration: the concentrated water of level-one dish tubular membrane component is passed through in sedimentation basin, first adjust pH to Flocculant is added in neutrality afterwards, so that calcium ions and magnesium ions and silica in water is formed precipitating, solution in sedimentation basin is separated by solid-liquid separation, Sedimentation basin solution is passed through tubular membrane group, forms circulating filtration in the concentrate recirculation to sedimentation basin of tubular membrane group；

Third step, sodium sulphate concentration, crystallisation by cooling: the production water of tubular membrane group is passed through second level dish tubular membrane component and carries out to sodium sulphate Concentration, carrying out cooling down to the concentrated water of second level dish tubular membrane component is precipitated sulfate crystal therein, will be molten after crystallization Liquid is back in the water inlet of second level dish tubular membrane component and in reflux course to the solution heat temperature raising after crystallization, makes it for sulfuric acid Sodium is in undersaturated condition, after being further concentrated using second level dish tubular membrane component, to concentrated water crystallisation by cooling, realizes the more of concentrated water Grade concentration, crystallisation by cooling；

4th step recycles solid sodium sulfate.

2. the no pollution of silica gel waste water according to claim 1 discharges and recycling treatment process, it is characterised in that: described Level-one dish tubular membrane component be dish tubular nanofiltration membrane group；The second level dish tubular membrane component is dish tubular nanofiltration membrane group or dish Tubular type reverse osmosis membrane group.

3. the no pollution of silica gel waste water according to claim 1 discharges and recycling treatment process, it is characterised in that: second In step, when calcium ions and magnesium ions concentration is lower than 1mmol/L in solution in sedimentation basin, when silica concentration is lower than 20mg/L, tubular membrane The production water of group is passed through the processing of second level dish tubular membrane component.

4. zero-emission and the recycling treatment process of silica gel waste water according to claim 1, it is characterised in that: in third step In, the concentrated water cooling down of second level dish tubular membrane component is to 10 DEG C or less；Solution after crystallization is back to second level dish tubular membrane group During part, temperature is heated to 30~35 DEG C.

5. the no pollution of silica gel waste water according to claim 1 or 2 discharges and recycling treatment process, it is characterised in that: In the third step, the production water recycling of the second level dish tubular membrane component is used for silica gel acid cleaning process water.

6. the no pollution of silica gel waste water according to claim 1 discharges and recycling treatment process, it is characterised in that: described Tubular membrane group be tubular ultra-filtration membrane group or tube microfiltration membrane group.

7. the no pollution of silica gel waste water according to claim 1 discharges and recycling treatment process, it is characterised in that: the In two steps, the flocculant is the combination of one or more of calcium chloride, magnesium chloride, aluminium polychloride, PAM.

8. a kind of silica gel waste water treatment system using treatment process described in claim 1, including wastewater equalization pond, feature It is:

It further include level-one dish tubular membrane component, second level dish tubular membrane component, sedimentation basin and tubular membrane group；

The water inlet end of level-one dish tubular membrane component is connect with wastewater equalization pond, and the concentrated water end of level-one dish tubular membrane component passes through precipitating Pond is connect with the water inlet end of tubular membrane group, and the concentrated water end of tubular membrane group is connect by the first return pipe with sedimentation basin；

The water inlet end of second level dish tubular membrane component is connect by intermediate water tank with the production water end (W.E.) of tubular membrane group, second level dish tubular membrane group The concentrated water end of part is connected with crystallizing pond, and the cooling device that can cool down to concentrated water is equipped in crystallizing pond, and crystallizing pond also passes through second time Flow tube is connect with the water inlet end of second level dish tubular membrane component, and the heat riser that can be heated up to phegma is equipped in the second return pipe.

9. silica gel waste water treatment system according to claim 8, it is characterised in that: the level-one dish tubular membrane component is Dish tubular nanofiltration membrane group；The second level dish tubular membrane component is dish tubular nanofiltration membrane group or disc tube reverse osmosis (dt-ro) film group.

10. silica gel waste water treatment system according to claim 8, it is characterised in that: the level-one dish tubular membrane component Production water end (W.E.) and second level dish tubular membrane component production water end (W.E.) with produce water reuse tank connect.