CN114804479A - Process method for treating inorganic silica gel production wastewater - Google Patents
Process method for treating inorganic silica gel production wastewater Download PDFInfo
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Abstract
The invention relates to the technical field of chemical wastewater treatment, in particular to a process method for treating inorganic silica gel production wastewater. The method comprises the following steps: 1) carrying out electrolytic silicon removal treatment on the pretreated silica gel production wastewater; 2) carrying out ultrafiltration treatment on the wastewater subjected to electrolytic desiliconization in the step 1) to obtain ultrafiltration treated water; 3) performing reverse osmosis treatment on the ultrafiltration treatment water provided in the step 2) to obtain a first water body and a second water body; 4) evaporating the second water body provided by the step 3) to obtain anhydrous sodium sulfate. The method can effectively remove soluble silicon in the silica gel production wastewater, well solves the problem of scaling and blocking of the ultrafiltration membrane and the reverse osmosis membrane, greatly prolongs the service time of the membrane, reduces the treatment cost, and realizes zero emission of the inorganic silica gel production wastewater.
Description
Technical Field
The invention relates to the technical field of chemical wastewater treatment, in particular to a process method for treating inorganic silica gel production wastewater.
Background
The silica gel is a silica xerogel with a three-dimensional network structure and belongs to the field of polymerThe pore material, which has a large inner surface area and a specific micropore volume, is mainly composed of silica. Usually, the sodium silicate is reacted with sulfuric acid and then is prepared by a series of post-treatment processes such as aging, acid soaking and the like. The chemical formula is mSiO 2 .nH 2 And O. Insoluble in water and any solvent, non-toxic, odorless, stable in chemical property, and non-reactive with any substance except strong alkali and hydrofluoric acid. Different types of silica gel form different microporous structures due to different manufacturing methods. The chemical components and physical structure of silica gel determine that the silica gel has the characteristics of difficult substitution of other similar materials: high adsorption performance, good thermal stability, stable chemical property, higher mechanical strength and the like.
The main raw materials for silica gel production: sodium silicate (chemical name, sodium silicate, commonly known as water glass) and sulfuric acid. The chemical reaction formula is as follows: na (Na) 2 SiO 3 +H 2 SO 4 ——Na 2 SO 4 +SiO 2 +H 2 O
The production process is briefly described as follows:
(1) acid and alkali preparation: the sulfuric acid and the liquid sodium silicate are prepared to a certain concentration (or pH value).
(2) Gel making (gel granulation): the method is characterized in that diluted foam lye prepared to a certain concentration and diluted sulfuric acid are fully reacted under a certain condition to form a sol-gel solution, and then gel particles are formed after the certain concentration is reached.
(3) Aging: the gel can be aged for a certain time under certain temperature and pH value conditions, so that the gel framework can be firm.
(4) Acid soaking and water washing: the acid soaking and washing of the gel are to form Na of granular gel 2 SO 4 And (4) washing off.
(5) And (3) drying: and (3) putting the prepared hydrogel into a drying room, and drying the water content of the hydrogel to a required range under the conditions of a certain temperature and a certain time.
(6) Screening: and (4) screening the dried silica gel by a ball separator according to certain granularity through screens with different apertures.
(7) Picking glue: and (4) sorting out the heterochromatic balls and impurities in the silica gel to finally obtain a qualified silica gel product.
(8) Packaging and warehousing: the packaging is carried out by using a woven bag (or a composite bag) and a pe film bag, the general requirement is 25 kg/bag, and the packaged silica gel product can be put in storage.
In the production process of silica gel, two kinds of waste water can be generated, the first kind is silica gel mother liquor (waste water), the mother liquor amount is less than or equal to 8m 3 T silica gel, wherein the sodium sulfate content is about 5.79%; the second is silica gel pickling water (waste water), the washing water amount is less than or equal to 17m 3 A/t silica gel having a sodium sulfate content of about 0.656%. The total amount of the waste water after mixing the mother liquor and the washing water is 25m 3 Pert silica gel, the average sodium sulfate content is about 2.559%. Meanwhile, the silica gel mother liquor and the washing wastewater also contain elemental substances such as colloidal silica and soluble silicon, and table 1 shows the content of some elemental substances in the silica gel production wastewater.
TABLE 1
Item | Unit of | Silica gel washing water | Silica gel mother liquor |
Cl | mg/L | ≥66 | ≥120 |
F | mg/L | ≥50 | ≥50 |
Ca 2+ | mg/L | ≥14 | ≥17 |
Mg 2+ | mg/L | ≥1.6 | ≥2.2 |
Al 3+ | mg/L | ≥0.05 | ≥0.11 |
Fe 2+ | mg/L | ≥0.05 | ≥0.09 |
Mn | mg/L | ≥0.1 | ≥0.15 |
Soluble silicon | mg/L | ≥200 | ≥380 |
The prior art mainly has two methods for treating the silica gel production wastewater. The first method employs direct evaporation, and has the disadvantages of large investment and high operation cost. A production system for producing 30000 tons of silica gel in one year adopts multi-effect direct evaporation or MVR direct evaporation, the one-time investment is more than 6000 ten thousand yuan, the cost of each ton of silica gel is increased by more than 800 yuan, and the production cost accounts for about 30% of the production cost, which is unacceptable for production enterprises. The second method adopts membrane separation concentration and evaporation, because the silica gel production wastewater contains a certain amount of silica, mainly colloidal silica and soluble silica, especially because of the existence of the soluble silica, silica scale can be formed on the membrane after the membrane separation equipment operates for hours, and thus, silica blockage is caused. No matter the ultrafiltration membrane or the reverse osmosis membrane is used, once the silicon plug is formed, the prior art means cannot be cleaned, and only a new membrane can be discarded and replaced, so that a pure membrane separation and concentration mode is fundamentally infeasible. Even if flocculation precipitation is carried out by adding a chemical silicon removal medicament before membrane separation, soluble silicon in wastewater cannot be fully removed, and in addition, the chemical silicon removal medicament has high cost, enterprises cannot bear high operating cost, and no production enterprise at home and abroad really realizes zero emission of silica gel production wastewater treatment so far.
From the above, how to provide a low-cost treatment method for silica gel production wastewater, and to realize zero discharge of silica gel production wastewater treatment is a technical problem to be solved urgently at present.
Disclosure of Invention
In view of the above-mentioned disadvantages of the prior art, it is an object of the present invention to provide a process for treating wastewater from the production of inorganic silica gel.
The purpose of the invention can be realized by the following technical scheme: the invention provides a process method for treating inorganic silica gel production wastewater, which comprises the following steps:
1) carrying out electrolytic silicon removal treatment on the pretreated silica gel production wastewater;
2) carrying out ultrafiltration treatment on the wastewater subjected to electrolytic desiliconization in the step 1) to obtain ultrafiltration treated water;
3) performing reverse osmosis treatment on the ultrafiltration treatment water provided in the step 2) to obtain a first water body and a second water body;
4) evaporating the second water body provided by the step 3) to obtain anhydrous sodium sulfate.
In some embodiments of the invention, the pre-treatment in step 1) comprises: naturally settling the wastewater to be treated; and adding alkali into the naturally settled wastewater to neutralize until the pH value is 6-7.
In some embodiments of the invention, the base is selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, in combination with one or more thereof.
In some embodiments of the invention, the step 1) of electrolytic silicon removal is to electrolyze the pretreated silica gel production wastewater under 100-200A current and 24-36V voltage, and the metal ions dissolved out from the metal anode are hydrolyzed in water to generate flocculation; the anode produces oxygen and the cathode produces hydrogen, which after electrolysis, colloidal and soluble silicon become flocs, which are oxides and hydroxides of metals.
In some embodiments of the invention, the metal ion is selected from Fe 2+ And/or Al 3+ 。
In some embodiments of the present invention, step 2) is performed by adding a silicon removing agent and a coagulant aid to the wastewater after electrolytic silicon removal in step 1) and then performing ultrafiltration treatment.
In some embodiments of the invention, the coagulant aid is selected from polyacrylamide.
In some embodiments of the invention, the silicon removal agent is selected from FeCl 3 One or more of polyaluminium chloride and Fe/Al complexing agent.
In some embodiments of the invention, the silicon removing agent is used in an amount of 0.05-0.15 kg/t water; the dosage of the coagulant aid is 0.002-0.005 kg/t of water.
In some embodiments of the invention floes are also obtained after the ultrafiltration treatment in step 2), and said floes are subjected to sludge dewatering to separate dewatered sludge.
In some embodiments of the invention, step 3) is performed by adding a high silica scale inhibitor to the ultrafiltration treatment water provided in step 2) to perform reverse osmosis treatment.
In some embodiments of the invention, the high silica scale inhibitor is selected from a combination of one or more of organophosphates, inorganic phosphates.
In some embodiments of the invention, the high silica scale inhibitor is used in an amount of 0.001 to 0.005kg/t water.
In some embodiments of the invention, the first body of water obtained in step 3) and the evaporated condensate of the evaporation process are reused for silica gel production.
In some embodiments of the invention, the evaporation temperature is from 90 ℃ to 120 ℃; the pressure is-0.1 to 0.1 mPa.
In some embodiments of the invention, the reverse osmosis treatment comprises SRO membranes.
In some embodiments of the invention, the SRO membrane is selected from the group consisting of a reverse osmosis RO membrane, a loose reverse osmosis membrane, and a combination between a reverse osmosis RO membrane and a loose reverse osmosis membrane.
Drawings
FIG. 1 is a process flow diagram for treating wastewater from silica gel production according to the present invention.
FIG. 2 is a schematic diagram of electrolytic silicon removal according to the present invention.
FIG. 3 is a schematic view of an electrolytic silicon removing apparatus according to the present invention. Wherein: a. a water inlet b, a water outlet c, a sewage discharge outlet d, an electrode plate anode interface e, and an electrode plate cathode interface.
FIG. 4 is a bottom sludge guide groove of the immersed ultrafiltration membrane of the invention.
Detailed Description
The process for treating wastewater from inorganic silica gel production according to the present invention is described in detail below.
In the prior art, a pure chemical silicon removal mode such as aluminum salt (PAC flocculant + PAM coagulant aid) is usually adopted for treating silica gel production wastewater, although the pure chemical silicon removal mode has a certain removal effect on the silica gel in the wastewater, the removal efficiency on soluble silicon is extremely low, a large amount of soluble silicon enters a subsequent ultrafiltration membrane and a reverse osmosis membrane, and silica scale is formed on the surface of the membrane after hours to pollute the plugging membrane. In the current technology, the best method for cleaning silicon dioxide pollution is to clean with hydrofluoric acid, but the use of hydrofluoric acid cleaning can cause irreparable damage to the film, so once the film forms a silicon plug, the film cannot be cleaned at all in actual operation, only a new film can be replaced, and the cost is too high due to the use of a large amount of chemical silicon removal agents, and enterprises cannot bear high operating cost. Therefore, no matter which treatment method is adopted for the silica gel production wastewater in the prior art, the high operation cost of wastewater treatment is difficult to avoid, so that production enterprises cannot really realize zero discharge of silica gel production wastewater treatment. Because the existing silica gel production wastewater treatment technology has the problems of high requirement on a treatment device, large investment and high treatment cost, and can not meet the requirement of production enterprises on realizing zero discharge of silica gel wastewater treatment. Therefore, the invention provides a process method for treating inorganic silica gel production wastewater, which comprises the following steps:
the invention provides a process method for treating inorganic silica gel production wastewater, which comprises the following steps:
1) carrying out electrolytic silicon removal treatment on the pretreated silica gel production wastewater;
2) carrying out ultrafiltration treatment on the wastewater subjected to electrolytic desiliconization in the step 1) to obtain ultrafiltration treated water;
3) performing reverse osmosis treatment on the ultrafiltration treatment water provided in the step 2) to obtain a first water body and a second water body;
4) evaporating the second water body provided by the step 3) to obtain anhydrous sodium sulfate.
In the process method for treating the inorganic silica gel production wastewater, the step 1) is to perform electrolytic desiliconization treatment on the pretreated silica gel production wastewater.
In step 1), in order to improve the effect of the electrolytic silicon removal treatment, in a preferred embodiment of the present invention, before the electrolytic silicon removal treatment, the silica gel production wastewater needs to be pretreated, and the pretreatment comprises: naturally settling the wastewater to be treated; and adding alkali into the naturally settled wastewater to neutralize until the pH value is 6-7. The natural sedimentation can be carried out, for example, in a sedimentation wastewater. The base may be, for example, one or a combination of more of sodium hydroxide, sodium carbonate, sodium bicarbonate, and the like. The addition amount of the alkali is 0.2-0.3 kg of 30% liquid alkali/t water. Namely, the amount of 30% caustic soda liquid contained in 1 ton of water is 0.2 to 0.3 kg.
Specifically, silica gel production wastewater containing sodium sulfate produced in the silica gel production process enters a workshop wastewater tank, then enters a precipitation wastewater tank for natural precipitation, and then wastewater from which impurities and part of precipitates are removed through precipitation is sent to an electric desiliconization device through a wastewater pump. Because the pH value of the wastewater is about 2.5, the wastewater is not suitable for electrolysis, and alkali is needed to be added to neutralize the wastewater to be neutral before the wastewater enters the electric desiliconization device.
Electrolytic silicon removal in the step 1) is carried out in an electric silicon removal device, and the electric silicon removal device comprises a water inlet, a cavity and a water outlet which are sequentially in fluid communication; a sewage draining outlet is formed in the bottom of the cavity; an anode plate and a cathode plate are arranged in the cavity; the device also comprises an electrode plate anode interface connected with the anode plate and an electrode plate cathode interface connected with the cathode plate.
And (3) electrolyzing the pretreated silica gel production wastewater under the current of 100-200A and the voltage of 24-36V to remove silicon.
Specifically, the invention utilizes electrolytic chemical flocculation technology to remove colloidal silicon and soluble silicon (electrical desiliconization or electrolytic desiliconization for short) in the silica gel wastewater. The electric desiliconization device (see figure 3) is desiliconization equipment which is drawn up according to the electrochemical electrolysis principle, and the working principle is as follows: the metal is used as an electrode, the silica gel production wastewater is electrolyzed between the electrode plates, chemical substances generated by the metal electrode during electrolysis and the colloidal silicon and soluble silicon in the silica gel production wastewater generate a series of complex electrochemical reactions, or are removed by oxidation, or are separated out by dissociation, or are taken out of a water body by secondary gas, or are subjected to reduction reaction, and the like, so that the removal of the colloidal silicon and the soluble silicon is finally realized.
In a specific implementation scenario, the specific flow of the electrolytic silicon removal process is briefly described as follows (see fig. 2): under the condition of certain current and voltage, Fe dissolved out of the metal anode 2+ 、Al 3+ (the preferred use of Fe dissolution in the present invention 2+ Electrochemical device) plasma is hydrolyzed in water to generate flocculation, and H is generated by the anode and the cathode 2 And O 2 The air bubbles in the air flow are equal to each other, so that good air floating effect is generated, and O is generated 2 The method also has an oxidation effect on the colloidal silicon and soluble silicon in the wastewater from the production of the silica gel and other substances to be removed for pollution. The colloidal silicon and soluble silicon in the silica gel production wastewater treated by the electrolytic chemical flocculation equipment are changed into metal oxygenFlocs such as oxides and hydroxides are removed by precipitation.
In the process method for treating the inorganic silica gel production wastewater, step 2) is to carry out ultrafiltration treatment on the wastewater after the electrolytic desiliconization in step 1) to obtain ultrafiltration treated water.
Further, in order to remove flocs such as metal oxides and hydroxides formed by electrolytic desiliconization more easily and efficiently. In a preferred embodiment of the invention, after the electrolytic desiliconization treatment and before the ultrafiltration treatment, a desiliconization agent and a coagulant aid are added to the wastewater after the electrolytic desiliconization.
In some embodiments, the silicon removal agent may be selected from FeCl, for example 3 PAC (polyaluminium chloride), Fe/Al complexing agent and the like. Wherein in the Fe/Al complexing agent, the mass ratio of Fe to Al is 1: 1-2: 1. The dosage of the silicon removing agent is 0.05-0.15 kg/t water. Namely 0.05-0.15 kg of silicon removing agent in 1 ton of water.
In some embodiments, the coagulant aid may be selected from PAM (polyacrylamide), for example. The dosage of the coagulant aid is 0.002-0.005 kg/t of water. Namely, the silicon removing agent is 0.002-0.005 kg in 1 ton water.
Specifically, flocs such as metal oxides, hydroxides and the like formed by electrolytic desiliconization are matched with a small amount of desiliconization agent and coagulant aid (or reducing agent and other auxiliary agents with the same action), so that the specific surface area of the particles of the flocs is increased, the activity is improved, the stability is good, and the precipitation effect is better. It is noted that the silica removing agent and the coagulant aid may be selected according to specific implementation conditions and are within the protection scope of the present invention.
The present invention utilizes an immersed ultrafiltration membrane module (patent No. 201720311859.3) to separate flocculate from brine to obtain ultrafiltration treated water. After the silica gel production wastewater is electrically desilicated, flocculated and precipitated, the rest suspended matters containing silicide are left, and then most of silicide in the water can be removed through a subsequent immersed ultrafiltration membrane component. The immersed ultrafiltration membrane component is membrane separation equipment adopting an immersed ultrafiltration membrane, can be directly immersed in the water tank, and is flushed by air disturbance, so that the ultrafiltration membrane can still stably run when the concentration of suspended matters in the silica gel production wastewater reaches 1-2%. Meanwhile, the immersed ultrafiltration component adopts a slotted design, so that the suspended matters containing silicide which are left after the electric desiliconization flocculation precipitation can be quickly separated from the membrane component without being accumulated in the ultrafiltration membrane, and the flux of the membrane is ensured. Therefore, the immersed ultrafiltration membrane component has stronger impact resistance to the water quality fluctuation of the silica gel production wastewater, can not be blocked after long-time operation, and also overcomes the problem of incomplete flocculation reaction of the traditional ultrafiltration membrane because the retention time of suspended matters in the membrane pool is prolonged.
In order to fully recover and treat the wastewater from silica gel production, in a preferred embodiment of the invention, the ultrafiltration flocs are sent to a sludge tank, and dewatered sludge is separated by a stack screw machine. Specifically, after silicon in the wastewater passing through the electric desiliconization device is flocculated by adding agents such as a desiliconization agent, a coagulant aid and the like, the wastewater enters an immersed ultrafiltration membrane assembly to separate flocculate from saline water, the separated flocculate (sludge) is discharged into a sludge tank, the sludge is pumped to a screw stacking machine by a sludge pump to be dewatered, and dewatered sludge with low water content is separated out and is pulled by a truck for subsequent treatment.
In the process method for treating the inorganic silica gel production wastewater provided by the invention, step 3) is to perform reverse osmosis treatment on the ultrafiltration treatment water provided in step 2) to obtain a first water body and a second water body.
In the step 3), the first water body is clear water, and the second water body is concentrated water containing impurities.
In step 3), the salt water after ultrafiltration treatment, i.e. ultrafiltration treatment water, is pressurized by a high-pressure pump and then enters an SRO reverse osmosis system for salt concentration, and in order to ensure that the SRO reverse osmosis membrane operates stably, in a preferred embodiment of the invention, a high silica scale inhibitor is added into the ultrafiltration production water before the reverse osmosis treatment. The high-silicon scale inhibitor is optimized according to the characteristics of silica scale, has high dispersibility, enhances the dispersion effect on soluble silicon, and is used for controlling scale formation and deposits in a reverse osmosis membrane separation system and reducing particle blockage. It should be noted that the high silica scale inhibitor can be selected according to the specific implementation, and this is within the protection scope of the present invention. The SRO reverse osmosis membrane has a parameter aperture of 0.01-1 nm, 0.01-0.1 nm, 0.1-0.3 nm, 0.3-0.5 nm, 0.5-0.8 nm, or 0.8-1 nm, etc.
In some embodiments, the SRO membrane is selected from the group consisting of a reverse osmosis RO membrane, a loose reverse osmosis membrane, and a combination between a reverse osmosis RO membrane and a loose reverse osmosis membrane.
In some embodiments, the high silica scale inhibitor can be selected, for example, from a combination of one or more of organophosphates, inorganic phosphates, and the like. The dosage of the high-silicon scale inhibitor is 0.001-0.005 kg/t water. Namely 0.001-0.005 kg of the medium-high silicon scale inhibitor in 1 ton of water.
In the process method for treating the inorganic silica gel production wastewater provided by the invention, in the step 4), the second water body provided in the step 3) is evaporated to obtain anhydrous sodium sulfate.
In the step 4), the salt content of the second water body concentrated by the reverse osmosis system is about 12%, and the second water body is pumped to an evaporation system for evaporation treatment to obtain the industrial I class anhydrous sodium sulfate with more than first class. The evaporation system can adopt multi-effect evaporation or MVR evaporation system. And the evaporation condensed water of the evaporation system and the first water body filtered by the reverse osmosis system are sent to a clear water tank for the recycling of the silica gel production system.
In the step 4), the evaporation temperature is 90-120 ℃, 90-100 ℃, 100-110 ℃, or 110-120 ℃ and the like. The pressure is-0.1 to 0.1 mPa.
The invention discloses a process method for treating inorganic silica gel production wastewater, which comprises the following steps of carrying out electrolytic desiliconization treatment on pretreated silica gel production wastewater through an electric desiliconization device; carrying out ultrafiltration treatment on the wastewater subjected to electrolytic desiliconization through an immersed ultrafiltration membrane component to obtain ultrafiltration treated water; performing reverse osmosis treatment on the ultrafiltration treatment water to obtain a first water body and a second water body; and sending the second water body to an evaporation system for evaporation treatment to obtain anhydrous sodium sulfate. Experiments prove that compared with the prior art, the process method disclosed by the invention can effectively remove soluble silicon in the silica gel production wastewater, well solves the problem of scaling and blocking of an ultrafiltration membrane and a reverse osmosis membrane, greatly prolongs the service time of the membrane, reduces the treatment cost and realizes zero emission of the inorganic silica gel production wastewater.
The following examples are provided to further illustrate the advantageous effects of the present invention.
In order to make the objects, technical solutions and advantageous technical effects of the present invention more clear, the present invention is further described in detail below with reference to examples. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. The examples were prepared under conventional conditions or conditions recommended by the material suppliers without specifying specific experimental conditions or operating conditions.
Furthermore, it is to be understood that one or more method steps mentioned in the present invention does not exclude that other method steps may also be present before or after the combined steps or that other method steps may also be inserted between these explicitly mentioned steps, unless otherwise indicated; it is also to be understood that a combined connection between one or more devices/apparatus as referred to in the present application does not exclude that further devices/apparatus may be present before or after the combined device/apparatus or that further devices/apparatus may be interposed between two devices/apparatus explicitly referred to, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, and changes or modifications in the relative relationship may be made without substantially changing the technical content.
In the following examples, reagents, materials and instruments used are commercially available unless otherwise specified.
Example 1
And (3) conveying the silica gel production wastewater from the workshop wastewater tank to a precipitation wastewater tank for natural sedimentation, adding a small amount of alkali into the naturally sedimentated wastewater for neutralization until the wastewater is slightly acidic, and then carrying out electrolytic desiliconization treatment by using an electric desiliconization device. Adding a small amount of desiliconization agent and coagulant aid after electrolytic desiliconization, carrying out ultrafiltration treatment by an immersed ultrafiltration membrane component, adding a high-silicon scale inhibitor into ultrafiltration treatment water, and carrying out reverse osmosis treatment by an SRO reverse osmosis system to obtain a first water body and a second water body. And (3) delivering the second water body to an evaporation system for evaporation treatment, and obtaining the anhydrous sodium sulfate at the temperature of 90-120 ℃ and under the pressure of-0.1 mPa. And (4) conveying the evaporation condensed water of the evaporation system and the first water body to a clear water tank for recycling of the silica gel production system. Wherein, the selection and dosage of the silica removing agent, the coagulant aid and the high silica scale inhibitor are shown in Table 6.
Comparative example 1
The method comprises the steps of conveying silica gel production wastewater from a workshop wastewater tank to a precipitation wastewater tank for natural sedimentation, adding a large amount of PAC flocculant and PAM coagulant aid for chemical desiliconization, carrying out ultrafiltration treatment through an immersed ultrafiltration membrane component after chemical desiliconization, and carrying out reverse osmosis treatment through an SRO reverse osmosis membrane component after adding a high-silicon scale inhibitor into ultrafiltration production water to obtain a first water body and a second water body. And (3) delivering the second water body to an evaporation system for evaporation treatment, and obtaining the anhydrous sodium sulfate at the temperature of 90-120 ℃ and under the pressure of-0.1 mPa. And sending the evaporation condensed water of the evaporation system and the first water body to a clear water tank for the silica gel production system to use. Wherein, the selection and dosage of the flocculating agent, the desiliconization agent, the coagulant aid and the high-silicon scale inhibitor are shown in table 5.
Example 1 is the process method for treating wastewater from silica gel production by electrolytic desiliconization provided by the invention, and the difference between comparative example 1 and example 1 is that the traditional chemical desiliconization technology in the prior art is adopted before the ultrafiltration treatment.
Table 2 compares the silicon content data of the water before entering the reverse osmosis membrane module for example 1 and comparative example 1
TABLE 2
Table 3 shows the operating data of the reverse osmosis system of comparative example 1.
TABLE 3
Table 4 shows the operating data of the reverse osmosis system of example 1.
TABLE 4
TABLE 5 comparative example 1 type and amount of chemicals used in conventional chemical silicon removal
TABLE 6 kinds and amounts of chemical agents used for the electrical desiliconization of example 1
As can be seen from Table 2, the silicon content in the wastewater from silica gel production can only be removed from 330mg/L to about 80mg/L by using the conventional chemical silicon removal technology, and although the service life of the membrane can be prolonged, the silicon blockage of the membrane can still be caused after long-term operation. As shown in Table 3, after the traditional chemical agent is adopted to remove silicon, the flow of the first water body and the flow of the second water body are reduced along with the time in the operation process of the reverse osmosis membrane, and the inlet-outlet pressure difference of the reverse osmosis membrane is larger and larger. This indicates that the reverse osmosis membrane becomes more clogged over time, and in fact after the system has been operating for 58 hours, the reverse osmosis system is forced to shut down because of the clogging.
This is because the conventional chemical silicon removal technology has the following disadvantages: 1. the traditional chemical flocculation forms a flocculating agent with small specific surface area, low activity and more bound water, so the stability is poor and the separation is not facilitated; 2. in the traditional chemical flocculation, flocculates are suspended in liquid in the flocculation process, so that the removal of suspended matters is not facilitated; 3. traditional chemical flocculation cannot effectively remove tiny colloidal substances.
And the traditional chemical silicon removal treatment of silica gel production wastewater has high cost and complex process. In the prior art, the oxidation, adsorption, flocculation, solid-liquid separation and other measures are generally carried out step by step, and the treatment process and the device are complicated and easily generate some uncontrollable adverse factors; a large amount of chemical agents are added in the chemical flocculation, secondary pollution is caused, and meanwhile, a process of neutralizing or removing anions is needed in the subsequent process, so that the process is complex; the total soluble solid content in the effluent of the chemical flocculation is higher, so that the water recovery cost is increased; the cost of the specific chemical agent is about 4.01 yuan/ton of wastewater, and the service life of the membrane is short and the membrane needs to be replaced frequently.
By utilizing the electrolytic silicon removal technology, the content of soluble silicon which is difficult to remove in the silica gel production wastewater can be economically removed from 330mg/L to below 30 mg/L. Practice proves that for the ultrafiltration membrane and the reverse osmosis membrane, silicon blockage can not be generated when the silicon content is below 30 mg/L. The water after silicon removal enters a membrane separation concentration and evaporation system with a relatively mature process, so that the zero discharge of the purification treatment of the silica gel production wastewater can be realized. As shown in Table 4, the flow rates of the first water body and the second water body in the reverse osmosis membrane operation process after the electrolytic silicon removal of the invention are not obviously changed along with the time, and the inlet-outlet pressure difference of the reverse osmosis membrane is not changed, so that the reverse osmosis system can still normally operate after continuously operating for 384 hours, and the membrane blocking phenomenon can not be generated. The method for removing silicon by electricity can achieve the purpose of removing silicon (mainly referring to soluble silicon) from the wastewater generated in the production of silica gel by consuming electricity and a small amount of electrodes, has relatively low operation cost, consumes electricity and electrodes for removing silicon by electricity at the cost of 1.4 yuan/ton of wastewater, and increases the cost within the acceptable range of enterprises. Meanwhile, the service life of the membrane is longer, so that the treatment cost of the waste water produced by the silica gel is greatly reduced.
Compared with the prior art, the invention also has the following advantages: 1. the specific surface area of a flocculating body formed in the flocculation process is large, the activity is high, and the bound water is less, so that the stability is high, the separation is easy, and the sedimentation time is greatly shortened; 2. the total soluble solid content in the effluent after flocculation by the technology is lower, so that the water recovery cost can be greatly reduced; 3. the metal hydroxide obtained by electrolysis has strong destabilization effect on the polluted colloid, so the invention is very effective in removing tiny colloid substances, and can greatly reduce the risk of blocking a subsequent reverse osmosis system membrane; 4. the technology of the invention does not need to add a large amount of chemical agents, thereby avoiding secondary pollution, and the electrolyzed metal hydroxide can neutralize water in the flocculation process, so that only a small amount of alkali is needed to be added in the early stage to neutralize the water to weak acidity, thereby reducing the alkali dosage; 5. the technology of the invention can generate micro bubbles in the flocculation process, and can carry flocculate to float to the surface of liquid, thereby leading the flocculate to be easier to remove; 6. the technology of the invention integrates various means such as oxidation, adsorption, flocculation, air flotation, solid-liquid separation and the like, so that the process flow is greatly shortened, the treatment device is simple and easy to operate, and the space of the device is greatly reduced.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not necessarily depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.
Claims (10)
1. A process method for treating inorganic silica gel production wastewater comprises the following steps:
1) carrying out electrolytic silicon removal treatment on the pretreated silica gel production wastewater;
2) carrying out ultrafiltration treatment on the wastewater subjected to electrolytic desiliconization in the step 1) to obtain ultrafiltration treated water;
3) performing reverse osmosis treatment on the ultrafiltration treatment water provided in the step 2) to obtain a first water body and a second water body;
4) evaporating the second water body provided by the step 3) to obtain anhydrous sodium sulfate.
2. The process for treating wastewater from inorganic silica gel production as claimed in claim 1, wherein the pretreatment in step 1) comprises: naturally settling the wastewater to be treated; adding alkali into the naturally settled wastewater to neutralize until the pH value is 6-7; preferably, the alkali is selected from one or more of sodium hydroxide, sodium carbonate and sodium bicarbonate.
3. The process for treating wastewater from inorganic silica gel production as claimed in claim 1, wherein in the step 1), the silicon removal by electrolysis is carried out on the pretreated wastewater from silica gel production under 100-200A current and 24-36V voltage, and metal ions dissolved out from the metal anode are hydrolyzed in water to generate flocculation; the anode produces oxygen and the cathode produces hydrogen, which after electrolysis, colloidal and soluble silicon become flocs, which are oxides and hydroxides of metals.
4. The process according to claim 3, wherein the metal ion is Fe 2+ And/or Al 3+ 。
5. The process for treating wastewater from inorganic silica gel production as claimed in claim 1, wherein in step 2), the wastewater from step 1) is subjected to ultrafiltration treatment after adding a silica removing agent and a coagulant aid; preferably, the coagulant aid is selected from polyacrylamide; the silicon removing agent is selected from FeCl 3 One or more of polyaluminium chloride and Fe/Al complexing agent; more preferably, the dosage of the silicon removing agent is 0.05-0.15 kg/t water; the dosage of the coagulant aid is 0.002-0.005 kg/t of water.
6. The process according to claim 1, wherein step 2) is carried out by ultrafiltration to obtain flocculates, and the flocculates are dewatered to separate dewatered sludge.
7. The process of treating wastewater from inorganic silica gel production as claimed in claim 1, wherein in step 3), a high silica scale inhibitor is added to the ultrafiltration treatment water provided in step 2) for reverse osmosis treatment; preferably, the high silica scale inhibitor is selected from one or more of organic phosphate and inorganic phosphate; more preferably, the dosage of the high-silicon scale inhibitor is 0.001-0.005 kg/t water.
8. The process for treating wastewater from inorganic silica gel production as claimed in claim 1, wherein the first water obtained in step 3) and the evaporated condensate water from the evaporation treatment are reused for silica gel production; preferably, the evaporation temperature is 90-120 ℃; the pressure is-0.1 mPa to 0.1 mPa.
9. The process of treating wastewater from the production of inorganic silica gel according to claim 1, wherein said reverse osmosis treatment comprises SRO reverse osmosis membrane; the aperture of the SRO reverse osmosis membrane is 0.01 nm-1 nm.
10. The process for treating inorganic silica gel production wastewater of claim 9 wherein the SRO reverse osmosis membrane is selected from the group consisting of a reverse osmosis RO membrane, a loose reverse osmosis membrane, and a combination of a reverse osmosis RO membrane and a loose reverse osmosis membrane.
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