阅读说明：本技术 一种绿色环保的特种二氧化硅及其生产方法 (Environment-friendly special silicon dioxide and production method thereof ) 是由 徐伟 陈建材 朱尔明 于 2020-12-31 设计创作，主要内容包括：本发明公开了绿色环保的特种二氧化硅及其生产方法,方法包括以下步骤：微硅粉收集活化处理；余热回收利用处理；高纯水玻璃制备；特种二氧化硅制备；废水处理。特种二氧化硅则采用上述绿色环保的特种二氧化硅生产方法制得。本发明利用工业硅尾气余热解决本工艺能源问题,同时通过焙烧将工业硅附产微硅粉除杂后再采用液相法反应、过滤生产高纯水玻璃硅源,最终得到成本低、品质好的特种二氧化硅产品；利用工业硅能源优势,采用膜浓缩和双极膜电渗析等处理方式对废水进行浓缩、电渗析分解的环保处理,可得到水、硫酸、氢氧化钠三种可以回用于系统的附产物,实现废水零排放；通过废水处理系统工艺作用,还进一步降低了工艺用水、硫酸、烧碱的有害杂质。(The invention discloses a green environment-friendly special silicon dioxide and a production method thereof, wherein the method comprises the following steps: collecting and activating micro silicon powder; waste heat recycling treatment; preparing high-purity water glass; preparing special silicon dioxide; and (4) treating wastewater. The special silicon dioxide is prepared by adopting the green and environment-friendly special silicon dioxide production method. According to the invention, the energy problem of the process is solved by using the waste heat of the industrial silicon tail gas, and simultaneously, the industrial silicon byproduct micro silicon powder is subjected to impurity removal through roasting, and then the high-purity water glass silicon source is produced through reaction and filtration by adopting a liquid phase method, so that a special silicon dioxide product with low cost and good quality is finally obtained; by utilizing the energy advantages of industrial silicon and adopting treatment modes such as membrane concentration, bipolar membrane electrodialysis and the like to carry out environment-friendly treatment of concentration and electrodialysis decomposition on the wastewater, three byproducts of water, sulfuric acid and sodium hydroxide which can be reused in a system can be obtained, and zero discharge of the wastewater is realized; the harmful impurities of process water, sulfuric acid and caustic soda are further reduced through the process effect of the wastewater treatment system.)

1. The production method of the green and environment-friendly special silicon dioxide is characterized by comprising the following steps:

and (3) collection and activation treatment of micro silicon powder: carrying out high-temperature roasting on the micro silicon powder obtained by thermal separation and collection in the industrial silicon smelting flue gas in an oxygen-rich atmosphere to obtain roasted micro silicon powder;

and (3) waste heat recycling treatment: exchanging heat between a part of industrial silicon smelting flue gas with the temperature of 450-900 ℃ and feed water, and using the obtained superheated steam for power generation to obtain recovered electric energy and waste heat recovery steam; exchanging heat between the other part of the industrial silicon smelting flue gas with the temperature of 450-900 ℃ and air to obtain heat exchange air;

preparing high-purity water glass: uniformly stirring and mixing the roasted micro silicon powder, a sodium hydroxide solution and process water, reacting by taking waste heat recovery steam as a heat source, cooling and filtering to obtain high-purity sodium silicate mother liquor;

preparing special silicon dioxide: diluting the high-purity water glass mother liquor to a preset concentration, uniformly stirring and mixing the diluted high-purity water glass mother liquor with sulfuric acid solution and process water, reacting by using waste heat recovery steam as a heat source, filtering and washing to obtain a special silicon dioxide filter cake and waste water, performing flash evaporation drying on the special silicon dioxide filter cake by using the heat exchange air as a drying heat source or performing spray drying on slurry obtained by pulping and homogenizing the special silicon dioxide filter cake, and performing ultrafine grinding to obtain special silicon dioxide;

wastewater treatment: pretreating the wastewater and then carrying out electrodialysis treatment to obtain strong brine and fresh water; sequentially carrying out chelate resin purification treatment and bipolar membrane electrodialysis treatment on the strong brine to obtain a sulfuric acid solution and a sodium hydroxide solution; and (3) carrying out reverse osmosis membrane separation treatment on the fresh water to obtain reuse water and a concentrated aqueous solution.

2. The method for producing green and environment-friendly special silica according to claim 1, wherein in the step of collecting and activating the micro silicon powder, the micro silicon powder comprises high-temperature micro silicon powder which is continuously separated from high-temperature flue gas generated in industrial silicon smelting by a cyclone separator and has a temperature of 450-900 ℃ and low-temperature micro silicon powder which is continuously separated from the high-temperature flue gas generated in industrial silicon smelting by waste heat recycling by a bag-type dust collector and has a temperature of 180-220 ℃.

3. The production method of the green and environment-friendly special silicon dioxide as claimed in claim 2, characterized by preheating the micro silicon powder to 560-650 ℃, then statically or dynamically roasting at 720-1100 ℃ in an oxygen-rich atmosphere, discharging and cooling after roasting for 15-90 minutes to obtain the roasted micro silicon powder, wherein the electric energy of the high-temperature roasting comes from the recovered electric energy.

4. The production method of the green and environment-friendly special silica as claimed in claim 1, wherein in the step of the waste heat recycling treatment, the temperature of the industrial silicon smelting flue gas after the waste heat recycling treatment is controlled to be 180-220 ℃, and the industrial silicon smelting flue gas is subjected to dust removal, desulfurization and denitration treatment in sequence and then discharged, the pressure of the waste heat recycling steam is controlled to be 1-3 MPa, the temperature of the waste heat recycling steam is controlled to be 220-450 ℃, and the temperature of the heat exchange air is controlled to be 350-550 ℃.

5. The method for producing green and environment-friendly special silica as claimed in claim 1, wherein in the step of preparing high-purity water glass, the predetermined concentration of dilution of the mother solution of the high-purity water glass is 18-26%, the concentration of the sodium hydroxide solution is 8-15%, and SiO in the raw materials is controlled₂:NaOH:H₂The mass ratio of O is 2-2.7: 1: 3-9.5, the reaction temperature is controlled to be 165-210 ℃, the reaction time is controlled to be 60-360 minutes, and sodium hydroxide solution obtained by wastewater treatment and reuse water are used as raw materials in the step.

6. The production method of the green and environment-friendly special silica as claimed in claim 1, wherein in the step of preparing the special silica, the concentration of the sulfuric acid solution is 8-10%, wherein the sulfuric acid solution obtained by wastewater treatment and reuse water are used as raw materials in the step.

7. The method for producing environment-friendly special silica according to claim 1, wherein the pretreatment comprises desiliconization, flocculation, precipitation and filtration, the concentrated aqueous solution is returned to be pretreated together with wastewater and wastewater zero discharge is realized, and the reuse water is used for filtration washing in the special silica preparation step.

8. The production method of the green and environment-friendly special silicon dioxide as claimed in claim 1, characterized in that a waste heat boiler is used for heat exchange between the industrial silicon smelting flue gas and the feed water, a generator is used for power generation, and an air heat exchanger is used for heat exchange between the industrial silicon smelting flue gas and the air.

9. A special silica, characterized in that it is produced by the method for producing the green environmental special silica according to any one of claims 1 to 8.

10. A specialty silica according to claim 9, wherein said specialty silica has a silica content of 99 wt% or more, an arsenic content of 2ppm or less, a lead content of 3ppm or less, an iron content of 120pm or less and a total other heavy metal (as lead) content of 15ppm or less.

Technical Field

The invention belongs to the technical field of silicon dioxide production, and particularly relates to green and environment-friendly special silicon dioxide and a production method thereof.

Background

The micro silicon powder is silicon-containing industrial micro dust which is obtained by escaping SiO and Si gases generated in an ore-smelting electric furnace, rapidly oxidizing by air and cooling in the production process of industrial silicon or ferrosilicon alloy, is micron-sized fine powder with high silicon dioxide content, is greatly harmful to human bodies after being inhaled by people, and belongs to solid waste. The special silicon dioxide is a high-purity, amorphous structure and porous material, the application field of the special silicon dioxide is continuously expanded along with the development of material application science and technology and the combination of excellent physical and chemical properties of the special silicon dioxide in recent years, the special silicon dioxide is widely applied to materials such as paint, toothpaste, food, medicine, cosmetics, printing ink, heat insulation, electronic packaging materials, resin and the like, different and excellent application properties are shown in different fields, and the special silicon dioxide is favored by more and more material fields along with the continuous innovation of the material application field.

The existing special silicon dioxide production technology comprises a hydrolysis method of taking orthosilicate as a silicon source, a sol method of taking water glass as a silicon source and a gel method of taking water glass as a silicon source, wherein the silicate hydrolysis method is high in overall production cost of products and limited in market application due to the fact that silicate raw materials are too high in cost and the difficulty in three-waste treatment is high. The main raw materials of the sol method and the gel method are water glass and sulfuric acid or hydrochloric acid, the purity requirements on the water glass and the sulfuric acid or hydrochloric acid are very high, the water glass and the sulfuric acid or hydrochloric acid which are supplied to the general market and reach the national standard cannot meet the production requirements, and the raw materials are subjected to impurity removal treatment or the purity requirements far higher than the national standard are provided during purchasing to meet the production requirements of the special silicon dioxide, so that the purchasing or treatment cost of the raw materials of the special silicon dioxide is increased, the production difficulty is increased, and the production cost is higher. A large amount of reaction and washing wastewater contains a large amount of sodium sulfate, is discharged after simple treatment, and has serious hidden danger of environmental protection.

The industrial silicon industry is a high-energy-consumption industry, an enterprise generally produces several electric furnaces at the same time, the quantity of generated tail gas is huge, the temperature of the discharged tail gas is as high as 450-900 ℃, the taken heat energy accounts for 19-35% of the electric energy consumption of the industrial silicon, and the content of silicon dioxide in the produced micro silicon powder is as high as about 94 wt%, the reaction activity is good, and the silicon dioxide is necessary to be fully utilized.

Disclosure of Invention

In order to solve the problems in the production of special silicon dioxide in the prior art, the invention aims to provide a method for producing environment-friendly special silicon dioxide, which has high heat utilization rate and can scientifically treat waste gas and waste water.

One aspect of the invention provides a method for producing a green and environment-friendly special silica, comprising the following steps:

and (3) collection and activation treatment of micro silicon powder: carrying out high-temperature roasting on the micro silicon powder obtained by thermal separation and collection in the industrial silicon smelting flue gas in an oxygen-rich atmosphere to obtain roasted micro silicon powder;

and (3) waste heat recycling treatment: exchanging heat between a part of industrial silicon smelting flue gas with the temperature of 450-900 ℃ and feed water, and using the obtained superheated steam for power generation to obtain recovered electric energy and waste heat recovery steam; exchanging heat between the other part of the industrial silicon smelting flue gas with the temperature of 450-900 ℃ and air to obtain heat exchange air;

preparing high-purity water glass: uniformly stirring and mixing the roasted micro silicon powder, a sodium hydroxide solution and process water, reacting by taking waste heat recovery steam as a heat source, cooling and filtering to obtain high-purity sodium silicate mother liquor;

preparing special silicon dioxide: diluting the high-purity water glass mother liquor to a preset concentration, uniformly stirring and mixing the diluted high-purity water glass mother liquor with sulfuric acid solution and process water, reacting by using waste heat recovery steam as a heat source, filtering and washing to obtain a special silicon dioxide filter cake and waste water, performing flash evaporation drying on the special silicon dioxide filter cake by using the heat exchange air as a drying heat source or performing spray drying on slurry obtained by pulping and homogenizing the special silicon dioxide filter cake, and performing ultrafine grinding to obtain special silicon dioxide;

wastewater treatment: pretreating the wastewater and then carrying out electrodialysis treatment to obtain strong brine and fresh water; sequentially carrying out chelate resin purification treatment and bipolar membrane electrodialysis treatment on the strong brine to obtain a sulfuric acid solution and a sodium hydroxide solution; and (3) carrying out reverse osmosis membrane separation treatment on the fresh water to obtain reuse water and a concentrated aqueous solution.

Further, in the step of collection and activation treatment of the micro silicon powder, the micro silicon powder comprises high-temperature micro silicon powder which is continuously separated from high-temperature flue gas generated in industrial silicon smelting through a cyclone separator and has the temperature of 450-900 ℃ and low-temperature micro silicon powder which is continuously separated from the high-temperature flue gas generated in industrial silicon smelting through waste heat recycling treatment through a bag-type dust collector and has the temperature of 180-220 ℃.

Further, preheating the micro silicon powder to 560-650 ℃, performing high-temperature roasting at 720-1100 ℃ in an oxygen-enriched atmosphere in a static or dynamic mode, discharging and cooling after roasting for 15-90 minutes to obtain roasted micro silicon powder, wherein electric energy of the high-temperature roasting is derived from the recovered electric energy.

Further, in the step of waste heat recycling treatment, the temperature of the industrial silicon smelting flue gas after the waste heat recycling treatment is controlled to be 180-220 ℃, the industrial silicon smelting flue gas is subjected to dust removal, desulfurization and denitration treatment in sequence and then discharged, the pressure of waste heat recycling steam is controlled to be 1-3 MPa, the temperature of the waste heat recycling steam is controlled to be 220-450 ℃, and the temperature of the heat exchange air is controlled to be 350-550 ℃.

Further, in the step of preparing the high-purity water glass, the preset concentration of the high-purity water glass mother liquor is 18-26% in a dilution mode, the concentration of the sodium hydroxide solution is 8-15%, and SiO in the raw materials is controlled₂:NaOH:H₂The mass ratio of O is 2-2.7: 1: 3-9.5, the reaction temperature is controlled to be 165-210 ℃, the reaction time is controlled to be 60-360 minutes, and sodium hydroxide solution obtained by wastewater treatment and reuse water are used as raw materials in the step.

Further, in the step of preparing the special silica, the concentration of the sulfuric acid solution is controlled to be 8-10%, wherein the sulfuric acid solution obtained by treating the wastewater and reuse water are used as raw materials in the step.

Further, the pretreatment comprises silicon removal, flocculation, precipitation and filtration, the concentrated aqueous solution is returned to be pretreated together with the wastewater, the zero discharge of the wastewater is realized, and the reuse water is used for filtering and washing in the special silicon dioxide preparation step.

Further, a waste heat boiler is used for exchanging heat between the industrial silicon smelting flue gas and the water supply, a generator is used for generating electricity, and an air heat exchanger is used for exchanging heat between the industrial silicon smelting flue gas and the air.

The invention also provides special silicon dioxide which is prepared by adopting the green and environment-friendly production method of the special silicon dioxide.

Furthermore, the content of silicon dioxide in the special silicon dioxide reaches more than 99 wt%, the content of arsenic is less than 2ppm, the content of lead is less than 3ppm, the content of iron is less than 120pm, and the total content of other heavy metals (calculated by lead) is less than 15 ppm.

Compared with the prior art, the invention solves the energy problem of the process by scientifically utilizing the waste heat of the industrial silicon tail gas, removes impurities from the industrial silicon byproduct micro-silicon powder by roasting, then adopts a liquid phase method to react and filter to produce high-purity water glass, and finally obtains a special silicon dioxide product with the cost about 30 percent lower than that of the product produced by the traditional mainstream process method and good quality; by utilizing the energy advantages of industrial silicon and adopting treatment modes such as membrane concentration, bipolar membrane electrodialysis and the like to carry out environment-friendly treatment of concentration and electrodialysis decomposition on the wastewater, three byproducts of water, sulfuric acid and sodium hydroxide which can be reused in a system can be obtained, and zero discharge of the wastewater is realized; the harmful impurities of process water, sulfuric acid and caustic soda are further reduced through the process action of the wastewater treatment system, the purity of raw materials and water is ensured, and a foundation is laid for producing high-purity special silicon dioxide.

Drawings

Fig. 1 shows a process flow diagram of a method for producing green and environmentally friendly specialty silicas according to an exemplary embodiment of the present invention.

Detailed Description

All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.

Any feature disclosed in this specification may be replaced by alternative features serving equivalent or similar purposes, unless expressly stated otherwise. That is, unless expressly stated otherwise, each feature is only an example of a generic series of equivalent or similar features.

The main technological process of special silica includes the first production of high quality solid water glass with quartz sand and high quality sodium carbonate through melting reaction at 1400 deg.c, the subsequent dissolving of the high quality solid water glass into liquid with steam, filtering to eliminate impurity, diluting to proper concentration, reaction with refined sulfuric acid liquid treated with impurity eliminating agent at certain temperature and stirring strength to produce special silica slurry and produce sodium sulfate as side product, filtering with filter press to eliminate mother liquid water, washing special silica cake with great amount of water to eliminate residual sodium sulfate, pulping the filter cake, final evaporation of water through centrifugal spray drying and superfine crushing to obtain the special silica product.

According to the process, on one hand, the special silicon dioxide is a high-energy-consumption chemical product, statistics shows that electricity, steam and coal consumption of the process accounts for 33% of the total production cost, coal is greatly used as a heat source, the heat energy utilization rate is low, and the environmental protection problem of emission of sulfur and nitrogen oxides of waste gas generated by burning coal also floats out of the water surface; the main raw materials of quartz sand, soda ash and sulfuric acid account for 52 percent of the total production cost; in addition, with the enhancement of national environmental protection, the problem of industrial wastewater treatment is increasingly prominent, the water consumption of one ton of special silicon dioxide produced by the process is up to more than 35 tons, the amount of wastewater to be discharged is at least 30 tons, and the wastewater contains low-concentration sodium sulfate.

Considering that the quantity of the tail gas generated in the industrial silicon production is huge, the temperature of the discharged tail gas is up to 450-900 ℃, the taken heat energy accounts for 19-35% of the electric energy consumption of the industrial silicon, and the heat energy can be scientifically utilized; the silicon dioxide content in the byproduct silicon micropowder reaches about 94 percent and the reaction activity is good, and if the silicon dioxide content can reach more than 96 percent through simple impurity removal and activation treatment, the silicon dioxide can also be scientifically utilized; in addition, by optimizing the wastewater treatment process, zero discharge of wastewater can be realized, and perfect recovery and cyclic utilization of byproducts can be realized.

Therefore, the production method of the special silicon dioxide aims at combining the process characteristics of industrial silicon and the special silicon dioxide, utilizing the waste heat of the tail gas of the industrial silicon and effectively utilizing the micro silicon powder to prepare the high-quality special silicon dioxide, and simultaneously fully treating the wastewater to realize zero discharge of the wastewater, so that the whole process realizes the full utilization of the solid waste and the waste heat energy of the micro silicon powder of the industrial silicon, and the wastewater realizes the cyclic utilization of water, sulfuric acid and caustic soda through environmental protection treatment, namely the steam, electricity and drying heat sources of the whole process are all solved through the recovery and utilization of the waste heat of the industrial silicon without additional consumption of coal; and three main raw materials: the silicon source is solved by utilizing industrial silicon production solid waste, namely micro silicon powder through scientific treatment, sulfuric acid and caustic soda are mainly recycled through wastewater treatment, and the problem can be completely solved by only supplementing a part lost in the process by a small amount. Compared with the traditional mainstream process, the production cost of the product is reduced by 30 percent, the process is an energy-saving green environment-friendly process for comprehensively utilizing solid waste and waste heat and scientifically treating waste water, and the high-quality special silicon dioxide product is obtained, so that the market competitiveness is stronger.

Fig. 1 shows a process flow diagram of a method for producing green and environmentally friendly specialty silicas according to an exemplary embodiment of the present invention.

As shown in fig. 1, the method for producing green environmental-friendly specialty silica according to an exemplary embodiment of the present invention includes the following steps.

Firstly, two pretreatment steps of collection and activation treatment of micro silicon powder and recovery and utilization treatment of waste heat are carried out.

The micro silicon powder collection and activation treatment is to perform high-temperature roasting on micro silicon powder obtained by thermal separation and collection in industrial silicon smelting flue gas in an oxygen-rich atmosphere to obtain roasted micro silicon powder; the waste heat recycling treatment is to exchange heat between a part of industrial silicon smelting flue gas with the temperature of 450-900 ℃ and feed water, use the obtained superheated steam for power generation to obtain recovered electric energy and waste heat recovery steam, and exchange heat between another part of industrial silicon smelting flue gas with the temperature of 450-900 ℃ and air to obtain heat exchange air.

Specifically, a waste heat boiler can be adopted to exchange out part of heat energy in the industrial silicon smelting flue gas, superheated steam is generated and then sent to a generator to generate electricity, exhausted steam after electricity generation is used for preparing water glass by a subsequent liquid phase method, preparing special silicon dioxide, treating waste water and the like, and recovered electric energy can be used as power electricity of the process. Meanwhile, the air heat exchanger can be adopted to convert the heat energy in the other part of the industrial silicon smelting flue gas into clean air, the heat exchange air is used for drying the special silicon dioxide and the like, and the main energy supply for producing the special silicon dioxide can be realized through the excavation of the waste heat of the industrial silicon smelting flue gas.

And the micro silicon powder in the industrial silicon smelting flue gas can be collected and then subjected to roasting to remove organic impurities, and then subjected to reaction with caustic soda solution to prepare high-quality water glass, so that high-quality special silicon dioxide can be further obtained. In the step, the micro silicon powder actually comprises high-temperature micro silicon powder which is continuously separated from high-temperature flue gas generated in industrial silicon smelting through a cyclone separator and has the temperature of 450-900 ℃ and low-temperature micro silicon powder which is continuously separated from the high-temperature flue gas generated in industrial silicon smelting through waste heat recycling treatment through a bag-type dust collector and has the temperature of 180-220 ℃. Because the cyclone separator can only separate about 80% of the micro silicon powder, the micro silicon powder can be fully separated and recovered by performing supplementary separation after the waste heat recycling treatment.

The above-mentioned roasting treatment process of the silica fume can refer to the technical scheme disclosed in ZL 201711439350.8. Specifically, the micro silicon powder is preheated to 560-650 ℃, then is statically or dynamically roasted at high temperature of 720-1100 ℃ in an oxygen-enriched atmosphere, and is discharged and cooled after being roasted for 15-90 minutes to obtain the roasted micro silicon powder. The micro silicon powder is roasted under the temperature and time conditions and the dynamic conditions, so that organic volatile matters such as coal tar, carbon and the like in the micro silicon powder can be fully combusted and decomposed, fine micro silicon powder particles can be sintered while being roasted at high temperature, the particle size is coarsened, the density is increased, and the high-quality preparation of subsequent products is facilitated.

The electric energy of the high-temperature roasting is derived from the recovered electric energy in the waste heat recovery and utilization process, so that the waste heat of the industrial silicon tail gas is effectively utilized, and the energy cost for producing the special silicon dioxide is greatly reduced.

Further, in the step of waste heat recycling treatment, the temperature of the industrial silicon smelting flue gas after the waste heat recycling treatment is controlled to be 180-220 ℃, and the industrial silicon smelting flue gas is discharged after being subjected to dust removal, desulfurization and denitration treatment in sequence, so that the environment is protected. The pressure of the waste heat recovery steam is controlled to be 1-3 MPa, the temperature of the waste heat recovery steam is controlled to be 220-450 ℃, the temperature of the heat exchange air is controlled to be 350-550 ℃, and subsequent recycling is facilitated.

In the two pretreatment steps, waste heat energy in part of industrial silicon smelting flue gas is converted into steam and electric energy through a waste heat boiler, and waste heat energy in part of industrial silicon smelting flue gas is converted into clean hot air through an air heat exchanger, so that energy is provided for a special silicon dioxide production line, the waste heat of industrial silicon tail gas is effectively utilized, and the production energy cost of special silicon dioxide is greatly reduced; in addition, the micro silicon powder solid waste recovered from the industrial silicon smelting flue gas is fully utilized to produce the special silicon dioxide, the hidden danger of industrial silicon solid waste pollution is solved, the clean production of industrial silicon is realized, and the higher economic value is realized by changing waste into valuable.

Secondly, preparing high-purity water glass and preparing special silicon dioxide.

The preparation of the high-purity water glass comprises the steps of uniformly stirring and mixing the roasted micro silicon powder, a sodium hydroxide solution and process water, reacting by taking waste heat recovery steam as a heat source, cooling and filtering to obtain a high-purity water glass mother liquor; the preparation of the special silicon dioxide is that the high-purity water glass mother liquor is diluted to a preset concentration, then is evenly mixed with sulfuric acid solution and process water by stirring, and reacts by taking waste heat recovery steam as a heat source, a special silicon dioxide filter cake and waste water are obtained after filtration and washing, the special silicon dioxide filter cake is subjected to flash evaporation drying by taking the heat exchange air as a drying heat source or is subjected to spray drying by slurry obtained by pulping and homogenizing the special silicon dioxide filter cake, and the special silicon dioxide is obtained after superfine grinding. The process water is water with national standard II type water quality reaching drinking water quality and above through conventional purification treatment.

The process for preparing the high-purity water glass can refer to the technical scheme disclosed by ZL201711439357. Specifically, the preset concentration of the diluted high-purity water glass mother liquor is controlled to be 18-26%, the concentration of the sodium hydroxide solution is controlled to be 8-15%, and SiO in the raw materials is controlled₂:NaOH:H₂The mass ratio of O is 2-2.7: 1: 3-9.5, the reaction temperature is controlled to be 165-210 ℃, and the reaction time is controlled to be 60-360 minutes.

In the preparation step of the special silicon dioxide, the colorless, tasteless and transparent high-purity water glass prepared in the above step is prepared into a certain concentration and then reacts with a sulfuric acid solution under certain stirring strength, temperature and time to obtain a mixed mother liquor of the special silicon dioxide and sodium sulfate, and the special silicon dioxide is separated from the sodium sulfate through treatments such as filter pressing and washing to obtain a special silicon dioxide filter cake and a large amount of wastewater containing sodium sulfate; and (3) pulping the special silicon dioxide filter cake to form flowing slurry, then carrying out flash drying or conveying the slurry to centrifugal spray drying equipment for drying and removing water, and carrying out ultrafine grinding treatment to obtain a high-quality special silicon dioxide finished product. Wherein the concentration of the sulfuric acid solution is 8-10%, and SiO in the raw material is controlled₂:H₂SO₄:H₂The mass ratio of O is 2-2.7: 1: 3-9.5, the reaction temperature is controlled to be 165-210 ℃, and the reaction time is controlled to be 60-360 minutes. According to the invention, the special silicon dioxide is produced by converting the roasted micro silicon powder subjected to roasting, impurity removal and activation to produce the water glass, so that the quality of the special silicon dioxide product is effectively ensured.

Finally, the post-treatment step of wastewater treatment is carried out.

Specifically, after pretreatment, the wastewater is subjected to electrodialysis treatment to obtain strong brine and fresh water; sequentially carrying out chelate resin purification treatment and bipolar membrane electrodialysis treatment on the strong brine to obtain a sulfuric acid solution and a sodium hydroxide solution; and (4) carrying out reverse osmosis membrane separation treatment on the fresh water to obtain reuse water and a concentrated aqueous solution. The electrodialysis treatment, the chelate resin purification treatment and the bipolar membrane electrodialysis treatment can be carried out by adopting the prior art.

The wastewater is treated by adopting reverse osmosis membrane concentration and bipolar membrane electrodialysis, water, sulfuric acid and sodium hydroxide are recycled, closed cycle utilization of materials is realized in a system, the effect of zero discharge of the wastewater is achieved, and the hidden danger of environmental protection of the wastewater of special silicon dioxide is eliminated. The method for treating the wastewater does not generate redundant cost, and the production cost is obviously reduced due to the recovery of water and sulfuric acid and sodium hydroxide.

According to the invention, the pretreatment can comprise the steps of desiliconization, flocculation, sedimentation, filtration and the like, the obtained fresh water is qualified reuse water and can be used as process water to return to the preparation of the special silicon dioxide for use, and the obtained concentrated aqueous solution returns to be pretreated together with the wastewater for desiliconization, flocculation, sedimentation, filtration and the like, and the zero discharge of the wastewater is realized.

For the by-products after wastewater treatment, the reuse water can be used for filtration and washing in the special silica preparation step, the obtained sodium hydroxide solution and the reuse water can be used as raw materials for preparing high-purity water glass, and the obtained sulfuric acid solution and the reuse water can be used as raw materials for preparing the special silica. Therefore, the whole process realizes the full utilization of solid waste and waste heat energy of the industrial silicon micro-silicon powder, the cyclic utilization of water, sulfuric acid and caustic soda is realized by the environmental protection treatment of the waste water, and the special silicon dioxide product with low production cost and good quality is finally obtained.

According to the invention, the wastewater is subjected to deep pretreatment except for metal ions (except sodium) before concentration and electrodialysis, so that the sulfuric acid solution and the sodium hydroxide solution obtained after bipolar membrane electrodialysis treatment contain extremely low positive and negative ions except sodium ions and sulfate ions, and the high purity of the raw materials is ensured; in addition, the recycled water contains trace sodium ions and sulfate ions, and also contains other positive ions and negative ions, and the special silicon dioxide produced by the recycled water, the self-produced sulfuric acid solution and the sodium hydroxide solution has high purity and low impurity content, can be used in high-end fields such as silicon rubber, food, medicines, cosmetics and the like, and further improves the added value of products.

Based on the above, the invention also provides the special silicon dioxide prepared by the production method of the green and environment-friendly special silicon dioxide, wherein the content of silicon dioxide in the special silicon dioxide reaches more than 99 wt%, the content of arsenic is less than 2ppm, the content of lead is less than 3ppm, the content of iron is less than 120pm, and the total content (calculated by lead) of other heavy metals is less than 15ppm, so that the special silicon dioxide can be used in many special fields such as high-temperature vulcanized silicone rubber, paint, toothpaste, food, medicine, cosmetics and the like, the product can completely match with the product of the traditional enterprise, even certain performances exceed the product of the traditional enterprise, and the quality is fully guaranteed.

The present invention will be further described with reference to the following specific examples.

Example 1:

the first step is as follows: the smelting high-temperature flue gas from the industrial silicon ore hot furnace passes through a cyclone separator, and the micro silicon powder is continuously separated from the high-temperature flue gas, the temperature of the micro silicon powder is 450 ℃, and then the micro silicon powder is roasted according to the technical scheme disclosed by ZL201711439350.8 to obtain the roasted micro silicon powder for later use.

The second step is that: a waste heat boiler and a generator set are arranged on a high-temperature tail gas pipe with the temperature of 450 ℃ of a part of industrial silicon furnaces, superheated steam is produced by utilizing heat energy of flue gas, the superheated steam is used for driving a generator to generate electricity, the steam after electricity generation is conveyed to a special silicon dioxide production line to be used for liquid phase method water glass reaction, special silicon dioxide reaction and the like, and the generated recovered electric energy is used as power electricity for producing special silicon dioxide.

An air heat exchanger is arranged on a 600 ℃ high-temperature tail gas pipe of the other part of the industrial silicon furnace to convert heat energy into clean air, the temperature of the clean air is 350 ℃, the heat exchange air is used for drying special silicon dioxide, and the temperature of the flue gas after heat exchange of the waste heat boiler and the air heat exchanger is reduced by 180 ℃ through a boiler water preheater.

The third step: and continuously separating the rest fine silicon powder from the industrial silicon smelting flue gas subjected to the two-step heat exchange by using a bag-type dust collector, and collecting the fine silicon powder by using an encryption bin, wherein the temperature of the fine silicon powder is 180 ℃, and then roasting according to the technical scheme disclosed by ZL201711439350.8 to obtain roasted fine silicon powder for later use.

The fourth step: mixing the obtained roasted silica fume with liquid caustic soda, heating and pressurizing by steam, reacting according to the technical scheme disclosed by ZL201711439357.X, filtering to obtain colorless, tasteless and transparent high-purity sodium silicate mother liquor, and preparing the mother liquor into 18 mass percent for later use.

The fifth step: preparing 10% solution from sulfuric acid, adding water and acid into a reaction kettle to enable the pH of the solution to be 6.5 +/-0.5, heating to 45 +/-1 ℃ by using steam, reacting 25% of the total mass of water glass with the sulfuric acid to generate crystal nuclei and gel under the environmental condition that the stirring speed is 60r/min, and aging for 30 minutes; adjusting the stirring speed to 80r/min, crushing the gel, and reacting the residual water glass with sulfuric acid under the environmental conditions that the pH is 9.5 +/-0.5 and the temperature is 85 +/-1 ℃; and finally, adjusting the pH value of the reaction solution to 4.5 +/-0.5 to obtain a mixed mother solution of the special silicon dioxide and the sodium sulfate.

And a sixth step: and (2) carrying out filter pressing washing on the mixed mother liquor, separating the special silicon dioxide from sodium sulfate to obtain a special silicon dioxide filter cake and wastewater containing sodium sulfate, washing and flash drying the special silicon dioxide filter cake or pulping the filter cake to form a fluid slurry, conveying the fluid slurry to centrifugal spray drying equipment, drying by using heat exchange air generated in the second step to remove water, and carrying out ultrafine grinding to obtain a high-quality special silicon dioxide finished product.

The seventh step: after pretreatment such as desiliconization, flocculation, precipitation, filtration and the like, mother liquor containing sodium sulfate and washing wastewater are subjected to electrodialysis to extract strong brine (sodium sulfate solution), the obtained fresh water is further separated by a reverse osmosis membrane to obtain qualified reuse water which is returned to a special silicon dioxide system for use, and the strong brine solution is returned to the previous pretreatment system for desiliconization, flocculation, precipitation, filtration and the like; after the strong brine extracted by electrodialysis is treated with polyvalent metal ions by chelating resin, the strong brine enters a bipolar electrodialysis system to be treated to obtain a sulfuric acid solution with the mass concentration of 10% and a sodium hydroxide solution with the mass concentration of 8%; and then returning the sulfuric acid solution and the sodium hydroxide solution to the system for recycling, thereby realizing the zero-discharge treatment of the wastewater.

Example 2:

the first step is as follows: the smelting high-temperature flue gas from the industrial silicon ore hot furnace passes through a cyclone separator, and the micro silicon powder is continuously separated from the high-temperature flue gas, the temperature of the micro silicon powder is 900 ℃, and then the micro silicon powder is roasted according to the technical scheme disclosed by ZL201711439350.8 to obtain roasted micro silicon powder for later use.

The second step is that: a waste heat boiler and a generator set are arranged on a 900 ℃ high-temperature tail gas pipe of a part of industrial silicon furnaces, superheated steam is produced by utilizing heat energy of flue gas, the superheated steam is used for driving a generator to generate electricity, the steam after electricity generation is conveyed to a special silicon dioxide production line to be used for liquid phase method water glass reaction, special silicon dioxide reaction and the like, and the generated recovered electric energy is used as power electricity for producing special silicon dioxide.

An air heat exchanger is arranged on a high-temperature tail gas pipe at 900 ℃ of the other part of the industrial silicon furnace to convert heat energy into clean air, the temperature of the clean air is 550 ℃, the heat exchange air is used for drying special silicon dioxide, and the temperature of the flue gas after heat exchange of the waste heat boiler and the air heat exchanger is reduced to 220 ℃ through a boiler water preheater.

The third step: and continuously separating the rest fine silicon powder from the industrial silicon smelting flue gas subjected to the two-step heat exchange by using a bag-type dust collector, and collecting the fine silicon powder by using an encryption bin, wherein the temperature of the fine silicon powder is 220 ℃, and then roasting according to the technical scheme disclosed by ZL201711439350.8 to obtain roasted fine silicon powder for later use.

The fourth step: mixing the obtained roasted silica fume with liquid caustic soda, heating and pressurizing by steam, reacting according to the technical scheme disclosed by ZL201711439357.X, filtering to obtain colorless, tasteless and transparent high-purity sodium silicate mother liquor, and preparing the mother liquor into the mother liquor with the mass concentration of 26% for later use.

The fifth step: preparing sulfuric acid into a 10% solution, adding water and a small amount of water glass into a reaction kettle to ensure that the pH of the solution is 10.5 +/-0.5, heating to 65 +/-1 ℃ by using steam, and carrying out concurrent flow reaction on 40% of the total mass of the water glass and the sulfuric acid for 40 minutes under the environmental condition of a stirring speed of 80 r/min; then, raising the temperature of the reaction liquid to 85 +/-1 ℃, carrying out concurrent flow reaction on the residual water glass and sulfuric acid, keeping the pH constant, and finishing the reaction within 60 minutes; and finally, adjusting the pH value of the reaction solution to 4.2 +/-0.3 to obtain a mixed mother solution of the special silicon dioxide and the sodium sulfate.

And a sixth step: and (2) carrying out filter pressing washing on the mixed mother liquor, separating the special silicon dioxide from sodium sulfate to obtain a special silicon dioxide filter cake and wastewater containing sodium sulfate, washing and flash drying the special silicon dioxide filter cake or pulping the filter cake to form a fluid slurry, conveying the fluid slurry to centrifugal spray drying equipment, drying by using heat exchange air generated in the second step to remove water, and carrying out ultrafine grinding to obtain a high-quality special silicon dioxide finished product.

The seventh step: after pretreatment such as desiliconization, flocculation, precipitation, filtration and the like, mother liquor containing sodium sulfate and washing wastewater are subjected to electrodialysis to extract strong brine (sodium sulfate solution), the obtained fresh water is further separated by a reverse osmosis membrane to obtain qualified reuse water which is returned to a special silicon dioxide system for use, and the strong brine solution is returned to the previous pretreatment system for desiliconization, flocculation, precipitation, filtration and the like; after the concentrated brine extracted by electrodialysis is treated with polyvalent metal ions by chelating resin, the concentrated brine enters a bipolar electrodialysis system to be treated to obtain a sulfuric acid solution with the mass concentration of 10% and a sodium hydroxide solution with the mass concentration of 8%, and the concentration of the 8% sodium hydroxide is extracted by electrodialysis to be up to 15%; and then returning the sulfuric acid solution and the sodium hydroxide solution to the system for recycling, thereby realizing the zero-discharge treatment of the wastewater.

Example 3:

the first step is as follows: the smelting high-temperature flue gas from the industrial silicon ore hot furnace passes through a cyclone separator, and the micro silicon powder is continuously separated from the high-temperature flue gas, the temperature of the micro silicon powder is 680 ℃, and then roasting is carried out according to the technical scheme disclosed by ZL201711439350.8 to obtain roasted micro silicon powder for later use.

The second step is that: a waste heat boiler and a generator set are arranged on a 680 ℃ high-temperature tail gas pipe of a part of industrial silicon furnaces, superheated steam is produced by utilizing heat energy of flue gas, the superheated steam is used for driving a generator to generate electricity, the generated steam is conveyed to a special silicon dioxide production line to be used for liquid phase method water glass reaction, special silicon dioxide reaction and the like, and the generated recovered electric energy is used as power electricity for producing special silicon dioxide.

An air heat exchanger is arranged on a 680 ℃ high-temperature tail gas pipe of the other part of the industrial silicon furnace to convert heat energy into clean air, the temperature of the clean air is 450 ℃, the heat exchange air is used for drying the special silicon dioxide, and the temperature of the flue gas after heat exchange of the waste heat boiler and the air heat exchanger is reduced to 200 ℃.

The third step: and continuously separating the rest fine silicon powder from the industrial silicon smelting flue gas subjected to the two-step heat exchange by using a bag-type dust collector, and collecting the fine silicon powder by using an encryption bin, wherein the temperature of the fine silicon powder is 200 ℃, and then roasting according to the technical scheme disclosed by ZL201711439350.8 to obtain roasted fine silicon powder for later use.

The fourth step: mixing the obtained roasted silica fume with liquid caustic soda, heating and pressurizing by steam, reacting according to the technical scheme disclosed by ZL201711439357.X, filtering to obtain colorless, tasteless and transparent high-purity sodium silicate mother liquor, and preparing the mother liquor into a mass concentration of 21% for later use.

The fifth step: preparing 9% solution of sulfuric acid, adding water and acid into a reaction kettle to ensure that the pH of the solution is 10.5 +/-0.5, heating to 75 +/-1 ℃, carrying out concurrent reaction on 30% of the total mass of water glass and the sulfuric acid for 30 minutes under the environmental condition of stirring speed of 90r/min, and aging for 15 minutes; heating to 90 +/-1 ℃ by using steam, adjusting the reaction pH to 8.5 +/-0.5, and carrying out cocurrent reaction on the residual water glass and sulfuric acid for 60 minutes; and finally, adjusting the pH value of the reaction solution to 4.2 +/-0.5 to obtain a mixed mother solution of the special silicon dioxide and the sodium sulfate.

And a sixth step: and (2) carrying out filter pressing washing on the mixed mother liquor, separating the special silicon dioxide from sodium sulfate to obtain a special silicon dioxide filter cake and wastewater containing sodium sulfate, washing and flash drying the special silicon dioxide filter cake or pulping the filter cake to form a fluid slurry, conveying the fluid slurry to centrifugal spray drying equipment, drying by using heat exchange air generated in the second step to remove water, and carrying out ultrafine grinding to obtain a high-quality special silicon dioxide finished product.

The seventh step: after pretreatment such as desiliconization, flocculation, precipitation, filtration and the like, mother liquor containing sodium sulfate and washing wastewater are subjected to electrodialysis to extract strong brine (sodium sulfate solution), the obtained fresh water is further separated by a reverse osmosis membrane to obtain qualified reuse water which is returned to a special silicon dioxide system for use, and the strong brine solution is returned to the previous pretreatment system for desiliconization, flocculation, precipitation, filtration and the like; after the concentrated brine extracted by electrodialysis is treated with polyvalent metal ions by chelating resin, the concentrated brine enters a bipolar electrodialysis system to be treated to obtain a sulfuric acid solution with the mass concentration of 10% and a sodium hydroxide solution with the mass concentration of 8%, and the concentration of the 8% sodium hydroxide is extracted by electrodialysis to reach the mass concentration of 10% at most; and then returning the sulfuric acid solution and the sodium hydroxide solution to the system for recycling, thereby realizing the zero-discharge treatment of the wastewater.

Table 1 shows the comparison of the properties of the specialty silica products obtained in the above examples with those of the commercial products. As can be seen from Table 1, the special silica product prepared by the invention can reach the national standard, and the comprehensive performance is equivalent to or higher than that of the product sold in the market, thereby being beneficial to cost saving and resource recycling.

TABLE 1 comparison of the Properties of the specialty silica products obtained in the examples with those of the commercial products

In conclusion, the invention well combines the energy consumption and resource characteristics of the industries of industrial silicon and special silicon dioxide, the comprehensive cost for producing the special silicon dioxide is 30 percent lower than that of the traditional mainstream process method, the metal impurity content of the product is low, the purity is high, the product can be completely compared with the product of the traditional mainstream process, even the product of which the performance exceeds that of the traditional mainstream process, and the quality is fully guaranteed.

The invention is not limited to the foregoing embodiments. The invention extends to any novel feature or any novel combination of features disclosed in this specification and any novel method or process steps or any novel combination of features disclosed.