CN105967191B - Process and device for preparing fumed silica by taking red mud as raw material - Google Patents

Process and device for preparing fumed silica by taking red mud as raw material Download PDF

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CN105967191B
CN105967191B CN201610534958.8A CN201610534958A CN105967191B CN 105967191 B CN105967191 B CN 105967191B CN 201610534958 A CN201610534958 A CN 201610534958A CN 105967191 B CN105967191 B CN 105967191B
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CN105967191A (en
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田辉明
杨水彬
田正芳
叶发兵
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Huanggang Normal University
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
    • C01B33/181—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by a dry process
    • C01B33/183—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by a dry process by oxidation or hydrolysis in the vapour phase of silicon compounds such as halides, trichlorosilane, monosilane
    • C01B33/184—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by a dry process by oxidation or hydrolysis in the vapour phase of silicon compounds such as halides, trichlorosilane, monosilane by hydrolysis of tetrafluoride
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/08—Compounds containing halogen
    • C01B33/10—Compounds containing silicon, fluorine, and other elements
    • C01B33/103—Fluosilicic acid; Salts thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/48—Halides, with or without other cations besides aluminium
    • C01F7/50—Fluorides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C01G23/053—Producing by wet processes, e.g. hydrolysing titanium salts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/02—Oxides; Hydroxides
    • C01G49/06—Ferric oxide [Fe2O3]
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B59/00—Obtaining rare earth metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
    • C22B7/006—Wet processes
    • C22B7/007—Wet processes by acid leaching
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01P2006/12—Surface area
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    • C01—INORGANIC CHEMISTRY
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    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity
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    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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Abstract

The invention provides a process for preparing fumed silica and recovering metal at low temperature by taking red mud as a raw material, wherein in the process, the red mud and other wastes are taken as the raw materials and react with fluorine-containing acid liquid, hydrochloric acid and nitric acid to prepare the high-added-value product fumed silica and recover AlF3Rare earth element, SiO in the product obtained2The content is more than 99.9 percent, and the specific surface area measured by a multipoint BET method is as follows: 350-500 m2The effect of changing waste into valuable is achieved; after the acid gas generated in the preparation process is absorbed by the negative pressure water absorption tank, the corresponding acid liquid can be prepared, and the acid liquid can be recycled after being concentrated to a certain concentration. Meanwhile, the invention also provides a production device used in the process, all parts used by the production device are common appliances in chemical plants, the cost is low, and large-scale industrial production can be realized.

Description

Process and device for preparing fumed silica by taking red mud as raw material
Technical Field
The invention relates to a process method and a device for preparing fumed silica by utilizing red mud, belonging to the technical field of chemical purification and environmental protection.
Background
According to the first year of 2016, the introduction of the research status and analysis of comprehensive utilization of red mud, which published under the heading of Zhuxiao, Li Wang and guang, in the first year: the red mud is tailings generated in the process of producing alumina from bauxite, and is called red mud because the red mud is reddish brown due to the fact that the red mud contains a large amount of hematite. The red mud is mainly divided into three types, namely a sintering method, a Bayer method and a combination method, the chemical components of the red mud are different in different places due to different raw material properties and alumina production processes, and the main chemical components in the red mud are usually alumina, silica, iron oxide, calcium oxide, titanium dioxide, sodium oxide and magnesium oxide, and also rhenium, gallium, yttrium, scandium, niobium, tantalum, uranium, thorium, lanthanide and the like. The mineral composition of red mud is closely related to the production process of alumina and the types of additives in the production process, and generally contains hematite, hydrated garnet, cancrinite, perovskite, dolomite, calcium aluminoferrite and the like. The red mud is an alkaline pollution source, and can cause underground water and soil pollution if not treated, and the naked stacked red mud can fly with wind due to extremely fine granularity, thereby causing air pollution. With the increasing year by year of the red mud production and the outstanding environmental problems, effective measures are urgently needed to treat the solid wastes.
Bauxite resources in China belong to high-aluminum, high-silicon, low-iron and single-water hardened aluminum types, the dissolving-out capability is poor, the types are special, except that the Guangxi Pingguo aluminum industry adopts a pure Bayer process, most aluminum industry companies adopt sintering or combined processes to smelt alumina, the alumina residue in red mud is not high, the alkali content is low, the contents of silica and calcium oxide are high, and the iron oxide content is very low.
At present, the research on the comprehensive utilization of the red mud mainly comprises the following three aspects: firstly, extracting and recovering valuable metals, such as leaching precipitation aluminum extraction, magnetizing roasting iron selection, acid leaching extraction of scandium, titanium, vanadium and other rare metals; secondly, preparing building materials, such as baking-free bricks, cement and the like; and thirdly, preparing an adsorbing material, and mainly applying to wastewater treatment.
The raw materials for preparing the white carbon black by the vapor phase method are silicon tetrachloride, oxygen (or air) and hydrogen which are reacted at high temperature. The chemical reaction formula is as follows: SiCl4+2H2+O2->SiO2+4HCl, silicon tetrachloride is gasified at high temperature (flame temperature is 1000-1800 ℃), and then is subjected to gas phase hydrolysis with a certain amount of hydrogen and oxygen (or air) at high temperature of about 1800 ℃; the fumed silica produced at this time is very fine in particle size, forms aerosol with gas, and is not easy to trap, so that it is first aggregated into larger particles in a collectorAnd collecting the silicon dioxide by a cyclone separator, sending the silicon dioxide into a deacidification furnace, and purging the fumed silica by nitrogen-containing air until the pH value is 4-6 to obtain a finished product. The method is adopted by most of the enterprises producing the fumed silica in China at present, and is also a universal international production method of the fumed silica. China also has enterprises to produce fumed silica by adopting methyltrichlorosilane and successfully finishes industrialized production. The existing production process of fumed silica not only has a high-temperature process, but also uses hydrogen and oxygen which are very dangerous, flammable and explosive, and the operating environment of workers is relatively hard in the production process; the requirement on the safety coefficient is high. Relevant data and Chinese patent documents are consulted, and no relevant report of producing the fumed silica by using other raw materials is found.
If the red mud can be processed and utilized for the second time and combined with the preparation of the fumed silica to be used for preparing the fumed silica product, the two technical problems in the field can be solved, and the method has obvious progress.
Disclosure of Invention
The invention provides a production process method and a device for preparing fumed silica by using red mud as a raw material; the invention successfully avoids the technical processes of using hydrogen and oxygen and carrying out high-temperature hydrolysis in the traditional fumed silica process, also solves the problem that the traditional red mud cannot be efficiently utilized, and simultaneously provides a novel process technology and a production device for producing fumed silica products at normal temperature and normal pressure.
The technical scheme adopted for realizing the above purpose of the invention is as follows:
a process for preparing fumed silica by using red mud as a raw material is characterized by comprising the following steps: (1) mixing the fluorine-containing acid solution with nitric acid to prepare a mixed acid solution for later use; mixing red mud and hydrogen peroxide, granulating, drying, grinding to fineness of below 200 meshes, magnetically separating to remove iron, dissolving metal oxides and rare earth elements in the magnetically separated red mud with hydrochloric acid, filtering, and collecting filter cakes for later use;
(2) putting the mixed acid liquid into a reaction kettle, starting a stirring device of the reaction kettle and a waste gas absorption device in a reaction system, and putting a filter cake or powder obtained by drying and grinding the filter cake into the reaction kettle;
(3) controlling the reaction temperature in the reaction kettle to be 75-90 ℃, reacting hydrofluoric acid or fluosilicic acid in the mixed acid liquid with silicon dioxide in a filter cake or powder to generate silicon tetrafluoride gas, and carrying the silicon tetrafluoride gas, acid gas volatilized from the mixed acid liquid and water vapor into the cooling kettle under negative pressure;
(4) controlling the cooling temperature in the cooling kettle to be 0-36 ℃, and reacting the mixed gas in the cooling kettle, wherein HF and NO are reacted2Is taken out from the cooling kettle by negative pressure and is absorbed by water to generate hydrofluoric acid, nitric acid and SiO which can be used repeatedly2·nH2O is condensed and adsorbed on a cooling device in a cooling kettle, and SiO in the cooling kettle is collected2·nH2O；
(5) Collecting the SiO2·nH2Preheating O in vacuum heater under negative pressure to remove residual HF and NO2Then drying, and obtaining the gas-phase white carbon black product after drying, wherein SiO in the product2The content is more than 99.9 percent, and the specific surface area is not less than 380m measured by a multipoint BET method2/g；
(6) In the reaction kettle, the fluorine-containing acid solution decomposes the silicon dioxide in the filter cake or powder; the nitric acid decomposes the residual metal in the material, and the decomposed metal is left in the mixed acid solution in the form of ions and salt; filtering after the reaction of the materials in the reaction kettle is finished, and separating out AlF in filter residue3(ii) a Then sending the filtrate into an evaporator to be evaporated to dryness to obtain residue, treating the residue with concentrated sulfuric acid, and recovering TiO2。
The mass concentration or volume concentration of the hydrofluoric acid is 2-30%, the mass concentration or volume concentration of the fluosilicic acid is 10-30%, and the mass concentration or volume concentration of the nitric acid is 2-30%.
Neutralizing the filtrate filtered in the step (1) with alkali, adding a sulfuric acid solution, precipitating and separating calcium sulfate, adding hydrofluoric acid, precipitating and separating aluminum trifluoride, and extracting and separating rare earth elements with oxalic acid; adjusting the pH value of the residual solution to 8.5-9 by using alkali liquor, precipitating, filtering and separating out iron hydroxide, calcining the iron hydroxide to obtain an iron oxide red product, concentrating the filtrate, and adding fluosilicic acid to obtain precipitated fluosilicate and hydrochloric acid; the hydrochloric acid is purified and then returned for use.
And (4) absorbing the acid mist gas generated in the evaporation in the step (6) by using a water absorption tank to obtain acid liquor, returning the acid liquor to a workshop for reuse after the acid liquor reaches a certain concentration, and neutralizing the unabsorbed tail gas by using an acid mist absorption tower and then emptying the tail gas.
The invention also provides a device used in the process, which comprises a hot air feeding system, a chemical reaction system, a cooling system and a waste gas absorption system, wherein the hot air feeding system is used for storing compressed air and heating the air and then feeding the air into the chemical reaction system; the chemical reaction system consists of an acid liquor storage tank, a storage bin and a reaction kettle, wherein the bottoms of the acid liquor storage tank and the storage bin are communicated with the reaction kettle through a pipeline, a stirring device is arranged in the reaction kettle, the lining of the reaction kettle is made of a temperature-resistant, acid-resistant and wear-resistant material, an annular round pipe is arranged above the bottom of the reaction kettle, air holes or air vent pipes are uniformly distributed on the round pipe, more than one vertical pipe communicated with the annular round pipe is arranged in the reaction kettle, and the top end of the vertical pipe is communicated with a hot air feeding system through a pipe valve on a kettle cover of the reaction kettle; the upper end and the lower end of the tube bundle are respectively connected with cold and hot media outside the kettle wall through a valve, and the heating or cooling is provided for a reaction system in the kettle by introducing the cold and hot media into the capillary tubes in the tube bundle.
The cooling system is formed by connecting a primary cooling kettle and a secondary cooling kettle in series; the device comprises a primary cooling kettle, a reaction kettle, a secondary cooling kettle, a cooling device, a discharge valve, a pipeline, a pressure sensor and a control system, wherein the primary cooling kettle is connected with the reaction kettle, the pipeline which is connected with the primary cooling kettle and extends into the center of the bottom of the primary cooling kettle is arranged on a kettle cover of the reaction kettle, the cooling device is arranged inside the primary cooling kettle, the discharge valve is arranged at the bottom of the secondary cooling kettle; the kettle cover of the secondary cooling kettle is provided with a pipeline connected with a waste gas absorption system, the waste gas absorption system consists of more than one negative pressure water absorption tank and an acid mist absorption device, and the top of the negative pressure water absorption tank is provided with a pipeline and is connected with an induced draft fan in the acid mist absorption device through the pipeline.
The hot air feeding system comprises an air compressor, an air storage tank, an air heater and a pipeline, wherein the air compressor, the air storage tank and the air heater are connected through the pipeline, and the pipeline is further provided with a valve and an instrument.
The reactor is characterized in that vent pipes with diameters of 10-20 mm and different orientations are uniformly distributed on the round pipe, the distance between every two adjacent vent pipes is 50-150 mm, the included angle between the extending directions of the adjacent vent pipes is 60-120 degrees, two vertical pipes are arranged in the reactor, and the two vertical pipes are respectively connected to the left end and the right end of the round pipe.
The cooling device of the primary cooling kettle consists of a rotating shaft and a cooling disc, the rotating shaft is a hollow round pipe wrapped with polytetrafluoroethylene, the top end of the rotating shaft extends out of the kettle cover of the primary cooling kettle, a cooling water pipe A from top to bottom is arranged in the rotating shaft, the top of the cooling water pipe A is a water inlet end, and the water inlet end is connected with a cooling water source; cooling discs are uniformly distributed on the rotating shaft, the cooling discs are fixedly arranged on the rotating shaft by taking the rotating shaft as the circle center and rotate along with the rotating shaft, the cooling discs are of a hollow structure, cooling water pipes B which are distributed in a spiral shape are arranged inside all the cooling discs, the cooling water pipes B in the cooling discs which are adjacent up and down are connected end to end, the water inlet end of the cooling water pipe B in the bottommost cooling disc is communicated with the bottom end of the cooling water pipe A, the water outlet end of the cooling water pipe B in the topmost cooling disc is communicated with a hollow circular pipe, and cooling water discharged from the cooling water pipe B overflows from the top end of the rotating shaft; the cooling disc is uniformly distributed with vertical vent holes, and the vent holes on the cooling disc adjacent to each other are staggered.
The kettle cover of the one-level cooling kettle is provided with a vacuum meter and a manhole convenient to overhaul, and the kettle cover of the one-level cooling kettle is also provided with a compressed air blowing device which is connected with a compressed gas source.
The cooling device in the secondary cooling kettle is of a multi-layer fin structure, a cooling water inlet and a cooling water outlet are formed in the kettle wall of the secondary cooling kettle, the cooling water inlet is communicated with a water inlet of the fin at the lowest layer, cooling water flows in from the fin at the lowest layer, the fins are of a continuous bending structure, the end parts of the adjacent upper and lower layers of fins are communicated, and the cooling water outlet is communicated with a water outlet of the fin at the uppermost layer; a compressed air blowing device is arranged on a kettle cover of the secondary cooling kettle and is connected with a compressed gas source, a vacuum meter is arranged on the kettle cover of the secondary cooling kettle, and manholes convenient to overhaul are arranged at the bottom of the kettle cover and the kettle.
The negative pressure water absorption tanks are arranged in two, and the two negative pressure water absorption tanks are connected in series or in parallel.
Compared with the prior art, the technical scheme provided by the invention has the following advantages: 1. the invention takes red mud and other wastes as raw materials to prepare the red mud and other wastes into the high value-added product fumed silica, and SiO in the prepared product2The content is more than 99.9 percent, and the specific surface area is not less than 350m by the multi-point BET method2The volume per gram is changed into the valuable. 2. The preparation process provided by the invention belongs to a brand new process idea, and overcomes the defects of high-temperature working procedures, use of dangerous, flammable and explosive hydrogen and oxygen and the like in the existing preparation process of the fumed silica. The production process provided by the invention can be used for preparing the nano-silver/nano-silver material at normal temperature and normal pressure. 3. The acid gas generated in the preparation process can be absorbed by the negative pressure water absorption tank to prepare corresponding acid liquid, and the acid liquid can be recycled after being concentrated to a certain concentration, so that the cost in production can be greatly saved, and the problem of waste water treatment in an environment-friendly manner can be solved. 4. The production device provided by the invention can realize large-scale industrial production, and the used parts are all common appliances of chemical plants, so that the cost is low. 5. The invention can recover TiO2, rare earth elements and ferric hydroxide in the red mud, and has great mensesEconomic benefit.
Drawings
FIG. 1 is a schematic view of the overall structure of a manufacturing apparatus according to the present invention;
FIG. 2 is a schematic structural diagram of a cooling disc in a primary cooling kettle;
FIG. 3 is a schematic structural view of fins in a secondary cooling kettle;
in the figure: 1-acid liquor storage tank, 2-stock bin, 3-reaction kettle, 4-stirring device, 5-round pipe, 6-vertical pipe, 7-primary cooling kettle, 8-secondary cooling kettle, 9-discharge valve, 10-negative pressure water absorption tank, 11-acid mist absorption device, 12-air compressor, 13-air storage tank, 14-air heater, 15-rotating shaft, 16-cooling disc, 17-cooling water pipe A, 18-vent hole and 19-fin.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and specific embodiments, but the scope of the present invention is not limited to the following embodiments.
The structure of the preparation device provided in this embodiment is as shown in fig. 1, and the device includes a hot air feeding system, a chemical reaction system, a cooling system, and an exhaust gas absorption system, where the hot air feeding system is configured to store compressed air and heat the air and then feed the air into the chemical reaction system, the hot air feeding system includes an air compressor 12, an air storage tank 13, an air heater 14, and a pipeline, the air compressor 12, the air storage tank 13, and the air heater 14 are connected by the pipeline, and the pipeline is further provided with a valve and an instrument.
The chemical reaction system comprises an acid liquor storage tank 1, a storage bin 2 and a reaction kettle 3, wherein the bottoms of the acid liquor storage tank 1 and the storage bin 2 are communicated with the reaction kettle 3 through a pipeline, a stirring device 4 is arranged in the reaction kettle 3, and the lining of the reaction kettle is made of temperature-resistant, acid-resistant and wear-resistant materials, such as silicon carbide, fluorine materials, graphite materials and the like. Department about 200mm in the top of 3 bottoms of reation kettle is equipped with an annular pipe 5, the diameter of pipe is 100 ~ 200mm, pipe 5 on evenly distributed have the diameter be 10 ~ 20mm and towards different permeability cell, the interval between the adjacent permeability cell is 50 ~ 150mm, and the contained angle between the direction of stretching out of adjacent permeability cell is 60 ~ 120. Two vertical pipes 6 communicated with an annular round pipe are arranged in the reaction kettle, the two vertical pipes 6 are respectively connected to the left end and the right end of the round pipe 5, and the top ends of the vertical pipes 6 are communicated with a hot air feeding system through pipe valves on a kettle cover of the reaction kettle. The kettle wall in the reaction kettle is provided with a spiral hook for supporting a polytetrafluoroethylene capillary tube bundle used for heating or cooling in the kettle.
The cooling system is formed by connecting a primary cooling kettle 7 and a secondary cooling kettle 8 in series; the primary cooling kettle 7 is connected with the reaction kettle 3, a pipeline which is connected with the primary cooling kettle 7 and extends into the center of the bottom of the primary cooling kettle is arranged on a kettle cover of the reaction kettle 3, a cooling device is arranged inside the primary cooling kettle 7, the cooling device of the primary cooling kettle consists of a rotating shaft 15 and a cooling disc 16, the rotating shaft 15 is a hollow round pipe wrapped with polytetrafluoroethylene, the top end of the rotating shaft extends out of the kettle cover of the primary cooling kettle, a cooling water pipe A17 from top to bottom is arranged in the rotating shaft, the top of the cooling water pipe A is a water inlet end, and the water inlet end is connected with a cooling water source; cooling discs 16 are uniformly distributed on the rotating shaft 15. The structure of cooling disc is as shown in fig. 2, cooling disc 16 uses pivot 15 to fix in the pivot as the installation of centre of a circle to rotatory along with the pivot, the cooling disc is hollow structure, and the inside of all cooling discs all is provided with and is the condenser tube B that spirals the form and distribute, and condenser tube B end to end in the adjacent cooling disc about and, and condenser tube B's in the cooling disc of bottommost intake end and condenser tube A's bottom is linked together, and condenser tube B's in the cooling disc of topmost water outlet end accesss to hollow pipe, and the cooling water of exhaust in the condenser tube B spills over by the top of pivot. The cooling disc is uniformly distributed with vertical vent holes 18, and the vent holes on the upper and lower adjacent cooling discs are staggered with each other to ensure the cooling effect of the gas. The diameter of each vent hole is 10-20 mm, and the center distance between every two adjacent vent holes is 20-30 mm.
The kettle cover of the one-level cooling kettle is provided with a vacuum meter and a manhole convenient to overhaul, and the kettle cover of the one-level cooling kettle is also provided with a compressed air blowing device which is connected with a compressed gas source. A pipeline which is connected with the second-stage cooling kettle 8 and extends into the center of the bottom of the second-stage cooling kettle 8 is arranged on the kettle cover of the first-stage cooling kettle 7. The bottom of the first-stage cooling kettle is provided with a discharge valve 9.
The inside of second grade cooling cauldron 8 be provided with cooling device, second grade cooling cauldron in cooling device be multilayer fin structure, be provided with cooling water inlet and cooling water outlet on second grade cooling cauldron 8's the cauldron wall, the cooling water inlet is linked together with the water inlet of lower floor's fin, cooling water flows in by the fin of lower floor, fin 19 is continuous bending structure, its structure is shown in fig. 3. The end parts of the adjacent upper and lower layers of fins are communicated, the cooling water outlet is communicated with the water outlet of the uppermost layer of fins, and the cooling water enters from the lowermost layer of fins and flows out from the uppermost layer of fins. And a compressed air blowing device is arranged on the kettle cover of the secondary cooling kettle and is connected with a compressed gas source, and compressed air is used for blowing during discharging. The kettle cover of the secondary cooling kettle is provided with a vacuum meter, and the kettle cover and the kettle bottom are provided with manholes convenient to overhaul. A discharge valve 9 is arranged at the bottom of the secondary cooling kettle; and a pipeline connected with the waste gas absorption system is arranged on the kettle cover of the secondary cooling kettle 8.
The waste gas absorption system consists of two negative pressure water absorption tanks 10 and an acid mist absorption device 11, and the two negative pressure water absorption tanks are connected in series or in parallel. The top of the negative pressure water absorption tank is provided with a pipeline and is connected with a draught fan in the acid mist absorption device through the pipeline. The acid mist absorbed by the secondary water absorption tank is neutralized with the fog drops of the liquid alkali solution in the acid mist absorption device and then discharged into the air, and when the acid liquid in the negative pressure water absorption tank reaches a certain concentration, the acid liquid is sent to a workshop for recycling.
The red mud produced by a certain mining company in Henan is taken as an example to explain the detailed preparation process of the invention in detail, and the red mud comprises the following components by analysis: CaO: 39-43% of Fe2O3：10～12.6％、SiO2：18.9～20.7％，Al2O3：5.96～8％，MgO：2.15～2.6％、K2O：0.47～0.59％，Na2O：2.58～2.68％，TiO2: 6.13 to 6.7 percent. The specific production steps are as follows:
(1) mixing one or two of hydrofluoric acid and fluosilicic acid with nitric acid to prepare mixed acid liquid, wherein the hydrofluoric acid, the fluosilicic acid and the nitric acid are all in industrial grade; or industrial by-products can be adopted. Preferably, the mass concentration or volume concentration of the hydrofluoric acid is 2-30%, the mass concentration or volume concentration of the fluosilicic acid is 10-30%, and the mass concentration or volume concentration of the nitric acid is 2-30%.
Mixing the red mud with hydrogen peroxide, granulating, drying, grinding to a fineness of below 200 meshes, magnetically separating to remove iron, dissolving metal oxides and rare earth elements in the magnetically separated red mud with hydrochloric acid, filtering, and collecting filter cakes for later use.
Neutralizing the filtrate filtered in the step with alkali, adding a sulfuric acid solution, precipitating and separating calcium sulfate, adding hydrofluoric acid, precipitating and separating aluminum trifluoride, and extracting and separating rare earth elements by using oxalic acid; adjusting the pH value of the residual solution to 8.5-9 by using alkali liquor, precipitating, filtering and separating out iron hydroxide, calcining the iron hydroxide to obtain an iron oxide red product, concentrating the filtrate, and adding fluosilicic acid to obtain precipitated fluosilicate and hydrochloric acid; the hydrochloric acid is purified and then returned for use.
(2) And putting the mixed acid liquid into the reaction kettle, starting a stirring device of the reaction kettle and a waste gas absorption device in the reaction system, and slowly putting the filter cake or powder obtained after drying and grinding the filter cake into the reaction kettle.
(3) If the added mixed acid liquid contains hydrofluoric acid, because the reaction process of the hydrofluoric acid and the silicon dioxide is a heat release process, a cooling water valve outside the reaction kettle needs to be opened to maintain the reaction temperature at 75-90 ℃. If the added mixed acid liquid does not contain hydrofluoric acid but contains fluosilicic acid, the steam of the jacket of the reaction kettle needs to be opened to slowly heat the reaction kettle. And reacting hydrofluoric acid or fluosilicic acid in the mixed acid liquid with silicon dioxide in the filter cake or powder to generate silicon tetrafluoride gas, dissolving one part of the gas in water in the reaction system to form fluosilicic acid to continuously dissolve the silicon dioxide in the red mud, and bringing the other part of the overflowing silicon tetrafluoride gas, the volatilized nitric acid gas and water vapor into the cooling kettle under negative pressure.
(4) Controlling the cooling temperature in the cooling kettle to be 0-36 ℃, and reacting the mixed gas in the cooling kettle, wherein HF and NO are reacted2Overflowing from the first-stage cooling kettle and the second-stage cooling kettle, entering a waste gas absorption system and being absorbed by water to generate hydrofluoric acid and nitric acid which can be reused, wherein the hydrofluoric acid and the nitric acid can be recycled after being concentrated to a certain concentration; thus greatly saving the cost in production and solving the problem of environmental protection wastewater treatment.
And SiO2·nH2O is slowly condensed and adsorbed on a cooling disc in a primary cooling kettle, condensed on the cooling disc from the beginning, slowly and naturally crystallized to form crystal grains which are glittering and translucent, and gathered together like roes, so that the cooling kettle is very attractive, when the cooling disc of the primary cooling kettle is gathered to a certain amount, a rotating shaft device is started, the rotating shaft drives the cooling disc to rotate, materials are thrown to the kettle wall under the action of centrifugal force, and then are blown to the bottom of the primary cooling kettle by compressed air and sent to a drying process through a discharge valve at the bottom; after the materials in the primary cooling kettle are treated, the secondary cooling kettle directly opens a compressed air valve, and the condensed materials are directly blown to the bottom of the kettle and then are sent to a drying procedure through a discharge valve at the bottom;
(5) the material contains water and is acidic, and the volatility of hydrofluoric acid, silicon tetrafluoride and nitric acid gas is extremely strong, so that the collected SiO is firstly dried2·nH2Preheating O in vacuum heater under negative pressure to remove residual HF and NO2Then drying, and obtaining the gas-phase white carbon black product after drying, wherein SiO in the product2The content is more than 99.9 percent, and the specific surface area is not less than 380m measured by a multipoint BET method2/g。
(6) Acid solution in the reaction process: the hydrofluoric acid or the fluosilicic acid decomposes the silicon dioxide in the material; the nitric acid decomposes other metals and alkali metals in the material; nitric acid mainly plays an oxidizing role in the process. The decomposed metal is left in the acid solution as ions and corresponding salt; after the reaction is finishedFiltering while the mixture is hot, wherein filter residues are a small amount of aluminum trifluoride and fluosilicate; the filtrate is sent into an evaporator to be evaporated while the filtrate is hot, acid mist gas generated during evaporation is absorbed by a water absorption tank for more than two stages to be changed into acid liquor, the acid liquor returns to a workshop to be reused after reaching a certain concentration, and unabsorbed tail gas is neutralized by an acid mist absorption tower and then is emptied; when the acid liquor in the evaporator is evaporated to dryness, the dry residue is treated by concentrated sulfuric acid, and then TiO is recovered2。

Claims (9)

1. A process for preparing fumed silica by using red mud as a raw material is characterized by comprising the following devices:
the device comprises a hot air feeding system, a chemical reaction system, a cooling system and a waste gas absorption system, wherein the hot air feeding system is used for storing compressed air, heating the air and then feeding the air into the chemical reaction system; the chemical reaction system consists of an acid liquor storage tank, a storage bin and a reaction kettle, wherein the bottoms of the acid liquor storage tank and the storage bin are communicated with the reaction kettle through a pipeline, a stirring device is arranged in the reaction kettle, the lining of the reaction kettle is made of a temperature-resistant, acid-resistant and wear-resistant material, an annular round pipe is arranged above the bottom of the reaction kettle, air holes or air vent pipes are uniformly distributed on the round pipe, more than one vertical pipe communicated with the annular round pipe is arranged in the reaction kettle, and the top end of the vertical pipe is communicated with a hot air feeding system through a pipe valve on a kettle cover of the reaction kettle; the upper end and the lower end of the tube bundle are respectively connected with a cold and hot medium outside the kettle wall through a valve, and the heating or cooling is provided for a reaction system in the kettle by introducing the cold and hot medium into the capillary tubes in the tube bundle;
the cooling system is formed by connecting a primary cooling kettle and a secondary cooling kettle in series; the device comprises a primary cooling kettle, a reaction kettle, a secondary cooling kettle, a cooling device, a discharge valve, a pipeline, a pressure sensor and a control system, wherein the primary cooling kettle is connected with the reaction kettle, the pipeline which is connected with the primary cooling kettle and extends into the center of the bottom of the primary cooling kettle is arranged on a kettle cover of the reaction kettle, the cooling device is arranged inside the primary cooling kettle, the discharge valve is arranged at the bottom of the secondary cooling kettle; a pipeline connected with a waste gas absorption system is arranged on a kettle cover of the secondary cooling kettle, the waste gas absorption system consists of more than one negative pressure water absorption tank and an acid mist absorption device, and the top of the negative pressure water absorption tank is provided with a pipeline and is connected with an induced draft fan in the acid mist absorption device through the pipeline;
the process for preparing the fumed silica by adopting the device and taking the red mud as the raw material comprises the following steps:
(1) mixing the fluorine-containing acid solution with nitric acid to prepare a mixed acid solution for later use; mixing red mud and hydrogen peroxide, granulating, drying, grinding to fineness of below 200 meshes, magnetically separating to remove iron, dissolving metal oxides and rare earth elements in the magnetically separated red mud with hydrochloric acid, filtering, and collecting filter cakes for later use;
(2) putting the mixed acid liquid into a reaction kettle, starting a stirring device of the reaction kettle and a waste gas absorption device in a reaction system, and putting a filter cake or powder obtained by drying and grinding the filter cake into the reaction kettle;
(3) controlling the reaction temperature in the reaction kettle to be 75-90 ℃, reacting hydrofluoric acid or fluosilicic acid in the mixed acid liquid with silicon dioxide in a filter cake or powder to generate silicon tetrafluoride gas, and carrying the silicon tetrafluoride gas, acid gas volatilized from the mixed acid liquid and water vapor into the cooling kettle under negative pressure;
(4) controlling the cooling temperature in the cooling kettle to be 0-36 ℃, and reacting the mixed gas in the cooling kettle, wherein HF and NO are reacted2Is taken out from the cooling kettle by negative pressure and is absorbed by water to generate hydrofluoric acid, nitric acid and SiO which can be used repeatedly2·nH2O is condensed and adsorbed on a cooling device in a cooling kettle, and SiO in the cooling kettle is collected2·nH2O；
(5) Collecting the SiO2·nH2Preheating O in vacuum heater under negative pressure to remove residual HF and NO2Then drying to obtain the gas-phase white carbonBlack products, SiO in products2The content is more than 99.9 percent, and the specific surface area is not less than 380m measured by a multipoint BET method2/g；
(6) In the reaction kettle, the fluorine-containing acid solution decomposes the silicon dioxide in the filter cake or powder; the nitric acid decomposes the residual metal in the material, and the decomposed metal is left in the mixed acid solution in the form of ions and salt; filtering after the reaction of the materials in the reaction kettle is finished, and separating out AlF in filter residue3(ii) a Then sending the filtrate into an evaporator to be evaporated to dryness to obtain residue, treating the residue with concentrated sulfuric acid, and recovering TiO2。
2. The process for preparing fumed silica according to claim 1, characterized in that: the mass concentration or volume concentration of the hydrofluoric acid is 2-30%, the mass concentration or volume concentration of the fluosilicic acid is 10-30%, and the mass concentration or volume concentration of the nitric acid is 2-30%.
3. The process for preparing fumed silica according to claim 1, characterized in that: neutralizing the filtrate filtered in the step (1) with alkali, adding a sulfuric acid solution, precipitating and separating calcium sulfate, adding hydrofluoric acid, precipitating and separating aluminum trifluoride, and extracting and separating rare earth elements with oxalic acid; adjusting the pH value of the residual solution to 8.5-9 by using alkali liquor, precipitating, filtering and separating out iron hydroxide, calcining the iron hydroxide to obtain an iron oxide red product, concentrating the filtrate, and adding fluosilicic acid to obtain precipitated fluosilicate and hydrochloric acid; the hydrochloric acid is purified and then returned for use.
4. The process for preparing fumed silica according to claim 1, characterized in that: and (4) absorbing the acid mist gas generated in the evaporation in the step (6) by using a water absorption tank to obtain acid liquor, returning the acid liquor to a workshop for reuse after the acid liquor reaches a certain concentration, and neutralizing the unabsorbed tail gas by using an acid mist absorption tower and then emptying the tail gas.
5. The apparatus of claim 1, wherein: the hot air feeding system comprises an air compressor, an air storage tank, an air heater and a pipeline, wherein the air compressor, the air storage tank and the air heater are connected through the pipeline, and the pipeline is further provided with a valve and an instrument.
6. The apparatus of claim 1, wherein: the reactor is characterized in that vent pipes with diameters of 10-20 mm and different orientations are uniformly distributed on the round pipe, the distance between every two adjacent vent pipes is 50-150 mm, the included angle between the extending directions of the adjacent vent pipes is 60-120 degrees, two vertical pipes are arranged in the reactor, and the two vertical pipes are respectively connected to the left end and the right end of the round pipe.
7. The apparatus of claim 1, wherein: the cooling device of the primary cooling kettle consists of a rotating shaft and a cooling disc, the rotating shaft is a hollow round pipe wrapped with polytetrafluoroethylene, the top end of the rotating shaft extends out of the kettle cover of the primary cooling kettle, a cooling water pipe A from top to bottom is arranged in the rotating shaft, the top of the cooling water pipe A is a water inlet end, and the water inlet end is connected with a cooling water source; cooling discs are uniformly distributed on the rotating shaft, the cooling discs are fixedly arranged on the rotating shaft by taking the rotating shaft as the circle center and rotate along with the rotating shaft, the cooling discs are of a hollow structure, cooling water pipes B which are distributed in a spiral shape are arranged inside all the cooling discs, the cooling water pipes B in the cooling discs which are adjacent up and down are connected end to end, the water inlet end of the cooling water pipe B in the bottommost cooling disc is communicated with the bottom end of the cooling water pipe A, the water outlet end of the cooling water pipe B in the topmost cooling disc is communicated with a hollow circular pipe, and cooling water discharged from the cooling water pipe B overflows from the top end of the rotating shaft; the cooling disc is uniformly distributed with vertical vent holes, and the vent holes on the cooling disc adjacent to each other are staggered.
8. The apparatus of claim 7, wherein: the kettle cover of the one-level cooling kettle is provided with a vacuum meter and a manhole convenient to overhaul, and the kettle cover of the one-level cooling kettle is also provided with a compressed air blowing device which is connected with a compressed gas source.
9. The apparatus of claim 1, wherein: the cooling device in the secondary cooling kettle is of a multi-layer fin structure, a cooling water inlet and a cooling water outlet are formed in the kettle wall of the secondary cooling kettle, the cooling water inlet is communicated with a water inlet of the fin at the lowest layer, cooling water flows in from the fin at the lowest layer, the fins are of a continuous bending structure, the end parts of the adjacent upper and lower layers of fins are communicated, and the cooling water outlet is communicated with a water outlet of the fin at the uppermost layer; a compressed air blowing device is arranged on a kettle cover of the secondary cooling kettle and is connected with a compressed gas source, a vacuum meter is arranged on the kettle cover of the secondary cooling kettle, and manholes convenient to overhaul are arranged at the bottom of the kettle cover and the kettle.
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