A system and method for preparing high-purity quartz sand based on a closed loop of silicon-containing tailings

Abstract

The present application relates to the technical field of high-purity quartz sand preparation, and particularly relates to a system and method for preparing high-purity quartz sand based on closed-loop preparation of silicon-containing tailings, which comprises: a raw material pretreatment unit for obtaining purified tailings; a reaction purification unit for chemical reaction of the purified tailings, and products generated by ion exchange, thermal decomposition, purification and hydrolysis reaction to generate silicon dioxide particles; a melting and granulation unit for melting the silicon dioxide particles, and water quenching and crushing to prepare high-purity quartz sand; and a medium recovery unit connected to related links of the reaction purification unit, for collecting HF gas and hydrofluoric acid generated in the process of production, and returning the purified HF gas and hydrofluoric acid to the reaction purification unit as raw materials for recycling. The silicon-containing tailings are used as raw materials to prepare high-purity quartz sand through steps such as dissolution and gas-phase hydrolysis, not only realizing high-value utilization of solid waste, but also reducing fluorine-containing pollution through fluoride recycling, and improving the purity of quartz sand.

Description

Technical Field

[0001] This invention relates to the field of high-purity quartz sand preparation technology, and in particular to a system and method for preparing high-purity quartz sand based on a closed-loop process using silicon-containing tailings. Background Technology

[0002] High-purity quartz sand, with its excellent physicochemical properties, is widely used in high-end fields such as photovoltaics, optical fibers, and semiconductors. However, the purification process for preparing high-purity quartz sand from natural quartz ore is complex, energy-intensive, and the purity is difficult to meet electronic-grade requirements.

[0003] Chinese patent CN116692882A discloses a method for preparing precipitated silica and high-purity quartz blocks from fluorosilicic acid, mainly including the following steps: first, heating a low-concentration fluorosilicic acid solution to generate steam, and then absorbing the steam with pure water; then collecting, separating, washing, and drying the deposits; finally, heating the deposits to densify them into synthetic quartz blocks. However, this process is energy-intensive and difficult to scale up. Chinese patent CN108793176A discloses a method for preparing ultrapure quartz from silicon tetrafluoride, mainly including the following steps: first, placing pure water and a mineralizing agent into a reaction vessel, and then introducing silicon tetrafluoride gas to heat and react; then, adding quartz crystal nuclei into the reaction vessel, waiting for the nuclei to grow into crystals, and then removing the quartz crystals; finally, obtaining ultrapure quartz sand through separation and drying. This method uses natural quartz sand as raw material, and the reaction conditions are strict, resulting in high energy consumption and cost.

[0004] Chinese patent CN117945654A discloses a method for preparing microcrystalline glass materials from quartz sand tailings, mainly including the following steps: first, the tailings, flux, additives, etc. are melted and water-quenched to form a preform; then, the base glass is crushed and pressed into a cylinder; finally, it is sintered, nucleated, and polished to form a microcrystalline glass material. This method can only produce low- to mid-range structural materials and cannot achieve a leap in value to high-purity quartz sand. Chinese patent CN120057928A discloses a method for preparing quartz sand from granite tailings, mainly including the following steps: first, the granite tailings are subjected to a first impurity removal process through wet separation, magnetic separation, flotation, and acid washing, and then dried to obtain coarse sand; then, the coarse sand is calcined at high temperature and cooled using liquid CO2; finally, the cooled quartz sand is subjected to a second impurity removal process to obtain high-purity quartz sand with a purity of 4N or higher. However, the quartz sand prepared by this method has low purity, and the tailings are not utilized at a high value.

[0005] The aforementioned technology for preparing high-purity quartz sand from silicon-containing waste lacks an organically integrated closed-loop production system. It cannot simultaneously achieve high-value utilization of silicon-containing solid waste, closed-loop recycling of fluorine media, low pollution and low energy consumption, and stable large-scale preparation of semiconductor-grade high-purity quartz sand. Consequently, the existing process suffers from problems such as large emissions of waste gas, wastewater, and solid waste, high consumption of fluorine reagents, large fluctuations in product purity, and inability to consistently meet the requirements of semiconductor-grade applications.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the general background of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] This invention provides a system and method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings. Using silicon-containing tailings as raw materials, high-purity quartz sand is prepared through steps such as dissolution and gas-phase hydrolysis. This not only realizes the high-value utilization of solid waste, but also reduces fluoride pollution through fluoride recycling, while improving the purity of quartz sand. This provides a green and environmentally friendly technical path for the production of semiconductor-grade quartz sand and solves the problems in the background technology.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a system for the closed-loop preparation of high-purity quartz sand based on silicon-containing tailings, the system comprising: The raw material pretreatment unit is used for crushing, pickling, and drying tailings to obtain purified tailings. The reaction purification unit is connected to the raw material pretreatment unit and is used to purify the tailings through chemical reactions. The products undergo ion exchange, thermal decomposition, purification and hydrolysis to generate silica particles. The melt granulation unit, connected to the reaction purification unit, is used to melt silica particles and then water-quench and crush them to prepare high-purity quartz sand. The media recovery unit connects all relevant parts of the reaction purification unit and is used to collect HF gas and hydrofluoric acid generated during the process. After purification, the HF gas and hydrofluoric acid are returned to the reaction purification unit as raw materials for recycling, thus realizing the recovery and recycling of fluorine.

[0009] Furthermore, the raw material pretreatment unit includes a crusher, a pickling tank, a washing tank, and a drying box connected in sequence; The reaction purification unit includes a reaction vessel, an ion exchange resin, an evaporation vessel, and a hydrolysis reactor connected in sequence. A separation vessel is installed between the reaction vessel and the ion exchange resin to separate HF gas and intermediate products. The HF gas enters the media recovery unit along a pipeline. A gas purifier, a condenser separator, and a two-stage axial cyclone mixer are connected in sequence between the evaporation vessel and the hydrolysis reactor. A steam pipeline is introduced between the condenser separator and the two-stage axial cyclone mixer. The intermediate products, after purification and condensation separation, enter the hydrolysis reactor. The hydrofluoric acid solution separated by the condenser separator enters the media recovery unit through a pipeline. A gas-solid separator is installed between the hydrolysis reactor and the melt granulation unit. The intermediate products, after hydrolysis, generate silica particles, which, after gas-solid separation, enter the melt granulation unit. The HF gas generated by the hydrolysis reactor and the gas-solid separator enters the media recovery unit through a pipeline. The melting and granulation unit includes a melting furnace, a water quenching device, and an impact crusher connected in sequence. High-purity quartz sand is obtained after the silica particles are melted, water quenched, and crushed.

[0010] The media recovery unit includes an absorption tower, a distillation tower, and a recovery tank connected in sequence. The HF gas generated by the reaction purification unit enters the absorption tower through a pipeline, the hydrofluoric acid solution enters the distillation tower through a pipeline, and the purified hydrofluoric acid enters the recovery tank as a raw material for the reaction purification unit, realizing a closed-loop cycle of fluorine.

[0011] A second aspect of the present invention provides a method for preparing high-purity quartz sand based on a closed-loop system using silicon-containing tailings. This method is based on the aforementioned system and includes: S1 uses silicon-containing tailings as raw materials, which are purified and pretreated by the raw material pretreatment unit to obtain purified tailings. This step removes metal or organic impurities attached to the surface of the raw materials by purifying and pretreating the silicon-containing tailings. At the same time, the particle size of the raw materials is adjusted to increase the reaction contact area, so as to obtain purified tailings with stable cleanliness. This controls the introduction of impurities from the source and provides a qualified raw material base for subsequent high-purity preparation.

[0012] S2 sends the purified tailings into the reaction vessel of the reaction purification unit to react with hydrofluoric acid to prepare fluorosilicic acid solution; this step achieves the directional conversion of solid elemental silicon to liquid fluorosilicic acid through the directional reaction of purified tailings and hydrofluoric acid, and completes the preliminary extraction and enrichment of silicon source. The reaction equation is: Si + 6HF → H2SiF6 + 2H2. S3 removes cationic impurities from the fluorosilicic acid solution to obtain a high-purity fluorosilicic acid solution. This step removes cationic impurities from the fluorosilicic acid solution to deeply remove metal impurities entrained in the solution, further improving the purity of the fluorosilicic acid solution and preventing impurities from entering subsequent processes along with the silicon source. S4 involves thermally decomposing a high-purity fluorosilicic acid solution to prepare high-purity silicon tetrafluoride gas. In this step, the liquid-phase silicon source is converted into gaseous silicon tetrafluoride through the thermal decomposition of the high-purity fluorosilicic acid solution. The difference in physical properties between the gas and liquid phase transition is used to achieve complete separation of the silicon source from residual non-volatile impurities, thereby obtaining an ultra-high-purity silicon source precursor. The reaction equation for thermal decomposition is: H2SiF6→SiF4+2HF. S5 involves a gas-phase hydrolysis reaction of high-purity silicon tetrafluoride gas with water vapor to prepare high-purity silica particles. This step synthesizes high-purity amorphous silica particles in a gas-phase environment through the gas-phase hydrolysis reaction of high-purity silicon tetrafluoride with water vapor, avoiding the impurity encapsulation problem that easily occurs in liquid-phase synthesis, and stably obtaining ultra-high-purity silica products. At the same time, it achieves the centralized precipitation of by-product hydrogen fluoride, providing conditions for the closed-loop recovery of fluorine media. The reaction equation is: SiF4 + 2H2O → SiO2 + 4HF. S6 feeds high-purity silica particles into the melt granulation unit, where they undergo densification molding to prepare high-purity quartz sand. This step transforms amorphous silica into high-purity quartz sand with a dense structure and stable physicochemical properties by densifying the high-purity silica particles, thereby controlling the product morphology and particle size distribution to meet the application requirements of high-end fields and completing the final product preparation.

[0013] This invention uses high intrinsic purity silicon-containing waste materials generated in the semiconductor and photovoltaic industries as raw materials, realizing the high-value resource utilization of industrial solid waste and replacing scarce natural quartz ore. It also eliminates the emission of fluorine-containing waste from the source through a closed-loop fluorine medium circulation throughout the entire process, significantly reducing the consumption of hydrofluoric acid reagents and environmental treatment costs. At the same time, relying on the synthesis route of liquid-phase purification and gas-phase hydrolysis, it can stably prepare high-purity quartz sand with a purity that meets semiconductor-grade requirements, solving the problem of large purity fluctuations in traditional processes that are difficult to meet the needs of high-end applications. Overall, it achieves multiple core advantages of solid waste utilization, green environmental protection, low cost, and high purity and stability of products.

[0014] Further, in step S1, the purification pretreatment specifically involves: crushing the silicon-containing tailings, acid washing, rinsing with high-purity water until neutral, and then drying; the silicon-containing tailings are one or more of polycrystalline silicon scraps, monocrystalline silicon head and tail materials, and silicon wafer cutting powder.

[0015] More specifically, crushing increases the contact area of ​​the raw materials for reaction, acid washing removes surface-attached impurities, water washing to neutrality eliminates interference from residual acid, and drying prevents moisture from affecting subsequent reactions, thus providing clean and stable raw materials for subsequent high-purity reactions.

[0016] Preferably, in step S1, the particle size of the crushed silicon-containing tailings is 50μm~1000μm; the acid used for pickling is one or more of dilute hydrochloric acid, dilute sulfuric acid, oxalic acid and hydrofluoric acid, the pickling temperature is 20℃~80℃; the drying temperature is 100℃~150℃, and the drying time is 1h~6h.

[0017] Further, in step S2, the purified tailings and hydrofluoric acid are fed at a silicon-fluorine molar ratio of 1:5.5~8.5, the mass concentration of the hydrofluoric acid solution is 25%~60%, the reaction temperature is 30℃~80℃, the stirring rate is 200r / min~600r / min, and the reaction time is 2h~6h.

[0018] More specifically, the above feed ratio ensures complete reaction of silicon raw materials and avoids excessive hydrofluoric acid. Appropriate concentration and reaction parameters can enhance mass transfer and ensure sufficient reaction, preventing insufficient or excessive reaction.

[0019] Preferably, the hydrogen generated by the reaction of the purified tailings with hydrofluoric acid solution is sent to a hydrogen treatment device after gas-liquid separation. The hydrogen treatment device is existing technology and will not be described in detail.

[0020] More specifically, the reaction between the purified waste and hydrofluoric acid produces hydrogen as a byproduct. Hydrogen enrichment can easily lead to safety risks. Gas-liquid separation can prevent hydrogen from carrying liquid materials and eliminate potential production safety hazards.

[0021] Furthermore, in step S3, the removal of cationic impurities specifically involves using a strong acid-type cation exchange resin to adsorb and remove impurities from the fluorosilicic acid solution.

[0022] More specifically, since the fluorosilicic acid solution contains metal cation impurities, which will enter the silicon tetrafluoride system in subsequent processes and affect the purity of the final product, the strong acid cation exchange resin can directionally adsorb the metal cations in the fluorosilicic acid solution without introducing new impurities.

[0023] Furthermore, in step S4, the thermal decomposition temperature is 60℃~160℃ and the pressure is 30kPa~100kPa; the mixed gas of silicon tetrafluoride and hydrogen fluoride obtained by thermal decomposition is purified and separated by two-stage condensation to obtain high-purity silicon tetrafluoride gas.

[0024] Furthermore, the above parameters allow fluorosilicic acid to undergo a full thermal decomposition reaction, purification can remove entrained impurities from the mixed gas, and two-stage condensation separation can separate hydrogen fluoride from the mixed gas.

[0025] Preferably, the purified fluorosilicic acid solution is placed in an evaporation kettle, where it undergoes thermal decomposition to generate a mixed gas of SiF4 and HF. After purification to remove entrained mist, the gas is then separated by a condenser to obtain high-purity SiF4 gas. The HF is condensed into hydrofluoric acid liquid and then purified by distillation.

[0026] Preferably, the two-stage condensation separation is as follows: first, the mixed gas is introduced into the first-stage condenser, and the pressure is controlled at 0.4MPa~0.8MPa and the temperature at 20℃~45℃ to condense and separate most of the hydrogen fluoride; then, the remaining gas is introduced into the second-stage condenser, and the pressure is controlled at 0.2MPa~0.6MPa and the temperature at -20℃~0℃ to deeply condense and remove the residual hydrogen fluoride to obtain high-purity silicon tetrafluoride gas.

[0027] More specifically, the temperature and pressure conditions of the first-stage condensation can condense and separate most of the HF in the mixed gas, and the low temperature and low pressure conditions of the second-stage condensation can further condense the remaining trace amounts of HF. By gradually removing HF from the mixed gas through staged condensation, high-purity silicon tetrafluoride gas is obtained.

[0028] Furthermore, in step S5, the molar ratio of high-purity silicon tetrafluoride gas to water vapor is 1:1.8~4.5; the temperature of the first stage of the gas-phase hydrolysis reaction is 350℃~600℃, and the temperature of the second stage is 80℃~105℃.

[0029] More specifically, the initial temperature meets the conditions for the hydrolysis reaction, while the subsequent temperature lowers the temperature of the reaction system, allowing silicon tetrafluoride to complete the gas-phase hydrolysis reaction with water vapor to generate silicon dioxide, while preventing the silicon dioxide particles from sintering.

[0030] Preferably, in step S5, the high-purity silicon tetrafluoride gas and water vapor are first thoroughly mixed before undergoing a gas-phase hydrolysis reaction; the generated high-purity silicon dioxide particles are collected by a gas-solid separator; the HF gas generated by hydrolysis enters an absorption tower and is further purified and recovered by distillation, which can be used as a raw material in step S2.

[0031] More specifically, high-purity silicon tetrafluoride gas and water vapor are pre-mixed thoroughly to form a uniform mixture of the two gaseous reactants before entering the hydrolysis reactor; the HF gas generated by hydrolysis is introduced into an absorption tower and purified by distillation to obtain hydrofluoric acid solution, which can be collected and treated as a reaction raw material for step S2 and reused.

[0032] Furthermore, in step S6, the densification molding process specifically involves melting high-purity silica particles, followed by water quenching and crushing to obtain high-purity quartz sand.

[0033] More specifically, melting causes the silica particles to fuse and become dense, water quenching makes the molten material brittle, and crushing processes it into the form of quartz sand. Through the above steps, loose silica powder is transformed into dense quartz sand material.

[0034] Preferably, the melting temperature is 1750℃~2050℃, the melting time is 0.5h~2.5h, and the melting atmosphere is one or more of nitrogen, argon, and helium; the water quenching uses deionized water with a resistivity ≥18.25MΩ・cm, the water jet speed is 5m / s~30m / s, and the water temperature is 10℃~40℃; the crushing uses an impact crusher with a crushing speed of 1200r / min~3000r / min.

[0035] Furthermore, it also includes a step for processing fluorine-containing materials: collecting the fluorine-containing materials generated in each stage through a media recovery unit, purifying them, and returning them to the reactor for recycling as raw materials for hydrofluoric acid reaction.

[0036] More specifically, unreacted hydrofluoric acid or byproduct hydrogen fluoride and other fluorine-containing materials are generated in the silicon-fluorine reaction, thermal decomposition of fluorosilicic acid, gas-phase hydrolysis, and various separation and purification stages. Depending on the form of the fluoride, an appropriate treatment method is selected to replenish the hydrofluoric acid raw material consumed in the reaction process.

[0037] Preferably, the purification of fluorine-containing materials specifically involves: absorbing the collected fluorine-containing gas through an absorption tower and purifying it through a distillation tower to obtain reusable hydrofluoric acid; and purifying the collected fluorine-containing liquid through a distillation tower to obtain reusable hydrofluoric acid.

[0038] More specifically, the fluorine-containing gas is absorbed by ultrapure water and converted into a liquid phase in the absorption tower. The fluorine-containing liquid can be directly purified by distillation. By adopting a purification method that matches the material form, hydrofluoric acid that can be directly used in the reaction of step S2 can be obtained.

[0039] Preferably, after the purified tailings react with hydrofluoric acid, the unreacted hydrofluoric acid is first removed by vacuum separation, and then the cationic impurity removal treatment in step S3 is carried out; the separated hydrofluoric acid is sent to the fluorine-containing material purification process for reuse.

[0040] More specifically, after the reaction in step S2 is completed, the fluorosilicic acid solution system contains a large amount of unreacted free hydrofluoric acid. If it directly enters the cationic impurity removal process in step S3, the high concentration of free hydrofluoric acid will affect the adsorption performance of the cation exchange resin, increase the resin treatment load, and even cause the resin to fail.

[0041] The technical solution of this invention can achieve the following technical effects: (1) This invention uses high intrinsic purity silicon-containing waste materials such as polycrystalline silicon scraps, monocrystalline silicon head and tail materials, and silicon wafer cutting powder, which are by-products of the photovoltaic and semiconductor industries, as raw materials. Through purification pretreatment, silicon-fluorine reaction to produce fluorosilicic acid, cation removal liquid phase purification, thermal decomposition gas phase purification, gas phase hydrolysis synthesis and densification molding, the high-value utilization of industrial solid waste can be realized, which can directly replace natural high-purity quartz ore raw materials. At the same time, through pretreatment to control impurities at the source, liquid phase resin adsorption to remove metal impurities, thermal decomposition gas-liquid phase change for further purification and gas phase hydrolysis synthesis to avoid impurity encapsulation, semiconductor-grade high-purity quartz sand can be stably prepared, solving the problem of insufficient product purity and poor batch consistency of traditional processes.

[0042] (2) This invention constructs a closed-loop fluorine medium circulation by uniformly collecting and selectively purifying and reusing fluorine-containing materials throughout the entire process. It can recover all fluorine-containing materials from the entire process, such as hydrofluoric acid not consumed in the silicon-fluorine reaction, thermal decomposition of fluorosilicic acid and hydrogen fluoride by-products of gas-phase hydrolysis. The gas-phase fluorine-containing materials are purified by absorption and distillation, and the liquid-phase fluorine-containing materials are purified by direct distillation. After these treatments, they can be reused as raw materials for the silicon-fluorine reaction, reducing the consumption of fresh hydrofluoric acid raw materials and reducing the discharge of fluorine-containing waste gas and wastewater. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of a system for preparing high-purity quartz sand based on a closed-loop process using silicon-containing tailings. Figure 2 This is a schematic diagram of a method for preparing high-purity quartz sand based on a closed-loop process using silicon-containing tailings. Figure 3 This is an optical microscope image of the high-purity synthetic quartz synthesized in Example 2; Reference numerals: 1. Raw material pretreatment unit; 2. Reactor; 3. Separator; 4. Ion exchange resin; 5. Evaporator; 6. Gas purifier; 7. Condenser separator; 8. Two-stage axial cyclone mixer; 9. Hydrolysis reactor; 10. Gas-solid separator; 11. Absorption tower; 12. Distillation tower; 13. Recovery tank; 14. Melting furnace; 15. Water quenching equipment; 16. Impact crusher. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0047] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application.

[0048] The embodiments of the present invention all employ the following system: Raw material pretreatment unit 1 includes a crusher, pickling tank, washing tank and drying box connected in sequence; The reaction purification unit includes a reaction vessel 2, an ion exchange resin 4, an evaporation vessel 5, and a hydrolysis reactor 9 connected in sequence. A separation vessel 3 is installed between the reaction vessel 2 and the ion exchange resin 4 to separate HF gas and intermediate products. The HF gas enters the media recovery unit along the pipeline. A gas purifier 6, a condenser separator 7, and a two-stage axial cyclone mixer 8 are connected in sequence between the evaporation vessel 5 and the hydrolysis reactor 9. A steam pipeline is introduced between the condenser separator 7 and the two-stage axial cyclone mixer 8. The intermediate products, after purification and condensation separation, enter the hydrolysis reactor 9. The hydrofluoric acid solution separated by the condenser separator 7 enters the media recovery unit through the pipeline. A gas-solid separator 10 is installed between the hydrolysis reactor 9 and the melting furnace 14. The intermediate products, after hydrolysis, generate silica particles, which, after gas-solid separation, enter the melting and granulation unit. The HF gas generated by the hydrolysis reactor 9 and the gas-solid separator 10 enters the media recovery unit through the pipeline. The gas purifier 6 uses a polytetrafluoroethylene (PTFE) filter element, and the gas-solid separator 10 uses a PTFE filter bag. The melting and granulation unit includes a melting furnace 14, a water quenching device 15, and an impact crusher 16 connected in sequence.

[0049] The media recovery unit includes an absorption tower 11, a distillation tower 12, and a recovery tank 13 connected in sequence. The HF gas generated by the reaction purification unit enters the absorption tower 11 along the pipeline, the hydrofluoric acid solution enters the distillation tower 12 along the pipeline, and the purified hydrofluoric acid enters the recovery tank 13 as a raw material for the reaction purification unit.

[0050] Example 1:

[0051] This embodiment uses monocrystalline silicon head and tail materials as raw materials and employs the closed-loop high-purity quartz sand preparation system of the present invention to prepare high-purity synthetic quartz sand. The specific steps are as follows: Step 1: First, crush the head and tail of monocrystalline silicon and control the particle size to be less than 200μm with a sieve. Then, transfer it to the pickling tank and pickle it with dilute hydrochloric acid at 60℃. After that, wash it continuously with high-purity water until it is neutral. Then, dry it in a drying oven at 120℃ for 3 hours to obtain purified raw material. Step 2: The purified raw material and hydrofluoric acid solution are added to the reactor at a silicon-to-fluorine molar ratio of 1:7 and reacted at 55℃ and 400 r / min for 3.5 h. After the reaction, the solution is pumped into a separation vessel, where the unreacted hydrofluoric acid solution is evaporated at low temperature at 45℃ and 40 kPa. Then, the fluorosilicic acid solution is passed through a strong acid cation exchange resin to remove metal ions. Meanwhile, hydrogen gas is transferred to a hydrogen treatment device via a polytetrafluoroethylene gas-liquid separator. After the hydrofluoric acid is evaporated, it is sent to an absorption tower for recycling. Step 3: The fluorosilicic acid solution from Step 2 is transferred to an evaporator at 105℃ and 60kPa for thermal decomposition. The mixed gas is purified by the filter element of a gas purifier and then sequentially passed through the primary and secondary condensers of a condenser separator to obtain high-purity SiF4 gas. The pressure of the primary condenser is 0.6MPa and the temperature is 33℃; the pressure of the secondary condenser is 0.4MPa and the temperature is -10℃. The hydrofluoric acid liquid recovered from the condensation is transferred to a distillation column for purification and recovery. Step 4: SiF4 gas and water vapor are introduced into a two-stage axial cyclone mixer at a molar ratio of 1:2.5. Then, the mixture is hydrolyzed at 420°C and quenched at 100°C in a hydrolysis reactor. The resulting silica particles are collected by a gas-solid separator. The HF gas generated during hydrolysis enters an absorption tower and is further purified by distillation to recover the hydrofluoric acid solution, which can be used as a raw material. Step 5: Transfer the silica particles into an induction high-frequency coil melting furnace and melt them at 1800℃ for 1.5 hours. The melt flows out through a nozzle and is quenched by high-purity water at 20℃ and a flow rate of 10m / s. The embrittled particles are then crushed by an impact crusher at 2500r / min to obtain high-purity quartz sand.

[0052] In this embodiment, the fluorine-containing materials are purified and reused in the entire process through the media recovery unit, and the fluorine media recycling rate reaches 96.2%. Compared with the traditional process without recycling, the consumption of fresh hydrofluoric acid raw materials is reduced by 92.7%, and there is no discharge of fluorine-containing wastewater or waste gas.

[0053] The test results of high-purity synthetic quartz sand are shown in Table 1: Table 1. Composition of high-purity quartz sand in Example 1 (unit: ppm) Example 2:

[0054] This embodiment uses silicon wafer cutting powder as raw material and employs the closed-loop high-purity quartz sand preparation system of the present invention to prepare high-purity synthetic quartz sand. The specific steps are as follows: Step 1: First, the silicon wafer cutting powder is crushed and the particle size is controlled to be less than 250μm by sieve. It is then transferred to an acid washing tank and acid washed at 55℃ using a mixture of dilute hydrochloric acid and dilute sulfuric acid. After that, it is continuously washed with high-purity water until neutral and then dried in a drying oven at 135℃ for 2 hours to obtain purified raw material. Step 2: The purified raw material and hydrofluoric acid solution are added to the reactor at a silicon-to-fluorine molar ratio of 1:6.5 and reacted at 47℃ and 450 r / min for 3.8 h. After the reaction, the solution is pumped into a separation vessel, where the unreacted hydrofluoric acid solution is evaporated at low temperature at 50℃ and 30 kPa. Then, the fluorosilicic acid solution is passed through a strong acid cation exchange resin to remove metal ions. Hydrogen gas is transferred to a hydrogen treatment device via a polytetrafluoroethylene gas-liquid separator. After the hydrofluoric acid is evaporated, it is sent to an absorption tower for recycling. Step 3: The fluorosilicic acid solution from Step 2 is transferred to an evaporator at 120℃ and 50kPa for thermal decomposition. The mixed gas is purified by the filter element of the gas purifier and then passes through the primary and secondary condensers of the condenser separator to obtain high-purity SiF4 gas. The pressure of the primary condenser is 0.5MPa and the temperature is 27℃; the pressure of the secondary condenser is 0.3MPa and the temperature is -12℃. The hydrofluoric acid liquid recovered by condensation is transferred to a distillation column for purification and recovery.

[0055] Step 4: SiF4 gas and water vapor are introduced into a two-stage axial cyclone mixer at a molar ratio of 1:3.2. Then, the mixture is hydrolyzed at 480°C and quenched at 85°C in a hydrolysis reactor. The resulting silica particles are collected by a gas-solid separator. The HF gas generated during hydrolysis enters an absorption tower and is further purified by distillation to recover the hydrofluoric acid solution, which can be used as a raw material. Step 5: Transfer the silica particles into an induction high-frequency coil melting furnace and maintain the melting temperature at 1860℃ for 1 hour; the melt flows out through a nozzle and is quenched by high-purity water at 25℃ and a flow rate of 12m / s. The embrittled particles are then crushed by an impact crusher at 2800r / min to obtain high-purity quartz sand.

[0056] In this embodiment, the fluorine-containing materials are purified and reused in the entire process through the media recovery unit, and the fluorine media recycling rate reaches 97.5%. Compared with the traditional process without recycling, the consumption of fresh hydrofluoric acid raw materials is reduced by 93.8%, and there is no discharge of fluorine-containing wastewater or waste gas.

[0057] The test results of the high-purity synthetic quartz sand are shown in Table 2. The optical microscope images of the high-purity synthetic quartz sand synthesized in this embodiment are shown below. Figure 3 As shown: Table 2. Composition of high-purity quartz sand in Example 2 (unit: ppm) Example 3:

[0058] This embodiment uses polycrystalline silicon scraps as raw materials and employs a closed-loop system for preparing high-purity quartz sand to produce high-purity synthetic quartz sand.

[0059] Step 1: First, the polycrystalline silicon scraps are crushed and the particle size is controlled to be less than 150μm by using a sieve. They are then transferred to an acid washing tank and acid washed with dilute sulfuric acid at 50℃. After that, they are continuously washed with high-purity water until neutral and then dried in a drying oven at 115℃ for 3.5h to obtain purified raw materials. Step 2: The purified raw material and hydrofluoric acid solution are added to the reactor at a silicon-to-fluorine molar ratio of 1:7.5 and reacted at 60℃ and 350 r / min for 2.7 h. After the reaction, the solution is pumped into a separation vessel, where the unreacted hydrofluoric acid solution is evaporated at a low temperature of 40℃ and 50 kPa. Then, the fluorosilicic acid solution is passed through a strong acid cation exchange resin to remove metal ions. Meanwhile, hydrogen gas is transferred to a hydrogen treatment device via a polytetrafluoroethylene gas-liquid separator. After the hydrofluoric acid is evaporated, it is sent to an absorption tower for recycling. Step 3: The fluorosilicic acid solution from Step 2 is transferred to an evaporator at 95℃ and 70kPa for thermal decomposition. The mixed gas is purified by the filter element of a gas purifier and then sequentially passed through the primary and secondary condensers of a condenser separator to obtain high-purity SiF4 gas. The primary condenser has a pressure of 0.7MPa and a temperature of 42℃, while the secondary condenser has a pressure of 0.5MPa and a temperature of -8℃. The hydrofluoric acid liquid recovered from the condensation is transferred to a distillation column for purification and recovery. Step 4: SiF4 gas and water vapor are introduced into a two-stage axial cyclone mixer at a molar ratio of 1:2.8, and then hydrolyzed at 500°C and quenched at 80°C in a hydrolysis reactor. The generated silica particles are collected by a gas-solid separator to obtain silica particles. The HF gas generated by hydrolysis enters an absorption tower and is further purified and recovered by distillation to recover hydrofluoric acid solution, which can be used as a raw material. Step 5: Transfer the silica particles into an induction high-frequency coil melting furnace and maintain the melting temperature at 1820℃ for 1.2 hours. The melt flows out through a nozzle and is quenched by high-purity water at 30℃ and a flow rate of 16m / s. The embrittled particles are then crushed by an impact crusher at 2600r / min to obtain high-purity quartz sand.

[0060] In this embodiment, the fluorine-containing materials are purified and reused in the entire process through the media recovery unit, and the fluorine media recycling rate reaches 95.8%. Compared with the traditional process without recycling, the consumption of fresh hydrofluoric acid raw materials is reduced by 92.1%, and there is no discharge of fluorine-containing wastewater or waste gas.

[0061] The test results of high-purity synthetic quartz sand are shown in Table 3: Table 3. Composition of high-purity quartz sand in Example 3 (unit: ppm) Example 4:

[0062] This embodiment utilizes the above three types of tailings as raw materials and employs the closed-loop high-purity quartz sand preparation system of the present invention to prepare high-purity synthetic quartz sand. The specific steps are as follows: Step 1: First, the mixed tailings are crushed and the particle size is controlled to be less than 200μm by sieve. They are then transferred to an acid washing tank and acid washed at 65℃ using a mixture of dilute hydrochloric acid and dilute sulfuric acid. After washing with high-purity water until neutral, they are dried in a drying oven at 125℃ for 3.2h to obtain purified raw materials.

[0063] Step 2: The purified raw material and hydrofluoric acid solution are added to the reactor at a silicon-to-fluorine molar ratio of 1:7.2 and reacted at 50℃ and 420 r / min for 3.5 h. After the reaction, the solution is pumped into a separation vessel, where the unreacted hydrofluoric acid solution is evaporated at a low temperature of 48℃ and 35 kPa. Then, the fluorosilicic acid solution is passed through a strong acid cation exchange resin to remove metal ions. Meanwhile, hydrogen gas is transferred to a hydrogen treatment device via a polytetrafluoroethylene gas-liquid separator. After the hydrofluoric acid is evaporated, it is sent to an absorption tower for recycling. Step 3: The fluorosilicic acid solution from Step 2 is transferred to an evaporator at 100℃ and 65kPa for thermal decomposition. The mixed gas is purified by the filter element of a gas purifier and then sequentially passed through the primary and secondary condensers of a condenser separator to obtain high-purity SiF4 gas. The primary condenser has a pressure of 0.6MPa and a temperature of 33℃; the secondary condenser has a pressure of 0.4MPa and a temperature of -10℃. The hydrofluoric acid liquid recovered from the condensation is transferred to a distillation column for purification and recovery. Step 4: SiF4 gas and water vapor are introduced into a two-stage axial cyclone mixer at a molar ratio of 1:3.5. Then, the mixture is hydrolyzed at 450°C and quenched at 95°C in a hydrolysis reactor. The resulting silica particles are collected by a gas-solid separator. The HF gas generated during hydrolysis enters an absorption tower and is further purified by distillation to recover the hydrofluoric acid solution, which can be used as a raw material. Step 5: Transfer the silica particles into an induction high-frequency coil melting furnace and maintain the melting temperature at 1840℃ for 1 hour; the melt flows out through a nozzle and is quenched by high-purity water at 28℃ and a flow rate of 15m / s. The embrittled particles are then crushed by an impact crusher at 2700r / min to obtain high-purity quartz sand.

[0064] In this embodiment, the fluorine-containing materials are purified and reused in the entire process through the media recovery unit, and the fluorine media recycling rate reaches 96.7%. Compared with the traditional process without recycling, the consumption of fresh hydrofluoric acid raw materials is reduced by 93.2%, and there is no discharge of fluorine-containing wastewater or waste gas.

[0065] The test results of high-purity synthetic quartz sand are shown in Table 4: Table 4. Composition of high-purity quartz sand in Example 4 (unit: ppm) To better demonstrate the advantages of this invention, high-purity quartz sand prepared by purifying natural quartz ore is used as a comparative example.

[0066] Comparative Example 1: This comparative example uses natural vein quartz ore as raw material to prepare high-purity quartz sand. The specific steps are as follows: Step 1: Remove obvious impurities from the surface of natural vein quartz ore and heat it in a high-temperature furnace to 980℃ and hold it for 1.5 hours. After holding, quench it in water. After quenching, dry it thoroughly in a drying oven. Use a jaw crusher for coarse crushing, and then use an impact crusher to crush the quartz blocks into quartz sand with a particle size of less than 200μm. Step 2: Add high-purity water, acid, activator, inhibitor and collector to the flotation cell. Add the crushed quartz sand to the flotation cell for flotation. After flotation for 0.5 hours, take it out to remove feldspar and low-density impurities from the quartz sand. After taking it out, rinse the quartz sand with high-purity water to remove surface impurities and flotation solution, and place it in a drying oven and heat it to 120°C to dry it thoroughly. Step 3: Calcine the quartz sand in a high-temperature furnace at 1400℃ for 6 hours. After cooling, leach it with a mixture of 5wt% dilute hydrochloric acid, 10wt% dilute sulfuric acid, 3wt% dilute nitric acid and 2wt% hydrofluoric acid. After leaching, take it out and transfer it to a reaction vessel. Stir and impregnate it with anhydrous ethanol to remove trace elements contained in the quartz inclusions that have been cracked after high temperature. Then wash it continuously with high-purity water until it is neutral. Step 4: Place the quartz sand in a vacuum drying oven and dry it at 110℃ for 3 hours to obtain high-purity quartz sand.

[0067] The test results of high-purity synthetic quartz sand are shown in Table 5: Table 5. Composition of high-purity quartz sand in Comparative Example 1 (unit: ppm) Comparative Example 1 uses natural vein quartz ore as raw material and adopts traditional physical and chemical purification processes such as high-temperature roasting, water quenching, flotation, and mixed acid leaching. Because natural quartz ore itself has many types of impurities, some of which exist in the form of lattice doping and inclusions, conventional purification methods are difficult to remove them deeply. Moreover, high-temperature treatment can easily lead to impurity diffusion and secondary pollution. In the end, the total impurity content of the quartz sand is much higher than that of the embodiment of the present invention, and the purity cannot meet the requirements of semiconductor grade.

[0068] Comparative Example 2: This comparative example uses natural vein quartz ore as raw material to prepare high-purity quartz sand. The specific steps are as follows: Step 1: After crushing the natural vein quartz into blocks, rinse it with high-purity water and place it in a drying oven at 100°C for 2 hours; Step 2: The quartz block is placed in a high-temperature furnace at 1300℃ and calcined for 5 hours. After being removed, it is quenched in a 2.5mol / L sodium carbonate solution to obtain quartz sand particles. Step 3: Crush the quartz sand particles to below 150μm using a double roller crusher, add them to a mixed acid solution of 5wt% dilute hydrochloric acid, 4wt% oxalic acid and 2wt% hydrofluoric acid with a liquid-to-solid ratio of 5:1, and leach them using microwave at 400℃ and 15MPa. After that, the quartz sand is continuously washed with high-purity water until neutral and then dried to obtain high-purity quartz sand. The test results for high-purity quartz sand are shown in Table 6: Table 6. Composition of high-purity quartz sand in Comparative Example 2 (unit: ppm) Comparative Example 2 also uses natural vein quartz ore as raw material and adopts a purification method of high-temperature roasting, alkaline quenching, and microwave leaching with mixed acid. The natural mineral raw material has low intrinsic purity and complex impurity occurrence state. Microwave leaching and acid treatment can only remove surface and some crack impurities, but cannot remove harmful impurities such as alkali metals, aluminum, and iron in the crystal lattice. In addition, the process is prone to introducing external pollution. Therefore, the total amount of impurities in the obtained quartz sand is high and the purity is significantly lower than that of the product synthesized from silicon-containing tailings in this invention.

[0069] Although this application has been described in conjunction with specific features and embodiments, it is apparent that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and accompanying drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A system for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings, characterized in that, The system includes: The raw material pretreatment unit is used for crushing, pickling, and drying tailings to obtain purified tailings. The reaction purification unit is connected to the raw material pretreatment unit and is used to purify the tailings through chemical reactions. The products undergo ion exchange, thermal decomposition, purification and hydrolysis to generate silica particles. The melt granulation unit, connected to the reaction purification unit, is used to melt silica particles and then water-quench and crush them to prepare high-purity quartz sand. The media recovery unit connects all relevant parts of the reaction purification unit and is used to collect HF gas and hydrofluoric acid generated during the process. After purification, the HF gas and hydrofluoric acid are returned to the reaction purification unit as raw materials for recycling, thus realizing the recovery and recycling of fluorine.

2. The system for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 1, characterized in that, The raw material pretreatment unit includes a crusher, an acid washing tank, a water washing tank, and a drying box connected in sequence. The reaction purification unit includes a reaction vessel, an ion exchange resin, an evaporation vessel, and a hydrolysis reactor connected in sequence. A separation vessel is installed between the reaction vessel and the ion exchange resin to separate HF gas and intermediate products. The HF gas enters the media recovery unit via a pipeline. A gas purifier, a condenser separator, and a two-stage axial cyclone mixer are connected in sequence between the evaporation vessel and the hydrolysis reactor. A steam pipeline is introduced between the condenser separator and the two-stage axial cyclone mixer. The intermediate products, after purification and condensation separation, enter the hydrolysis reactor. The hydrofluoric acid solution separated by the condenser separator enters the media recovery unit via a pipeline. A gas-solid separator is installed between the hydrolysis reactor and the melt granulation unit. The intermediate products, after hydrolysis, generate silica particles, which, after gas-solid separation, enter the melt granulation unit. The HF gas generated by the hydrolysis reactor and the gas-solid separator enters the media recovery unit via a pipeline. The melt granulation unit includes a melting furnace, a water quenching device, and an impact crusher connected in sequence; The media recovery unit includes an absorption tower, a distillation tower, and a recovery tank connected in sequence. The HF gas generated by the reaction purification unit enters the absorption tower through a pipeline, the hydrofluoric acid solution enters the distillation tower through a pipeline, and the purified hydrofluoric acid enters the recovery tank as a raw material for the reaction purification unit.

3. A method for preparing high-purity quartz sand based on silicon-containing tailings using the system described in claim 1 or 2, characterized in that, Based on the collaborative operation of the system, the method includes: S1 uses silicon-containing tailings as raw materials, which are purified and pretreated by the raw material pretreatment unit to obtain purified tailings; S2 sends the purified tailings into the reaction vessel of the reaction purification unit to react with hydrofluoric acid to prepare a fluorosilicic acid solution. S3 performs cationic impurity removal treatment on the fluorosilicic acid solution to obtain a high-purity fluorosilicic acid solution. S4 thermally decomposes the high-purity fluorosilicic acid solution to prepare high-purity silicon tetrafluoride gas; S5 involves reacting the high-purity silicon tetrafluoride gas with water vapor in a gas-phase hydrolysis reaction to prepare high-purity silicon dioxide particles. S6 feeds high-purity silica particles into the melting and granulation unit, and after densification and molding treatment, prepares high-purity quartz sand.

4. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S1, the purification pretreatment specifically involves: crushing the silicon-containing tailings, acid washing, rinsing with high-purity water until neutral, and then drying; the silicon-containing tailings are one or more of polycrystalline silicon scraps, monocrystalline silicon head and tail materials, and silicon wafer cutting powder.

5. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S2, the purified tailings and hydrofluoric acid are fed at a silicon-fluorine molar ratio of 1:5.5~8.5, the mass concentration of the hydrofluoric acid solution is 25%~60%, the reaction temperature is 30℃~80℃, the stirring rate is 200r / min~600r / min, and the reaction time is 2h~6h.

6. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S3, the cationic impurity removal process specifically involves using a strong acid-type cation exchange resin to adsorb and remove impurities from the fluorosilicic acid solution.

7. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S4, the thermal decomposition temperature is 60℃~160℃ and the pressure is 30kPa~100kPa; the mixed gas of silicon tetrafluoride and hydrogen fluoride obtained by thermal decomposition is purified and separated by two-stage condensation to obtain the high-purity silicon tetrafluoride gas.

8. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S5, the molar ratio of high-purity silicon tetrafluoride gas to water vapor is 1:1.8~4.5; the temperature of the first stage of the gas-phase hydrolysis reaction is 350℃~600℃, and the temperature of the second stage is 80℃~105℃.

9. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, In step S6, the densification molding process specifically involves melting the high-purity silica particles, followed by water quenching and crushing to obtain high-purity quartz sand.

10. The method for preparing high-purity quartz sand based on closed-loop processing of silicon-containing tailings according to claim 3, characterized in that, It also includes a step for processing fluorine-containing materials: fluorine-containing materials generated in each stage are collected through a media recovery unit, purified, and returned to the reactor for recycling as raw materials for hydrofluoric acid reaction.

Images