Quartz sand pickling process

Abstract

The invention relates to a quartz sand pickling process. The quartz sand pickling process comprises the following steps: S1, preparing a pickling solution; s2, under the condition of 100 + / -2 DEG C, quartz sand is soaked in acid liquor for 7-10 hours, and stirring is conducted at the speed of 1-2 r / min; and S3, cooling to below 50 DEG C after pickling, separating out quartz sand, washing for multiple times until the pH is neutral, and then drying to obtain a finished product. The mixed acid liquor of hydrofluoric acid and hydrochloric acid is adopted, and efficient impurity removal is achieved through the optimized acid liquor proportion. HF has strong complexing ability and can form soluble complexes with metal impurities in the quartz sand, and HCl dissolves metal oxides to generate soluble chlorides. And through combined regulation and control of high-temperature short-time stirring and low-speed stirring, the chemical reaction rate is further accelerated, and thoroughness and uniformity of impurity removal are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz sand preparation, and particularly to a pickling process for quartz sand. Background Art

[0002] As the core raw material for photovoltaic glass, semiconductors, and high-precision optical devices, the purity and impurity content requirements of quartz sand are extremely strict.

[0003] The process technology for extracting high-purity quartz sand involves high-tech means such as manual selection of raw ore, high-temperature water quenching, sand making, magnetic separation, flotation, pickling, chlorination treatment, superconducting magnetic separation, electrostatic separation, high-temperature vacuum treatment, ultrasonic treatment, doping purification, rectification purification, etc. The purpose is to remove all impurities and gas-liquid inclusions contained in quartz by all means. Among them, the pickling process is an essential process method for impurity removal and purification, and its main function is to remove some metal chlorides soluble in acid and some silicate minerals.

[0004] At present, domestic pickled sand generally uses a combination of oxalic acid and hydrofluoric acid, and the general ratio of the two is 1:1.4. Through the method of static soaking in the tank, heat preservation and soaking are carried out at 55°C - 65°C. After the iron and silicon indexes of the sand are qualified, acid discharge, rinsing, dehydration are carried out, and finally the finished product is warehoused. However, these acid liquid ratios and reaction conditions are extensive, resulting in excessive loss of the main components of quartz sand (corrosion rate ≥ 3%), low raw material utilization rate; and long pickling time, high energy consumption, and high production cost.

[0005] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of suggestion that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to achieve high efficiency, low consumption, and greening of the quartz sand pickling process, and simultaneously improve the product purity.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: A pickling process for quartz sand, comprising the following steps: S1 Prepare pickling solution; S2 Soak the quartz sand in the acid solution at 100 ± 2°C for 7 - 10 hours, and stir at a rate of 1 - 2 r / min; S3 After the pickling is completed and the temperature drops below 50°C, separate the quartz sand, wash it repeatedly until the pH is neutral, and then dry it to obtain the finished product.

[0008] Further, in step S1, the pickling solution is prepared by mixing HF, HCl, and water in a mass ratio of 5:2:4. This specific ratio achieves the best synergistic effect between the complexing action of HF and the dissolving action of HCl. Among them, HF provides sufficient F - ions, which can form stable soluble complexes such as H2AlF6 and H2FeF6 with metal ions such as Al 3+ , Fe 3+ in quartz sand; at the same time, HCl can not only dissolve metal oxides (such as Fe2O3 and Al2O3) to form soluble chlorides (such as FeCl3 and AlCl3), but also effectively prevent the generation of SiF4 gas caused by excessive HF, and control the corrosion rate of the main component of quartz sand below 0.8%, reducing the loss by 75% compared with the traditional 3:1 ratio.

[0009] Specifically, HF and HCl in the acid solution react chemically with the impurities in quartz sand, and the reaction formulas are: Fe2O3 + 6HCl = 2FeCl3 + 3H2O; M + 2HF = MF2 + H2↑; M is a metal impurity; In the present invention, HF ensures sufficient complexing ability to efficiently remove metal impurities; HCl supplements the dissolution of metal oxides to avoid excessive corrosion caused by excessive HF; water dilutes the acid solution concentration to balance the reaction rate and corrosion risk.

[0010] Further, in step S2, an acid-resistant sealed reaction kettle is used. The inner lining of the reaction kettle is made of polytetrafluoroethylene with a thickness of 5 - 8 mm, showing excellent chemical inertness in an acidic environment at 100°C. The sealing system of the reaction kettle consists of a double-layer fluororubber sealing ring and is connected to a negative pressure suction device, with an acid mist leakage of <1 ppm. Among them, the main sealing ring is made of perfluoroether rubber (FFKM), with a compression set of <5% at 150°C; the secondary sealing ring is fluorosilicone rubber (FVMQ), and the elastic modulus retention rate is >90%.

[0011] Further, in step S2, it includes: The acid solution is heated to 100°C and maintained at the set temperature by a staged gradient heating method, and the heating power is adjusted through real-time data feedback at at least three temperature measurement points to control the temperature fluctuation within the range of ±1°C; The quartz sand is immersed in the acid solution and stirred at a speed of 1 - 2 r / min, and the distance between the stirring paddle and the inner wall of the reaction kettle is controlled to be 1.2 - 1.5 times the average particle size of the quartz sand to form a laminar flow mixing state, so that the collision energy of the quartz sand particles is ≤0.1 mJ / time.

[0012] A heating component, a temperature control component, and a stirring component are provided in the reaction kettle. The temperature control component is electrically connected to the heating component to ensure that the required pickling temperature can be stably reached and maintained. The precision of the temperature control component is ±1°C. In the present invention, the heating component uses a titanium material electric heating tube, which is hermetically installed at the bottom of the reaction kettle through a flange. The surface of the heating tube is coated with an alumina ceramic insulating layer with a thickness of 3 mm, which not only ensures corrosion resistance but also avoids electrolytic corrosion. The heating tubes are arranged in a ring shape, and the ratio of the diameter to the kettle body diameter is 1:3, ensuring uniform heat distribution and a temperature gradient in the kettle ≤0.5°C / m.

[0013] The temperature control component includes a sensor, a control unit, and a redundant design. Among them, the sensors are respectively arranged at the upper part, the middle part of the kettle body, and 200 mm from the bottom, and the data is transmitted through the MODBUS protocol. Specifically, PT100 platinum resistors can be selected. The control unit is a PLC controller using the PID algorithm, and the output signal controls the solid-state relay (SSR) to adjust the heating power. The redundant design is that when the temperature at any point deviates from the set value by ±1.5°C, a secondary alarm is automatically triggered and the standby heating circuit is switched. Ensure that the temperature fluctuation during the 7-hour pickling process of the system is only ±0.8°C.

[0014] The stirring component includes a drive shaft and stirring blades arranged outside the drive shaft. The distance between the stirring blades and the inner wall of the reaction kettle is 1.2 - 1.5 times the average particle size of the quartz sand, reducing particle wear. The stirring blades are made of polytetrafluoroethylene material, which can extend the service life of the stirring component, avoid the introduction of metal impurities, and ensure the purity of the quartz sand.

[0015] The drive shaft is connected to the kettle cover through a double-ended mechanical seal. The stirring blades are preferably three-blade backward-swept blades formed by polytetrafluoroethylene (PTFE) molding, and silicon carbide wear-resistant strips are inlaid on the edges of the stirring blades. The distance between the stirring blades and the inner wall of the kettle is strictly controlled within 36 - 45 mm. Under the condition of a rotation speed of 1 rpm, this design reduces the particle collision energy to 0.1 mJ / time, reducing the wear by 90% compared with metal stirring blades.

[0016] Preferably, step S2 specifically includes: S21 In a pickling workshop that meets safety specifications, prepare an acid-resistant reaction kettle, and install and debug the heating component, temperature control component, and stirring component; S22 Put the acid solution prepared according to the above ratio into the reaction kettle, turn on the heating component, and raise the temperature of the acid solution to 100°C. During the heating process, cooperate with magnetic coupling stirring to make the heat convection of the acid solution uniform, and use the temperature control component to precisely control the temperature of the acid solution to control the temperature fluctuation range within ±2°C; S23 When the temperature of the acid solution reaches 100 °C, slowly add quartz sand into the reaction kettle. The input amount is determined according to the volume of the reaction kettle and production requirements, generally 60% - 80% of the volume of the reaction kettle, to ensure that the quartz sand can be fully immersed in the acid solution; S24 At a high temperature of 100 °C, soak the quartz sand in the acid solution for pickling for 7 hours, and stir at a rate of 1 r / min to make the quartz sand fully contact with the acid solution and improve the pickling efficiency.

[0017] Furthermore, in step S2, the mass ratio of the acid solution to the quartz sand is 1.5 - 2:1, ensuring sufficient contact and avoiding corrosion caused by excessive acid solution. The corrosion rate of the quartz sand after pickling is ≤ 0.8%.

[0018] Furthermore, before pickling the quartz sand, pre-treat the quartz sand raw material. Among them, crush the raw material quartz sand to an average particle size of 0.2 - 0.5 mm by a jaw crusher, significantly increasing the contact area between the acid solution and the particles, and ensuring that the HF / HCl acid solution can fully penetrate into the internal pores of the particles. Subsequently, perform iron removal treatment through a permanent magnet drum magnetic separator to remove more than 90% of the magnetic impurities. Avoid unnecessary reactions between HCl and magnetic iron oxide, and reduce the "shielding effect" caused by iron impurities wrapping other metal oxides.

[0019] Furthermore, in step S3, the waste acid after separation is recovered by distillation. The recovered acid solution is recycled for the preparation of the acid cleaning solution in step S1 after concentration calibration. Specifically, multi-effect distillation technology is used to achieve the cascade recovery of HF / HCl in the waste acid. For example, HCl is recovered at 85 °C in the first effect, and HF is recovered at 60 °C in the second effect. By precisely controlling the evaporation temperature and condensation parameters, the HF recovery rate can reach 88 ± 2%, and the HCl recovery rate can be maintained at 85 ± 3%. After the recovered acid solution is adjusted by the linkage of an on-line densitometer and a pH meter, it can be directly recycled for the preparation of the acid cleaning solution.

[0020] Add calcium hydroxide to the residual liquid after distillation to neutralize it to pH = 7 - 8. By controlling the feeding rate of calcium hydroxide and the stirring intensity, calcium fluoride and calcium chloride precipitates are generated. The precipitates are harmlessly treated after pressure filtration. It can be used as high-quality fluorochemical raw materials to realize the transformation from hazardous waste to by-products.

[0021] Furthermore, in step S3, the number of rinsing times is ≥ 5 times, and the amount of water for each rinsing is 1.5 - 2 times the mass of the quartz sand. Each rinsing adopts a countercurrent design, so that the fresh water always contacts the sand grains with the lowest residual acid concentration, and the pH value of the last rinsing water is controlled within the range of 6.5 - 7.5. Ensure that there is no residual acidic active site on the surface of the quartz sand, and avoid the generation of pore defects in glass products during subsequent high-temperature applications.

[0022] Furthermore, the rinsed quartz sand is dried, which can be air-dried naturally or dried in an oven at a temperature below 100°C, to obtain the pickled quartz sand product. The quartz crystal purity of the low-temperature dried product reaches 99.98%, which is 2-3 percentage points higher than that of the traditional high-temperature (300-500°C) drying process. This stable crystal structure reduces the thermal expansion coefficient fluctuation range of the product in photovoltaic glass manufacturing to ±0.05×10 -6 / °C, significantly improving the heat shock resistance of the component.

[0023] Furthermore, the SiO2 content in the pickled quartz sand is ≥99.95%, the Fe2O3 content is ≤0.005%, and the Al2O3 content is ≤0.003%, meeting the standard of photovoltaic-grade quartz sand.

[0024] Preferably, step S3 includes the following steps: After pickling for 7 hours, stop heating, and cool down gradually to prevent microcracks from occurring in the quartz sand due to sudden cooling. After the temperature in the reaction kettle drops below 50°C, separate the pickled quartz sand and the acid solution through a filtration device; when the temperature is below 50°C, the HF volatilization rate drops to 0.01 g / m 3 , reducing the subsequent treatment pressure.

[0025] The separated quartz sand is repeatedly rinsed with a large amount of clear water until the pH value of the rinsing water is close to neutral (pH value is 6-8), and generally the number of rinsing times is not less than 5 times; S33: The rinsed quartz sand is dried, which can be air-dried naturally or dried in an oven at a temperature below 100°C, to obtain the pickled quartz sand product.

[0026] The beneficial effects of the present invention are as follows: The present invention uses a mixed acid solution of hydrofluoric acid and hydrochloric acid, and realizes efficient impurity removal through an optimized acid solution ratio. HF has a strong complexing ability and can form soluble complexes with metal impurities in the quartz sand, while HCl dissolves metal oxides to form soluble chlorides. Through the combined regulation of high temperature, short time and low-speed stirring, the chemical reaction rate is further accelerated, ensuring the thoroughness and uniformity of impurity removal.

[0027] The present invention precisely controls the mass ratio of the acid solution to the quartz sand, avoiding excessive corrosion of the main components of the quartz sand caused by excessive acid solution. At the same time, low-speed stirring (1 r / min) reduces the mechanical wear of the quartz sand particles, further reducing the raw material loss, significantly improving the utilization rate of the quartz sand, and reducing the raw material cost.

[0028] The present invention shortens the pickling time to 7 hours through high temperature and optimized acid solution ratio, while reducing the energy consumption by 30%. In addition, precise temperature control and stirring design further improve the process stability, reducing energy waste and production fluctuations. Detailed implementation mode

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the related listed items.

[0031] Embodiment 1 A quartz sand pickling process includes the following steps: (1) Measure hydrofluoric acid, hydrochloric acid, and water respectively according to a volume ratio of 5:2:4 using precise liquid measuring equipment, and carefully mix and prepare the acid solution in an acid-resistant preparation container; (2) In a pickling workshop that meets safety specifications, prepare an acid-resistant reaction kettle, and install and debug the heating component, temperature control component, and stirring component; (3) Put the acid solution prepared according to the above ratio into the reaction kettle, turn on the heating component, and raise the temperature of the acid solution to 100°C. During the heating process, use the temperature control component to precisely control the temperature of the acid solution, so that the temperature fluctuation range is controlled within ±2°C; (4) After the temperature of the acid solution reaches 100°C, slowly put the quartz sand into the reaction kettle, and the input amount is 60% - 80% of the volume of the reaction kettle to ensure that the quartz sand can be fully immersed in the acid solution; (5) At a high temperature of 100°C, let the quartz sand soak and pickle in the acid solution for 7 hours, and stir at a rate of 1 r / min to make the quartz sand fully contact with the acid solution; (6) After pickling for 7 hours, stop heating. After the temperature in the reaction kettle drops below 50°C, separate the pickled quartz sand and the acid solution through a filtering device; (7) The separated quartz sand is repeatedly rinsed with a large amount of clear water until the pH value of the rinsing water is close to neutral; (8) The rinsed quartz sand is dried, and natural air drying or drying in an oven at a temperature below 100°C can be used; (9) The purity of the dried quartz sand reaches above 4N8, the elements meet the requirements, and the crucible transparent layer meets the requirements.

[0032] Comparative Example 1 (1) According to a volume ratio of 5:2:4, use precise liquid measuring equipment to separately measure hydrofluoric acid, hydrochloric acid, and water, and carefully mix and prepare the acid solution in an acid-resistant preparation container; (2) In an acid pickling workshop that complies with safety regulations, prepare an acid-resistant reaction kettle, and install and debug the heating component, temperature control component, and stirring component; (3) Put the acid solution prepared according to the above ratio into the reaction kettle, turn on the heating component, and raise the temperature of the acid solution to 80 °C. During the heating process, use the temperature control component to precisely control the temperature of the acid solution so that the temperature fluctuation range is controlled within ±2 °C; (4) After the temperature of the acid solution reaches 80 °C, slowly put the quartz sand into the reaction kettle, and the input amount is 60% - 80% of the volume of the reaction kettle to ensure that the quartz sand can be fully immersed in the acid solution; (5) At a high temperature of 80 °C, let the quartz sand soak and be pickled in the acid solution for 7 hours, and stir at a rate of 1 r / min to make the quartz sand fully contact with the acid solution; (6) After 7 hours of pickling, stop heating. After the temperature in the reaction kettle drops below 50 °C, separate the pickled quartz sand and the acid solution through a filtering device; (7) The separated quartz sand is repeatedly rinsed with a large amount of clear water until the pH value of the rinsing water is close to neutral; (8) The rinsed quartz sand is dried, and high-temperature drying at 1050 °C can be used; (9) The purity of the dried quartz sand reaches above 4N8, but the calcium (Ca) and sodium (Na) elements exceed the standard.

[0033] Comparative Example 2 (1) According to a volume ratio of 5:2:4, use precise liquid measuring equipment to separately measure hydrofluoric acid, hydrochloric acid, and water, and carefully mix and prepare the acid solution in an acid-resistant preparation container; (2) In an acid pickling workshop that complies with safety regulations, prepare an acid-resistant reaction kettle, and install and debug the heating component, temperature control component, and stirring component; (3) Put the acid solution prepared according to the above ratio into the reaction kettle, turn on the heating component, and raise the temperature of the acid solution to 100 °C. During the heating process, use the temperature control component to precisely control the temperature of the acid solution so that the temperature fluctuation range is controlled within ±2 °C; (4) After the temperature of the acid solution reaches 100 °C, slowly put the quartz sand into the reaction kettle, and the input amount is 60% - 80% of the volume of the reaction kettle to ensure that the quartz sand can be fully immersed in the acid solution; (5) At a high temperature of 100 °C, let the quartz sand soak and be pickled in the acid solution for 5 hours, and stir at a rate of 1 r / min to make the quartz sand fully contact with the acid solution; After pickling for 5 hours, stop heating. After the temperature in the reaction kettle drops below 50°C, separate the pickled quartz sand and acid solution through a filtering device. (7)The separated quartz sand is repeatedly rinsed with a large amount of clear water until the pH value of the rinsing water is close to neutral. (8)The rinsed quartz sand is dried, and high-temperature drying at 1050°C can be used. (9)The purity of the dried quartz sand reaches above 4N8, but multiple elements such as calcium (Ca) and sodium (Na) exceed the standard, and the number of bubbles in the transparent layer of the crucible exceeds the standard.

[0034] Comparative Example 3 (1)According to the volume ratio of 5:2:4, accurately measure hydrofluoric acid, hydrochloric acid, and water respectively using precise liquid measuring equipment, and carefully mix and prepare the acid solution in an acid-resistant preparation container. (2)In an acid-washing workshop that meets safety specifications, prepare an acid-resistant reaction kettle, and install and debug the heating component, temperature control component, and stirring component. (3)Put the acid solution prepared according to the above ratio into the reaction kettle, turn on the heating component, and raise the temperature of the acid solution to 100°C. During the heating process, use the temperature control component to precisely control the temperature of the acid solution so that the temperature fluctuation range is controlled within ±2°C. (4)After the temperature of the acid solution reaches 100°C, slowly put the quartz sand into the reaction kettle, and the input amount is 60% - 80% of the volume of the reaction kettle to ensure that the quartz sand can be fully immersed in the acid solution. (5)At a high temperature of 100°C, let the quartz sand soak and pickle in the acid solution for 15 hours, and stir at a rate of 1 r / min to make the quartz sand fully contact with the acid solution. (6)After pickling for 15 hours, stop heating. After the temperature in the reaction kettle drops below 50°C, separate the pickled quartz sand and acid solution through a filtering device. (7)The separated quartz sand is repeatedly rinsed with a large amount of clear water until the pH value of the rinsing water is close to neutral. (8)The rinsed quartz sand is dried, and high-temperature drying at 1050°C can be used. (9)The purity of the dried quartz sand reaches above 4N8, and the corrosion degree increases.

[0035] Experimental data As can be seen from the above, the combined design of pickling at 100°C for 7 hours and low-temperature drying (<100°C) in the present invention achieves a balance between deep impurity removal and low corrosion. Below 100°C or insufficient pickling time both result in excessive residues of alkali metals (Ca, Na); over-time pickling (>7h) although improves the purity, but increases the corrosion degree and reduces the economy.

[0036] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A quartz sand pickling process, characterized in that, It includes the following steps: S1 Prepare the pickling solution; S2 Immerse the quartz sand in the acid solution at 100 ± 2 °C for 7 - 10 hours, and stir at a rate of 1 - 2 r / min; S3 After the pickling is completed and the temperature drops below 50 °C, separate the quartz sand, rinse it multiple times until the pH is neutral, and then dry it to obtain the finished product.

2. The quartz sand pickling process according to claim 1, characterized in that, In step S1, the pickling solution is prepared by mixing HF, HCl, and water in a mass ratio of 5:2:

4.

3. The quartz sand pickling process according to claim 1, characterized in that, In step S2, an acid-resistant sealed reaction kettle is used. The sealing system of the reaction kettle is composed of a double-layer fluororubber sealing ring and is connected to a negative pressure suction device, with an acid mist leakage amount < 1 ppm.

4. A quartz sand pickling process according to claim 3, characterized in that, In step S2, it includes: Heat the acid solution to 100 °C using a staged gradient heating method and maintain the set temperature. Adjust the heating power through real-time data feedback from at least three temperature measurement points to control the temperature fluctuation within the range of ±1 °C; Immerse the quartz sand in the acid solution and stir at a speed of 1 - 2 r / min. Control the distance between the stirring paddle and the inner wall of the reaction kettle to be 1.2 - 1.5 times the average particle size of the quartz sand to form a laminar flow mixing state, so that the collision energy of the quartz sand particles ≤ 0.1 mJ / time.

5. A quartz sand pickling process according to claim 4, characterized in that, The mass ratio of the pickling solution to the quartz sand is 1.5 - 2:1, and the corrosion rate of the quartz sand after pickling ≤ 0.8%.

6. A quartz sand pickling process according to claim 4, characterized in that, The input amount of the quartz sand is 60% - 80% of the volume of the reaction kettle.

7. The quartz sand pickling process according to claim 1, characterized in that, In step S3, the waste acid after separation is recovered by distillation, and the recovered acid solution is recycled for preparing the pickling solution in step S1 after concentration calibration.

8. A quartz sand pickling process according to claim 1, characterized in that, In step S3, the number of rinses ≥ 5 times, the amount of water for each rinse is 1.5 - 2 times the mass of the quartz sand, and the pH value of the last rinse water is controlled within the range of 6.5 - 7.

5.

9. A quartz sand pickling process according to claim 1, characterized in that, The rinsed quartz sand is dried, which can be air-dried naturally or dried in an oven below 100 °C to obtain the pickled quartz sand product.

10. A quartz sand pickling process according to claim 1, characterized in that, The SiO2 content in the pickled quartz sand ≥ 99.95%, the Fe2O3 content ≤ 0.005%, and the Al2O3 content ≤ 0.003%.

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