A fluorine-free preparation process for high-purity quartz sand

Abstract

This invention discloses a fluorine-free preparation process for high-purity quartz sand, comprising the following steps: S1, crushing and screening of raw quartz ore; S2, magnetic separation; S3, flotation; S4, calcination and water quenching; S5, hot-pressing acid leaching; S6, chlorination calcination; S7, hot-pressing acid leaching; S8, washing and drying to obtain high-purity quartz sand. The high-purity quartz sand obtained by this invention has a total impurity content of less than 50 ppm and a purity greater than 99.99%. This invention demonstrates significant advantages over the traditional hydrofluoric acid leaching system in terms of environmental friendliness, selectivity, economy, safety, and wide applicability. It not only meets the current urgent needs of society for green production and energy conservation and emission reduction, but also improves product quality and production efficiency through technological innovation, providing strong support for the transformation and upgrading of related industrial fields.

Description

Technical Field

[0001] This invention relates to the field of mineral processing technology, specifically to a fluorine-free preparation process for high-purity quartz sand. Background Technology

[0002] Quartz, a gem of nature's silicon dioxide, is indispensable in modern industrial systems due to its wide range of applications. From everyday glassware and exquisite ceramics in traditional crafts, to high-tech refractory materials, metallurgical aids, chemical catalysis, and even precision components in aerospace engineering, experimental carriers in biotechnology, the cornerstone of the semiconductor industry, and core materials for solar cells, each application of quartz marks a solid step forward in human technological progress. However, as these fields place increasingly stringent demands on material performance, the chemical purity of quartz products has become a key factor determining their application value and market competitiveness.

[0003] The current surge in demand for high-purity quartz is not only due to its unique physicochemical properties, but also because it supports the development of a range of advanced technologies. However, this increased demand exposes serious challenges facing traditional quartz purification technologies. Traditional purification processes, such as flotation and magnetic separation, while effectively removing some impurities, fall short when dealing with trace amounts, insoluble impurities, or chemically stable impurities. Chemical methods, such as acid and alkali leaching, while highly effective, rely heavily on strongly corrosive chemicals like hydrofluoric acid and nitric acid, resulting in high production costs and generating large amounts of difficult-to-treat wastewater and exhaust gases, posing a serious threat to the environment. This "environment-at-the-cost" development model clearly contradicts the contemporary concept of sustainable development.

[0004] Therefore, addressing the environmental issues arising from quartz purification and developing greener, more efficient purification technologies has become an urgent need for the industry. The introduction of green chemistry concepts offers new insights into this problem. Optimizing process flows, reducing the amount of chemical reagents used, employing biodegradable alternatives, and strengthening end-of-pipe treatment of wastewater and exhaust gases can effectively reduce the negative environmental impact of quartz purification. Simultaneously, exploring new purification mechanisms, such as utilizing non-traditional energy fields like ultrasound and microwaves to promote impurity separation, or developing more efficient catalysts to improve reaction efficiency and reduce energy consumption, are key areas for future research.

[0005] Application CN117699804A discloses a process for preparing high-purity quartz sand, including the following steps: S1, mineral processing; S2, ore washing: washing the ore with water, then acid washing, then alkali washing, and filtering out impurities; S3, calcination; S5, crushing; S6, screening.

[0006] S7. Washing; S8. Draining; S9. Drying; S10. Magnetic separation; S11. Entering the flotation machine for further selection. In step S2 of this invention, the acid used for washing the ore is hydrofluoric acid, sulfuric acid, and hydrochloric acid. The concentration of the mixed acid is not high. After purification of quartz by this method, the purity reaches above 4N. However, the amount of fluoride-containing wastewater generated will also increase when using this method in industrial production. This is because the mixed acid system used contains hydrofluoric acid, which is harmful to the environment, and the fluoride-containing wastewater is difficult and costly to treat. This requires us to further balance the relationship between purification effect and environmental protection cost in practical applications.

[0007] Application CN112916199A discloses a method for purifying quartz raw materials, including the following steps: (1) grinding; (2) magnetic separation roughing; (3) magnetic separation cleaning; (4) flotation roughing; (5) flotation cleaning; (6) acid leaching to obtain the final quartz concentrate. This invention uses a mixed acid solution made of sulfuric acid, hydrochloric acid, and hydrofluoric acid to leach quartz. The volume ratio of sulfuric acid, hydrochloric acid, and hydrofluoric acid is 2:2:3, and the mass concentration of each is 30%. Although the concentration and ratio of the acid are optimized, the concentration of the acid used is relatively high, which causes some environmental pollution. Furthermore, it lacks key steps such as calcination and water quenching or chlorination calcination, which may result in poor removal of impurities inside the quartz or lattice impurities. Therefore, the purity of the final purified quartz sand does not reach 4N, failing to meet higher application requirements.

[0008] The two existing technologies mentioned above remind us that technological innovation should not only pursue higher purity indicators, but also take into account environmental friendliness and economic benefits to achieve true sustainable development.

[0009] In conclusion, addressing the environmental challenges of quartz purification technology is not only an inherent requirement for the industry's development but also a reflection of social and future responsibility. Only by continuously promoting technological innovation and exploring green and efficient purification pathways can we ensure that this valuable resource of quartz supports scientific and technological progress while contributing to a greener future for the planet. Summary of the Invention

[0010] This invention provides a fluorine-free preparation process for high-purity quartz sand, which can reduce pollution during the quartz sand purification process. To address the problem of difficult-to-remove lattice impurities in quartz, chlorination calcination is used, where chloride ions react with impurity ions in the lattice at high temperature, which can effectively solve the problem of difficult-to-remove lattice impurities in quartz.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] A process for preparing high-purity fluorine-free quartz sand includes the following steps:

[0013] S1. Quartz Ore Crushing and Screening: The quartz ore is crushed, ground, and screened.

[0014] S2. Magnetic separation: Dry magnetic separation is performed on the quartz sand to remove magnetic minerals from it.

[0015] S3. Flotation: The magnetically separated quartz sand is poured into a flotation machine for flotation to remove impurities such as mica and feldspar from the quartz sand.

[0016] S4. Calcination and water quenching: The flotated quartz sand is placed in a muffle furnace for calcination, and water quenching is performed immediately after the heat preservation is completed.

[0017] S5. Hot pressing and acid leaching: The water-quenched quartz is subjected to hot pressing and acid leaching.

[0018] S6. Chlorination calcination: The quartz after the first hot pressing and acid leaching is subjected to chlorination calcination.

[0019] S7. Hot-press acid leaching: The chlorinated and calcined quartz sand is subjected to a second hot-press acid leaching.

[0020] S8. Cleaning and drying: Finally, the quartz that has undergone secondary hot pressing and acid leaching is cleaned and dried to obtain high-purity quartz sand.

[0021] Furthermore, the quartz ore refers to quartz ore with a quartz content of 99% or more; the particle size range of the ore obtained after crushing, grinding, and screening in step S1 is 0.075-0.250 mm.

[0022] Furthermore, in step S2, a high-gradient magnetic separator is used for magnetic separation, with a magnetic field strength of 2.3-4.0T.

[0023] Furthermore, in step S3, flotation is performed using a hanging flotation machine with a pulp pH of 2.6-4.0.

[0024] Furthermore, in step S4, a ceramic fiber resistance furnace is used, the calcination temperature is 850-1200℃, the holding time is 4-9h, and after water quenching, it is dried at 105℃.

[0025] Furthermore, in step S5, the mixed acid used in the hot-pressing acid leaching process includes phosphoric acid, oxalic acid, and sulfuric acid. The acid leaching temperature is 200-250℃, the acid leaching time is 3-5 hours, and the solid-liquid ratio is 1:2-1:10.

[0026] Furthermore, the concentrations of the mixed acids are: phosphoric acid 0.2-1.0 mol / L, oxalic acid 5-30 g / L, and sulfuric acid 0.5-2.5 mol / L.

[0027] Furthermore, in step S6, the chlorinating agent used in the chlorination calcination process is ammonium chloride, and the amount of chlorinating agent is 2-3%; the chlorination calcination temperature is 850-1200℃, and the calcination time is 5-7h.

[0028] Furthermore, the secondary hot-press acid leaching in step S7 involves calcining the chlorinated calcined quartz sand again under the optimal hot-press acid leaching conditions described in step S5.

[0029] Furthermore, in step S8, the cleaning and drying process involves washing with deionized water more than 5 times until the cleaning solution becomes neutral, and then drying at 105°C.

[0030] Technical principle of the invention:

[0031] In the field of modern materials science, high-purity quartz sand is a key raw material for high-tech industries such as semiconductors, optical fiber communication, and solar cells. Improving its purity directly affects the performance and stability of these products. The fluorine-free preparation process for high-purity quartz sand described in this invention, through a series of carefully designed steps, not only effectively removes impurities from the raw quartz ore but also ensures the environmental friendliness of the entire process, avoiding the use of fluorides. This process demonstrates significant technological innovation and environmental friendliness.

[0032] 1. Pretreatment of raw quartz ore: crushing, screening and magnetic separation

[0033] Quartz ore, as the starting material, requires a high purity (≥99%), which is fundamental for the preparation of high-purity quartz sand. Crushing and grinding refine large ore pieces, followed by screening to ensure particle size is controlled within the range of 0.075-0.250 mm. This step provides a uniform material basis for subsequent processing. The magnetic separation stage utilizes a high-gradient magnetic separator. Under a strong magnetic field of 2.3-4.0 T, it efficiently removes magnetic minerals such as iron oxides from the quartz sand. Residual magnetic impurities will severely affect the purity of the quartz sand and its subsequent application performance. This step works synergistically with subsequent flotation to jointly improve the cleanliness of the raw material.

[0034] 2. Flotation: Deep purification of quartz sand

[0035] In the flotation process, the application of hanging flotation machines, combined with specific pulp pH values ​​(2.6-4.0), effectively utilizes the differences in mineral surface properties. Through bubble adhesion and separation mechanisms, non-magnetic impurities such as mica and feldspar are separated from quartz sand. Precise pH control is crucial in this step, as it directly affects the adsorption efficiency and selectivity of flotation reagents and is one of the key parameters for optimizing flotation results.

[0036] 3. Calcination and water quenching: structural restructuring and stress release

[0037] The calcination process utilizes a ceramic fiber resistance furnace. At high temperatures of 850-1200℃, the quartz sand undergoes phase transformation and structural reorganization, which facilitates further removal of volatile impurities and residual organic matter. The set holding time (4-9 hours) ensures sufficient heat treatment, while the subsequent water quenching rapidly cools the quartz, generating thermal stress and promoting the formation of microcracks. These microcracks contribute to further impurity leaching in subsequent treatments. This step seamlessly integrates with the subsequent hot-pressing acid leaching, creating favorable conditions for deep impurity removal.

[0038] 4. Hot-pressing acid leaching and chlorination calcination: Key to deep purification

[0039] During the hot-pressing acid leaching process, the synergistic effect of the mixed acids (phosphoric acid, oxalic acid, and sulfuric acid) is significant. By controlling the acid concentration (phosphoric acid 0.2-1.0 mol / L, oxalic acid 5-30 g / L, sulfuric acid 0.5-2.5 mol / L) and leaching conditions (temperature 200-250℃, time 3-5 h), deep dissolution of trace impurities in the quartz sand is achieved. Chlorination calcination utilizes ammonium chloride as a chlorinating agent, reacting with impurities in the quartz at 850-1200℃ to generate volatile chlorides, further improving the purity of the quartz. Optimizing the parameters of these two processes directly affects the purity and production efficiency of the final product and is a core step in the preparation of high-purity quartz sand.

[0040] 5. Cleaning and drying: Ensure the purity of the final product.

[0041] As the final step in the preparation process, the importance of cleaning and drying is self-evident. Multiple cleanings (≥5 times) with deionized water are performed until the cleaning solution is neutral, ensuring the complete removal of residual impurities from the surface and interior of the quartz sand. Subsequently, drying is carried out at 105℃ to avoid the influence of residual moisture on the properties of the quartz sand. Strict adherence to this step is crucial to ensuring the high purity of the final product.

[0042] In summary, the various steps in the fluorine-free preparation process of high-purity quartz sand are closely interconnected. The selection of raw materials, the control of their dosage, and the optimization of process parameters all have a profound impact on the purity of the final product. Through synergistic effects, these steps achieve deep purification of the raw quartz ore, which not only enhances the product's market competitiveness but also provides solid material support for the development of related high-tech industries.

[0043] Compared with the prior art, the present invention has the following technical advantages:

[0044] 1. Significant improvement in environmental friendliness

[0045] This invention innovatively employs a mixed acid leaching system of sulfuric acid, oxalic acid, and phosphoric acid. This design fundamentally eliminates the high toxicity problem associated with traditional hydrofluoric acid leaching methods. Hydrofluoric acid is known for its strong corrosiveness and toxicity, posing a serious threat to the environment and the safety of operators. In contrast, the mixed acid system of this invention significantly reduces toxicity, greatly mitigating potential harm to the ecological environment, while also providing operators with a safer working environment. Furthermore, the waste liquid generated by this system has a relatively simple composition and can be effectively treated using mature technologies such as chemical precipitation, ion exchange, or advanced oxidation, thereby further reducing the risk of environmental pollution and demonstrating a deep commitment to the concept of sustainable development.

[0046] 2. Targeted impurity removal through efficient iron removal and selective dissolution of silicates.

[0047] This invention fully utilizes the strong chelating ability of oxalic acid for iron ions. This characteristic allows iron ions to rapidly and efficiently combine with oxalic acid to form stable and soluble complexes, thereby achieving deep removal of iron impurities. This process not only improves iron removal efficiency but also ensures product purity, which is of great significance for improving the quality and performance of downstream products. Simultaneously, the introduction of phosphoric acid cleverly achieves selective dissolution of silicates. This function can, to some extent, replace the etching effect of hydrofluoric acid in certain processes, retaining the necessary chemical reaction effects while avoiding many of the adverse factors associated with the use of hydrofluoric acid. This represents a significant advancement in the field of material purification technology.

[0048] 3. Safety and economic advantages of chlorination calcination technology

[0049] In the process of removing impurities from quartz crystal lattices, this invention creatively employs ammonium chloride as the chlorinating agent, combined with chlorination calcination technology. This method not only effectively removes impurities, but also offers significant safety advantages compared to other chlorinating agents. Ammonium chloride is chemically stable and less prone to causing fires or explosions. Furthermore, as a common chemical raw material, ammonium chloride is relatively inexpensive and does not introduce new impurity elements during the entire process, ensuring product purity while significantly reducing production costs and improving the economics of the process.

[0050] 4. Enhanced overall performance, leading a new trend in industrial applications.

[0051] This invention demonstrates significant advantages over traditional hydrofluoric acid leaching systems in multiple dimensions, including environmental friendliness, selectivity, economy, safety, and wide applicability. It not only meets the urgent societal demand for green production and energy conservation and emission reduction but also improves product quality and production efficiency through technological innovation, providing strong support for the transformation and upgrading of related industrial sectors. Therefore, this invention is particularly suitable for promotion and application in industrial fields with increasingly stringent environmental protection requirements and is expected to become the mainstream direction of future material purification and processing technologies, leading the industry towards a more environmentally friendly, efficient, and safe direction. Attached Figure Description

[0052] Figure 1 This is a flowchart of the high-purity fluorine-free quartz sand preparation process of the present invention.

[0053] Figure 2 The single-factor experimental diagrams investigated the effects of phosphoric acid concentration (a), oxalic acid concentration (b), sulfuric acid concentration (c), acid leaching time (d), acid leaching temperature (e), acid leaching solid-liquid ratio (f), calcination temperature (g), and calcination time (h) on the Al removal rate. Detailed Implementation

[0054] To investigate the influence of hot pressing and acid leaching conditions in step S5 of the high-purity fluorine-free quartz sand preparation process on quartz purification, this invention used quartz sand after magnetic separation and flotation as raw material and conducted single-factor experiments on phosphoric acid concentration, oxalic acid concentration, sulfuric acid concentration, acid leaching time, acid leaching temperature, acid leaching solid-liquid ratio, calcination temperature, and calcination time, with Al removal rate as the indicator.

[0055] 1. Materials and Methods

[0056] 1.1 Materials and Reagents

[0057] The experimental materials were provided by Guangxi Gangqiao New Building Materials Co., Ltd.; phosphoric acid, sulfuric acid and oxalic acid were all of analytical grade.

[0058] 1.2 Instruments and Equipment

[0059] LX0711 Ceramic Fiber Resistance Furnace, Tianjin Laiboteri Instrument Equipment Co., Ltd.; 101-0S Electric Heating Blower Drying Oven, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.; BSA24S Electronic Balance, Sartorius Scientific Instruments (Beijing) Co., Ltd.

[0060] 1.3 Methods

[0061] Calcination pretreatment: A certain amount of raw quartz ore is placed in a quartz crucible and calcined in a muffle furnace. After being kept at a certain temperature for a period of time, it is immediately subjected to water quenching treatment. After being washed with deionized water 4-5 times, it is dried for later use.

[0062] Hot-press acid leaching: 4.0000±0.0005g of calcined pretreated quartz ore sample was weighed and placed in the lining of a hydrothermal reactor. A certain volume of mixed acid solution was added, and the sample was ultrasonically cleaned for 10 minutes. Hot-press leaching was then performed at different acid leaching temperatures, times, and solid-liquid ratios. After acid leaching was completed and the sample cooled to room temperature, the leached sample was removed and washed with deionized water at least five times until the pH of the washing solution was neutral. The sample was then dried at 105℃. After digestion, the remaining elemental impurities in the acid-leached sample were tested using ICP-OES to calculate the removal rate. After determining the optimal acid leaching conditions, the calcination temperature and time were further investigated to finally obtain the optimal calcination and acid leaching conditions.

[0063] 1.3.1 Single-factor experiment

[0064] Phosphoric acid concentrations of 0.2, 0.4, 0.6, 0.8, and 1.0 mol / L were selected, and hot-press acid leaching was carried out at an acid leaching temperature of 200℃, an acid leaching time of 2 h, and a solid-liquid ratio of 1:4. The effect of different concentrations of phosphoric acid on the removal of Al was investigated.

[0065] Oxalic acid was added to 0.8 mol / L phosphoric acid to prepare mixed acids of oxalic acid and phosphoric acid with concentrations of 5, 10, 15, 20, and 25 g / L, respectively. Hot-press acid leaching was performed under the conditions of an acid leaching temperature of 200℃, an acid leaching time of 2 h, and a solid-liquid ratio of 1:4. The effect of different concentrations of mixed oxalic acid and phosphoric acid on the removal of Al was investigated.

[0066] Sulfuric acid was added to a mixture of 0.8 mol / L phosphoric acid and 20 g / L oxalic acid to prepare three-component mixed acids with sulfuric acid concentrations of 0.5, 1.0, 1.5, 2.0, and 2.5 mol / L. Hot-press acid leaching was performed at 200℃ for 2 hours with a solid-liquid ratio of 1:4 to investigate the effect of different concentrations of sulfuric acid mixed with oxalic acid on the removal of Al.

[0067] Acid leaching experiments were conducted for different durations in a mixed acid solution prepared from 0.8 mol / L phosphoric acid, 20 g / L oxalic acid, and 2.0 mol / L sulfuric acid. The leaching times were 1, 2, 3, 4, and 5 hours, the leaching temperature was 200℃, and the solid-liquid ratio was 1:4. The effects of leaching time on the removal of Al were investigated.

[0068] The acid leaching process was carried out with the mixed acid concentration kept constant. The acid leaching temperatures were set to 150, 175, 200, 225, 250, and 275℃, the acid leaching time was 4 hours, and the solid-liquid ratio was 1:4. The effect of acid leaching temperature on the removal of Al element was investigated.

[0069] With the mixed acid concentration constant, the acid leaching temperature at 250℃, and the acid leaching time at 4h, different solid-liquid ratios were set for acid leaching experiments, namely 1:2, 1:4, 1:6, 1:8, and 1:10, to explore the effect of the solid-liquid ratio on the removal of Al element.

[0070] Five calcination temperatures were set at 600, 750, 900, 1050, and 1200℃, with a calcination time of 5 hours. Immediately after calcination, the samples were water-quenched, washed, and dried. The mixed acid concentration was kept constant, and the acid leaching temperature was 250℃ for 4 hours. Hot-press acid leaching was performed under a solid-liquid ratio of 1:6 to investigate the effect of calcination temperature on the removal of Al.

[0071] Calcination experiments were conducted at a calcination temperature of 900℃ for different durations of 1, 3, 5, 7, and 9 hours. After calcination, the samples were immediately quenched in water, washed, and dried. With a constant mixed acid concentration, an acid leaching temperature of 250℃, an acid leaching time of 4 hours, and a solid-liquid ratio of 1:6, hot-press acid leaching was performed to investigate the effect of calcination time on the removal of Al.

[0072] 2 Results Analysis

[0073] 2.1 Results of Single-Factor Experiment

[0074] 2.1.1 Effect of different concentrations of phosphoric acid on Al removal rate

[0075] Depend on Figure 2 (a) It can be seen that the removal rate of Al element increases with the increase of phosphoric acid concentration, reaching a maximum of 62.73% at 0.8 mol / L, and then showing a slight downward trend. Therefore, a phosphoric acid concentration of 0.8 mol / L is the optimal choice.

[0076] 2.1.2 Effect of different concentrations of oxalic acid mixed with phosphoric acid on Al removal rate

[0077] Depend on Figure 2 (b) It can be seen that the removal rate of Al element increases significantly before the oxalic acid concentration reaches 20 g / L, reaching a peak of 64.33% at 20 g / L. When the concentration is greater than 20 g / L, the removal of Al element tends to level off. Therefore, an oxalic acid concentration of 20 g / L is the optimal choice.

[0078] 2.1.3 Effect of different concentrations of sulfuric acid mixed with oxalic acid and phosphoric acid on Al removal rate

[0079] Depend on Figure 2(c) It can be seen that the removal rate of Al element continuously increases with the increase of sulfuric acid concentration, reaching its maximum value of 70.89% at a sulfuric acid concentration of 2.0 mol / L. This is 6.56% higher than the 64.33% achieved by leaching with a mixture of oxalic acid and acetic acid. When the sulfuric acid concentration continues to increase, the removal rate of Al element decreases by 3.70%. Therefore, the optimal concentration of sulfuric acid is 2.0 mol / L. Sulfuric acid can react with various metal oxides to form soluble sulfates, thereby achieving the purpose of impurity removal.

[0080] 2.1.4 Effect of acid leaching time on Al removal rate

[0081] Depend on Figure 2 (d) It can be seen that the Al removal rate increases with increasing acid leaching time. When the acid leaching time is 4 hours, the Al removal rate reaches 70.06%. Beyond 4 hours, the Al removal rate tends to remain constant. In the initial stage, the acid rapidly removes surface and easily soluble impurities. As time progresses, the removal rate slows down due to decreased impurity concentration and reaction kinetic limitations. Ultimately, the removal efficiency approaches saturation, and further extending the time does not significantly improve the effect. Therefore, the optimal acid leaching time is selected as 4 hours.

[0082] 2.1.5 Effect of acid leaching temperature on Al removal rate

[0083] Depend on Figure 2 (e) shows that as the temperature increases, the Al removal rate increases, accelerating the chemical reaction rate, increasing solubility and diffusion rate, thereby speeding up the leaching process. When the temperature exceeds 250℃, the Al removal rate does not change significantly, remaining at approximately 73.5%. Therefore, from the perspective of energy conservation and consumption reduction, the optimal acid leaching temperature is selected as 250℃.

[0084] 2.1.5 Effect of Acid Leaching Solid-Liquid Ratio on Al Removal Rate

[0085] Depend on Figure 2 (f) shows that the Al removal rate increases with increasing liquid content, reaching a maximum of 77.32% at a solid-liquid ratio of 1:6. Increasing the solid-liquid ratio allows the mixed acid to react more fully with impurities in the quartz mineral. As the liquid content continues to increase, the Al removal rate decreases slowly. Therefore, the optimal solid-liquid ratio is selected as 1:6.

[0086] 2.1.6 Effect of calcination temperature on Al removal rate

[0087] Depend on Figure 2(g) It can be seen that the Al removal rate increases with increasing calcination temperature, reaching a turning point at 900℃, where the Al removal rate is 81.0%. As the calcination temperature rises, the cracks generated by the expansion of quartz increase continuously, and impurities accumulate on the quartz surface along these cracks, increasing the removal of impurities during subsequent acid leaching. When the calcination temperature continues to increase, the Al removal rate increases slowly and remains essentially unchanged. Therefore, the optimal calcination temperature is selected as 900℃.

[0088] 2.1.7 Effect of calcination time on Al removal rate

[0089] Depend on Figure 2 (h) It can be seen that the Al removal rate reaches its maximum of 83.97% when the calcination time is 7 hours. Further increasing the calcination time leads to a decrease in the Al removal rate. This is because during the heating process, the quartz volume expands during the crystal transformation, generating cracks. The water quenching process deepens these cracks, exposing more impurities to the quartz surface. The fine particles on the quartz surface melt due to prolonged calcination, forming a coating that covers existing cracks on the quartz matrix surface, thus reducing the effective contact area between the mixed acid and the quartz. Therefore, the optimal calcination time is 7 hours.

[0090] 3. Conclusion

[0091] The optimal process conditions for hot-pressing acid leaching, determined through the above single-factor experiments, are: phosphoric acid 0.8 mol / L, oxalic acid 20 g / L, sulfuric acid 2 mol / L, solid-liquid ratio 1:6, leaching time 4 h, and leaching temperature 250 °C. In the calcination experiment, the Al removal rate reached its optimal level when calcined at 900 °C for 7 h.

[0092] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0093] Example 1

[0094] A process for preparing high-purity fluorine-free quartz sand includes the following steps:

[0095] S1. Quartz Ore Crushing and Screening: After crushing and grinding, the quartz ore is screened to select quartz sand with a particle size range of 0.150mm-0.250mm.

[0096] S2. Magnetic separation: A high-gradient magnetic separator with a magnetic field strength of 2.5T is used. The magnetic separation is repeated 3 times to remove magnetic minerals.

[0097] S3, Flotation: Using a hanging flotation cell, the pulp pH is 3.0;

[0098] S4. Calcination and water quenching: The quartz sand after reverse flotation is placed in a ceramic fiber resistance furnace for calcination to remove gas-liquid inclusions inside the quartz sand. The calcination temperature is 1200℃ and the temperature is held for 5 hours. After the temperature is held, water quenching is performed immediately. After washing with deionized water 5 times, it is placed in an environment of 105℃ for drying.

[0099] S5. Hot-press acid leaching: Weigh 4g of dried quartz sand and place it in the inner liner of the reactor. Prepare a mixed acid solution of a certain concentration (0.8mol / L phosphoric acid, 20g / L oxalic acid, 2mol / L sulfuric acid). The solid-liquid ratio of acid leaching is 1:6. Sonicate in an ultrasonic cleaner for 10 minutes to ensure that the acid solution is in full contact with the quartz sand. Then place the reactor in an oven and heat it at 250℃ for 4 hours to remove most of the impurities in the quartz sand. After the heat preservation is completed and the mixture has cooled to room temperature, take out the quartz sand and wash it 5 times with deionized water. After the washing solution is neutral, dry it at 105℃ for later use.

[0100] S6. Chlorination calcination: The dried quartz sand concentrate is uniformly mixed with 3% ammonium chloride and placed in a quartz crucible. It is then calcined in a ceramic fiber resistance furnace at a temperature of 900℃ for 7 hours. The hydrogen chloride gas produced by the decomposition of ammonium chloride reacts with the impurity metal oxides to generate volatile or sublimable metal chlorides, thereby separating the impurities from the minerals. After the heat treatment, the minerals are washed five times with deionized water and finally dried at 105℃.

[0101] S7. Hot-press acid leaching: The chlorinated roasted quartz sand is subjected to a second hot-press acid leaching, and the acid leaching conditions are the same as those for the first hot-press acid leaching.

[0102] S8. Cleaning and drying: Finally, the quartz sand after the second hot pressing and acid leaching is washed 5 times with deionized water until the pH value of the cleaning solution is neutral, and then dried at 105℃ to obtain high-purity quartz sand.

[0103] Example 2

[0104] A process for preparing high-purity fluorine-free quartz sand includes the following steps:

[0105] S1. Quartz Ore Crushing and Screening: After crushing and grinding, the quartz ore is screened to select quartz sand with a particle size range of 0.150mm-0.250mm.

[0106] S2. Magnetic separation: A high-gradient magnetic separator with a magnetic field strength of 3.0T is used. The magnetic separation is repeated 3 times to remove magnetic minerals.

[0107] S3, Flotation: Using a hanging flotation cell, the pulp pH is 3.5;

[0108] S4. Calcination and water quenching: The quartz sand after reverse flotation is placed in a ceramic fiber resistance furnace for calcination to remove gas-liquid inclusions inside the quartz sand. The calcination temperature is 900℃ and the temperature is held for 7 hours. After the temperature is held, water quenching is performed immediately. After washing with deionized water 5 times, it is placed in an environment of 105℃ for drying.

[0109] S5. Hot-press acid leaching: Weigh 4g of dried quartz sand and place it in the inner liner of the reactor. Prepare a mixed acid solution of a certain concentration (0.8mol / L phosphoric acid, 20g / L oxalic acid, 2mol / L sulfuric acid). The solid-liquid ratio of acid leaching is 1:6. Sonicate in an ultrasonic cleaner for 10 minutes to ensure that the acid solution is in full contact with the quartz sand. Then place the reactor in an oven and heat it at 250℃ for 4 hours to remove most of the impurities in the quartz sand. After the heat preservation is completed and the mixture has cooled to room temperature, take out the quartz sand and wash it 5 times with deionized water. After the washing solution is neutral, dry it at 105℃ for later use.

[0110] S6. Chlorination calcination: The dried quartz sand concentrate is uniformly mixed with 2% ammonium chloride and placed in a quartz crucible. It is then calcined in a ceramic fiber resistance furnace at a temperature of 900℃ for 7 hours. The hydrogen chloride gas produced by the decomposition of ammonium chloride reacts with the impurity metal oxides to generate volatile or sublimable metal chlorides, thereby separating the impurities from the minerals. After the heat treatment, the minerals are washed five times with deionized water and finally dried at 105℃.

[0111] S7. Hot-press acid leaching: The chlorinated roasted quartz sand is subjected to a second hot-press acid leaching, and the acid leaching conditions are the same as those for the first hot-press acid leaching.

[0112] S8. Cleaning and drying: Finally, the quartz sand after the second hot pressing and acid leaching is washed 5 times with deionized water until the pH value of the cleaning solution is neutral, and then dried at 105℃ to obtain high-purity quartz sand.

[0113] The main chemical elemental composition of the present invention in Embodiment 1 and Embodiment 2 is shown in Table 1 below.

[0114] Table 1. Main chemical element composition (ppm) of raw quartz ore and high-purity quartz sand in Examples 1 and 2.

[0115]

[0116] The detailed data in Table 1 clearly demonstrates that the quartz sand purification processes shown in Examples 1 and 2 produce finished products with a purity ≥4N4. This achievement not only signifies a leap in product quality but also represents a major breakthrough in the preparation technology of high-purity quartz materials. In this process, the total impurity removal rates reach as high as 97.52% and 97.99%, respectively. Such high purification efficiency undoubtedly represents a powerful challenge to and surpasses traditional purification methods.

[0117] Compared to the two existing technologies CN117699804A and CN112916199A mentioned in the background section, the innovation of this invention lies not only in the increased complexity and precision of the process, but also in its profound understanding of the chemical properties and reaction mechanisms of impurities in raw quartz ore, thereby designing a highly efficient and environmentally friendly purification system. This system first uses magnetic separation and flotation pretreatment to effectively remove most of the physical impurities from the raw ore, laying a solid foundation for subsequent chemical purification.

[0118] Of particular note is the ingenious use of a mixed hot-press acid leaching technique involving sulfuric acid, phosphoric acid, and oxalic acid. Sulfuric acid, as a strong acid, fully utilizes its powerful dissolving ability to convert metal oxides such as iron, aluminum, calcium, and sodium into soluble sulfates. These sulfates are then efficiently separated through subsequent processing steps, significantly reducing the impact of these impurities on the purity of the quartz. The introduction of phosphoric acid demonstrates the selectivity and precision of the process. It focuses on dissolving silicates, not only improving the purification effect but also effectively removing phosphate ions from wastewater through a simple polymerization precipitation reaction, thus mitigating environmental pollution.

[0119] The use of oxalic acid further demonstrates the invention's profound commitment to environmental protection. As a naturally occurring organic acid, oxalic acid can effectively form stable complexes with iron ions, thereby efficiently removing iron-containing mineral impurities from the surface of quartz. Its biodegradable nature also means that its environmental impact during production is negligible, significantly reducing the potential ecological threat posed by chemical purification processes.

[0120] In summary, the quartz sand purification process of this invention demonstrates unparalleled advantages over the traditional hydrofluoric acid system in multiple dimensions, including environmental friendliness, selectivity in impurity removal, economic efficiency in production costs, safety of operation, and wide applicability. This series of technological advancements not only drives innovation in high-purity quartz material preparation technology but also injects new vitality and possibilities into the development of related industries.

[0121] The examples mentioned above are some preferred embodiments of the present invention, but the scope of the invention extends far beyond these. We encourage various forms of adjustment, optimization, substitution, integration, and simplification without departing from the core concepts and basic principles of the present invention. These modifications are all considered equivalent innovative means and are naturally included within the protection scope of the present invention.

Claims

1. A fluorine-free preparation process for high-purity quartz sand, characterized in that, Includes the following steps: S1. Quartz Ore Crushing and Screening: The quartz ore is crushed, ground, and screened. S2. Magnetic separation: Dry magnetic separation is performed on the quartz sand to remove magnetic minerals from it. S3. Flotation: The magnetically separated quartz sand is poured into a flotation machine for flotation to remove mica and feldspar impurities from the quartz sand. S4. Calcination and water quenching: The flotated quartz sand is placed in a muffle furnace for calcination, and water quenching is performed immediately after the heat preservation is completed. S5. Hot pressing and acid leaching: The water-quenched quartz is subjected to hot pressing and acid leaching. S6. Chlorination calcination: The quartz after the first hot pressing and acid leaching is subjected to chlorination calcination. S7. Hot-press acid leaching: The chlorinated and calcined quartz sand is subjected to a second hot-press acid leaching. S8. Cleaning and drying: Finally, the quartz that has undergone secondary hot pressing and acid leaching is cleaned and dried to obtain high-purity quartz sand. The mixed acid used in the hot-pressing acid leaching process in step S5 includes phosphoric acid, oxalic acid, and sulfuric acid. The acid leaching temperature is 200-250℃, the acid leaching time is 3-5h, the solid-liquid ratio is 1:2-1:10, and the concentration of the mixed acid is 0.2-1.0mol / L for phosphoric acid, 5-30g / L for oxalic acid, and 0.5-2.5mol / L for sulfuric acid.

2. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: The quartz ore referred to is quartz ore with a silica content of 99% or more; the particle size range of the ore obtained after crushing, grinding and screening in step S1 is 0.075-0.250 mm.

3. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: In step S2, a high-gradient magnetic separator is used for magnetic separation, with a magnetic field strength of 2.3-4.0T.

4. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: In step S3, flotation is performed using a hanging flotation machine with a pulp pH of 2.6-4.

0.

5. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: In step S4, a ceramic fiber resistance furnace is used, with a calcination temperature of 850-1200℃ and a holding time of 4-9 hours. After water quenching, the material is dried at 105℃.

6. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: In step S6, the chlorinating agent used in the chlorination calcination process is ammonium chloride, and the amount of chlorinating agent used is 2-3%; the chlorination calcination temperature is 850-1200℃, and the calcination time is 5-7h.

7. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: The secondary hot-press acid leaching in step S7 involves calcining the chlorinated calcined quartz sand again under the optimal hot-press acid leaching conditions described in step S5.

8. The process for preparing high-purity fluorine-free quartz sand according to claim 1, characterized in that: In step S8, the cleaning and drying process involves washing with deionized water more than 5 times until the cleaning solution becomes neutral, and then drying at 105°C.

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