A method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz

Abstract

The present invention belongs to the field of high-purity quartz preparation and relates to a method for preparing 4N8-grade high-purity quartz sand from pegmatite quartz. The method comprises: step 1: subjecting quartz concentrate obtained from pegmatite granite to a first acid leaching with a first acid solution, followed by washing and drying to obtain primary quartz sand and leachate III; step 2: subjecting the primary quartz sand to doping, roasting, water quenching, and drying to obtain primary mineral; step 3: subjecting the primary mineral to a second acid leaching with a second acid solution, followed by washing and drying to obtain intermediate quartz sand and leachate II; step 4: subjecting the intermediate quartz sand to a third acid leaching with a third acid solution, followed by washing and drying to obtain high-purity quartz sand and leachate I. The novel three-stage leaching and two-stage roasting / calcining process of the present invention is simple, easy to operate, has low energy consumption, and has excellent purification effects. It can produce a high-purity quartz sand product with SiO2 ≥ 99.998% while reducing leachate consumption.

Description

Technical Field

[0001] The invention belongs to the field of high-purity quartz preparation, and particularly relates to a method for preparing 4N8-grade high-purity quartz sand from pegmatite quartz. Background Art

[0002] High-purity quartz possesses excellent optical properties, corrosion resistance, high insulation properties, and a high coefficient of thermal expansion. It is an indispensable and irreplaceable functional material in industries such as semiconductors, optical fiber, photovoltaics, optics, and electro-optical sources. High-purity quartz is often identified by its total impurity content. Quartz with a SiO2 content of 99.995% (4N5) is considered high-purity quartz, while quartz with a content of 99.998% (4N8) is considered high-end high-purity quartz. my country is the world's largest importer of high-purity quartz industrial raw materials, with a high demand for high-purity quartz resources and a high degree of external dependence. Accelerating the domestication and independent supply of high-purity quartz resources is urgent.

[0003] The main raw materials for high-purity quartz include crystal, vein quartz, pegmatite quartz, and quartzite. With the gradual depletion of crystal, domestic prospecting has focused on vein quartz. However, vein quartz deposits are small in scale and unstable in quality, making them difficult to meet the needs of large-scale production. Global high-purity quartz raw material deposits are primarily located in the United States, Norway, Canada, and Australia. The Spruce Pine pegmatite quartz deposit in North Carolina, USA, is recognized worldwide as a high-quality quartz deposit. Given the success of international projects and its advantages, such as large scale, low fluid inclusion content, and stable ore quality, pegmatite quartz resources are gradually replacing vein quartz as the new focus of high-purity quartz resources in my country.

[0004] The primary rock-forming minerals in pegmatite-type quartz resources are quartz, feldspar, and mica. Beneficiation and impurity removal can remove nearly all dissociated gangue minerals and the vast majority of impure intergrowths, yielding a quartz concentrate with a quartz content exceeding 99.5%. However, high-end, high-purity quartz requires extremely high purity, and the key to its purification is to maximize the removal of fine-particle impurities and inclusions. Furthermore, the leaching process, a crucial step in the purification of high-purity quartz, generates large amounts of acidic wastewater, which adversely impacts the ecological environment. Therefore, there is an urgent need to develop a deep chemical purification technology for high-purity quartz that consumes minimal leaching solution while delivering superior purification results. Summary of the Invention

[0005] The purpose of the present application is to provide a method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz. The preparation method has simple process, low energy consumption, easy operation, excellent purification effect, and can obtain a high-purity quartz sand product with SiO2 ≥ 99.998%. The leachate consumption is small, and the problem of high acid consumption in the prior art is effectively solved.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz comprises:

[0008] Step 1: subjecting the quartz concentrate obtained from the pegmatite granite to a first acid leaching with a first acid solution, washing and drying to obtain primary quartz sand and leachate III;

[0009] Step 2: doping, roasting, water quenching and drying the primary quartz sand to obtain a primary mineral; wherein the doping substance is a composite mixture of AlCl3·6H2O and NH4Cl, the roasting temperature is 500-700°C, and the holding time is ≥1h;

[0010] Step 3, subjecting the primary mineral to a second acid leaching with a second acid solution, washing, and drying to obtain intermediate quartz sand and leachate II;

[0011] Step 4: calcining, water quenching and drying the intermediate quartz sand to obtain an intermediate mineral, wherein the calcination temperature is 900-1100° C. and the holding time is ≥3 hours;

[0012] Step 5: The intermediate mineral is subjected to a third acid leaching with a third acid solution, and after washing and drying, the high-purity quartz sand and leachate I are obtained.

[0013] The method for preparing 4N8 grade high-purity quartz sand from the above-mentioned pegmatite quartz is a preferred embodiment: in step 1, the SiO2 content in the quartz concentrate is ≥99.9wt%, and the particle size is 0.10-0.25mm.

[0014] The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz is a preferred embodiment: in step 2, the mass ratio of AlCl3·6H2O to NH4Cl in the doping substance is 2 to 4:1; the mass ratio of the primary quartz sand to the composite mixture is 20 to 200:1.

[0015] The above method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz is a preferred embodiment: in step 2, the roasting temperature is 600-700°C, and room temperature water quenching is performed immediately after roasting.

[0016] The above method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz is a preferred embodiment: in step 4, the calcination temperature is 900-1000°C, and room temperature water quenching is performed immediately after calcination.

[0017] The method for preparing 4N8 grade high-purity quartz sand from the above-mentioned pegmatite quartz is a preferred embodiment: in step 1 and / or step 3, the acid leaching is performed by heated acid leaching or room temperature acid leaching; the temperature of the heated acid leaching is 60-95°C and the leaching time is 4-8 hours; the time of the room temperature acid leaching is 24-72 hours;

[0018] In step 5, the third acid leaching includes ultrasonic-assisted acid leaching and heated acid leaching in sequence; wherein the ultrasonic-assisted acid leaching is carried out at room temperature and pressure, the ultrasonic power is 1000-1200W, and the ultrasonic-assisted acid leaching time is 0.5-1.5h; the temperature of the heated acid leaching is 60-95°C, and the leaching time is 4-8h; alternatively, the third acid leaching is ultrasonic-assisted heated acid leaching.

[0019] The above-mentioned method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz is a preferred embodiment: the first acid solution, the second acid solution and / or the third acid solution is a mixed acid including HCl, HF and HNO3, or a mixed acid including HCl, HF and H2C2O4; in the mixed acid, the concentration of HNO3 is 0.5-1 mol / L, the concentration of H2C2O4 is 0.5-1 mol / L, the concentration of HCl is 2-4 mol / L, and the concentration of HF is 0.5-2 mol / L.

[0020] The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz is preferably implemented as follows: the leachate II obtained in step 3 is introduced into step 1 for use as the first acid solution; and / or the leachate I obtained in step 5 is introduced into step 3 for use as the second acid solution;

[0021] Preferably, the leachate II obtained in step three completely replaces the first acid solution in step one; and / or, the leachate I obtained in step five completely replaces the second acid solution in step three.

[0022] The method for preparing 4N8 grade high-purity quartz sand from the above-mentioned pegmatite quartz is a preferred embodiment: in the first acid leaching, the second acid leaching and / or the third acid leaching, the liquid-to-solid ratio is ≥1.5ml:1g, more preferably 1.5ml:1g-3ml:1g.

[0023] The above method for preparing 4N8 grade high purity quartz sand from pegmatite quartz is a preferred embodiment: in step 1, step 3 and / or step 5, the washing is performed by ultrasonic washing with ultrapure water until no Cl is detected. - .

[0024] Compared with the prior art, the solution of this application has the following beneficial effects:

[0025] (1) High-temperature roasting / calcination water quenching is a common method for deep purification of high-purity quartz, but most people choose 900℃ for calcination based on experience, or choose to introduce Cl2 for chlorination roasting. The former lacks a scientific definition of the calcination temperature, and the latter is highly polluting and difficult to operate. This application proposes a new process for preparing high-purity quartz sand by three-stage leaching + two-stage roasting / calcination, taking into full consideration the advantages and disadvantages of calcination. Before roasting, mixed leaching is carried out to remove mineral impurities to the maximum extent, preventing impurity elements from entering the crystal lattice under high temperature conditions or forming new objects that are difficult to remove. Afterwards, the phase transition temperature of α-quartz to β-quartz (573℃) and the phase transition temperature of β-quartz to β-tridymite (870℃) are used to gradually open the inclusions. The key to doping in this invention is to effectively reduce impurity elements without introducing new ones. By adding AlCl3·6H2O and NH4Cl and performing chlorination roasting for a certain period of time, the present invention can effectively remove alkali metal impurities such as K and Na. At the same time, the Al element is controlled to prevent it from entering the crystal lattice during this roasting time, allowing it to be effectively removed in the next mixed leaching stage. Subsequently, calcination and water quenching are performed using the phase transition temperature (870°C) of β-quartz to β-tridymite. This transition results in a greater change in the lattice structure, which can promote further thermal cracking of the fine-grained inclusions, generate a large number of cracks, and form more migration channels, maximizing the removal of residual impurity elements in the subsequent mixed acid leaching.

[0026] (2) Chemical leaching is the most important method for deep purification of quartz. It is used to treat inclusion impurities on the surface of quartz particles or embedded in the particles. Among them, acid leaching is the most important and widely studied leaching process of chemical leaching. A mixed solution of hydrofluoric acid, sulfuric acid, hydrochloric acid and nitric acid is often used to purify quartz sand. During acid leaching, different acids will produce a synergistic effect, which improves the leaching effect. As the leaching reaction proceeds, the mixed acid reacts with the various mineral phases in the quartz sand to form a thicker product layer that wraps around the unreacted core, restricting the reaction. The leaching reaction will be controlled by the diffusion of the product. Therefore, increasing the number of leaching and washing times can improve the leaching effect and increase the purity of high-purity quartz. However, a large amount of acid waste liquid will be generated during the acid leaching process, which has an adverse impact on the ecological environment. In order to remove impurity elements to the maximum extent and reduce the output of acid waste liquid, the present invention adopts a multi-stage countercurrent leaching method for chemical deep purification. On the one hand, it can improve the purity of the high-purity quartz product, and on the other hand, it can greatly reduce the output of acid waste liquid.

[0027] (3) Compared with other chemical purification methods at room temperature and pressure, the method of the present invention adopts a two-stage roasting and calcining method to gradually open the inclusions, which can significantly improve the purity of high-purity quartz. Furthermore, the method adopts a multi-stage countercurrent leaching method to improve the purity of the high-purity quartz product while reducing the output of acid waste liquid, greatly reducing the leaching cost and mitigating the adverse impact on the ecological environment. This method consumes less leachate, but has excellent purification effect, and can obtain a high-purity quartz sand product with SiO2 ≥ 99.998%. The preparation method is simple, has low energy consumption, and is easy to operate. This method effectively solves the problem of high acid consumption in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 The present invention provides a process flow chart of a preferred method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings. Figure 1 As shown, a method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz provided in a preferred embodiment of the present invention comprises the following steps:

[0031] (1) Add the quartz concentrate to the first acid solution for the first acid leaching, and obtain the leaching product and leachate III after acid leaching. The leaching product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , drying to obtain primary quartz sand;

[0032] (2) After the primary quartz sand is doped and roasted, it is immediately quenched with deionized water at room temperature and then dried in an oven at 180°C to obtain the primary mineral;

[0033] (3) The primary mineral is added to the second acid solution for the second acid leaching, and the leaching product and leachate II are obtained after the acid leaching. The leaching product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried to obtain intermediate quartz sand;

[0034] (4) After calcining the intermediate quartz sand, immediately quench it with deionized water at room temperature, and then dry it in an oven at 180°C to obtain the intermediate mineral;

[0035] (5) The intermediate mineral is added to the third acid solution for the third acid leaching, and the leaching product and leachate I are obtained after acid leaching. The leaching product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried to obtain 4N8 grade high-purity quartz sand.

[0036] In step (1), the quartz concentrate used is generally pegmatite granite quartz ore which is pretreated (selective crushing - fine classification - coarse particle preselection), grinding sand making, gravity separation, magnetic separation, and flotation to obtain quartz concentrate. The SiO2 content of the quartz concentrate is ≥99.9wt%, and the particle size is 0.10-0.25mm. The quartz ore is muscovite pegmatite granite quartz, and the muscovite content is 5%-15%.

[0037] In step (1), the first acid leaching adopts heated acid leaching or room temperature acid leaching; the temperature of the heated acid leaching is 60-95°C (for example, 62°C, 65°C, 70°C, 75°C, 80°C, 85°C, 88°C, etc.), and the leaching time is 4-8h (for example, 4.5h, 5h, 6h, 7h, 7.5h, etc.), usually first heated to the acid leaching temperature, and then kept warm for a period of time for leaching; the time of the room temperature acid leaching is 24-72h (for example, 30h, 36h, 42h, 48h, 54h, 60h, 66h, etc.).

[0038] In step (2), the doping calcination is to mix the primary quartz sand and the doped substance uniformly and then perform a calcination treatment; the doped substance is a composite mixture of AlCl3·6H2O and NH4Cl, wherein the mass ratio of AlCl3·6H2O to NH4Cl is 2 to 4:1 (for example, 2.5:1, 3:1, 3.5:1, etc.); the mass ratio of the primary quartz sand to the composite mixture is 20 to 200:1 (for example, 30:1, 40:1, 60:1, 80:1, 100:1, 120:1, 140:1, 160:1, 180:1, 190:1, etc.).

[0039] In step (2), the roasting temperature is 500-700°C (e.g., 520°C, 550°C, 600°C, 620°C, 650°C, 680°C, etc.), and the temperature is raised to the roasting temperature and kept warm for ≥1h (i.e., the roasting time can be 1h, 2h, 3h, 4h, etc.); after roasting, it is immediately quenched in water at room temperature. The advantage of selecting this temperature range is that while the layered structure of the muscovite is not destroyed, the impurities in the inclusions and cracks are exposed to the surface of the particles, and the addition of AlCl3 reduces the crystal phase transition temperature of the quartz to produce larger cracks, allowing more impurities to be removed in the subsequent mixed acid leaching. The roasting temperature is more preferably 600-700°C.

[0040] In step (3), the second acid leaching adopts heated acid leaching or room temperature acid leaching; the temperature of the heated acid leaching is 60-95°C (such as 62°C, 65°C, 70°C, 75°C, 80°C, 85°C, 88°C, etc.), and the leaching time is 4-8h (such as 4.5h, 5h, 6h, 7h, 7.5h, etc.), usually first heated to the acid leaching temperature, and then kept warm for a period of time for leaching; the time of the room temperature acid leaching is 24-72h (such as 30h, 36h, 42h, 48h, 54h, 60h, 66h, etc.).

[0041] In step (4), the calcination temperature is 900-1100°C (for example, it can be 920°C, 950°C, 980°C, 1000°C, 1020°C, 1050°C, 1080°C, etc.), and the temperature is raised to the calcination temperature with the furnace and kept warm for a time of ≥3h (i.e., the calcination time can be 3h, 4h, 5h, 6h, etc.). After calcination, water quenching at room temperature is immediately performed. The advantage of selecting this temperature range is that as the bond angle changes, β-quartz gradually transforms into β-tridymite. The lattice structure of this transformation changes more, and more cracks can be generated, further opening the inclusions. In a short period of time, the quartz sand crystal form changes quickly, and then slowly. As the holding time increases, the quartz sand crystal form transformation slows down until the transformation is complete. Therefore, compared with roasting, a relatively long holding time is selected in the calcination system. The calcination temperature is preferably 900-1000°C.

[0042] Optionally, in steps (1), (3) and (5), the first acid solution, the second acid solution and / or the third acid solution are mixed acids, and an oxidizing acid or a reducing acid can be used. The oxidizing acid is, for example, a mixed acid comprising HCl, HF and HNO3, and the reducing acid is, for example, a mixed acid comprising HCl, HF and H2C2O4. Experiments have shown that the oxidizing acid is more effective. In the mixed acid, the concentration of HNO3 is 0.5-1 mol / L (for example, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L). ol / L, 0.9mol / L, etc.), the concentration of H2C2O4 is 0.5-1mol / L (such as 0.6mol / L, 0.7mol / L, 0.8mol / L, 0.9mol / L, etc.), the concentration of HCl is 2-4mol / L (2.5mol / L, 3mol / L, 3.5mol / L, etc.), and the concentration of HF is 0.5-2mol / L (such as 0.8mol / L, 0.1mol / L, 1.5mol / L, 1.8mol / L, etc.).

[0043] Preferably, in the first acid leaching, the second acid leaching and / or the third acid leaching, the liquid-to-solid ratio is ≥1.5 ml:1 g, preferably 1.5 ml:1 g-3 ml:1 g (such as 1.8 ml:1 g, 2.0 ml:1 g, 2.2 ml:1 g, 2.5 ml:1 g, 2.8 ml:1 g, etc.).

[0044] In step (5), the third acid leaching includes ultrasonic-assisted acid leaching and heated acid leaching in sequence; wherein the ultrasonic-assisted acid leaching is carried out at room temperature and pressure, the ultrasonic power is 1000-1200W (for example, 1020W, 1050W, 1100W, 1150W, 1180W, etc.), and the ultrasonic mixed acid leaching time is 0.5-1.5h (for example, 0.8h, 1h, 1.2h, etc.);

[0045] The temperature of the heated acid leaching is 60-95°C (such as 62°C, 65°C, 70°C, 75°C, 80°C, 85°C, 88°C, etc.), and the leaching time is 4-8h (such as 4.5h, 5h, 6h, 7h, 7.5h, etc.). Usually, it is first heated to the acid leaching temperature and then kept warm for a period of time for leaching.

[0046] In step (5), the third acid leaching may also be ultrasonic-assisted heating acid leaching, that is, directly performing heating acid leaching and simultaneously assisting it with ultrasonic treatment.

[0047] In step (5), the content of SiO2 in the obtained 4N8 grade high-purity quartz sand is ≥99.998wt%.

[0048] Preferably, the leachate II obtained in step (3) is directed to step (1) for use as the first acid solution; and / or, the leachate I obtained in step (5) is directed to step (3) for use as the second acid solution; that is, a so-called multi-stage countercurrent leaching method is adopted to maximize the removal of impurity elements while reducing the output of acid waste liquid. More preferably, the leachate II obtained in step (3) completely replaces the first acid solution in step (1); and / or, the leachate I obtained in step (5) completely replaces the second acid solution in step (3).

[0049] The present invention will be further described in detail below through examples. The protection scope of the present invention includes but is not limited to the following examples.

[0050] If specific experimental steps or conditions are not specified in the examples, the experiments can be carried out according to the conventional steps or conditions described in the literature in the art.

[0051] Unless otherwise specified, all reagents and raw materials used in the examples are commercially available products.

[0052] The quartz raw material used in the examples of the present invention is a quartz concentrate with a SiO2 content of ≥99.9% and a particle size of 0.10-0.25 mm, obtained by physical separation of raw ore. The raw quartz ore is muscovite pegmatite granite quartz with a muscovite content of 5%. The impurity element contents of the quartz concentrate are shown in Table 1.

[0053] Table 1 Impurity elements and quartz content in quartz concentrate

[0054]

[0055] Example 1

[0056] This embodiment provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0057] First, a first round of experiments was conducted. A newly prepared mixed acid was used in the first, second, and third acid leachings. The formula was 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3. The liquid-to-solid ratio was maintained at 2 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0058] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0059] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 80°C for 8 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0060] (2) the primary quartz sand obtained in step (1) is mixed uniformly with the composite mixture (i.e., doped) and then roasted, immediately quenched with deionized water at room temperature after roasting, and then dried in an oven at 180°C to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 3:1, and the mass ratio of the primary quartz sand to the composite mixture is 80:1; the roasting temperature is 600°C, and the roasting time is 1 hour, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm for 1 hour.

[0061] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching at a leaching temperature of 80°C for 8 hours to obtain a leached product and leachate II. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0062] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0063] (5) The intermediate mineral obtained in step (4) is added to a newly prepared mixed acid for a third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to a set temperature. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain 4N8 grade high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 2 ml:1 g. Ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 80°C and the leaching time is 8 hours.

[0064] The 4N8 grade high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0065] Example 2

[0066] This embodiment provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0067] First, a first round of experiments was conducted. A newly prepared mixed acid, 1 mol / L HF, 3 mol / L HCl, and 1 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0068] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0069] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 80°C for 8 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. -, dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0070] (2) The primary quartz sand obtained in step (1) is mixed uniformly with the composite mixture (i.e., doped) and then roasted, and immediately quenched with deionized water at room temperature after roasting, and then placed in an oven at 180°C for drying to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 3:1, and the mass ratio of the primary quartz sand to the composite mixture is 40:1; the roasting temperature is 650°C, and the roasting time is 2h, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm for 2h.

[0071] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching at a leaching temperature of 80°C for 8 hours to obtain a leached product and leachate II. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0072] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 950°C and the calcination time is 4 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 4 hours.

[0073] (5) The intermediate mineral obtained in step (4) is added to a newly prepared mixed acid for a third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to a set temperature. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain 4N8 grade high-purity quartz sand. The mixed acid formula is: 1 mol / L HF, 3 mol / L HCl, 1 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g. Ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 80°C and the leaching time is 8 hours.

[0074] The 4N8 grade high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0075] Example 3

[0076] This embodiment provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0077] First, a first round of experiments was conducted. A newly prepared mixed acid, 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0078] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0079] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 60°C for 8 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0080] (2) the primary quartz sand obtained in step (1) is uniformly mixed with the composite mixture (i.e., doped) and then roasted, and immediately quenched with deionized water at room temperature after roasting, and then dried in an oven at 180°C to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 4:1, and the mass ratio of the primary quartz sand to the composite mixture is 120:1; the roasting temperature is 600°C, and the roasting time is 1 hour, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm for 1 hour.

[0081] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching at a leaching temperature of 60°C for 8 hours to obtain a leached product and leachate II. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0082] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0083] (5) The intermediate mineral obtained in step (4) is added to a newly prepared mixed acid for a third acid leaching: first, ultrasonic-assisted acid leaching is performed, and then the acid leaching is performed by heating to a set temperature. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain 4N8 grade high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g. Ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 60°C and the leaching time is 8 hours.

[0084] The 4N8 grade high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0085] Example 4

[0086] This embodiment provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0087] First, a first round of experiments was conducted. A newly prepared mixed acid, 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0088] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0089] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 60°C for 6 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0090] (2) The primary quartz sand obtained in step (1) is mixed evenly with the composite mixture (i.e., doped) and then roasted, and immediately quenched with deionized water at room temperature after roasting, and then placed in an oven at 180°C for drying to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 3:1, and the mass ratio of the primary quartz sand to the composite mixture is 80:1; the roasting temperature is 600°C, and the roasting time is 1 hour, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm for 1 hour.

[0091] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching at a leaching temperature of 60°C for 6 hours to obtain a leached product and leachate II. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0092] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0093] (5) The intermediate mineral obtained in step (4) is added to a newly prepared mixed acid for a third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to a set temperature. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain 4N8 grade high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g. Ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 60°C and the leaching time is 6 hours.

[0094] The 4N8 grade high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0095] Example 5

[0096] This embodiment provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , only the first round of experiments (i.e., the first round of experiments of Example 1) was carried out, including the following steps:

[0097] (1) The quartz concentrate was added to a mixed acid (the formula of the mixed acid was: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3) for the first acid leaching, with a liquid-solid ratio of 3 ml:1 g, a leaching temperature of 80 ° C, and a leaching time of 8 h to obtain a leached product and a leachate III. The leached product was repeatedly washed with ultrapure water until the washing water was free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0098] (2) The primary quartz sand obtained in step (1) is mixed evenly with the composite mixture (i.e., doped) and then roasted, and immediately quenched with deionized water at room temperature after roasting, and then placed in an oven at 180°C for drying to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 4:1, and the mass ratio of the primary quartz sand to the composite mixture is 80:1; the roasting temperature is 600°C, and the roasting time is 1 hour, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm, the heating time is controlled at 4 to 6 hours, and the holding time is 1 hour.

[0099] (3) The primary mineral obtained in step (2) was added to a mixed acid (the formula of the mixed acid is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3) for a second acid leaching, with a liquid-solid ratio of 3 ml:1 g; the leaching temperature was 80°C, the time was 8 hours, and the leaching product and leachate II were obtained after acid leaching. The leached product was repeatedly washed with ultrapure water until the washing water was free of Cl using AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0100] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0101] (5) The intermediate mineral obtained in step (4) is added to the mixed acid for the third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to the set temperature. After acid leaching, the leached product and leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. -, and dried in an oven at 180°C to obtain 4N8 grade high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g. Ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 80°C and the leaching time is 8 hours.

[0102] The 4N8 grade high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0103] Comparative Example 1

[0104] This comparative example provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0105] First, a first round of experiments was conducted. A newly prepared mixed acid, 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0106] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0107] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 60°C for 6 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0108] (2) The primary quartz sand obtained in step (1) is mixed evenly with the composite mixture (i.e., doped) and then roasted, and immediately quenched with deionized water at room temperature after roasting, and then placed in an oven at 180°C for drying to obtain a primary mineral; wherein the substance used for doping is a composite mixture of AlCl3·6H2O and NH4Cl, the mass ratio of AlCl3·6H2O to NH4Cl is 3:1, and the mass ratio of the primary quartz sand to the composite mixture is 80:1; the roasting temperature is 600°C, and the roasting time is 1 hour, that is, the temperature is raised to the above-mentioned roasting temperature with the furnace and then kept warm for 1 hour.

[0109] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching, and the mixed acid is the leachate I obtained in step (5); the leaching temperature is 60°C, the time is 6 hours, and the leaching product and leachate II are obtained after acid leaching. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0110] (4) Omit.

[0111] (5) The intermediate mineral obtained in step (4) (i.e., the intermediate quartz sand obtained in step (3)) is added to the mixed acid for the third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to the set temperature. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g; ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 60°C and the leaching time is 6 hours.

[0112] The high-purity quartz sand prepared in this comparative example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0113] Comparative Example 2

[0114] This comparative example provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0115] First, a first round of experiments was conducted. A newly prepared mixed acid, 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0116] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0117] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 60°C for 6 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0118] (2) The primary quartz sand obtained in step (1) is directly roasted without being doped, and then immediately quenched with deionized water at room temperature, and then dried in an oven at 180° C. to obtain a primary mineral; wherein the roasting temperature is 600° C. and the roasting time is 1 hour, that is, the temperature is raised to the above roasting temperature in the furnace and then kept warm for 1 hour.

[0119] (3) The primary mineral obtained in step (2) is added to the leachate I obtained in step (5) for a second acid leaching, and the mixed acid is the leachate I obtained in step (5); the leaching temperature is 60°C, the time is 6 hours, and the leaching product and leachate II are obtained after acid leaching. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0120] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0121] (5) The intermediate mineral obtained in step (4) is added to the mixed acid for the third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the acid leaching is continued after heating to the set temperature. After acid leaching, the leached product and leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , and dried in an oven at 180°C to obtain high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g; ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 60°C and the leaching time is 6 hours.

[0122] The high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0123] Comparative Example 3

[0124] This comparative example provides a method for preparing 4N8 grade high purity quartz sand from pegmatite quartz. Figure 1 , a total of two rounds of experiments were conducted:

[0125] First, a first round of experiments was conducted. A newly prepared mixed acid, 0.5 mol / L HF, 2 mol / L HCl, and 0.5 mol / L HNO3, was used in the first, second, and third acid leachings. The liquid-to-solid ratio was maintained at 3 ml:1 g. The leachate III produced by the first acid leaching was subsequently neutralized and harmlessly treated. The leachate II produced by the second acid leaching was retained for standby use. The leachate I produced by the third acid leaching was retained for standby use.

[0126] Then, a second round of tests was conducted using a countercurrent circulation process, wherein the first acid leaching used the leachate II produced by the second acid leaching in the first round of tests, and the second acid leaching used the leachate I produced by the third acid leaching in the first round of tests. The specific steps were as follows:

[0127] (1) Add the quartz concentrate to the leachate II obtained in step (3) for the first acid leaching at a temperature of 60°C for 6 hours to obtain a leached product and a leachate III. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain primary quartz sand; leachate III is separately subjected to harmless treatment;

[0128] (2) Omit.

[0129] (3) The primary mineral obtained in step (2) (i.e., the primary quartz sand obtained in step (1)) is added to the leachate I obtained in step (5) for a second acid leaching, wherein the mixed acid is the leachate I obtained in step (5); the leaching temperature is 60°C, the time is 6 hours, and the leaching product and leachate II are obtained after acid leaching. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. - , dried in an oven at 180°C to obtain intermediate quartz sand;

[0130] (4) After calcining the intermediate quartz sand obtained in step (3), it is immediately quenched with deionized water at room temperature, and then placed in an oven at 180°C for drying to obtain an intermediate mineral; wherein the calcination temperature is 900°C and the calcination time is 3 hours, that is, the temperature is raised to the above calcination temperature in the furnace and then kept warm for 3 hours.

[0131] (5) The intermediate mineral obtained in step (4) is added to the mixed acid for the third acid leaching: first, ultrasonic assisted acid leaching is performed, and then the mixture is heated to the set temperature for the third acid leaching. After acid leaching, a leached product and a leachate I are obtained. The leached product is repeatedly washed with ultrapure water until the washing water is free of Cl by AgNO3 detection. -, and dried in an oven at 180°C to obtain high-purity quartz sand. The mixed acid formula is: 0.5 mol / L HF, 2 mol / L HCl, 0.5 mol / L HNO3; the liquid-to-solid ratio is 3 ml:1 g; ultrasonic-assisted acid leaching is carried out at room temperature and pressure, with an ultrasonic power of 1200 W and an ultrasonic mixed acid leaching time of 1 hour. The subsequent heated acid leaching temperature is 80°C and the leaching time is 8 hours.

[0132] The high-purity quartz sand prepared in this example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0133] Comparative Example 4

[0134] The only difference between this comparative example and Example 1 is the dopant in step (4), and the other aspects are the same; specifically, in this comparative example, the doping substance is NaCl, and the mass ratio of primary quartz sand to NaCl is 80:1.

[0135] The high-purity quartz sand prepared in this comparative example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0136] Comparative Example 5

[0137] This comparative example is the same as Example 1 only in that the dopant in step (4) is different; specifically, the doping substance is KCl, and the mass ratio of primary quartz sand to KCl is 100:1.

[0138] The high-purity quartz sand prepared in this comparative example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0139] Comparative Example 6

[0140] The only difference between this comparative example and Example 1 is the dopant in step (4), and the other aspects are the same; specifically, the doping substance is CaCl2, and the mass ratio of primary quartz sand to CaCl2 is 100:1.

[0141] The high-purity quartz sand prepared in this comparative example was tested. The precise content of each impurity element in the quartz sand was analyzed using ICP-MS. The results are shown in Table 3.

[0142] Comparative Example 7

[0143] This comparative example is based on Example 1, except that the dopant in step (4) is replaced. Specifically, the dopant is Na2CO3, and the mass ratio of primary quartz sand to Na2CO3 is 100:1. A small amount of quartz sand was found to be agglomerated in the product after roasting. It is considered that at high temperature, sodium carbonate and silicon dioxide react to form sodium silicate, causing the quartz sand to agglomerate. In addition, an increase in the Na impurity content was also detected.

[0144] For ease of understanding, the process conditions for preparing high-purity quartz sand in the examples and comparative examples of the present application are summarized in Table 2 below.

[0145] Table 2 Summary of process conditions for preparing high-purity quartz sand in the examples and comparative examples of this application

[0146]

[0147]

[0148]

[0149] The impurity elements and quartz contents in the high-purity quartz sand prepared by multi-stage countercurrent leaching in the examples and comparative examples of the present application are shown in Table 3 below.

[0150] Table 3 Contents of impurity elements and quartz in high-purity quartz prepared in Examples and Comparative Examples of the present application

[0151]

[0152] It can be seen from Table 3 that Examples 1 to 4 and Example 5 can all prepare 4N8 grade high-purity quartz sand.

[0153] Example 5 does not adopt the countercurrent circulation process for leaching. The leaching solutions of steps (1) and (3) are both made of mixed acid with a new ratio. Compared with the countercurrent leaching process adopted in Examples 1 to 4, the research results show that both the countercurrent leaching process and the non-countercurrent leaching process can produce 4N8 grade high-purity quartz, but the countercurrent leaching process can effectively reduce the amount of acid without affecting the purity of the high-purity quartz.

[0154] In Comparative Example 1, step (4) was omitted, i.e., calcination and water quenching at 900°C were not performed, and only roasting and water quenching at 600°C were performed. Although at this temperature (600°C), the layered muscovite mica had not yet begun to remove hydroxyl groups and no new difficult-to-remove objects were formed, at this temperature, α-quartz was transformed into β-quartz. Although the Si-O bond angle changed, the displacement-type transformation was small. At this temperature, the degree of inclusion explosion was low, and the fine-grained inclusions were not effectively opened, resulting in the high-purity quartz obtained in Comparative Example 1 failing to reach 4N8.

[0155] In step (2) of Comparative Example 2, only calcination and water quenching at 600°C were performed, and no doping calcination was performed. The results showed that the K and Na alkali metal contents were not effectively removed, and the doping was better than the undoped one. Doping can lower the crystal phase transition temperature of quartz to produce larger cracks, so that more impurities can be removed in the mixed acid leaching. At the same time, the HCl produced can reduce the K and Na alkali metal contents.

[0156] Comparative Example 3 omits step (2), i.e., no doping and 600°C roasting and water quenching are performed, and only 900°C calcination and water quenching are performed. At this temperature (900°C), as the bond angle changes, β-quartz gradually transforms into β-tridymite. The lattice structure changes more greatly during this transformation. When quartz passes through this transformation point rapidly, a large number of cracks will be generated, which is conducive to the removal of impurities. However, at this temperature, muscovite reconstructs to form new objects that are difficult to remove. Some impurity elements enter the lattice, making the impurities difficult to remove, resulting in the high-purity quartz obtained in Comparative Example 3 failing to reach 4N8.

[0157] Through a large number of experiments, the inventors found that Al is stable and generally difficult to remove. The above examples and comparative examples 4-6 show that the chlorination roasting of the present application can directly remove Al, while other doping will cause the content of impurities such as K, Na, and Ca to increase significantly.

[0158] From the above embodiments and comparative examples, it can be seen that the SiO2 content of the high-purity quartz sand produced by the method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz proposed in the present invention reaches 99.998wt% or more, and the high-purity quartz sand produced can meet the industry's demand for high-purity quartz sand; the invention has a simple process, low leachate consumption, and is easy to operate. While improving the purity of the high-purity quartz product, it reduces the output of acid waste liquid, greatly reduces the leaching cost, and at the same time reduces the adverse impact on the ecological environment, laying the foundation for future industrialization.

[0159] It should be noted that, in the present invention, unless otherwise understood in conjunction with the entire context, the expression "A and / or B" should be interpreted as any of the following three parallel situations: A; B; A and B. For example, the first acid liquid, the second acid liquid, and / or the third acid liquid should be interpreted as any of the following seven parallel situations: the first acid liquid; the second acid liquid; the third acid liquid; the first acid liquid and the second acid liquid; the second acid liquid and the third acid liquid; the first acid liquid and the third acid liquid; the first acid liquid, the second acid liquid, and the third acid liquid.

[0160] It should also be noted that, in the present invention, except for otherwise understanding in conjunction with the full text, if any, the relevant terms should be understood as follows. Relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements includes not only those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the sentence "comprise a..." do not exclude the presence of other identical elements in the process, method, article or equipment comprising the elements.

[0161] Although the present invention has been disclosed above through the description of specific embodiments of the present invention, it should be understood that those skilled in the art may design various modifications, improvements or equivalents of the present invention within the spirit and scope of the attached solutions. Such modifications, improvements or equivalents should also be considered to be included in the scope of protection claimed by the present invention.

Claims

1. A method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz, characterized by: include: Step 1: subjecting the quartz concentrate obtained from the pegmatite granite to a first acid leaching with a first acid solution, washing and drying to obtain primary quartz sand and leachate III; Step 2: doping, roasting, water quenching and drying the primary quartz sand to obtain a primary mineral; wherein the doping substance is a composite mixture of AlCl3•6H2O and NH4Cl, the roasting temperature is 500-700°C, and the holding time is ≥1h; Step 3, subjecting the primary mineral to a second acid leaching with a second acid solution, washing, and drying to obtain intermediate quartz sand and leachate II; Step 4: calcining, water quenching and drying the intermediate quartz sand to obtain an intermediate mineral; wherein the calcination temperature is 900-1100° C. and the holding time is ≥3 hours; Step 5: The intermediate mineral is subjected to a third acid leaching with a third acid solution, and after washing and drying, the high-purity quartz sand and leachate I are obtained.

2. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 1, characterized in that: In step 1, the SiO2 content in the quartz concentrate is ≥99.9wt%, and the particle size is 0.10~0.25mm.

3. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 1, characterized in that: In step 2, the mass ratio of AlCl3•6H2O to NH4Cl in the doped substance is 2-4:1; the mass ratio of the primary quartz sand to the composite mixture is 20-200:

1.

4. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1 to 3, characterized in that: In step 2, the calcination temperature is 600-700°C, and the calcination is immediately followed by water quenching at room temperature.

5. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1 to 3, characterized in that: In step 4, the calcination temperature is 900-1000°C, and the calcination is immediately followed by room temperature water quenching.

6. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 4, characterized in that: In step 4, the calcination temperature is 900-1000°C, and the calcination is immediately followed by room temperature water quenching.

7. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1 to 3 and 6, characterized in that: In step 1 and / or step 3, the acid leaching is carried out by heated acid leaching or room temperature acid leaching; the temperature of the heated acid leaching is 60-95° C., and the leaching time is 4-8 hours; the time of the room temperature acid leaching is 24-72 hours; In step 5, the third acid leaching includes ultrasonic-assisted acid leaching and heated acid leaching in sequence; wherein the ultrasonic-assisted acid leaching is carried out at room temperature and pressure, the ultrasonic power is 1000-1200W, and the ultrasonic-assisted acid leaching time is 0.5-1.5h; the temperature of the heated acid leaching is 60-95°C, and the leaching time is 4-8h; alternatively, the third acid leaching is ultrasonic-assisted heated acid leaching.

8. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1 to 3 and 6, characterized in that: The first acid solution, the second acid solution and / or the third acid solution is a mixed acid including HCl, HF and HNO3, or a mixed acid including HCl, HF and H2C2O4; in the mixed acid, the concentration of HNO3 is 0.5-1mol / L, the concentration of H2C2O4 is 0.5-1mol / L, the concentration of HCl is 2-4mol / L, and the concentration of HF is 0.5-2mol / L.

9. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1 to 3 and 6, characterized in that: The leachate II obtained in step 3 is introduced into step 1 for use as the first acid solution; and / or the leachate I obtained in step 5 is introduced into step 3 for use as the second acid solution.

10. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 9, characterized in that: The leachate II obtained in step three completely replaces the first acid solution in step one; and / or, the leachate I obtained in step five completely replaces the second acid solution in step three.

11. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 8, characterized in that: In the first acid leaching, the second acid leaching and / or the third acid leaching, the liquid-to-solid ratio is ≥1.5 ml:1 g.

12. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to claim 11, characterized in that: In the first acid leaching, the second acid leaching and / or the third acid leaching, the liquid-to-solid ratio is 1.5 ml:1g to 3 ml:1g.

13. The method for preparing 4N8 grade high-purity quartz sand from pegmatite quartz according to any one of claims 1-3, 6, and 10-12, characterized in that: In step 1, step 3 and / or step 5, the washing is performed by ultrasonic washing with ultrapure water until no Cl is detected. - .

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