A method for directional removal of impurity elements in pegmatite-type high-purity quartz

Abstract

The present invention belongs to the field of high-purity quartz preparation and relates to a method for directional removal of impurity elements in pegmatite-type high-purity quartz, comprising: (1) crushing the raw material with a crusher, washing, grinding, grading, gravity separation, and flotation to obtain quartz concentrate; (2) adding the raw material to a leaching solution A for constant temperature and micro-pressure leaching to obtain primary quartz sand by washing; the leaching solution A is a mixed acid of HF, HCl, and HNO3, wherein the HF concentration is 1-6 mol / L, the HCl and HNO3 concentration ratio is 3-12:1, the HCl+HNO3 and HF concentration ratio is ≤3, and the sum of the three concentrations is ≥3 mol / L; (3) roasting and water quenching to obtain intermediate quartz sand; (4) adding the raw material to a leaching solution B for ultrasonic leaching, washing, and high-temperature heat treatment to obtain high-purity quartz sand; the leaching solution B is a mixed acid of HF and HCl, wherein the HF concentration is 0.5-2 mol / L, and the HCl and HF concentration ratio is ≤3. The method can obtain 4N8 grade high-purity quartz sand with high yield, simple process, and easy operation.

Description

Technical Field

[0001] The invention belongs to the field of high-purity quartz preparation, and particularly relates to a method for directional removal of impurity elements in pegmatite-type high-purity quartz. Background Art

[0002] High-purity quartz has a unique molecular chain structure, lattice shape and lattice change law, which gives it excellent chemical stability, extremely low volume expansion coefficient, high temperature resistance, high insulation and voltage resistance, low and stable ultrasonic delay performance, mechanical properties superior to ordinary glass, ultraviolet spectrum transmission performance, visible light and near-infrared spectrum transmission performance. It occupies a pivotal position in the fields of semiconductors, photovoltaics, optical fibers, electric light sources, etc., and is an indispensable raw material for strategic high-tech industries.

[0003] Globally, there are few deposits capable of processing high-purity quartz. The main deposit types include granite pegmatite, vein quartz, and quartzite. 90% of the world's high-end, high-purity quartz raw materials come from the granite pegmatite deposit in Spruce Pine, North Carolina, USA. Due to its successful case studies, large scale, low fluid inclusion content, and stable ore quality, pegmatite-type high-purity quartz resources are currently considered the world's most important source of high-purity quartz raw materials.

[0004] Impurities in pegmatite-type high-purity quartz resources primarily fall into three categories: mineral impurities, inclusion impurities, and lattice impurities. High-end, high-purity quartz demands extremely high purity, imposing strict regulations not only on the total amount of impurities but also on key impurities such as Al, Na, and K. Maximizing impurity removal is crucial for high-purity quartz purification. Traditional purification processes primarily involve coarse crushing, calcination and water quenching, grinding and sand production, magnetic separation, flotation, and acid leaching. However, pegmatite-type high-purity quartz contains significant amounts of gangue minerals such as feldspar and mica. Calcination and water quenching prior to grinding and sand production can cause impurities such as K, Na, and Ca to enter the crystal lattice or interstices at high temperatures, making their removal more difficult. Leaching is a crucial step in high-purity quartz purification. Existing processes generally prioritize the highest acid concentration, neglecting the proper ratio of various acids, resulting in low yields and low quartz purity. There is an urgent need to develop targeted impurity removal technologies for pegmatite-type high-purity quartz to improve product purity. Summary of the Invention

[0005] The purpose of this application is to propose a method for the directional removal of impurity elements in pegmatite-type high-purity quartz. This method has excellent purification effect and effectively solves the problems of low yield and low impurity removal rate in the existing high-purity quartz purification process. It can achieve directional removal of key impurity elements and obtain high-purity quartz sand products with SiO2 ≥ 99.998%.

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

[0007] A method for directional removal of impurity elements in pegmatite-type high-purity quartz comprises the following steps:

[0008] (1) After the pegmatite-type high-purity quartz raw material is crushed by a crusher, it is washed and then ground and classified to obtain quartz sand raw material of a certain particle size, and then subjected to gravity separation and flotation to obtain quartz concentrate;

[0009] (2) adding the quartz concentrate to a leachate A for constant temperature micro-pressure leaching, and washing to obtain primary quartz sand; the leachate A is a mixed acid of HF, HCl, and HNO3, wherein the concentration of HF is 1 mol / L to 6 mol / L, the concentration ratio of HCl to HNO3 is 3:1 to 12:1, the concentration ratio of (HCl+HNO3) to HF is ≤3, and the sum of the concentrations of HF, HCl, and HNO3 is ≥3 mol / L;

[0010] (3) roasting and water quenching the primary quartz sand to obtain intermediate quartz sand;

[0011] (4) adding the intermediate quartz sand into leachate B for ultrasonic leaching, washing, and then performing high-temperature heat treatment to finally obtain high-purity quartz sand; the leachate B is a mixed acid of HF and HCl, wherein the concentration of HF is 0.5-2 mol / L, and the concentration ratio of HCl to HF is ≤3.

[0012] In the above method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (1), the pegmatite-type high-purity quartz raw material is directly crushed without any high-temperature heat treatment.

[0013] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (1), grinding and classification are performed to obtain quartz sand raw material with a particle size of -60 mesh to +180 mesh.

[0014] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (2), the leaching temperature is 50°C to 160°C, the leaching time is ≥4h, and the liquid-solid ratio is 1:1 to 3:1.

[0015] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (2), the washing includes: first repeatedly washing with high-purity water until the pH is neutral; and then ultrasonically washing with an ethanol solution.

[0016] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (2), during the ultrasonic washing, the ultrasonic power is 1000W to 1200W, the mass concentration of the ethanol solution is 10-30%, the liquid-solid ratio is ≥1, and more preferably the liquid-solid ratio is 10:1 to 3:1.

[0017] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (2), the washing includes: first washing with high-purity water for 5 to 10 times, and then ultrasonically washing with ethanol solution for 2 to 3 times.

[0018] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (3), the primary quartz sand is subjected to chlorination roasting in a tubular furnace, immediately followed by water quenching, and centrifugal dehydration to obtain the intermediate quartz sand; more preferably, the roasting temperature is 600°C to 1150°C, the roasting gas is Cl2 and / or HCl, and the roasting time is ≥6h; further preferably, the water quenching is performed by using high-purity water at room temperature.

[0019] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (4), the ultrasonic leaching time is 1h to 3h, the temperature is room temperature, the ultrasonic power is 1000W to 1200W, and the liquid-solid ratio is 1:1 to 5:1.

[0020] In the above-mentioned method for directional removal of impurity elements in pegmatite-type high-purity quartz, as a preferred embodiment, in step (4), the temperature of the high-temperature heat treatment is 1100°C to 1200°C, and the time is 0.5h to 5h.

[0021] Compared with the prior art, the solution of this application has the following beneficial effects:

[0022] (1) Compared with the traditional process, the process method adopted in the present invention does not perform calcination and water quenching before grinding, which prevents impurity elements such as K, Na, and Ca from entering the lattice or quartz gap at high temperature, thereby improving the purity of the high-purity quartz product finally obtained.

[0023] (2) The inventors conducted a detailed study on the ratio of various acids in the leaching stage and found that as the HF concentration increases, the loss rate of quartz itself increases, and when it reaches a certain critical point, it increases rapidly. And as the acid concentration increases, the purity of the high-purity quartz product shows a downward trend after reaching a certain level. And H + The concentration will affect the ionization of HF. + When the ratio of concentration to HF concentration is too high, HF2 -The formation of ions leads to a weakening of the dissolution effect and a reduction in the purity of the high-purity quartz product. The leaching agent A used in the method of the present invention can effectively remove impurities in mineral conjoined bodies and some inclusions, while ensuring the yield and removing impurity elements to a great extent.

[0024] (3) The method of the present invention combines the calcination-water quenching and chlorination roasting processes. The chlorination roasting-water quenching process can effectively open the inclusions while removing impurities.

[0025] (4) The leaching agent B used in the present invention primarily removes inclusions opened by the chlorination roasting-water quenching process. Ultrasound is used to bring leaching agent B into contact with impurities along the cracks, effectively removing the impurity elements. The impurity content at this stage is low, and the acid ratio of leaching agent B can effectively increase the yield of high-purity quartz.

[0026] (5) The process method adopted by the present invention fully considers the impurity removal rate, the yield of high-purity quartz and energy consumption issues as a whole. It utilizes the characteristics of different impurities to selectively dissolve the impurity elements, and has an excellent purification effect. It can obtain a high-purity quartz sand product with SiO2 ≥ 99.998% and a high yield. The process method is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] Figure 1 The present invention provides a process flow chart of a preferred embodiment of the method for directional removal of impurity elements in pegmatite-type high-purity quartz. DETAILED DESCRIPTION

[0029] 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 preferred embodiment of a method for directional removal of impurity elements in pegmatite-type high-purity quartz provided by the present invention comprises the following steps:

[0030] (1) After the pegmatite-type high-purity quartz raw material is crushed by a crusher (such as a jaw crusher), it is washed, ground and classified to obtain quartz sand raw material of a certain particle size, and then subjected to gravity separation and flotation to obtain quartz concentrate;

[0031] (2) adding the quartz concentrate to the leaching solution A for constant temperature and micro-pressure leaching, and obtaining primary quartz sand after washing;

[0032] (3) calcining the primary quartz sand at a certain temperature and then quenching it with water to obtain intermediate quartz sand;

[0033] (4) The intermediate quartz sand is added to the leaching solution B for ultrasonic leaching, and after washing, it is subjected to high-temperature heat treatment (baked sand) to finally obtain high-purity quartz sand.

[0034] In the above method for directional removal of impurity elements in pegmatite-type high-purity quartz, in step (1), the pegmatite-type high-purity quartz raw material is crushed by a crusher (such as a jaw crusher), washed to remove surface impurities, then ground and classified to obtain quartz sand raw material of a certain particle size, and then the quartz sand raw material is re-selected to remove heavy minerals and light minerals, and then flotation is performed to remove monomer-dissociated feldspar and mica to obtain quartz concentrate.

[0035] Preferably, in step (1), the pegmatite-type high-purity quartz raw material is directly crushed without any high-temperature heat treatment before grinding. In other words, compared to conventional processes, the method of the present application does not perform calcination and water quenching before grinding, thereby preventing impurity elements such as K, Na, and Ca from entering the crystal lattice or quartz interstices at high temperatures, thereby improving the purity of the final high-purity quartz product.

[0036] Preferably, in step (1), grinding and classification are performed to obtain quartz sand raw material with a particle size of -60 mesh to +180 mesh (i.e., above 180 mesh sieve and below 60 mesh sieve).

[0037] In the above method for directional removal of impurity elements from pegmatite-type high-purity quartz, in step (2), the quartz concentrate is first added to the leachate A and subjected to constant-temperature micro-pressure leaching in a sealed container; then, the quartz concentrate is repeatedly washed with high-purity water until the pH is neutral; then, an ethanol solution is ultrasonically washed to remove organic matter remaining on the quartz surface; and finally, a centrifugal dehydration treatment is performed to obtain primary quartz sand. The constant-temperature micro-pressure leaching is performed in a sealed container, wherein the saturated vapor pressure increases with increasing temperature, for example, 0.04 MPa at 50°C and 0.12 MPa at 90°C.

[0038] Preferably, in step (2), the leachate A is a mixed acid of HF, HCl and HNO3, wherein the concentration of HF is 1 mol / L to 6 mol / L, the concentration ratio of HCl to HNO3 is 3:1 to 12:1, the concentration ratio of (HCl+HNO3) to HF is ≤3, and the sum of the concentrations of HF, HCl and HNO3 is ≥3 mol / L. Regarding the ratio of leachate A, the inventors have found through experiments that the results of the test of the concentration ratio of hydrochloric acid to nitric acid in this range are better. Preliminary analysis shows that this is because HNO3 has strong oxidizing properties, while hydrochloric acid has complexing properties, which can further promote the reaction; the reason for limiting the concentration ratio of (HCl+HNO3) to HF to ≤3 is that the appropriate amount of H + It will promote the reaction, and too high a concentration of H+ This will inhibit the ionization of HF, resulting in a decrease in the purity of the high-purity quartz product; the sum of the concentrations of all acids is limited to ≥3 mol / L to avoid incomplete reaction due to an overall concentration that is too low. In leachate A, for example, the HF concentration can be 1.5 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 5.5 mol / L, etc.; for example, the concentration ratio of HCl to HNO3 can be 12:1, 11:1, 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, etc.; for example, the concentration ratio of (HCl+HNO3) to HF can be 0.25, 0.5, 1, 2, 3, etc.

[0039] Preferably, in step (2), the leaching temperature is 50°C to 160°C, a closed micro-pressure is used, the pressure increases with increasing temperature, the leaching time is ≥4h, and the liquid-solid ratio (the liquid-solid ratio herein refers to the weight ratio) is 1:1 to 3:1. For example, the leaching temperature can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 155°C, 160°C; for example, the leaching time can be 4.5h, 6h, 8h, 10h, etc.; for example, the liquid-solid ratio can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.

[0040] Preferably, in step (2), the washing is first repeated 5 to 10 times with high-purity water (conductivity <0.1 μs / cm) until the pH is neutral, and then ultrasonically washed with ethanol solution for 2 to 3 times to remove organic matter remaining on the quartz surface; more preferably, during the ultrasonic washing, the ultrasonic power is 1000W to 1200W, the mass concentration of the ethanol solution is 10-30%, the liquid-solid ratio is ≥1, and more preferably the liquid-solid ratio is 10:1 to 3:1. For example, the ultrasonic power can be 1000W, 1050W, 1100W, 1150W, 1200W, etc.; for example, the concentration of the ethanol solution can be 10%, 15%, 20%, 25%, 30%, etc., and the liquid-solid ratio can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc., and more preferably the liquid-solid ratio is 10:1 to 3:1. In the present application, ethanol cleaning is also used in step (2) to more thoroughly remove organic matter remaining on the quartz surface, such as mineral processing agents, and better ensure the quality of the subsequently prepared product without large bubbles.

[0041] In the above method for directional removal of impurity elements in pegmatite-type high-purity quartz, in step (3), the primary quartz sand is subjected to chlorination roasting in a tubular furnace, and then immediately water quenched and centrifuged to obtain intermediate quartz sand.

[0042] Preferably, in step (3), the calcination temperature is 600°C to 1150°C, the calcination gas is Cl2 and / or HCl, and the calcination time is ≥ 6 hours. For example, the calcination temperature may be 650°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, etc.; the calcination gas may be Cl2, HCl, or a mixture of Cl2 and HCl; and the calcination time may be 6.5 hours, 8 hours, 10 hours, 12 hours, etc.

[0043] Preferably, in step (3), the water quenching is performed by using high-purity water at room temperature.

[0044] In the above method for directional removal of impurity elements in pegmatite-type high-purity quartz, in step (4), the intermediate quartz sand is added to the leachate B, ultrasonically leached, and then repeatedly washed with high-purity water until the pH is neutral. After centrifugal dehydration, high-temperature heat treatment is performed to finally obtain high-purity quartz sand.

[0045] Preferably, in step (4), the leachate B is a mixed acid of HF and HCl, wherein the concentration of HF is 0.5 to 2 mol / L, and the concentration ratio of HCl to HF is ≤ 3. For example, the concentration of HF may be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.; for example, the concentration ratio of HCl to HF may be 0.25, 0.5, 1, 2, 3, etc.

[0046] Preferably, in step (4), the ultrasonic time is 1 hour to 3 hours, the ultrasonic temperature is room temperature, the ultrasonic power is 1000W to 1200W, and the liquid-solid ratio is 1:1 to 5:1. For example, the ultrasonic time can be 1.5 hours, 2 hours, 2.5 hours, etc., the ultrasonic power can be 1000W, 1050W, 1100W, 1150W, 1200W, etc.; for example, the liquid-solid ratio can be 1.5:1, 2:1, 3:1, 4:1, 4.5:1, etc.

[0047] Preferably, in step (4), the high temperature heat treatment temperature is 1100° C. to 1200° C., and the time is 0.5 h to 5 h. For example, the high temperature heat treatment temperature can be 1110° C., 1120° C., 1130° C., 1140° C., 1150° C., 1160° C., 1170° C., 1180° C., 1190° C., etc., and the time can be 0.5 min, 1 h, 2 h, 3 h, 4 h, 5 h, etc. High temperature heat treatment will affect the performance of the crucible prepared from the high purity quartz product. If the high temperature heat treatment is not performed properly, the hydroxyl content will be high, the crucible will be difficult to form, or bubbles and bubble groups will be easily formed.

[0048] The present invention will be further described in detail below through the examples. The scope of the present invention includes but is not limited to the following examples. Where specific experimental steps or conditions are not specified in the examples, the procedures or conditions described in the literature in the art may be followed. Unless otherwise specified, all reagents and raw materials used in the examples are commercially available products.

[0049] The quartz raw material used in the embodiments and comparative examples of the present invention is of pegmatite type, and its main minerals are quartz (about 28%), plagioclase (about 62%), muscovite (about 8%) and a small amount of garnet (about 2%), and does not contain other dark minerals.

[0050] Examples 1-12 and Comparative Examples 1-9

[0051] A method for directional removal of impurity elements in pegmatite-type high-purity quartz, the process flow of which is shown in Figure 1 , including the following steps:

[0052] (1) After the pegmatite-type high-purity quartz raw material is crushed by a crusher, it is washed to remove surface impurities; then it is ground and classified to obtain quartz sand raw material with a mesh size of -60 to +180 (i.e., above 180 mesh and below 60 mesh), and then the quartz sand raw material is subjected to gravity separation to remove heavy minerals and light minerals, and flotation is performed to remove monomer-dissociated feldspar and mica to obtain quartz concentrate;

[0053] (2) adding the quartz concentrate obtained in step (1) to the leachate A, performing constant temperature micro-pressure leaching in a closed container under leaching temperature conditions, then repeatedly washing with high-purity water (conductivity between <0.1 μs / cm) until the pH is neutral, then ultrasonically washing with ethanol to remove organic matter remaining on the quartz surface, and obtaining primary quartz sand after centrifugal dehydration; wherein the leachate A is a mixed acid of HF, HCl and HNO3, wherein the concentration of HF is 1 mol / L to 6 mol / L , the concentration ratio of HCl and HNO3 is 3:1 to 12:1, the ratio of the sum of the concentrations of HCl + HNO3 to the concentration of HF is ≤3, and the sum of the concentrations of HF, HCl and HNO3 is ≥3 mol / L; the leaching temperature varies from 50°C to 160°C, a closed micro-pressure is used, the pressure increases with increasing temperature, the leaching time is ≥4h, and the liquid-solid ratio is 1:1 to 3:1; the ultrasonic washing is specifically carried out 3 times with an ethanol solution of 10% by mass, the liquid-solid ratio is 1, and the ultrasonic power is 1200W;

[0054] (3) chlorination roasting the primary quartz sand obtained in step (2) in a tube furnace, immediately quenching with high-purity water at room temperature, and centrifuging and dehydrating to obtain intermediate quartz sand; wherein the roasting temperature is 600° C. to 1150° C., the roasting gas is Cl2, HCl, or a mixture of Cl2 and HCl, and the roasting time is ≥6 h;

[0055] (4) adding the intermediate quartz sand obtained in step (3) to the leachate B, performing ultrasonic leaching, and then repeatedly washing with high-purity water until the pH is neutral, centrifugally dehydrating and performing high-temperature heat treatment to finally obtain high-purity quartz sand; wherein the leachate B is a mixed acid of HF and HCl, wherein the concentration of HF is 0.5-2 mol / L, and the concentration ratio of HCl to HF is ≤3; the ultrasonic leaching time is 1 h to 3 h, the ultrasonic leaching temperature is room temperature, the ultrasonic power is 1200 W, and the liquid-solid ratio is 2:1-4:1; the high-temperature heat treatment temperature is 1150° C. and the time is 30 min.

[0056] For ease of understanding, the experimental conditions for directional removal of impurity elements from pegmatite-type high-purity quartz in the Examples and Comparative Examples of this application are summarized in Table 1 below.

[0057] Table 1 Summary of implementation conditions for directional removal of impurity elements in pegmatite-type high-purity quartz in various embodiments and comparative examples of this application

[0058]

[0059]

[0060]

[0061] The quartz concentrate obtained without calcination treatment in step (1) of Examples 1-12 and Comparative Examples 2-8 and

[0062] The content of the quartz concentrate obtained by calcination in step (1) of comparative example 1 (unit: μg / g) is shown in Table 1.

[0063] Table 2.

[0064] Table 2 Impurity element content in quartz concentrate prepared by different methods in this application (μg / g)

[0065] sample Al Ca Fe K Mg Na Ti B Cu Li Mn Ni P total Uncalcined 102.00 26.25 22.97 11.38 4.15 42.87 3.34 0.49 0.12 0.14 0.61 0.00 12.23 226.54 Calcination 121.32 46.23 42.93 51.23 6.18 96.23 3.45 0.51 0.15 0.15 0.77 0.00 13.25 382.40

[0066] The high purity quartz sand obtained in the examples and comparative examples was tested. ICP-MS was used to analyze the quartz

[0067] The precise content of each impurity element in the sand. The impurity elements of the high-purity quartz prepared in the examples and comparative examples of this application

[0068] (Unit: μg / g) and quartz content (wt%) and yield are shown in Table 3.

[0069] Table 3 Impurity elements and quartz content (μg / g) and yield of high-purity quartz obtained in various examples and comparative examples of this application

[0070]

[0071] As can be seen from Table 3, Examples 1-12 and Comparative Examples 2 and 8 were able to produce 4N8 grade high-purity quartz sand. However, the high-purity quartz yields of Examples 1-12 were all above 80%, while the yields of Comparative Examples 2 and 8 were lower. The HF concentration in leachate A of Comparative Example 2 was 10 mol / L, resulting in a sharp decrease in yield at this stage. The HF concentration in leachate B of Comparative Example 8 was 4 mol / L, resulting in a decrease in yield at this stage. Comparative Examples 2 and 8, in addition to the decrease in yield, did not show significant improvement in product purity compared to the Examples.

[0072] Comparative Example 1 follows the conventional process and adds a calcination-water quenching process between crushing and grinding. At this stage, the impurity content is high, resulting in the impurity elements entering the lattice or lattice gap under high temperature conditions, increasing the difficulty of subsequent processing and making it difficult to remove some impurity elements.

[0073] Since HF is a weak acid, the dimer (HF)2 and HF2 - It will produce nucleophilic corrosion on Si atoms, break the Me-O bond, produce dissolution and promote the leaching of impurity elements. + Inhibits HF2 - The formation of HF leads to the weakening of the dissolution effect and incomplete leaching of impurity elements. In Comparative Example 4, the leaching solution A used reduced the HF concentration. Since HF is a weak acid, when HF does not reach a certain concentration, the content of (HF)2 is low, resulting in the weakening of the dissolution effect and the reduction of the impurity removal rate. Comparative Examples 3 and 4 both resulted in the reduction of Ca 2+ The impurity content is high, which affects the preparation of subsequent products.

[0074] After high temperature and water quenching, quartz produces a large number of cracks and pits on the particle surface, exposing inclusions and interstitial metal impurities, thereby increasing the chance of impurities contacting acid and improving the impurity removal rate. Comparative Example 6 did not implement step (3) of chlorination roasting treatment, resulting in some inclusions not bursting, reducing the impurity removal rate. In Comparative Example 5, step (3) only calcined and water quenched, without using gas (i.e., chlorination roasting was not used), which reduced the removal effect of impurity elements such as K and Na. The chlorination roasting in the present invention can chlorine some metal oxides such as K and Na, effectively reducing the impurity content. Not using chlorination roasting and only using calcination and water quenching will reduce the removal rate of alkali metals such as potassium and sodium. In Comparative Example 7, the chlorination roasting temperature in step (3) was 500°C, which did not reach the removal temperature of impurity elements such as K and Na, so the impurity removal effect was poor. In addition, no water quenching was performed and the quartz crystal transformation temperature was not reached, resulting in insufficient inclusion bursting and poor impurity removal effect.

[0075] The present invention provides a method for the targeted removal of impurity elements in pegmatite-type high-purity quartz. The obtained high-purity quartz sand has an SiO2 content of 99.998 wt% or more and a low content of impurities. The sum of the contents of thirteen impurity elements is ≤20.00 μg / g, the sum of the contents of Li, Na, and K is ≤2.00 μg / g, the Fe content is ≤0.50 μg / g, and the B content is ≤0.20 μg / g. The yield is above 80%. Therefore, the method for the targeted removal of impurity elements in pegmatite-type high-purity quartz provided by the present invention has the advantages of simple process, high product purity, and high yield, laying a foundation for future industrial implementation.

[0076] It should be noted that, in the present invention, unless otherwise understood in conjunction with the entire text, any expression "A and / or B" should be interpreted as any of the following three parallel situations: A; B; A and B. Regarding the gas used in the chlorination roasting being Cl2 and / or HCl, it should be interpreted as any of the following three parallel situations: Cl2; HCl; or a mixture of Cl2 and HCl.

[0077] 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.

[0078] 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 directional removal of impurity elements in pegmatite-type high-purity quartz, characterized in that: The following steps are involved: (1) After the pegmatite-type high-purity quartz raw materials are crushed by a crusher, they are washed, ground and classified to obtain quartz sand raw materials of a certain particle size, and then subjected to gravity separation and flotation to obtain quartz concentrate. No high-temperature heat treatment is used before grinding; (2) adding the quartz concentrate to leachate A and performing constant temperature micro-pressure leaching in a closed container to obtain primary quartz sand after washing; the leachate A is a mixed acid of HF, HCl and HNO3, wherein the concentration of HF is 2 mol / L, the concentration ratio of HCl to HNO3 is 3:1~12:1, the concentration ratio of (HCl+HNO3) to HF is ≤3, and the sum of the concentrations of HF, HCl and HNO3 is ≥3 mol / L; the washing comprises: firstly repeatedly washing with high-purity water until the pH is neutral; and then performing ultrasonic washing with ethanol solution; (3) chlorination roasting and water quenching of the primary quartz sand to obtain intermediate quartz sand; the roasting temperature is 1050°C to 1150°C, the roasting gas is Cl2 and / or HCl, and the roasting time is ≥6h; the water quenching is performed by using high-purity water at room temperature; (4) The intermediate quartz sand is added to the leachate B for ultrasonic leaching, and then subjected to high-temperature heat treatment after washing to finally obtain high-purity quartz sand; the leachate B is a mixed acid of HF and HCl, wherein the concentration of HF is 0.5~2mol / L, and the concentration ratio of HCl to HF is ≤3.

2. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to claim 1, characterized in that: In step (1), quartz sand raw material with a particle size of -60 mesh to +180 mesh is obtained by grinding and classification.

3. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to claim 1 or 2, characterized in that: In step (2), the leaching temperature is 50°C to 160°C, the leaching time is ≥4h, and the liquid-solid ratio is 1:1 to 3:

1.

4. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to claim 3, characterized in that: In step (2), during the ultrasonic washing, the ultrasonic power is 1000W~1200W, the mass concentration of the ethanol solution is 10-30%, and the liquid-solid ratio is ≥1.

5. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to claim 4, characterized in that: In step (2), during the ultrasonic washing, the liquid-to-solid ratio is 10:1 to 3:

1.

6. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to claim 4, characterized in that: In step (2), the washing includes: first washing with high-purity water for 5 to 10 times, and then ultrasonically washing with ethanol solution for 2 to 3 times.

7. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to any one of claims 1-2 and 4-6, characterized in that: In step (3), the primary quartz sand is subjected to chlorination roasting in a tubular furnace, and then immediately water quenched and centrifuged to obtain the intermediate quartz sand.

8. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to any one of claims 1-2 and 4-6, characterized in that: In step (4), the ultrasonic leaching time is 1 h to 3 h, the temperature is room temperature, the ultrasonic power is 1000 W to 1200 W, and the liquid-solid ratio is 1:1 to 5:

1.

9. The method for directional removal of impurity elements in pegmatite-type high-purity quartz according to any one of claims 1-2 and 4-6, characterized in that: In step (4), the temperature of the high-temperature heat treatment is 1100° C. to 1200° C., and the time is 0.5 h to 5 h.

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