Purification method of quartz sand and quartz sand prepared by purification method

Abstract

The invention belongs to the technical field of quartz sand purification, and relates to a quartz sand purification method and quartz sand prepared by the same. The invention provides a quartz sand purification method, which comprises: carrying out steam explosion on a quartz sand sample, roasting, carrying out first hot-pressing acid leaching, washing and drying, immersing in a deep eutectic solvent, washing and drying, and finally carrying out second hot-pressing acid leaching and washing and drying to complete the purification of the quartz sand, the eutectic solvent is a transparent liquid solvent formed by mixing a hydrogen bond acceptor compound and a hydrogen bond donor compound and then heating the mixture; the hydrogen bond acceptor compound is choline chloride, and the hydrogen bond donor compound is at least one of acetic acid, citric acid and malonic acid; the molar ratio of the hydrogen bond acceptor compound to the hydrogen bond donor compound is (1: 2)-(2: 1). The method aims to solve the technical problems that when quartz sand is purified through a roasting-pickling process, the removal effect on Al and Fe elements is insufficient, and the requirement for preparing higher-purity quartz sand cannot be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of quartz sand purification, and relates to a purification method of quartz sand and the quartz sand obtained thereby. Background Art

[0002] Quartz, with the main component of SiO2, is a typical non-metallic mineral with relatively rich reserves. The occurrence states of impurities in quartz are mainly divided into mineral inclusions, fluid inclusions and lattice impurities, and purification is mainly carried out through combined processes such as magnetic separation - flotation - acid leaching. The roasting - pickling process for purifying quartz sand is one of the important purification methods for quartz sand. To reduce the Gibbs free energy of the decomposition of quartz sand raw ore and increase the reaction degree, it is a common means to destroy its crystal structure before hot - pressure acid leaching. Oxidative roasting pretreatment is often used to activate the mineral inclusion muscovite in vein quartz. Due to its unique layered structure, muscovite is prone to losing interlayer water during oxidative roasting, resulting in an increase in the interlayer spacing, which is beneficial for the leaching agent to enter the interlayer of muscovite; high - temperature roasting not only causes muscovite to remove interlayer water, but also further promotes the destruction of the muscovite structure, generating an active Si - O - Al structure, and these active structures may react with quartz under specific conditions to form secondary phases; for the encapsulated mineral muscovite, the difference in thermal expansibility and cold shrinkage will cause cracks to occur, exposing the inclusion muscovite to the leaching solution, providing greater chemical activity for quartz crystals and being beneficial for chemical leaching purification. Under high - temperature and high - pressure conditions in hot - pressure acid leaching, the acid solution can penetrate into stress - concentrated areas such as gaps, and then enter the interior of the particles to dissolve the impurity phases, improving the impurity removal rate.

[0003] Currently, the research on quartz sand purification focuses on metal impurities such as iron and aluminum. These two metal impurities are widely distributed in quartz sand. In addition to existing on the surface or in the crystal of quartz particles in the form of inclusions, a part of the impurities also exist in the quartz lattice in the form of isomorphic substitution. For example, too much aluminum impurity in the lattice will cause crystallization of quartz products due to strong chemical bonds, thus affecting their performance. As a raw material to replace crystal, using ordinary quartz, especially vein quartz, to prepare high - purity quartz has become the focus of research. Although the roasting - pickling process for purifying quartz sand has achieved good purification of quartz sand, it is still necessary to further obtain higher - purity quartz sand to meet the requirements of high - tech industries for high - purity quartz. Summary of the Invention

[0004] The purpose of the present invention is to solve the technical problem that it is difficult to further improve the purity of quartz sand by the existing roasting - pickling process. In this regard, the present invention provides a purification method of quartz sand and the quartz sand obtained thereby to solve this need in the field.

[0005] On the one hand, the present invention relates to a method for purifying quartz sand, which includes: subjecting a quartz sand sample to steam explosion and then roasting, followed by first hot-press acid leaching, washing with water and drying, then immersing in a deep eutectic solvent, washing with water and drying, and finally performing second hot-press acid leaching, washing with water and drying to complete the purification of the quartz sand;

[0006] The deep eutectic solvent is formed by mixing a hydrogen bond acceptor compound and a hydrogen bond donor compound and heating until a transparent liquid solvent is formed;

[0007] The hydrogen bond acceptor compound is choline chloride, and the hydrogen bond donor compound is at least one of acetic acid, citric acid, and malonic acid;

[0008] The molar ratio of the hydrogen bond acceptor compound to the hydrogen bond donor compound is 1:2 to 2:1.

[0009] Further, in the method for purifying quartz sand provided by the present invention, the time of steam explosion is 30 to 600 s, the temperature is 140 to 200 °C, and the initial pressure is 0.5 to 3.0 Mpa.

[0010] Further, in the method for purifying quartz sand provided by the present invention, the roasting temperature is 800 to 1000 °C, and the time is 4 to 8 h.

[0011] Further, in the method for purifying quartz sand provided by the present invention, the acid used in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from at least one of hydrochloric acid, nitric acid, or hydrofluoric acid.

[0012] Further, in the method for purifying quartz sand provided by the present invention, the volume concentration of the acid used in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 30 to 50%.

[0013] Further, in the method for purifying quartz sand provided by the present invention, the acid leaching temperature in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 250 to 300 °C.

[0014] Further, in the method for purifying quartz sand provided by the present invention, the acid leaching time in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 5 to 7 h.

[0015] Further, in the method for purifying quartz sand provided by the present invention, any water washing is carried out using deionized water until neutral.

[0016] Further, in the method for purifying quartz sand provided by the present invention, the reaction temperature for immersing in the deep eutectic solvent is 60 to 100 °C, and the reaction time is 1 to 3 h.

[0017] On the other hand, the present invention relates to a quartz sand prepared by the purification method of the quartz sand described above.

[0018] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0019] The present invention solves the problem of insufficient removal effect of Al and Fe elements during the purification of quartz sand by the roasting-pickling process, meeting the preparation requirements of higher-purity quartz sand; through the purification method of the present invention, silicon dioxide with a purity > 99.99% can be prepared, significantly improving the purity of quartz sand; the present invention introduces steam explosion and deep eutectic solvents, effectively improving the process of oxidative roasting-hot pressure acid leaching for purifying quartz sand; steam explosion synergistically with oxidative roasting increases the pore channels of the quartz sand sample, generates a large number of cracks, improves the effect of hot pressure acid leaching of quartz sand, and at the same time can also destroy the surface structure of quartz sand to form microcracks, which is beneficial to the migration and dissolution of impurities; deep eutectic solvents effectively treat the product layer and fluid film generated by hot pressure acid leaching, further promoting the impurity removal by hot pressure acid leaching and more effectively removing impurities; the present invention selects acetic acid, citric acid, malonic acid, etc. as hydrogen bond donor compounds, avoiding the problem that amide group-containing compounds are prone to adhere to the surface of quartz sand and block the crack channels; by optimizing process parameters such as steam explosion, roasting, and hot pressure acid leaching, the present invention achieves a better purification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0021] Figure 1 It is a schematic diagram of the quartz sand sample to be purified.

[0022] Figure 2 It is a test diagram of the influence of acid combinations with different ratios on iron removal.

[0023] Figure 3 It is a test diagram of the influence of different hot pressure acid leaching times on iron removal.

[0024] Figure 4 It is a test diagram of the influence of different oxidative roasting times on iron removal.

[0025] Figure 5 It is a test diagram of the influence of different treatments on aluminum removal. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Next, the technical solutions of the present invention will be described in conjunction with embodiments. However, the present invention is not limited to the following embodiments. The experimental methods and detection methods described in each embodiment are conventional methods unless otherwise specified; the reagents and materials described, unless otherwise specified, can be obtained on the market. The % in the following embodiments is the mass percentage content unless otherwise specified. The ratios in the following embodiments are mass ratios unless otherwise specified.

[0027] In the following embodiments, the quartz sand samples to be purified are as Figure 1 shown, and their main impurity element contents and purities are shown in Table 1.

[0028] Table 1 Purity and main impurity contents of the quartz sand samples to be purified

[0029] Serial Number Test Item Norm / Technical Requirement Test Result Single Item Judgment Test Method NO. Test Item Norm Test Result Evaluation Test Standard 1 <![CDATA[Silicon dioxide (SiO2), %]]> / 99.938 / GB / T 3284-2015 2 Aluminum (Al), μg / g / 303.46 / GB / T 3284-2015 3 Calcium (Ca), μg / g / 5.32 / GB / T 3284-2015 4 Iron (Fe), μg / g / 163.08 / GB / T 3284-2015 5 Sodium (Na), μg / g / 19.38 / GB / T 3284-2015 6 Potassium (K), μg / g / 76.07 / GB / T 3284-2015 7 Lithium (Li), μg / g / Not Detected (<0.1) / GB / T 3284-2015 8 Magnesium (Mg), μg / g / 16.18 / GB / T 3284-2015 9 Chromium (Cr), μg / g / Not Detected (<0.1) / SJ / T 3228.7-2016 10 Nickel (Ni), μg / g / Not Detected (<0.1) / GB / T 3284-2015 11 Boron (B), μg / g / 15.28 / GB / T 3284-2015 12 Manganese (Mn), μg / g / 8.27 / GB / T 3284-2015 13 Copper (Cu), μg / g / Not Detected (<0.1) / GB / T 3284-2015 14 Titanium (Ti), μg / g / 6.29 / GB / T 3284-2015 15 Others, μg / g / 6.67 / /

[0030] As can be seen from Table 1, the elemental contents of Al and Fe account for 75.25% of the total impurity content, and they are the main impurity elements of this quartz sand sample.

[0031] Example 1

[0032] This example provides a process flow of oxidative roasting - hot - press acid leaching.

[0033] During the chemical treatment process, acid leaching is a commonly used purification method, which can be divided into two categories: atmospheric - pressure acid leaching and hot - press acid leaching according to different pressure conditions. Atmospheric - pressure acid leaching refers to acid leaching carried out under a constant pressure, while hot - press acid leaching involves a higher temperature and pressure environment to accelerate the reaction rate and improve the purification efficiency. Hydrochloric acid has good metal - dissolving ability and complexing properties for metal ions; nitric acid can effectively oxidize metal elements to form soluble salts, but its effect is not good when used alone; hydrofluoric acid has obvious corrosion effects on silica, mica, feldspar, etc. Adding hydrofluoric acid can significantly improve the iron - removal effect. Currently, it is found that the effect of using a mixed acid to remove impurities during acid leaching is relatively good. Quartz will be dissolved by hydrofluoric acid, so the concentration of hydrofluoric acid in the mixed acid should not be too high. In this example, taking iron as the main impurity element, the optimal process parameters of oxidative roasting - hot - press acid leaching are investigated.

[0034] (1) Influence of different acid combinations with different ratios on iron removal.

[0035] Weigh 100 g of quartz sand sample in each group and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for 6 h of roasting treatment on the sample. After the roasting treatment, use crucible tongs to take out the sample from the hearth and immediately pour it into the pre-prepared acid solution for hot-pressure acid leaching. The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. Put 10 g of quartz sand sample in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%, the leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 8 h.

[0036] In this part, the iron removal effect of the mixed acid of hydrochloric acid, nitric acid and hydrofluoric acid under the condition of volume ratio of 3~1:3~1:1 is mainly investigated. By volume ratio, the experiments are set as hydrochloric acid:nitric acid:hydrofluoric acid = 3:3:1, hydrochloric acid:nitric acid:hydrofluoric acid = 2:3:1, hydrochloric acid:nitric acid:hydrofluoric acid = 1:3:1, hydrochloric acid:nitric acid:hydrofluoric acid = 3:2:1, hydrochloric acid:nitric acid:hydrofluoric acid = 3:1:1. There are 3 specimens in each group of experiments, and the experimental results are as Figure 2 shown.

[0037] From Figure 2 it can be seen that when using hot-pressure acid leaching to remove impurities in quartz sand, by volume ratio, the best impurity removal effect is achieved with the mixed acid of hydrochloric acid:nitric acid:hydrofluoric acid = 3:2:1.

[0038] (2)The influence of different hot-pressure acid leaching times on iron removal.

[0039] Weigh 100 g of quartz sand sample in each group and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for 6 h of roasting treatment on the sample. After the roasting treatment, use crucible tongs to take out the sample from the hearth and immediately pour it into the pre-prepared acid solution for hot-pressure acid leaching. The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. Put 10 g of quartz sand sample in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume ratio of the selected mixed acid of hydrochloric acid:nitric acid:hydrofluoric acid is 3:2:1, the leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction times are set as 2 h, 4 h, 5 h, 6 h, 8 h, 10 h, 12 h in the experiments. There are 3 specimens in each group of experiments, and the experimental results are as Figure 3 shown.

[0040] From Figure 3 it can be seen that when using hot-pressure acid leaching to remove impurities in quartz sand, before the reaction time reaches 6 h, the removal rates of various impurity metal elements increase rapidly. When the reaction time reaches 6 h, the impurity removal efficiency begins to enter a plateau period. Even if the reaction time of hot-pressure acid leaching is increased, the removal rates of impurity elements will no longer increase significantly.

[0041] (3)The influence of different oxidation roasting times on iron removal.

[0042] Weigh 100 g of quartz sand samples in each group and place them in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the samples. The oxidation roasting tests are set for 2 h, 4 h, 5 h, 6 h, 8 h, and 10 h. After the roasting treatment, use crucible tongs to take out the specimens from the hearth and immediately pour them into the pre-prepared acid solution for hot-pressure acid leaching. The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. Place 10 g of quartz sand samples in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%. The mixed acid selected is hydrochloric acid:nitric acid:hydrofluoric acid with a volume ratio of 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 8 h. There are 3 specimens in each group of experiments, and the experimental results are as Figure 4 shown.

[0043] It can be Figure 4 seen that when purifying quartz sand by oxidation roasting - hot-pressure acid leaching, in the initial stage of high-temperature roasting, the crystal form transformation rate of quartz sand significantly accelerates, and at the same time, the removal efficiency of iron elements during the pickling treatment also shows a rapid increasing trend; however, as the holding time continues to extend, the change rate of quartz sand crystal form transformation gradually flattens out. At this time, the impurity removal efficiency begins to enter a plateau period, and even if the reaction time of hot-pressure acid leaching is increased, the removal rate of impurity elements no longer increases significantly.

[0044] In summary, in the process of purifying quartz sand by oxidation roasting - hot-pressure acid leaching, weigh 100 g of quartz sand samples in each group and place them in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the samples for 6 h. After the roasting treatment, use crucible tongs to take out the specimens from the hearth and immediately pour them into the pre-prepared acid solution for hot-pressure acid leaching. The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. Place 10 g of quartz sand samples in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%. The mixed acid selected is hydrochloric acid:nitric acid:hydrofluoric acid with a volume ratio of 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 8 h. At this time, even if the oxidation roasting temperature is further increased, the oxidation roasting time is extended, the volume concentration of acid in the mixed acid leaching solution is increased, the leaching temperature is increased, the liquid-solid ratio is increased, and the hot-pressure acid leaching reaction time is extended, the removal rate of impurity elements no longer increases significantly, and it is difficult to obtain a higher purity quartz product.

[0045] After adopting the above optimal oxidation roasting - hot-pressure acid leaching process for purifying quartz sand, the purity and main impurity contents of the prepared quartz sand are shown in Table 2.

[0046] Table 2 Purity and main impurity contents of quartz sand samples after oxidation roasting - hot-pressure acid leaching purification

[0047] Serial Number Test Item Norm / Technical Requirement Test Result Single Item Judgment Test Method NO. Test Item Norm Test Result Evaluation Test Standard 1 <![CDATA[Silicon dioxide (SiO2), %]]> / 99.977 / GB / T 3284-2015 2 Aluminum (Al), μg / g / 124.43 / GB / T 3284-2015 3 Calcium (Ca), μg / g / 3.65 / GB / T 3284-2015 4 Iron (Fe), μg / g / 28.91 / GB / T 3284-2015 5 Sodium (Na), μg / g / 10.56 / GB / T 3284-2015 6 Potassium (K), μg / g / 30.61 / GB / T 3284-2015 7 Lithium (Li), μg / g / Not Detected (<0.1) / GB / T 3284-2015 8 Magnesium (Mg), μg / g / 8.11 / GB / T 3284-2015 9 Chromium (Cr), μg / g / Not Detected (<0.1) / SJ / T 3228.7-2016 10 Nickel (Ni), μg / g / Not Detected (<0.1) / GB / T 3284-2015 11 Boron (B), μg / g / 9.18 / GB / T 3284-2015 12 Manganese (Mn), μg / g / 4.96 / GB / T 3284-2015 13 Copper (Cu), μg / g / Not Detected (<0.1) / GB / T 3284-2015 14 Titanium (Ti), μg / g / 5.44 / GB / T 3284-2015 15 Others, μg / g / 4.15 / /

[0048] As can be seen from Table 2, under the optimal oxidation roasting - hot - press acid leaching process for purifying quartz sand, the impurity removal rate reached 62.90%, and silicon dioxide with a purity of 99.977% was finally obtained, meeting the quality requirements of low - end high - purity quartz sand products (SiO2≥99.950%), but it was difficult to obtain quartz sand with higher purity.

[0049] Example 2

[0050] This example provides the improvement effect of steam explosion and deep eutectic solvents on the oxidation roasting - hot - press acid leaching process for purifying quartz sand.

[0051] Experimental group 1: Take a quartz sand sample and put it into a steam explosion tank. Set the steam explosion time to 30 s, the temperature to 140 °C, and the initial pressure to 0.5 Mpa. Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the sample for 6 h of oxidation roasting. After the roasting treatment, use crucible tongs to take out the specimen from the hearth and immediately pour it into a pre - prepared acid solution for the first hot - press acid leaching. While performing the first hot - press acid leaching, prepare a deep eutectic solvent. The deep eutectic solvent is a mixture of choline chloride and acetic acid in a molar ratio of 1:2. Add it to a round - bottom flask and heat it in a water bath at 60 °C until a transparent liquid solvent is formed. After the first hot - press acid leaching is completed, wash the specimen with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C. After drying, immerse it in the deep eutectic solvent and keep heating in a water bath for 1 h. After the deep eutectic solvent treatment is completed, wash the specimen with deionized water until it is neutral, and then perform the second hot - press acid leaching. After the second hot - press acid leaching is completed, wash the specimen with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C to obtain purified quartz sand. The reaction conditions for the first hot - press acid leaching and the second hot - press acid leaching are the same. Specifically: it is carried out in a high - pressure leaching reaction device. Each group of experiments places 10 g of quartz sand samples. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume ratio of the mixed acid is hydrochloric acid: nitric acid: hydrofluoric acid = 3:2:1. The leaching temperature is 260 °C, the liquid - to - solid ratio is 3 mL:1 g, and the reaction time is 4 h.

[0052] Experimental group 2: Take the quartz sand sample and put it into the steam explosion tank. Set the steam explosion time to 60 s, the temperature to 160 °C, and the initial pressure to 1.0 Mpa; Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting treatment of the sample, with oxidative roasting for 6 h; After the roasting treatment, use crucible tongs to take out the specimen from the furnace hearth and immediately pour it into the pre-prepared acid solution for the first hot-pressure acid leaching; While performing the first hot-pressure acid leaching, prepare a deep eutectic solvent. The deep eutectic solvent is a mixture of choline chloride, acetic acid, and citric acid in a molar ratio of 1:0.5:0.5. Add it to a round-bottom flask and heat it in a water bath at 70 °C until a transparent liquid solvent is formed; After the first hot-pressure acid leaching is completed, wash the specimen with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C. After drying, immerse it in the deep eutectic solvent and maintain water bath heating for 2 h; After the deep eutectic solvent treatment is completed, wash the specimen with deionized water until it is neutral, and then perform the second hot-pressure acid leaching; After the second hot-pressure acid leaching is completed, wash the specimen with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C to obtain purified quartz sand; The reaction conditions for the first hot-pressure acid leaching and the second hot-pressure acid leaching are the same. Specifically: It is carried out in a high-pressure leaching reaction device. Each group of experiments places 10 g of quartz sand samples. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume ratio of the mixed acid selected is hydrochloric acid: nitric acid: hydrofluoric acid = 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 4 h.

[0053] Experimental group 3: Take the quartz sand sample and put it into the steam explosion tank. Set the steam explosion time to 300 s, the temperature to 160 °C, and the initial pressure to 1.0 Mpa; Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting treatment of the sample. Roast it oxidatively for 6 h; After the roasting treatment, use crucible tongs to take out the sample from the furnace hearth and immediately pour it into the pre-prepared acid solution for the first hot-pressure acid leaching; While carrying out the first hot-pressure acid leaching, prepare a deep eutectic solvent. The deep eutectic solvent is a mixture of choline chloride, acetic acid, citric acid, and malonic acid in a molar ratio of 1:0.3:0.3:0.3. Add it to a round-bottom flask and heat it in a water bath at 80 °C until a transparent liquid solvent is formed; After the first hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C. After drying, immerse it in the deep eutectic solvent and keep heating in a water bath for 2 h; After the deep eutectic solvent treatment is completed, wash the sample with deionized water until it is neutral, and then carry out the second hot-pressure acid leaching; After the second hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C to obtain purified quartz sand; The reaction conditions for the first hot-pressure acid leaching and the second hot-pressure acid leaching are the same. Specifically: Carry out the reaction in a high-pressure leaching reaction device. Put 10 g of quartz sand sample in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume ratio of the mixed acid selected is hydrochloric acid: nitric acid: hydrofluoric acid = 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 4 h.

[0054] Experimental group 4: Take the quartz sand sample and put it into the steam explosion tank. Set the steam explosion time to 600 s, the temperature to 200 °C, and the initial pressure to 3.0 Mpa; Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting treatment of the sample. Conduct oxidative roasting for 6 h; After the roasting treatment, use crucible tongs to take out the sample from the furnace hearth and immediately pour it into the pre-prepared acid solution for the first hot-pressure acid leaching; While conducting the first hot-pressure acid leaching, prepare a deep eutectic solvent. The deep eutectic solvent is a mixture of choline chloride, citric acid, and malonic acid in a molar ratio of 2:0.5:0.5. Add it to a round-bottom flask and heat it in a water bath at 100 °C until a transparent liquid solvent is formed; After the first hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C. After drying, immerse it in the deep eutectic solvent and keep heating in a water bath for 3 h; After the treatment with the deep eutectic solvent is completed, wash the sample with deionized water until it is neutral, and then conduct the second hot-pressure acid leaching; After the second hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C to obtain purified quartz sand; The reaction conditions for the first hot-pressure acid leaching and the second hot-pressure acid leaching are the same. Specifically: Conduct in a high-pressure leaching reaction device. Put 10 g of quartz sand sample in each group of experiments. The volume concentration of acid in the mixed acid leaching solution is 40%. The volume concentration of acid in the mixed acid leaching solution is 40%. The mixed acid selects hydrochloric acid: nitric acid: hydrofluoric acid with a volume ratio of 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 4 h.

[0055] Control Group 1: Take a quartz sand sample and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the sample. Perform oxidative roasting for 6 h. After the roasting treatment, use crucible tongs to take out the sample from the hearth and immediately pour it into a pre-prepared acid solution for the first hot-pressure acid leaching. While performing the first hot-pressure acid leaching, prepare a deep eutectic solvent. The deep eutectic solvent is a mixture of choline chloride, acetic acid, and citric acid in a molar ratio of 1:0.5:0.5. Add it to a round-bottom flask and heat it in a water bath at 70 °C until a transparent liquid solvent is formed. After the first hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C. After drying, immerse it in the deep eutectic solvent and keep heating in a water bath for 2 h. After the deep eutectic solvent treatment is completed, wash the sample with deionized water until it is neutral, and then perform the second hot-pressure acid leaching. After the second hot-pressure acid leaching is completed, wash the sample with deionized water until it is neutral, place it in a vacuum drying oven for drying at 100 °C to obtain purified quartz sand. The reaction conditions for the first hot-pressure acid leaching and the second hot-pressure acid leaching are the same. Specifically, it is carried out in a high-pressure leaching reaction device. For each group of experiments, 10 g of quartz sand samples are placed. The volume concentration of acid in the mixed acid leaching solution is 40%. The mixed acid selects hydrochloric acid:nitric acid:hydrofluoric acid with a volume ratio of 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 4 h.

[0056] Control Group 2: Take a quartz sand sample and put it into a steam explosion tank. Set the steam explosion time to 60 s, the temperature to 160 °C, and the initial pressure to 1.0 Mpa. Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the sample. Perform oxidative roasting for 6 h. After the roasting treatment, use crucible tongs to take out the sample from the hearth and immediately pour it into a pre-prepared acid solution for hot-pressure acid leaching. The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. For each group of experiments, 10 g of quartz sand samples are placed. The volume concentration of acid in the mixed acid leaching solution is 40%. The mixed acid selects hydrochloric acid:nitric acid:hydrofluoric acid with a volume ratio of 3:2:1. The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL:1 g, and the reaction time is 8 h.

[0057] Control Group 3: Take a quartz sand sample and put it into a steam explosion tank. Set the steam explosion time to 60 s, the temperature to 160 °C, and the initial pressure to 1.0 Mpa; Take the product after steam explosion and place it in an alumina crucible. Put the crucible in the hearth of a pit furnace and heat it to 900 °C for roasting the sample. Roast it oxidatively for 6 h; After the roasting treatment, use crucible tongs to take out the sample from the furnace hearth and immediately pour it into a pre-prepared acid solution for hot-pressure acid leaching; The hot-pressure acid leaching treatment is carried out in a high-pressure leaching reaction device. Each group of experiments places 10 g of quartz sand samples. The mixed acid leaching solution is composed of a first mixed acid with a volume concentration of 40% and a second mixed acid with a volume concentration of 10%. In the first mixed acid, the volume ratio of hydrochloric acid: nitric acid: hydrofluoric acid is 3:2:1, and the second mixed acid is a mixture of choline chloride, acetic acid and citric acid in a molar ratio of 1:0.5:0.5; The leaching temperature is 260 °C, the liquid-solid ratio is 3 mL: 1 g, and the reaction time is 8 h.

[0058] In this example, aluminum is the main impurity element. The removal effects of different treatment groups are investigated. Taking the treatment result of the optimal oxidative roasting - hot-pressure acid leaching process for purifying quartz sand as the control group, the test results are as Figure 5 shown.

[0059] As Figure 5 can be seen, steam explosion and deep eutectic solvents have a good improvement effect on the oxidative roasting - hot-pressure acid leaching process for purifying quartz sand. However, with the increase of the steam explosion time, temperature and initial pressure, the improvement effect tends to level off. From Control Group 1 and Control Group 2, it can be seen that the improvement effect of steam explosion on the oxidative roasting - hot-pressure acid leaching process for purifying quartz sand is relatively small compared with deep eutectic solvents. And from the further experiment of Control Group 3, it can be known that the improvement effect of deep eutectic solvents on hot-pressure acid leaching is not due to complexing the impurities in it. For this reason, one purified quartz sand sample from the 3 replicates of Test Group 3 was sent for inspection, and the results are shown in Table 3.

[0060] Table 3 Purity and Main Impurity Contents of Purified Quartz Sand Samples in Test Group 3

[0061] Serial Number Test Item Norm / Technical Requirement Test Result Single Item Judgment Test Method NO. Test Item Norm Test Result Evaluation Test Standard 1 <![CDATA[Silicon dioxide (SiO2), %]]> / 99.998 / GB / T 3284-2015 2 Aluminum (Al), μg / g / 3.37 / GB / T 3284-2015 3 Calcium (Ca), μg / g / 1.31 / GB / T 3284-2015 4 Iron (Fe), μg / g / 2.65 / GB / T 3284-2015 5 Sodium (Na), μg / g / 1.46 / GB / T 3284-2015 6 Potassium (K), μg / g / 2.12 / GB / T 3284-2015 7 Lithium (Li), μg / g / Not detected (<0.1) / GB / T 3284-2015 8 Magnesium (Mg), μg / g / 1.46 / GB / T 3284-2015 9 Chromium (Cr), μg / g / Not detected (<0.1) / SJ / T 3228.7-2016 10 Nickel (Ni), μg / g / Not detected (<0.1) / GB / T 3284-2015 11 Boron (B), μg / g / 1.95 / GB / T 3284-2015 12 Manganese (Mn), μg / g / 1.37 / GB / T 3284-2015 13 Copper (Cu), μg / g / Not detected (<0.1) / GB / T 3284-2015 14 Titanium (Ti), μg / g / 1.42 / GB / T 3284-2015 15 Others, μg / g / 2.89 / /

[0062] As can be seen from Table 3, the silica finally prepared by the present invention has a purity > 99.99%, and quartz sand with a higher purity can be obtained. Based on the above test results, the improvement effect of steam explosion on the process of oxidative roasting - hot - press acid leaching for purifying quartz sand may be that, in cooperation with oxidative roasting, it increases the pore channels of the quartz sand sample, generates a large number of cracks, improves the effect of hot - press acid leaching of quartz sand. It can not only destroy the surface structure of flaky quartz sand, make more debris transform into active debris, and form rich micro - cracks on the surface and between layers, which is beneficial to the migration and dissolution of impurities. The improvement effect of deep eutectic solvent on the process of oxidative roasting - hot - press acid leaching for purifying quartz sand may be that it can better handle the product layer and fluid film formed around the particles during hot - press acid leaching, facilitating the removal of impurities by hot - press acid leaching and more effectively removing impurities. In addition, the hydrogen - bond donor compound should not be a compound containing an amide group, as it is easy to adhere to the surface of quartz sand, block the crack channels, and affect the subsequent hot - press acid leaching effect. Generally speaking, steam explosion can cooperate with oxidative roasting to increase the pore channels of the quartz sand sample, but the purification effect of steam explosion alone on quartz sand is small. The reason is that the increase in pore channels is beneficial to improving the impurity removal rate of hot - press acid leaching, but at the same time, it will generate the product layer and fluid film around the particles faster, hindering the further impurity removal of hot - press acid leaching. By adopting the deep eutectic solvent in this application, within a similar treatment time, the product layer and fluid film generated during hot - press acid leaching are handled, thus making full use of the increased pore channels of the quartz sand sample and achieving a better impurity removal effect.

[0063] As described above, the basic principle, main features and advantages of the present invention are well described. The above embodiments and the description are only for describing the preferred embodiments of the present invention. The present invention is not limited by the above embodiments. Without departing from the spirit and scope of the present invention, various changes and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the present invention.

Claims

1. A method for purifying quartz sand, characterized in that, Comprising: The quartz sand sample is steam-exploded and then calcined, followed by first hot-press acid leaching, washed with water and dried, then immersed in a deep eutectic solvent, washed with water and dried, and finally subjected to second hot-press acid leaching, washed with water and dried to complete the purification of the quartz sand; The deep eutectic solvent is formed by mixing a hydrogen bond acceptor compound and a hydrogen bond donor compound and heating until a transparent liquid solvent is formed; The hydrogen bond acceptor compound is choline chloride, and the hydrogen bond donor compound is at least one of acetic acid, citric acid, and malonic acid; The molar ratio of the hydrogen bond acceptor compound to the hydrogen bond donor compound is 1:2 to 2:

1.

2. The purification method of quartz sand according to claim 1, wherein The time of the steam explosion is 30 to 600 s, the temperature is 140 to 200 °C, and the initial pressure is 0.5 to 3.0 Mpa.

3. The purification method of quartz sand according to claim 1, characterized in that, The temperature of the calcination is 800 to 1000 °C, and the time is 4 to 8 h.

4. The purification method of quartz sand according to claim 1, characterized in that, The acid used in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from at least one of hydrochloric acid, nitric acid, or hydrofluoric acid.

5. The purification method of quartz sand according to claim 1, wherein, The volume concentration of the acid used in the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 20 to 50%.

6. The purification method of quartz sand according to claim 1, wherein The acid leaching temperature of the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 250 to 300 °C.

7. The purification method of quartz sand according to claim 1, characterized in that, The acid leaching time of the first hot-press acid leaching or the second hot-press acid leaching is independently selected from 5 to 7 h.

8. The purification method of quartz sand according to claim 1, characterized in that, Any water wash is to wash with deionized water until neutral.

9. The purification method of quartz sand according to claim 1, wherein, The reaction temperature for immersing in the deep eutectic solvent is 60 to 100 °C, and the reaction time is 1 to 3 h.

10. A kind of quartz sand, characterized in that, Obtained by the purification method of quartz sand according to any one of claims 1 to 9.

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