A method for purifying quartz sand and quartz sand obtained therefrom

Abstract

The present invention belongs to the technical field of quartz sand purification and relates to a method for purifying quartz sand and quartz sand obtained therefrom. The present invention provides a method for purifying quartz sand, comprising: roasting a quartz sand sample after steam explosion, then performing a first hot-pressing acid leaching, washing and drying, and then immersing it in a low eutectic solvent, washing and drying, and finally performing a second hot-pressing acid leaching, washing and drying to complete the purification of the quartz sand; the low eutectic solvent is a mixture of a hydrogen bond acceptor compound and a hydrogen bond donor compound, heated 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 1:2~2:1. The present invention intends to solve the technical problem that when quartz sand is purified by the roasting-acid washing process, the removal effect of Al and Fe elements is insufficient, and the preparation demand of higher purity quartz sand cannot be met.

Description

Technical Field

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

[0002] Quartz, primarily composed of SiO2, is a typical non-metallic mineral with relatively abundant reserves. Impurities in quartz are primarily found as mineral inclusions, fluid inclusions, and lattice impurities. Purification is primarily achieved through a combination of magnetic separation, flotation, and acid leaching. Roasting and acid washing are key methods for purifying quartz sand. To reduce the Gibbs free energy of decomposition and increase the reaction rate, destroying the quartz sand ore's crystal structure prior to hot-pressing and acid leaching is a common method. Oxidative roasting pretreatment is often used to activate the mineral inclusions of muscovite within vein quartz. Due to its unique layered structure, muscovite easily loses interlayer water during oxidation roasting, resulting in an increase in interlayer spacing, which facilitates the entry of leaching agents into the muscovite interlayers. High-temperature roasting not only removes interlayer water from muscovite but also further promotes structural destruction, generating active Si-O-Al structures. These active structures may also react with quartz to form secondary phases under certain conditions. For the mineral muscovite, the difference in thermal expansion and cold contraction can lead to cracks, exposing the included muscovite to the leachate, providing greater chemical activity for the quartz crystals and facilitating chemical leaching and purification. Under the high temperature and high pressure conditions of hot-pressed acid leaching, the acid can penetrate into stress concentration points such as crevices, and then enter the interior of the particles to dissolve impurities, thereby improving the impurity removal rate.

[0003] Currently, research on quartz sand purification focuses on metallic impurities such as iron and aluminum. These two metallic impurities are widely distributed in quartz sand. In addition to existing as inclusions on the surface of quartz particles or within the crystals, some impurities also exist in the quartz lattice in the form of isomorphs. For example, excessive aluminum impurities in the lattice can cause crystallization of quartz products due to strong chemical bonds, thereby affecting their performance. As a raw material to replace crystal, the production of high-purity quartz from ordinary quartz, especially vein quartz, has become a research focus. Although the roasting-pickling process for quartz sand purification has achieved good purification, further research is still needed to obtain quartz sand of higher purity to meet the demand for high-purity quartz in high-tech industries. Summary of the Invention

[0004] The present invention aims to solve the technical problem that the existing roasting-pickling process is difficult to further improve the purity of quartz sand. To this end, the present invention provides a method for purifying quartz sand and the quartz sand produced therefrom to address this need in the art.

[0005] In one aspect, the present invention relates to a method for purifying quartz sand, comprising: subjecting a quartz sand sample to steam explosion and then roasting it, then performing a first hot-pressing acid leaching, washing and drying it with water, then immersing it in a deep eutectic solvent, washing and drying it with water, and finally performing a second hot-pressing acid leaching, and washing and drying it with water to complete the purification of the quartz sand;

[0006] The deep eutectic solvent is a mixture of a hydrogen bond acceptor compound and a hydrogen bond donor compound, and then heated 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] Furthermore, in the quartz sand purification method provided by the present invention, the steam explosion time is 30-600s, the temperature is 140-200°C, and the initial pressure is 0.5-3.0Mpa.

[0010] Furthermore, in the quartz sand purification method provided by the present invention, the roasting temperature is 800-1000° C. and the time is 4-8 hours.

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

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

[0013] Furthermore, in the quartz sand purification method provided by the present invention, the acid leaching temperature of the first hot-pressing acid leaching or the second hot-pressing acid leaching is independently selected from 250-300°C.

[0014] Furthermore, in the quartz sand purification method provided by the present invention, the leaching time of the first hot-pressing acid leaching or the second hot-pressing acid leaching is independently selected from 5 to 7 hours.

[0015] Furthermore, in the quartz sand purification method provided by the present invention, any water washing is washing with deionized water until neutral.

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

[0017] On the other hand, the present invention relates to quartz sand, which is prepared by adopting the quartz sand purification method.

[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 that the roasting-pickling process is insufficient in removing Al and Fe elements when purifying quartz sand, and meets the demand for preparing higher-purity quartz sand; through the purification method of the present invention, silicon dioxide with a purity of more than 99.99% can be prepared, which significantly improves the purity of quartz sand; the present invention introduces steam explosion and low eutectic solvents to effectively improve the oxidation roasting-hot pressing acid leaching purification process of quartz sand; steam explosion and oxidation roasting cooperate to increase the pore channels of the quartz sand sample, generate a large number of cracks, and improve the hot pressing acid leaching of quartz sand The invention can achieve the effect of removing impurities from the quartz sand and destroy the surface structure of the quartz sand to form microcracks, which is conducive to the migration and dissolution of impurities; the low eutectic solvent effectively treats the product layer and fluid film generated by hot-pressing acid leaching, further promotes the impurity removal by hot-pressing acid leaching, and more effectively removes impurities; the present invention selects acetic acid, citric acid, malonic acid, etc. as hydrogen bond donor compounds to avoid the problem that amide-containing compounds easily adhere to the surface of the quartz sand and block the crack channels; by optimizing process parameters such as steam explosion, roasting, and hot-pressing acid leaching, the present invention achieves better purification effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 Schematic diagram of the quartz sand sample to be purified.

[0022] Figure 2 This is an experimental diagram showing the effects of different acid ratios on iron removal.

[0023] Figure 3 This is an experimental diagram showing the effect of different hot pressing and pickling times on iron removal.

[0024] Figure 4 This is an experimental diagram showing the effect of different oxidation roasting times on iron removal.

[0025] Figure 5 This is an experimental diagram showing the effects of different treatments on aluminum removal. DETAILED DESCRIPTION

[0026] The technical solutions of the present invention are described below with reference to the following examples. However, the present invention is not limited to the following examples. The experimental methods and detection methods described in each example are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified. The percentages in the following examples are percentages by mass unless otherwise specified. The ratios in the following examples are ratios by mass unless otherwise specified.

[0027] In the following examples, the quartz sand sample to be purified is as follows Figure 1 The content and purity of its main impurity elements are shown in Table 1.

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

[0029] Serial number Test items Indicators / technical requirements Test results Single judgment Detection 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 shown in Table 1, the element contents of Al and Fe account for 75.25% of the total impurity content, and are the main impurity elements of the quartz sand sample.

[0031] Example 1

[0032] This embodiment provides a process flow of oxidation roasting-hot pressing and acid leaching.

[0033] During the chemical treatment process, acid leaching is a commonly used purification method, which can be divided into two categories: normal pressure acid leaching and hot pressure acid leaching according to different pressure conditions. Normal pressure acid leaching refers to acid leaching under constant pressure, while hot pressure 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 has complexing properties for metal ions; nitric acid can effectively oxidize metal elements to form soluble salts, but the effect is poor when used alone; hydrofluoric acid has a significant dissolving effect on silica, mica, feldspar, etc., and the addition of hydrofluoric acid can significantly improve the iron removal effect. Current studies have found that the use of mixed acid to remove impurities during acid leaching is more effective, and 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, iron is used as the main impurity element to investigate the optimal process parameters of oxidative roasting-hot pressure acid leaching.

[0034] (1) The effect of different acid ratios on iron removal.

[0035] For each group, 100g of quartz sand sample was weighed and placed in an alumina crucible. The crucible was then placed in a pit furnace and heated to 900°C for 6 hours. After calcination, the sample was removed from the furnace using crucible tongs and immediately poured into a pre-prepared acid solution for hot-pressing acid leaching. Hot-pressing acid leaching was performed in a high-pressure leaching reactor. For each experiment, 10g of quartz sand sample was placed in the mixed acid leaching solution, with an acid concentration of 40% by volume, a leaching temperature of 260°C, a liquid-to-solid ratio of 3mL:1g, and a reaction time of 8 hours.

[0036] In this section, the focus is on the iron removal effect of mixed acids of hydrochloric acid, nitric acid and hydrofluoric acid at a volume ratio of 3~1:3~1:1. In terms of volume ratio, the experiments were 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, and hydrochloric acid: nitric acid: hydrofluoric acid = 3:1:1. Each group of experiments had 3 samples in total. The experimental results are as follows: Figure 2 shown.

[0037] Depend on Figure 2 It can be seen that when hot-pressed acid leaching is used to remove impurities from quartz sand, the best impurity removal effect is achieved by using a mixed acid of hydrochloric acid: nitric acid: hydrofluoric acid = 3:2:1 in terms of volume ratio.

[0038] (2) Effect of different hot pressing and acid leaching times on iron removal.

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

[0040] Depend on Figure 3 It can be seen that when hot-pressing acid leaching is used to remove impurities in quartz sand, when the reaction time is before 6 hours, the removal rate of various impurity metal elements increases rapidly. When the reaction time reaches 6 hours, the impurity removal efficiency begins to enter a plateau period. Even if the reaction time of hot-pressing acid leaching is increased, the removal rate of impurity elements no longer increases significantly.

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

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

[0043] Depend on Figure 4 It can be seen that during the oxidation roasting and hot-pressing acid leaching process of quartz sand purification, the crystal transformation rate of the quartz sand significantly accelerates during the initial high-temperature roasting stage, and the iron removal efficiency during the acid washing process also shows a rapid upward trend. However, as the holding time continues to increase, the rate of change in the quartz sand crystal transformation gradually slows down. At this point, the impurity removal efficiency begins to plateau, and even increasing the hot-pressing acid leaching reaction time does not significantly increase the impurity element removal rate.

[0044] In summary, in the oxidation roasting-hot-pressing acid leaching process for quartz sand purification, 100g of each quartz sand sample was placed in an alumina crucible. The crucible was then placed in a pit furnace and heated to 900°C for 6 hours. After calcination, the sample was removed from the furnace using crucible tongs and immediately poured into a pre-prepared acid solution for hot-pressing acid leaching. The hot-pressing acid leaching process was performed in a high-pressure leaching reactor. Each experimental group was loaded with 10g of quartz sand sample. The acid concentration in the mixed acid leaching solution was 40% by volume. The mixed acid ratio of hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1 by volume. The leaching temperature was 260°C, the liquid-to-solid ratio was 3mL:1g, and the reaction time was 8 hours. At this point, even if the oxidation roasting temperature is further increased, the oxidation roasting time is prolonged, the volume concentration of the acid in the mixed acid leaching solution is increased, the leaching temperature is increased, the liquid-solid ratio is increased, and the hot pressing acid leaching reaction time is prolonged, the removal rate of the impurity elements will no longer increase significantly, and it is difficult to obtain a higher purity quartz product.

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

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

[0047] Serial number Test items Indicators / technical requirements Test results Single judgment Detection 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 shown in Table 2, under the optimal oxidation roasting-hot pressing acid leaching process for quartz sand purification, the impurity removal rate reached 62.90%, and silicon dioxide with a purity of 99.977% was finally produced, which meets the quality requirements of low-end high-purity quartz sand products (SiO2 ≥ 99.950%), but it is difficult to obtain quartz sand with higher purity.

[0049] Example 2

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

[0051] Experimental group 1: A quartz sand sample was placed in a steam explosion tank, and the steam explosion time was set to 30s, the temperature was 140℃, and the initial pressure was 0.5Mpa; the product after steam explosion was placed in an alumina crucible, and the crucible was placed in the furnace of a pit furnace, heated to 900℃ for calcination of the sample, and oxidative calcination was performed for 6h; after calcination, the sample was taken out of the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for the first hot-pressing acid leaching; while performing the first hot-pressing acid leaching, a low eutectic solvent was prepared, which was a mixture of choline chloride and acetic acid in a molar ratio of 1:2, added to a round-bottom flask, and heated in a water bath at 60℃ until a transparent liquid solvent was formed; after the first hot-pressing acid leaching was completed, the sample was washed with deionized water until neutral, and placed in a vacuum drying oven for 10 The quartz sand was dried at 0°C, immersed in a low eutectic solvent and kept heated in a water bath for 1 hour; after the low eutectic solvent treatment, the sample was washed with deionized water until neutral, and then subjected to a second hot-pressing acid leaching; after the second hot-pressing acid leaching, the sample was washed with deionized water until neutral, placed in a vacuum drying oven for drying at 100°C to obtain purified quartz sand; the reaction conditions of the first hot-pressing acid leaching and the second hot-pressing acid leaching were the same, specifically: carried out in a high-pressure leaching reaction device, 10g of quartz sand sample was placed in each group of experiments, the volume concentration of acid in the mixed acid leaching solution was 40%, the volume concentration of acid in the mixed acid leaching solution was 40%, the mixed acid selected hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1 by volume, the leaching temperature was 260°C, the liquid-solid ratio was 3mL:1g, and the reaction time was 4h.

[0052] Experimental Group 2: A quartz sand sample was placed in a steam explosion tank, and the steam explosion time was set to 60s, the temperature was 160°C, and the initial pressure was 1.0Mpa; the product after steam explosion was placed in an alumina crucible, and the crucible was placed in the furnace of a pit furnace, heated to 900°C, and the sample was calcined for 6 hours of oxidation roasting; after roasting, the sample was removed from the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for the first hot-pressing acid leaching; while performing the first hot-pressing acid leaching, a low eutectic solvent was prepared, which was a mixture of choline chloride, acetic acid, and citric acid in a molar ratio of 1:0.5:0.5, added to a round-bottom flask, and heated in a water bath at 70°C until a transparent liquid solvent was formed; after the first hot-pressing acid leaching was completed, the sample was washed with deionized water until neutral and placed in a vacuum drying oven. After the leaching, the quartz sand was dried at 100 ° C., immersed in a low eutectic solvent and kept heated in a water bath for 2 hours; after the low eutectic solvent treatment, the sample was washed with deionized water until neutral, and then subjected to a second hot-pressing acid leaching; after the second hot-pressing acid leaching, the sample was washed with deionized water until neutral, placed in a vacuum drying oven for drying at 100 ° C. to obtain purified quartz sand; the reaction conditions of the first hot-pressing acid leaching and the second hot-pressing acid leaching were the same, specifically: carried out in a high-pressure leaching reaction device, 10 g of quartz sand sample was placed in each group of experiments, the volume concentration of acid in the mixed acid leaching solution was 40%, the volume concentration of acid in the mixed acid leaching solution was 40%, the mixed acid selected hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1 in a volume ratio, the leaching temperature was 260 ° C., the liquid-solid ratio was 3 mL:1 g, and the reaction time was 4 hours.

[0053] Experimental group 3: A quartz sand sample was placed in a steam explosion tank, and the steam explosion time was set to 300s, the temperature was 160℃, and the initial pressure was 1.0Mpa; the product after steam explosion was placed in an alumina crucible, and the crucible was placed in the furnace of a pit furnace, heated to 900℃, and the sample was roasted for 6 hours of oxidation roasting; after roasting, the sample was taken out of the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for the first hot-pressing acid leaching; while performing the first hot-pressing acid leaching, a low eutectic solvent was prepared, which was a mixture of choline chloride, acetic acid, citric acid, and malonic acid in a molar ratio of 1:0.3:0.3:0.3, added to a round-bottom flask, and heated in a water bath at 80℃ until a transparent liquid solvent was formed; after the first hot-pressing acid leaching was completed, the sample was washed with deionized water until neutral and placed in a vacuum flask. The sample was dried at 100°C in an empty drying oven, immersed in a low eutectic solvent and kept heated in a water bath for 2 hours; after the low eutectic solvent treatment, the sample was washed with deionized water until neutral, and then subjected to a second hot-pressing acid leaching; after the second hot-pressing acid leaching, the sample was washed with deionized water until neutral, placed in a vacuum drying oven and dried at 100°C to obtain purified quartz sand; the reaction conditions of the first hot-pressing acid leaching and the second hot-pressing acid leaching were the same, specifically: the high-pressure leaching reaction device was used, 10g of quartz sand sample was placed in each group of experiments, the volume concentration of acid in the mixed acid leaching solution was 40%, the volume concentration of acid in the mixed acid leaching solution was 40%, the mixed acid selected hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1, the leaching temperature was 260°C, the liquid-solid ratio was 3mL:1g, and the reaction time was 4h.

[0054] Experimental Group 4: A quartz sand sample was placed in a steam explosion tank, and the steam explosion time was set to 600s, the temperature was 200°C, and the initial pressure was 3.0Mpa; the product after steam explosion was placed in an alumina crucible, and the crucible was placed in the hearth of a pit furnace, heated to 900°C, and the sample was calcined for 6 hours of oxidation roasting; after roasting, the sample was removed from the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for the first hot-pressing acid leaching; while performing the first hot-pressing acid leaching, a low eutectic solvent was prepared, which was a mixture of choline chloride, citric acid, and malonic acid in a molar ratio of 2:0.5:0.5, added to a round-bottom flask, and heated in a water bath at 100°C until a transparent liquid solvent was formed; after the first hot-pressing acid leaching was completed, the sample was washed with deionized water until neutral and placed in a vacuum dryer. The sample was dried at 100°C in a vacuum oven, immersed in a low eutectic solvent and kept heated in a water bath for 3 hours; after the low eutectic solvent treatment, the sample was washed with deionized water until neutral, and then subjected to a second hot-pressing acid leaching; after the second hot-pressing acid leaching, the sample was washed with deionized water until neutral, placed in a vacuum drying oven for drying at 100°C to obtain purified quartz sand; the reaction conditions of the first hot-pressing acid leaching and the second hot-pressing acid leaching were the same, specifically: the high-pressure leaching reaction device was used, 10g of quartz sand sample was placed in each group of experiments, the volume concentration of acid in the mixed acid leaching solution was 40%, the volume concentration of acid in the mixed acid leaching solution was 40%, the mixed acid selected hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1 by volume, the leaching temperature was 260°C, the liquid-solid ratio was 3mL:1g, and the reaction time was 4h.

[0055] Comparative Group 1: A quartz sand sample was placed in an alumina crucible, the crucible was placed in the furnace of a pit furnace, heated to 900°C for calcination, and oxidative calcination for 6 hours; after calcination, the sample was taken out of the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for the first hot-pressing acid leaching; while performing the first hot-pressing acid leaching, a low eutectic solvent was prepared, and the low eutectic solvent was a mixture of choline chloride, acetic acid and citric acid in a molar ratio of 1:0.5:0.5, added to a round-bottom flask, and heated in a water bath at 70°C until a transparent liquid solvent was formed; after the first hot-pressing acid leaching was completed, the sample was washed with deionized water to neutrality, placed in a vacuum drying oven for drying at 100°C, and immersed in a low eutectic solvent and kept in a water bath Heating and reacting for 2 hours; after the low eutectic solvent treatment is completed, the sample is washed with deionized water to neutrality, and then a second hot-pressing acid leaching is performed; after the second hot-pressing acid leaching is completed, the sample is washed with deionized water to neutrality, placed in a vacuum drying oven for drying at 100°C to obtain purified quartz sand; the reaction conditions of the first hot-pressing acid leaching and the second hot-pressing acid leaching are the same, specifically: carried out in a high-pressure leaching reaction device, 10g of quartz sand sample is placed 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 is selected with a volume ratio of hydrochloric acid: nitric acid: hydrofluoric acid of 3:2:1, the leaching temperature is 260°C, the liquid-solid ratio is 3mL:1g, and the reaction time is 4h.

[0056] Comparative Group 2: A quartz sand sample was placed in a steam explosion tank, and the steam explosion time was set to 60s, the temperature was 160°C, and the initial pressure was 1.0Mpa; the product after steam explosion was placed in an alumina crucible, and the crucible was placed in the hearth of a pit furnace, heated to 900°C for calcination of the sample, and oxidative calcination for 6h; after calcination, the sample was removed from the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for hot-pressing acid leaching; the hot-pressing acid leaching treatment was carried out in a high-pressure leaching reaction device, 10g of quartz sand sample was placed in each group of experiments, the volume concentration of acid in the mixed acid leaching solution was 40%, the volume ratio of hydrochloric acid: nitric acid: hydrofluoric acid was 3:2:1, the leaching temperature was 260°C, the liquid-solid ratio was 3mL:1g, and the reaction time was 8h.

[0057] Comparative Group 3: Quartz sand samples were placed in a steam explosion tank, with the steam explosion time set to 60 seconds, the temperature set to 160°C, and the initial pressure set to 1.0 MPa. The steam explosion product was placed in an alumina crucible, which was placed in the hearth of a pit furnace and heated to 900°C for calcination. The sample was oxidatively calcined for 6 hours. After calcination, the sample was removed from the furnace with crucible tongs and immediately poured into a pre-prepared acid solution for hot-pressing acid leaching. The hot-pressing acid leaching treatment was carried out in a high-pressure leaching reactor. 10 g of quartz sand sample was placed in each experimental group. The mixed acid leaching solution consisted of a first mixed acid with a volume concentration of 40% and a second mixed acid with a volume concentration of 10%. The volume ratio of hydrochloric acid: nitric acid: hydrofluoric acid in the first mixed acid was 3:2:1, and the second mixed acid was a mixture of choline chloride, acetic acid, and citric acid in a molar ratio of 1:0.5:0.5. The leaching temperature was 260°C, the liquid-solid ratio was 3 mL:1 g, and the reaction time was 8 hours.

[0058] In this example, aluminum is used as the main impurity element to investigate the removal effect of different treatment groups. The treatment results of the optimal oxidation roasting-hot pressure acid leaching purification quartz sand process are used as the control group. The test results are as follows: Figure 5 shown.

[0059] Depend on Figure 5 It can be seen that steam explosion and deep eutectic solvents have a significant improvement effect on the oxidative roasting-hot-pressing acid leaching process for quartz sand purification. However, the improvement becomes less pronounced with increasing steam explosion time, temperature, and initial pressure. Comparative Groups 1 and 2 show that steam explosion has a smaller improvement on the oxidative roasting-hot-pressing acid leaching process than deep eutectic solvents. Further experiments in Comparative Group 3 show that the improvement in hot-pressing acid leaching by deep eutectic solvents is not due to the complexation of impurities. To address this issue, one purified quartz sand sample from the three replicates of Experimental Group 3 was submitted for testing, and the results are shown in Table 3.

[0060] Table 3 Purity and main impurity content of purified quartz sand samples in experimental group 3

[0061] Serial number Test items Indicators / technical requirements Test results Single judgment Detection 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] Table 3 shows that the present invention ultimately produces silica with a purity greater than 99.99%, enabling the production of quartz sand of even higher purity. Based on the above experimental results, the improvement effect of steam explosion on the oxidative roasting-hot-pressing acid leaching process for quartz sand purification may be due to its synergistic effect with oxidative roasting, which increases the pore channels of the quartz sand sample, generating a large number of cracks and improving the effectiveness of hot-pressing acid leaching. It not only destroys the surface structure of thin quartz sand, converting more debris into active debris, but also forms abundant microcracks on the surface and between layers, which facilitates the migration and dissolution of impurities. The improvement effect of deep eutectic solvents on the oxidative roasting-hot-pressing acid leaching process for quartz sand purification may be due to its better treatment of the product layer and fluid film surrounding the particles generated by hot-pressing acid leaching, facilitating the impurity removal process during hot-pressing acid leaching and enabling more effective impurity removal. Furthermore, hydrogen bond donor compounds should not be amide-containing compounds, as they tend to adhere to the quartz sand surface, block crack channels, and affect the subsequent hot-pressing acid leaching results. In general, steam explosion can cooperate with oxidation roasting to increase the pore channels of quartz sand samples, while steam explosion alone has little purification effect on quartz sand. The reason is that the increase in pore channels is conducive to improving the impurity removal rate of hot pressing and acid leaching, but at the same time it will generate product layers and fluid films surrounding the particles more quickly, hindering further impurity removal by hot pressing and acid leaching; the present application solves the problem of processing the product layers and fluid films generated by hot pressing and acid leaching within a similar processing time by adopting a low eutectic solvent, thereby making full use of the increased pore channels of the quartz sand samples and achieving better impurity removal.

[0063] As described above, the basic principles, main features and advantages of the present invention are well described. The above embodiments and descriptions are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the scope of protection determined by the present invention.

Claims

1. A method for purifying quartz sand, characterized in that: include: The quartz sand sample is steam exploded and then calcined, and then subjected to the first hot pressing acid leaching, washed and dried, and then immersed in a deep eutectic solvent, washed and dried, and finally subjected to the second hot pressing acid leaching, washed and dried to complete the purification of the quartz sand; The deep eutectic solvent is a mixture of a hydrogen bond acceptor compound and a hydrogen bond donor compound, and then heated 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 method for purifying quartz sand according to claim 1, wherein The steam explosion time is 30-600s, the temperature is 140-200°C, and the initial pressure is 0.5-3.0Mpa.

3. The method for purifying quartz sand according to claim 1, wherein The calcination temperature is 800-1000° C. and the calcination time is 4-8 hours.

4. The method for purifying quartz sand according to claim 1, wherein 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 method for purifying 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 method for purifying quartz sand according to claim 1, wherein The pickling temperature of the first hot-press pickling or the second hot-press pickling is independently selected from 250-300°C.

7. The method for purifying quartz sand according to claim 1, wherein: The pickling time of the first hot-press pickling or the second hot-press pickling is independently selected from 5 to 7 hours.

8. The method for purifying quartz sand according to claim 1, wherein: Any water washing is performed using deionized water until the surface is neutral.

9. The method for purifying quartz sand according to claim 1, wherein: The reaction temperature of the immersion in the deep eutectic solvent is 60-100° C., and the reaction time is 1-3 hours.

10. A quartz sand, characterized in that: The quartz sand is prepared by the purification method according to any one of claims 1 to 9.

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