A method for purifying silica sand by alkali dissolution and co-producing calcium silicate hydrate

Abstract

A method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand, comprising the following steps: mixing silica sand, lime, caustic soda and water, and performing a hydrothermal reaction; filtering to obtain alkali-soluble silica sand and calcium silicate slurry; further cleaning the alkali-soluble silica sand with organic acid and ultrasonic wave, filtering and drying to obtain a high-purity silica sand product; filtering, washing, drying and breaking up the calcium silicate hydrate slurry to obtain a calcium silicate hydrate product. The present application utilizes calcium hydroxide and silicon dioxide to generate calcium silicate hydrate by high-temperature hydrothermal reaction under the catalytic action of caustic soda, removes the surface and epidermis of silica sand by alkali dissolution, obtains relatively pure quartz sand, and generates calcium silicate hydrate with higher added value; the present invention has cheap raw materials, simple process, low production cost, little impact on human body and environment during industrial application, and the entire production process does not generate three wastes, thereby eliminating the subsequent three wastes treatment cost, and has huge economic benefits.

Description

Technical Field

[0001] The invention relates to a method for purifying silica sand, in particular to a method for purifying silica sand and co-producing calcium silicate hydrate. Background Art

[0002] Silica sand is a hard, wear-resistant, chemically stable silicate mineral. Its main mineral component is SiO2. Its color is milky white, light yellow, brown or colorless and translucent. Its relative density is 2.65. It is insoluble in acid, slightly soluble in KOH solution and hot alkali solution, and its melting point is 1750℃. Silica sand often contains some associated aluminum silicate minerals such as feldspar and mica, and iron-containing substances. The iron mainly exists on the surface of silica sand in the form of impregnated iron and encapsulated iron. Impregnated iron is micron-sized clay iron-containing substances that are impregnated into the cracks of silica sand particles and iron ions that penetrate into the surface lattice of silica sand particles. Encapsulated iron is usually clay iron-containing substances that are encapsulated and adsorbed on the surface of silica sand particles.

[0003] Hydrated calcium silicate is a compound generated by the high-temperature hydrothermal reaction of calcium oxide and calcium hydroxide with silicon dioxide. Its chemical formula is CaO·mSiO2·nH2O. It is in a gel state at room temperature and is a microcrystal with short-range order and long-range disorder. It has fibrous, mesh, and particle morphologies, about 1μm long and 0.2μm wide. The most important of them are dicalcium silicate and tricalcium silicate. Due to its unique physical and chemical properties and mineralogical characteristics, it is mainly used in special soaps, adhesives, dyes, rubber fillers, catalysts, as well as textiles, papermaking, coatings, printing and dyeing, medicine, explosives, etc., and is widely used as fertilizers, construction and insulation materials.

[0004] Silica sand needs to be purified before being used in the silicon dioxide industry to meet the industry's requirements for high purity. Currently, the industry purifies silica sand through pickling, such as sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid and other inorganic acids, using the principle that most impurity minerals can be dissolved by strong acid liquid to purify silica sand. Using inorganic acids to purify silica sand will produce a large amount of waste liquid, which is highly acidic and contains a large amount of impurity ions such as iron ions and aluminum ions. The processing cost is very high and has a great impact on the environment. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for purifying silica sand by alkali dissolution and co-producing calcium silicate hydrate with simple process and low pollution.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows: a method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand, comprising the following steps:

[0007] (1) Mixing silica sand, lime, caustic soda and water to perform a hydrothermal reaction to obtain a solid-liquid mixture;

[0008] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0009] (3) treating the silica sand II with an organic acid solution to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0010] (4) ultrasonically cleaning silica sand III in water to obtain silica sand IV and turbid water III;

[0011] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0012] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0013] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 7-9, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0014] Preferably, in step (1), after mixing, the concentration of the caustic soda is 5 to 50 g / L, more preferably 10 to 35 g / L.

[0015] Preferably, in step (1), the caustic alkali is caustic soda and / or caustic potash.

[0016] Preferably, in step (1), the amount of water used is 3 to 10 times, more preferably 4 to 6 times, the amount of silica sand by weight.

[0017] Preferably, in step (1), the amount of lime used is 5% to 50% of the silica sand by weight, and more preferably 15% to 30%. The amount of lime used is determined by the content of iron and aluminum impregnations and inclusions on the silica sand surface, the impregnation depth, and the desired calcium silicate hydrate.

[0018] Preferably, in step (1), the particle size of the silica sand is 0.71 mm to 0.1 mm. This particle size facilitates the separation of silica sand and calcium silicate hydrate in the solid-liquid mixture obtained by the hydrothermal reaction. This is mainly because the silicate compound generated during the high-temperature hydrothermal reaction of the finished product has a particle size of less than 0.074 mm, which is very different from the particle size of the silica sand and can be separated by filtration; the silica sand particles with a particle size less than 0.1 mm are also too small to cause mutual collision, friction, and scrubbing between the silica sand particles even under stirring, making it difficult to remove the iron and aluminate adsorbed on the surface of the silica sand particles. Silica sand with a larger particle size is easier to separate from the calcium silicate hydrate, further improving the purity and quality of the silica sand.

[0019] Preferably, in step (1), the reaction temperature of the hydrothermal reaction is 100-180° C., and the reaction time is 1-6 hours; the hydrothermal reaction is used to dissolve impregnations and inclusions such as iron and aluminum on the surface of the silica sand and its epidermis.

[0020] Preferably, in step (3), the organic acid solution is a mixture solution of one or more of oxalic acid, ascorbic acid and citric acid; the organic acid can react with calcium hydroxide to form water-insoluble calcium salts, which further dissolve the iron, aluminum and calcium silicate compounds in silica sand II.

[0021] Preferably, in step (3), the concentration of the organic acid solution is 5-100 g / L, more preferably 20-50 g / L.

[0022] Preferably, in step (3), the silica sand II is stirred and soaked in the organic acid solution for 1 to 24 hours at a temperature of 60 to 120° C.; more preferably, it is soaked for 1 to 4 hours at a temperature of 95 to 100° C.

[0023] Preferably, in step (4), the ultrasonic cleaning time is 15 to 60 minutes, and the ultrasonic frequency is 28 KHz to 80 KHz.

[0024] Preferably, the filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as cleaning water.

[0025] The quartz industry has very high requirements for the purity of silica sand, especially the iron oxide content, so silica sand needs to be purified and iron-reduced before use. Traditional acid leaching methods for purifying silica sand mostly use inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and hydrofluoric acid. The waste liquid produced is highly acidic and contains more impurities such as iron ions and aluminum ions, and the subsequent treatment cost is very high.

[0026] After research and analysis, the inventors found that a non-volatile hot solution of strong alkali can react with the ferric oxide in silica sand to form ferrite, and can also react with the silicon dioxide and aluminum oxide in silicate minerals (such as feldspar, mica, etc.) to form metasilicate and aluminate. Ferrite, metasilicate and aluminate are soluble in caustic soda solution and water, thereby achieving the purpose of purifying silica sand. However, since the hot alkali dissolves more silicon dioxide, the utilization rate of silica sand is low.

[0027] Furthermore, the inventors used calcium hydroxide and caustic soda in combination, and utilized the causticizing reaction of ferrite, metasilicate, and aluminate with calcium hydroxide to generate water-insoluble hydrated silicates and caustic soda with added value, thereby achieving the separation of iron, aluminum and silica sand. The caustic soda can be recycled, and the entire production process does not generate the three wastes, thereby eliminating the subsequent treatment costs of the three wastes, and achieving huge economic benefits.

[0028] In the method of purifying silica sand and producing calcium silicate hydrate by alkali dissolution with calcium hydroxide and sodium hydroxide, the key chemical reactions are as follows:

[0029] Al2Si2O7·2H2O +NaOH→NaAlO2+ Na2SiO3+H2O;

[0030] Fe2(Fe,Si)2O5(OH)5+NaOH→2Na3Fe(OH)6+ Na2SiO3+H2O;

[0031] Na3Fe(OH)6→2Fe(OH)3↓+6NaOH;

[0032] NaAl(OH)4→Al(OH)3↓+NaOH;

[0033] SiO2+Ca(OH)2→CaO·mSiO2·nH2O↓;

[0034] Na2SiO3+Ca(OH)2→CaO·mSiO2·nH2O↓+NaOH;

[0035] H2C2O4+Ca(OH)2→CaC2O4↓+H2O.

[0036] By adopting this scheme, in the mixed solution of quartz sand, calcium hydroxide and caustic alkali, silicon dioxide reacts with caustic alkali to form metasilicate, and ferric oxide in quartz sand reacts to form ferrite, and can also react with silicon dioxide and aluminum oxide in aluminosilicate minerals (such as feldspar, mica, etc.) to form metasilicate and metaaluminate, thereby dissolving the aluminosilicate minerals, and ferrite, metasilicate, and metaaluminate react with calcium hydroxide to form water-insoluble calcium silicate and caustic alkali, thereby separating iron- and aluminum-containing inclusions and impregnations from the surface of silica sand. Since the surface area of ​​silica sand is further increased by alkali corrosion, the water-insoluble silicate generated during the reaction is easy to adhere to the surface of silica sand, and the silica sand is added to the organic acid solution for soaking and washing, which can remove the attachments on the surface of silica sand, and further react with the silica sand impregnation iron and aluminum ions to improve the purity of silica sand.

[0037] Beneficial effects of the present invention:

[0038] The present application utilizes calcium hydroxide and silicon dioxide to generate calcium silicate hydrate by high-temperature hydrothermal reaction under the catalytic action of caustic soda, removes the surface and epidermis of silica sand by alkali dissolution, and obtains relatively pure quartz sand by controlling the appropriate degree of reaction, and generates calcium silicate hydrate with higher added value; about 90% of ferric oxide in silica sand can be removed, and the content of silicon dioxide can be increased by about 2%, with excellent iron removal rate and purification rate; the raw material price of the present invention is cheap, the process is simple, the production cost is low, the impact on human body and environment during industrial application is very small, the entire production process does not generate three wastes, and the subsequent treatment cost of three wastes is eliminated, and the economic benefit is huge. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments for understanding the inventive concept of the present invention, and cannot represent all the embodiments, nor are they interpreted as the only embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field under the premise of understanding the inventive concept of the present invention are within the scope of protection of the present invention.

[0040] The raw materials used in the embodiments of the present invention are all obtained through conventional commercial channels.

[0041] The main components of the silica sand used in each embodiment are: SiO2 is 98.68%, Fe2O3 is 0.074%, Al2O3 is 0.56%; the particle size is 0.35 mm to 0.1 mm. Through component analysis, the impurities in the silica sand are mainly iron-containing and aluminum-containing silicate minerals such as pearlite and chlorite, which meets the general silica sand standards for float glass. Example 1

[0042] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0043] (1) 4000 g of silica sand, 600 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 4 h to obtain a solid-liquid mixture;

[0044] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0045] (3) soaking the silica sand II in a 50 g / L oxalic acid solution at 95° C. for 1 hour to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0046] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 1 h to obtain silica sand IV and turbid water III;

[0047] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0048] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0049] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 8.0, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0050] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0051] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Example 2

[0052] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0053] (1) 4000 g of silica sand, 800 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 4 h to obtain a solid-liquid mixture;

[0054] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0055] (3) soaking the silica sand II in a 50 g / L oxalic acid solution at 95° C. for 2 h to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0056] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 2 h to obtain silica sand IV and turbid water III;

[0057] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0058] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0059] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 7.5, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0060] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0061] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Example 3

[0062] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0063] (1) 4000 g of silica sand, 1000 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 3 h to obtain a solid-liquid mixture;

[0064] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0065] (3) soaking the silica sand II in a 50 g / L oxalic acid solution at 120° C. for 2 h to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0066] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 2 h to obtain silica sand IV and turbid water III;

[0067] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0068] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0069] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 8.5, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0070] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0071] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Example 4

[0072] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0073] (1) 4000 g of silica sand, 800 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 4 h to obtain a solid-liquid mixture;

[0074] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0075] (3) soaking the silica sand II in a 25 g / L oxalic acid solution at 120° C. for 2 h to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0076] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 1 h to obtain silica sand IV and turbid water III;

[0077] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0078] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0079] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 9.0, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0080] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0081] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Example 5

[0082] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0083] (1) 4000 g of silica sand, 800 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 4 h to obtain a solid-liquid mixture;

[0084] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0085] (3) soaking the silica sand II in a 25 g / L oxalic acid solution at 120° C. for 4 h to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0086] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 1 h to obtain silica sand IV and turbid water III;

[0087] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0088] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0089] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 7.0, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0090] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0091] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Example 6

[0092] The method of alkali dissolution and purification of silica sand to co-produce calcium silicate hydrate in this embodiment comprises the following steps:

[0093] (1) 4000 g of silica sand, 800 g of lime, 20 L of water and caustic soda were mixed evenly (the concentration of caustic soda after mixing was 20 g / L), and subjected to hydrothermal reaction at 160 °C for 4 h to obtain a solid-liquid mixture;

[0094] (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and calcium silicate hydrate slurry; washing the silica sand I to separate the calcium silicate hydrate attached to the surface of the silica sand I to obtain silica sand II and turbid water I;

[0095] (3) soaking the silica sand II in a 25 g / L oxalic acid solution at 120° C. for 4 h to further dissolve the iron, aluminum, and calcium silicate compounds in the silica sand II, and performing solid-liquid separation to obtain silica sand III and turbid water II;

[0096] (4) Cleaning silica sand III in water using 40 kHz ultrasonic waves for 1 h to obtain silica sand IV and turbid water III;

[0097] (5) Drying silica sand IV, removing iron by dry method, removing the mixed mechanical iron filings, and obtaining high-purity silica sand finished product;

[0098] (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I;

[0099] (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 8.2, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

[0100] The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

[0101] The test results of the obtained silica sand finished product and calcium silicate hydrate finished product are shown in Table 1. Comparative Example

[0102] The same batch of silica sand used in Examples 1 to 6 was purified by the acid washing method commonly used in the industry, and the test was repeated three times, which were respectively recorded as Comparative Example 1, Comparative Example 2, and Comparative Example 3. The test results of the obtained silica sand products are shown in Table 1.

[0103] Table 1 Test results of the products obtained in Examples 1 to 6 and Comparative Examples 1 to 3

[0104]

[0105] It can be seen from the data in Table 1 that the purity of ferric oxide, aluminum oxide and silicon dioxide after alkali dissolution and purification of silica sand in Examples 1 to 6 reaches the standard of silica sand for photovoltaic use, and some reach the standard of 3N high-purity quartz sand, and the co-produced hydrated calcium silicate products can all reach the industrial grade standard. The purity of the silica sand obtained in Examples 1 to 6 is improved compared with that of Comparative Examples 1 to 3 using the conventional acid washing method.

[0106] The embodiments of this specific implementation method are all preferred embodiments for facilitating understanding or implementing the technical solutions of the present invention, and are not intended to limit the protection scope of the present invention. All equivalent changes made according to the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand, characterized in that: The following steps are involved: (1) mixing silica sand, lime, caustic soda and water, and performing a hydrothermal reaction to obtain a solid-liquid mixture; after the silica sand, lime, caustic soda and water are mixed, the concentration of the caustic soda is 5 to 20 g / L; (2) filtering the solid-liquid mixture by graded filtering to obtain silica sand I and hydrated calcium silicate slurry; washing the silica sand I to obtain silica sand II and turbid water I; (3) treating the silica sand II with an organic acid solution to obtain silica sand III and turbid water II by solid-liquid separation; (4) ultrasonically cleaning silica sand III in water to obtain silica sand IV and turbid water III; (5) Drying silica sand IV and removing iron by dry method to obtain high-purity silica sand finished product; (6) The obtained calcium silicate hydrate slurry is further filtered to obtain calcium silicate hydrate filter cake I and filtrate I; (7) The calcium silicate hydrate filter cake I, turbid water I, turbid water II, and turbid water III are mixed, the pH value is adjusted to 7-9, and filtered to obtain a calcium silicate hydrate filter cake II and a filtrate II; the calcium silicate hydrate filter cake II is dried and broken up to obtain a calcium silicate hydrate finished product.

2. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to claim 1, characterized in that: In step (1), the caustic soda is caustic soda and / or caustic potash; and the amount of water used is 3 to 10 times the amount of silica sand by weight.

3. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to claim 1 or 2, characterized in that: In step (1), the amount of lime used is 5% to 50% of the silica sand by weight.

4. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 3, characterized in that: In step (1), the particle size of the silica sand is 0.71 mm to 0.1 mm.

5. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 4, characterized in that: In step (1), the reaction temperature of the hydrothermal reaction is 100 to 180° C., and the reaction time is 1 to 6 hours.

6. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 5, characterized in that: In step (3), the organic acid solution is a solution of one or a mixture of two or more of oxalic acid, ascorbic acid, and citric acid.

7. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 6, characterized in that: In step (3), the concentration of the organic acid solution is 5 to 100 g / L.

8. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 7, characterized in that: In step (3), the silica sand II is stirred and soaked in an organic acid solution for 1 to 24 hours at a temperature of 60 to 120°C.

9. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 8, characterized in that: In step (4), the ultrasonic cleaning time is 15 to 60 minutes, and the ultrasonic frequency is 28 kHz to 80 kHz.

10. The method for purifying and co-producing calcium silicate hydrate by alkali dissolution of silica sand according to any one of claims 1 to 9, characterized in that: The filtrate I is recycled for the next high-temperature hydrothermal reaction; after adding a flocculant to the filtrate II to remove metal ions, it is used as washing water.

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