Synthetic sand purification method

Abstract

The synthetic sand purification method comprises the following steps: preparing micron-sized silicon dioxide powder by a wet chemical method; feeding the obtained silicon dioxide powder into a pickling reaction kettle for heating, adding acid liquor for pickling, taking out silicon dioxide, cleaning the silicon dioxide with high-purity water until the silicon dioxide is neutral, drying the silicon dioxide, and roasting the dried silicon dioxide powder with a roasting furnace; and carrying out dehydroxylation on the roasted silicon dioxide in an atmosphere furnace so as to prepare the high-purity quartz sand. By utilizing the characteristics of large specific surface area and high surface activity of porous silicon dioxide, acid liquor can be more easily and fully contacted with the porous silicon dioxide for reaction, the acid pickling efficiency is higher in a porous state before the synthetic sand is roasted, and compared with the dried wet silicon dioxide, the wet silicon dioxide is larger in specific surface area, higher in surface activity and easier to react with the acid liquor; therefore, the removal rate of the metal impurities is increased, the content of the metal impurities is reduced, and large-scale continuous production is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of purifying appetitive quartz sand, and in particular to a method for purifying synthetic sand. Background Art

[0002] The application areas of high-purity quartz sand have very high requirements on the purity of quartz sand.

[0003] The quartz sand used for quartz crucibles in the semiconductor industry for pulling single crystal silicon rods requires an alkali metal impurity content of less than 1ppm. Limited by the quality of the ore, quartz sand above grade 5N is currently mainly imported.

[0004] Chemically synthesized quartz sand has been a research hotspot in recent years. The total amount of metal impurities in the currently available synthetic quartz sand is less than 1ppm. At present, the synthetic sand technology is in the pilot stage, and there are no batch products. One of the main reasons is that the metal impurities in synthetic sand are difficult to meet the requirements. Although the purity of the finished product can be improved by selecting high-purity raw materials, the chemical synthesis method requires more process links from raw material preparation to finished quartz sand. Due to factors such as the environment and equipment, the product is constantly contaminated during the production process, resulting in the impurity content of the final product failing to meet the requirements. Summary of the invention

[0005] The purpose of the present invention is to provide a method for purifying synthetic sand, so as to solve the problem that the existing synthetic sand cannot be mass-produced due to the high content of metal impurities.

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

[0007] Step 1: preparing micron-sized silicon dioxide powder by wet chemical method;

[0008] Step 2: Place the silicon dioxide powder obtained in step 1 into a pickling reactor and heat it to 40-100°C, add acid solution for pickling for 20-50h, take out the silicon dioxide, wash it with high-purity water with a resistivity of >10MΩ*cm until it is neutral, and dry it, and use a roasting furnace to roast the dried silicon dioxide powder at a roasting temperature of 1200-1350°C for 20-40h;

[0009] Step 3: The calcined silicon dioxide is dehydroxylated in an atmosphere furnace at a temperature of 900-1100° C. for 2-4 hours. After the dehydroxylation is completed, high-purity quartz sand is obtained.

[0010] As a further solution of the present invention, the wet chemical method in step 1 adopts one of the sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

[0011] As a further solution of the present invention, the silicon dioxide powder before being fed into the pickling reactor in step 2 is filtered or vacuum filtered.

[0012] As a preferred embodiment of the present invention, the acid solution in step 2 is prepared from hydrogen chloride, hydrofluoric acid, nitric acid and water, wherein the preparation ratio is water: hydrogen chloride: hydrofluoric acid: nitric acid = 1: (0.5-1.5): (0.01-0.1): (0.001-0.01).

[0013] As a further solution of the present invention, in the pickling process of step 2, the ratio of silicon dioxide to acid solution is 1:(0.5-2).

[0014] As a further solution of the present invention, the dehydroxylation atmosphere in the atmosphere furnace of step three is a mixture of one or more of nitrogen, helium, hydrogen chloride and chlorine.

[0015] As a further solution of the present invention, in step 2, the drying temperature is less than 600° C. and the drying time is less than 10 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] Taking advantage of the large specific surface area and high surface activity of porous silica, the acid can more easily come into full contact with it for reaction. Compared with the pickling process of natural sand, the pickling efficiency is higher in the porous state before the synthetic sand is roasted. In addition, the wet silica has a larger specific surface area and higher surface activity than that after drying, making it easier to react with acid, and the metal impurity removal rate is higher, and its content can be reduced to 1ppm.

[0018] The product structural characteristics in the process of preparing synthetic sand by wet chemical method, when there is a porous structure before roasting, are pickled. Compared with the existing method of pickling after roasting, the impurity removal efficiency is greatly improved, and the silicon dioxide that has not been dried retains the maximum reactivity of its surface and is easier to react with acid.

[0019] The present invention reduces the intermediate step of drying, saves energy, reduces the limitation of raw material selection, and can obtain high-purity quartz sand without high-purity raw materials. It can be produced continuously on a large scale and is suitable for industrial production. DETAILED DESCRIPTION

[0020] Embodiment 1:

[0021] Embodiment 1 of the present invention is a method for purifying synthetic sand, comprising the following steps:

[0022] Step 1: Prepare micron-sized silicon dioxide powder by using one of the wetting methods including sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

[0023] Step 2: Filter or filter the silica powder obtained in step 1 and send it into a pickling reactor, heat it to 60°C, add acid solution prepared in the ratio of water: hydrogen chloride: hydrofluoric acid: nitric acid = 1:0.5:0.05:0.01, pickle for 48 hours, wherein the ratio of silica to acid solution during the pickling process is 1:1.5, take out the pickled silica, and wash it with high-purity water with a resistivity of >10MΩ*cm until it is neutral, dry it at a drying temperature of 400°C and a drying time of 24 hours, and roast the dried silica powder in a roasting furnace at a roasting temperature of 1300°C and a roasting time of 32 hours.

[0024] Step 3: The calcined silicon dioxide is dehydroxylated in a furnace with hydrogen chloride and nitrogen atmosphere, the dehydroxylation temperature is 1100° C., the dehydroxylation time is 4 hours, and high-purity synthetic quartz sand is obtained after the dehydroxylation is completed.

[0025] The impurity content of the high-purity synthetic quartz sand prepared in Example 1 above is as follows:

[0026] Impurity Type Al Ca Co Cu Fe K Li Mg Na Ni Ti Total Content / ppm 0.41 0.15 0.01 0.01 0.07 0.05 0.01 0.03 0.02 0.01 0.1 0.87

[0027] Embodiment 2:

[0028] Embodiment 2 of the present invention is a method for purifying synthetic sand, comprising the following steps:

[0029] Step 1: Prepare micron-sized silicon dioxide powder by using one of the wetting methods including sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

[0030] Step 2: Filter or filter the silica powder obtained in step 1 and send it into a pickling reactor, heat it to 60°C, add acid solution prepared in the ratio of water: hydrogen chloride: hydrofluoric acid: nitric acid = 1:0.5:0.02:0.005, pickle for 48 hours, wherein the ratio of silica to acid solution during the pickling process is 1:2, take out the pickled silica, and wash it to neutrality with high-purity water with a resistivity of >10MΩ*cm, dry it at a drying temperature of 400°C and a drying time of 24 hours, and roast the dried silica powder in a roasting furnace at a roasting temperature of 1300°C and a roasting time of 32 hours.

[0031] Step 3: The calcined silicon dioxide is dehydroxylated in a furnace with hydrogen chloride and nitrogen atmosphere, the dehydroxylation temperature is 1100° C., the dehydroxylation time is 4 hours, and high-purity synthetic quartz sand is obtained after the dehydroxylation is completed.

[0032] The impurity content of the high-purity synthetic quartz sand prepared in Example 2 above is as follows:

[0033] Impurity Type Al Ca Co Cu Fe K Li Mg Na Ni Ti Total Content / ppm 0.58 0.20 0.01 0.01 0.13 0.05 0.01 0.04 0.04 0.01 0.1 1.18

[0034] Embodiment 3:

[0035] Embodiment 3 of the present invention is a method for purifying synthetic sand, comprising the following steps:

[0036] Step 1: Prepare micron-sized silicon dioxide powder by using one of the wetting methods including sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

[0037] Step 2: Filter or filter the silica powder obtained in step 1 and send it into a pickling reactor, heat it to 80°C, add acid solution prepared in the ratio of water: hydrogen chloride: hydrofluoric acid: nitric acid = 1:0.6:0.05:0.005 for pickling for 32 hours, wherein the ratio of silica to acid solution during the pickling process is 1:1.5, take out the pickled silica, and wash it with high-purity water with a resistivity of >10MΩ*cm until it is neutral, dry it at a drying temperature of 600°C and a drying time of 24 hours, and roast the dried silica powder in a roasting furnace at a roasting temperature of 1350°C for 24 hours.

[0038] Step 3: The calcined silicon dioxide is dehydroxylated in a furnace with a chlorine and helium atmosphere. The dehydroxylation temperature is 1100° C. and the dehydroxylation time is 4 hours. After the dehydroxylation is completed, high-purity synthetic quartz sand is obtained.

[0039] The impurity content of the high-purity synthetic quartz sand prepared in Example 3 above is as follows:

[0040] Impurity Type Al Ca Co Cu Fe K Li Mg Na Ni Ti Total Content / ppm 0.42 0.18 0.01 0.01 0.10 0.05 0.01 0.03 0.04 0.01 0.1 0.96

[0041] Embodiment 4:

[0042] A method for purifying synthetic sand comprises the following steps:

[0043] Step 1: Prepare micron-sized silicon dioxide powder by using one of the wetting methods including sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

[0044] Step 2: Filter or vacuum filter the silicon dioxide powder obtained in step 1, wash it with high-purity water with a resistivity of >10MΩ*cm until it becomes neutral, and dry it at a drying temperature of 400°C for 24 hours.

[0045] Step 3: The dried sand obtained in step 2 is sent into a pickling reactor and heated to 60°C. Acid solution prepared in the ratio of water: hydrogen chloride: hydrofluoric acid: nitric acid = 1:0.5:0.05:0.01 is added for pickling for 48 hours. The ratio of silicon dioxide to acid solution during the pickling process is 1:1.5. The silicon dioxide after pickling is taken out and washed with high-purity water with a resistivity of >10MΩ*cm until it is neutral, and then dried at a drying temperature of 400°C and a drying time of 24 hours.

[0046] Step 4: calcining the dried silicon dioxide powder in a calcining furnace at a temperature of 1300°C for 32 hours. The calcined silicon dioxide is dehydroxylated in a furnace in an atmosphere of hydrogen chloride and nitrogen at a temperature of 1100°C for 4 hours, and high-purity synthetic quartz sand is obtained after dehydroxylation.

[0047] The impurity content of the high-purity synthetic quartz sand prepared in Example 4 above is as follows:

[0048] Impurity Type Al Ca Co Cu Fe K Li Mg Na Ni Ti Total Content / ppm 1.17 0.34 0.05 0.05 0.42 0.08 0.05 0.2 0.18 0.05 0.24 2.83

[0049] The preparation process of the above-mentioned Example 4 is based on the preparation parameters of Example 1. The silicon dioxide powder is first dried and then acid-washed and roasted to prepare high-purity quartz sand. Compared with the purification method of first acid-washing and then drying and roasting in Example 1, the total impurity content of the high-purity quartz sand prepared in Example 4 is higher than the total impurity content of the high-purity quartz sand obtained in Example 1.

[0050] In summary, the synthetic sand purification method proposed in the present invention can effectively purify synthetic sand, and the purification efficiency of quartz sand obtained by acid washing and then drying and roasting is higher, and the impurity content of synthetic sand can be as low as 0.87ppm.

[0051] The above shows and describes the basic principles of the present invention. The above are only preferred embodiments of the present invention and are not intended to limit the present invention. The above embodiments and descriptions in the specification are only intended to illustrate the principles of the present invention. Without departing from the scope of the present invention, any modifications, equivalent substitutions and improvements made within the spirit and scope of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying synthetic sand, Features The steps include: Step 1: preparing micron-sized silicon dioxide powder by wet chemical method; Step 2: Place the silicon dioxide powder obtained in step 1 into a pickling reactor and heat it to 40-100°C, add acid solution for pickling for 20-50h, take out the silicon dioxide, wash it with high-purity water with a resistivity of >10MΩ*cm until it is neutral, and dry it, and use a roasting furnace to roast the dried silicon dioxide powder at a roasting temperature of 1200-1350°C for 20-40h; Step 3: The calcined silicon dioxide is dehydroxylated in an atmosphere furnace at a temperature of 900-1100° C. for 2-4 hours. After the dehydroxylation is completed, high-purity quartz sand is obtained.

2. A method for purifying synthetic sand according to claim 1, Features: The wet chemical preparation in step 1 adopts one of the sol-gel method, chemical precipitation method, liquid phase hydrolysis method and microemulsion method.

3. A method for purifying synthetic sand according to claim 1, Features: The silicon dioxide powder before being fed into the pickling reactor in step 2 is filtered or vacuum filtered.

4. A method for purifying synthetic sand according to claim 2 or 3, Features: In the step 2, the acid solution is prepared from hydrogen chloride, hydrofluoric acid, nitric acid and water, wherein the preparation ratio is water: hydrogen chloride: hydrofluoric acid: nitric acid = 1: (0.5-1.5): (0.01-0.1): (0.001-0.01).

5. A method for purifying synthetic sand according to claim 4, Features: During the pickling process of step 2, the ratio of silicon dioxide to acid solution is 1:(0.0.5-2).

6. A method for purifying synthetic sand according to claim 5, Features: The dehydroxylation atmosphere in the atmosphere furnace of step 3 is a mixture of one or more of nitrogen, helium, hydrogen chloride and chlorine.

7. A method for purifying synthetic sand according to claim 6, Features: In the step 2, the drying temperature is less than 600° C. and the drying time is less than 10 hours.