A method for removing impurity elements from high-purity quartz sand

Abstract

The present invention discloses a method for removing impurity elements from high-purity quartz sand, belonging to the field of processing high-purity high-end inorganic non-metallic materials. This method involves mixing quartz sand raw materials containing lattice doping impurities below 4N6 level with a sulfiding agent and then performing sulfiding roasting. The roasted product is quartz sand above 4N8 level; the dosage of the sulfiding agent is 0.9 to 1.5 times the total molar amount of impurity elements in the quartz sand. Based on the chemical bond characteristics of impurities in the quartz crystal structure, this method uses sulfiding roasting to convert lattice impurities such as B, Al, Ti, and Ca into more stable impurity sulfides, and combines their volatile characteristics to achieve deep removal of impurities in the quartz sand.

Description

Technical Field

[0001] The present invention belongs to the field of processing high-purity high-end inorganic non-metallic materials, and relates to a method for removing impurity elements from high-purity quartz sand above 4N8 grade. Background Art

[0002] High-purity quartz sand above 4N8 grade has become a model of high-end high-purity quartz products due to its extremely high purity standard. However, the production of high-purity quartz sand faces the dual challenges of scarce resources and great technical difficulties.

[0003] Impurities in quartz minerals can be classified into three categories according to their characteristics such as size and occurrence state: gangue mineral impurities, inclusion impurities, and crystal structure impurities. Among them, gangue mineral impurities such as mica and feldspar are often attached to the surface of quartz sand particles or filled in the particle gaps, and these impurities can be effectively removed through beneficiation techniques such as monomer dissociation.

[0004] An inclusion is an external substance captured by the interface during the growth of a mineral crystal or a medium component during diagenesis and mineralization, and it is not directly connected to the host mineral. An effective method for removing inclusions is roasting. This method heats the inside of the inclusion and causes it to expand at high temperature, and finally it bursts due to thermal stress. It should be noted that factors such as the composition, size, position, and morphology of the inclusion will all have an important impact on its bursting behavior at high temperature. For example, some extremely tiny inclusions are difficult to burst even at high temperature; inclusions located on the surface of quartz particles are more likely to burst under low-pressure conditions compared to internal inclusions; in addition, inclusions with irregular shapes require a lower internal pressure to burst compared to inclusions with regular shapes.

[0005] Crystal structure impurities refer to elements that can undergo isomorphous substitution with Si atoms in the silicon-oxygen tetrahedron, such as B, Al, Ti, etc., which will form new tetrahedral structures. Since this substitution is usually non-equivalent, it will lead to charge imbalance inside the crystal lattice. In order to maintain charge balance, ions such as Li, Na, K, and Ca, Mg will exist in the channels of the tetrahedral intervals to play a charge compensation role. These crystal structure impurities are tightly wrapped by silicon-oxygen tetrahedrons, so it is difficult to achieve deep removal through conventional magnetic separation, flotation, acid leaching and other processes. Although chlorination roasting has a good effect on removing elements such as K and Na, its effect on removing impurities such as B, Al, Ti, and Ca is not significant. Given the complexity of removing crystal structure impurities in quartz sand, it is particularly important to develop efficient and targeted deep removal technologies. Summary of the Invention

[0006] Aiming at the problems in the production process of high-purity quartz sand, such as complex types of impurity elements, diverse bonding behaviors of impurity bonds in the crystal structure, and difficult removal, the purpose of the present invention is to provide a method for removing impurity elements from high-purity quartz sand. According to the chemical bond characteristics of impurities in the quartz crystal structure, this method uses sulfidation roasting to convert lattice impurities such as B, Al, Ti, Ca, etc. into more stable impurity sulfides, and combines their volatile characteristics to achieve deep removal of impurities in quartz sand.

[0007] To achieve the above technical purpose, the present invention provides a method for removing impurity elements from high-purity quartz sand. In this method, quartz sand raw materials containing lattice doping impurities below 4N6 level are mixed with a sulfiding agent and then subjected to sulfidation roasting. The roasted product is quartz sand above 4N8 level; the dosage of the sulfiding agent is 0.9 - 1.5 times the total molar amount of impurity elements in the quartz sand.

[0008] The quartz sand raw materials containing lattice doping impurities below 4N6 level involved in the present invention generally refer to quartz sand with preliminary lattice purification, which contains almost no associated ore impurities and mainly retains trace lattice doping impurities.

[0009] Based on the chemical bond characteristics of impurity elements in the quartz crystal structure, aiming at the problem that impurities such as B, Al, Ti, Ca, etc. form stable chemical bonds with oxygen elements, the present invention proposes a deep purification method. Although the traditional chlorination roasting process can partially remove the above impurities, the formation of chlorides is slow due to the strong binding force of the impurity-oxygen bond, resulting in limited removal efficiency. The technical breakthrough of the present invention lies in using the characteristic that the affinity of impurity elements for sulfur is significantly higher than that for oxygen. By introducing a sulfiding agent, impurities are promoted to combine with sulfur to form more stable sulfides. Compared with chlorination roasting, sulfidation roasting not only accelerates the reaction process under the same temperature conditions, but also the metal sulfides generated have volatile physical properties, thus achieving efficient and deep removal of impurity elements. This technical solution effectively solves the core problem of low removal efficiency of traditional methods and realizes a method for further deep removal of impurities from high-purity quartz sand raw materials.

[0010] Experiments have found that the sulfidation removal reaction of impurity elements in quartz sand is affected by the dosage of the sulfiding agent. During the purification process of quartz sand, the reduction amount of impurity elements is the removal amount. To ensure that impurities can be effectively removed, the dosage of the sulfiding agent needs to reach at least the theoretical molar amount required for the reaction of the removal amount of impurities. Appropriately increasing the dosage of the sulfiding agent can accelerate the process of the chlorination reaction and improve the chlorination removal efficiency of impurities. However, when the dosage of the sulfiding agent is too high, it will correspondingly increase the production cost and also increase the difficulty of tail gas treatment.

[0011] As a preferred embodiment, the sulfurizing agent is elemental sulfur and / or hydrogen sulfide. The selection of the sulfurizing agent is the key to achieving the sulfurization and removal of impurity elements. Commonly used sulfurizing media can be classified into elemental sulfur, hydrogen sulfide gas, and salt compounds (metal sulfides, sulfates, etc.) according to their forms. Since metal sulfides need to decompose and release gaseous sulfur-containing components during roasting, the reaction process is complex and slow. In addition, residual impurity elements such as sodium, potassium, and calcium after the roasting of sulfides easily lead to a decrease in the purity of quartz sand. In sulfates, the sulfur valence state is high, and the decomposition is generally slow during roasting, and the sulfur-containing components after decomposition exist in the form of sulfur dioxide, etc., which are difficult to combine with the impurity elements in quartz sand. However, the elemental sulfur and hydrogen sulfide selected in the present invention are easily reacted with impurity elements such as B, Al, Ti, and Ca during roasting to form stable sulfides, and no other impurities will be introduced. Further preferably, the sulfurizing agent is hydrogen sulfide.

[0012] As a preferred embodiment, the temperature of the sulfurization roasting is 800 - 1200 °C, and the time is 5 - 35 min. The core process elements in the sulfurization roasting process are the roasting temperature and time. Increasing the temperature and prolonging the roasting time can accelerate the reaction between impurity elements and the sulfurizing agent, and accelerate the breaking speed and degree of the chemical bond between impurity elements and oxygen. However, it will also bring an increase in process energy consumption. And long-term high-temperature sulfurization roasting has higher requirements for equipment, increasing costs in terms of equipment and the like. On the contrary, if the roasting temperature is set too low, it cannot provide the necessary energy for the breaking of the chemical bond between impurity elements and oxygen in quartz sand, making it difficult for the chemical bond to break. Similarly, too short a roasting time will also result in incomplete breaking of the chemical bond.

[0013] As a preferred embodiment, the sulfurization roasting method is dynamic roasting, wherein the horizontal inclination angle of the roasting furnace during dynamic roasting is 3 - 28°, and the rotation speed is 5 - 30 r / min. Dynamic roasting means that the roasting furnace rotates during the production process, driving the quartz sand in the furnace to rotate at the same time. At this time, a horizontal roasting furnace is preferably used to achieve continuous feeding and discharging production. When using a horizontal roasting furnace for dynamic roasting, the inclination angle and rotation speed of the equipment have an important impact on the combination and movement behavior of quartz sand and the sulfurizing agent. When the quartz sand is put into the roasting furnace, it will move longitudinally along the furnace chamber under the combined effect of the inclination angle and rotation action of the roasting furnace. The moving speed of the quartz sand and its residence time in the furnace are jointly determined by the inclination angle and rotation speed of the roasting furnace. If the inclination angle is too large and the rotation speed is too fast, the residence time of the quartz sand in the furnace will be shortened, which is likely to cause problems such as incomplete reaction and incomplete removal of impurities. On the contrary, when the inclination angle is small and the rotation speed is slow, it can ensure that the quartz sand has sufficient reaction time in the furnace, thereby improving the removal efficiency of impurities, but it will reduce the production efficiency.

[0014] As a preferred solution, the content of SiO2 in the quartz sand raw material containing lattice doping impurities below 4N6 level is ≥ 99.99%, and the content of SiO2 in the quartz sand above 4N8 level is ≥ 99.998%.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) Based on the chemical bond characteristics of impurity elements in the quartz crystal structure, aiming at the problem that lattice impurities such as B, Al, Ti, and Ca form stable chemical bonds with oxygen element, the present invention proposes a deep purification method. By utilizing the characteristic that the affinity of impurity elements for sulfur is significantly higher than that for oxygen, a sulfiding agent is introduced to promote the combination of impurities with sulfur to form more stable sulfides, accelerating the reaction process. The metal sulfides generated are volatile, realizing the efficient and deep removal of impurity elements.

[0017] (2) The technical solution provided by the present invention has the processes of simple process flow, easy operation, good purification effect, etc., and is suitable for large-scale industrial production. Description of the Drawings

[0018] Figure 1 It is the micrograph of the quartz sand obtained by the removal method of the present invention.

[0019] Figure 2 It is the XRD pattern of the quartz sand raw material in Example 1. Detailed Embodiments

[0020] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative efforts still fall within the protection scope of the present invention.

[0021] Unless otherwise specified, all kinds of raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0022] The dynamic roasting furnace involved in the following examples and comparative examples is a rotary kiln.

[0023] Example 1

[0024] Load quartz sand with a SiO₂ content of 99.9941% into a dynamic roasting furnace. Use XRD to analyze that the sample mineral phase is a pure quartz phase without associated mineral impurities, that is, impurity elements are present in the quartz sand lattice. Roast at 1150 °C. During the roasting process, introduce H₂S with a total molar amount 1.5 times that of the impurity elements in the quartz sand for 25 minutes. The horizontal inclination angle of the roasting furnace is 3°, and the rotation speed is 30 r / min. After collecting and cooling the roasting product, according to the requirements of GB∕T 32650-2016, digest the sample and measure the contents of 13 impurity components. The removal rates of B, Al, Ti, and Ca are 99.71%, 95.29%, 93.46%, and 98.56% respectively, and the SiO₂ content of the roasted quartz sand is 99.9981%.

[0025] Example 2

[0026] Load quartz sand with a SiO₂ content of 99.9951% into a dynamic roasting furnace. Use XRD to analyze that the sample mineral phase is a pure quartz phase without associated mineral impurities, that is, impurity elements are present in the quartz sand lattice. Roast at 1200 °C. During the roasting process, introduce H₂S with a total molar amount 1.1 times that of the impurity elements in the quartz sand for 30 minutes. The horizontal inclination angle of the roasting furnace is 28°, and the rotation speed is 5 r / min. After collecting and cooling the roasting product, according to the requirements of GB∕T 32650-2016, digest the sample and measure the contents of 13 impurity components. The removal rates of B, Al, Ti, and Ca are 98.94%, 96.37%, 92.69%, and 99.01% respectively, and the SiO₂ content of the roasted quartz sand is 99.9993%.

[0027] Example 3

[0028] Mix quartz sand with a SiO₂ content of 99.9940% with elemental sulfur and then load it into a dynamic roasting furnace. Use XRD to analyze that the sample mineral phase is a pure quartz phase without associated mineral impurities, that is, impurity elements are present in the quartz sand lattice. Roast at 1200 °C. During the roasting process, introduce H₂S. The molar ratio of elemental sulfur to H₂S is 1:1, and its total content is 0.9 times that of the total molar amount of impurity elements in the quartz sand for 20 minutes. The horizontal inclination angle of the roasting furnace is 28°, and the rotation speed is 5 r / min. After collecting and cooling the roasting product, according to the requirements of GB∕T32650-2016, digest the sample and measure the contents of 13 impurity components. The removal rates of B, Al, Ti, and Ca are 98.95%, 92.83%, 91.46%, and 96.76% respectively, and the SiO₂ content of the roasted quartz sand is 99.9980%.

[0029] Example 4

[0030] Mix quartz sand with a SiO₂ content of 99.9951% and elemental sulfur with a total molar amount 1.0 times that of the total amount of impurity elements in the quartz sand, then load them into a dynamic roasting furnace. Use XRD to analyze that the sample mineral phase is a pure quartz phase without associated mineral impurities, that is, the impurity elements are present in the quartz sand lattice. Roast at 800 °C for 30 min, with the horizontal inclination angle of the roasting furnace being 28° and the rotation speed being 5 r / min. After collecting and cooling the roasted product, measure the contents of 13 impurity components after digesting the sample according to the requirements of GB∕T 32650-2016. The removal rates of B, Al, Ti, and Ca are 98.65%, 94.03%, 92.11%, and 96.62% respectively, and the SiO₂ content of the roasted quartz sand is 99.9982%.

[0031] Example 5

[0032] Mix quartz sand with a SiO₂ content of 99.9946% and elemental sulfur with a total molar amount 1.3 times that of the total amount of impurity elements in the quartz sand, then load them into a dynamic roasting furnace. Use XRD to analyze that the sample mineral phase is a pure quartz phase without associated mineral impurities, that is, the impurity elements are present in the quartz sand lattice. Roast at 1150 °C for 5 min, with the horizontal inclination angle of the roasting furnace being 28° and the rotation speed being 5 r / min. After collecting and cooling the roasted product, measure the contents of 13 impurity components after digesting the sample according to the requirements of GB∕T 32650-2016. The removal rates of B, Al, Ti, and Ca are 93.91%, 94.07%, 94.15%, and 96.78% respectively, and the SiO₂ content of the roasted quartz sand is 99.9982%.

[0033] Comparative Example 1

[0034] Compared with Example 2, the only difference is that the dosage of H₂S is 0.6 times the total molar amount of the impurity elements in the quartz sand, and the SiO₂ content of the finally obtained roasted product is 99.9972%.

[0035] Comparative Example 2

[0036] Compared with Example 2, the only difference is that H₂S is replaced with an equimolar amount of hydrogen chloride, and the quartz sand is chlorinated roasted. The SiO₂ content of the finally obtained roasted product is 99.9968%, but the removal rates of B, Al, Ti, and Ca are 65.43%, 48.76%, 31.45%, and 38.26% respectively. This comparative example shows that when sulfide roasting is not used, the lattice impurities of B, Al, Ti, and Ca in the quartz sand cannot be effectively removed.

[0037] Comparative Example 3

[0038] Compared with Example 4, the only difference is that the roasting temperature is 700 °C, and the SiO₂ content of the finally obtained roasted product is 99.9963%.

[0039] Comparative Example 4

[0040] Compared with Example 1, the only difference is that during the dynamic roasting process, the horizontal inclination angle is 30° and the rotation speed is 45 r / min. The SiO2 content of the finally obtained roasted product is 99.9958%. This comparative example shows that when the horizontal inclination angle of the dynamic roasting is too high and the rotation speed is too fast, the impurity removal effect of quartz sand will decline.

Claims

1. A method for removing impurity elements from high-purity quartz sand, characterized in that: Mix the quartz sand raw material containing lattice-doped impurities below grade 4N6 with a sulfurizing agent and then conduct sulfurizing roasting. The roasted product is quartz sand above grade 4N8; the dosage of the sulfurizing agent is 0.9 to 1.5 times the total molar amount of impurity elements in the quartz sand; The sulfurizing agent is elemental sulfur and / or hydrogen sulfide; The temperature of the sulfurizing roasting is 800 to 1200 °C, and the time is 5 to 35 minutes; The way of the sulfurizing roasting is dynamic roasting. When dynamically roasting, the horizontal inclination angle of the roasting furnace is 3 to 28°, and the rotation speed is 5 to 30 r / min.

2. A method for removing impurity elements from high-purity quartz sand according to claim 1, characterized in that: In the quartz sand raw material containing lattice-doped impurities below grade 4N6, the SiO2 content is ≥ 99.99%, and in the quartz sand above grade 4N8, the SiO2 content is ≥ 99.998%.

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