A quartz sand dry process for photovoltaic glass based on pebble raw materials

Abstract

The application discloses a quartz sand dry preparation process for photovoltaic glass based on pebble raw materials. The process is as follows: after the pebble raw materials which have been pre-cleaned on the surface are crushed and ground to micron level, the iron-containing minerals are removed through magnetic separation, double-waveband color selection and identification and air-spraying separation, so that the quartz sand product with iron content less than 100 ppm is obtained. The iron-containing minerals include mechanical iron, magnetite, hematite and lattice iron introduced in the sand making process. Based on the basic physicochemical properties of the pebble and the occurrence state of the iron element, the quartz sand with high iron content is efficiently screened and removed, and then the quartz sand product meeting the use requirements of the photovoltaic glass is obtained. The method does not use the processes such as flotation and acid leaching, and has the characteristics of simple process flow, no chemical reagent consumption and no waste water generation.

Description

Technical Field

[0001] This invention relates to a dry process for preparing quartz sand for photovoltaic glass based on pebble raw materials. Specifically, it relates to a method for low-consumption and high-efficiency production of low-iron quartz sand by cleverly using a combination of magnetic separation and dual-band color sorting based on the occurrence and embedding characteristics of iron elements in pebbles. This method belongs to the field of high-purity mineral material processing. Background Technology

[0002] The photovoltaic (PV) industry is a core pillar of energy transition, propelling humanity towards a clean energy system through the efficient use of solar energy. The PV industry not only significantly reduces greenhouse gas emissions, providing a key solution to addressing climate change, but also, leveraging the unlimited and widely distributed nature of solar energy resources, breaks down the geographical limitations of traditional energy sources, significantly enhancing energy self-sufficiency and security for various countries.

[0003] Photovoltaic glass sand is a high-purity quartz sand used in the manufacture of solar photovoltaic glass. It has a high silica (SiO2) content and low levels of impurities such as iron and titanium to ensure high light transmittance and weather resistance. It mainly comes from natural quartzite or quartz sandstone deposits. The ore undergoes multiple purification processes, including crushing, magnetic separation, flotation, and acid washing, to obtain low-iron quartz sand, which becomes the core raw material for photovoltaic glass. High-purity quartz ore resources are scarce and unevenly distributed. Globally, high-quality deposits are limited, and long-term mining can easily lead to resource depletion. In particular, the demand for ore with extremely low levels of impurities such as iron and titanium has surged, exacerbating supply pressure. The mining process also causes ecological damage, such as vegetation destruction, soil erosion, and groundwater pollution, with high costs for environmental restoration around mining areas. Secondly, the ore purification process is complex, requiring multiple processes such as magnetic separation, flotation, and acid washing to remove impurities. This not only consumes a lot of energy but also generates pollutants such as acidic wastewater and heavy metal slag. Improper treatment can cause secondary pollution to soil and water bodies.

[0004] Pebbles are abundant, have low mining costs, and generally have an initial SiO2 content of >90%, making them an ideal alternative to traditional high-purity quartz raw materials. However, the occurrence of iron impurities in pebbles is complex and diverse, including surface inclusions such as hematite and goethite, as well as lattice iron substitution phenomena. Traditional purification processes struggle to balance economic efficiency and environmental friendliness. Currently, mainstream quartz sand purification technologies can be divided into three main categories: physical separation, chemical leaching, and high-temperature treatment, but all have significant limitations. In physical separation, high-gradient magnetic separation is not efficient enough for separating weakly magnetic iron minerals, while flotation technology, although capable of partially separating iron-containing minerals, relies on chemical reagents and is prone to causing surface contamination of quartz. Chemical leaching can deeply remove iron impurities using a hydrochloric acid-hydrofluoric acid mixture, but the use of strong acids leads to high wastewater treatment costs, and the potential hazards of hydrofluoric acid limit its large-scale application.

[0005] Therefore, there is an urgent need to develop a new process that can both avoid chemical pollution and achieve deep removal of iron impurities. Summary of the Invention

[0006] To address the problems of high resource dependence and large water consumption in the sorting process of photovoltaic glass sand in existing technologies, the purpose of this invention is to provide a dry preparation process of quartz sand for photovoltaic glass based on pebble raw materials. This method develops a dry sorting process based on the characteristics of associated minerals in pebbles. The pebble particle size is controlled by multi-stage crushing and grinding. Magnetic separation is used to remove strongly magnetic impurities and some weakly magnetic impurities from the quartz sand. At the same time, a dual-band color sorter is used to identify iron-containing minerals, and high-pressure air jet is used to accurately remove iron impurities, resulting in a high-purity quartz sand product.

[0007] To achieve the above-mentioned technical objectives, this invention provides a dry process for preparing quartz sand for photovoltaic glass based on pebble raw materials. The method involves crushing and grinding the pebble raw materials, which have undergone surface pre-cleaning treatment, to the micron level, followed by magnetic separation, dual-band color sorting identification, and air-jet separation to remove iron-containing minerals, thereby obtaining a quartz sand product with an iron content of <100ppm. The iron-containing minerals include mechanical iron, magnetite, hematite, and lattice iron introduced during the sand making process.

[0008] Iron impurities in quartz sand prepared from pebbles exhibit diverse forms, including mechanical iron, magnetite and hematite, and lattice iron introduced during the sand-making process. Mechanical iron is mostly adsorbed on the surface of the quartz sand, while magnetite and hematite are intercalated with or encapsulated within the quartz sand particles. Lattice iron is iron element that is isomorphously embedded within the quartz lattice during mineralization. Mechanical iron can be efficiently removed by magnetic separation, while lattice iron, due to its presence within the quartz lattice and its low content, is difficult to remove using processes such as magnetic separation and color sorting. Therefore, the efficient removal of magnetite and hematite from pebble sand is crucial for obtaining high-purity quartz sand products.

[0009] In this invention, based on the physical differences between quartz and iron-bearing minerals in pebbles, targeted iron removal is achieved through the synergistic effect of magnetic separation and dual-band color sorting. Specifically, during magnetic separation, iron-bearing minerals, such as ferromagnetic iron, magnetite, and some hematite, are captured and separated in a gradient magnetic field due to their strong magnetism. Therefore, magnetic separation can simultaneously remove some magnetite minerals associated with or coated with quartz sand, but the removal of hematite is limited. These impurities enter the next stage with the diamagnetic quartz via airflow. Experiments have shown that hematite, magnetite, and quartz have obvious colors and mineral textures. However, pebbles have low iron content, and the color difference is not significant under visible light, resulting in poor accuracy of conventional color recognition. In contrast, the dual-band color sorting of this invention can penetrate the mineral surface. Furthermore, the light source and sensor are typically active, unaffected by external light interference, thus overcoming the physical limitations of color recognition and enabling sorting based on a color sorting device with an embedded image recognition system. Specifically targeting magnetite and hematite, which are difficult to separate using magnetic separation methods, this method utilizes the difference in spectral reflectance characteristics between iron-bearing minerals and quartz to accurately identify iron impurities using dual-band imaging. An image processing system then employs a convolutional neural network to efficiently identify color differences and texture features of the iron-bearing minerals, combined with high-pressure air jetting to remove discolored particles. This process overcomes the bottlenecks of traditional flotation and acid leaching processes, employing a completely dry physical separation method with no chemical reagents or wastewater discharge. It solves the problem of low separation efficiency of associated minerals and significantly reduces raw material costs and environmental impact.

[0010] As a preferred embodiment, the pebble raw material contains ≥95% SiO2 by mass and ≤800ppm iron; the quartz sand product has SiO2 content of 2N or higher. This invention uses pebbles to produce quartz sand for photovoltaic glass. If the SiO2 content in the quartz sand is too low, the impurity content will be high, leading to reduced sorting efficiency and affecting the yield and purity of the finished product. In particular, when the iron content exceeds 800ppm, an increase in lattice iron content is inevitable.

[0011] As a preferred embodiment, the grinding process controls the pebble particle size to be 70-350 μm. In the magnetic separation stage of this invention, particles within the selected size range, due to their moderate volumetric magnetic susceptibility, can be fully subjected to Lorentz force within the magnetic field strength range of this invention, effectively separating iron-containing mineral impurities. Excessively coarse particles result in incomplete dissociation of associated mineral coatings, leading to a sharp drop in magnetic separation efficiency, while excessively fine particles are prone to retaining impurities due to insufficient magnetic adsorption. In the color sorting stage, this particle size range is compatible with the optical resolution threshold of the color sorter, enabling accurate identification of iron-containing particle surface features. Finer particles may increase the false positive rate due to image noise, while coarser particles may lead to missed detection due to surface roughness and uneven reflection.

[0012] As a preferred embodiment, the magnetic separation conditions are: magnetic field strength of 0.5~1.5T. In this invention, magnetic separation is mainly used to remove mechanical iron impurities, magnetite, and some hematite impurities from the sand-making process. When the magnetic field is too low, although it can separate strongly magnetic minerals through weak magnetic action, it cannot effectively remove the widely present weakly magnetic hematite impurities and iron-stained mica in the pebbles, leading to the need to process excessive iron-containing particles in subsequent color sorting, increasing the misjudgment rate and raw material loss. While a high-strength magnetic field can further improve the iron removal rate, the magnetic medium rod is prone to clogging due to the adsorption of ultrafine iron minerals. Simultaneously, the strong magnetic field will non-selectively adsorb some weakly magnetic feldspar or clay minerals, thus reducing the purity of the quartz sand. The number of cycles in the magnetic separation of this invention can be adjusted according to the quality of the pebbles.

[0013] As a preferred embodiment, the dual-band color sorting identification process simultaneously activates visible light and infrared light, and simultaneously detects the reflected signals of visible light and near-infrared light; wherein, the visible light ranges from 500 to 600 nm, and the near-infrared light ranges from 900 to 1700 nm. In this invention, the setting range of the two bands in the dual-band color sorting identification is crucial for deep iron removal. In the visible light band, typical iron-containing impurities in quartz sand are removed due to Fe... 3+ The dd electron transitions exhibit significant color differences, and the quartz matrix has a reflectivity of 85%~90% in this wavelength range. The equipment can accurately identify the surface features of iron-stained particles, achieving high-contrast capture of particle surface texture and color spots. The near-infrared band can penetrate the surface of quartz particles, providing specific identification capabilities for non-magnetic iron-containing impurities remaining after magnetic separation. Furthermore, the energy of this band matches the thermal radiation characteristics of quartz sand, avoiding the signal-to-noise ratio degradation problem caused by low photon energy in the mid- and far-infrared bands. In addition, while a single visible light band can detect some iron oxides, it cannot effectively distinguish low-iron impurities and associated minerals remaining after magnetic separation from quartz. A single near-infrared band, however, suffers from increased misjudgment rates due to Mie scattering caused by fine-grained quartz sand. Therefore, the dual-band synergy covers both surface color and internal structure detection dimensions and complements the magnetic separation process. Further preferably, the infrared light is 900~1300nm.

[0014] As a preferred embodiment, the airflow pressure of the air jet sorting is 0.4~0.8 MPa. When the pressure is too low, although energy consumption can be reduced through a weak airflow, it cannot drive the separation of large particles or impurities with strong adhesion within the particles, leading to a decrease in the color sorting rejection rate. Conversely, when the pressure is too high, although the impurity separation efficiency can be improved, the high-pressure airflow will create significant backflow within the nozzle channel, interfering with the accurate positioning of the optical sensor. Furthermore, the high-pressure airflow can cause fine particles to escape and diffuse due to airflow overload, affecting the sorting effect. Therefore, the present invention has a better overall effect within a further preferred airflow pressure range.

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

[0016] (1) The method of the present invention is designed for the characteristics of associated minerals in pebbles. A dry separation process is developed. The particle size of pebbles is controlled by multi-stage crushing and grinding. Magnetic separation is used to remove strong magnetic impurities and some weak magnetic impurities in quartz sand. At the same time, a dual-band color sorter is used to identify iron-containing minerals. High-pressure air jet is used to accurately remove iron impurities, resulting in high-purity quartz sand products. This process breaks through the bottleneck of traditional flotation and acid leaching processes. The entire process adopts dry physical separation, with no chemical reagents or wastewater discharge. It not only solves the problem of low separation efficiency of associated minerals, but also greatly reduces raw material costs and environmental impact.

[0017] (2) This invention uses pebbles, which are abundant and widely distributed, as raw materials to prepare quartz sand for photovoltaic glass. This breaks the dependence of existing methods on quartz ore, not only realizing the high-value utilization of pebbles, but also helping to break the dependence of the photovoltaic glass industry on resource endowment sites and promote industrial development.

[0018] (3) The method provided by the present invention has the advantages of simple process flow, good sorting effect and no pollution, and can quickly and efficiently produce quartz sand products, which is suitable for large-scale industrial production.

[0019] (4) The quartz sand product obtained by the method of the present invention has an iron content of <100ppm and SiO2 of 2N grade or above, and can be used in the production of photovoltaic glass, etc. Attached Figure Description

[0020] Figure 1 The microstructure of the quartz sand product for photovoltaic glass prepared using pebbles as raw material in Example 1 of the present invention is shown. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the scope of protection 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 effort are still within the scope of protection of the present invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] The embodiments and comparative examples of this invention employ a dual-band color sorter. During the dual-band color sorting and identification process, visible light and infrared light are simultaneously activated, and the reflected signals of visible light and near-infrared light are simultaneously detected. The identification process utilizes an image processing system, employing a convolutional neural network to efficiently identify the color difference and texture features of iron-containing minerals. All pebble raw materials used undergo pretreatment to remove surface sludge before crushing.

[0024] Example 1

[0025] Pebbles with a quartz content of 96.36 wt% (i.e., SiO2 content) and an iron content of 540 ppm were crushed and ground to a particle size of 70-150 μm. The concentrate, after dry magnetic separation in a 1.0T magnetic field, was found to have an iron content of 341 ppm. This concentrate was then fed into a dual-band color sorter (visible light 500 nm and near-infrared light 1300 nm) with an air jet separation pressure of 0.4 MPa. The separated concentrate was collected and its chemical composition was analyzed, revealing a SiO2 content of 99.93 wt% and an iron content of 77 ppm. The microstructure of the resulting product is shown below. Figure 1 As shown.

[0026] Example 2

[0027] Pebbles with a quartz content of 95.40 wt% and an iron content of 670 ppm were crushed and ground to a particle size of 125-350 μm. The concentrate after dry magnetic separation with a magnetic field strength of 1.5T was tested and found to have an iron content of 394 ppm. The concentrate was then fed into a dual-band color sorter with visible light at 600 nm and near-infrared light at 1500 nm. The airflow pressure for air jet separation was 0.8 MPa. The separated concentrate was collected and its chemical composition was analyzed. The SiO2 content was 99.82 wt% and the iron content was 83 ppm.

[0028] Example 3

[0029] Pebbles with a quartz content of 97.49 wt% and an iron content of 800 ppm were crushed and ground to a particle size of 125-350 μm. The concentrate after dry magnetic separation with a magnetic field strength of 1.3T was tested and found to have an iron content of 416 ppm. The concentrate was then fed into a dual-band color sorter with visible light at 600 nm and near-infrared light at 1700 nm. The airflow pressure for air jet separation was 0.6 MPa. The separated concentrate was collected and its chemical composition was analyzed. The SiO2 content was 99.79 wt% and the iron content was 96 ppm.

[0030] Example 4

[0031] Pebbles with a quartz content of 98.55% wt and an iron content of 300 ppm were crushed and ground to a particle size of 100-300 μm. The concentrate after dry magnetic separation with a magnetic field strength of 0.5T was tested and found to have an iron content of 201 ppm. The concentrate was then fed into a dual-band color sorter with visible light at 500 nm and near-infrared light at 900 nm. The airflow pressure for air jet separation was 0.5 MPa. The separated concentrate was collected and its chemical composition was analyzed. The SiO2 content was 99.91 wt% and the iron content was 53 ppm.

[0032] Example 5

[0033] The only difference between this embodiment and Embodiment 1 is that the wavelength of the near-infrared light is changed to 1500nm. All other steps and conditions are the same. The sorted concentrate is collected and its chemical composition is tested. The SiO2 content is 99.86wt% and the iron content is 92ppm.

[0034] Example 6

[0035] The only difference compared to Example 3 is that the airflow pressure for the air jet sorting is 0.2 MPa.

[0036] The final quartz SiO2 content was 99.21 wt%, and the iron content was 99 ppm.

[0037] Comparative Example 1

[0038] The only difference compared to Example 1 is that magnetic separation is not used.

[0039] The final quartz SiO2 content was 97.09 wt%, and the iron content was 260 ppm.

[0040] Comparative Example 2

[0041] The only difference compared to Example 3 is that color selection uses only 600nm visible light.

[0042] The final quartz SiO2 content was 98.94 wt%, and the iron content was 410 ppm.

[0043] Comparative Example 3

[0044] The only difference compared to Example 1 is that the ore was ground to a particle size of 400-600 μm.

[0045] The final quartz SiO2 content was 98.55 wt%, and the iron content was 145 ppm.

[0046] Comparative Example 4

[0047] The only difference from Example 3 is that the visible light band is turned off, and only the near-infrared light band with a wavelength of 1700nm is turned on.

[0048] The final quartz SiO2 content was 99.45 wt%, and the iron content was 148 ppm.

Claims

1. A quartz sand dry process for the production of photovoltaic glass based on pebble raw material, characterized by: The pebble raw material after surface pre-cleaning treatment is crushed and ground to micron level, and then sequentially subjected to magnetic separation, double-waveband color selection identification and air jet separation to remove iron-containing minerals, thereby obtaining a quartz sand product with iron content less than 100 ppm; The iron-containing minerals include mechanical iron, magnetite, hematite and lattice iron introduced in the sand making process; The pebble raw material has a mass content of SiO2 of not less than 95% and an iron element content of not more than 800 ppm; and the SiO2 of the quartz sand product is 2N grade or above. In the process of double-waveband color selection identification, visible light and infrared light are synchronously turned on, and the reflection signals of visible light and near-infrared light are synchronously detected; wherein the visible light is 500-600 nm, and the near-infrared light is 900-1700 nm.

2. A dry process for the preparation of quartz sand for photovoltaic glass based on pebble raw material according to claim 1, characterized in that: The grinding controls the pebble particle size to be 70-350 μm.

3. A dry process for the preparation of quartz sand for photovoltaic glass based on pebble raw material according to claim 2, characterized in that: The magnetic separation is performed under the condition that the magnetic field strength is 0.5-1.5 T.

4. A dry process for the preparation of quartz sand for photovoltaic glass based on pebble raw material according to claim 3, characterized in that: The air jet separation is performed under the condition that the air flow pressure is 0.4-0.8 MPa.

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