Mica removing method for machine-made sand

Abstract

The invention discloses a method for efficiently removing machine-made sand mica. Firstly, the machine-made sand is subjected to drying and screening pretreatment; then, high-voltage electrostatic separation is adopted, and mica enrichment is preliminarily separated out according to the conductivity difference; and then, according to the particle size characteristics of the particles, secondary precise separation of winnowing (aiming at coarse particles) or shaking table sorting (aiming at fine particles) is carried out on the enriched substances, so that residual impurities such as quartz are removed. And finally, other particles in the adsorbate are recycled, all levels of purified sand are mixed, and the high-purity machine-made sand meeting the grading requirement is obtained. The method is high in sorting efficiency, high in pertinence and remarkable in mica removing effect.

Description

Technical Field

[0001] This invention belongs to the field of building material processing, and in particular relates to a method for removing mica from manufactured sand. Background Technology

[0002] Manufactured sand, as an important alternative to natural sand, plays an increasingly important role in infrastructure construction. However, during the crushing and sand-making process, rocks are prone to producing flaky and needle-like particles, which may lead to the enrichment of lightweight flaky minerals such as mica from the original rock in the sand product. Excessive mica content can severely degrade concrete performance—due to its smooth surface and poor adhesion to cement paste, it significantly reduces the strength and durability of concrete while increasing water consumption. Therefore, the national standard "Construction Sand" (GB / T 14684-2022) sets clear and strict limits on the mica content in manufactured sand (e.g., ≤2%).

[0003] Currently, common methods for removing mica from manufactured sand include water washing, rod milling, and magnetic separation. Water washing separates mica from sand particles based on their settling velocity difference in water; however, this method consumes a large amount of water and is effective for removing clay and silt particles, but its efficiency is limited for flaky mica with a density similar to sand. Rod milling processes mica through a "grinding" action, grinding coarse mica particles to below 0.3mm (0.315mm square-hole sieve side length) to meet specifications. However, rod milling alters the original gradation of the sand and introduces a large amount of mica into the stone powder. Magnetic separation is more energy-efficient, but it is only effective for magnetic or weakly magnetic mica (such as biotite), and ineffective for the more common, non-magnetic muscovite. Furthermore, it may adsorb some weakly magnetic aggregate particles during the separation process.

[0004] Electrostatic separation is a technology that separates materials based on differences in their electrical behavior in an electric field. It has been widely applied in mineral sorting and waste resource recycling. However, its industrial application in removing mica from manufactured sand is still limited. The basic principle is that different minerals, due to their different electrical properties, undergo charge transfer and accumulation in an electric field, thus effectively separating the target material from impurities. The advantage of this technology lies in its ability to utilize the difference in electrical properties between the platy structure of mica and sand particles, resulting in a more significant separation effect on mica under the same particle size conditions compared to methods such as water washing, rod milling, and magnetic separation. However, when processing wide-particle-size manufactured sand, excessively high electrostatic field strength can lead to the simultaneous adsorption of fine-particle mica and quartz; while excessively low field strength makes it difficult to effectively remove coarse-particle mica, thus affecting the sorting effect.

[0005] Therefore, the industry urgently needs a comprehensive solution that can overcome the inherent defects of the above-mentioned methods such as water washing, magnetic separation, and rod milling, and can effectively improve the efficiency of high-voltage electrostatic separation and resource recovery rate. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a highly efficient method for removing mica from manufactured sand, effectively improving the efficiency of high-voltage electrostatic separation and the resource recovery rate. To achieve the above objective, this invention adopts the following technical solution: A method for removing mica from machine-made sand, characterized by comprising the following steps: S1. Pretreatment: The raw material manufactured sand is dried and screened to obtain multiple narrow particle sizes of manufactured sand; S2. Electrostatic separation: In a dry environment, each narrow-particle-size manufactured sand is fed into a high-voltage electrostatic separation device for processing. By utilizing the difference in conductivity between mica and manufactured sand, mica is electrostatically adsorbed, thereby separating the initially purified manufactured sand and the electrostatically adsorbed material rich in mica. S3. Secondary physical sorting: The electrostatic adsorbents obtained in step S2 are sorted differently according to their particle size. S4. Product recycling: The pre-purified manufactured sand of each particle size obtained in step S2 is combined with the non-mica particles recovered after secondary sorting in step S3, and mixed according to the gradation requirements of building sand to obtain manufactured sand with mica removed.

[0007] To achieve higher efficiency and better sorting results, the present invention may also adopt the following preferred and further defined technical solutions: Furthermore, in step S1, the screening process preferably involves precisely screening the manufactured sand into six key particle sizes: 0~0.15mm, 0.15~0.3mm, 0.3~0.6mm, 0.6~1.18mm, 1.18~2.36mm, and 2.36~4.75mm. The drying process requires strictly controlling the moisture content of the manufactured sand to below 1% to ensure the material exhibits good electrical properties.

[0008] Preferably, in step S2, the high-voltage electrostatic separation should be carried out in a dry environment with air humidity below 40%. The electrostatic field strength of the high-voltage electrostatic separation equipment can be precisely adjusted within the range of 0~30kV / cm for different particle sizes. Furthermore, to efficiently collect mica products, the separation process includes the desorption of the electrode from the electrostatic adsorbate. This can be achieved by cutting off the electrostatic field and applying mechanical vibration, or by blowing ion wind onto the adsorption surface to neutralize its charge, so that the electrostatic adsorbate completely detaches from the adsorption surface.

[0009] Preferably, in step S3, when the electrostatic adsorbents are sorted differently according to their particle size: For coarse-grained electrostatic adsorbents with a nominal particle size ≥1.18mm (square-hole sieve side length ≥1.25mm), air separation equipment is preferred for separation, utilizing the aerodynamic differences of the particles to remove mica. Furthermore, optimal separation of mica and heavy mineral particles can be achieved by controlling the horizontal airflow velocity within the range of 0-15m / s.

[0010] For fine-grained electrostatic adsorbents with a nominal particle size <1.18mm (square-hole sieve side length <1.25mm), a sloped separation device is preferred for separation, utilizing friction and kinetic differences to remove mica. Furthermore, the sloped separation device should have a chute with a slope of 1~30° and a length of not less than 30cm, and can be equipped with devices such as vibrators, shaking tables, or impactors to assist particle movement and enhance the separation effect.

[0011] Preferably, in step S4, in order to meet the requirements of high-standard construction, the gradation requirements of the construction sand are preferably mixed in accordance with the gradation requirements of Zone II sand specified in GB / T 14684.

[0012] The core principle of this invention lies in overcoming the fundamental challenges faced by electrostatic separation technology in processing wide-sized, multi-phase mixed manufactured sand materials through the strategies of "gradual optimization" and "cooperative sorting". Its scientific basis is mainly reflected in the following three aspects: (1) Utilizing the differences in electrical properties (such as conductivity and dielectric constant) between mica and quartz, the main sand particles. In a high-voltage electrostatic field, different minerals become charged due to contact, collision, induction and other effects. As a layered silicate mineral, mica usually has a higher surface conductivity than quartz and other sand particles, and is more likely to acquire and maintain charge in a corona field or contact charge. Charged particles move under the action of electric field force, and mica particles with better conductivity will quickly transfer their charge to the electrode plate, thereby being adsorbed by the opposite polarity and achieving separation from the sand particles. (2) Secondary physical sorting is used to refine the electrostatic "enrichment" based on the differences in physical properties (such as shape and coefficient of friction). For coarse particles ≥1.18mm, the density and shape of mica and sand particles differ significantly. Air separation can take advantage of the difference in their aerodynamic properties—flaky mica has a larger windward area and a smaller mass, making it easier to be blown away in horizontal airflow, while near-equiaxed sand particles fall into the heavier products due to their larger mass inertia, thus achieving efficient separation. For fine particles <1.18mm, the particle mass is small, reducing the efficiency of air separation. Instead, inclined chute separation is used, taking advantage of the difference in kinematic properties between the smooth surface and low friction coefficient of mica and the rough surface and high friction coefficient of sand particles. On the inclined chute, mica tends to slide down quickly, while sand particles move more by rolling or jumping. The different trajectories and speeds of the two particles allow for spatial separation at the end of the chute, recovering the fine sand particles that were accidentally trapped. This synergistic process greatly improves the resource recovery rate. (3) From pretreatment drying and electrostatic separation to secondary physical separation, the entire process constitutes a closed-loop dry separation system. This system completely avoids water consumption and mud pollution problems, while maintaining the original particle morphology and gradation of the manufactured sand. Finally, through precise mixing in step S4, a high-quality manufactured sand product that meets both the mica content requirements and the target gradation can be obtained.

[0013] Compared with the prior art, the present invention has the following significant advantages: (1) It solves the problem of electrostatic separation of wide-particle-size materials: Through the core step of "pre-screening into narrow-particle-size", the optimal electrostatic field strength conditions are created for materials of different particle sizes, which fundamentally avoids the problem of low separation efficiency caused by the difference in electrostatic response of wide-particle-size materials, and realizes efficient and accurate removal of mica of all particle sizes from fine powder to coarse particles. (2) It realizes efficient resource recovery: The innovative "particle size differential secondary separation" of electrostatic adsorbents can effectively recover qualified manufactured sand particles that are mistakenly adsorbed by the electrostatic field, especially coarse particles, which significantly improves the yield of the final product and reduces resource waste. (3) Significant comprehensive benefits: The entire process of the present invention is carried out in a dry environment without water, avoiding the environmental protection and energy consumption problems of water washing; it does not rely on the magnetism of minerals and is effective for common muscovite and biotite; at the same time, it maintains the original gradation of manufactured sand, and the final product can be accurately compounded according to national standards, with stable and controllable quality. This invention provides a comprehensive solution for removing mica from manufactured sand that is efficient, environmentally friendly, economical, and widely applicable. Attached Figure Description

[0014] Figure 1 This is a flowchart of the method for removing mica from machine-made sand according to the present invention.

[0015] Figure 2 Schematic diagram of electrostatic adsorption and desorption process.

[0016] Figure 3 This is a schematic diagram of the secondary physical sorting process. Detailed Implementation Example

[0017] Raw materials: The raw material is manufactured sand produced by crushing a certain granite. Its initial mica content is 3.5% (mass fraction) and the moisture content is 3.2%.

[0018] Implementation process: Preprocessing: Drying: The raw material, manufactured sand, is fed into a dryer and dried at a temperature of 105±5℃ to reduce its moisture content to 0.8%.

[0019] Screening: The dried manufactured sand is precisely screened into the following 6 narrow particle sizes using a standard square-hole sieve: 0~0.15mm, 0.15~0.3mm, 0.3~0.6mm, 0.6~1.18mm, 1.18~2.36mm, and 2.36~4.75mm.

[0020] Electrostatic sorting: In a closed workshop where the ambient humidity is controlled at 30%, the above six particle sizes of manufactured sand are fed separately and independently into a roller-type high-voltage electrostatic separator for processing.

[0021] The electrostatic field strength was optimized for different particle sizes: for fine particles below 0.6 mm, the field strength was set to 15-20 kV / cm; for coarse particles above 0.6 mm, the field strength was set to 22-28 kV / cm.

[0022] After sorting, "preliminary purified manufactured sand" and "mica-rich electrostatic adsorbents" of various particle sizes are obtained. By periodically cutting off the electrostatic field and starting the mechanical vibrator, the mica-rich adsorbents on the electrodes are detached and collected.

[0023] Secondary physical sorting: All collected electrostatic adsorbates were combined and then differentiated according to their particle size: For the coarse-grained portion (≥1.18mm): it is fed into an air separator. The horizontal airflow velocity is stabilized at 10 m / s by adjusting the fan. The flaky, lightweight mica is blown into the collector by the airflow, while the nearly isometric, heavy sand particles (the qualified particles that are accidentally aspirated) fall into another collection chamber under gravity.

[0024] For the fine particles (<1.18mm): they are fed into a 15° inclined chute separator with a length of 1.2 meters, and supplemented with high-frequency micro-vibration. Mica flakes, due to their smooth surface and low coefficient of friction, slide quickly down to the far end collection tank; while the rough sand particles, due to their high coefficient of friction, are collected at the near end.

[0025] Product recycling: The "preliminary purified manufactured sand" of each particle size obtained in step S2 is used as the main product.

[0026] The non-mica particles (i.e. qualified sand particles that were accidentally aspirated) recovered by air classification and inclined plane separation in step S3 are treated as by-products.

[0027] The main product and by-products are precisely proportioned and mixed according to the gradation requirements of Zone II sand in "Construction Sand" (GB / T 14684) to finally obtain high-quality manufactured sand with mica content reduced to 0.4%. Example

[0028] Raw materials: The raw material is manufactured sand produced by crushing a certain type of mica quartz schist, with an initial mica content of 2.8% (mass fraction) and a moisture content of 4.0%.

[0029] Implementation process: Preprocessing: Drying: The raw materials are rapidly dried using a fluidized bed dryer to reduce their moisture content to 0.5%.

[0030] Screening: Using the same standard square hole sieve, the manufactured sand is screened into 6 particle sizes: 0~0.15mm, 0.15~0.3mm, 0.3~0.6mm, 0.6~1.18mm, 1.18~2.36mm, and 2.36~4.75mm.

[0031] Electrostatic sorting: The operation takes place in a sorting chamber where the ambient humidity is maintained below 35% by a dehumidification system. Materials of different particle sizes are sequentially fed into a plate-type high-voltage electrostatic separator.

[0032] Based on the characteristics of the manufactured sand from bimbocite quartz schist, the electrostatic field strength was uniformly set within the range of 18-25 kV / cm for sorting.

[0033] The separation process uses ion wind to blow onto the adsorption plate to neutralize the charge of the mica particles, causing them to fall off naturally and be collected.

[0034] Secondary physical sorting: The collected electrostatic adsorbents were sieved and divided into two parts: coarse (≥1.18 mm) and fine (<1.18 mm).

[0035] Coarse-grained portion: Separation is carried out using a wind-powered shaking table with a horizontal airflow velocity of 8 m / s. The combined effect of airflow and table vibration achieves efficient separation of mica and sand particles.

[0036] Fine-grained fraction: An adjustable-slope vibrating chute is used, with the slope set at 25°. Separation is achieved by utilizing the difference in sliding speed and trajectory between mica and sand particles.

[0037] Product recycling: The main product after electrostatic separation is combined with the sand particles recovered from secondary separation.

[0038] According to the project requirements, the sand was mixed in accordance with the lower limit gradation of Zone II sand in GB / T 14684, and finally a high-quality manufactured sand product with a mica content of only 0.3% was obtained, which fully meets the material requirements of high-standard concrete.

[0039] Effect description: The above two embodiments demonstrate that the method provided by this invention can effectively process manufactured sand with different lithologies (granite, mica-quartz schist) and different initial mica contents. Through a combination of "narrow-particle-size electrostatic separation" and "differentiated particle size secondary separation," the final product's mica content is significantly lower than the national standard (≤2%). Furthermore, the entire process is a dry production method with no wastewater discharge and high resource recovery rate, demonstrating significant industrial application value. The above are preferred embodiments of this invention and are not intended to limit the scope of protection of this application. Any modifications or equivalent substitutions made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for removing mica from machine-made sand, characterized in that, Includes the following steps: S1. Pretreatment: The raw material manufactured sand is dried and screened to obtain multiple narrow particle sizes of manufactured sand; S2. Electrostatic separation: In a dry environment, each narrow-particle-size manufactured sand is fed into a high-voltage electrostatic separation device for processing. By utilizing the difference in conductivity between mica and manufactured sand, mica is electrostatically adsorbed, thereby separating the initially purified manufactured sand and the electrostatically adsorbed material rich in mica. S3. Secondary physical sorting: The electrostatic adsorbents obtained in step S2 are sorted differently according to their particle size. S4. Product recycling: The pre-purified manufactured sand of each particle size obtained in step S2 is combined with the non-mica particles recovered after secondary sorting in step S3, and mixed according to the gradation requirements of building sand to obtain manufactured sand with mica removed.

2. The method according to claim 1, characterized in that, Step S3, which involves differentiated sorting of electrostatic adsorbates based on their particle size distribution, specifically includes: Coarse-grained electrostatic adsorbents with a nominal particle size ≥1.18mm were separated using an air classifier, and mica was removed by utilizing the aerodynamic differences of the particles. Fine-grained electrostatic adsorbents with a nominal particle size of <1.18 mm were separated using an inclined plane sorting device, and mica was removed by utilizing the difference in tribodynamics.

3. The method according to claim 1, characterized in that, In step S1, the screening process involves screening the manufactured sand into six particle sizes: 0~0.15mm, 0.15~0.3mm, 0.3~0.6mm, 0.6~1.18mm, 1.18~2.36mm, and 2.36~4.75mm; the drying process involves reducing the moisture content of the manufactured sand to below 1%.

4. The method according to claim 1, characterized in that, In step S2, the humidity of the drying environment is maintained below 40%; the electrostatic field strength of the high-voltage electrostatic separation equipment is 0~30kV / cm; the separation process includes the desorption of the electrode from the electrostatic adsorbent by cutting off the electrostatic field and applying mechanical vibration, or by blowing ion wind onto the adsorption surface to neutralize its charge, so that the electrostatic adsorbent is removed from the adsorption surface.

5. The method according to claim 1, characterized in that, In step S3, when using an air classifier to treat coarse-grained adsorbents, the horizontal airflow velocity is controlled to be 0-15 m / s.

6. The method according to claim 1, characterized in that, In step S3, the inclined plane sorting equipment should have a chute with a slope of 1~30° and a length of ≥30cm, and a device to assist particle movement.

7. The method according to any one of claims 1 to 6, characterized in that, In step S4, the gradation requirements for the building sand are the Zone II sand gradation requirements specified in GB / T 14684.

Images