A complete device and green preparation method for preparing high-purity magnesium hydroxide by using magnesite flotation tailings

Abstract

This invention provides a complete set of equipment and a green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime, belonging to the field of mining solid waste resource recycling technology. The equipment includes: a pretreatment unit, a continuous acid leaching magnesium extraction unit, a deep purification and impurity removal unit, a tubular mixing and magnesium crystallization unit, a multi-stage countercurrent washing and dewatering unit, and a flash drying unit, connected sequentially along the process flow. The pretreatment unit includes a slurry mixing tank, a vibrating screen, a permanent magnet separator, and a hydrocyclone. The continuous acid leaching magnesium extraction unit includes a steam preheater, a continuous acid leaching reactor with a heating jacket, a pH online control system, and solid-liquid separation equipment. This method reduces energy consumption by constructing a fully continuous production device and improves water recycling rate by designing a closed-loop circulation system for washing water. It utilizes a composite calcium removal agent for deep impurity removal, improving product purity. Furthermore, this method can precisely control crystal form and particle size.

Description

Technical Field

[0001] This invention belongs to the field of mining solid waste resource recycling technology, specifically relating to a complete set of equipment and green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings mud. Background Technology

[0002] Magnesite is an advantageous mineral resource in my country. Flotation is the mainstream process for upgrading magnesite. The flotation process generates a large amount of fine-grained tailings mud with a high magnesium oxide content. Long-term stockpiling not only occupies land, pollutes water and soil, but also causes serious waste of magnesium resources. It is urgent to utilize it in a high-value and resource-oriented manner.

[0003] Magnesium hydroxide, as an important inorganic magnesium salt product, is widely used in high-end fields such as halogen-free flame retardants, electronic ceramics, lithium battery materials, and environmental catalysis. These scenarios impose stringent standards on product purity, crystal morphology, particle size distribution, and chloride ion content.

[0004] At present, there are many technical defects in the existing technology for preparing magnesium hydroxide: (1) The raw materials are mostly magnesite ore, and there is a lack of resource utilization processes for magnesite flotation tailings mud. The pretreatment is simple, and impurities such as silicon, calcium, iron and aluminum are not completely removed, resulting in low product purity and stability; (2) Most of the production is intermittent, with long process, high energy consumption and unstable operating conditions, which makes it difficult to meet the needs of stable industrial production; (3) The washing water consumption is large, the wastewater discharge is under great environmental pressure, and there is a lack of closed-loop water recycling system; (4) It is difficult to accurately control the crystal form and particle size, and the chloride ion content of some products is too high, which limits the application in high-end flame retardant, electronics, ceramics and other fields.

[0005] Therefore, there is an urgent need for a method that can solve the problems of low purity, high energy consumption, high water consumption, and uncontrollable crystal form in existing technologies. Summary of the Invention

[0006] Based on the above-mentioned technical problems, the purpose of this invention is to provide a complete set of equipment and a green preparation method for preparing high-purity magnesium hydroxide using magnesite flotation tailings mud. This method reduces energy consumption by constructing a continuous production device throughout the entire process and designs a closed-loop circulation system for washing water to improve the water recycling rate; it also uses a composite calcium removal agent to deeply remove impurities and improve the purity of the product; and this method can also precisely control the crystal form and particle size.

[0007] The specific technical solution is as follows: A complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime includes a pretreatment unit, a continuous acid leaching magnesium extraction unit, a deep purification and impurity removal unit, a tubular mixing and magnesium precipitation crystallization unit, a multi-stage countercurrent washing and dewatering unit, and a flash drying unit, connected sequentially along the process flow. The pretreatment unit includes a slurry mixing tank, a vibrating screen, a permanent magnet separator, and a hydrocyclone. The continuous acid leaching magnesium extraction unit includes a steam preheater, a continuous acid leaching reactor with a heating jacket, an online pH control system, and solid-liquid separation equipment. The deep purification and impurity removal unit includes... The system includes a pH neutralization and adjustment tank, a plate and frame filter press, and a precision filter; a tubular mixing and magnesium precipitation crystallization unit includes a tubular static mixer and a crystallization kettle for crystallization and crystallization; a multi-stage countercurrent washing and dewatering unit includes a three-stage countercurrent washing tank, a centrifugal dewatering machine, and a wash water reuse pump; and a flash drying finished product unit includes a flash dryer, a cyclone separator, a bag filter, and a finished product silo. Each unit is connected in sequence through pipes, valves, and transfer pumps. The wash water from the three-stage countercurrent washing tank is returned to the slurry preparation tank of the pretreatment unit via a reuse pump, forming a closed-loop water circulation.

[0008] In addition, the complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime provided by the present invention may also have the following additional technical features: In the above technical solution, the temperature control range of the continuous acid leaching reactor is 50–80℃.

[0009] A green preparation method for producing high-purity magnesium hydroxide from magnesite flotation tailings slime includes the following steps: S1: Raw material pretreatment: Magnesite flotation tailings mud is mixed with water to form a slurry, which is then screened to remove coarse slag, removed by permanent magnet iron removal, and classified by hydrocyclone to obtain fine-grained pure slurry; S2: Continuous acid leaching for magnesium extraction: The slurry is preheated with steam and then enters a continuous acid leaching reactor. It is leached at normal pressure and temperature under acidic conditions. After solid-liquid separation, magnesium-containing leaching filtrate is obtained. S3: Deep purification and impurity removal: Adjust the pH of the magnesium-containing filtrate, add a calcium chloride and trisodium phosphate composite calcium removal agent to deeply remove calcium, silicon, iron and aluminum impurities, and filter to obtain high-purity magnesium solution; S4: Tubular Mixing Magnesium Precipitation Crystallization: High-purity magnesium solution and sodium hydroxide solution are rapidly and homogenously mixed in a tubular static mixer, and magnesium precipitation, crystallization, and aging are completed in a crystallization kettle with crystal form control to obtain crude magnesium hydroxide; S5: Multi-stage countercurrent washing and dehydration: Crude magnesium hydroxide is washed in three stages to remove impurity ions, and then centrifuged to dehydrate to obtain wet base material; S6: Flash drying: High-purity magnesium hydroxide powder is obtained by flash drying of wet materials.

[0010] In the above technical solution, the acidic system in step S2 is a hydrochloric acid system or a mixed acid system with a hydrochloric acid and sulfuric acid molar ratio of 9:1; the acid leaching temperature is 65–75℃, pH 1.0–1.8, and the leaching time is 70–90 min.

[0011] In the above technical solution, in step S3, the pH of the magnesium-containing filtrate is adjusted to 4.2–5.0, and the reaction time of the composite calcium removal agent is 20–30 min, so as to achieve deep co-precipitation removal of impurity ions.

[0012] In the above technical solution, the precipitation temperature in step S4 is 50–60℃, the final pH is 9.8–10.5, and the aging time is 80–120 min; during the aging stage, 0.05%–0.1% sodium stearate may be added for in-situ surface modification.

[0013] In the above technical solution, in step S5, the washing water temperature is 40–50℃, and the washing is continued until the chloride ion content of the filtrate is ≤0.05%; in step S6, the flash drying inlet temperature is 170–190℃, and the outlet temperature is 85–95℃.

[0014] In the above technical solution, the product specifications are as follows: Mg(OH)2 purity ≥ 99.2%, CaO ≤ 0.08%, SiO2 ≤ 0.05%, chloride ion ≤ 0.05%; electronic grade product purity ≥ 99.4%, and low-chlorine high-dispersion flame retardant grade product chloride ion ≤ 0.02%, meeting the requirements of high-end application scenarios.

[0015] The present invention provides a complete set of equipment and a green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime. Compared with the prior art, the advantages are as follows: 1. Achieve efficient resource utilization of magnesite flotation tailings slime, with a magnesium recovery rate of ≥85%.

[0016] 2. Construct a continuous production line throughout the entire process, reducing energy consumption by more than 20%; 3. A compound calcium removal agent is used for deep impurity removal, ensuring a stable product purity of ≥99.2%; 4. Achieve closed-loop circulation of washing water, with a water reuse rate of ≥95% and near-zero external discharge; 5. Precise control of crystal form and particle size allows for customization of electronic-grade and low-chlorine, highly dispersed flame-retardant products. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow of the present invention; Detailed Implementation

[0018] The following are specific implementation cases and appendices. Figure 1 The present invention will be further described, but the present invention is not limited to these embodiments.

[0019] A complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings mud includes a pretreatment unit, a continuous acid leaching magnesium extraction unit, a deep purification and impurity removal unit, a tubular mixing magnesium precipitation and crystallization unit, a multi-stage countercurrent washing and dewatering unit, and a flash drying unit connected sequentially along the process flow.

[0020] The pretreatment unit includes a slurry preparation tank, a vibrating screen, a permanent magnet iron separator, and a hydrocyclone, which completes the preparation, screening, iron removal, and particle size classification of the raw materials, removes physical impurities, and provides qualified fine-grained slurry for acid leaching.

[0021] The continuous acid leaching magnesium extraction unit includes a steam preheater, a continuous acid leaching reactor with a heating jacket, an online pH control system, and solid-liquid separation equipment, which enables efficient and continuous leaching of magnesium, reducing energy consumption by more than 20% compared to batch processes.

[0022] The deep purification and impurity removal unit includes a neutralization and pH adjustment tank, a plate and frame filter press, and a precision filter. Composite calcium agents are used for synergistic co-precipitation to deeply remove Ca, Si, Fe, and Al impurities, ensuring a high concentration of the finished product.

[0023] The tubular mixing magnesium precipitation crystallization unit includes a tubular static mixer and a crystallization kettle with a precise temperature control system to achieve rapid homogeneous magnesium precipitation and crystallization control.

[0024] The multi-stage countercurrent washing and dewatering unit includes a three-stage countercurrent washing tank, a centrifugal dewatering machine, and a washing water recycling pump, which efficiently removes impurities and achieves water circulation.

[0025] The flash drying finished product unit includes a flash dryer, a cyclone separator, a bag filter, and a finished product silo.

[0026] The units are connected in sequence through pipes, valves and pumps to achieve continuous automated production throughout the entire process; the washing water from the three-stage countercurrent washing tank is returned to the slurry tank to form a closed-loop water circulation, which greatly reduces water consumption.

[0027] Among them, the washing water from the three-stage countercurrent washing tank is returned to the slurry preparation tank of the pretreatment unit by the reuse pump, forming a closed-loop water circulation.

[0028] In an embodiment of the present invention, the temperature control range of the continuous acid leaching reactor is 50–80°C.

[0029] A green preparation method for producing high-purity magnesium hydroxide from magnesite flotation tailings slime includes the following steps: S1: Raw material pretreatment: Magnesite flotation tailings mud is fed into a slurry mixing tank, water is added to adjust the solid content to 18% to 22%, and the mixture is stirred evenly; coarse slag is removed by a vibrating screen, iron is removed by a permanent magnet separator, and the slurry is classified by a hydrocyclone to obtain fine-grained slurry. S2: Continuous acid leaching for magnesium extraction: The slurry is preheated to 50-60℃ by steam and then enters the continuous acid leaching reactor; leaching is carried out using a hydrochloric acid system or a mixed acid system of hydrochloric acid and sulfuric acid in a molar ratio of 9:1, with the reaction temperature controlled at 65-75℃, pH 1.0-1.8, and residence time at 70-90 min, so that the magnesium minerals are fully dissolved into a magnesium chloride solution, and the tailings are removed by filtration; S3: Deep purification and impurity removal: Add magnesium oxide emulsion to magnesium leaching solution, adjust pH to 4.2-5.0, add calcium chloride + trisodium phosphate composite calcium removal agent, stir and react for 20-30 min to form calcium, silicon, iron and aluminum into precipitates, and obtain pure magnesium chloride solution by plate and frame filter press + precision filtration. S4: Tubular Mixing Magnesium Precipitation Crystallization: The purified magnesium chloride solution and 25%–32% sodium hydroxide solution are rapidly mixed through a tubular static mixer and introduced into the crystallization kettle. The precipitation temperature is controlled at 50–60℃, the final pH is 9.8–10.5, and the aging time is 80–120 min. During the aging stage, 0.05%–0.1% sodium stearate can be selectively added for in-situ surface modification to obtain magnesium hydroxide precipitates with regular morphology and uniform particle size. S5: Multi-stage countercurrent washing: Three-stage countercurrent washing is adopted, the washing water temperature is 40-50℃, and the filtrate chloride ion is ≤0.05%. The washing water is returned to the mixing tank for reuse. S6: Dehydration and drying: After centrifugal dehydration, the product enters a flash dryer, with the inlet temperature controlled at 170-190℃ and the outlet temperature at 85-95℃. After drying, high-purity magnesium hydroxide powder is obtained.

[0030] In an embodiment of the present invention, the acidic system in step S2 is a hydrochloric acid system or a mixed acid system with a hydrochloric acid to sulfuric acid molar ratio of 9:1; the acid leaching temperature is 65–75°C, the pH is 1.0–1.8, and the leaching time is 70–90 min.

[0031] In an embodiment of the present invention, in step S3, the pH of the magnesium-containing filtrate is adjusted to 4.2–5.0, and the reaction time of the composite calcium removal agent is 20–30 min, so as to achieve deep co-precipitation removal of impurity ions.

[0032] In an embodiment of the present invention, the precipitation temperature in step S4 is 50–60°C, the final pH is 9.8–10.5, and the aging time is 80–120 min; during the aging stage, 0.05%–0.1% sodium stearate may be added for in-situ surface modification.

[0033] In an embodiment of the present invention, in step S5, the washing water temperature is 40–50°C, and the washing is continued until the chloride ion content of the filtrate is ≤0.05%; in step S6, the flash drying inlet temperature is 170–190°C, and the outlet temperature is 85–95°C.

[0034] In the embodiments of the present invention, the product specifications are as follows: Mg(OH)2 purity ≥ 99.2%, CaO ≤ 0.08%, SiO2 ≤ 0.05%, chloride ion ≤ 0.05%; electronic grade product purity ≥ 99.4%, and low-chlorine high-dispersion flame retardant grade product chloride ion ≤ 0.02%, meeting the requirements of high-end application scenarios.

[0035] This method has the following specific characteristics: High resource utilization rate: Using magnesite flotation tailings mud as raw material, the magnesium recovery rate is ≥85%, realizing the high-value utilization of solid waste and meeting the requirements of environmental protection policies; Continuous and low-energy consumption: The entire process is continuous and automated, with stable operating conditions. Energy consumption is reduced by 22%–28% compared to intermittent processes, thus improving production efficiency. Deep purification: The compound calcium removal agent synergistically removes calcium, silicon, iron and aluminum, with a product purity of ≥99.2%, meeting the needs of high-end applications; Green, water-saving and environmentally friendly: Three-stage counter-current washing + closed-loop water circulation, water reuse rate ≥95%, basically no external wastewater discharge, reducing environmental protection costs; Product customization: Crystal form, particle size and chloride ion content can be precisely controlled to customize electronic grade and low-chlorine high-dispersion flame retardant products, thus broadening the application range.

[0036] Example 1: A conventional method for preparing high-purity magnesium hydroxide Raw material: Magnesite flotation tailings slime, MgO 36.5%; S1: Slurry with a solid content of 20%, sieved, iron removed, and hydrocyclone classified; S2: Acid leaching temperature 70℃, pH 1.5, time 80 min; S3: Adjust pH to 4.5, add calcium chloride + trisodium phosphate composite calcium removal agent, react for 25 min, and filter; S4: Sodium hydroxide precipitation, temperature 55℃, endpoint pH 10.0, aging for 90 min; S5: Three-stage countercurrent washing, centrifugal dehydration, flash drying, inlet 180℃.

[0037] Performance results: Mg(OH)2 purity: 99.25%; CaO: 0.07%; SiO2: 0.04%; whiteness: 93.5%; median particle size D50: 3.2 μm.

[0038] Example 2: Electronic-grade high-purity magnesium hydroxide S1: Slurry solids content 18%; S2: Acid leaching temperature 72℃, pH 1.3, time 90 min; S3: The purification pH is adjusted to 4.7, and the dosage of calcium removal agent is increased by 10%; S4: Precipitation temperature 52℃, endpoint pH 10.2, aging for 100 min; S5: Wash until chloride ions ≤0.03%.

[0039] Performance results: Mg(OH)2 purity: 99.42%; CaO: 0.04%; SiO2: 0.025%; whiteness: 94.8%, suitable for electronic ceramics and lithium battery materials.

[0040] Example 3: Low-chlorine, highly dispersed, flame-retardant magnesium hydroxide S1: Acid leaching uses a mixture of hydrochloric acid and a small amount of sulfuric acid, with a molar ratio of 9:1, to suppress secondary entrainment of calcium and silicon. S2: Precipitation uses a composite precipitant of sodium hydroxide and ammonia at a volume ratio of 8:2 to improve crystal regularity; S3: During the aging stage, 0.1% sodium stearate surface modifier is added for in-situ coating modification; S4: Aging time extended to 120 min, drying temperature 170℃.

[0041] Performance results: Mg(OH)2 purity: 99.30%; Cl⁻: 0.02%; oil absorption value: ≤28 mL / 100g; dispersibility: no agglomeration, suitable for halogen-free flame-retardant polymer materials.

[0042] Example 4: Industrialized Continuous Pilot Production With a processing capacity of 1 t / h of tailings sludge, the entire process can operate continuously for 72 hours, achieving a magnesium recovery rate of 86.2%, a water reuse rate of 96%, and a product purity of 99.31%. The process is stable and reliable, and has industrial application value.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime, characterized in that, It includes a pretreatment unit, a continuous acid leaching magnesium extraction unit, a deep purification and impurity removal unit, a tubular mixing magnesium precipitation crystallization unit, a multi-stage countercurrent washing and dehydration unit, and a flash drying unit connected sequentially along the process flow. The pretreatment unit includes a slurry mixing tank, a vibrating screen, a permanent magnet separator, and a hydrocyclone. The continuous acid leaching magnesium extraction unit includes a steam preheater, a continuous acid leaching reactor with a heating jacket, an online pH control system, and a solid-liquid separation device. The deep purification and impurity removal unit includes a neutralization and pH adjustment tank, a plate and frame filter press, and a precision filter. The tubular mixed magnesium precipitation crystallization unit includes a tubular static mixer and a crystallization kettle with crystal form control; The multi-stage countercurrent washing and dewatering unit includes a three-stage countercurrent washing tank, a centrifugal dewatering machine, and a washing water recycling pump. The flash drying finished product unit includes a flash dryer, a cyclone separator, a bag filter, and a finished product silo. Each unit is connected in sequence through pipes, valves, and transfer pumps. The washing water from the three-stage countercurrent washing tank is returned to the slurry tank of the pretreatment unit via a reuse pump, forming a closed-loop water circulation.

2. The complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to claim 1, characterized in that, The temperature control range of the continuous acid leaching reactor is 50–80℃.

3. A green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime, based on the complete set of equipment for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime as described in claim 2, characterized in that, Includes the following steps: S1: Raw material pretreatment: Magnesite flotation tailings mud is mixed with water to form a slurry, which is then screened to remove coarse slag, removed by permanent magnet iron removal, and classified by hydrocyclone to obtain fine-grained pure slurry; S2: Continuous acid leaching for magnesium extraction: The slurry is preheated with steam and then enters a continuous acid leaching reactor. It is leached at normal pressure and temperature under acidic conditions. After solid-liquid separation, magnesium-containing leaching filtrate is obtained. S3: Deep purification and impurity removal: Adjust the pH of the magnesium-containing filtrate, add a calcium chloride and trisodium phosphate composite calcium removal agent to deeply remove calcium, silicon, iron and aluminum impurities, and filter to obtain high-purity magnesium solution; S4: Tubular Mixing Magnesium Precipitation Crystallization: High-purity magnesium solution and sodium hydroxide solution are rapidly and homogenously mixed in a tubular static mixer, and magnesium precipitation, crystallization, and aging are completed in a crystallization kettle with crystal form control to obtain crude magnesium hydroxide; S5: Multi-stage countercurrent washing and dehydration: Crude magnesium hydroxide is washed in three stages to remove impurity ions, and then centrifuged to dehydrate to obtain wet base material; S6: Flash drying: High-purity magnesium hydroxide powder is obtained by flash drying of wet materials.

4. The green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to claim 3, characterized in that, The acidic system in step S2 is a hydrochloric acid system or a mixed acid system with a hydrochloric acid to sulfuric acid molar ratio of 9:1; the acid leaching temperature is 65–75℃, pH 1.0–1.8, and the leaching time is 70–90 min.

5. The green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to claim 3, characterized in that, In step S3, the pH of the magnesium-containing filtrate is adjusted to 4.2–5.0, and the reaction time of the composite calcium removal agent is 20–30 min, so as to achieve deep co-precipitation removal of impurity ions.

6. The green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to claim 3, characterized in that, In step S4, the precipitation temperature is 50–60℃, the final pH is 9.8–10.5, and the aging time is 80–120 min. During the aging stage, 0.05%–0.1% sodium stearate may be added for in-situ surface modification.

7. The green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to claim 3, characterized in that, In step S5, the washing water temperature is 40–50℃, and the washing continues until the chloride ion content in the filtrate is ≤0.05%. In step S6, the flash drying inlet temperature is 170–190℃, and the outlet temperature is 85–95℃.

8. A green preparation method for preparing high-purity magnesium hydroxide from magnesite flotation tailings slime according to any one of claims 3-7, characterized in that, The resulting product specifications are as follows: Mg(OH)2 purity ≥ 99.2%, CaO ≤ 0.08%, SiO2 ≤ 0.05%, chloride ion ≤ 0.05%; electronic grade product purity ≥ 99.4%, and low-chlorine, high-dispersion flame-retardant grade product chloride ion ≤ 0.02%, meeting the requirements of high-end application scenarios.

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