A gradient activation synergistic leaching method for low-grade nickel-bearing silicate tailings

Abstract

This invention discloses a gradient activation and synergistic leaching method for low-grade nickel-containing silicate tailings, belonging to the field of non-ferrous metal tailings resource utilization and hydrometallurgical technology. The method includes the following steps: the tailings are crushed, finely ground, and then air-classified; the coarse particles are returned for regrinding, while the fine particles are used as gradient activation raw materials; the tailings are sequentially activated through a three-stage coupled activation process involving low-temperature mechanochemical oxidation, medium-temperature directional roasting, and ultrasonic-assisted hydration to obtain a gradient activated tailings slurry; a compound leaching agent is added for pH-controlled leaching, and solid-liquid separation yields leaching tailings and a nickel-containing leachate; the tailings washing liquid is incorporated into the leaching liquid; the leaching liquid undergoes selective oxidation to remove iron and aluminum, followed by solvent countercurrent extraction-back-extraction to obtain a nickel sulfate solution, with byproducts of iron-aluminum slag and raffinate; the leaching tailings are used to prepare activated silica powder, the iron-aluminum slag is used to prepare ironmaking feedstock or water purification agents, and the raffinate is used for stepwise precipitation to recover manganese and magnesium; the magnesium-precipitated filtrate is purified and returned to the leaching process for recycling.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal tailings resource utilization and hydrometallurgical technology, specifically relating to a gradient activation and synergistic leaching method for low-grade nickel-containing silicate tailings. Background Technology

[0002] With the continued growth in demand for nickel resources, high-grade sulfide nickel ore resources are becoming increasingly depleted, and the development and utilization of low-grade silicate nickel ore has become an industry trend. However, after nickel extraction from this type of ore, a large amount of nickel-bearing silicate tailings with a nickel grade of less than 0.3 wt% are generated, which are currently mainly disposed of through open-pit stockpiling. Stockpiling not only occupies a large amount of land resources, but also poses a risk of leaching and seeping of heavy metal ions such as nickel and cobalt with rainwater, easily causing soil and groundwater pollution and seriously threatening ecological and environmental safety.

[0003] Current technologies for treating low-grade nickel-bearing silicate tailings primarily rely on wet acid leaching. However, conventional acid leaching processes have significant drawbacks: because nickel is encapsulated in a dense silicate lattice, acid leaching at room temperature and pressure is insufficient to disrupt the lattice structure, resulting in nickel leaching rates generally below 65%. High-temperature, high-pressure leaching, on the other hand, suffers from high acid consumption, severe equipment corrosion, and high operating costs, hindering industrial application. To improve leaching efficiency, some processes incorporate mechanical grinding or high-temperature roasting activation pretreatment. However, single activation methods have clear limitations: mechanical grinding only refines mineral particle size but cannot fundamentally destroy the silicate lattice, leading to low activation efficiency and high energy consumption; while high-temperature roasting can destroy the lattice, it easily causes mineral sintering and agglomeration, reducing subsequent leaching mass transfer efficiency and resulting in persistently high energy costs. Furthermore, existing processes generally suffer from low overall recovery rates of valuable elements. The leaching tailings still contain a large amount of valuable components such as silicon, magnesium, aluminum, and iron, most of which are not effectively recovered and utilized. Direct stockpiling generates a large amount of secondary solid waste. Separating multiple metal ions from the leachate is difficult; when using stepwise neutralization and impurity removal, nickel and cobalt are prone to co-precipitation with magnesium and manganese, resulting in low purity of nickel products and significant loss of recovery rate. Furthermore, the leaching wastewater is mostly not recycled in a closed loop, leading to high wastewater treatment costs and further reducing the economic and environmental benefits of the process.

[0004] In summary, existing technologies cannot simultaneously achieve efficient leaching, full element recovery, and green and environmentally friendly disposal of low-grade nickel-containing silicate tailings. There is an urgent need to develop a new gradient activation-synergistic leaching and full element resource recovery method. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a gradient activation and synergistic leaching method for low-grade nickel-containing silicate tailings, particularly suitable for the harmless treatment and high-value utilization of silicate-type tailings with nickel grades below 0.3 wt% and complex silicon, magnesium, aluminum, and iron components. This method addresses the technical problems in the prior art, such as the dense encapsulation of nickel in the silicate lattice making conventional leaching difficult to destroy, low nickel leaching rate, high energy consumption and poor effect of single activation processes, inability to achieve directional dissociation of tailings components, low separation accuracy of polymetallic ions in the leaching solution, insufficient purity of nickel products and low comprehensive recovery rate of valuable elements, as well as the lack of closed-loop utilization of leaching tailings and waste liquid, large discharge of solid waste and wastewater, and poor environmental protection and economic efficiency.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a gradient activation synergistic leaching method for low-grade nickel-containing silicate tailings, comprising the following steps: S1, Raw material pretreatment and classification: Low-grade nickel-containing silicate tailings are crushed, finely ground and then air classified. The coarse-grained tailings are returned for regrinding, and the fine-grained tailings are used as gradient activation raw materials. S2, Gradient Coupling Activation: Fine-grained tailings are sequentially subjected to three-stage coupled gradient activation treatment: low-temperature mechanical and chemical activation, medium-temperature directional roasting activation, and ultrasonic-assisted hydration activation to obtain gradient activated tailings slurry. S3, weak acid-complex synergistic leaching: a compound leaching agent system is added to the gradient activated tailings slurry and synergistic leaching is carried out at a set pH value. After leaching, solid and liquid separation is obtained to obtain leaching tailings and nickel-containing leaching solution. The leaching tailings are washed and the washing liquid is incorporated into the nickel-containing leaching solution. S4, Leachate purification and enrichment: The nickel-containing leaching solution is subjected to selective oxidation to remove iron and aluminum, and solvent countercurrent extraction-back-extraction in sequence to separate and purify the nickel sulfate solution, producing iron and aluminum slag and raffinate. S5, closed-loop resource utilization of all elements: the leaching tailings are dried, calcined, finely ground and classified to prepare active silica powder; iron and aluminum slag is used to prepare ironmaking sintering ingredients or polyaluminum ferric chloride water purification agent; the raffinate is subjected to stepwise pH adjustment and precipitation to recover manganese and magnesium products in sequence, and magnesium precipitation filtrate is obtained; after pH adjustment and solid-liquid separation purification, the magnesium precipitation filtrate is returned to the weak acid-complex synergistic leaching as leaching water for recycling.

[0007] In one embodiment, the process of crushing and finely grinding low-grade nickel-containing silicate tailings followed by air classification, with the coarse-grained tailings returned for regrinding and the fine-grained tailings used as gradient activation raw material, is as follows: Low-grade nickel-containing silicate tailings are fed into a double-toothed roll crusher at a constant feed rate of 3.2-3.8 t / h, and the output particle size is controlled to be 8-12 mm to obtain the crushed product. The crushed product is fed into a vertical impact mill for fine grinding. High-chromium cast iron balls of 20mm, 15mm and 10mm are graded in a mass ratio of 4:3:3, with a media filling rate of 38%-42%, a slurry concentration of 62%-68%, and a grinding time of 25-35min to obtain finely ground tailings powder with D90≤74μm. The finely ground tailings powder is fed into a horizontal air classifier with an inlet pressure of 0.45-0.55MPa and a classifier wheel speed of 1200-1400r / min. The dry classification yields coarse-grained tailings of 45-74μm and fine-grained tailings of ≤45μm. The coarse-grained tailings are returned for regrinding, while the fine-grained tailings are stored in a sealed silo with a humidity of less than 45% for later use.

[0008] In one embodiment, the low-temperature mechanochemical activation process is as follows: Fine-grained tailings and compound activation aids are mixed at a mass ratio of 1:0.08-0.12 and fed into a horizontal planetary ball mill for mechanochemical activation to obtain a low-temperature mechanochemical activated product. By mass, the compound activating agent consists of 12-18 parts sodium bisulfate, 5-9 parts ammonium bifluoride, and 2-5 parts sodium tripolyphosphate. The horizontal planetary ball mill uses 12mm, 8mm, and 5mm zirconia grinding balls in a mass ratio of 5:3:2, with a ball-to-material ratio of 15:1-20:1. The revolution speed is 380-420 r / min, and the rotation speed is 1.2 times the revolution speed. During mechanochemical activation, the circulating water bath temperature is controlled at 45-55℃, and the mechanochemical activation time is 40-60 min.

[0009] In one embodiment, the process of medium-temperature directional calcination activation is as follows: The low-temperature mechanical and chemical activation product is fed into a mesh belt roasting furnace, and nitrogen gas is introduced to maintain the oxygen volume fraction in the furnace below 0.5%, with a nitrogen flow rate of 0.8-1.2 m³ / h. 3 / h; segmented heating is adopted: the first stage is to heat up to 380-420℃ at 6-9℃ / min and hold at a constant temperature for 70-90min; the second stage is to heat up to 520-560℃ at 5-7℃ / min and hold at a constant temperature for 50-70min; after roasting, the product is rapidly cooled to below 80℃ by indirect water cooling and then stored in a sealed container.

[0010] In one embodiment, the ultrasound-assisted hydration activation process is as follows: The calcined product and deionized water with a conductivity ≤10μS / cm were added to an ultrasonic hydration reactor at a liquid-to-solid mass ratio of 3:1-4:1. The stirring speed was 180-220 r / min; the dual-frequency ultrasonic frequency was 22-26 kHz, and the power density was 0.35-0.45 W / cm². 3 The system temperature is 65-75℃, and the hydration reaction is carried out for 30-45 minutes to obtain gradient activated tailings slurry.

[0011] In one embodiment, the addition of a compound leaching agent system to the gradient-activated tailings slurry for synergistic leaching at a set pH value, followed by solid-liquid separation to obtain leaching tailings and nickel-containing leachate, and the washing of the leaching tailings followed by the incorporation of the washing liquid into the nickel-containing leachate, is as follows: The gradient-activated tailings slurry is fed into a leaching reaction tank, and a compound leaching agent system is added for synergistic leaching. The liquid-to-solid mass ratio is controlled at 4.5:1-5.5:1, the system temperature at 78-85℃, and the stirring speed at 220-260 r / min. Dilute ammonia is added dropwise to maintain the set pH value at 2.8-3.3, and the leaching reaction is carried out for 120-150 min. After leaching, plate and frame filter press is used to separate the solid and liquid, resulting in leaching tailings and nickel-containing leachate. The leaching tailings are washed multiple times with deionized water at 55-65℃, and the washing liquid is added to the nickel-containing leachate. By mass fraction, the compound leaching agent contains 12%-16% citric acid, 3%-5% aminosulfonic acid, 0.8%-1.2% sodium citrate, and the remainder is water. The mass concentration of the dilute ammonia solution is 15%-20%; The plate and frame filter press has a filtration pressure of 0.6-0.8 MPa and a filtration time of 20-25 min.

[0012] In one embodiment, the selective oxidation process for removing iron and aluminum is as follows: Heat the nickel-containing leaching solution to 62-68℃, stir at 200-240 r / min, add 3%-5% hydrogen peroxide (8%-12% by mass) of the leaching solution and oxidize for 25-35 min; then add 18%-22% magnesium oxide emulsion at a dropping rate of 5-8 mL / min, adjust the pH to 4.1-4.4, stir at a constant temperature for 35-45 min, and filter to obtain iron-aluminum slag and the liquid after iron and aluminum removal.

[0013] In one embodiment, the solvent countercurrent extraction-back-extraction process is as follows: After removing iron and aluminum, the liquid is cooled to 35-42℃. The extractable organic phase is prepared by mixing P507 and sulfonated kerosene at a volume ratio of 17:83-23:77. The extractable organic phase is then saponified with a 10% sulfuric acid solution, with a saponification rate of 65%-75%. A three-stage countercurrent extraction is used, with a volume ratio of extractable organic phase to aqueous phase of 2:1-3:1. The centrifugal extractor speed is 4500-5500 r / min, and the single-stage residence time is 3-5 min, yielding a nickel-loaded organic phase and a raffinate containing magnesium and manganese. The nickel-loaded organic phase was subjected to three-stage countercurrent back-extraction using 1.5%-2.5% dilute sulfuric acid, with a back-extraction ratio of 1:2-1:3, a back-extraction temperature of 28-35℃, and a single-stage back-extraction time of 2-4 min, to obtain a nickel sulfate solution with a nickel concentration ≥45g / L.

[0014] In one embodiment, the process of preparing active silica powder from the leaching tailings by drying, calcining, fine grinding, and classification is as follows: The leaching tailings are dried at 105-115℃ until the moisture content is ≤1%, calcined at a constant temperature of 620-680℃ for 45-60 minutes, finely ground to D90≤20μm, and then air-separated to obtain active silicon micro powder with SiO2 content ≥85%.

[0015] In one embodiment, the raffinate is subjected to stepwise pH adjustment and precipitation to recover manganese and magnesium products sequentially, yielding a magnesium-precipitated filtrate. After pH adjustment and solid-liquid separation purification, the magnesium-precipitated filtrate is entirely returned to the weak acid-complexation synergistic leaching process for reuse as leaching water, as follows: Heat the raffinate to 42-48℃, stir at 180-220 r / min, and adjust the pH to 9.2-9.6 by adding a 25%-28% sodium hydroxide solution dropwise. Then, introduce 0.3-0.5 m³ of [aluminum / water] into the solution. 3 Oxidation with compressed air for 30-40 minutes per hour, followed by pressure filtration to obtain manganese slag with a manganese content ≥35% and filtrate after manganese precipitation; After manganese precipitation, add 25%-28% sodium hydroxide solution to adjust the pH to 10.8-11.2, stir at a constant temperature for 25-35 minutes, and filter by pressure to obtain magnesium hydroxide with a purity ≥92% and magnesium precipitation filtrate. After magnesium precipitation, dilute sulfuric acid is added to the filtrate to adjust the pH to 6.5-7.5. After filtration, the filtrate is returned to the weak acid-complex synergistic leaching process and reused as leaching water.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a gradient activation and synergistic leaching method for low-grade nickel-containing silicate tailings. Through a raw material pretreatment and classification process, the tailings are crushed and finely ground, followed by air-jet classification and re-grinding of coarse particles to ensure uniform particle size of the activated raw materials, laying the foundation for subsequent efficient activation. The method innovatively employs a three-stage coupled gradient activation process: low-temperature mechanochemical activation, medium-temperature directional roasting activation, and ultrasonic-assisted hydration activation. This process gradually and directionally dissociates the dense silicate lattice, fully exposing the encapsulated nickel components, solving the problems of high energy consumption and poor efficiency associated with single activation methods, and significantly improving nickel leaching kinetics. The method utilizes a weak acid-complex synergistic leaching system to achieve efficient and selective nickel leaching under mild temperature and pH control conditions, avoiding the problems associated with traditional methods. The high corrosion and high acid consumption problems of strong acid leaching are addressed by reducing the dissolution of impurity ions and lowering the load on subsequent impurity removal. By selectively oxidizing to remove iron and aluminum combined with a solvent countercurrent extraction-back-extraction process, efficient separation of nickel from impurities such as iron, aluminum, magnesium, and manganese is achieved, producing a high-purity nickel sulfate solution. This solves the problems of low metal separation accuracy and insufficient purity of nickel products in existing processes. A closed-loop resource recovery system for all elements is constructed, using leaching tailings to prepare active silica powder, stepwise precipitation and recovery of manganese and magnesium products from raffinate, and resource recovery of iron and aluminum slag to prepare ironmaking feedstock or water purification agents. The filtrate after magnesium precipitation is adjusted and purified before being returned to the leaching process for recycling, achieving full recovery and utilization of nickel, silicon, magnesium, aluminum, and iron in tailings without secondary solid waste or wastewater discharge.

[0017] Furthermore, the entire process employs online monitoring and automatic control to ensure stable and reliable operation. The recycling of reagents and organic phases significantly reduces the consumption of raw and auxiliary materials, thereby greatly improving the environmental friendliness and industrial feasibility of the process. Detailed Implementation

[0018] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0019] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0020] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0021] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0022] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0023] This invention provides a gradient activation synergistic leaching method for low-grade nickel-containing silicate tailings, comprising the following steps: S1, Raw material pretreatment and classification: Low-grade nickel-containing silicate tailings are crushed, finely ground and then air classified. The coarse-grained tailings are returned for regrinding, and the fine-grained tailings are used as gradient activation raw materials. S2, Gradient Coupling Activation: Fine-grained tailings are sequentially subjected to three-stage coupled gradient activation treatment: low-temperature mechanical and chemical activation, medium-temperature directional roasting activation, and ultrasonic-assisted hydration activation to obtain gradient activated tailings slurry. S3, weak acid-complex synergistic leaching: a compound leaching agent system is added to the gradient activated tailings slurry and synergistic leaching is carried out at a set pH value. After leaching, solid and liquid separation is obtained to obtain leaching tailings and nickel-containing leaching solution. The leaching tailings are washed and the washing liquid is incorporated into the nickel-containing leaching solution. S4, Leachate purification and enrichment: The nickel-containing leaching solution is subjected to selective oxidation to remove iron and aluminum, and solvent countercurrent extraction-back-extraction in sequence to separate and purify the nickel sulfate solution, producing iron and aluminum slag and raffinate. S5, closed-loop resource utilization of all elements: the leaching tailings are dried, calcined, finely ground and classified to prepare active silica powder; iron and aluminum slag is used to prepare ironmaking sintering ingredients or polyaluminum ferric chloride water purification agent; the raffinate is subjected to stepwise pH adjustment and precipitation to recover manganese and magnesium products in sequence, and magnesium precipitation filtrate is obtained; after pH adjustment and solid-liquid separation purification, the magnesium precipitation filtrate is returned to the weak acid-complex synergistic leaching as leaching water for recycling.

[0024] This invention provides a gradient activation and synergistic leaching method for low-grade nickel-containing silicate tailings, specifically including the following steps: I. Raw material pretreatment and graded crushing The collected low-grade nickel-containing silicate tailings are first fed into a double-toothed roller crusher at a constant feed rate of 3.2-3.8 t / h via a plate feeder. The gap between the crusher teeth is set to 9 mm, and the output particle size is controlled to be stable in the range of 8-12 mm. The crushed product is then conveyed by a belt conveyor to a vertical impact mill for fine grinding. High-chromium cast iron balls are used as the grinding media in the fine grinding process. The media diameters are divided into three types: 20 mm, 15 mm, and 10 mm, which are added in a mass ratio of 4:3:3. The media filling rate is controlled at 38%-42%, the grinding slurry concentration is strictly maintained at 62%-68%, and the grinding time is set to 25-35 min. After grinding, finely ground tailings powder with a particle size distribution D90≤74μm is obtained.

[0025] The finely ground tailings powder is fed into a horizontal air classifier via a screw feeder. The classifier's inlet air pressure is adjusted to 0.45-0.55 MPa, and the classifying wheel speed is controlled at 1200-1400 r / min. Under these conditions, dry precision classification is performed to separate coarse particles (45-74 μm) and fine particles (≤45 μm). The coarse particles are re-fed into a vertical impact mill via a return conveyor belt for regrinding, ensuring that all materials meet the target particle size requirements. The fine particles are collected in a sealed silo as a dedicated raw material for subsequent gradient activation. The raw material storage environment is kept dry, with humidity controlled below 45% to prevent moisture absorption and agglomeration that could affect the activation effect.

[0026] II. Gradient Coupling Activation Process (I) Low-temperature mechanochemical activation Fine-grained tailings powder and compound activation aids are uniformly mixed at a mass ratio of 1:0.08-0.12 and then fed into a horizontal planetary ball mill for mechanochemical activation. The activation aids are prepared by mixing 12-18 parts by mass of sodium bisulfate, 5-9 parts by mass of ammonium bifluoride, and 2-5 parts by mass of sodium tripolyphosphate in a high-speed mixer at 300 r / min for 15 min. The ball mill uses zirconia grinding balls with diameters of 12 mm, 8 mm, and 5 mm, graded at a mass ratio of 5:3:2, with a ball-to-material ratio set at 15:1-20:1. The ball mill's revolution speed is 380-420 r / min, and its rotation speed is 1.2 times the revolution speed. The activation process uses a circulating water bath to control the temperature, keeping the material temperature inside the tank stable at 45-55℃, and the activation time lasts for 40-60 min. This process increases the surface energy of the tailings through mechanical force, causing initial distortion and microcracks in the silicate mineral lattice, thus reducing the difficulty of subsequent processing.

[0027] (II) Activation by medium-temperature directional calcination The mechanochemically activated product is fed into a mesh belt roasting furnace via a sealed screw conveyor. High-purity nitrogen is continuously introduced into the furnace to create an inert atmosphere, with the nitrogen flow rate controlled at 0.8-1.2 m³ / h. 3The oxygen volume fraction in the furnace is below 0.5% per hour. The roasting furnace adopts a segmented heating mode. The first stage heats up at a rate of 6-9℃ / min, reaching 380-420℃ and then holding at that temperature for 70-90min to remove bound water from the mineral surface and break weak bonds. The second stage continues to heat up at a rate of 5-7℃ / min to 520-560℃, holding at that temperature for 50-70min to directionally disrupt the dense lattice structure of silicates, allowing the encapsulated nickel component to fully dissociate and be exposed. After roasting, the product enters the cooling section at the tail of the furnace via a mesh belt, where indirect water cooling is used to rapidly cool the material to below 80℃ to avoid secondary oxidation of the high-temperature product. After cooling, the product is collected in a sealed buffer silo.

[0028] (III) Ultrasonic-assisted hydration activation The calcined and activated product is added to the ultrasonic hydration reactor along with deionized water (conductivity ≤10 μS / cm) at a liquid-to-solid mass ratio of 3:1-4:1. The stirring device is turned on, and the stirring speed is set to 180-220 r / min to ensure thorough dispersion of the materials and the formation of a uniform slurry. The hydration reactor is equipped with a dual-frequency ultrasonic generator system, with the ultrasonic frequency switching between 22-26 kHz and the ultrasonic power density controlled at 0.35-0.45 W / cm³. 3 The system temperature is stabilized at 65-75℃ by jacket steam heating, and the hydration reaction lasts for 30-45 minutes. The microjets and shock waves generated by ultrasonic cavitation can further loosen mineral aggregates, expand lattice cracks, enhance the surface wettability of mineral particles, and significantly improve the mass transfer efficiency of subsequent leaching processes. After hydration, a gradient activated tailings slurry with good fluidity is obtained and can be directly entered into the next leaching process.

[0029] III. Weak Acid-Complex Synergistic Leaching Separation The gradient-activated tailings slurry is pumped into a PTFE-lined leaching reaction tank via a corrosion-resistant pump. A compound leaching agent system is continuously added to the tank for synergistic leaching. The compound leaching agent is prepared by mixing a 12%-16% (w / w) citric acid solution, a 3%-5% (w / w) aminosulfonic acid solution, and 0.8-1.2 (w / w) sodium citrate complexing agent in a stirred tank for 30 minutes. The liquid-solid mass ratio is controlled at 4.5:1-5.5:1 during the leaching process. The system temperature is stabilized at 78-85℃ by steam heating coils, and the stirring speed is set at 220-260 r / min.

[0030] The entire leaching process was monitored in real-time using an online pH meter. A 15%-20% concentration of dilute ammonia solution was slowly added dropwise via a metering pump to precisely maintain the system pH between 2.8 and 3.3, preventing premature hydrolysis of metal ions due to pH fluctuations. The leaching reaction lasted 120-150 minutes, with samples taken every 30 minutes to measure the nickel leaching rate and ensure complete reaction. After leaching, the slurry was pumped to a plate and frame filter press for solid-liquid separation at a filtration pressure of 0.6-0.8 MPa and a filtration time of 20-25 minutes, yielding a nickel-containing leachate and leaching tailings. The leaching tailings were washed three times in a washing tank with deionized water at 55-65℃, with a solid-liquid ratio of 2:1 for each wash and a stirring time of 10 minutes. All three washes were combined into the nickel-containing leachate to minimize nickel loss.

[0031] IV. Deep purification of leaching solution and nickel enrichment (a) Selective oxidation to remove iron and aluminum The combined nickel-containing leaching solution is fed into a heated reactor and heated to 62-68°C using a jacketed steam heater. Stirring is initiated at a speed of 200-240 r / min. Hydrogen peroxide (8%-12% by mass) is slowly added as an oxidant, at a concentration of 3%-5% of the leaching solution volume. The oxidation reaction continues for 25-35 minutes, completely oxidizing the ferrous iron (Fe2+) in the leaching solution to ferric iron (Fe3+). After oxidation, a light magnesium oxide emulsion (18%-22% by mass) is slowly added dropwise using a metering pump at a rate of 5-8 mL / min, while stirring continuously. The pH of the system is adjusted to 4.1-4.4, and the mixture is stirred at a constant temperature for 35-45 minutes to ensure complete hydrolysis of iron and aluminum ions, forming hydroxide precipitates. After the reaction, the slurry is filtered using a plate and frame filter press to obtain iron-aluminum hydroxide slag and a liquid after iron and aluminum removal. The iron-aluminum slag is washed twice with deionized water, and the washing liquid is returned to the impurity removal process.

[0032] (ii) Solvent extraction separation and enrichment of nickel After removing iron and aluminum, the liquid is cooled to 35-42℃ using a plate cooler and then fed into a centrifugal extractor for nickel extraction and separation. The organic phase for extraction is prepared by mixing acidic phosphorus extractant P507 with sulfonated kerosene at a volume ratio of 17:83-23:77. The organic phase is pre-saponified with a 10% sulfuric acid solution, with the saponification rate controlled at 65%-75%. The extraction adopts a three-stage countercurrent mode, with an organic phase to aqueous phase volume ratio of 2:1-3:1. The centrifugal extractor speed is set to 4500-5500 r / min, and the residence time for each extraction stage is 3-5 min to ensure that nickel ions are fully transferred to the organic phase, resulting in a nickel-loaded organic phase and a raffinate containing magnesium and manganese.

[0033] The nickel-loaded organic phase is fed into the back-extraction section, where a 1.5%-2.5% (w / w) dilute sulfuric acid solution is used as the back-extraction agent. Three-stage countercurrent back-extraction is performed, with a back-extraction ratio (organic phase: aqueous phase) of 1:2-1:3. The back-extraction temperature is controlled at 28-35℃, and the single-stage back-extraction time is 2-4 min. After back-extraction, a high-purity nickel sulfate solution with a nickel concentration ≥45 g / L is obtained. The organic phase is recycled after regeneration.

[0034] V. Comprehensive Resource Utilization of Tailings and Waste Liquid (a) Preparation of activated silica powder from leaching tailings The leaching tailings obtained from pressure filtration are first fed into a rotary dryer and dried at 105-115℃ until the moisture content is ≤1%. After drying, the material is fed into a rotary kiln and calcined at a constant temperature of 620-680℃ for 45-60 minutes to convert the amorphous silica in the tailings into a highly active phase. The calcined product is then finely ground in a horizontal ball mill to a D90 ≤ 20μm, and then sent to an air classifier for classification to remove coarse particles, yielding active silica micropowder with a silica content ≥85%, which can be directly used as a functional filler for rubber, coatings, and plastics.

[0035] (ii) Stepwise precipitation of manganese and magnesium in the raffinate The raffinate is transferred to a precipitation reactor and heated to 42-48℃. Stirring is started at 180-220 r / min. A 25%-28% sodium hydroxide solution is added dropwise using a metering pump to adjust the pH of the system to 9.2-9.6. Simultaneously, compressed air is introduced into the reactor at a flow rate of 0.3-0.5 m³ / min. 3 The oxidation reaction is carried out at a rate of 30-40 minutes per hour, allowing manganese ions to be completely oxidized and precipitated. The slurry is then filtered to obtain high-purity manganese slag with a manganese content ≥35%.

[0036] The filtrate after manganese precipitation is fed into the next reactor, where the temperature is maintained at 42-48℃ and the stirring speed remains constant. The aforementioned sodium hydroxide solution is added dropwise to adjust the pH to 10.8-11.2. The mixture is stirred at a constant temperature for 25-35 minutes until magnesium ions are completely precipitated as magnesium hydroxide. The magnesium hydroxide product is obtained by pressure filtration with a purity ≥92%. The filtrate after magnesium precipitation is adjusted to pH 6.5-7.5 using dilute sulfuric acid. After filtering through a sand filter to remove suspended impurities, the entire filtrate is returned to the leaching process as process water for recycling, achieving a closed-loop water resource system.

[0037] (III) Resource utilization of iron and aluminum slag The iron-aluminum hydroxide slag obtained after impurity removal is washed with deionized water until the pH value of the filtrate is 6.5-7.5. It is then sent to a hot air dryer and dried at 120℃ until the moisture content is ≤2%. The dried product can be used directly as a raw material for ironmaking sintering, or it can be acid-dissolved and polymerized to prepare polyaluminum ferric chloride water purification agent, thereby realizing the high-value utilization of iron and aluminum elements.

[0038] VI. Closed-loop control of the entire process The entire process system is equipped with an online monitoring and automatic control unit to monitor and automatically adjust key parameters such as crushing particle size, activation temperature, leaching pH, extraction ratio, and precipitation pH in real time. During the process, the washing water, back-extraction waste liquid, and clarified liquid after magnesium and manganese precipitation are all directionally recycled, with no wastewater discharge; the leaching tailings, iron-aluminum slag, manganese slag, and magnesium slag are all utilized as resources, with no solid waste generated; the recycling loss of compound leaching agent and extraction organic phase is less than 8%, significantly reducing the consumption of raw and auxiliary materials; the total recovery rate of nickel is stable at ≥88%, and the comprehensive recovery rate of valuable elements such as silicon, magnesium, aluminum, and iron is ≥82%, achieving green, efficient, and full-element resource utilization of low-grade nickel-containing silicate tailings.

[0039] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0040] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0041] Examples and Experimental Results Example 1 The low-grade nickel-containing silicate tailings raw material has a nickel grade of 0.26wt%. It is pretreated according to the following technical scheme: the output particle size of the double-toothed roller crusher is 9mm, the grinding concentration of the vertical impact mill is 64%, the grinding time is 29min, and the fine-ground tailings powder D90=68μm; the air classifier inlet pressure is 0.49MPa, the classifier wheel speed is 1280r / min, and the fine particle yield is 76.3%.

[0042] Gradient activation: The mechanochemical activation aid consisted of 15 parts sodium bisulfate, 7 parts ammonium bifluoride, and 3.5 parts sodium tripolyphosphate, with a ball-to-material ratio of 17:1. The activation temperature was 49℃, and the activation time was 52 min. The calcination stages were: 395℃ for 82 min and 542℃ for 58 min, with a nitrogen flow rate of 1.0 m³ / min. 3 / h; ultrasonic hydration frequency 24kHz, power density 0.40W / cm³ 3 Temperature 71℃, time 38min.

[0043] Co-leaching: The leaching agent was 14.2% citric acid + 4.1% aminosulfonic acid + 1.0 part sodium citrate, the liquid-to-solid ratio was 5.1:1, the temperature was 82℃, the pH was 3.0, and the time was 136 min.

[0044] Impurity removal extraction: Oxidation to remove iron and aluminum at 65℃, pH=4.2; Extraction of organic phase P507:sulfonated kerosene = 19:81, 3-stage countercurrent extraction; Back-extraction sulfuric acid concentration 2.0%.

[0045] Tailings resource utilization: calcination temperature 650℃, time 52min.

[0046] Experimental results: Nickel leaching rate 89.1%, total nickel recovery rate 88.4%, silicon recovery rate 83.7%, magnesium recovery rate 82.9%, aluminum recovery rate 82.1%, iron recovery rate 83.2%, nickel concentration of nickel sulfate solution 46.3 g / L, magnesium hydroxide purity 92.6%, and SiO2 content of active silicon micropowder 86.2%.

[0047] Example 2 The raw material has a nickel grade of 0.23 wt%, a crushing output particle size of 8 mm, a grinding concentration of 63%, a grinding time of 27 min, and a D90 of 72 μm. The classification pressure is 0.47 MPa, the rotation speed is 1240 r / min, and the fine particle yield is 74.8%.

[0048] The activating agent consisted of 13 parts sodium bisulfate, 6 parts ammonium bifluoride, and 2.8 parts sodium tripolyphosphate. The pellet-to-material ratio was 16:1, the temperature was 47℃, and the time was 47 min. Calcination was carried out at 388℃ for 77 min and then at 533℃ for 54 min, with a nitrogen flow rate of 0.9 m³ / min. 3 / h; hydration frequency 23kHz, power density 0.38W / cm³ 3 Temperature 68℃, time 33min.

[0049] The leaching agent consisted of 13.5% citric acid, 3.7% sulfamic acid, and 0.9 parts sodium citrate. The liquid-to-solid ratio was 4.8:1, the temperature was 80℃, the pH was 2.9, and the time was 128 min.

[0050] The impurity removal temperature was 64℃, and the pH was 4.1. The organic phase extraction was P507: sulfonated kerosene = 18:82, and the sulfuric acid concentration for back-extraction was 1.8%.

[0051] Calcination temperature 635℃, time 48min.

[0052] Experimental results: Nickel leaching rate 87.6%, total nickel recovery rate 86.7%, silicon recovery rate 82.4%, magnesium recovery rate 81.5%, aluminum recovery rate 80.8%, iron recovery rate 81.9%, nickel concentration of nickel sulfate solution 44.7 g / L, magnesium hydroxide purity 91.8%, and SiO2 content of active silicon micropowder 85.3%.

[0053] Example 3 The raw material has a nickel grade of 0.28 wt%, a crushing output particle size of 10 mm, a grinding concentration of 66%, a grinding time of 32 min, and a D90 of 65 μm. The classification pressure is 0.52 MPa, the rotation speed is 1330 r / min, and the fine particle yield is 78.1%.

[0054] The activating agent consisted of 17 parts sodium bisulfate, 8 parts ammonium bifluoride, and 4.2 parts sodium tripolyphosphate. The pellet-to-material ratio was 19:1, the temperature was 52℃, and the time was 57 min. Calcination was carried out at 412℃ for 87 min and then at 554℃ for 65 min, with a nitrogen flow rate of 1.1 m³ / min. 3 / h; hydration frequency 25kHz, power density 0.43W / cm³ 3 Temperature 73℃, time 42min.

[0055] The leaching agent consisted of 15.3% citric acid, 4.6% sulfamic acid, and 1.1 parts sodium citrate. The liquid-to-solid ratio was 5.3:1, the temperature was 84℃, the pH was 3.2, and the time was 144 min.

[0056] The impurity removal temperature was 67℃ and the pH was 4.3. The organic phase extraction ratio was P507: sulfonated kerosene = 21:79, and the sulfuric acid concentration for back-extraction was 2.3%.

[0057] Calcination temperature: 665℃, time: 57min.

[0058] Experimental results: Nickel leaching rate 90.4%, total nickel recovery rate 89.7%, silicon recovery rate 84.9%, magnesium recovery rate 84.2%, aluminum recovery rate 83.6%, iron recovery rate 84.5%, nickel concentration of nickel sulfate solution 47.8 g / L, magnesium hydroxide purity 93.3%, and SiO2 content of active silicon micropowder 87.1%.

[0059] Example 4 The raw material has a nickel grade of 0.21 wt%, a crushing output particle size of 11 mm, a grinding concentration of 62%, a grinding time of 25 min, and a D90 of 73 μm. The classification pressure is 0.45 MPa, the rotation speed is 1210 r / min, and the fine particle yield is 73.2%.

[0060] The activating agent consisted of 12 parts sodium bisulfate, 5 parts ammonium bifluoride, and 2.1 parts sodium tripolyphosphate. The pellet-to-material ratio was 15:1, the temperature was 45℃, and the time was 42 min. Calcination was carried out at 380℃ for 70 min and then at 520℃ for 50 min, with a nitrogen flow rate of 0.8 m³ / min. 3 / h; hydration frequency 22kHz, power density 0.35W / cm³ 3 Temperature 65℃, time 30min.

[0061] The leaching agent consisted of 12.1% citric acid, 3.1% sulfamic acid, and 0.8 parts sodium citrate. The liquid-to-solid ratio was 4.5:1, the temperature was 78℃, the pH was 2.8, and the time was 120 min.

[0062] The impurity removal temperature was 62℃, and the pH was 4.1. The organic phase to be extracted was P507: sulfonated kerosene = 17:83, and the sulfuric acid concentration for back-extraction was 1.5%.

[0063] Calcination temperature 620℃, time 45min.

[0064] Experimental results: nickel leaching rate 86.2%, total nickel recovery rate 85.3%, silicon recovery rate 81.1%, magnesium recovery rate 80.2%, aluminum recovery rate 79.4%, iron recovery rate 80.6%, nickel concentration of nickel sulfate solution 43.2 g / L, magnesium hydroxide purity 90.7%, and SiO2 content of active silicon micropowder 84.2%.

[0065] Example 5 The raw material has a nickel grade of 0.29 wt%, a crushing output particle size of 9 mm, a grinding concentration of 67%, a grinding time of 34 min, and a D90 of 63 μm. The classification pressure is 0.54 MPa, the rotation speed is 1370 r / min, and the fine particle yield is 79.4%.

[0066] The activating agent consisted of 18 parts sodium bisulfate, 9 parts ammonium bifluoride, and 4.8 parts sodium tripolyphosphate. The pellet-to-material ratio was 20:1, the temperature was 54℃, and the time was 59 min. Calcination was carried out at 420℃ for 90 min and then at 560℃ for 70 min, with a nitrogen flow rate of 1.2 m³ / min. 3 / h; hydration frequency 26kHz, power density 0.45W / cm³ 3 Temperature 75℃, time 45min.

[0067] The leaching agent consisted of 15.8% citric acid, 4.9% sulfamic acid, and 1.2 parts sodium citrate. The liquid-to-solid ratio was 5.5:1, the temperature was 85℃, the pH was 3.3, and the time was 150 min.

[0068] The impurity removal temperature was 68℃, and the pH was 4.4. The organic phase extraction ratio was P507: sulfonated kerosene = 23:77, and the sulfuric acid concentration for back-extraction was 2.5%.

[0069] Calcination temperature 680℃, time 60min.

[0070] Experimental results: Nickel leaching rate 91.2%, total nickel recovery rate 90.5%, silicon recovery rate 85.7%, magnesium recovery rate 85.1%, aluminum recovery rate 84.3%, iron recovery rate 85.4%, nickel concentration of nickel sulfate solution 48.5 g / L, magnesium hydroxide purity 93.9%, and SiO2 content of active silicon micropowder 87.8%.

[0071] Example 6 The raw material has a nickel grade of 0.24 wt%, a crushing output particle size of 10 mm, a grinding concentration of 65%, a grinding time of 30 min, and a D90 of 69 μm. The classification pressure is 0.50 MPa, the rotation speed is 1300 r / min, and the fine particle yield is 75.9%.

[0072] The activating agent consisted of 14 parts sodium bisulfate, 6.5 parts ammonium bifluoride, and 3.2 parts sodium tripolyphosphate. The pellet-to-material ratio was 17:1, the temperature was 48℃, and the time was 50 min. Calcination was carried out at 398℃ for 80 min and then at 540℃ for 57 min, with a nitrogen flow rate of 1.0 m³ / min. 3 / h; hydration frequency 24kHz, power density 0.40W / cm³ 3 Temperature 70℃, time 37min.

[0073] The leaching agent consisted of 14.0% citric acid, 3.9% sulfamic acid, and 0.95 parts sodium citrate. The liquid-to-solid ratio was 5.0:1, the temperature was 81℃, the pH was 3.0, and the time was 132 min.

[0074] The impurity removal temperature was 65℃, and the pH was 4.2. The organic phase extraction ratio was P507: sulfonated kerosene = 19:81, and the sulfuric acid concentration for back-extraction was 2.0%.

[0075] Calcination temperature: 645℃, time: 51 min.

[0076] Experimental results: Nickel leaching rate 88.3%, total nickel recovery rate 87.5%, silicon recovery rate 83.1%, magnesium recovery rate 82.3%, aluminum recovery rate 81.6%, iron recovery rate 82.7%, nickel concentration of nickel sulfate solution 45.6 g / L, magnesium hydroxide purity 92.2%, and SiO2 content of active silicon micropowder 85.9%.

[0077] Example 7 The raw material has a nickel grade of 0.22 wt%, a crushing output particle size of 8 mm, a grinding concentration of 64%, a grinding time of 28 min, and a D90 of 71 μm. The classification pressure is 0.48 MPa, the rotation speed is 1260 r / min, and the fine particle yield is 74.1%.

[0078] The activating agent consisted of 13.5 parts sodium bisulfate, 5.8 parts ammonium bifluoride, and 2.6 parts sodium tripolyphosphate. The pellet-to-material ratio was 16:1, the temperature was 46℃, and the time was 45 min. Calcination was carried out at 385℃ for 74 min and then at 528℃ for 52 min, with a nitrogen flow rate of 0.9 m³ / min. 3 / h; hydration frequency 23kHz, power density 0.37W / cm³ 3 Temperature 67℃, time 32min.

[0079] The leaching agent consisted of 13.1% citric acid, 3.5% sulfamic acid, and 0.85 parts sodium citrate. The liquid-to-solid ratio was 4.7:1, the temperature was 79℃, the pH was 2.9, and the time was 125 min.

[0080] The impurity removal temperature was 63℃, and the pH was 4.1. The organic phase extraction ratio was P507: sulfonated kerosene = 18:82, and the sulfuric acid concentration for back-extraction was 1.7%.

[0081] Calcination temperature 630℃, time 47min.

[0082] Experimental results: Nickel leaching rate 86.9%, total nickel recovery rate 86.0%, silicon recovery rate 81.8%, magnesium recovery rate 81.0%, aluminum recovery rate 80.2%, iron recovery rate 81.3%, nickel concentration of nickel sulfate solution 44.1 g / L, magnesium hydroxide purity 91.3%, and SiO2 content of active silicon micropowder 84.8%.

[0083] Example 8 The raw material has a nickel grade of 0.27 wt%, a crushing output particle size of 11 mm, a grinding concentration of 66%, a grinding time of 33 min, and a D90 of 66 μm. The classification pressure is 0.53 MPa, the rotation speed is 1350 r / min, and the fine particle yield is 77.5%.

[0084] The activating agent consisted of 16 parts sodium bisulfate, 7.5 parts ammonium bifluoride, and 3.9 parts sodium tripolyphosphate. The pellet-to-material ratio was 18:1, the temperature was 51℃, and the time was 55 min. Calcination was carried out at 406℃ for 84 min and then at 548℃ for 62 min, with a nitrogen flow rate of 1.1 m³ / min. 3 / h; hydration frequency 25kHz, power density 0.42W / cm³ 3 Temperature 72℃, time 40min.

[0085] The leaching agent consisted of 14.8% citric acid, 4.4% sulfamic acid, and 1.05 parts sodium citrate. The liquid-to-solid ratio was 5.2:1, the temperature was 83℃, the pH was 3.2, and the time was 140 min.

[0086] The impurity removal temperature was 66℃, and the pH was 4.3. The organic phase extraction ratio was P507: sulfonated kerosene = 21:79, and the sulfuric acid concentration for back-extraction was 2.2%.

[0087] Calcination temperature: 655℃, time: 54 min.

[0088] Experimental results: Nickel leaching rate 89.7%, total nickel recovery rate 89.0%, silicon recovery rate 84.3%, magnesium recovery rate 83.5%, aluminum recovery rate 82.9%, iron recovery rate 83.9%, nickel concentration of nickel sulfate solution 47.1 g / L, magnesium hydroxide purity 93.0%, and SiO2 content of active silicon micropowder 86.7%.

[0089] Example 9 The raw material has a nickel grade of 0.25 wt%, a crushing output particle size of 9 mm, a grinding concentration of 65%, a grinding time of 31 min, and a D90 of 67 μm. The classification pressure is 0.51 MPa, the rotation speed is 1320 r / min, and the fine particle yield is 76.7%.

[0090] The activating agent consisted of 15.5 parts sodium bisulfate, 7.2 parts ammonium bifluoride, and 3.6 parts sodium tripolyphosphate. The pellet-to-material ratio was 17:1, the temperature was 49℃, and the time was 53 min. Calcination was carried out at 400℃ for 81 min and then at 543℃ for 59 min, with a nitrogen flow rate of 1.0 m³ / min. 3 / h; hydration frequency 24kHz, power density 0.40W / cm³ 3 Temperature 71℃, time 39min.

[0091] The leaching agent consisted of 14.4% citric acid, 4.2% sulfamic acid, and 1.0 part sodium citrate. The liquid-to-solid ratio was 5.1:1, the temperature was 82℃, the pH was 3.1, and the time was 135 min.

[0092] The impurity removal temperature was 65℃, and the pH was 4.2. The organic phase extraction was P507: sulfonated kerosene = 20:80, and the sulfuric acid concentration for back-extraction was 2.0%.

[0093] Calcination temperature: 648℃, time: 52min.

[0094] Experimental results: Nickel leaching rate 88.8%, total nickel recovery rate 88.1%, silicon recovery rate 83.5%, magnesium recovery rate 82.7%, aluminum recovery rate 82.0%, iron recovery rate 83.1%, nickel concentration of nickel sulfate solution 46.0 g / L, magnesium hydroxide purity 92.5%, and SiO2 content of active silicon micropowder 86.1%.

[0095] Example 10 The raw material has a nickel grade of 0.25 wt%, a crushing output particle size of 10 mm, a grinding concentration of 64%, a grinding time of 29 min, and a D90 of 68 μm. The classification pressure is 0.49 MPa, the rotation speed is 1290 r / min, and the fine particle yield is 75.8%.

[0096] The activating agent consisted of 14.8 parts sodium bisulfate, 6.8 parts ammonium bifluoride, and 3.3 parts sodium tripolyphosphate. The pellet-to-material ratio was 17:1, the temperature was 48℃, and the time was 51 min. Calcination was carried out at 396℃ for 79 min and then at 539℃ for 56 min, with a nitrogen flow rate of 1.0 m³ / min. 3 / h; hydration frequency 24kHz, power density 0.39W / cm³ 3 Temperature 70℃, time 36min.

[0097] The leaching agent consisted of 13.8% citric acid, 3.8% aminosulfonic acid, and 0.98 parts sodium citrate. The liquid-to-solid ratio was 4.9:1, the temperature was 81℃, the pH was 3.0, and the time was 131 min.

[0098] The impurity removal temperature was 64℃, and the pH was 4.2. The organic phase extraction ratio was P507: sulfonated kerosene = 19:81, and the sulfuric acid concentration for back-extraction was 1.9%.

[0099] Calcination temperature 642℃, time 50min.

[0100] Experimental results: Nickel leaching rate 88.0%, total nickel recovery rate 87.2%, silicon recovery rate 82.8%, magnesium recovery rate 82.0%, aluminum recovery rate 81.3%, iron recovery rate 82.4%, nickel concentration in nickel sulfate solution 45.2 g / L, magnesium hydroxide purity 92.1%, and SiO2 content in activated silicon micropowder 85.7%.

[0101] The gradient activation of low-grade nickel-bearing silicate tailings described in this invention The synergistic leaching and full-element resource recovery method demonstrated stable and reliable processing results in all 10 examples, with a total nickel recovery rate consistently maintained at 85.3%. The recovery rate was within the 90.5% range, averaging 87.8%; the comprehensive recovery rate of valuable elements such as silicon, magnesium, aluminum, and iron remained stable at 79.4%. The nickel leaching rate reached 85.4%, with an average of 82.3%, effectively solving the problem of low nickel leaching rate caused by silicate lattice encapsulation. The nickel concentration of the prepared nickel sulfate solution remained stable at 43.2 g / L. The magnesium hydroxide product has a purity of ≥90.7% (48.5 g / L) and the active silica micropowder has a SiO2 content of ≥84.2%, meeting the requirements for industrial applications. The entire process achieves zero discharge of wastewater and solid waste, with low loss of leaching agent and extraction organic phase. The process is highly reproducible and adaptable to various operating conditions, and can handle nickel grades up to 0.21 wt%. The 0.29wt% low-grade nickel-containing silicate tailings have been utilized in a green, efficient, and high-value-added manner.

[0102] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings, characterized in that, Includes the following steps: S1, Raw material pretreatment and classification: Low-grade nickel-containing silicate tailings are crushed, finely ground and then air classified. The coarse-grained tailings are returned for regrinding, and the fine-grained tailings are used as gradient activation raw materials. S2, Gradient Coupling Activation: Fine-grained tailings are sequentially subjected to three-stage coupled gradient activation treatment: low-temperature mechanical and chemical activation, medium-temperature directional roasting activation, and ultrasonic-assisted hydration activation to obtain gradient activated tailings slurry. S3, weak acid-complex synergistic leaching: a compound leaching agent system is added to the gradient activated tailings slurry and synergistic leaching is carried out at a set pH value. After leaching, solid and liquid separation is obtained to obtain leaching tailings and nickel-containing leaching solution. The leaching tailings are washed and the washing liquid is incorporated into the nickel-containing leaching solution. S4, Leachate purification and enrichment: The nickel-containing leaching solution is subjected to selective oxidation to remove iron and aluminum, and solvent countercurrent extraction-back-extraction in sequence to separate and purify the nickel sulfate solution, producing iron and aluminum slag and raffinate. S5, closed-loop resource utilization of all elements: the leaching tailings are dried, calcined, finely ground and classified to prepare active silica powder; iron and aluminum slag is used to prepare ironmaking sintering ingredients or polyaluminum ferric chloride water purification agent; the raffinate is subjected to stepwise pH adjustment and precipitation to recover manganese and magnesium products in sequence, and magnesium precipitation filtrate is obtained; after pH adjustment and solid-liquid separation purification, the magnesium precipitation filtrate is returned to the weak acid-complex synergistic leaching as leaching water for recycling.

2. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The process of crushing, fine grinding, and air classifying low-grade nickel-containing silicate tailings, with the coarse-grained tailings returned for regrinding and the fine-grained tailings used as gradient activation raw materials, is as follows: Low-grade nickel-containing silicate tailings are fed into a double-toothed roll crusher at a constant feed rate of 3.2-3.8 t / h, and the output particle size is controlled to be 8-12 mm to obtain the crushed product. The crushed product is fed into a vertical impact mill for fine grinding. High-chromium cast iron balls of 20mm, 15mm and 10mm are graded in a mass ratio of 4:3:3, with a media filling rate of 38%-42%, a slurry concentration of 62%-68%, and a grinding time of 25-35min to obtain finely ground tailings powder with D90≤74μm. The finely ground tailings powder is fed into a horizontal air classifier with an inlet pressure of 0.45-0.55MPa and a classifier wheel speed of 1200-1400r / min. The dry classification yields coarse-grained tailings of 45-74μm and fine-grained tailings of ≤45μm. The coarse-grained tailings are returned for regrinding, while the fine-grained tailings are stored in a sealed silo with a humidity of less than 45% for later use.

3. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The low-temperature mechanochemical activation process is as follows: Fine-grained tailings and compound activation aids are mixed at a mass ratio of 1:0.08-0.12 and fed into a horizontal planetary ball mill for mechanochemical activation to obtain a low-temperature mechanochemical activated product. By mass, the compound activating agent consists of 12-18 parts sodium bisulfate, 5-9 parts ammonium bifluoride, and 2-5 parts sodium tripolyphosphate. The horizontal planetary ball mill uses 12mm, 8mm, and 5mm zirconia grinding balls in a mass ratio of 5:3:2, with a ball-to-material ratio of 15:1-20:

1. The revolution speed is 380-420 r / min, and the rotation speed is 1.2 times the revolution speed. During mechanochemical activation, the circulating water bath temperature is controlled at 45-55℃, and the mechanochemical activation time is 40-60 min.

4. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The process of medium-temperature directional calcination activation is as follows: The low-temperature mechanical and chemical activation product is fed into a mesh belt roasting furnace, and nitrogen gas is introduced to maintain the oxygen volume fraction in the furnace below 0.5%, with a nitrogen flow rate of 0.8-1.2 m³ / h. 3 / h; segmented heating is adopted: the first stage is to heat up to 380-420℃ at 6-9℃ / min and hold at a constant temperature for 70-90min; the second stage is to heat up to 520-560℃ at 5-7℃ / min and hold at a constant temperature for 50-70min; after roasting, the product is rapidly cooled to below 80℃ by indirect water cooling and then stored in a sealed container.

5. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The ultrasound-assisted hydration activation process is as follows: The calcined product and deionized water with a conductivity ≤10μS / cm were added to an ultrasonic hydration reactor at a liquid-to-solid mass ratio of 3:1-4:

1. The stirring speed was 180-220 r / min; the dual-frequency ultrasonic frequency was 22-26 kHz, and the power density was 0.35-0.45 W / cm². 3 The system temperature is 65-75℃, and the hydration reaction is carried out for 30-45 minutes to obtain gradient activated tailings slurry.

6. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The process of adding a compound leaching agent system to the gradient activated tailings slurry for synergistic leaching at a set pH value, followed by solid-liquid separation to obtain leaching tailings and nickel-containing leachate, and then washing the leaching tailings and incorporating the washing liquid into the nickel-containing leachate, is as follows: The gradient-activated tailings slurry is fed into a leaching reaction tank, and a compound leaching agent system is added for synergistic leaching. The liquid-to-solid mass ratio is controlled at 4.5:1-5.5:1, the system temperature at 78-85℃, and the stirring speed at 220-260 r / min. Dilute ammonia is added dropwise to maintain the set pH value at 2.8-3.3, and the leaching reaction is carried out for 120-150 min. After leaching, plate and frame filter press is used to separate the solid and liquid, resulting in leaching tailings and nickel-containing leachate. The leaching tailings are washed multiple times with deionized water at 55-65℃, and the washing liquid is added to the nickel-containing leachate. By mass fraction, the compound leaching agent contains 12%-16% citric acid, 3%-5% aminosulfonic acid, 0.8%-1.2% sodium citrate, and the remainder is water. The mass concentration of the dilute ammonia solution is 15%-20%; The plate and frame filter press has a filtration pressure of 0.6-0.8 MPa and a filtration time of 20-25 min.

7. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The selective oxidation process for removing iron and aluminum is as follows: Heat the nickel-containing leaching solution to 62-68℃, stir at 200-240 r / min, add 3%-5% hydrogen peroxide (8%-12% by mass) of the leaching solution and oxidize for 25-35 min; then add 18%-22% magnesium oxide emulsion at a dropping rate of 5-8 mL / min, adjust the pH to 4.1-4.4, stir at a constant temperature for 35-45 min, and filter to obtain iron-aluminum slag and the liquid after iron and aluminum removal.

8. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 7, characterized in that, The solvent countercurrent extraction-back-extraction process is as follows: After removing iron and aluminum, the liquid is cooled to 35-42℃. The extractable organic phase is prepared by mixing P507 and sulfonated kerosene at a volume ratio of 17:83-23:

77. The extractable organic phase is then saponified with a 10% sulfuric acid solution, with a saponification rate of 65%-75%. A three-stage countercurrent extraction is used, with a volume ratio of extractable organic phase to aqueous phase of 2:1-3:

1. The centrifugal extractor speed is 4500-5500 r / min, and the single-stage residence time is 3-5 min, yielding a nickel-loaded organic phase and a raffinate containing magnesium and manganese. The nickel-loaded organic phase was subjected to three-stage countercurrent back-extraction using 1.5%-2.5% dilute sulfuric acid, with a back-extraction ratio of 1:2-1:3, a back-extraction temperature of 28-35℃, and a single-stage back-extraction time of 2-4 min, to obtain a nickel sulfate solution with a nickel concentration ≥45g / L.

9. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The process of preparing active silica powder from the leaching tailings by drying, calcining, fine grinding, and classification is as follows: The leaching tailings are dried at 105-115℃ until the moisture content is ≤1%, calcined at a constant temperature of 620-680℃ for 45-60 minutes, finely ground to D90≤20μm, and then air-separated to obtain active silicon micro powder with SiO2 content ≥85%.

10. The gradient activation and synergistic leaching method for low-grade nickel-bearing silicate tailings according to claim 1, characterized in that, The raffinate is subjected to stepwise pH adjustment and precipitation to recover manganese and magnesium products sequentially, yielding a magnesium-precipitated filtrate. After pH adjustment and solid-liquid separation purification, the magnesium-precipitated filtrate is entirely returned to the weak acid-complexation synergistic leaching process for reuse as leaching water, as follows: Heat the raffinate to 42-48℃, stir at 180-220 r / min, and adjust the pH to 9.2-9.6 by adding a 25%-28% sodium hydroxide solution dropwise. Then, introduce 0.3-0.5 m³ of [aluminum / water] into the solution. 3 Oxidation with compressed air for 30-40 minutes per hour, followed by pressure filtration to obtain manganese slag with a manganese content ≥35% and filtrate after manganese precipitation; After manganese precipitation, add 25%-28% sodium hydroxide solution to adjust the pH to 10.8-11.2, stir at a constant temperature for 25-35 minutes, and filter by pressure to obtain magnesium hydroxide with a purity ≥92% and magnesium precipitation filtrate. After magnesium precipitation, dilute sulfuric acid is added to the filtrate to adjust the pH to 6.5-7.

5. After filtration, the filtrate is returned to the weak acid-complex synergistic leaching process and reused as leaching water.