Method for comprehensively recovering silicon and magnesium based on rotary kiln-electric furnace type ferronickel slag

Abstract

The invention discloses a method for comprehensively recovering silicon and magnesium based on rotary kiln-electric furnace type ferronickel slag. The method comprises the following steps: carrying out ball milling, leaching and solid-liquid separation on the rotary kiln-electric furnace type ferronickel slag, standing supersaturated silicon in a leaching solution at normal temperature to generate a gel phenomenon, stirring and crushing to obtain a mixed phase of a magnesium sulfate solution and a silica gel block, and separating the gel solution to obtain a magnesium sulfate crude solution and wet crude silica gel; preparing high-purity hydrated magnesium sulfate with the purity of 99.9% from the magnesium sulfate crude liquid through processes of purification, crystallization and the like; the wet coarse silica gel is subjected to further alkali dissolution, gel forming and other processes to produce silica gel with the purity of 99%; the method has the advantages of low energy consumption, high product added value and element recovery rate and convenience in industrialization, and has excellent popularization and application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of recovering silicon and magnesium from nickel-iron slag, and in particular to a method for comprehensively recovering silicon and magnesium from nickel-iron slag based on a rotary kiln-electric furnace type. Background Art

[0002] Ferronickel slag is the fourth largest smelting slag after blast furnace slag, steel slag and red mud. As an industrial solid waste, it is still mainly stored and landfilled to date, which not only occupies a large amount of land, but also poses a certain threat to the ecological environment. There have been many studies on the utilization of ferronickel slag, such as the preparation of concrete aggregate, slag silicate cement, glass fiber, foamed ceramics, slag wool, refractory materials, etc. There are also studies on the recovery of iron, silicon, aluminum, magnesium, nickel, chromium and other aspects from ferronickel slag, but most of these methods have various problems such as low economic value, high production energy consumption, large equipment investment, and small consumption of ferronickel slag. For example, ferronickel slag can replace part of quartz sand as aggregate for preparing concrete, or as a cementitious material for producing slag silicate cement. Due to the large demand for concrete and cement, it is a method that contributes relatively high to the current utilization rate of ferronickel slag. However, this method has low economic value and is limited by the MgO content in ferronickel slag, so the addition amount cannot be too high. The recovery of nickel and chromium from ferronickel slag is only for a few special types of ferronickel slag with high nickel and chromium content. Although the use of nickel-iron slag in the preparation of refractory materials has certain industrial applications, it is still limited by the composition and physical phase of the raw materials, and the market space makes it difficult to apply it on a large scale. Other methods such as glass fiber and foamed ceramics are also difficult to industrialize due to various reasons. As a result, compared with solid wastes such as blast furnace slag, steel slag, and manganese slag, the utilization rate of nickel-iron slag is still relatively low, only about 14wt%.

[0003] On the one hand, nickel ferroslag has the characteristics of high silicon and magnesium content, especially for rotary kiln-electric furnace (RKEF) nickel ferroslag, which is the main slag type produced by the nickel ferrogeneration process at home and abroad, accounting for about 2 / 3 of the total nickel ferroslag. 2 The content is usually as high as 35-60wt%, and the MgO content is as high as 20-40wt%. For the newly produced RKEF slag type, it is mainly an amorphous structure, in which SiO 2 and MgO are highly active and easy to dissolve, and have important recycling value. 2 It is a common beneficial component in building materials. However, MgO is a harmful component for most building materials. Therefore, in the standards of some building materials products (such as Portland cement), there are strict regulations on the MgO content in building materials. Reducing the MgO content in nickel-iron slag is of great significance to improving the application of nickel-iron slag in building materials.

[0004] There have been some reports on methods for recovering valuable elements from nickel-iron slag: Liang Wenyu et al. published a patent titled "A method for extracting silicon, aluminum, iron and magnesium from nickel-iron slag (CN 112195298 A)", which recovers silicon, aluminum, iron and magnesium from nickel-iron slag through two high-temperature reduction smeltings (including one vacuum smelting). Although this method can obtain metal elements with high economic value, it has high smelting temperature, high energy consumption, and requires multiple distillations and condensations after metal reduction to achieve separation between the metals. Ding Xiangjuan et al. reported a patent titled "A method for extracting magnesium from nickel-iron slag (CN 110423900 A)", which obtains metal element magnesium by mixing nickel-iron slag with carbonaceous reducing agent, fluorite, quicklime, etc., and then reducing it in vacuum. This method has a short process flow and high product added value, but it still requires high-temperature vacuum smelting equipment, and requires inert atmosphere protection when magnesium crystallizes. A large amount of ingredients need to be added before smelting, which makes the reduction of nickel-iron slag not obvious. Yu Haijun et al. reported the patent "A method for recovering magnesium oxide from nickel-iron slag (CN 113735146 A)". The patent adopts the method of hydrochloric acid dissolution, obtains magnesium chloride through purification and crystallization, and then obtains high-purity magnesium oxide through high-temperature thermal decomposition. The advantages of this method are high added value and good product quality. However, hydrochloric acid is used as a solvent, which is easy to volatilize and has poor environmental friendliness. In addition, it is necessary to keep the temperature at 150-240°C in a closed environment of a strongly acidic chlorine-containing system, which not only consumes a lot of energy, but also places high demands on the equipment and container materials. The applicant has previously reported "A method for recovering magnesium from nickel-iron slag (CN 111926193 B)" and "A method for preparing high-purity magnesium sulfate using nickel-iron slag as raw material (CN114314619A). Both methods use sulfuric acid as a solvent and recover magnesium through leaching, crystallization and other processes to prepare magnesium sulfate. The process flow of these two methods is simple, and they also use full-wet extraction. However, the type of nickel-iron slag they target is aged nickel-iron slag, which has a very long storage time and is mainly composed of magnesium-iron olivine crystal phase. As a result, high temperature (140-210°C) and high acid (5-18N) leaching conditions must be used during leaching, and the leaching time is relatively long. The subsequent crystallization and purification processes must also be adapted to the high-acid system. The nickel-iron slag used in the present invention mainly exists in an amorphous state, and the activity of the slag is very strong. Even if a low-concentration sulfuric acid solution of 1.5 mol / L is used, it can be leached in a short time, and high silicon and magnesium leaching rates can be achieved by leaching at room temperature, and the requirements for the leaching equipment container material are relatively low. Furthermore, the method previously disclosed by the research group cannot be used for comprehensive recovery of silicon, and most of the silicon still remains in the leached slag, resulting in a slag rate (the ratio of the mass of the slag produced during the recovery process to the mass of the raw nickel-iron slag) of about 70%. However, most of the silicon and magnesium in the present invention are recovered, the product has a high economic value, and the comprehensive recovery effect is good, and the slag rate is less than 30%.Therefore, the present invention has obvious innovations compared with previous research methods in terms of the type of nickel-iron slag to be treated, product types, energy consumption, acid consumption, amount of neutralizer, production efficiency and nickel-iron slag reduction.

[0005] In conclusion, the present invention adopts a fully wet method to comprehensively recover silicon and magnesium from nickel-iron slag, which has important economic value and environmental significance. This method will become a key to open the nickel-iron slag mainly in amorphous state as an important "silicon-magnesium resource treasure house", which is of great significance for promoting the efficient utilization and reduction of nickel-iron slag resources. Summary of the invention

[0006] The invention aims to overcome the disadvantages of the prior art and provides a method for comprehensively recovering silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag. The method comprises the following steps: subjecting the rotary kiln-electric furnace type nickel-iron slag to ball milling, leaching and solid-liquid separation, allowing supersaturated silica in the leaching solution to stand at room temperature to produce gelation, stirring and crushing to obtain a mixed phase of magnesium sulfate solution and silica gel blocks, separating the gel and liquid to obtain a crude magnesium sulfate solution and wet crude silica gel; the crude magnesium sulfate solution is subjected to purification, crystallization and other processes to prepare high-purity hydrated magnesium sulfate with a purity of 99.9%; and the wet crude silica gel is subjected to further alkali dissolution, gelling and other processes to produce silica gel with a purity of 99%. The method has the advantages of low energy consumption, high product added value and element recovery rate, and is convenient for industrialization, and has an excellent prospect for promotion and application.

[0007] In order to achieve the above technical effects, the following technical solutions are adopted:

[0008] A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag, the specific steps are:

[0009] Step S1: Pretreatment of ferronickel slag

[0010] The rotary kiln-electric furnace type nickel-iron slag is dried and then ground in a ball mill, sieved to obtain nickel-iron slag fine powder, which is weighed as the solute for the next step of acid leaching;

[0011] Step S2: Acid leaching

[0012] The nickel-iron slag fine powder obtained in step S1 is leached with a sulfuric acid solution, stirred at room temperature, the reaction will tend to equilibrium, and then the stirring is stopped to obtain a liquid-solid mixture;

[0013] Step S3: Slag-liquid separation

[0014] The liquid-solid mixture obtained in step S2 is centrifuged to obtain a leachate and a leach residue, and the leachate is further vacuum filtered to obtain a leachate containing supersaturated silicic acid, magnesium sulfate and impure metal ions;

[0015] Step S4: Standing to form gel

[0016] The leachate obtained in step S3 is allowed to stand to allow the supersaturated silicate in the solution to gradually condense into a jelly-like colloid, and then mechanically stirred and crushed to release the solution in the colloid to form a colloid mixture consisting of the colloid fragments and the leachate mainly containing magnesium sulfate and impurity metal ions;

[0017] Step S5: Glue-liquid separation

[0018] The colloid-liquid mixture obtained in step S4 is centrifuged to obtain a semi-solid colloid and a magnesium sulfate solution containing impurities and a small amount of silica gel fine particles;

[0019] After washing the semi-solid colloid, wet crude silica gel is obtained, which is used as a raw material for further preparing pure silica gel; and the magnesium sulfate solution containing impurities and silica gel fine particles is filtered to remove the silica gel fine particles, and the obtained solution is used as a raw material for further preparing high-purity magnesium sulfate, that is, a crude magnesium sulfate solution;

[0020] After the above steps S1 to S5, wet crude silica gel and crude magnesium sulfate liquid are obtained respectively, and the wet crude silica gel and crude magnesium sulfate liquid are purified to prepare pure silica gel and high-purity magnesium sulfate respectively.

[0021] Furthermore, in step S1, the product is sieved through a 200-mesh sieve.

[0022] Furthermore, in step S2, stirring is performed at room temperature for 5 to 15 minutes; the leaching conditions are: sulfuric acid concentration is 1.5 to 3 mol / L, the liquid-solid ratio of sulfuric acid solution to nickel-iron slag is controlled at 10 to 20 L / kg, the stirring rate is controlled at 200 to 800 rpm, the initial reaction temperature is room temperature, and no heating is required.

[0023] Furthermore, the impurity metal ions in step S3 are mainly Fe 3+ , Ca 2+ 、Al 3+ Cr 3+ ion.

[0024] Furthermore, the leaching solution in step S4 is allowed to stand for 4 to 12 hours; a shearing stirring blade is used to mechanically stir and crush the colloid; the impurity metal ions are mainly Fe 3+ , Ca 2+ 、Al 3+ Cr 3+ ion.

[0025] Furthermore, the specific steps of the wet crude silica gel purification treatment in step S5 are:

[0026] Step A1: Primary drying

[0027] The wet crude silica gel prepared in step S5 is placed in a drying oven at 120-150° C. and dried to a constant weight to obtain dry crude silica gel; after drying, the mass of the silica gel is reduced to 7-12% of that before drying;

[0028] Step A2: Alkaline Dissolution

[0029] The dry crude silica gel obtained in step A1 is dissolved with caustic soda solution, and the dissolution process is carried out by heating and stirring at low temperature, or stirring without heating; SiO2 in the silica gel is removed during the dissolution process. 2 Reacting with NaOH to generate sodium silicate entering the solution, the crude silica gel that is not completely dissolved and most of the impurities that are insoluble in alkali form a precipitate; thereby obtaining a liquid-solid mixture formed by the sodium silicate solution and the precipitate; the alkali dissolution conditions are: the liquid-solid ratio of the NaOH solution to the wet silica gel is 8-12L / kg, the concentration of the NaOH alkali solution is 1.5-3mol / L, the reaction temperature is room temperature to 90°C, the reaction time is 30-120min, and the stirring rate is 200-800rpm;

[0030] Step A3: Separation of slag and liquid

[0031] The liquid-solid mixture obtained in step A2 is filtered to obtain a sodium silicate solution and a small amount of alkaline slag containing impurities.

[0032] Step A4: Gluing

[0033] Slowly add dilute sulfuric acid with a concentration of 0.5 to 2 mol / L to the sodium silicate solution obtained in step A3, stirring at the same time, and adjusting the pH value of the solution; when the pH value of the solution is 10.5 to 11, stop dripping the dilute acid and continue stirring for 1 hour; then slowly add acid until a large amount of silica gel is generated, adjust the pH value to 3 to 4, stop heating, continue stirring to age the silica gel for 4 to 12 hours, and then the gelling process is completed to obtain a gel mixture;

[0034] Step A5: Glue-liquid separation

[0035] The gel mixture obtained in step A4 is centrifuged and the liquid phase is filtered to obtain jelly-like wet silica gel and a solution whose main component is sodium sulfate;

[0036] Step A6: Silicone Washing

[0037] The wet silica gel obtained in step A5 is acid-washed with dilute sulfuric acid for 4 to 5 times and washed with water for 2 to 3 times to obtain relatively pure wet silica gel; the washing liquid is 10% by volume of dilute sulfuric acid and pure water; the liquid-to-solid ratio of each washing is ≥1L / Kg;

[0038] Step A7: Secondary Drying

[0039] The wet silica gel washed in step A6 is dried at 100-120° C. to a constant weight to obtain dry pure silica gel; the silica gel is used as the final product of silicon recovery;

[0040] The pure silica gel is SiO 2 Calculated by mass percentage, the purity is above 99%.

[0041] Furthermore, the specific steps of purifying the crude magnesium sulfate solution in step S5 are as follows:

[0042] Step B1: Primary crystallization

[0043] The crude magnesium sulfate solution obtained in step S5 is heated to evaporate water, and after being concentrated to 1 / 6 to 1 / 3 of the volume of the original solution, the solution temperature is adjusted to 70 to 85° C. as the starting temperature of the primary crystallization, and the cooling rate of the solution is controlled so that the solution is cooled to room temperature or below room temperature after 6 to 10 hours; during the primary crystallization process, the solution is cooled while stirring, and when the temperature drops to 35 to 20° C., a seed crystal of magnesium sulfate heptahydrate is added to the solution, and the seed coefficient is 0.2 to 0.4; during the crystallization process, hydrated magnesium sulfate crystals are continuously precipitated from the solution and settled to the bottom of the crystallization tank;

[0044] Step B2: Solid-liquid separation

[0045] The liquid-solid mixture obtained in step B1 is filtered to obtain fine block solids as magnesium sulfate heptahydrate crystals, and the filtrate is the liquid after the primary crystallization; the magnesium sulfate heptahydrate crystals contain a small amount of impurities, and further purification is required to prepare high-purity magnesium sulfate; the liquid after the primary crystallization contains a large amount of sulfuric acid and incompletely crystallized magnesium sulfate, which can be added with new acid and returned to the leaching process as a solvent, thereby improving the utilization rate of the acid and the recovery rate of magnesium;

[0046] Step B3: Dissolution

[0047] The magnesium sulfate heptahydrate obtained in step B2 is dissolved in water, and the liquid-solid ratio of water to the primary crystallization product magnesium sulfate heptahydrate is controlled at 3 to 7 L / kg; the magnesium sulfate heptahydrate crystals are easily dissolved and are completely dissolved by slight stirring for 5 to 10 minutes to form a crude magnesium sulfate solution;

[0048] Step B4: Purification

[0049] After heating the magnesium sulfate crude solution obtained in step B3 to 70-90° C., adding a neutralizing agent MgO thereto, stirring at the same time, and stopping adding the neutralizing agent after adjusting the pH value of the solution from 2-3 to 6-8; during this process, the impurity metal ions undergo a hydrolysis reaction to generate corresponding hydroxide precipitates to form purified slag, and at the same time, a magnesium sulfate supernatant slurry is obtained;

[0050] Step B5: Separation of slag and liquid

[0051] The solid separated from the slurry obtained in step B4 is the purified slag after filtering, and the amount of the purified slag is very small, less than 5% of the nickel-iron slag raw material; the separated liquid is the magnesium sulfate purified liquid;

[0052] Step B6: Secondary crystallization

[0053] The purified magnesium sulfate solution obtained in step B5 is heated to evaporate water, and concentrated to 1 / 10 to 1 / 5 of the volume of the original solution to become a secondary crystallization original solution. After adjusting the temperature to 70 to 85° C., cooling crystallization is started; the crystallization conditions are: the final crystallization temperature is between 0 and 20° C., the crystallization time is 5 to 12 hours, and when the solution temperature drops to 35 to 20° C., magnesium sulfate heptahydrate seed crystals are added to the solution, and the seed coefficient is 0.4 to 0.6; during the crystallization process, hydrated magnesium sulfate crystals gradually precipitate from the solution and settle to the bottom of the crystallization tank;

[0054] Step B7: Centrifugation

[0055] The liquid-solid mixture containing magnesium sulfate crystals in step B6 is centrifuged to obtain high-purity hydrated magnesium sulfate crystals, i.e., a high-purity magnesium sulfate product; in order to reduce the free water in the high-purity hydrated magnesium sulfate crystals, the drum speed is controlled at 3000-5000 rpm during centrifugation; the secondary crystallized liquid obtained by centrifugation can be returned to the dissolution process B3 for recycling, thereby improving the recovery rate of magnesium and the utilization rate of water;

[0056] The high-purity magnesium sulfate product has a purity of more than 99.9% calculated based on the mass percentage of hydrated magnesium sulfate.

[0057] Furthermore, the primary drying in step A1 and the secondary drying in step A6 are not limited to heating and drying the wet silica gel using electric heat or fuel combustion heat, and can also be naturally dried in the sun or with the aid of flowing air; the natural drying method is not limited to the temperature and time parameters during drying.

[0058] Furthermore, during the purification of the wet crude silica gel in step A1, the wet crude silica gel can be directly subjected to an alkaline dissolution operation; when the wet crude silica gel is used as the solute, the liquid-to-solid ratio of the NaOH solution to the wet silica gel is 8 to 12 L / kg, and the other dissolution conditions are the same as when the dry crude silica gel is used as the solute.

[0059] Furthermore, the concentration of the magnesium sulfate solution before crystallization is not limited to the process methods and parameters described in the above-mentioned step B2 primary crystallization and step B7 secondary crystallization step. It is also possible to use a sun shed to evaporate and concentrate the solution with the help of sunlight and wind when the temperature is high during the day, and cool and crystallize the solution at night when the temperature is low to obtain magnesium sulfate crystals; it is not limited to the cooling crystallization method used in the B6 secondary crystallization step, and full evaporation can also be used, that is, evaporating all free water molecules in the secondary crystallization stock solution to obtain hydrated magnesium sulfate crystals; when full evaporation is used, there is no need to add seed crystals, and after crystallization, there is no need for step B8 centrifugation step, and hydrated magnesium sulfate crystals can be directly obtained, so that the process is simplified and the product purity can still reach more than 99.9wt%.

[0060] The beneficial effects of the present invention are:

[0061] 1. The comprehensive recovery effect of silicon and magnesium is good, the recovery rate of silicon exceeds 70%, and the recovery rate of magnesium exceeds 80%. At the same time, it can produce two products with a purity of more than 99wt% silica gel and 99.9wt% high-purity magnesium sulfate. Under certain optimized conditions, the purity of high-purity magnesium sulfate can reach 99.99wt%.

[0062] 2. The product is highly flexible, and can produce agricultural or industrial grade magnesium sulfate products with lower purity but larger usage by reducing the process flow. The product chain can also be extended downstream, such as silica gel can be used to produce white carbon black after roasting, high-purity magnesium sulfate can be made into high-purity magnesium oxide after roasting, and high-purity magnesium sulfate can also be used to make high-purity magnesium hydroxide or other high-purity magnesium salts through solution hydrolysis, replacement, etc.

[0063] 3. The slag rate (the mass ratio of the sum of the mass of the acid-soluble slag, alkali-soluble slag and purified slag in the preparation process to the mass ratio of the raw material ferronickel slag) does not exceed 30%, and the iron, chromium and nickel elements in the leached slag and purified slag are enriched, which is convenient for recycling and returning to the ferronickel and ferrochrome production system. Since the MgO content in the residual slag is significantly reduced, it is more suitable as a building material. Through the method of the present invention, in addition to effectively utilizing the ferronickel slag as a resource to produce high-value-added silica gel and high-purity magnesium sulfate, the reduction of ferronickel slag solid waste can reach 70%.

[0064] 4. The present invention solves the problem that many minerals containing silicon impurities generate silicate during the dilute acid leaching of valuable metals, which leads to difficulty in subsequent solid-liquid separation and even inability to recover. Instead, the silicate generated during the magnesium recovery process is recycled as a valuable element. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings in the following description are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0066] Figure 1 is the XRD diagram of the nickel-iron slag used in the embodiments of the present invention;

[0067] Figure 2 This is the XRD pattern of the silica gel prepared by the process of the present invention in Example 1 of the present invention;

[0068] Figure 3 This is a visible-infrared absorption spectrum of the silica gel prepared in Example 1 of the present invention;

[0069] Figure 4 This is a SEM image of the silica gel prepared in Example 1 of the present invention;

[0070] Figure 5 This is the XRD pattern of the high-purity magnesium sulfate prepared in Example 1 of the present invention;

[0071] Figure 6 This is a SEM image of the high-purity magnesium sulfate prepared in Example 1 of the present invention;

[0072] Figure 7 This is a SEM image of the high-purity magnesium sulfate prepared in Example 1 of the present invention;

[0073] Figure 8 This is a SEM image of the high-purity magnesium sulfate prepared in Example 1 of the present invention;

[0074] Fig. 9 This is a SEM image of the high-purity magnesium sulfate prepared in Example 1 of the present invention;

[0075] Fig.10 This is the XRD diagram of the aged nickel-iron slag with relatively intact crystal form used in Comparative Example 1;

[0076] Fig.11 The present invention is a process flow chart for preparing pure silica gel and high-purity magnesium sulfate. DETAILED DESCRIPTION

[0077] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0078] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0079] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0080] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0081] The starch-based epoxy resin and the preparation method thereof provided by the present invention are described below in conjunction with the embodiments, but the protection scope of the present invention is not limited by the following embodiments.

[0082] Embodiment 1:

[0083] like Fig.11 As shown, the present embodiment provides a method for comprehensively recovering silicon and magnesium from rotary kiln-electric furnace type nickel-iron slag by a full wet method, and the specific steps are as follows:

[0084] (1) Preparation of wet crude silica gel and crude magnesium sulfate solution

[0085] The nickel-iron slag is dried and ground in a ball mill, and then passed through a 200-mesh sieve to obtain nickel-iron slag fine powder. The XRD pattern of the nickel-iron slag used is as follows: Figure 1 Its chemical composition is shown in Table 1, which shows that nickel-iron slag has SiO 2 and MgO content is high, CaO, NiO and Cr 2 O 3 The content is low. Dry at 120°C for 6h, and weigh 40g as the solute for acid leaching. Leach with sulfuric acid solution at room temperature for 5min, stirring at the same time, to obtain a solid-liquid mixture. The leaching conditions are: sulfuric acid concentration is 1.5mol / L, the liquid-solid ratio of sulfuric acid solution to nickel-iron slag is controlled at 20:1 (L / Kg), the stirring rate is controlled at 200rpm, the initial reaction temperature is room temperature, and no heating is required. The obtained solid-liquid mixture is separated by centrifugation to obtain leaching residue and leachate, and the leachate is further vacuum filtered to obtain a liquid mainly containing supersaturated silicon, magnesium sulfate and impurities Fe 3+ , Ca 2+ 、Al 3+ Cr 3+The leachate is left to stand for 4 hours to allow the supersaturated silicon in the solution to gradually condense into a jelly-like colloid, and then the colloid is mechanically stirred and crushed using a shear-type stirring paddle to form a colloid fragment and a jelly-like colloid containing mainly magnesium sulfate and impurities Fe. 3+ , Ca 2+ 、Al 3+ Cr 3+ The colloid-liquid mixture is formed by the leachate of the leaching liquid. After centrifugation of the colloid-liquid mixture, a semi-solid colloid and a magnesium sulfate solution containing impurities and a small amount of silica gel fine particles are obtained. After washing the semi-solid colloid, wet crude silica gel is obtained, which is used as an intermediate product for further preparing pure silica gel in the present invention. The magnesium sulfate solution containing impurities and silica gel fine particles is filtered to remove the silica gel fine particles and used as an intermediate product for further preparing high-purity magnesium sulfate in the present invention.

[0086] Table 1 Chemical composition of nickel-iron slag used (wt%)

[0087]

[0088] Note: *This symbol indicates that the unit of content is g / t.

[0089] (2) Purification of wet crude silica gel

[0090] The prepared wet crude silica gel is placed in a drying oven and dried at 120-150°C for 10 hours to obtain dry crude silica gel. The dry crude silica gel is dissolved with caustic soda solution. The dissolution process is carried out at room temperature and stirred at the same time. A mixture consisting of a sodium silicate solution and a small amount of precipitate is generated. The alkali dissolution conditions are: liquid-solid ratio (NaOH solution: wet silica gel) = 15:1 (L / Kg), alkali solution concentration (NaOH) is 1.5 mol / L, reaction time is 30 min, and stirring rate is 800 rpm. After filtering the mixture, a sodium silicate solution and a small amount of Fe 2 O 3 , CaO, SiO 2 、Al 2 O 3The leaching residue with the main impurities such as etc. is slowly added to the sodium silicate solution with a concentration of 0.5 mol / L dilute sulfuric acid, while stirring to adjust the pH value of the solution. When the pH value of the solution is ≈11, stop dripping the dilute acid and continue stirring for 1h; then slowly add acid until a large amount of silica gel is generated, adjust the pH value to 3, stop heating, continue stirring to age the silica gel for 12h, and the gelling process is completed to obtain a gel mixture. After the gel mixture is centrifuged and filtered, jelly-like wet silica gel and a solution with sodium sulfate as the main component are obtained. The wet silica gel is acid-washed with dilute sulfuric acid 4 times and washed with water 3 times, and then dried at 120°C to a constant weight to obtain a relatively pure dry silica gel. During washing, the concentration of the washing liquid is 10% (volume fraction) of dilute sulfuric acid (or pure water), the liquid-to-solid ratio of each washing is equal to 1 (L / Kg), and the concentration of the dilute sulfuric acid used is 10% (volume fraction). The silica gel is used as the final product for recovering silicon. The XRD pattern of the prepared silica gel is shown in Figure 2 As shown, it shows that the prepared silica gel product is mainly amorphous silica; the visible-infrared absorption spectrum of the prepared silica gel is shown in Figure 3 As shown, combined Figure 2 The XRD results of the silica gel absorption spectrum confirmed that the prepared product was silica gel; the SEM image of the prepared silica gel is shown in Figure 4 As shown, the prepared silica gel is an aggregate of microscopic porous structures formed by the agglomeration and growth of a large number of fine particles, which is consistent with the porous microscopic morphology characteristics of silica gel.

[0091] (3) Purification and crystallization of magnesium sulfate crude solution to prepare high-purity magnesium sulfate

[0092] The crude magnesium sulfate solution was heated to evaporate the water and concentrated to 1 / 6 of the original solution. The solution temperature was adjusted to 70°C as the starting temperature for the primary crystallization. The cooling rate of the solution was controlled so that it cooled to 5°C after 6 hours. During the primary crystallization process, the solution was cooled while stirring. When the temperature dropped to 35°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H 2 O), the seed coefficient is 0.2. The liquid-solid mixture obtained by the primary crystallization is filtered to obtain fine block magnesium sulfate heptahydrate crystals. The magnesium sulfate crystals are dissolved in water, and the liquid-solid ratio of water to magnesium sulfate crystals is controlled at 7:1 (L / Kg). After gentle stirring for 5 minutes, a crude magnesium sulfate solution is formed. After the crude magnesium sulfate solution is heated to 70°C, a neutralizing agent MgO is added thereto while stirring. After the solution is adjusted from a pH value of 2 to 6, the addition of the neutralizing agent is stopped. Fe 3+ 、Al 3+ Cr 3+The plasma undergoes a hydrolysis reaction to generate the corresponding hydroxide precipitate, which forms a liquid-solid mixture with the magnesium sulfate solution. The solid separated after filtration is the purified slag, and the liquid is the purified magnesium sulfate solution. The purified magnesium sulfate solution is heated to evaporate the water, and after being concentrated to 1 / 10 of the volume of the original solution, it becomes the secondary crystallization stock solution. After being heated to 70°C, it begins to cool and crystallize, and the hydrated magnesium sulfate crystals gradually precipitate from the solution and settle to the bottom of the crystallization tank. The crystallization conditions are: the final crystallization temperature is around 2°C, the crystallization time is 5h, and when the solution temperature drops to 35°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H 2 O), the seed coefficient is 0.4. The liquid-solid mixture after secondary crystallization is centrifuged to obtain high-purity hydrated magnesium sulfate crystals. The drum speed during centrifugation is 3000rpm. The magnesium sulfate is used as the final product of magnesium recovery. The XRD diagram of the prepared high-purity magnesium sulfate is as follows Figure 5 As shown, it is confirmed that the prepared sample is a single MgSO 4 7H 2 O phase; SEM image of the prepared high-purity magnesium sulfate is shown in Figure 6 As shown, high-purity magnesium sulfate is agglomerated by many crystals.

[0093] Embodiment 2:

[0094] The present embodiment provides a method for comprehensively recovering silicon and magnesium from rotary kiln-electric furnace type nickel-iron slag by a fully wet method. The process method is the same as that of Example 1, but some process parameters are different, as follows:

[0095] (1) Preparation of wet crude silica gel and crude magnesium sulfate solution

[0096] After the nickel-iron slag is dried, it is ground in a ball mill and passed through a 200-mesh sieve to obtain nickel-iron slag fine powder. It is dried at 120°C for 6 hours, and 40g is weighed as the solute for acid leaching. Leach with sulfuric acid solution at room temperature for 15 minutes while stirring to obtain a solid-liquid mixture. The leaching conditions are: sulfuric acid concentration is 3 mol / L, the liquid-solid ratio of sulfuric acid solution to nickel-iron slag is controlled at 10:1 (L / Kg), the stirring rate is controlled at 800rpm, the initial reaction temperature is room temperature, and no heating is required. The obtained solid-liquid mixture is centrifuged to obtain leached residue and leachate, and the leachate is further vacuum filtered to obtain a liquid mainly containing supersaturated silicon, magnesium sulfate and impurities Fe 3+ , Ca 2+ 、Al 3+ Cr 3+ The leachate is left to stand for 12 hours to allow the supersaturated silicon in the solution to gradually condense into a jelly-like colloid, and then a shear-type stirring paddle is used to mechanically stir and crush the colloid to form a colloid fragment and a jelly-like colloid mainly containing magnesium sulfate and impurities Fe. 3+ , Ca 2+、Al 3+ Cr 3+ The colloid-liquid mixture is formed by the leachate of the leaching liquid. After centrifugation of the colloid-liquid mixture, a semi-solid colloid and a magnesium sulfate solution containing impurities and a small amount of silica gel fine particles are obtained. After washing the semi-solid colloid, wet crude silica gel is obtained, which is used as an intermediate product for further preparing pure silica gel in the present invention. The magnesium sulfate solution containing impurities and silica gel fine particles is filtered to remove the silica gel fine particles and used as an intermediate product for further preparing high-purity magnesium sulfate in the present invention.

[0097] (2) Purification of wet crude silica gel

[0098] The prepared wet crude silica gel is placed in a drying oven and dried at 120-150°C for 10 hours to obtain dry crude silica gel. The dry crude silica gel is dissolved with caustic soda solution, heated and stirred to generate a mixture of sodium silicate solution and a small amount of precipitate. The alkali dissolution conditions are: liquid-solid ratio (NaOH solution: wet silica gel) = 8:1 (L / Kg), alkali solution concentration (NaOH) is 3 mol / L, heating temperature is 90°C, reaction time is 120min, and stirring speed is 200rpm. After filtering the mixture, a sodium silicate solution and a small amount of Fe 2 O 3 , CaO, SiO 2 、Al 2 O 3 The leaching residue with the main impurities of etc. is slowly added to the sodium silicate solution with a concentration of 2 mol / L dilute sulfuric acid, while stirring to adjust the pH value of the solution. When the pH value of the solution is ≈10.5, stop dripping the dilute acid and continue stirring for 1h; then slowly add acid until a large amount of silica gel is generated, adjust the pH value to 4, stop heating, continue stirring to age the silica gel for 4h, and the gelling process is completed to obtain a gel mixture. After centrifugation and filtration of the gel mixture, jelly-like wet silica gel and a solution with sodium sulfate as the main component are obtained. The wet silica gel is acid-washed with dilute sulfuric acid 5 times and washed with water 2 times, and then dried at 100°C to a constant weight to obtain a relatively pure dry silica gel. During washing, the concentration of the washing liquid is 10% (volume fraction) of dilute sulfuric acid (or pure water), the liquid-to-solid ratio of each washing is equal to 2 (L / Kg), and the concentration of the dilute sulfuric acid used is 10% (volume fraction). The silica gel is used as the final product of silicon recovery.

[0099] (3) Purification and crystallization of magnesium sulfate crude solution to prepare high-purity magnesium sulfate

[0100] The crude magnesium sulfate solution was heated to evaporate the water and concentrated to 1 / 3 of the original solution. The solution temperature was adjusted to 85°C as the starting temperature for the primary crystallization. The cooling rate of the solution was controlled so that it cooled to 20°C after 10 hours. During the primary crystallization process, the solution was cooled while stirring. When the temperature dropped to 30°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H2 O), the seed coefficient is 0.4. The liquid-solid mixture obtained by the primary crystallization is filtered to obtain fine block magnesium sulfate heptahydrate crystals. The magnesium sulfate crystals are dissolved in water, and the liquid-solid ratio of water to magnesium sulfate crystals is controlled at 3:1 (L / Kg). After gentle stirring for 10 minutes, a crude magnesium sulfate solution is formed. After the crude magnesium sulfate solution is heated to 90°C, a neutralizing agent MgO is added thereto while stirring. After the solution is adjusted from a pH value of 3 to 8, the addition of the neutralizing agent is stopped. Fe 3+ 、Al 3+ Cr 3+ The plasma undergoes a hydrolysis reaction to generate the corresponding hydroxide precipitate, which forms a liquid-solid mixture with the magnesium sulfate solution. The solid separated after filtration is the purified slag, and the liquid is the purified magnesium sulfate solution. The purified magnesium sulfate solution is heated to evaporate the water, and after being concentrated to 1 / 5 of the volume of the original solution, it becomes the secondary crystallization stock solution. After it is heated to 85°C, it begins to cool and crystallize, and the hydrated magnesium sulfate crystals gradually precipitate from the solution and settle to the bottom of the crystallization tank. The crystallization conditions are: the final crystallization temperature is around 20°C, the crystallization time is 12h, and when the solution temperature drops to 30°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H 2 O), the seed coefficient is 0.6. The liquid-solid mixture after secondary crystallization is centrifuged to obtain high-purity hydrated magnesium sulfate crystals. The drum speed during centrifugation is 5000rpm. The magnesium sulfate is used as the final product of magnesium recovery. The SEM image of the prepared high-purity magnesium sulfate is as follows Figure 7 As shown, high-purity magnesium sulfate is agglomerated by many crystals.

[0101] Embodiment 3:

[0102] The present embodiment provides a method for comprehensively recovering silicon and magnesium from rotary kiln-electric furnace type nickel-iron slag by a fully wet method. The process method is the same as that of Example 1, but some process parameters are different, as follows:

[0103] (1) Preparation of wet crude silica gel and crude magnesium sulfate solution

[0104] After the nickel-iron slag is dried, it is ground in a ball mill and passed through a 200-mesh sieve to obtain nickel-iron slag fine powder. It is dried at 120°C for 6 hours, and 40g is weighed as the solute for acid leaching. Leach with sulfuric acid solution at room temperature for 10 minutes while stirring to obtain a solid-liquid mixture. The leaching conditions are: sulfuric acid concentration is 2.5 mol / L, the liquid-solid ratio of sulfuric acid solution to nickel-iron slag is controlled at 15:1 (L / Kg), the stirring rate is controlled at 500rpm, the initial reaction temperature is room temperature, and no heating is required. The obtained solid-liquid mixture is separated by centrifugation to obtain leached residue and leachate, and the leachate is further vacuum filtered to obtain a liquid mainly containing supersaturated silicon, magnesium sulfate and impurities Fe 3+ , Ca 2+ 、Al 3+Cr 3+ The leachate is left to stand for 8 hours to allow the supersaturated silicon in the solution to gradually condense into a jelly-like colloid, and then the colloid is mechanically stirred and broken with a shear-type stirring paddle to form a colloid fragment and a jelly-like colloid containing mainly magnesium sulfate and impurities Fe. 3+ , Ca 2+ 、Al 3+ Cr 3+ The colloid-liquid mixture is formed by the leachate of the leaching liquid. After centrifugation of the colloid-liquid mixture, a semi-solid colloid and a magnesium sulfate solution containing impurities and a small amount of silica gel fine particles are obtained. After washing the semi-solid colloid, wet crude silica gel is obtained, which is used as an intermediate product for further preparing pure silica gel in the present invention. The magnesium sulfate solution containing impurities and silica gel fine particles is filtered to remove the silica gel fine particles and used as an intermediate product for further preparing high-purity magnesium sulfate in the present invention.

[0105] (2) Purification of wet crude silica gel

[0106] The prepared wet crude silica gel was placed in a drying oven and dried at 135°C for 10 hours to obtain dry crude silica gel. The dry crude silica gel was dissolved with caustic soda solution, heated and stirred to generate a mixture of sodium silicate solution and a small amount of precipitate. The alkali dissolution conditions were: liquid-solid ratio (NaOH solution: wet silica gel) = 10:1 (L / Kg), alkali solution concentration (NaOH) was 2 mol / L, heating temperature was 90°C, reaction time was 60min, and stirring speed was 500rpm. After filtering the mixture, a sodium silicate solution and a small amount of Fe 2 O 3 , CaO, SiO 2 、Al 2 O 3 The leaching residue with the main impurities such as etc. is slowly added to the sodium silicate solution with a concentration of 1 mol / L dilute sulfuric acid, while stirring to adjust the pH value of the solution. When the pH value of the solution is ≈11, stop dripping the dilute acid and continue stirring for 1 hour; then slowly add acid until a large amount of silica gel is generated, adjust the pH value to 3.5, stop heating, continue stirring to age the silica gel for 8 hours, and the gelling process is completed to obtain a gel mixture. After the gel mixture is centrifuged and filtered, jelly-like wet silica gel and a solution with sodium sulfate as the main component are obtained. The wet silica gel is acid-washed with dilute sulfuric acid 5 times and washed with water 2 times, and then dried at 110°C to a constant weight to obtain a relatively pure dry silica gel. During washing, the washing liquid concentration is 10% dilute sulfuric acid (or pure water), the liquid-to-solid ratio of each washing is equal to 2 (L / Kg), and the concentration of dilute sulfuric acid used is 10%. The silica gel is used as the final product of silicon recovery.

[0107] (3) Purification and crystallization of magnesium sulfate crude solution to prepare high-purity magnesium sulfate

[0108] The crude magnesium sulfate solution was heated to evaporate the water and concentrated to 1 / 4 of the original solution. The solution temperature was adjusted to 75°C as the starting temperature for the primary crystallization. The cooling rate of the solution was controlled so that it cooled to 10°C after 8 hours. During the primary crystallization process, the solution was cooled while stirring. When the temperature dropped to 30°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H 2 O), the seed coefficient is 0.3. The liquid-solid mixture obtained by the primary crystallization is filtered to obtain fine block magnesium sulfate heptahydrate crystals. The magnesium sulfate crystals are dissolved in water, and the liquid-solid ratio of water to magnesium sulfate crystals is controlled at 4:1 (L / Kg). After gentle stirring for 5 minutes, a crude magnesium sulfate solution is formed. After the crude magnesium sulfate solution is heated to 80°C, a neutralizing agent MgO is added thereto while stirring, and the solution is adjusted from a pH value of 2.5 to 6.5, and then the addition of the neutralizing agent is stopped. Fe 3+ 、Al 3+ Cr 3+ The plasma undergoes a hydrolysis reaction to generate the corresponding hydroxide precipitate, which forms a liquid-solid mixture with the magnesium sulfate solution. The solid separated after filtration is the purified slag, and the liquid is the purified magnesium sulfate solution. The purified magnesium sulfate solution is heated to evaporate the water, and after being concentrated to 1 / 7 of the volume of the original solution, it becomes the secondary crystallization stock solution. After it is heated to 75°C, it begins to cool and crystallize, and the hydrated magnesium sulfate crystals gradually precipitate from the solution and settle to the bottom of the crystallization tank. The crystallization conditions are: the final crystallization temperature is around 10°C, the crystallization time is 8h, and when the solution temperature drops to 30°C, a seed crystal of magnesium sulfate heptahydrate (MgSO 4 7H 2 O), the seed coefficient is 0.5. The liquid-solid mixture after secondary crystallization is centrifuged to obtain high-purity hydrated magnesium sulfate crystals. The drum speed during centrifugation is 4000rpm. The magnesium sulfate is used as the final product of magnesium recovery. The SEM image of the prepared high-purity magnesium sulfate is as follows Figure 8 As shown, high-purity magnesium sulfate is agglomerated by many crystals.

[0109] Embodiment 4:

[0110] This embodiment provides a method for comprehensively recovering silicon and magnesium from rotary kiln-electric furnace type nickel-iron slag by a fully wet method. The process method thereof is identical to that of Example 1 except that the B6 secondary crystallization step is different from that of Example 1, and the specific process methods are as follows:

[0111] B6 secondary crystallization

[0112] The purified magnesium sulfate solution obtained in step B5 is heated under normal pressure to volatilize the water, and the purified solution is completely evaporated to dryness, and hydrated magnesium sulfate crystals are crystallized at the bottom of the vessel wall. The crystals are shoveled out of the container to obtain high-purity hydrated magnesium sulfate. However, the hydrated magnesium sulfate obtained by this method is magnesium sulfate hexahydrate (MgSO 4 6H2 O), the SEM picture of the prepared high-purity magnesium sulfate is as follows Fig. 9 As shown, high-purity magnesium sulfate is agglomerated by many crystals.

[0113] The chemical compositions of silica gel and magnesium sulfate prepared by the above examples are shown in Tables 2 and 3.

[0114] Table 2 Chemical composition of silica gel prepared by the present invention (wt%)

[0115]

[0116] Note: *This symbol indicates that the unit of content is g / t. -Indicates that the content is below the detection limit of the testing instrument and is not detected.

[0117] Table 3 Chemical composition (wt%) of high-purity magnesium sulfate prepared by the present invention

[0118]

[0119] Note: *This symbol indicates that the unit of content is g / t.

[0120] Comparative Example 1:

[0121] This embodiment uses aged nickel-iron slag with a high degree of crystallization as raw material, and its chemical composition is shown in Table 4, and its phase structure is shown in Table 4. Fig.10 shown.

[0122] Table 4 Chemical composition of the aged ferronickel slag used in Comparative Example 1 (wt%)

[0123]

[0124] The operation steps of this embodiment include raw material pretreatment, leaching, slag-liquid separation and standing to form gel, which are exactly the same as those of embodiment 1, except that the raw materials are different from those of embodiment 1. The preparation process is as follows:

[0125] After the nickel-iron slag is dried, it is ground in a ball mill and passed through a 200-mesh sieve to obtain fine nickel-iron slag powder. Dry at 120°C for 6 hours, and weigh 40g as the solute for acid leaching. Leach with sulfuric acid solution at room temperature for 5 minutes while stirring to obtain a solid-liquid mixture. The leaching conditions are: sulfuric acid concentration is 1.5 mol / L, the liquid-solid ratio of sulfuric acid solution to nickel-iron slag is controlled at 20:1 (L / Kg), the stirring rate is controlled at 200 rpm, the initial reaction temperature is room temperature, and no heating is required. The obtained solid-liquid mixture is separated by centrifugation to obtain leached residue and leachate, and the leachate is further vacuum filtered to obtain a liquid mainly containing supersaturated silicon, magnesium sulfate and impurities Fe 3+ , Ca 2+ 、Al 3+ Cr 3+The leaching solution was left to stand for 4 hours, but no colloid was formed, and no silica gel was precipitated after standing for 12 hours. Therefore, it was determined that the technology used in the present invention is not suitable for aging slag of nickel-iron slag with intact crystal form.

[0126] In summary, the invention discloses a method for comprehensively recovering silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag; the method comprises the following steps: subjecting the rotary kiln-electric furnace type nickel-iron slag to ball milling, leaching and solid-liquid separation, wherein supersaturated silica in the leaching solution generates gelation when left standing at room temperature, and a mixed phase of magnesium sulfate solution and silicate gel blocks is obtained by stirring and crushing, and a magnesium sulfate crude liquid and wet crude silica gel are obtained after gel-liquid separation; the magnesium sulfate crude liquid is subjected to purification, crystallization and other processes to prepare high-purity hydrated magnesium sulfate with a purity of 99.9%; the wet crude silica gel is subjected to further alkali dissolution, gelling and other processes to produce silica gel with a purity of 99%; the method has the advantages of low energy consumption, high product added value and element recovery rate, and is convenient for industrialization, and has an excellent prospect for promotion and application.

[0127] At this point, those skilled in the art recognize that, although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the contents disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all such other variations or modifications.

Claims

1. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag, characterized in that: The specific steps of the method are: Step S1: Pretreatment of ferronickel slag The rotary kiln-electric furnace type nickel-iron slag is dried and then ground in a ball mill, sieved to obtain nickel-iron slag fine powder, which is weighed as the solute for the next step of acid leaching; Step S2: Acid leaching The nickel-iron slag fine powder obtained in step S1 is leached with a sulfuric acid solution, stirred at room temperature, the reaction will tend to equilibrium, and then the stirring is stopped to obtain a liquid-solid mixture; Step S3: Slag-liquid separation The liquid-solid mixture obtained in step S2 is centrifuged to obtain a leachate and a leach residue, and the leachate is further vacuum filtered to obtain a leachate containing supersaturated silicic acid, magnesium sulfate and impure metal ions; Step S4: Standing to form gel The leachate obtained in step S3 is allowed to stand to allow the supersaturated silicate in the solution to gradually condense into a jelly-like colloid, and then mechanically stirred and crushed to release the solution in the colloid to form a colloid mixture consisting of the colloid fragments and the leachate mainly containing magnesium sulfate and impurity metal ions; Step S5: Glue-liquid separation The colloid-liquid mixture obtained in step S4 is centrifuged to obtain a semi-solid colloid and a magnesium sulfate solution containing impurities and a small amount of silica gel fine particles; After washing the semi-solid colloid, wet crude silica gel is obtained, which is used as a raw material for further preparing pure silica gel; and the magnesium sulfate solution containing impurities and silica gel fine particles is filtered to remove the silica gel fine particles, and the obtained solution is used as a raw material for further preparing high-purity magnesium sulfate, that is, a crude magnesium sulfate solution; After the above steps S1 to S5, wet crude silica gel and crude magnesium sulfate liquid are obtained respectively, and the wet crude silica gel and crude magnesium sulfate liquid are purified to prepare pure silica gel and high-purity magnesium sulfate respectively.

2. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: In the step S1, the mixture is sieved through a 200-mesh sieve.

3. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: In the step S2, stirring is performed at room temperature for 5 to 15 minutes; the leaching conditions are: the sulfuric acid concentration is 1.5 to 3 mol / L, the liquid-solid ratio of the sulfuric acid solution to the nickel-iron slag is controlled at 10 to 20 L:1 kg, the stirring rate is controlled at 200 to 800 rpm, the initial reaction temperature is room temperature, and no heating is required.

4. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: The impurity metal ions in step S3 are mainly Fe 3+ , Ca 2+ 、Al 3+ Cr 3+ ion.

5. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: In step S4, the leachate is allowed to stand for 4 to 12 hours; a shearing stirring paddle is used to mechanically stir and crush the colloid; the impurity metal ions are mainly Fe 3+ , Ca 2+ 、Al 3+ Cr 3+ ion.

6. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: The specific steps of the wet crude silica gel purification treatment in step S5 are: Step A1: Primary drying The wet crude silica gel prepared in step S5 is placed in a drying oven at 120-150° C. and dried to a constant weight to obtain dry crude silica gel; after drying, the mass of the silica gel is reduced to 7-12% of that before drying; Step A2: Alkaline Dissolution The dry crude silica gel obtained in step A1 is dissolved with caustic soda solution, and the dissolution process is heated and stirred at low temperature, or stirred without heating; during the dissolution process, SiO2 in the silica gel reacts with NaOH to generate sodium silicate which enters the solution, and the crude silica gel that is not completely dissolved forms a precipitate with most of the impurities insoluble in alkali; thereby obtaining a liquid-solid mixture formed by the sodium silicate solution and the precipitate; the alkali dissolution conditions are: the liquid-solid ratio of the NaOH solution to the wet silica gel is 8L-12:1kg, the concentration of the NaOH alkali solution is 1.5-3mol / L, the reaction temperature is room temperature-90°C, the reaction time is 30-120min, and the stirring rate is 200-800rpm; Step A3: Separation of slag and liquid The liquid-solid mixture obtained in step A2 is filtered to obtain a sodium silicate solution and a small amount of alkaline slag containing impurities. Step A4: Gluing Slowly add dilute sulfuric acid with a concentration of 0.5 to 2 mol / L to the sodium silicate solution obtained in step A3, stirring at the same time, and adjusting the pH value of the solution; when the pH value of the solution is 10.5 to 11, stop dripping the dilute acid and continue stirring for 1 hour; then slowly add acid until a large amount of silica gel is generated, adjust the pH value to 3 to 4, stop heating, continue stirring to age the silica gel for 4 to 12 hours, and then the gelling process is completed to obtain a gel mixture; Step A5: Glue-liquid separation The gel mixture obtained in step A4 is centrifuged and the liquid phase is filtered to obtain jelly-like wet silica gel and a solution whose main component is sodium sulfate; Step A6: Silicone Washing The wet silica gel obtained in step A5 is acid-washed with dilute sulfuric acid for 4 to 5 times and washed with water for 2 to 3 times to obtain relatively pure wet silica gel; the washing liquid is 10% by volume of dilute sulfuric acid and pure water; the liquid-to-solid ratio of each washing is ≥1L / Kg; Step A7: Secondary Drying The wet silica gel washed in step A6 is dried at 100-120° C. to a constant weight to obtain dry pure silica gel; the silica gel is used as the final product of silicon recovery; The pure silica gel is calculated based on the mass percentage of SiO2 and has a purity of more than 99%.

7. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 1, characterized in that: The specific steps of purifying the crude magnesium sulfate solution in step S5 are as follows: Step B1: Primary crystallization The crude magnesium sulfate solution obtained in step S5 is heated to evaporate water, and after being concentrated to 1 / 6 to 1 / 3 of the volume of the original solution, the solution temperature is adjusted to 70 to 85° C. as the starting temperature of the primary crystallization, and the cooling rate of the solution is controlled so that the solution is cooled to room temperature or below room temperature after 6 to 10 hours; during the primary crystallization process, the solution is cooled while stirring, and when the temperature drops to 35 to 20° C., a seed crystal of magnesium sulfate heptahydrate is added to the solution, and the seed coefficient is 0.2 to 0.4; During the crystallization process, hydrated magnesium sulfate crystals continuously precipitate from the solution and settle to the bottom of the crystallization tank; Step B2: Solid-liquid separation The liquid-solid mixture obtained in step B1 is filtered to obtain fine block solids as magnesium sulfate heptahydrate crystals, and the filtrate is the liquid after the primary crystallization; the magnesium sulfate heptahydrate crystals contain a small amount of impurities, and further purification is required to prepare high-purity magnesium sulfate; the liquid after the primary crystallization contains a large amount of sulfuric acid and incompletely crystallized magnesium sulfate, which can be added with new acid and returned to the leaching process as a solvent, thereby improving the utilization rate of the acid and the recovery rate of magnesium; Step B3: Dissolution The magnesium sulfate heptahydrate obtained in step B2 is dissolved in water, and the liquid-solid ratio of water to the primary crystallization product magnesium sulfate heptahydrate is controlled at 3 to 7 L / kg; the magnesium sulfate heptahydrate crystals are easily dissolved and are completely dissolved by slight stirring for 5 to 10 minutes to form a crude magnesium sulfate solution; Step B4: Purification After heating the magnesium sulfate crude solution obtained in step B3 to 70-90° C., adding a neutralizing agent MgO thereto, stirring at the same time, and stopping adding the neutralizing agent after adjusting the pH value of the solution from 2-3 to 6-8; during this process, the impurity metal ions undergo a hydrolysis reaction to generate corresponding hydroxide precipitates to form purified slag, and at the same time, a magnesium sulfate supernatant slurry is obtained; Step B5: Separation of slag and liquid The solid separated from the slurry obtained in step B4 is the purified slag after filtering, and the amount of the purified slag is very small, less than 5% of the nickel-iron slag raw material; the separated liquid is the magnesium sulfate purified liquid; Step B6: Secondary crystallization The purified magnesium sulfate solution obtained in step B5 is heated to evaporate water, and concentrated to 1 / 10 to 1 / 5 of the volume of the original solution to become a secondary crystallization solution, and the temperature thereof is adjusted to 70 to 85° C., and cooling crystallization is started; The crystallization conditions are as follows: the final crystallization temperature is between 0 and 20°C, the crystallization time is 5 to 12 hours, when the solution temperature drops to 35 to 20°C, a seed crystal of magnesium sulfate heptahydrate is added to the solution; the seed coefficient is 0.4 to 0.6; During the crystallization process, hydrated magnesium sulfate crystals gradually precipitate from the solution and settle to the bottom of the crystallization tank; Step B7: Centrifugation The liquid-solid mixture containing magnesium sulfate crystals in step B6 is centrifuged to obtain high-purity hydrated magnesium sulfate crystals, i.e., a high-purity magnesium sulfate product; in order to reduce the free water in the high-purity hydrated magnesium sulfate crystals, the drum speed is controlled at 3000-5000 rpm during centrifugation; the secondary crystallized liquid obtained by centrifugation can be returned to the dissolution process B3 for recycling, thereby improving the recovery rate of magnesium and the utilization rate of water; The high-purity magnesium sulfate product has a purity of more than 99.9% calculated based on the mass percentage of hydrated magnesium sulfate.

8. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 6, characterized in that: The primary drying in step A1 and the secondary drying in step A6 are not limited to heating and drying the wet silica gel using electric heat or fuel combustion heat, and can also be dried naturally in the sun or with the help of flowing air; the natural drying method is not limited to the temperature and time parameters during drying.

9. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 6, characterized in that: During the purification of the wet crude silica gel in step A1, the wet crude silica gel can be directly subjected to an alkali dissolution operation; when the wet crude silica gel is used as the solute, the liquid-to-solid ratio of the NaOH solution to the wet silica gel is 8 to 12 L / kg, and the other dissolution conditions are the same as when the dry crude silica gel is used as the solute.

10. A method for comprehensive recovery of silicon and magnesium based on rotary kiln-electric furnace type nickel-iron slag as claimed in claim 7, characterized in that: The concentration of the magnesium sulfate solution before crystallization is not limited to the process methods and parameters described in the above-mentioned step B2 primary crystallization and step B7 secondary crystallization step. It can also be a method in which a sun shed is used to evaporate and concentrate the solution with the help of sunlight and wind when the temperature is high during the day, and the solution is cooled and crystallized to obtain magnesium sulfate crystals when the temperature is low at night; it is not limited to the cooling crystallization method used in step B6 secondary crystallization, and full evaporation can also be used, that is, evaporating all free water molecules in the secondary crystallization stock solution to obtain hydrated magnesium sulfate crystals; when full evaporation is used, it is not necessary to add seed crystals, and the step B8 centrifugal separation step is not required after crystallization, and hydrated magnesium sulfate crystals can be directly obtained, so that the process is simplified and the product purity can still reach more than 99.9wt%.

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