Method for efficiently removing impurities from steel slag calcium extraction filtrate and preparing light calcium carbonate

Abstract

The invention relates to the technical field of calcium carbonate preparation, in particular to a method for efficiently removing impurities from steel slag calcium extraction filtrate and preparing light calcium carbonate, which comprises the following steps: S1, mixing steel slag solid waste with an ammonium salt solution, reacting, and filtering to obtain calcium extraction filtrate; s2, adding a pH regulator into the calcium extraction filtrate, introducing an oxidizing agent for reaction, filtering to obtain high-purity calcium-containing filtrate and a slag phase, and drying to obtain a multi-element composite hydroxide; and S3, mixing the high-purity calcium-containing filtrate, the CO2-containing gas and a crystal form control agent, reacting, and filtering to obtain the high-purity light calcium carbonate. The method is easy to operate, the process of preparing calcium carbonate through calcium extraction and mineralization of the steel slag is greatly shortened, impurity components are not introduced in the impurity removal process of the calcium extraction filtrate, and the problems of safety, equipment, poor pH stability, step-by-step oxidation and impurity removal, difficult filtration, low impurity removal efficiency and the like in the impurity removal process of an ammonia method are solved. The obtained high-purity light calcium carbonate is low in cost and low in energy consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium carbonate preparation, and in particular to a method for efficiently removing impurities from the filtrate of calcium extraction from steel slag and preparing light calcium carbonate. Background Art

[0002] The iron and steel industry is a typical energy and resource-intensive industry, and a large amount of energy consumption and pollutant emissions occur during its production process. During the iron and steel smelting process, a large amount of carbon dioxide is generated. In 2023, the carbon dioxide emission intensity of the global iron and steel industry reached 1.92 tons of CO2 / ton of crude steel. In addition, the steel slag produced per ton of steel accounts for 15% to 20% of the steel output. China is the world's largest iron and steel producer, and the stockpile of steel slag solid waste exceeds 1 billion tons, with an annual increment of about 100 million tons. At present, the comprehensive utilization rate of steel slag is less than 30%. The stacking of a large amount of steel slag not only occupies land but also may cause potential harm to soil and groundwater. Therefore, the recycling and resource utilization of steel slag and the reduction of carbon dioxide emissions have become extremely urgent.

[0003] The main components of steel slag include CaO, SiO2, Al2O3, and MgO, and the content of these four components can reach 75%. In addition, steel slag also contains 25% of Fe2O3, and the main mineral phases are tricalcium silicate, dicalcium silicate, and calcium aluminate. Steel slag has a relatively high calcium content, with the content of CaO being approximately 45%. Its carbonation activity is also very high and can be directly used as a mineralization raw material for the mineralization absorption of CO2. Patent CN117700137A studied a preparation method and application of industrialized carbonized steel slag, grinding the steel slag into powder, preparing aerated blocks, and carrying out the processes of carbonation and re-grinding, which can achieve the goals of large-scale and rapid carbonization of steel slag powder and high CO2 absorption. Adding the carbonized steel slag powder to asphalt to replace mineral powder can increase the water stability of asphalt mixture by 18%. Using the indirect method to extract calcium from steel slag and then carrying out a carbonation reaction on the calcium-extracted filtrate with carbon dioxide not only realizes efficient mineralization and carbon fixation but also can obtain high-purity calcium carbonate products and enrich the iron phase in steel slag. With the country's strong advocacy for the development of energy-saving and low-carbon circular economy, the indirect calcium extraction and carbon fixation of steel slag have become an important direction for the high-quality green and sustainable development of the steel industry. Patent CN117623360A studied a method for indirectly carbonating steel slag to prepare metastable calcium carbonate, using the reaction of steel slag and ammonium chloride solution to leach calcium and preparing high-purity metastable calcium carbonate through a carbonation reaction. Patent CN117682542A studied a method for simultaneously preparing light calcium carbonate and cement raw materials from steel slag. This method crushes the steel slag and reacts it with acetic acid to obtain a calcium-containing filtrate and tailings, and then CO2 gas is introduced into the calcium-containing filtrate, and light calcium carbonate and cement raw materials are obtained by filtration. Patent CN105197975A discloses a method for preparing light calcium carbonate from converter steel slag, using microwave-assisted reaction of steel slag and ammonium chloride to achieve efficient leaching of calcium components, and carrying out a carbonation reaction after filtration to obtain calcium carbonate. This method has the characteristics of high leaching rate and reusable ammonium chloride solution. With the country's strong advocacy for the development of energy-saving and low-carbon circular economy, the indirect calcium extraction and carbon fixation of steel slag have gradually become an important method for the high-quality green and sustainable development of the steel industry.

[0004] The indirect method for calcium extraction and carbon sequestration from steel slag often requires the use of chemical reagents (acids or ammonium salts) to leach the Ca and Mg components in the steel slag. However, in this process, the simultaneous leaching of metal components such as Fe, Mn, and Al often occurs, and the existing patents or research pay little attention to this part. The efficient separation of metal components such as Fe, Mn, Al, and Mg from the Ca component in the calcium extraction filtrate is the prerequisite and guarantee for improving the quality of calcium carbonate products and broadening the application fields of calcium carbonate products. Currently, ammonia gas is usually introduced into the calcium extraction filtrate from steel slag to adjust the pH of the system, so that metal components such as Fe, Mg, and Al are separated and purified from the Ca-containing filtrate in the form of precipitates. However, the above method involves a gas-liquid two-phase reaction, and the use of ammonia gas in the process will cause safety hazards and high requirements for the equipment material; at the same time, due to the volatility of ammonia gas and ammonia water, it is difficult to stably control the pH of the system, and the generated precipitate phase is mainly single-metal amorphous hydroxide (Fe(OH) x , Mg(OH)2, Al(OH)3), mostly amorphous flocculent precipitates, which are difficult to separate and have low impurity removal efficiency. The impurity removal filtrate still contains Mn 2+ , Fe 2+ and other non-ferrous metals, thus affecting the whiteness and quality of calcium carbonate.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for efficient impurity removal of calcium extraction filtrate from steel slag and preparation of light calcium carbonate. The method uses alkaline calcium oxide or calcium hydroxide as a pH regulator, uses oxygen in the oxidant as an oxidant to treat the calcium-containing filtrate, and synchronously removes metal ions such as Fe 2+ , Fe 3+ , Mg 2+ , Al 3+ , Mn 2+ in the calcium extraction filtrate in the form of a multi-metal composite hydroxide, avoiding the formation of amorphous flocculent precipitates in the traditional ammonia method for impurity removal, realizing the synchronous improvement of the purity and concentration of the calcium extraction filtrate, and preparing high-purity light calcium carbonate through a carbonation reaction.

[0007] The present invention provides a method for efficient impurity removal of calcium extraction filtrate from steel slag and preparation of light calcium carbonate, including the following steps:

[0008] S1: Mix the steel slag solid waste and the ammonium salt solution and react, and obtain the calcium extraction filtrate through filtration;

[0009] S2: Add a pH regulator to the calcium extraction filtrate, and introduce an oxidant to react, and obtain a high-purity calcium-containing filtrate and a slag phase through filtration, and obtain a multi-metal composite hydroxide after drying;

[0010] S3: mixing the high-purity calcium-containing filtrate, the CO2-containing gas and the crystal form control agent, and reacting them to obtain high-purity light calcium carbonate through filtration.

[0011] Preferably, in step S1, the steel slag is at least one of converter slag, electric furnace slag and casting slag; the mass content of ammonium salt in the ammonium salt solution is 9%-20%, and the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride and ammonium acetate, preferably ammonium chloride.

[0012] Preferably, the mass ratio of steel slag to ammonium salt solution is (0.05-0.3):1, for example 0.08:1; the reaction temperature is 60-120°C, for example 105°C, the reaction time is 1-6h, for example 3h, and the mass content of calcium chloride in the calcium extraction filtrate is 5%-14%, for example 12%.

[0013] Preferably, in step S2, the pH adjuster is one of CaO or Ca(OH)2, preferably Ca(OH)2; an oxidant is blown in to oxidize and remove impurities from the calcium extraction solution, and the oxidant comprises at least one of air, oxygen, ozone and hydrogen peroxide.

[0014] Preferably, the reaction temperature in step S2 is 70-120° C., such as 90° C., and the reaction time is 1-6 h, such as 3 h; and the pH value of the final reaction system is controlled at 8.0-10.0, such as 8.5.

[0015] Preferably, in step S2, the drying temperature of the slag phase is 60-80° C., such as 70° C., and the drying time is 6-24 h, such as 12 h.

[0016] In step S3, the crystal form control agent is at least one of sodium polyphosphate, dodecylbenzene sulfonic acid, polyethylene glycol, sodium sulfate, and citric acid; the mass ratio of the crystal form control agent to calcium carbonate is (0.002-0.005):1, preferably (0.003-0.005):1; the mass content of CO2 in the CO2-containing gas is 2%-100%, for example 80%, and the CO2-containing gas can be introduced in a self-priming manner, for example, a venturi tube can be used to introduce the CO2-containing gas; the reaction temperature is 20-50°C, for example 25°C, and the reaction time is 10-60min, for example 30min; after the reaction is completed, it is filtered and washed, and then dried at 60-80°C for 6-24h, for example 70°C for 12h to obtain light calcium carbonate.

[0017] Preferably, in steps S1-S3, an emulsifying pump is used in conjunction with a reactor device for mixing, and the speed of the agitator of the reactor is set to 600-800 r / min.

[0018] Preferably, in step S1, the rotation speed of the emulsifying pump is 1000 - 3000 r / min; in step S2, the rotation speed of the emulsifying pump is 1000 - 2000 r / min; in step S3, the rotation speed of the emulsifying pump is 1000 - 6000 r / min.

[0019] The slag phase obtained by impurity removal of the above-mentioned calcium-extracted filtrate is a flaky multi-component composite metal hydroxide precipitate with a particle size of 500 nm - 3 μm. The larger particle size facilitates the efficient separation of the slag phase and the calcium-containing filtrate. The light calcium carbonate prepared from the high-purity calcium-containing filtrate obtained after impurity removal has a regular morphology, which is a cubic-like morphology, with a particle size of 1 - 5 μm, a narrow particle size distribution, a purity > 99.2%, a chlorine content < 40 ppm, the contents of impurity metals such as Fe, Mg, Al, and Mn are all less than 100 ppm, an alkalinity of 7.5 - 7.8, a sedimentation volume of 2.8 - 3.6 mL / g, the product is white, and there are no visible impurities visually.

[0020] Beneficial effects:

[0021] The present invention provides a method for efficient impurity removal of calcium-extracted filtrate from steel slag and the preparation of light calcium carbonate. This method utilizes a dynamic circulation device equipped with an emulsifying pump and a reaction kettle to strengthen the mixing reaction of steel slag and ammonium salt solution, accelerate the reaction rate, and achieve efficient leaching of calcium components. At the same time, the reaction time of ammonium salt with metal components such as iron, magnesium, aluminum, and manganese in steel slag is inhibited, reducing the leaching of impurity metal components to obtain a calcium-extracted filtrate. Subsequently, CaO or Ca(OH)2 is introduced into the system as a pH regulator, and an oxidant is introduced into the calcium-extracted filtrate through Bernoulli's principle to fully oxidize low-valent metal ions such as Fe 2+ 、Mn 2+ and so on. Aging is carried out for 1 - 6 hours at 70 - 120 °C, and in the form of multi-metal hydroxide ([M 2+ 1-x M 3+ x (OH)2] x+ (A n- ) x / n ·mH2O) to achieve Mg 2+ 、Al 3+ 、Fe 3+Synchronous removal of various metal ions, thereby realizing efficient impurity removal of the calcium-extracted filtrate, obtaining a high-purity calcium-containing filtrate and a micron-scale multi-metal composite hydroxide precipitate; in the carbonation stage of the calcium-containing filtrate, the Bernoulli principle is used to preliminarily premix the gas containing CO2 with the calcium-containing filtrate. At the same time, the extrusion and shearing effects generated by the stator and rotor of the emulsifying pump during high-speed rotation are used to strengthen the efficient mixing of CO2 and the calcium-containing filtrate. By precisely controlling the CO2 absorption rate and the supersaturation degree of the reaction system during the reaction process, light calcium carbonate with small particle size and narrow particle size distribution is successfully prepared. Compared with the existing related methods, the method of the present invention is simple to operate, greatly shortens the process of preparing calcium carbonate by steel slag calcium extraction mineralization, and is easy to realize stable batch production. No impurity components are introduced during the impurity removal process, avoiding problems such as safety problems, equipment problems, poor pH stability, the necessity of separating oxidation and impurity removal steps, difficult filtration, and low impurity removal efficiency during the impurity removal process by the ammonia method. The prepared light calcium carbonate has low cost and low energy consumption, has good industrial application prospects, provides an important way for large-scale consumption of steel slag, realizing carbon emission reduction and iron enrichment, and promotes the green resource utilization of steel slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is the scanning electron microscope photograph of steel slag;

[0024] Figure 2 is the energy spectrum surface scan of steel slag;

[0025] Figure 3 is the scanning electron microscope photograph of the steel slag after ammonium salt calcium extraction in Example 1;

[0026] Figure 4 is the energy spectrum surface scan of the steel slag after ammonium salt calcium extraction in Example 1;

[0027] Figure 5 is the XRD pattern of the slag phase after impurity removal of the ammonium salt calcium extraction filtrate in Example 1;

[0028] Figure 6 is the scanning electron microscope photograph of the slag phase after impurity removal of the ammonium salt calcium extraction filtrate in Example 1;

[0029] Figure 7 is the scanning electron microscope photograph of the slag phase after impurity removal of the ammonium salt calcium extraction filtrate in Example 2;

[0030] Figure 8SEM photograph of the impurity-removing slag phase of the ammonium salt calcium extraction filtrate in Example 3;

[0031] Figure 9 XRD pattern of the calcium extraction filtrate slag phase in the control example

[0032] Figure 10 SEM photograph of the calcium extraction filtrate slag phase in the control example;

[0033] Figure 11 XRD pattern of the light calcium carbonate prepared in Example 1;

[0034] Figure 12 SEM photograph of the light calcium carbonate prepared in Example 1;

[0035] Figure 13 Particle size distribution curve of the light calcium carbonate prepared in Example 1;

[0036] Figure 14 SEM photograph of the light calcium carbonate prepared in Example 2.

[0037] Figure 15 SEM photograph of the light calcium carbonate prepared in the control example.

[0038] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0040] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined. In addition, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] The calcium-containing solid wastes adopted in each embodiment are as follows:

[0042] Steel slag: It is an irregular block at the micron scale, mainly containing components such as calcium, silicon, iron, aluminum, magnesium, and phosphorus. Among them, the distributions of calcium, silicon, and phosphorus elements are consistent, and the distributions of iron, magnesium, manganese, etc. elements are consistent. The content of calcium in the steel slag calculated as CaO is 45.81%, the content of silicon calculated as SiO2 is 12.35%, the content of iron calculated as Fe2O3 is 28.01%, the content of manganese calculated as MnO is 2.60%, and the content of phosphorus calculated as P2O5 is 2.38%; the morphology and element distribution are as Figure 1 and Figure 2 shown.

[0043] Example 1

[0044] The method for efficient impurity removal of the calcium-extracted filtrate from steel slag and the preparation of light calcium carbonate in this example is as follows:

[0045] (1) Calcium extraction from steel slag by ammonia distillation

[0046] Dissolve 50 kg of ammonium chloride in 200 L of water to form a clear ammonium chloride solution, and the mass content of ammonium chloride in the ammonium chloride solution is 20.00%.

[0047] Weigh 40 kg of steel slag and disperse it in the above ammonium chloride solution to form a stable suspension, and control the mass ratio of steel slag to ammonium chloride solution to be 0.16:1.

[0048] Add the above suspension to the reaction kettle, set the rotation speed of the reaction kettle to 600 r / min, set the rotation speed of the emulsifying pump to 2000 r / min, react at 105 °C for 3 h, and obtain an insoluble slag phase and a calcium-extracted filtrate after filtration.

[0049] (2) Impurity removal of the calcium-extracted filtrate

[0050] 7 kg of calcium hydroxide was added to the calcium extraction filtrate obtained in step (a), and an oxidant was added, the air intake of the oxidant was 20 L / min, the speed of the stirrer of the reactor was set to 600 r / min, the speed of the emulsification pump was set to 2000 r / min, the reaction was carried out at 90 ° C for 1 h, and the pH of the final reaction system was 9.2. After filtration and separation, a high-purity calcium-containing filtrate was obtained, and the slag phase was dried at 60 ° C for 12 h to obtain a multi-component composite metal hydroxide.

[0051] (III) Preparation of light calcium carbonate

[0052] The CO2-containing gas is introduced into the high-purity calcium-containing filtrate obtained in step (ii) through a venturi tube, the flow rate of the CO2-containing gas is set to 300 L / min, wherein the mass content of CO2 is 80%, and ammonium polyphosphate is added simultaneously as a crystal form control agent, and the mass ratio of ammonium polyphosphate to calcium carbonate is 0.005; the speed of the agitator of the reactor is set to 800 r / min, the speed of the emulsification pump is set to 5000 r / min, the reaction is carried out at 25°C for 30 min, and after centrifugation and washing, it is dried at 60°C for 12 h to obtain light calcium carbonate.

[0053] The mass ratio of calcium oxide dissolved in steel slag to total calcium oxide in steel slag was calculated, and the calcium extraction rate of steel slag was 62.6%. Figure 3 and Figure 4 As shown, the content of calcium element is significantly reduced, the content of iron element is significantly increased, the percentage of calcium chloride in the obtained calcium-containing filtrate is 12.96%, and the yield of light calcium carbonate is 91.6%.

[0054] The XRD pattern of the slag phase obtained by removing impurities from the calcium extraction filtrate in this embodiment is as follows: Figure 5 As shown in Figure 2, the characteristic diffraction peaks corresponding to the layered structure of hydrotalcite appeared, and the scanning electron microscopy results were as follows: Figure 6 As shown in the figure, it can be seen that the two-dimensional lamellar structure is 500nm to 2μm, which is a typical morphological feature of hydrotalcite. The elemental analysis results show that it contains Fe, Mg, Mn, Al, and Ca metal components, indicating that it is a multi-component composite metal hydroxide.

[0055] The calcium carbonate product prepared in this embodiment is white, with no visible impurities, a purity of 99.6%, a chlorine content of 30ppm, an iron content of 85ppm, a Mg content of 62ppm, an Al content of 54ppm, and a Mn content of 42ppm; a basicity of 7.5, and a sedimentation volume of 3.6mL / g, which is a high-purity light calcium carbonate. Figure 11 It can be seen from the XRD diagram that calcium carbonate has a calcite crystal structure. Figure 12 As shown, from Figure 12It can be seen that calcium carbonate is micron-sized cubic particles, and the size of a single particle is about 2.0 μm. Figure 13 It is the particle size distribution curve. From the figure, we can see that the particle size distribution is narrow. 50 is 2.5μm.

[0056] Example 2

[0057] The method for efficiently removing impurities from the calcium extraction filtrate from steel slag and preparing light calcium carbonate in this embodiment comprises the following steps:

[0058] (I) Extracting calcium from ammonium salt of steel slag

[0059] 50 kg of ammonium chloride was dissolved in 200 L of water to form a clear ammonium chloride solution, wherein the mass content of ammonium chloride in the ammonium chloride solution was 20.00%.

[0060] Weigh 40 kg of steel slag and disperse it in the above ammonium chloride solution to form a stable suspension, and control the mass ratio of steel slag to ammonium chloride solution to be 0.16:1.

[0061] The above suspension was added into the reactor, the speed of the reactor was set to 600 r / min, the speed of the emulsification pump was set to 2000 r / min, and the reaction was carried out at 105°C for 6 hours. After filtration, an insoluble slag phase and a calcium extraction filtrate were obtained.

[0062] (II) Removal of impurities from calcium extraction filtrate

[0063] 7 kg of calcium hydroxide was added to the calcium extraction filtrate obtained in step (a), and an oxidant was added, the air intake of the oxidant was 20 L / min, the speed of the stirrer of the reactor was set to 600 r / min, the speed of the emulsification pump was set to 2000 r / min, and the reaction was carried out at 80 ° C for 3 h. The pH of the final reaction system was 8.8. After filtration and separation, a high-purity calcium-containing filtrate was obtained. The slag phase was dried at 60 ° C for 12 h to obtain a multi-component composite metal hydroxide.

[0064] (III) Preparation of light calcium carbonate

[0065] The CO2-containing gas is introduced into the high-purity calcium-containing filtrate obtained in step (ii) through a venturi tube, the flow rate of the CO2-containing gas is set to 300 L / min, wherein the mass content of CO2 is 80%, and sodium sulfate is added simultaneously as a crystal form control agent, and the mass ratio of sodium sulfate to calcium carbonate is 0.005; the speed of the stirrer of the reactor is set to 800 r / min, the speed of the emulsification pump is set to 5000 r / min, the reaction is carried out at 25°C for 60 min, and after centrifugation and washing, it is dried at 60°C for 12 h to obtain light calcium carbonate.

[0066] The mass ratio of the dissolved calcium oxide in the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was 64.7%. After the ammonium salt leaching of calcium from the steel slag, the calcium element content in the slag phase decreased significantly, and the iron element content increased significantly. The percentage content of calcium chloride in the obtained calcium-containing filtrate was 13.06%, and the yield of light calcium carbonate was 93.5%.

[0067] The slag phase obtained from the impurity removal of the calcium extraction filtrate in this example was the characteristic diffraction peak of the hydrotalcite-like layered structure, and its scanning electron microscope was as Figure 7 shown. It can be seen from the figure that it was two-dimensional hexagonal flakes with a size of 500 - 800 nm, which was the typical morphological feature of hydrotalcite. The elemental analysis results showed that it contained metal components such as Fe, Mg, Mn, Al, and Ca, indicating that it was a multi-component composite metal hydroxide.

[0068] The calcium carbonate product prepared in this example was white, with no visible impurities visually. The purity of calcium carbonate was 99.5%, the chlorine content was 28 ppm, the iron content was 25 ppm, the Mg content was 22 ppm, the Al content was 14 ppm, and the Mn content was 12 ppm; the alkalinity was 7.6, and the sedimentation volume was 3.8 mL / g, which was high-purity light calcium carbonate. The XRD results showed that the obtained calcium carbonate was a calcite-type crystal structure, and its scanning electron microscope photograph was as Figure 14 shown. It can be seen from Figure 14 that the calcium carbonate was micron-sized cubic particles with a narrow particle size distribution, and the particle size was about 1.5 μm. The particle size distribution in the particle size distribution curve was narrow, and D50 was 2.2 μm.

[0069] Example 3

[0070] The method for efficient impurity removal of the calcium extraction filtrate from steel slag and the preparation of light calcium carbonate in this example is as follows:

[0071] (1) Calcium extraction from steel slag with ammonium salt

[0072] 40 kg of ammonium chloride was dissolved in 200 L of water to form a clear ammonium chloride solution, and the mass content of ammonium chloride in the ammonium chloride solution was 16.67%.

[0073] 40 kg of steel slag was weighed and dispersed in the above ammonium chloride solution to form a stable suspension, and the mass ratio of steel slag to ammonium chloride solution was controlled to be 0.166:1.

[0074] The above suspension was added to the reaction kettle, the rotation speed of the reaction kettle was set at 600 r / min, the rotation speed of the emulsifying pump was set at 1000 r / min, and the reaction was carried out at 90 °C for 3 h. After filtration, an insoluble slag phase and a calcium extraction filtrate were obtained.

[0075] (2) Impurity removal of the calcium extraction filtrate

[0076] 7 kg of calcium hydroxide was added to the calcium extraction filtrate obtained in step (a), and an oxidant was added, the air intake of the oxidant was 20 L / min, the speed of the stirrer of the reactor was set to 600 r / min, the speed of the emulsification pump was set to 2000 r / min, the reaction was carried out at 90 ° C for 6 hours, and the pH of the final reaction system was 9.4. After filtration and separation, a high-purity calcium-containing filtrate was obtained, and the slag phase was dried at 60 ° C for 12 hours to obtain a multi-component composite metal hydroxide.

[0077] (III) Preparation of light calcium carbonate

[0078] The CO2-containing gas is introduced into the high-purity calcium-containing filtrate obtained in step (ii) through a venturi tube, the flow rate of the CO2-containing gas is set to 300 L / min, wherein the mass content of CO2 is 80%, and polyethylene glycol is added simultaneously as a crystal form control agent, and the mass ratio of polyethylene glycol to calcium carbonate is 0.005; the speed of the stirrer of the reactor is set to 800 r / min, the speed of the emulsification pump is set to 5000 r / min, the reaction is carried out at 25°C for 60 min, and after centrifugation and washing, it is dried at 60°C for 12 h to obtain light calcium carbonate.

[0079] The mass ratio of calcium oxide dissolved in the steel slag to the total calcium oxide in the steel slag was calculated, and the calcium extraction rate of the steel slag was 52.7%. The calcium content in the slag phase after the steel slag was calcium-leached with ammonium salt was significantly reduced, and the iron content was significantly increased. The percentage of calcium chloride in the obtained calcium-containing filtrate was 12.59%, and the yield of light calcium carbonate was 91.3%.

[0080] The slag phase obtained by removing impurities from the calcium extraction filtrate in this embodiment is a characteristic diffraction peak of the layered structure of hydrotalcite. Figure 8 As shown in the figure, it can be seen that the two-dimensional flakes are 1-2 μm, which are typical morphological characteristics of hydrotalcite. The elemental analysis results show that it contains Fe, Mg, Mn, Al, and Ca metal components, indicating that it is a multi-component composite metal hydroxide.

[0081] The calcium carbonate product obtained in this embodiment is white, with no visible impurities, a purity of 99.4%, a chlorine content of 30ppm, an iron content of 20ppm, a Mg content of 18ppm, an Al content of 10ppm, and a Mn content of 11ppm; the alkalinity is 7.4, and the sedimentation volume is 3.5mL / g, which is a high-purity light calcium carbonate. The XRD results show that the obtained calcium carbonate has a calcite crystal structure, and the calcium carbonate is a micron-sized cubic particle with a narrow particle size distribution of about 2.3μm. The particle size distribution curve has a narrow particle size distribution, D 50 It is 3.2μm.

[0082] Comparative Example 1

[0083] The calcium-extracted filtrate is first passed through an oxidant at a rate of 20 L / min, and an oxidation reaction is carried out at 90 °C for 3 h. Subsequently, ammonia gas is used as the pH regulator, and the pH of the final system is controlled at 9.2. The rest is the same as in Example 1. That is, in this comparative example, the calcium-extracted filtrate is first oxidized with an oxidant, and then ammonia water is used as the pH regulator for precipitation and impurity removal. Subsequently, the impurity-removed filtrate is used for the preparation of calcium carbonate.

[0084] The XRD of the residue phase obtained by impurity removal of the calcium-extracted filtrate in this comparative example is as Figure 9 shown. It can be seen from the figure that the characteristic peaks are typical of iron oxide, which is mainly due to the dehydration and oxidation of iron hydroxide generated during the precipitation process during drying. Its scanning electron microscope image is as Figure 10 shown. It is spherical aggregates of particles about 5 nm in size aggregated into secondary spherical aggregates about 50 - 100 nm in size. The elemental analysis results show that its main component is Fe2O3, and it contains a small amount of Mg and Al metal components, which is due to the attachment of Mg or Al hydroxides on the surface.

[0085] The calcium carbonate product prepared in this comparative example is white, with visual inspection showing light yellow and black impurities. The purity of calcium carbonate is 97.2%, the chlorine content is 30 ppm, the iron content is 870 ppm, the Mg content is 262 ppm, the Al content is 317 ppm, and the Mn content is 402 ppm. The alkalinity is 7.9, and the sedimentation volume is 3.2 mL / g, which is light calcium carbonate. The XRD results show that the obtained calcium carbonate is a calcite crystal structure. Its scanning electron microscope photograph is as Figure 15 shown. From Figure 15 it can be seen that the calcium carbonate is micron-sized cubic particles, but they are severely adhered to each other, and the particle size is about 3 μm. The particle size distribution curve has a narrow particle size distribution, and D 50 is 3.8 μm.

[0086] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for efficiently removing impurities from the filtrate of calcium extraction from steel slag and preparing light calcium carbonate, characterized in that, The steps include: S1: mixing the steel slag solid waste and the ammonium salt solution and reacting them, and filtering to obtain a calcium extraction filtrate; S2: adding a pH regulator to the calcium extraction filtrate, and introducing an oxidant to react, filtering to obtain a high-purity calcium-containing filtrate and a slag phase, and drying to obtain a multi-component composite hydroxide; S3: mixing the high-purity calcium-containing filtrate, the CO2-containing gas and the crystal form control agent, and reacting them to obtain high-purity light calcium carbonate through filtration.

2. The method according to claim 1, characterized in that, In the step S1, the steel slag is at least one of converter slag, electric furnace slag and casting slag; the mass content of ammonium salt in the ammonium salt solution is 9%-20%, and the ammonium salt is selected from at least one of ammonium nitrate, ammonium chloride and ammonium acetate.

3. The method according to claim 1, wherein The mass ratio of steel slag to ammonium salt solution is (0.05-0.3):1; the reaction temperature is 60-120°C, and the reaction time is 1-6h.

4. The method according to claim 1, wherein In step S2, the pH regulator is one of CaO and Ca(OH)2; an oxidant is blown into the calcium extraction solution to oxidize and remove impurities, and the oxidant includes at least one of air, oxygen, ozone, and hydrogen peroxide.

5. The method according to claim 1, wherein The reaction temperature in step S2 is 70-120° C. and the reaction time is 1-6 hours; the pH value of the final reaction system is controlled at 8.0-10.

0.

6. The method according to claim 1, wherein In step S2, the drying temperature of the slag phase is 60-80° C., and the drying time is 6-24 hours.

7. The method according to claim 1, wherein After the calcium extraction filtrate is impurity-removed in step S2, the slag phase is a flaky structure of 500nm-3μm, which is a multi-component composite metal hydroxide containing Ca, Fe, Mg, Al and Mn.

8. The method according to claim 1, characterized in that, In steps S1-S3, an emulsifying pump is used in conjunction with a reactor device for mixing, and the speed of the agitator provided in the reactor is set to 600-800 r / min.

9. The method according to claim 8, wherein In step S1, the rotation speed of the emulsification pump is 1000-3000 r / min; in step S2, the rotation speed of the emulsification pump is 1000-2000 r / min; in step S3, the rotation speed of the emulsification pump is 1000-6000 r / min.

10. The method according to claim 1, characterized in that, The light calcium carbonate prepared from the obtained high-purity calcium-containing filtrate has a regular cubic morphology, a particle size of 1-5 μm, a narrow particle size distribution, a purity of >99.2%, a chlorine content of <40 ppm, the content of Fe, Mg, Al, and Mn impurity metals are all less than 100 ppm, the basicity is 7.5-7.8, the sedimentation volume is 2.8-3.6 mL / g, the product is white, and no impurities are visible to the naked eye.

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