Methods and apparatus for sodium slag recovery

Abstract

This invention relates to the fields of high-purity sodium preparation and safe disposal of sodium-calcium slag, and discloses a method and apparatus for preparing high-purity sodium and safely disposing of sodium-calcium slag using a gravity separation-controlled combustion-alkali leaching process. The method includes the following steps: (1) gravity separation of liquid sodium slag to obtain pure sodium and high-calcium sodium slag; (2) calcination of the high-calcium sodium slag to obtain calcined slag; (3) leaching of the calcined slag with an alkaline solution to obtain sodium hydroxide solution and calcium hydroxide. The method and apparatus provided by this invention have advantages such as high efficiency in separating sodium and calcium, saving separation time, safe and controllable production process, and continuous production process. It provides a safe and efficient method for the preparation of high-purity sodium and safely disposes of the new sodium-calcium slag generated by this method, realizing the continuous preparation of high-purity sodium and the safe recycling of new sodium-calcium slag.

Description

Technical Field

[0001] This invention relates to the field of sodium metal production, and more specifically to a method and apparatus for recovering sodium slag. Background Technology

[0002] Sodium metal is a chemically active alkali metal, widely used in the pharmaceutical, chemical, and nuclear industries due to its non-toxicity, good electrical and thermal conductivity, low melting point, and moderate price. Existing sodium metal producers include China Salt Lantai Group (45,000 tons / year), Inner Mongolia Ruixin Chemical (32,000 tons / year), Henan Luoyang Wanji Co., Ltd. (18,000 tons / year), and Shandong Morui Technology Co., Ltd. (15,000 tons / year). Statistics show that my country's current annual sodium metal production reaches 110,000 tons, surpassing the United States and Germany, making it the world's largest producer of sodium metal. Because pure sodium chloride has a melting point as high as 801℃, excessively high electrolysis temperatures not only consume a large amount of electricity but also easily cause the loss of sodium metal through volatilization and oxidation. Therefore, in actual electrolysis, calcium chloride and barium chloride are added to form a ternary molten salt to lower the electrolysis temperature, allowing sodium metal electrolysis to be carried out at 580-620℃. The addition of calcium chloride and barium chloride significantly reduces the temperature of the electrolysis process. Just as a coin has two sides, the problem it presents is that the cathodic reduction potentials of calcium and sodium ions are close, resulting in the reduction of a small amount of metallic calcium along with the formation of metallic sodium at the cathode. This necessitates refining the liquid sodium obtained from electrolysis in a refining tank to remove any impurities of metallic calcium. During the refining process of metallic sodium, metallic calcium (density ρ = 1.55 g / cm³)... 3 The density of sodium (ρ = 0.968 g / cm³) is greater than that of metallic sodium. 3 Sodium chloride has a high density, resulting in 99.5-99.8% pure metallic sodium at the top and sodium slag containing metallic sodium and calcium at the bottom. According to the national high-calcium sodium industry standard (HG / T5550—2019), analysis shows that the sodium slag contains 60-90% metallic sodium and 10-40% metallic calcium. Because metallic sodium and calcium readily react chemically in air or water, even exploding, the storage and transportation of sodium slag must comply with relevant regulations for the safety supervision and management of dangerous goods transportation by rail, road, and waterway, as well as the requirements of JT / T617.1-JT / T617.7. Based on the consumption ratio of sodium chloride and calcium chloride raw materials and material balance calculations, the amount of sodium slag generated is 9-12% of the metallic sodium production, which is equivalent to approximately 900-1200 tons of sodium slag generated annually during the production of 10,000 tons of metallic sodium. How to safely dispose of these by-product sodium slags and recover the sodium and calcium resources within them has significant economic and environmental value.

[0003] Existing methods for treating sodium slag mainly include alcoholysis, vacuum distillation, and melt pressure filtration. Regarding sodium slag alcoholysis, for example, patent CN208562194U reports a system for reacting sodium slag and methanol in a methanol tank to obtain sodium methoxide and its recycling. This method uses methanol, ethanol, or water as raw materials to react with sodium slag to produce byproducts such as sodium methoxide, sodium ethoxide, and sodium hydroxide. Regarding sodium slag vacuum distillation, CN103667708B, CN102634671A, and CN203668481U report methods for heating sodium slag under vacuum to obtain sodium vapor, which is then condensed into liquid sodium to obtain sodium ingots. The main problem with this process is the high energy consumption of the high-temperature evaporation process for metallic sodium, and the fact that sodium vapor is more flammable and explosive than metallic sodium, requiring high resistance to high-temperature corrosion and explosion-proof properties of the equipment, significantly increasing recovery costs. Regarding the sodium slag melt pressure filtration method, CN2846436Y, CN203487209U, CN2846437Y, CN109371250A, and CN107574318B report a method of separating molten sodium and unmelted calcium metals by mechanical extrusion after high-temperature melting of sodium slag, yielding a portion of metallic sodium and residual sodium slag. This method extracts metallic sodium through extrusion, typically achieving an extraction rate of 40-50%. A considerable portion of the metallic sodium remains mixed with the calcium metal, making separation difficult. Furthermore, the sodium-calcium mixture produced as a byproduct during extrusion is still classified as hazardous waste and requires oxygen- and water-proof storage. Regarding the sodium slag molten salt replacement recovery process, Chinese patent application (CN109371250A) reports a preparation process for extracting metallic sodium from sodium slag using the molten replacement method. The steps are as follows: 1) Sodium slag is placed in a sodium slag melting tank and heated under nitrogen protection to obtain molten sodium slag; 2) The molten sodium slag is added to a reactor, and sodium chloride is added simultaneously to carry out a replacement reaction to form metallic sodium, calcium chloride, and calcium oxide, obtaining metallic sodium with a purity of 96-98%; 3) It then enters a refiner, and after cooling and settling treatment, 99.7% metallic sodium is obtained and transferred to a refined sodium storage tank; the residue generated by cooling and settling in the refiner is added to the sodium slag melting tank and then transferred to the reactor to carry out a replacement reaction again; 4) The obtained 99.7% metallic sodium is used to obtain sodium through a sodium casting machine, which is close to the existing refined sodium production process. In the flotation separation of sodium slag, a recent Chinese patent application CN105821217A discloses a method that utilizes a liquid dispersion medium for repeated heating and cooling, combined with mechanical stirring. Subsequent cooling separates the solid metallic sodium, achieving a sodium recovery rate of over 80-95% from the sodium slag, significantly improving the recovery efficiency. The main problems with this process are: firstly, the repeated heating and cooling processes increase the pressure and energy consumption of the heating and cooling equipment; secondly, the use of large amounts of flammable alcohol and ether organic solvents poses safety risks.

[0004] A comprehensive analysis of the aforementioned sodium slag treatment technologies reveals that the reported sodium slag treatment processes involve flammable and explosive substances such as alcohols, organic solvents, or high-temperature sodium vapor volatilization. Therefore, developing a process for the safe disposal of sodium slag and the recovery of sodium and calcium resources without the use of hazardous substances such as organic solvents or sodium vapor has become an urgent problem to be solved in the metallic sodium industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method and apparatus for sodium slag recovery. The method and apparatus for sodium slag recovery provided by this invention are safe and controllable.

[0006] The first aspect of this invention provides a method for recovering sodium slag, the method comprising the following steps:

[0007] (1) The liquid sodium slag is separated by gravity to obtain pure sodium and high-calcium sodium slag;

[0008] (2) The high-calcium sodium slag is roasted to obtain roasted slag;

[0009] (3) The roasted residue is leached with an alkaline solution to obtain sodium hydroxide solution and calcium hydroxide.

[0010] Preferably, the roasting in step (2) includes the following steps:

[0011] (2-1) The high-calcium sodium slag is subjected to a first roasting to obtain the first roasted product slag;

[0012] (2-2) The first roasted product residue is crushed and then roasted a second time to obtain the roasted residue. This preferred embodiment is more conducive to converting the high-calcium sodium slag into sodium peroxide, sodium oxide, calcium oxide, and a small amount of residual sodium-calcium slag to the greatest extent.

[0013] Preferably, the solute in the alkaline solution in step (3) is a hydrate, most preferably sodium hydroxide tetrahydrate. This preferred embodiment can reduce the free water concentration, moderate the reaction, and thus achieve the goal of safe production.

[0014] A second aspect of the present invention provides an apparatus for recovering sodium slag, the apparatus comprising a layered unit, a first roasting unit, a pulverizer, a second roasting unit, and a reaction vessel connected in series;

[0015] The layering unit is used to separate sodium slag into layers to obtain pure sodium and high-calcium sodium slag.

[0016] The layered unit is equipped with a high-calcium sodium slag outlet, and the high-calcium sodium slag outlet is connected to the inlet of the first roasting unit.

[0017] The reactor is used to leach the roasting residue obtained from the second roasting unit with an alkaline solution.

[0018] The method and apparatus for recovering metallic sodium and calcium resources from sodium slag provided by this invention are safe, controllable, and consume no chemicals. Furthermore, they enable the secondary development of hazardous waste sodium slag, converting it into sodium hydroxide solution and calcium hydroxide solid, thus realizing the high-value utilization of sodium slag. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a recycling device according to a specific embodiment of the present invention;

[0020] Figure 2 The image shows the XRD pattern of calcium hydroxide recovered in Example 1 of this invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] In the description of this invention, unless otherwise stated, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0023] Unless otherwise explicitly stated, terms relating to connections, such as “connection” and “interconnection”, refer to a relationship in which structures are fixed or connected to each other directly or indirectly through an intermediate structure, as well as a relationship of active or rigid connection.

[0024] As used herein, when an element, component, or unit is described as being “connected to,” “linked to,” or “in contact with” another element, component, or unit, that element, component, or unit may be directly connected to, directly linked to, or directly in contact with the particular element, component, or unit, or may be connected, linked to, or in contact with the particular element, component, or unit through an intermediate element, component, or unit. When an element is described as being “directly connected to,” “directly linked to,” or “in contact with” another element, there is no intermediate element, component, or unit.

[0025] As used herein, the terms “fluidly connected to” or “fluid connection” will be understood as a component being connected to a pipe or pipeline and configured to allow gas or liquid to flow through the component.

[0026] The term “ambient temperature” as used in this article will be understood as the temperature under ambient conditions, such as room temperature of 20-25°C.

[0027] The terms "first" and "second" used in this article are only for distinguishing the materials or operations used in different steps or stages, and do not limit the specific materials or operations.

[0028] In this invention, when a value is expressed as an approximation using the antecedent "about," it should be understood that a particular value forms another embodiment. As used herein, "about X" (where X is a numerical value) preferably refers to ±10% of the referenced value, including endpoint values. For example, the phrase "about 8" preferably refers to a value in the range of 7.2 to 8.8 (inclusive of endpoint values ​​7.2 and 8.8). When present, all ranges are inclusive and composable. For example, when listing a range of "1 to 5," the listed range should be interpreted as including ranges "1 to 4," "1 to 3," "1-2 and 4-5," "1-3 and 5," "2-5," etc. Furthermore, when a list of alternatives is provided, the list can be interpreted as meaning that any alternative can be excluded, for example, by negative limitation in the claims. For example, when listing the range “1 to 5”, the listed range can be interpreted to include cases where any one of 1, 2, 3, 4, or 5 is negatively excluded; therefore, the statement “1 to 5” can be interpreted as “1 and 3-5, but not 2”, or simply as “excluding 2”. It is intended that any component, element, property, or step expressly referenced herein may be expressly excluded from the claims, whether such component, element, property, or step is listed as an alternative or whether it is referenced separately.

[0029] Unless otherwise explicitly stated, the terms “substantially” or “substantially the same” as used herein shall be understood to cover parameters that fluctuate within a suitable range, such as ±10% or ±15% fluctuation of the parameter. In some implementations, the fluctuation range is within ±10%.

[0030] Unless otherwise expressly stated, the terms "optionally" or "optionally" as used herein mean either performing the operation or not performing it, or adding or not adding the material. In this invention, gas concentrations, such as "oxygen concentration," unless otherwise specified, refer to the volume concentration of the gas.

[0031] The first aspect of this invention provides a method for recovering sodium slag, such as... Figure 1As shown, the method includes the following steps:

[0032] (1) The liquid sodium slag is separated by gravity to obtain pure sodium and high-calcium sodium slag;

[0033] (2) The high-calcium sodium slag is roasted to obtain roasted slag;

[0034] (3) The roasted residue is leached with an alkaline solution to obtain sodium hydroxide solution and calcium hydroxide.

[0035] The method provided by this invention is applicable to the recovery of sodium slag in most industries, which can be directly obtained industrial sodium slag, preferably the hazardous waste sodium slag generated from the electrolysis of sodium chloride to prepare metallic sodium, or sodium slag processed by existing technology.

[0036] According to a preferred embodiment of the present invention, the sodium slag contains Na and Ca; preferably, based on the total amount of the sodium slag, the Na content is 60-90% by weight and the Ca content is 10-40% by weight. In addition to Na and Ca, the sodium slag in the method provided by the present invention may also contain trace amounts (e.g., no more than 2%) of other metallic elements, including but not limited to barium, magnesium, and potassium. Furthermore, the present invention does not particularly limit the form in which Na and Ca exist in the sodium slag; sodium slag containing Na and Ca in various forms is applicable to the recovery method provided by the present invention.

[0037] This invention does not impose any particular limitation on the phase state of the sodium slag; it can be liquid or solid. Those skilled in the art will understand that when it is liquid, the layering can be performed directly, and when it is solid, it can be melted first and then layered.

[0038] The present invention allows for a wide range of selection for the melting conditions, ensuring smooth subsequent layering. Preferably, in step (1-1), the melting conditions include: a heating temperature of 98-320℃, preferably 110-210℃, such as 110℃, 130℃, 150℃, 170℃, 190℃, 210℃, or any value between the two; a heating time of 5-120 min, preferably 10-60 min, such as 5 min, 10 min, 15 min, 20 min, 30 min, 50 min, 60 min; preferably, the melting is carried out in an inert or reducing atmosphere, more preferably in an inert atmosphere, preferably provided by at least one of nitrogen, helium, neon, and argon.

[0039] This invention does not particularly limit the specific form of gravity stratification. Preferably, the gravity stratification includes sedimentation and / or centrifugation under high gravity, more preferably centrifugation under high gravity. The gravity stratification described in this invention is preferably performed under high gravity. This preferred embodiment not only provides better separation results but also achieves high separation efficiency.

[0040] In order to better achieve the supergravity separation effect of the present invention, the inventors of the present invention found in the research process that selecting a suitable centrifugal separation factor is more conducive to obtaining pure sodium and high-calcium sodium slag. Preferably, in step (1), the separation factor Fr of the supergravity centrifugation is 100-8500, preferably 500-5500, and more preferably 1500-4500.

[0041] According to the present invention, the stratification can be carried out under the action of hypergravity. Preferably, the hypergravity centrifugation time is 1-500 min, more preferably 2-20 min, for example 2 min, 5 min, 10 min, 15 min, 20 min, or any value between the two.

[0042] When the amount of sodium slag to be processed is small, the sodium slag roasting process can be completed in one roasting. Preferred step (2) roasting temperature is controlled at 220-750℃, more preferably 240-450℃.

[0043] Preferably, the roasting is controlled oxygen roasting, which is carried out under controlled oxygen supply conditions. Unless otherwise specified, the oxygen supply includes the combined control of oxygen concentration and / or oxygen flow rate. To ensure safer controlled roasting of sodium slag, this invention proposes using the oxygen flow rate per ton of sodium slag per hour as the unit of measurement, i.e., m³ / h. 3 The unit of measurement, t·min, is used to accurately measure and control the oxygen roasting rate and heat dissipation rate during the roasting process. Experiments show that this unit of measurement is a composite unit, and its effective combination with oxygen concentration achieves the goal of controllable roasting. The preferred controllable oxygen flow rate during roasting is 0.50 m³ / min. 3 / t·min-10m 3 / t·min, more preferably 1m 3 / t·min-6m 3 / t·min.

[0044] According to a preferred embodiment of the present invention, the oxygen concentration during roasting is 5-40%, preferably 10-30%.

[0045] Preferably, the roasting time is 5-180 min, more preferably 10-90 min, for example 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, or any value between the two.

[0046] According to a preferred embodiment of the present invention, the calcination in step (2) includes the following steps:

[0047] (2-1) The high-calcium sodium slag is subjected to a first roasting to obtain the first roasted product slag;

[0048] (2-2) The first roasted residue is pulverized and then roasted a second time to obtain the roasted residue. During the research process, the inventors of this invention discovered that when processing large quantities of sodium slag, for example, when the processing volume is >0.5 kg per batch, the first roasted residue (first roasted product) often contains a small amount of residual sodium and calcium metals. During the leaching process, these residual sodium and calcium metal components react directly with water, generating a small amount of hydrogen gas as a byproduct, which exacerbates the danger of the disposal process. To improve the safety of the roasted residue leaching process, this invention preferably involves first pulverizing the first roasted residue, then roasting it a second time before proceeding with the leaching process, significantly improving the safety of the roasted residue leaching. The purpose of using a one-step or two-step roasting process in this invention is to ensure a controllable oxidation process and safe production of the sodium slag, so that the vast majority of sodium and calcium are converted into oxides, improving the alkali leaching efficiency and the recovery rate of sodium and calcium resources.

[0049] According to the present invention, there are no particular limitations on the conditions for the first roasting, so that, under the premise of safe production, the high-calcium sodium slag can be first roasted to obtain a first roasted product containing sodium peroxide, sodium oxide, calcium oxide and a small amount of residual sodium-calcium slag.

[0050] According to a preferred embodiment of the present invention, the first roasting time in step (2-1) is 5-180 min, preferably 10-90 min, for example 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, or any value between the two.

[0051] According to a preferred embodiment of the present invention, the temperature of the first calcination in step (2-1) is 220-720°C, preferably 220-450°C, for example 220°C, 250°C, 300°C, 350°C, 400°C, 420°C, 450°C, or any value between the two.

[0052] According to a preferred embodiment of the present invention, the second calcination temperature in step (2-2) is 230-800℃, preferably 260-600℃, for example 260℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, or any value between the two.

[0053] According to a preferred embodiment of the present invention, the second calcination time in step (2-2) is 10-240 min, preferably 10-60 min, for example 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any value between the two.

[0054] According to a preferred embodiment of the present invention, steps (2-1) and (2-2), the first roasting and the second roasting, are each independently controlled oxygen roasting. This controlled oxygen roasting transforms the high-calcium sodium slag into sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag while meeting safe operating conditions. In this invention, controlled oxygen roasting means that the oxygen supply and concentration are controllable through various means, and the control conditions are designed to meet safe operating conditions and maximize the transformation of the high-calcium sodium slag into sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag.

[0055] Preferably, the oxygen flow rate for the first roasting is 0.5-10 m³ / ton of high-calcium sodium slag. 3 / t·min, preferably 1-6m 3 / t·min, for example, 1m 3 / t·min、2m 3 / t·min、3m 3 / t·min、4m 3 / t·min、5m 3 / t·min、6m 3 / t·min, or any value between the two.

[0056] Preferably, the oxygen flow rate for the second roasting is 1-20 m³ / ton, calculated per ton of the residue from the first roasting. 3 / t·min, preferably 1-10m 3 / t·min, for example, 1m 3 / t·min、2m 3 / t·min、3m 3 / t·min、4m 3 / t·min、5m 3 / t·min、6m 3 / t·min、7m 3 / t·min、8m 3 / t·min、9m 3 / t·min、10m 3 / t·min, or any value in between. This oxygen concentration refers to the oxygen content in air or oxygen-deficient air. This new unit of measurement facilitates the scientific control of the heat balance and roasting rate during the sodium slag roasting process.

[0057] According to a preferred embodiment of the present invention, the oxygen concentration in the first roasting step (2-1) is 5-30%, preferably 10-25%.

[0058] According to a preferred embodiment of the present invention, the oxygen concentration in step (2-2) of the second roasting is 10-60%, preferably 15-40%.

[0059] In this invention, pulverizing the first roasted product in step (2-2) yields roasted slag with uniform particle size, improving the safety of the roasted slag leaching process. This invention does not particularly limit the pulverizing method; for example, mechanical pulverization can be used.

[0060] Preferably, the pulverization in step (2-2) yields pulverized residue with a particle size of 10-160 mesh, more preferably 20-80 mesh, and even more preferably 20-60 mesh.

[0061] As long as the above-mentioned particle size can be obtained, there are no particular restrictions on the specific rotation speed, time, and number of grinding cycles.

[0062] Preferably, the method further includes recovering the tail gas from step (2-1), and providing the recovered tail gas (referred to as the first roasting tail gas) with or without supplemental air or oxygen (depending on the oxidation state) to provide a second roasting atmosphere for the pulverization process described in step (2-2) or the second roasting process in step (2-2). The tail gas obtained from the first roasting process is mainly nitrogen, which, after being collected and cooled, can be used as a protective gas for subsequent pulverization processes or to dilute the oxygen concentration in the air, thus ensuring the safe operation of the roasting process and reducing costs.

[0063] Preferably, the pulverization is carried out under a protective atmosphere, which is provided by at least one of the following: first roasting tail gas, nitrogen, helium, argon, and neon. To reduce the cost of using the protective atmosphere in the pulverization process, the first roasting tail gas is preferred as the source of the protective atmosphere.

[0064] This invention, through roasting, especially secondary roasting (first roasting and second roasting), found that most of the sodium and calcium components in sodium slag have been transformed into sodium oxide and calcium oxide. Analysis of the hydration process of sodium oxide or calcium oxide revealed that this hydration reaction is rapid and generates a large amount of heat, sometimes resulting in alkali splashing and boiling, increasing the difficulty and safety risks of the disposal process. Extensive research by the inventors revealed that the hydration process of sodium oxide or calcium oxide depends on the content of free water in the solution and the contact temperature. For example, because sodium hydroxide exists in water as dihydrate and tetrahydrate, the presence of these hydrations greatly reduces the content of free water in the solution. Therefore, this invention preferably uses hydrates to hydrate the secondary roasted sodium slag, thereby safely leaching the secondary roasted slag. Preferably, the solute in the alkali solution in step (3) is a hydrate, preferably sodium hydroxide hydrate and / or calcium hydroxide hydrate, and most preferably sodium hydroxide hydrate, such as sodium hydroxide tetrahydrate or sodium hydroxide dihydrate.

[0065] According to a preferred embodiment of the invention, the concentration of the alkali solution, calculated as hydroxide hydrate, is 20-100% by weight, preferably 30-100% by weight. For example, when the solute of the alkali solution is sodium hydroxide tetrahydrate, the concentration of the alkali solution, calculated as NaOH, is 11-36% by weight. By using such a high concentration of hydrate to hydrate the secondary roasted slag of sodium slag, the secondary roasted slag can be safely leached, converting it into a mixture of sodium hydroxide solution and calcium hydroxide.

[0066] Preferably, the leaching reaction temperature is -18°C to 45°C, more preferably -15°C to 30°C, and even more preferably -15°C to 10°C. This preferred embodiment is more conducive to improving the safety of the roasted residue leaching process.

[0067] Preferably, the leaching reaction time is 10-300 min, more preferably 15-60 min, for example 15 min, 20 min, 30 min, 40 min, 50 min, 60 min, or any value between the two.

[0068] According to the present invention, preferably, the method further includes solid-liquid separation of the leaching mixture to obtain a liquid (sodium hydroxide solution) and a solid (calcium hydroxide). More preferably, the method further includes recycling at least a portion of the liquid back into the leaching process to provide at least a portion of the alkali solution. Specifically, a portion of the concentrated sodium hydroxide solution can be used as a byproduct, and another portion of the sodium hydroxide, after replenishment of water content, is converted into sodium hydroxide tetrahydrate and / or sodium hydroxide dihydrate, and reused in the hydration process of the next batch of secondary roasted slag.

[0069] A second aspect of the present invention provides an apparatus for recovering sodium slag, such as... Figure 1As shown, the device includes a layered unit 1, a first calcination unit 2, a pulverizer 3, a second calcination unit 4, and a reaction vessel 5 connected in series.

[0070] The layering unit 1 is used to separate sodium slag into layers to obtain pure sodium and high-calcium sodium slag.

[0071] The layered unit 1 is provided with a high-calcium sodium slag outlet, and the high-calcium sodium slag outlet is connected to the inlet of the first roasting unit 2.

[0072] The reaction vessel 5 is used to leach the roasting residue obtained from the second roasting unit with an alkaline solution.

[0073] According to the apparatus provided by the present invention, preferably, the layering unit 1 is provided with a liquid sodium slag inlet, a pure sodium outlet, and a high-calcium sodium slag outlet. The sodium slag is layered in the layering unit 1 to obtain pure sodium and high-calcium sodium slag, which are output from the pure sodium outlet and the high-calcium sodium slag outlet, respectively.

[0074] As mentioned above, the need to melt the sodium slag is determined based on its phase state. If necessary, the apparatus preferably includes a melting device for melting the sodium slag, the outlet of which is connected to the inlet of the layering unit 1.

[0075] According to a preferred embodiment of the present invention, the stratification unit 1 includes a settling device and / or a centrifuge, preferably a centrifuge. Both the settling device and the centrifuge can be various devices conventionally used in the art. The settling device enables static stratification of the sodium slag, while the centrifuge enables centrifugal stratification of the sodium slag using gravity.

[0076] According to one specific embodiment of the present invention, the inlet of the centrifuge is connected to the liquid sodium slag supply unit.

[0077] Preferably, the outlet of the high-calcium sodium slag from the layered unit is connected to the inlet of the first roasting unit. This arrangement allows the layered high-calcium sodium slag to undergo a first roasting in the first roasting unit. The present invention does not particularly limit the equipment of the first roasting unit; preferably, the first roasting unit 2 includes a first roasting furnace for performing the first roasting, preferably a tubular furnace or a rotary kiln.

[0078] Preferably, the first roasting furnace is equipped with a first flow meter and a first oxygen concentration meter for controlling the oxygen supply to the first roasting furnace. The present invention does not particularly limit the specific arrangement of the first flow meter and the first oxygen concentration meter. As mentioned above, the purpose of these two detection devices is to enable controlled oxygen roasting in the first roasting unit. Therefore, the arrangement of the first flow meter and the first oxygen concentration meter only needs to achieve controlled oxygen roasting in the first roasting unit. Specifically, a flow meter and an oxygen concentration meter can be installed at both the inlet and outlet of the first rotary kiln.

[0079] Preferably, the pulverizer 3 is equipped with a protective gas pipeline for supplying protective gas to the pulverizer 3 to provide a protective atmosphere for pulverization in the pulverizer 3. The types of protective atmospheres are as described above and will not be repeated here.

[0080] Preferably, the second roasting unit 4 includes a second roasting furnace for performing the second roasting, preferably a tubular furnace or a rotary kiln. Preferably, the second roasting furnace is equipped with a second flow meter and a second oxygen concentration meter for controlling the oxygen supply to the second roasting furnace. The arrangement and considerations for the second flow meter and the second oxygen concentration meter have been described above and will not be repeated here.

[0081] Preferably, the reaction vessel 5 is provided with an alkali inlet.

[0082] Preferably, the apparatus further includes a solid-liquid separation device 6 connected in series with the reactor 5. The solid-liquid separation device 6 is used to separate the material obtained by leaching from the reactor 5 into solid and liquid components. The outlet of the reactor 5 is connected to the inlet of the solid-liquid separation device 6. Specifically, the solid-liquid separation device is provided with a liquid outlet and a solid outlet.

[0083] Preferably, the liquid outlet of the solid-liquid separation device 6 is connected to the inlet of the reaction vessel 5. Using this preferred embodiment, the recovered liquid can be recycled back to the leaching process to provide at least a portion of the alkali solution. The remaining liquid and solid can be used as byproducts.

[0084] According to a preferred embodiment of the present invention, the gas outlet of the first roasting unit is connected to the gas inlet of the pulverizer and / or the second roasting unit. This preferred embodiment allows for the recovery of exhaust gas generated during the first roasting process, which is then used to supplement air or oxygen (depending on the oxidation state) to provide a protective atmosphere for the pulverizing process or an atmosphere for the second roasting.

[0085] The present invention enables the secondary development of sodium slag, a hazardous waste generated from the electrolytic preparation of metallic sodium using sodium chloride, through the above-described method and apparatus, thereby achieving high-value utilization of sodium slag.

[0086] The present invention will be described in detail below through embodiments.

[0087] Example 1

[0088] (1) One kilogram of liquid sodium slag at 190°C (85% by weight of metallic sodium, 14% by weight of metallic calcium, and the remainder of 1% by weight of sodium oxide and calcium oxide produced by surface oxidation) was centrifuged in a centrifuge at a separation factor of 3200 for 3 minutes under insulated conditions, yielding 497 grams of high-purity sodium and 502 grams of high-calcium sodium slag. Analysis according to the national industry standard HG / T5550-2019 showed that the high-purity sodium had a purity of 99.93% by weight, and the high-calcium sodium slag contained 71% by weight of metallic sodium, 28% by weight of metallic calcium, and 1% by weight of sodium oxide and calcium oxide produced by surface oxidation.

[0089] (2) 502 g of high-calcium sodium slag after stratification was roasted in a first tube furnace with a diameter of 60 mm. A flow meter for detecting oxygen flow rate was installed at the inlet and an oxygen concentration meter was installed at the outlet. Controlled oxygen roasting was carried out under an oxidizing atmosphere, with the oxygen concentration controlled at 15%, the oxygen component flow rate set at 6 L / kg·min, the oxidation temperature range controlled at 420-450℃, and the oxidation time at 80 min. Sodium peroxide, sodium oxide, calcium oxide and residual sodium-calcium slag were obtained. After separation and titration analysis, the amount of residual unoxidized sodium-calcium slag was about 5% by weight.

[0090] (3) In the reactor, 17.5 liters of sodium hydroxide tetrahydrate solution (equivalent to a NaOH weight percentage concentration of approximately 35.7%) was used to directionally leach the calcined product from step (2) (temperature 5°C, time 15 min), and the product was separated into concentrated sodium hydroxide alkali solution and calcium hydroxide solid in a solid-liquid separation device. Subsequently, 2 liters of deionized water were added to the concentrated sodium hydroxide alkali solution for dilution, resulting in approximately 19 liters of sodium hydroxide tetrahydrate solution. 17.5 liters of the sodium hydroxide solution were separated for the next batch, and the remaining 1.5 liters were the newly added sodium hydroxide product. The filter residue was washed and dried to obtain approximately 257 grams of calcium hydroxide. Figure 2 This is the XRD pattern of solid calcium hydroxide.

[0091] Example 2

[0092] (1) Take 1000g of sodium slag, the same as in Example 1, heat it to 200°C, and then place it in a heat-insulated PTFE centrifuge cup and centrifuge it for 5min of supergravity separation. Control the separation factor to 3500 to obtain 590g of pure sodium (purity 99.1%) and 405g of high-calcium sodium slag (sodium 64 wt%, calcium 35 wt%, oxides 1 wt%).

[0093] (2) The separated high-calcium sodium slag was subjected to controlled oxygen roasting in a first tubular furnace (equipped as in Example 1). The oxygen concentration was controlled at 21%, the oxygen flow rate at 1.8 L / kg·min, the oxidation temperature at 430-500℃, and the oxidation time at 85 min, resulting in sodium-calcium slag containing pale yellow sodium peroxide, white sodium oxide, calcium oxide, and residual unroasted sodium slag. Titration analysis showed that the amount of residual unroasted sodium-calcium slag was approximately 6% by weight. The exhaust gas from the tubular furnace was collected and used as protective gas for the pulverization process.

[0094] (3) The roasted slag from step (2) was ball-milled using a planetary ball mill at a speed of 120 rpm for 30 min. The protective gas for the ball mill was the roasting tail gas. The roasted slag with a particle size of 60 mesh was obtained by sieving. The roasted slag was then roasted a second time in a second tube furnace (equipped the same as the first tube furnace). The roasting temperature was controlled at 460℃, the roasting time was 15 min, and the roasting atmosphere was an oxygen-deficient atmosphere with an oxygen concentration of 15%. The oxygen flow rate was 2.4 L / kg·min based on the product slag after the first roasting. Approximately 540 grams of a mixture of sodium oxide and calcium oxide was obtained.

[0095] (4) In the reactor, the calcined product from step (3) was leached directionally using 8 liters of sodium hydroxide tetrahydrate solution (equivalent to approximately 35% NaOH by weight) (temperature 10°C, time 20 min). The leached product was then separated into concentrated sodium hydroxide solution and calcium hydroxide in a solid-liquid separation device. Subsequently, 0.8 liters of deionized water were added to the concentrated sodium hydroxide solution for dilution, regenerating it into approximately 8.8 liters of sodium hydroxide tetrahydrate solution. 8 liters of this solution were used for the next batch, and the remaining 0.8 liters were the newly produced sodium hydroxide product. The filter residue was dried to obtain approximately 260 grams of calcium hydroxide.

[0096] Example 3

[0097] (1) 10 kg of sodium slag (86% sodium by weight and 14% calcium by weight) from Inner Mongolia Ruixin Company at 170℃ was placed in a centrifuge for centrifugation for 3 min. The separation factor was set to 4200, and 6.2 kg of pure sodium (99.75% sodium by weight) and 3.75 kg of high-calcium sodium slag (63% sodium by weight and 37% calcium by weight) were obtained.

[0098] (2) The above-mentioned high-calcium sodium slag was subjected to controlled oxygen roasting in the first rotary kiln (equipped as in Example 1) under an air atmosphere. The roasting temperature was 350-400℃, the roasting time was 60min, and the oxygen flow rate was controlled at 4.1L / kg·min to obtain sodium peroxide, sodium oxide, calcium oxide and residual sodium-calcium slag. After separation and titration analysis, the amount of residual unoxidized sodium-calcium slag was about 17% by weight.

[0099] (3) The calcined slag from step (2) is pulverized twice by a mechanical pulverizer at a speed of 10,000 rpm for 3s + 3s. The pulverizer is protected by nitrogen. The calcined slag with a particle size of 40 mesh is obtained by sieving. The calcined slag is then calcined a second time in a second rotary kiln (equipped the same as the first rotary kiln). The calcination temperature is controlled at 400℃, the calcination time is 15min, the oxygen concentration is 20%, and the oxygen flow rate is 2.2L / kg·min. Approximately 5.03 kg of a mixture containing sodium oxide and calcium oxide is obtained.

[0100] (4) In the reactor, the calcined product from step (3) was leached directionally using 30L of sodium hydroxide tetrahydrate solution (equivalent to approximately 30% NaOH by weight) (temperature 5℃, time 30min). The product was then separated into concentrated sodium hydroxide solution and calcium hydroxide in a solid-liquid separation device. Subsequently, 14L of deionized water was added to the concentrated sodium hydroxide solution to dilute it, yielding 43L of a 30% by weight sodium hydroxide solution. 30L of this solution was used for the next batch, and the remaining 13L was the newly added sodium hydroxide product. The filter residue was dried to obtain approximately 2.6 kg of calcium hydroxide.

[0101] Example 4

[0102] (1) 200g of sodium slag from Example 3 was placed in a centrifuge at 180°C for 2 minutes and the separation factor was set to 2800 to obtain 110g of metallic sodium (Na: 99.10% by weight) and 90g of high-calcium sodium slag (Na: 61% by weight, Ca: 39% by weight).

[0103] (2) The high-calcium sodium slag was subjected to controlled roasting in a first tube furnace (equipped as in Example 1) under a lean oxygen atmosphere (oxygen concentration 10%). The oxygen flow rate was controlled at 1.3 L / kg·min, the roasting temperature at 400-420℃, and the roasting time at 60 min, yielding sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag. After separation and titration analysis, the amount of residual unoxidized sodium-calcium slag was approximately 15% by weight.

[0104] (3) The roasted slag from step (2) is crushed twice by a pulverizer at a speed of 10,000 rpm for 3s + 3s. The pulverizer is protected by nitrogen. The slag is then sieved to obtain a 40-mesh slag. The slag is then roasted a second time in a second tube furnace (equipped the same as the first tube furnace). The roasting temperature is controlled at 350℃, the roasting time is 15min, the oxygen concentration is 21%, and the oxygen flow rate is 3L / kg·min based on the product slag after the first roasting. Approximately 122 grams of sodium oxide and calcium oxide mixture are obtained.

[0105] (4) In the reactor, the calcined product from step (3) was directionally leached using 200 mL of concentrated sodium hydroxide tetrahydrate solution (equivalent to approximately 35% NaOH by weight) (temperature 8°C, time 20 min). The product was then separated into concentrated sodium hydroxide solution and calcium hydroxide in a solid-liquid separation device. Approximately 190 mL of deionized water was added to the concentrated sodium hydroxide solution for dilution, regenerating it into approximately 370 mL of a 35% by weight sodium hydroxide solution. 200 mL of this solution was used for the next batch, and the remaining 170 mL was the newly added sodium hydroxide product. The filter residue was dried to obtain approximately 64 g of calcium hydroxide.

[0106] Example 5

[0107] (1) 210 grams of solid sodium slag at 150°C, identical to that in Example 3, was placed in an insulated centrifuge cup and centrifuged for 3 minutes in a high-gravity centrifuge. The separation factor was set to 3500, yielding 117 grams of pure sodium and 93 grams of high-calcium sodium slag. Analysis according to the national industry standard HG / T5550-2019 showed that the purity of the metallic sodium was 99.70%, the weight percentage content of metallic sodium in the high-calcium sodium slag was 59%, and the weight percentage content of metallic calcium was 41%.

[0108] (2) The high-calcium sodium slag was subjected to controlled oxygen roasting in a first tube furnace (equipped as in Example 1) under a lean oxygen atmosphere (oxygen concentration of 15%). The roasting temperature was 450°C and the roasting time was 55 min. The oxygen flow rate was controlled at 3 L / kg·min. Sodium peroxide, sodium oxide, calcium oxide and residual sodium-calcium slag were obtained. After separation and titration analysis, the amount of residual unoxidized sodium-calcium slag was about 10% by weight.

[0109] (3) The roasted slag from step (2) is crushed twice by a pulverizer at a speed of 10,000 rpm for 3s + 3s. The pulverizer is protected by nitrogen. The slag is then sieved to obtain a 40-mesh slag. The slag is then roasted a second time in a second tube furnace (equipped the same as the first tube furnace). The roasting temperature is controlled at 600℃, the roasting time is 10min, the oxygen concentration is 20%, and the oxygen flow rate is 3L / kg·min based on the product slag after the first roasting. The resulting slag contains a mixture of sodium oxide and calcium oxide of approximately 126g.

[0110] (4) In the reactor, the calcined product from step (3) was directionally leached using 300 mL of concentrated sodium hydroxide tetrahydrate solution (equivalent to approximately 30% NaOH by weight) (temperature: -5℃, time: 30 min). The product was then separated into concentrated sodium hydroxide solution and calcium hydroxide in a solid-liquid separation device. Subsequently, 250 mL of deionized water was added to the concentrated sodium hydroxide solution for dilution, regenerating it into approximately 530 mL of 30% sodium hydroxide solution. 300 mL of this solution was used for the next batch, and the remaining 230 mL was the newly added sodium hydroxide product. The filter residue was dried to obtain approximately 70 g of calcium hydroxide.

[0111] Example 6

[0112] (1) 200g of sodium slag, the same as in Example 1, was kept at 140°C and centrifuged in a centrifuge for 5 min. The separation factor was controlled at 4200 to obtain 118g of metallic sodium (99.93%) and 82g of high-calcium sodium slag (Na: 58 wt%; Ca: 42 wt%).

[0113] (2) The stratified high-calcium sodium slag was placed in a tubular furnace (assembled as in Example 1), with the oxygen concentration controlled at 30% and the gas flow rate at 1 L / kg·min for 30 min. The flow rate was then increased to 3 L / kg·min for another 30 min, resulting in a total single roasting time of 60 min. This yielded 108 g of slag containing sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag. Titration analysis showed that the amount of residual unoxidized sodium-calcium slag was approximately 3% by weight.

[0114] (3) The calcined product from step (2) was leached directionally using 300 mL of sodium hydroxide tetrahydrate solution (approximately 32% NaOH by weight) at -5℃ for 10 min. Solid-liquid separation was then performed to obtain concentrated sodium hydroxide solution and calcium hydroxide. The concentrated sodium hydroxide solution was then diluted with 240 mL of deionized water to regenerate approximately 510 mL of a 32% sodium hydroxide solution. 300 mL of this solution was used for the next batch, and the remaining 210 mL was the newly produced sodium hydroxide product. The filter residue was dried to obtain approximately 62 g of calcium hydroxide.

[0115] Example 7

[0116] 200g of sodium slag (identical to that in Example 1) at 180℃ was placed in a centrifuge (model: TDL-5) and separated for 2 minutes at a separation factor of 3500 to obtain 105g of metallic sodium and 91g of high-calcium sodium slag. Analysis showed that the purity of the metallic sodium was 99.5%. The high-calcium sodium slag contained 68% sodium by weight, 32% calcium by weight, and the remaining 4g consisted of sodium oxide and calcium oxide slag produced by oxidation.

[0117] (2) The stratified high-calcium sodium slag was placed in a tube furnace and roasted under controlled conditions with an air + nitrogen (volume ratio 1:1) atmosphere at a controlled temperature of 440℃. Oxygen was supplied at a flow rate of 2 L / kg·min for 70 min, yielding approximately 129 g of roasted slag containing sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag. Nitrogen tail gas was recovered. Separation and titration analysis showed that the amount of residual unoxidized sodium-calcium slag was approximately 5% by weight.

[0118] (3) In the reactor, 300 mL of sodium hydroxide tetrahydrate (approximately 11% NaOH by weight) + calcium hydroxide suspension (approximately 3% Ca(OH)₂ by weight) at -18℃ was used to directionally leach the calcined product from step (2) in a three-necked flask. The mixture was stirred at 150 rpm for 30 min, with recovered nitrogen gas purging the three-necked flask as a protective gas. Subsequently, solid-liquid separation yielded concentrated sodium hydroxide alkali solution and calcium hydroxide. The concentrated sodium hydroxide alkali solution was then diluted with 1000 mL of deionized water to regenerate approximately 1200 mL of 11% sodium hydroxide solution. 300 mL of the sodium hydroxide solution was used for the next batch, and the remaining 900 mL was the newly added sodium hydroxide product. Another portion of the NaOH solution was mixed in with the filter cake. The alkaline washing liquid obtained after washing and filtration could be returned for the next leaching. The filter residue was dried to obtain approximately 61 g of calcium hydroxide.

[0119] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering sodium slag, the method comprising the following steps: (1) The liquid sodium slag is separated by gravity to obtain pure sodium and high-calcium sodium slag; (2) The high-calcium sodium slag is roasted to obtain roasted slag; (3) The roasted residue is leached with an alkaline solution to obtain a sodium hydroxide solution and calcium hydroxide; The roasting in step (2) includes the following steps: (2-1) The high-calcium sodium slag is subjected to a first roasting to obtain the first roasted product slag; (2-2) The first roasted product residue is crushed and then roasted a second time to obtain the roasted residue; The gravity stratification in step (1) is centrifugation under hypergravity; the separation factor of the hypergravity centrifugation is 3500-4500, and the separation time of the hypergravity centrifugation is 2-20 min; In step (2-1), the temperature of the first roasting is 220-450℃; In step (2-2), the second calcination temperature is 260-600℃; The alkaline solution mentioned in step (3) is sodium hydroxide hydrate and / or calcium hydroxide hydrate; The concentration of the alkaline solution, calculated as hydroxide hydrate, is 20-35% by weight.

2. The method according to claim 1, wherein, The sodium slag contains Na and Ca.

3. The method according to claim 2, wherein, Based on the total amount of sodium slag, the Na content is 60-90% by weight and the Ca content is 10-40% by weight.

4. The method according to claim 1, wherein, Step (2-1) The first roasting time is 5-180 min.

5. The method according to claim 4, wherein, Step (2-1) The first roasting time is 10-90 min.

6. The method according to claim 1, wherein, The second roasting time in step (2-2) is 10-240 min.

7. The method according to claim 6, wherein, The second roasting time in step (2-2) is 10-60 min.

8. The method according to claim 1 or 2, wherein, Steps (2-1) and (2-2) are each independently controlled oxygen calcination.

9. The method according to claim 8, wherein, The controlled oxygen roasting process transforms high-calcium sodium slag into sodium peroxide, sodium oxide, calcium oxide, and residual sodium-calcium slag while meeting safe operating conditions.

10. The method according to claim 8, wherein, In step (2-1), the oxygen concentration during the first roasting is 5-30%.

11. The method according to claim 10, wherein, In step (2-1), the oxygen concentration during the first roasting is 10-25%.

12. The method according to claim 8, wherein, Step (2-1): The oxygen flow rate for the first roasting is 0.5-10 m³ / ton of high-calcium sodium slag. 3 / t min.

13. The method according to claim 12, wherein, Step (2-1) The oxygen flow rate for the first roasting is 1-6 m³ / ton of high-calcium sodium slag. 3 / t min.

14. The method according to claim 8, wherein, The oxygen concentration in the second roasting process in step (2-2) is 10-60%.

15. The method according to claim 14, wherein, The oxygen concentration in the second roasting process in step (2-2) is 15-40%.

16. The method according to claim 8, wherein, In step (2-2), during the second roasting process, the oxygen flow rate is 1-20 m³ / ton, calculated per ton of the first roasted product residue. 3 / t min.

17. The method according to claim 16, wherein, In step (2-2), during the second roasting process, the oxygen flow rate is 1-10 m³ / ton per ton of the first roasted product residue. 3 / t min.

18. The method according to claim 1, wherein, The pulverization process described in step (2-2) yields pulverized residue with a particle size of 10-160 mesh.

19. The method according to claim 18, wherein, The pulverization process described in step (2-2) yields pulverized residue with a particle size of 20-80 mesh.

20. The method according to claim 19, wherein, The pulverization process described in step (2-2) yields pulverized residue with a particle size of 20-60 mesh.

21. The method according to claim 1, wherein, The pulverization is carried out under a protective atmosphere provided by at least one of the following: first roasting exhaust gas, nitrogen, helium, argon, and neon.

22. The method according to claim 21, wherein, The protective atmosphere is provided by the exhaust gas from the first roasting process.

23. The method according to claim 1, wherein, The alkaline solution mentioned in step (3) is sodium hydroxide hydrate.

24. The method according to claim 23, wherein, The concentration of the alkaline solution, calculated as hydroxide hydrate, is 30-35% by weight.

25. The method according to any one of claims 1-3, wherein, The leaching reaction temperature is from -18°C to 45°C.

26. The method according to claim 25, wherein, The leaching reaction temperature is from -15°C to 30°C.

27. The method according to claim 26, wherein, The leaching reaction temperature is from -15°C to 10°C.

28. The method according to any one of claims 1-3, wherein, The leaching reaction time is 10-300 min.

29. The method according to claim 28, wherein, The leaching reaction time is 15-60 minutes.

30. The method according to any one of claims 1-3, wherein, The method also includes solid-liquid separation of the leached material to obtain liquid and solid.

31. The method according to claim 30, wherein, The method also includes recycling at least a portion of the liquid back into the leaching process to provide at least a portion of the alkali solution.

32. An apparatus for the method of sodium slag recovery according to any one of claims 1-31, the apparatus comprising a layered unit (1), a first roasting unit (2), a crusher (3), a second roasting unit (4), and a reactor (5) connected in series. in, The layering unit (1) is used to separate sodium slag into layers to obtain pure sodium and high-calcium sodium slag. The layered unit (1) is provided with a high-calcium sodium slag outlet, and the high-calcium sodium slag outlet is connected to the inlet of the first roasting unit (2). The reactor (5) is used to leach the roasting residue obtained from the second roasting unit with an alkaline solution.

33. The apparatus according to claim 32, wherein, The layered unit (1) includes a supergravity centrifuge; the inlet of the supergravity centrifuge is connected to the liquid sodium slag supply unit.

34. The apparatus according to claim 32, wherein, The first roasting unit (2) includes a first roasting furnace for performing the first roasting.

35. The apparatus according to claim 34, wherein, The first roasting furnace is a tube furnace or a rotary kiln.

36. The apparatus according to claim 35, wherein, The first roasting furnace is equipped with a first flow meter and a first oxygen concentration meter for controlling the oxygen supply to the first roasting furnace.

37. The apparatus according to claim 32, wherein, The pulverizer (3) is equipped with a protective gas pipeline for supplying protective gas to the pulverizer (3) to provide a protective atmosphere for pulverization in the pulverizer (3).

38. The apparatus according to claim 32, wherein, The second roasting unit (4) includes a second roasting furnace for performing the second roasting.

39. The apparatus according to claim 38, wherein, The second roasting furnace is equipped with a second flow meter and a second oxygen concentration meter for controlling the oxygen supply to the second roasting furnace.

40. The apparatus according to claim 32, wherein, The device also includes a solid-liquid separation device (6) connected in series with the reactor (5), the solid-liquid separation device (6) being used to separate the material obtained by leaching from the reactor (5) into solid and liquid.

41. The apparatus according to claim 40, wherein, The liquid outlet of the solid-liquid separation device (6) is connected to the inlet of the reactor (5).

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