A method for cascade separation and resource utilization of calcium-free chromium residue by reducing alkali roasting reinforced calcium-free chromium residue

Abstract

This invention relates to a method for enhanced cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkaline roasting. The specific steps are as follows: Calcium-free roasted chromium slag, a reducing agent, and an alkaline reagent are mixed to obtain a chromium slag mixture; the chromium slag mixture is placed at a first temperature and held for a first time under an inert atmosphere, causing the iron oxides in the chromium slag mixture to be reduced, and the aluminum and chromium oxides to be sodium-treated, while inhibiting the reduction of chromium oxides, resulting in a reduced chromium slag mixture; the reduced chromium slag mixture is filtered to obtain filter residue and an aluminum-enriched filtrate, which can be used for alumina production and the recovery of the alkaline reagent; under an inert atmosphere, the filter residue is placed at a second temperature and held for a second time. Due to the separation of aluminum in the filter residue, metallic iron can be efficiently separated by melting, and chromium can be efficiently enriched in the molten residue. This invention can efficiently achieve the cascade resource utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

Description

Technical Field

[0001] This invention relates to the field of chromium slag resource utilization technology, specifically to a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting. Background Technology

[0002] Chromium salts (represented by sodium chromate) possess many unique properties and are widely used in aerospace, military, nuclear energy, steel, ceramics, electroplating, pigments, corrosion protection, printing and dyeing, inks, pharmaceuticals, catalysts, and organic synthesis, making them an indispensable raw material for national economic and defense construction. However, current chromium salt production processes generate a byproduct called "chromium slag," which contains a certain amount of highly toxic hexavalent chromium. Furthermore, a large amount of trivalent chromium in the slag is easily oxidized to hexavalent chromium. Additionally, valuable metal components such as iron, chromium, and aluminum account for approximately 60% of the chromium slag. If not properly treated, this slag will not only cause environmental pollution but also result in the waste of valuable metal resources.

[0003] Currently, the main focus of chromium slag treatment is to achieve both harmless detoxification and resource utilization of chromium slag. For different chromium salt production processes, the mainstream methods for treating chromium slag include using calcium roasted slag and liquid phase oxide slag directly as raw materials for ironmaking.

[0004] CN 102191390 A discloses a method of first leaching chromium slag with acid to obtain a chromium-containing leachate, and then extracting chromium from the leachate through reduction and precipitation. This process consumes large amounts of acid and alkali, leading to secondary environmental pollution and low economic efficiency. CN 102978376 A discloses a detoxification process for dry reduction of chromium slag, using carbon powder as a reducing agent under a reducing atmosphere. However, the chromium element in the slag is not effectively recovered, and the reaction requires a high temperature, resulting in high implementation costs. CN 110330248 A discloses a method for harmlessly disposing of chromium-containing solid waste to produce vitrified aggregate. This method involves first simply detoxifying the chromium slag, and then using the detoxified chromium slag as raw material. However, valuable elements in the chromium slag are not recovered. CN114717371 A discloses a method for producing chromium-containing sponge iron by reducing chromium slag in a rotary kiln. The method involves reducing a mixture of specially prepared coal powder and chromium slag pellets in a rotary kiln to prepare chromium-containing sponge iron. However, the chromium content in the sponge iron is low, the chromium element is not effectively recovered, and the energy consumption is high.

[0005] The numerous examples above demonstrate that the main approach to treating chromium slag is to reduce the highly water-soluble and highly toxic hexavalent chromium ions to low-toxic trivalent chromium ions and then fix them. For example, after detoxification, the chromium slag can be used as a raw material for cement, brick blanks, steel and other products. However, this approach has drawbacks such as low utilization rate of valuable metals in chromium slag, difficulty in separating reduced iron, low utilization value, and unstable detoxification.

[0006] The main approach to chromium slag detoxification involves first reducing highly soluble and toxic hexavalent chromium to trivalent chromium and then solidifying it. However, this method suffers from the problem of a large amount of valuable elements not being recovered and utilized. Furthermore, once the trivalent chromium is fixed, it is exposed to the environment and, under the influence of complex external factors over a long period, is oxidized back to hexavalent chromium, thus rendering the detoxification ineffective. Currently, the main approach to the resource utilization of chromium slag is to detoxify it and then use it as an auxiliary material in the production of other products. However, this approach is subject to many limitations in practical applications, such as high energy consumption, limited slag capacity, and incomplete extraction of valuable elements. Summary of the Invention

[0007] The purpose of this invention is to provide a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting, so as to effectively achieve the cascade separation and resource utilization of iron, chromium and aluminum components in calcium-free roasted chromium slag, and utilize the iron, chromium and aluminum components after cascade resource utilization to solve the threat of chromium slag to the ecological environment.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0010] S1. Mix calcium-free roasted chromium slag, reducing agent and alkaline reagent to obtain chromium slag mixture;

[0011] S2. In a nitrogen atmosphere, the chromium slag mixture is kept at a first temperature for a first time, so that the iron oxides, aluminum oxides and chromium oxides in the chromium slag mixture are reduced, while the reduction of chromium oxides in the chromium slag mixture is suppressed, to obtain a pre-reduced chromium slag mixture.

[0012] S3. Place the pre-reduced chromium slag mixture in water and filter it to obtain filter residue and aluminum-enriched filtrate.

[0013] S4. In an inert atmosphere, the filter residue is placed at a second temperature and kept at that temperature for a second time. Due to the separation of aluminum in the filter residue, metallic iron can be efficiently separated by melting, and chromium can be efficiently enriched in the molten residue. The molten separation yields metallic iron and chromium-enriched residue.

[0014] Based on the aforementioned technical methods, by adding a reducing agent and alkaline reagent to calcium-free roasted chromium slag, the chromium slag mixture is reduced and sodium-treated in a nitrogen atmosphere. By rationally controlling the temperature and time, the iron oxides are reduced as much as possible, while the aluminum and chromium oxides are sodium-treated, and the reduction of chromium oxides is simultaneously inhibited. The pre-reduced chromium slag mixture is then dissolved in water and filtered to obtain aluminum-enriched filtrate and filter residue. The filter residue is heated and held at a constant temperature in an inert atmosphere. By rationally controlling the heating temperature and holding time, the metallic iron in the filter residue melts and separates, while chromium is further enriched in the molten and separated slag phase. Iron is enriched in the molten and separated metallic phase. The aluminum-enriched filtrate is used for alumina production and sodium carbonate recovery, thus achieving efficient detoxification of calcium-free roasted chromium slag and the tiered resource utilization of iron, chromium, and aluminum components in the slag. The molten and separated metallic iron can be used as a high-quality raw material for steel smelting, while the chromium-enriched molten slag can be used as rebaked slag for chromium salt production. The aluminum-enriched filtrate is used for alumina production and sodium carbonate recovery, thus effectively realizing the high-value utilization of the iron, chromium and aluminum components in the calcium-free roasted chromium slag.

[0015] The present invention proposes a method for enhancing the graded separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting, which includes the following steps: First, since the iron and chromium elements in the calcium-free roasted chromium slag mainly exist in the spinel structure, and a small portion of the chromium outside the spinel structure coexists in trivalent and hexavalent forms, and the aluminum component in the chromium slag mainly exists in the form of gibbsite, the iron, chromium, and aluminum elements inside and outside the spinel structure can be reduced and extracted in a gradient by carbothermic reducing alkali roasting; Second, there are differences in the reduction thermodynamics of iron oxides and chromium oxides in the calcium-free roasted chromium slag (wherein, iron begins to be reduced by carbon at around 900℃, and chromium begins to be reduced by carbon at around 1300℃), while the sodiumization of aluminum oxides and chromium oxides both occur at around 600℃, and the reduction reaction and sodiumization reaction occur relatively independently. Therefore, in the preparation of the pre-reduced chromium slag mixture, the process conditions and the type of reducing agent are precisely controlled to promote the reduction of iron components and the sodiumization of aluminum oxides and chromium oxides as much as possible, while inhibiting the reduction of chromium oxides. Moreover, the water solubility of each component in the pre-reduced chromium slag mixture is significantly different. Therefore, by dissolving and filtering the pre-reduced chromium slag mixture, the aluminum components are separated, while the chromium and iron components remain in the slag phase. Furthermore, by high-temperature melting and separation of the filter residue, the reduced iron is melted and removed from the slag phase for recovery and used as a high-quality raw material for steel production. At the same time, the reduced and detoxified chromium remains in the slag phase and is used again as rebaking slag for chromium salt production, so that the chromium, iron and aluminum components are fully utilized.

[0016] Preferably, in S1, the reducing agent is selected from at least one of coke, graphite, pulverized coal, and biomass.

[0017] Preferably, the biomass is selected from at least one of peanut shells, plant straw, and pond sludge.

[0018] Preferably, in S1, the alkaline reagent is selected from sodium carbonate.

[0019] Preferably, in S1, the reducing agent is selected from coke.

[0020] Preferably, in S1, the molar ratio of reduced carbon to available oxygen in the chromium slag mixture is 1 to 1.5:1.

[0021] Preferably, in S1, the molar ratio of reduced carbon to available oxygen in the chromium slag mixture is 1.2:1.

[0022] Reduced carbon refers to the sum of elemental carbon and organic carbon in the chromium slag mixture; available oxygen refers to the total amount of oxygen in the chromium slag mixture that is combined with chromium, iron and silicon.

[0023] Preferably, in S1, the molar ratio of alkaline reagent to aluminum oxide (alumina) in the chromium slag mixture is 0.7 to 1.3:1.

[0024] Preferably, in S1, the molar ratio of alkaline reagent to aluminum oxide (alumina) in the chromium slag mixture is 0.9:1.

[0025] Preferably, in step S1, before mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, the process further includes: ball milling and sieving the calcium-free roasted chromium slag and reducing agent, respectively. The ball milling speed is 20-30 r / min, the ball milling time is 30 min-180 min, and the sieving process is to pass the calcium-free roasted chromium slag through a 50-mesh sieve and the reducing agent through a 100-200-mesh sieve.

[0026] Preferably, the ball mill rotation speed is 25 r / min and the ball milling time is 45 min.

[0027] Preferably, in step S1, after mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, the mixture is further further subjected to pressing into a disc shape to obtain a chromium slag mixture, wherein the pressing pressure is 0.05–0.2 MPa, the disc diameter is 20–70 mm, and the thickness is 5–30 mm.

[0028] By pressing the mixture into a disc shape, the chromium slag mixture has a large surface area and specific surface area, which allows it to be heated rapidly and evenly during the reaction, which is conducive to the reaction. Furthermore, the sample will harden after pre-reduction, and the disc shape makes it easier to dissolve and filter after subsequent crushing.

[0029] Preferably, the pressing pressure is 0.09 MPa, the diameter of the disc is 40 mm, and the thickness is 10 mm.

[0030] Preferably, in step S2, the first temperature is 900℃~1200℃.

[0031] Preferably, in S2, the first time is 10 to 60 minutes.

[0032] Preferably, in step S2, the flow rate of nitrogen is 100 ml / min.

[0033] Preferably, in step S2, the heat preservation treatment further includes cooling and grinding to obtain the pre-reduced chromium slag mixture. During the cooling process, the nitrogen flow rate remains constant to ensure uniform cooling of the material.

[0034] Preferably, in step S2, the first temperature is 1100°C.

[0035] Preferably, in S2, the first time is 30 minutes.

[0036] Preferably, step S3 includes: placing the pre-reduced chromium slag mixture in water and stirring for a third time, then filtering to obtain filter residue and aluminum-enriched filtrate.

[0037] Preferably, in step S3, the mass ratio of the pre-reduced chromium slag mixture to water is 1:50 to 70.

[0038] Preferably, in step S3, the mass ratio of the pre-reduced chromium slag mixture to water is 1:55.

[0039] Preferably, in step S3, the third time is 10 to 60 minutes.

[0040] Preferably, in S3, the third time is 15 minutes.

[0041] Preferably, in step S4, the second temperature is 1500℃~1700℃.

[0042] Preferably, in S4, the second time is 10 to 60 minutes.

[0043] Preferably, in step S4, the inert atmosphere is an argon atmosphere, and the argon flow rate is 100 ml / min.

[0044] Preferably, in step S4, the second temperature is 1600℃ and the second time is 30 minutes.

[0045] Preferably, step S4 includes: adding the filter residue into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm, outer height 120mm, inner height 115mm), then placing them together in a melting furnace, and holding the pre-reduced chromium slag mixture at a second temperature for a second time under an inert atmosphere, thereby melting and separating to obtain metallic iron and chromium-enriched residue. The slender graphite cylindrical crucible is a specially made laboratory crucible.

[0046] By adding the filter residue to a graphite crucible and then placing them together in a melting furnace, the stratification effect of slag-gold separation is further enhanced.

[0047] Preferably, in step S3, the aluminum-enriched filtrate obtained from filtration is used for the production of alumina and the recovery of sodium carbonate. The recovered sodium carbonate can be reused as an alkaline reagent, achieving the goal of recycling.

[0048] Preferably, in step S3, the aluminum-enriched filtrate obtained by filtration can consume carbon dioxide to precipitate aluminum hydroxide as a raw material for the production of alumina, and then be further evaporated to recover sodium carbonate, thereby improving economic efficiency.

[0049] Preferably, in step S4, the separated metallic iron is used as a raw material for steel production to achieve iron recycling, and the separated chromium-enriched residue is used in the rebaking residue for chromium salt production to achieve chromium recycling.

[0050] By using the aluminum-enriched filtrate (rich in aluminum and sodium ions) obtained from filtration as a raw material for alumina and sodium carbonate production, using the molten and separated metallic iron as a high-quality raw material for steel smelting, and using the separated chromium-enriched residue as re-roasting slag for chromium salt production, the recycling and reuse of iron, chromium, and aluminum elements are simultaneously achieved, providing a new possibility for the comprehensive utilization of calcium-free roasted chromium slag.

[0051] The beneficial effects of this invention are:

[0052] This invention discloses a method for enhanced cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkaline roasting. The method involves adding a reducing agent and alkaline reagent to the calcium-free roasted chromium slag, reducing and sodium-modifying the chromium slag mixture in an inert atmosphere. By rationally controlling the temperature and time, the method aims to reduce and sodium-modify iron oxides, aluminum oxides, and chromium oxides respectively, while suppressing the reduction of chromium oxides, resulting in a pre-reduced chromium slag mixture. Then, through dissolution and filtration, aluminum-enriched filtrate and chromium- and iron-enriched slags are obtained respectively. Based on the above, the chromium- and iron-enriched slags are melt-separated in an inert atmosphere. By rationally controlling the heating temperature and holding time, metallic iron melts and separates, while chromium is enriched in the molten slag phase, thereby further separating the iron and chromium components in the calcium-free roasted chromium slag. It is noteworthy that the removal of aluminum oxides in the slag reduces the viscosity of the molten slag, facilitating the aggregation and growth of metallic iron, thus simplifying the slag separation operation. For chromium in the slag, its enrichment efficiency is further improved, and the chromium grade is increased.

[0053] Based on the above separation, the resource utilization of iron, chromium, and aluminum in calcium-free roasted chromium slag can be realized. For example, the aluminum enrichment filtrate can be used for alumina production and sodium carbonate recovery, metallic iron can be used as a high-quality raw material for steel smelting, and the molten slag enriched with chromium can be used as re-roasting slag for chromium salt production. This effectively realizes the high-value utilization of the main components of iron, chromium, and aluminum in calcium-free roasted chromium slag. Moreover, the process is simple, efficient, has a large slag processing capacity, thoroughly detoxifies the chromium slag, and has high recovery rates of iron, chromium, and aluminum. The process also has the advantages of no by-products generated during implementation, making it valuable for promotion and application in the field of chromium slag resource utilization technology. Attached Figure Description

[0054] Figure 1 This is a flowchart of the method for enhanced cascade resource utilization of calcium-free roasted chromium slag by reducing alkali roasting according to the present invention.

[0055] Figure 2 This is a schematic diagram of the structure of a slender graphite cylindrical crucible. Detailed Implementation

[0056] The embodiments of the present invention will be described below with reference to the accompanying drawings and examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the embodiments are only for illustrating the present invention and are not intended to limit the scope of protection of the present invention.

[0057] This invention aims to disclose a method for the tiered resource utilization of calcium-free roasted chromium slag through reducing alkali roasting. The steps are as follows:

[0058] S1. Mix calcium-free roasted chromium slag, reducing agent and alkaline reagent to obtain chromium slag mixture;

[0059] S2. In a nitrogen atmosphere, the chromium slag mixture is kept at a first temperature for a first time, so that the iron oxides, aluminum oxides and chromium oxides in the chromium slag mixture are reduced, while the reduction of chromium oxides in the chromium slag mixture is inhibited, and a pre-reduced chromium slag mixture is obtained.

[0060] S3. Place the pre-reduced chromium slag mixture in water, filter, and obtain filter residue and aluminum-enriched filtrate;

[0061] S4. In an inert atmosphere, the filter residue is kept at a second temperature for a second time, and then melted and separated to obtain metallic iron and chromium-enriched residue.

[0062] In some embodiments, in S1, the reducing agent is selected from at least one of coke, graphite, pulverized coal, and biomass. This can be understood as the reducing agent being coke, graphite, pulverized coal, or biomass, or any possible combination of coke, graphite, pulverized coal, and biomass.

[0063] In some embodiments, in S1, the biomass is selected from at least one of peanut shells, plant straw, and pond sludge. This can be understood as the biomass being peanut shells, plant straw, or pond sludge, or any possible combination of these.

[0064] For example, in S1, the alkaline reagent is selected from sodium carbonate.

[0065] For example, in S1, the reducing agent is selected from coke.

[0066] In some embodiments, in S1, the molar ratio of reduced carbon to available oxygen in the chromium slag mixture is 1 to 1.5:1.

[0067] For example, in S1, the molar ratio of reduced carbon to available oxygen in the chromium slag mixture is any possible molar ratio between 1:1, 1.2:1, 1.5:1, or 1 to 1.5:1.

[0068] In some embodiments, in S1, the molar ratio of alkaline reagent to aluminum oxide (alumina) in the chromium slag mixture is 0.7 to 1.3:1.

[0069] For example, in S1, the molar ratio of alkaline reagent to aluminum oxide (alumina) in the chromium slag mixture is 0.7:1, 0.9:1, 1.1:1, 1.3:1 or any possible molar ratio between 0.7 and 1.3:1.

[0070] In some embodiments, S1, before mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, further includes: ball milling and sieving the calcium-free roasted chromium slag and reducing agent, respectively. The ball milling speed is 20-30 r / min, the ball milling time is 30 min-180 min, and the sieving process is to pass the calcium-free roasted chromium slag through a 50-mesh sieve and the reducing agent through a 100-200-mesh sieve.

[0071] For example, the rotational speed of the ball mill can be selected as any possible value between 20 r / min, 25 r / min, 30 r / min or 20 to 30 r / min, and the ball milling time can be selected as any possible value between 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 130 min, 145 min, 160 min, 175 min, 180 min or 30 min to 180 min.

[0072] In some embodiments, S1, after mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, in order to ensure that the chromium slag mixture has a large surface area and specific surface area, and that it can be heated rapidly and uniformly during the reaction to facilitate the reaction, the method further includes: pressing the mixture into a disc shape to obtain the chromium slag mixture, wherein the pressing pressure is 0.05–0.2 MPa, the diameter of the disc is 20–70 mm, and the thickness is 5–30 mm. Furthermore, since the sample hardens after pre-reduction, pressing the mixture into a disc shape facilitates subsequent dissolution and filtration after crushing.

[0073] For example, the pressing pressure is 0.09 MPa, the diameter of the disc is 40 mm, and the thickness is 10 mm.

[0074] In some embodiments, in S2, the first temperature is 900°C to 1200°C.

[0075] In some embodiments, the first time in S2 is 10 to 60 minutes.

[0076] For example, in S2, the flow rate of nitrogen is 100 ml / min.

[0077] In some embodiments, S2 further includes cooling and grinding after the heat preservation treatment to obtain a pre-reduced chromium slag mixture. During the cooling process, the nitrogen flow rate remains constant to ensure uniform cooling of the material.

[0078] For example, in S2, the first temperature can be selected as 900℃, 1000℃, 1100℃, 1200℃ or any possible value between 900℃ and 1200℃.

[0079] For example, in S2, the first time is any possible value between 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, or 10 to 60 min.

[0080] In some embodiments, S3 includes: placing the pre-reduced chromium slag mixture in water and stirring for a third time, then filtering to obtain filter residue and aluminum-enriched filtrate.

[0081] In some embodiments, in S3, the mass ratio of the pre-reduced chromium slag mixture to water is 1:50 to 70.

[0082] For example, in S3, the mass ratio of the pre-reduced chromium slag mixture to water can be selected as 1:50, 1:55, 1:60, 1:65, 1:70 or any possible mass ratio between 1:50 and 70.

[0083] In some embodiments, the third time in S3 is 10 to 60 minutes.

[0084] For example, in S3, the third time can be selected as 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min or any time value between 10 and 60min.

[0085] In some embodiments, in S4, the second temperature is 1500°C to 1700°C.

[0086] In some embodiments, in S4, the second time is 10 to 60 minutes.

[0087] In some embodiments, in S4, the inert atmosphere is an argon atmosphere, and the argon flow rate is 100 ml / min.

[0088] For example, in S4, the second temperature can be selected as any possible temperature value between 1500℃, 1600℃, 1700℃ or 1500℃ and 1700℃, and the second time can be selected as any possible time value between 10min, 20min, 30min, 40min, 50min, 60min or 10 to 60min.

[0089] In some embodiments, S4, to enhance the stratification effect of slag-metal separation, includes: adding filter residue into a graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm, outer height 120mm, inner height 115mm), and then placing them together in a melting furnace. Under an inert atmosphere, the pre-reduced chromium slag mixture is held at a second temperature for a second time, and then melted and separated to obtain metallic iron and chromium-enriched residue. The graphite cylindrical crucible is a specially made laboratory crucible.

[0090] In some embodiments, in S3, the aluminum-enriched filtrate obtained from filtration is used for the production of alumina and the recovery of sodium carbonate.

[0091] In some embodiments, in S3, the aluminum-enriched filtrate obtained by filtration can consume carbon dioxide to precipitate aluminum hydroxide as a raw material for the production of alumina, and then be further evaporated to recover sodium carbonate, thereby improving economic efficiency.

[0092] In some embodiments, in S4, the separated metallic iron is used as a raw material for steel production to achieve iron recycling, and the separated chromium-enriched residue is used in the rebaking residue of chromium salt production to achieve chromium recycling.

[0093] The above method can simultaneously recover and reuse iron, chromium, and aluminum, providing new possibilities for the comprehensive utilization of calcium-free roasted chromium slag.

[0094] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with specific embodiments and accompanying drawings. Obviously, the specific embodiments described are merely some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the specific embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0095] Where specific techniques or conditions are not specified in the detailed embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0096] Example 1

[0097] Taking the calcium-free roasted chromium slag produced by a company in Chongqing during the production of chromates as an example, XRF analysis revealed that the composition and content of the calcium-free roasted chromium slag are shown in Table 1. In the following specific embodiments, this chromium slag is used as the raw material for the cascade resource utilization treatment of calcium-free roasted chromium slag.

[0098] Table 1. XRF analysis results of calcium-free roasted chromium slag

[0099]

[0100] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0101] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0102] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0103] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e. aluminum oxide) is 0.9:1.

[0104] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0105] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0106] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0107] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0108] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. The residue is then melted and separated to obtain metallic iron and chromium enriched residue.

[0109] Example 2

[0110] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0111] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0112] The coarse coal powder was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain fine coal powder.

[0113] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag, pulverized coal, and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1, and the molar ratio of sodium carbonate to aluminum oxide is 0.7:1.

[0114] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0115] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0116] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0117] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0118] External height 120mm, internal height 115mm, such as Figure 2 (As shown), and then placed together in a melting furnace under an argon atmosphere.

[0119] When the chromium and iron enriched filter residue was placed at a temperature of 1600℃ and kept at that temperature for 30 minutes, the separation of slag and gold was not effectively achieved.

[0120] Example 3

[0121] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0122] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0123] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0124] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.3:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0125] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0126] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0127] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:65. Then, it is filtered to obtain aluminum-enriched filtrate and chromium and iron-enriched filter residue.

[0128] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0129] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. The residue is then melted and separated to obtain metallic iron and chromium enriched residue.

[0130] Example 4

[0131] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0132] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0133] Coarse graphite was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain fine graphite powder.

[0134] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, graphite powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0135] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0136] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1200℃ and kept at that temperature for 30 min to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0137] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0138] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0139] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. The residue is then melted and separated to obtain metallic iron and chromium enriched residue.

[0140] Example 5

[0141] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0142] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0143] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0144] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0145] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0146] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1000℃ and kept at that temperature for 60 min to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0147] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0148] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0149] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. The residue is then melted and separated to obtain metallic iron and chromium enriched residue.

[0150] Example 6

[0151] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0152] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0153] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0154] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0155] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0156] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0157] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0158] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0159] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1500℃ and held for 60 minutes to melt and separate the metallic iron and chromium enriched residue.

[0160] Example 7

[0161] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0162] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0163] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0164] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0165] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0166] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 10 min to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0167] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0168] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0169] External height 120mm, internal height 115mm, such as Figure 2 (as shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. The residue is then melted and separated to obtain metallic iron and chromium enriched residue.

[0170] Example 8

[0171] like Figure 1 As shown, a method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0172] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0173] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0174] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1:1.2 and the molar ratio of sodium carbonate to aluminum oxide (i.e., alumina) is 0.9:1.

[0175] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0176] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0177] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0178] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm).

[0179] External height 120mm, internal height 115mm, such as Figure 2 (As shown) and then placed together in a melting furnace. Under an argon atmosphere, the chromium and iron enriched filter residue is placed at a temperature of 1600℃ and held for 10 minutes to melt and separate to obtain metallic iron and chromium enriched residue.

[0180] Example 9

[0181] like Figure 1 As shown, a method for enhanced cascade resource utilization of calcium-free roasted chromium slag through reducing alkali roasting includes the following steps:

[0182] S1. The above calcium-free roasted chromium slag was ball-milled for 45 minutes using a planetary ball mill with a rotation speed of 22 r / min, and then passed through a 50-mesh sieve to obtain calcium-free roasted chromium slag powder.

[0183] Coke was ball-milled for 45 minutes using a planetary ball mill at a speed of 22 r / min, and then passed through a 100-200 mesh sieve to obtain coke powder.

[0184] A mixture is obtained by thoroughly mixing calcium-free roasted chromium slag powder, coke powder and sodium carbonate. In the mixture, the molar ratio of reduced carbon to available oxygen is 1.2:1 and the molar ratio of sodium carbonate to aluminum oxide (i.e. aluminum oxide) is 1:1.

[0185] The mixture was then placed in a mold and pressed into a disc shape with a diameter of 40 mm and a thickness of 10 mm using a press with a pressure of 0.09 MPa, thus obtaining the chromium slag mixture.

[0186] S2. In a nitrogen atmosphere, the chromium slag mixture obtained in S1 is placed at a temperature of 1100℃ and kept at that temperature for 30 minutes to reduce the iron oxides and sodium the aluminum oxides and chromium oxides in the pre-reduced chromium slag mixture, while simultaneously inhibiting the reduction of chromium oxides. After cooling, the mixture is placed in a mortar and crushed and coarsely ground to obtain the pre-reduced chromium slag mixture. The flow rate of nitrogen is 100 ml / min.

[0187] S3. The pre-reduced chromium slag mixture obtained in S2 is placed in water and stirred for 15 minutes at a slag-to-water mass ratio of 1:55. Then it is filtered to obtain aluminum enriched filtrate and chromium and iron enriched filter residue.

[0188] S4. Add the chromium and iron enriched filter residue obtained in S3 into a slender graphite cylindrical crucible (outer diameter 35mm, inner diameter 25mm, outer height 120mm, inner height 115mm, as shown). Figure 2 As shown in the figure, the chromium and iron enriched filter residue was placed together in a melting furnace. Under an argon atmosphere, the filter residue was placed at a temperature of 1600℃ and kept at that temperature for 30 minutes. However, the slag-gold separation was not effectively achieved.

[0189] Detection and Analysis

[0190] The separation efficiency of iron, the maximum diameter of the separated iron metal pellets, the enrichment rate of aluminum, the enrichment rate of chromium in the chromium enrichment residue, and the content of hexavalent chromium in the chromium enrichment residue were tested in Examples 1 to 9. The separation efficiency of iron was first tested according to the standard "Direct Reduction of Iron—Determination of Metallic Iron Content—Titration Method of Potassium Dichromate Decomposition with Ferric Chloride" (GB / T38812.2—2020) on the molten separated metallic iron, and then the iron separation efficiency was calculated by converting the test results with the XRF test results. The diameter of the iron pellets was measured using vernier calipers. The concentration of aluminum in the aluminum enrichment solution was detected by ICP emission spectroscopy. The enrichment rate of chromium in the chromium enrichment residue was tested according to the standard "Chemical Analysis Methods for Cobalt-Chromium-Tungsten Alloy Powder—Part 2: Determination of Chromium Content—Titration Method of Ferrous Ammonium Sulfate". The temperature of the first step of the microwave digestion instrument was modified according to the industry-recognized phosphoric acid digestion method, setting it to 120℃ for 15 min with a heating rate of 3.2℃ / min. -1 The second step involves setting the temperature to 150℃ and holding it there for 1 hour, with a heating rate of 2℃ / min. -1 The digestion solution of 15 mL hydrochloric acid, 5 mL nitric acid, and 1 mL hydrofluoric acid was replaced with 20 mL phosphoric acid to fully digest the residue sample. The detection method for hexavalent chromium content in the chromium-enriched residue was to test the supernatant after acid leaching of the chromium-enriched residue according to the method specified in the "Identification Standard for Solid Waste - Leaching Toxicity Identification" (GB5085.3-2007). The test results of each example are as follows.

[0191] In Example 1, the iron separation efficiency was 98%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enrichment slag was 8.13mm. The aluminum enrichment rate in the aluminum enrichment liquid was 92%, and the chromium enrichment rate in the chromium enrichment residue was 39% (the wt% of chromium oxide in the original chromium slag was 10.24%). Moreover, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). This effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0192] In Example 2, the iron separation efficiency was 85%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 6.13mm. The aluminum enrichment rate in the aluminum enrichment solution was 87%, and the chromium enrichment rate in the chromium enrichment residue was 31% (the wt% of chromium oxide in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 2 mainly focuses on the comparison of sodium carbonate and aluminum oxide proportions in coke, alkaline reagents, and chromium slag molding blocks. When the sodium carbonate ratio is below 0.9, the aluminum oxide in the chromium slag mixture cannot be completely reacted into soluble sodium salts for dissolution and leaching. The residual aluminum oxide increases the viscosity of the slag, weakening the subsequent melting and separation effect. However, it effectively achieves the cascade separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0193] In Example 3, the iron separation efficiency was 82%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 6.86mm. The aluminum enrichment rate in the aluminum enrichment solution was 90%, and the chromium enrichment rate in the chromium enrichment residue was 32% (the wt% of chromium oxide in the original chromium slag was 10.24%). Moreover, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 3 mainly focuses on the comparison of the molar ratio of reduced carbon to effective oxygen in coke, alkaline reagent, and chromium slag molding blocks. When the reduced carbon ratio is greater than 1.2, the excess carbon reacts with iron to form iron carbide, which reduces the total amount of iron that can be melted and separated, and reduces the diameter of the metal iron pellets dripped out in the subsequent melting and separation stage. However, it also effectively achieves the stepwise separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0194] In Example 4, the iron separation efficiency was 75%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 5.77mm. The aluminum enrichment rate in the aluminum enrichment solution was 92%, and the chromium enrichment rate in the chromium enrichment residue was 27% (the wt% of chromium oxide in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 4 mainly focused on the comparison of reducing agent types. When a reducing agent with a low percentage of reduced carbon was selected, excessive impurities (such as ash) were introduced, reducing the mass transfer efficiency of each reaction. This resulted in a decrease in the reduction degree of iron oxides and the sodiumization degree of chromium and aluminum oxides, leading to a smaller diameter of the metal iron pellets dripped out in the subsequent melting stage. However, it also effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0195] In Example 5, the iron separation efficiency was 65%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 4.88mm. The aluminum enrichment rate in the aluminum enrichment solution was 93%, and the chromium enrichment rate in the chromium enrichment residue was 21% (the wt% of chromium oxide in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 5 mainly focused on the selection and comparison of the first temperature. When the first temperature was below 1100℃, the iron oxides in the chromium slag mixture were difficult to be reduced to metallic iron by carbon, resulting in a decrease in the total amount of iron that could be melted and separated. This led to a decrease in the diameter of the metallic iron pellets dripping out in the subsequent melting and separation stages. However, it also effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in the calcium-free roasted chromium slag.

[0196] In Example 6, the iron separation efficiency was 60%. The maximum diameter of the metallic iron pellets obtained from the melting and separation of 20g of ferrochrome enrichment slag was 2.94mm. The aluminum enrichment rate in the aluminum enrichment solution was 90%, and the chromium enrichment rate in the chromium enrichment residue was 28% (the wt% of chromium oxide in the original chromium slag was 10.24%). Moreover, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 6 mainly focused on the comparison of the second temperature selection. The results showed that when the second temperature was less than 1600℃, the metallic iron reduced by coke was more difficult to melt and drip out, resulting in a smaller diameter of the metallic iron pellets. However, it also effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0197] In Example 7, the iron separation efficiency was 65%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 4.92mm. The aluminum enrichment rate in the aluminum enrichment solution was 95%, and the chromium enrichment rate in the chromium enrichment residue was 20% (the wt% of chromium oxides in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 7 mainly focused on the comparison of the first holding time. When the first holding time was less than 30min, the reduction degree of iron oxides in the chromium slag mixture decreased, resulting in a reduction in the total amount of iron that could be melted and separated, and thus a smaller diameter of the metal iron pellets. However, it also effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in the calcium-free roasted chromium slag.

[0198] In Example 8, the iron separation efficiency was 67%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 4.88mm. The aluminum enrichment rate in the aluminum enrichment solution was 93%, and the chromium enrichment rate in the chromium enrichment residue was 26% (the wt% of chromium oxide in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 8 mainly focused on the selection and comparison of the second holding time. When the second holding time was less than 30min, the iron that could be melted and separated did not fully melt and drip out, resulting in a smaller diameter of the metal iron pellets. However, it still effectively achieved the stepwise separation and high-value utilization of iron, chromium, and aluminum components in the calcium-free roasted chromium slag.

[0199] In Example 9, the iron separation efficiency was 90%. The maximum diameter of the iron metal pellets obtained from the melting and separation of 20g of ferrochrome enriched slag was 6.15mm. The aluminum enrichment rate in the aluminum enrichment solution was 92%, and the chromium enrichment rate in the chromium enrichment residue was 34% (the wt% of chromium oxide in the original chromium slag was 10.24%). Furthermore, the hexavalent chromium content in the chromium enrichment residue was 0.0002% (less than the national emission standard of 0.0005%). Example 9 mainly focuses on the comparison of sodium carbonate and aluminum oxide proportions in coke, alkaline reagents, and chromium slag molding blocks. When the sodium carbonate ratio is greater than 0.9, some iron oxides in the chromium slag mixture are also sodium-treated, reducing the degree of reduction of iron oxides in the chromium slag mixture. This reduces the total amount of iron that can be melted and separated, resulting in a smaller diameter of the metal iron pellets. However, it also effectively achieves the cascade separation and high-value utilization of iron, chromium, and aluminum components in calcium-free roasted chromium slag.

[0200] This invention discloses a method for enhanced cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkaline roasting. The method involves adding a reducing agent and alkaline reagent to the calcium-free roasted chromium slag, reducing and sodium-modifying the chromium slag mixture in an inert atmosphere. By rationally controlling the temperature and time, the reduction and sodium-modification of iron oxides, aluminum oxides, and chromium oxides are maximized, while the reduction of chromium oxides is suppressed, resulting in a pre-reduced chromium slag mixture. Then, through dissolution and filtration, aluminum-enriched filtrate and chromium- and iron-enriched slags are obtained separately. Based on the above, the chromium- and iron-enriched slags are melt-separated in an inert atmosphere. By rationally controlling the heating temperature and holding time, metallic iron melts and separates, while chromium is enriched in the molten slag phase, thereby further separating the iron and chromium components in the calcium-free roasted chromium slag. It is noteworthy that due to the removal of aluminum oxides in the slag, the viscosity of the molten slag decreases, facilitating the aggregation and growth of metallic iron, and simplifying the separation operation. For chromium in the slag, its enrichment efficiency is further improved, and the chromium grade is increased.

[0201] Based on the above separation, the resource utilization of iron, chromium, and aluminum in calcium-free roasted chromium slag can be realized. For example, the aluminum enrichment filtrate can be used for alumina production and sodium carbonate recovery, metallic iron can be used as a high-quality raw material for steel smelting, and the molten slag enriched with chromium can be used as re-roasting slag for chromium salt production. This effectively realizes the high-value utilization of the main components of iron, chromium, and aluminum in calcium-free roasted chromium slag. Moreover, the process is simple, efficient, has a large slag processing capacity, thoroughly detoxifies the chromium slag, and has high recovery rates of iron, chromium, and aluminum. The process also has the advantages of no by-products generated during implementation, making it valuable for promotion and application in the field of chromium slag resource utilization technology.

[0202] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for enhancing the cascade separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting, characterized in that, Includes the following steps: S1. A calcium-free roasted chromium slag, a reducing agent, and an alkaline reagent are mixed to obtain a chromium slag mixture; the reducing agent is selected from coke, and the alkaline reagent is selected from sodium carbonate; the molar ratio of reduced carbon to available oxygen in the chromium slag mixture is 1.0~1.2:1, and the molar ratio of alkaline reagent to aluminum oxide in the chromium slag mixture is 0.9:1; S2. In a nitrogen atmosphere, the chromium slag mixture is placed at a first temperature and kept at that temperature for a first time, so that the iron oxides, aluminum oxides, and chromium oxides in the chromium slag mixture are reduced, while the reduction of chromium oxides in the chromium slag mixture is inhibited. After the heat treatment, the mixture is further subjected to cooling and grinding to obtain a pre-reduced chromium slag mixture. The first temperature is 1100℃~1200℃, the first time is 30~60min, and the nitrogen flow rate is 100ml / min. S3. Place the pre-reduced chromium slag mixture in water and filter it to obtain filter residue and aluminum-enriched filtrate. S4. In an argon atmosphere, the filter residue is placed at a second temperature for a second time to melt and separate to obtain a residue enriched with metallic iron and chromium; the second temperature is 1600℃~1700℃, the second time is 30~60min, and the argon flow rate is 100ml / min.

2. The method for enhanced separation and resource utilization of calcium-free roasted chromium slag by reducing alkali roasting according to claim 1, characterized in that, In step S1, before mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, the process further includes: ball milling and sieving the calcium-free roasted chromium slag and reducing agent, respectively. The ball milling speed is 20~30 r / min, the ball milling time is 30 min~180 min, and the sieving process is to pass the calcium-free roasted chromium slag through a 50-mesh sieve and the reducing agent through a 100~200-mesh sieve.

3. The method for enhanced separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting according to claim 1, characterized in that, In step S1, after mixing the calcium-free roasted chromium slag, reducing agent, and alkaline reagent, the process further includes: pressing the mixture into a disc shape to obtain a chromium slag mixture, wherein the pressing pressure is 0.05~0.2MPa, the disc diameter is 20~70mm, and the thickness is 5~30mm.

4. The method for enhanced separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting according to claim 1, characterized in that, S3 includes: placing the pre-reduced chromium slag mixture in water and stirring for a third time, then filtering to obtain filter residue and aluminum-enriched filtrate; The mass ratio of the pre-reduced chromium slag mixture to water is 1:50~70; The third time is 10~60 minutes.

5. The method for enhanced separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting according to claim 1, characterized in that, In step S3, the aluminum-enriched filtrate obtained from filtration is used for the production of alumina and the recovery of sodium carbonate.

6. The method for enhanced separation and resource utilization of calcium-free roasted chromium slag through reducing alkali roasting according to claim 1, characterized in that, In step S4, the separated metallic iron is used as a raw material for steel production, realizing the recycling of iron, and the separated chromium-enriched residue is used in the rebaking slag for chromium salt production, realizing the recycling of chromium.

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